Chemistry (School of)https://hdl.handle.net/10023/182024-03-26T03:20:22Z2024-03-26T03:20:22ZOptimisation of the interfaces of solid-state batteriesBathgate, Cameronhttps://hdl.handle.net/10023/294732024-03-13T03:08:58Z2024-06-13T00:00:00ZThe development of solid-state batteries aims to implement lithium metal in a battery to utilise the total capacity and voltage it applies. A full solid-state battery would also prevent a fire hazard by removing the volatile organics. Solid oxide electrolytes of Li₃ₓLa₂/₃-₃ₓTiO₃ (LLTO) and Li₇La₃Zr₂O₁₂ (LLZO) are promising electrolyte materials that can be used in these applications. However, one of the main limitations is the high interfacial tension at the interface between lithium metal and the solid electrolyte.
In this work, LLTO electrolytes were synthesised using an aqueous system providing a double perovskite structure with a pseudo-cubic structure after sintering the material at 1350°C for 6 hours provided a unit cell parameter of a = 3.86 Å. It was also possible to dope the b-site with aluminium to allow for a cubic phase formation at a lower temperature, 1100°C, at a shorter time of ten minutes.
This thesis describes the use of LLTO and LLZO electrolytes wetting experiments investigating the intrinsic wetting of solid lithium. The results demonstrated that lithium is intrinsically poor at wetting solid electrolyte surfaces with contact angles greater than 90°. The adhesion of lithium to these electrolytes is also low, which explains why pressure is typically implemented to cause lithium to stick to the surface. Using wetting state calculations, most of the interactions between lithium and the solid oxide electrolytes are described as Cassie-Baxter wetting states. By the same calculations, some interactions present capillary filling, providing evidence that electrolyte modification may permit lithium infiltration. This can be done by coating protective sacrificial electrolytes (LLTO) on top of others (LLZO). Another conclusion from the wetting experiments was that altering the surface tension of lithium is one of the easiest and most beneficial ways to allow for the impregnation of the lithium into the pores, improving the contact angle at the micro-scale.
The coating of an LLZO pellet with a sol-precursor of LLTO was successful. It provided some improvement (1x10⁻³ Scm⁻¹) to the ionic conduction when placed in a symmetrical cell with lithium, and the contact angle of lithium to this coated LLZO improved in the microscale. Bulk lithium adhesion and impregnation will require further improvement by either improved coverage of LLTO on the surface of LLZO or by using higher vacuum pumps at a temperature of around 180°C.
The LLTO coating also protects the LLZO surface from absorbing CO₂ to form impurities of La₂Zr₂O₇. LLTO stability with the desired cathode material LiFePO₄ (LFP) is noted and may lead to an implementation of LFP, LLTO and LLZO in a full cell, which would be an exciting step as a proof of concept.
2024-06-13T00:00:00ZBathgate, CameronThe development of solid-state batteries aims to implement lithium metal in a battery to utilise the total capacity and voltage it applies. A full solid-state battery would also prevent a fire hazard by removing the volatile organics. Solid oxide electrolytes of Li₃ₓLa₂/₃-₃ₓTiO₃ (LLTO) and Li₇La₃Zr₂O₁₂ (LLZO) are promising electrolyte materials that can be used in these applications. However, one of the main limitations is the high interfacial tension at the interface between lithium metal and the solid electrolyte.
In this work, LLTO electrolytes were synthesised using an aqueous system providing a double perovskite structure with a pseudo-cubic structure after sintering the material at 1350°C for 6 hours provided a unit cell parameter of a = 3.86 Å. It was also possible to dope the b-site with aluminium to allow for a cubic phase formation at a lower temperature, 1100°C, at a shorter time of ten minutes.
This thesis describes the use of LLTO and LLZO electrolytes wetting experiments investigating the intrinsic wetting of solid lithium. The results demonstrated that lithium is intrinsically poor at wetting solid electrolyte surfaces with contact angles greater than 90°. The adhesion of lithium to these electrolytes is also low, which explains why pressure is typically implemented to cause lithium to stick to the surface. Using wetting state calculations, most of the interactions between lithium and the solid oxide electrolytes are described as Cassie-Baxter wetting states. By the same calculations, some interactions present capillary filling, providing evidence that electrolyte modification may permit lithium infiltration. This can be done by coating protective sacrificial electrolytes (LLTO) on top of others (LLZO). Another conclusion from the wetting experiments was that altering the surface tension of lithium is one of the easiest and most beneficial ways to allow for the impregnation of the lithium into the pores, improving the contact angle at the micro-scale.
The coating of an LLZO pellet with a sol-precursor of LLTO was successful. It provided some improvement (1x10⁻³ Scm⁻¹) to the ionic conduction when placed in a symmetrical cell with lithium, and the contact angle of lithium to this coated LLZO improved in the microscale. Bulk lithium adhesion and impregnation will require further improvement by either improved coverage of LLTO on the surface of LLZO or by using higher vacuum pumps at a temperature of around 180°C.
The LLTO coating also protects the LLZO surface from absorbing CO₂ to form impurities of La₂Zr₂O₇. LLTO stability with the desired cathode material LiFePO₄ (LFP) is noted and may lead to an implementation of LFP, LLTO and LLZO in a full cell, which would be an exciting step as a proof of concept.An investigation into novel solid state electrolytes for lithium-ion batteriesBoyle, Colm Williamhttps://hdl.handle.net/10023/293682024-03-08T15:11:47Z2024-06-13T00:00:00ZAbstract redacted
2024-06-13T00:00:00ZBoyle, Colm WilliamAbstract redactedExpanding the GenoChemetic toolbox : radical halogenases and aqueous alkyl halide cross-couplingMolyneux, Samuel Aaronhttps://hdl.handle.net/10023/292922024-02-21T03:01:57Z2024-06-13T00:00:00ZNatural products are a very important class of bioactive and often medicinally relevant molecules, however strategies for their chemical diversification are often hindered by their complexity and high number of unactivated aliphatic carbons. The GenoChemetic strategy represents a powerful tool for natural product diversification, merging the biosynthetic production of reactive metabolites with mild aqueous chemistries to enable modification in biological conditions. The merger of biosynthetic production of aliphatically halogenated compounds by radical halogenases with aqueous alkyl halide coupling chemistries remains an unexploited but promising strategy for enabling functionalisation at C(sp³)-H centres in this way.
This PhD thesis focuses on the stepwise process to expand the GenoChemetic method of natural product diversification through biocatalytic halogenation from the sp² realm to the sp³ realm. To this end in silico techniques have been used to mine novel radical halogenase from genomic libraries to discover five novel radical halogenases from cyanobacteria, myxobacteria, and bacteroidetes. Furthermore, one vanadium dependent halogenase was discovered from algae which produce a distinct halo-metabolite signature when virally infected. These novel enzymes have been examined in a phylogenetic, structural, and genomic context, and recombinantly produced in Escherichia coli. Halogenation assays were designed, and a wide range of substrates used to probe these novel proteins for halogenation activity.
Methods for the aqueous coupling of sp³ alkyl halides have also been explored. By screening catalysts and ligands, it has been shown that that the water-soluble palladium source Na₂PdCl₄ can be used in conjunction with a tris(2,4-dimethyl-5-sulfophenyl)phosphine trisodium salt (TXPTS) ligand to enable the first fully aqueous, air tolerant, and mild Suzuki-Miyaura coupling. This aqueous coupling was able to derivatise a wide range of functionalised hydrophilic and hydrophobic primary alkyl halides. It was also used to tag two halogenated natural products with fluorescent and ionisable groups in a method for natural product analysis and analogue generation.
2024-06-13T00:00:00ZMolyneux, Samuel AaronNatural products are a very important class of bioactive and often medicinally relevant molecules, however strategies for their chemical diversification are often hindered by their complexity and high number of unactivated aliphatic carbons. The GenoChemetic strategy represents a powerful tool for natural product diversification, merging the biosynthetic production of reactive metabolites with mild aqueous chemistries to enable modification in biological conditions. The merger of biosynthetic production of aliphatically halogenated compounds by radical halogenases with aqueous alkyl halide coupling chemistries remains an unexploited but promising strategy for enabling functionalisation at C(sp³)-H centres in this way.
This PhD thesis focuses on the stepwise process to expand the GenoChemetic method of natural product diversification through biocatalytic halogenation from the sp² realm to the sp³ realm. To this end in silico techniques have been used to mine novel radical halogenase from genomic libraries to discover five novel radical halogenases from cyanobacteria, myxobacteria, and bacteroidetes. Furthermore, one vanadium dependent halogenase was discovered from algae which produce a distinct halo-metabolite signature when virally infected. These novel enzymes have been examined in a phylogenetic, structural, and genomic context, and recombinantly produced in Escherichia coli. Halogenation assays were designed, and a wide range of substrates used to probe these novel proteins for halogenation activity.
Methods for the aqueous coupling of sp³ alkyl halides have also been explored. By screening catalysts and ligands, it has been shown that that the water-soluble palladium source Na₂PdCl₄ can be used in conjunction with a tris(2,4-dimethyl-5-sulfophenyl)phosphine trisodium salt (TXPTS) ligand to enable the first fully aqueous, air tolerant, and mild Suzuki-Miyaura coupling. This aqueous coupling was able to derivatise a wide range of functionalised hydrophilic and hydrophobic primary alkyl halides. It was also used to tag two halogenated natural products with fluorescent and ionisable groups in a method for natural product analysis and analogue generation.Title redactedReid, Elliehttps://hdl.handle.net/10023/292912024-02-25T03:01:15Z2024-06-13T00:00:00ZAbstract redacted
2024-06-13T00:00:00ZReid, EllieAbstract redactedStudies of hydride ion conductors using combined spectroscopy techniquesIrvine, Gavin Johnhttps://hdl.handle.net/10023/292732024-02-22T14:45:47Z2022-06-15T00:00:00ZThis thesis presents research into two superionic conductors: BaH₂ and β-Ca₂NH. The research presented herein explores the diffusion pathway of hydride ions (H⁻) in the solid-state of these materials.
Using novel combined spectroscopic techniques, we show that BaH₂ has a diffusion pathway that involves the partial melting of its crystal lattice. This "liquid-like" sublattice is analysed in detail in order to elucidate the origins of such behaviour as well as provide a physical description of a sublattice manifesting as "liquid-like."
The second material explored in this thesis is a novel superionic conductor not previously published, β-Ca2NH. The analysis shows that Ca₂NH (nitride- hydride) materials come in at least two distinct polymorphs, with dramatically different ionic conductivities. Using in situ neutron powder diffraction along with several other techniques, we explore the unique configurations of the different Ca₂NH polymorphs and identify what gives rise to ionic conductivity in one form and not the other. Furthermore, Ca₂NH is contrasted to the closely related imide (NH₂⁻) and amide (NH₂⁻).
Barium hydride is shown to have an ionic conductivity of 0.32 S/cm at 600 ◦C and its conduction due to the presence of a liquid-like sublattice. Calcium nitride-hydride, on the other hand, is shown to have an ionic conductivity of 0.08 S/cm at 600 ◦C and its conduction defined by an intrinsic vacancy concentration created by anti-Frenkel defects. Thus, the thesis explores two excellent solid-state ionic conductors with dramatically different ionic conduction mechanisms.
The synthesis route for the following compounds are detailed in this thesis: BaH₂, BaD₂, Ca₂NH - both polymorphs, CaNH, and Ca(NH₂)₂.
2022-06-15T00:00:00ZIrvine, Gavin JohnThis thesis presents research into two superionic conductors: BaH₂ and β-Ca₂NH. The research presented herein explores the diffusion pathway of hydride ions (H⁻) in the solid-state of these materials.
Using novel combined spectroscopic techniques, we show that BaH₂ has a diffusion pathway that involves the partial melting of its crystal lattice. This "liquid-like" sublattice is analysed in detail in order to elucidate the origins of such behaviour as well as provide a physical description of a sublattice manifesting as "liquid-like."
The second material explored in this thesis is a novel superionic conductor not previously published, β-Ca2NH. The analysis shows that Ca₂NH (nitride- hydride) materials come in at least two distinct polymorphs, with dramatically different ionic conductivities. Using in situ neutron powder diffraction along with several other techniques, we explore the unique configurations of the different Ca₂NH polymorphs and identify what gives rise to ionic conductivity in one form and not the other. Furthermore, Ca₂NH is contrasted to the closely related imide (NH₂⁻) and amide (NH₂⁻).
Barium hydride is shown to have an ionic conductivity of 0.32 S/cm at 600 ◦C and its conduction due to the presence of a liquid-like sublattice. Calcium nitride-hydride, on the other hand, is shown to have an ionic conductivity of 0.08 S/cm at 600 ◦C and its conduction defined by an intrinsic vacancy concentration created by anti-Frenkel defects. Thus, the thesis explores two excellent solid-state ionic conductors with dramatically different ionic conduction mechanisms.
The synthesis route for the following compounds are detailed in this thesis: BaH₂, BaD₂, Ca₂NH - both polymorphs, CaNH, and Ca(NH₂)₂.Fluorite type oxide-ion conductors : new approachesZhang, Shuoshuohttps://hdl.handle.net/10023/292712024-02-16T23:03:39Z2021-06-30T00:00:00ZThe development of electrolyte materials for the high temperature (800-1000 ∘C) solid oxide fuel cell (SOFC) is mostly based on anion-deficient fluorite oxides, especially cubic stabilised zirconia and ceria. The 8 mol % yttria stabilised zirconia (8YSZ) is so far the most commonly used one owing to its fairly high ionic conductivity and good stability at high temperature cell operation. However, new materials with higher ionic conductivities are demanded to reduce the cell ohmic loss at high temperatures. Although doped ceria provides a higher ionic conductivity than doped zirconia, the reduction of Ce⁴⁺ in the fuel cell reducing atmosphere introduces electronic conduction and lattice expansion which can be detrimental to cell performance. The perovskite structured strontium-magnesium doped lanthanum gallate (LSGM) has high ionic conductivity that is comparable to doped ceria. The limitation for this material comes from its interaction with the traditional Ni-YSZ anode. This means developments of new anode materials, or interlayer designs are required. The scandia stabilised zirconia (SSZ) in the doped zirconia family is a very attractive candidate as it offers the highest ionic conductivity amount the doped zirconia systems. However, 11SSZ, which offers the highest ionic conductivity in the Sc₂O₃ − ZrO₂ system that is comparable to doped ceria and LSGM in the high temperature operating range, undergoes a
rhombohedral-cubic phase transition at about 600 ∘C, with the cubic phase existing only at T > 600 ∘C. Apart from this phase stability issue, most SSZ compositions show a significant conductivity degradation behaviour over time.
Accordingly, this thesis is to investigate new electrolyte materials, with a particular focus on the co-doped 11SSZ systems, that may offer higher ionic conductivities, and improved phase and conductivity stabilities for the high temperature fuel cell application. The material's properties are all related to its underlying chemistry. As a matter of fact, this thesis provides new approaches in evaluating the observed properties and conductivity behaviours in the fluorite materials, links the experimental evidence to its underlying chemistry. This thesis aims to provide a deep level understanding on the fundamental of zirconia and stabilised zirconia: its chemistry and defect structure, in order to uncover the fundamental of phase stabilisation, factors that limit the maximum ionic conductivity and driving forces for the conductivity degradation, etc., in doped zirconia systems. This is extended to all the fluorite-based and related systems. It follows that the electrolyte performance is closely related to its microdomain structural changes. In particular, the problem of conductivity degradation is tackled by the elimination of short-range ordering of oxygen vacancies. Apart from the microdomain structure, the total ionic conductivity is also closely related to the crystal phase assembly and microstructures.
The elimination of conductivity degradation in one of the Mg, In co-doped zirconia composition (IMSSZ) significantly improves the long-term conductivity stability, together with a stable, simple crystal structure and a high ionic conductivity (0.14 S cm⁻¹ at 850 ∘C and the ionic conductivity can reach 0.4 S cm⁻¹ at 1000 ∘C). This will contribute to an overall improved cell performance when integrating into the SOFC. The theory, concepts and characterisation methods developed in this study for fluorite and fluorite-related materials, especially those related to microdomain structural studies and characterisations, can be applied further to any energy material with a certain adaptation. This is hoped to provide some insights into new material design, in particular the electrolyte.
2021-06-30T00:00:00ZZhang, ShuoshuoThe development of electrolyte materials for the high temperature (800-1000 ∘C) solid oxide fuel cell (SOFC) is mostly based on anion-deficient fluorite oxides, especially cubic stabilised zirconia and ceria. The 8 mol % yttria stabilised zirconia (8YSZ) is so far the most commonly used one owing to its fairly high ionic conductivity and good stability at high temperature cell operation. However, new materials with higher ionic conductivities are demanded to reduce the cell ohmic loss at high temperatures. Although doped ceria provides a higher ionic conductivity than doped zirconia, the reduction of Ce⁴⁺ in the fuel cell reducing atmosphere introduces electronic conduction and lattice expansion which can be detrimental to cell performance. The perovskite structured strontium-magnesium doped lanthanum gallate (LSGM) has high ionic conductivity that is comparable to doped ceria. The limitation for this material comes from its interaction with the traditional Ni-YSZ anode. This means developments of new anode materials, or interlayer designs are required. The scandia stabilised zirconia (SSZ) in the doped zirconia family is a very attractive candidate as it offers the highest ionic conductivity amount the doped zirconia systems. However, 11SSZ, which offers the highest ionic conductivity in the Sc₂O₃ − ZrO₂ system that is comparable to doped ceria and LSGM in the high temperature operating range, undergoes a
rhombohedral-cubic phase transition at about 600 ∘C, with the cubic phase existing only at T > 600 ∘C. Apart from this phase stability issue, most SSZ compositions show a significant conductivity degradation behaviour over time.
Accordingly, this thesis is to investigate new electrolyte materials, with a particular focus on the co-doped 11SSZ systems, that may offer higher ionic conductivities, and improved phase and conductivity stabilities for the high temperature fuel cell application. The material's properties are all related to its underlying chemistry. As a matter of fact, this thesis provides new approaches in evaluating the observed properties and conductivity behaviours in the fluorite materials, links the experimental evidence to its underlying chemistry. This thesis aims to provide a deep level understanding on the fundamental of zirconia and stabilised zirconia: its chemistry and defect structure, in order to uncover the fundamental of phase stabilisation, factors that limit the maximum ionic conductivity and driving forces for the conductivity degradation, etc., in doped zirconia systems. This is extended to all the fluorite-based and related systems. It follows that the electrolyte performance is closely related to its microdomain structural changes. In particular, the problem of conductivity degradation is tackled by the elimination of short-range ordering of oxygen vacancies. Apart from the microdomain structure, the total ionic conductivity is also closely related to the crystal phase assembly and microstructures.
The elimination of conductivity degradation in one of the Mg, In co-doped zirconia composition (IMSSZ) significantly improves the long-term conductivity stability, together with a stable, simple crystal structure and a high ionic conductivity (0.14 S cm⁻¹ at 850 ∘C and the ionic conductivity can reach 0.4 S cm⁻¹ at 1000 ∘C). This will contribute to an overall improved cell performance when integrating into the SOFC. The theory, concepts and characterisation methods developed in this study for fluorite and fluorite-related materials, especially those related to microdomain structural studies and characterisations, can be applied further to any energy material with a certain adaptation. This is hoped to provide some insights into new material design, in particular the electrolyte.Metal nanoparticle growth through in situ exsolution from barium cerate zirconateWang, Meihttps://hdl.handle.net/10023/292702024-03-05T03:03:32Z2021-06-30T00:00:00ZProtonic ceramic fuel cells (PCFCs) have great potential in applications compared with oxygen-ion-conducting-electrolyte based cells due to their relatively high ionic conductivity under intermediate and low temperature operating conditions. In addition, water is produced at the air electrode side of a proton-conducting fuel cell without diluting the fuel in the fuel electrode side, which provides higher operating voltage than an oxygen ion conducting SOFC. Among the proton-conducting materials, the most traditionally and widely used one is barium cerate-zirconate based perovskite oxide. It is simple to tailor its proton conductivity and stability by adjusting the doping concentration of Ce⁴⁺ and Zr⁴⁺. In a highly performed cell, the fuel electrode plays a vital role. The conventional fuel electrode is fabricated by metal-electrolyte composites, where the metal particles provide the catalytic activity and electronic conductivity and the electrolyte material ensures the proton conductivity. The main drawbacks of this cermet electrode are metal sintering and carbon coking, which degrades the cell performance in a long run.
In past decades, exsolution has been proposed as an effective way for in situ nanoparticles growth from perovskite oxide by a controlled phase decomposition process. Exsolved nanoparticles are socketed strongly in parent perovskite and show better resistance towards coarsening and coking compared with conventional electrodes. The nanoparticles exsolution from perovskite can be simply accomplished by doping the catalytically active transition metal into the perovskite structure, followed by chemical or electrochemical reduction.
The exsolution phenomenon has been well investigated on perovskite titanate oxide. However, little study has been focused on the exsolution from protonic conducting oxides and their applications in PCFCs. This thesis explores the exsolution behavior from the doped barium cerate zirconate oxide. Generally, nicely distributed particles are obtained on the BCZY perovskite through the in situ exsolution approach.
2021-06-30T00:00:00ZWang, MeiProtonic ceramic fuel cells (PCFCs) have great potential in applications compared with oxygen-ion-conducting-electrolyte based cells due to their relatively high ionic conductivity under intermediate and low temperature operating conditions. In addition, water is produced at the air electrode side of a proton-conducting fuel cell without diluting the fuel in the fuel electrode side, which provides higher operating voltage than an oxygen ion conducting SOFC. Among the proton-conducting materials, the most traditionally and widely used one is barium cerate-zirconate based perovskite oxide. It is simple to tailor its proton conductivity and stability by adjusting the doping concentration of Ce⁴⁺ and Zr⁴⁺. In a highly performed cell, the fuel electrode plays a vital role. The conventional fuel electrode is fabricated by metal-electrolyte composites, where the metal particles provide the catalytic activity and electronic conductivity and the electrolyte material ensures the proton conductivity. The main drawbacks of this cermet electrode are metal sintering and carbon coking, which degrades the cell performance in a long run.
In past decades, exsolution has been proposed as an effective way for in situ nanoparticles growth from perovskite oxide by a controlled phase decomposition process. Exsolved nanoparticles are socketed strongly in parent perovskite and show better resistance towards coarsening and coking compared with conventional electrodes. The nanoparticles exsolution from perovskite can be simply accomplished by doping the catalytically active transition metal into the perovskite structure, followed by chemical or electrochemical reduction.
The exsolution phenomenon has been well investigated on perovskite titanate oxide. However, little study has been focused on the exsolution from protonic conducting oxides and their applications in PCFCs. This thesis explores the exsolution behavior from the doped barium cerate zirconate oxide. Generally, nicely distributed particles are obtained on the BCZY perovskite through the in situ exsolution approach.Positive electrode materials for high energy rechargeable batteriesKim, Eun Jeonghttps://hdl.handle.net/10023/292682024-02-17T03:09:13Z2020-07-29T00:00:00ZWith the growth of environmental concerns, rechargeable batteries – lithium ion batteries (LIBs) and sodium ion batteries (SIBs) - have been employed in a large number of different applications. To meet the market needs in terms of their performance, positive electrode materials with high energy density are in high demand.
The aim of this thesis work is to provide strategies which enhance electrochemical performance of LiCoPO₄ as a high voltage positive electrode material for LIBs (chapter 3 and chapter 4) and an insight into the mechanism which triggers oxygen redox activity of P3-type Na₀.₆₇M₀.₂Mn₀.₈O₂ (M= Mg and Ni in chapter 5 and 6, respectively) as potential candidates for high capacity positive electrode materials in SIBs.
Studies on the improvement of cyclability of LiCoPO₄ were carried out using aqueous binders, of which, sodium carboxymethyl cellulose (CMC) permits more stable cycling performance and better rate capability with respect to the conventional organic solvent-soluble binders. In addition, substitution of magnesium for cobalt was investigated, which demonstrates that doping with magnesium can be one of the solutions to obtain stable capacity on extended cycling.
Both P3-type Na₀.₆₇Mg₀.₂Mn₀.₈O₂ and Na₀.₆Ni₀.₂Mn₀.₈O₂ were synthesised by a co-precipitation method and studied to understand the origin of abnormal capacity on the first charge. Careful electrochemical and structural characterisation combined with bulk and surface spectroscopic techniques (XAS, XPS) reveal the oxygen redox activity in Na0.67Mg0.2Mn0.8O2. As a consequence of vacancies in the transition metal layers of Na₀.₆₇Mg₀.₂Mn₀.₈O₂ prepared under oxygen, reversible oxygen redox is enhanced. Subsequently, substitution of nickel for manganese was carried out to increase capacity using the Ni²⁺/Ni⁴⁺ redox couple of nickel. The presence of oxygen redox activity in Na₀.₆Ni₀.₂Mn₀.₈O₂ is also demonstrated by using a range of spectroscopic techniques (XAS, SXAS, RIXS), which is stabilised by reduction of nickel through the reductive coupling mechanism.
2020-07-29T00:00:00ZKim, Eun JeongWith the growth of environmental concerns, rechargeable batteries – lithium ion batteries (LIBs) and sodium ion batteries (SIBs) - have been employed in a large number of different applications. To meet the market needs in terms of their performance, positive electrode materials with high energy density are in high demand.
The aim of this thesis work is to provide strategies which enhance electrochemical performance of LiCoPO₄ as a high voltage positive electrode material for LIBs (chapter 3 and chapter 4) and an insight into the mechanism which triggers oxygen redox activity of P3-type Na₀.₆₇M₀.₂Mn₀.₈O₂ (M= Mg and Ni in chapter 5 and 6, respectively) as potential candidates for high capacity positive electrode materials in SIBs.
Studies on the improvement of cyclability of LiCoPO₄ were carried out using aqueous binders, of which, sodium carboxymethyl cellulose (CMC) permits more stable cycling performance and better rate capability with respect to the conventional organic solvent-soluble binders. In addition, substitution of magnesium for cobalt was investigated, which demonstrates that doping with magnesium can be one of the solutions to obtain stable capacity on extended cycling.
Both P3-type Na₀.₆₇Mg₀.₂Mn₀.₈O₂ and Na₀.₆Ni₀.₂Mn₀.₈O₂ were synthesised by a co-precipitation method and studied to understand the origin of abnormal capacity on the first charge. Careful electrochemical and structural characterisation combined with bulk and surface spectroscopic techniques (XAS, XPS) reveal the oxygen redox activity in Na0.67Mg0.2Mn0.8O2. As a consequence of vacancies in the transition metal layers of Na₀.₆₇Mg₀.₂Mn₀.₈O₂ prepared under oxygen, reversible oxygen redox is enhanced. Subsequently, substitution of nickel for manganese was carried out to increase capacity using the Ni²⁺/Ni⁴⁺ redox couple of nickel. The presence of oxygen redox activity in Na₀.₆Ni₀.₂Mn₀.₈O₂ is also demonstrated by using a range of spectroscopic techniques (XAS, SXAS, RIXS), which is stabilised by reduction of nickel through the reductive coupling mechanism.A Trojan horse route to emergent active and stable platinum nanoparticles from a perovskite systemKothari, Maadhavhttps://hdl.handle.net/10023/292672024-02-17T03:06:23Z2021-06-30T00:00:00ZPlatinum (Pt), generally dispersed on a solid oxide support, has been widely used for catalytic chemical reactions in automobile, petroleum and energy industries. During the reactions, Pt is exposed to severe conditions, for example, heat and impurities, that cause Pt agglomeration and poisoning, respectively, resulting in activity/stability decrease. Here, perovskite materials are designed with Pt for significant catalytic properties through novel doping and exsolution methods.
Perovskite structured materials (ABO₃) are selected because these are basically stable at heat and redox environments with coke/sulfur resistances at the catalytic or electrochemical conditions. When perovskite oxides are employed as supporting frameworks, certain catalysts like Pt can be incorporated as cations on the B site of the perovskite lattice under oxidizing conditions (doping). By tailoring the stoichiometry of the doped perovskite materials, the dopants can be partly exsolved as nanoparticles (NP) on subsequent reductions, which provides the possibility of the in situ growth of NP (emergence). This method can improve the catalytic property of Pt by less loading, proper size, high dispersion, unique active sites and strong bonding structure with the perovskite.
Because only a few studies have been carried out due to the difficulty in the handling of Pt, the goal is to develop an innovative Pt perovskite catalyst to use in various catalytic applications.
2021-06-30T00:00:00ZKothari, MaadhavPlatinum (Pt), generally dispersed on a solid oxide support, has been widely used for catalytic chemical reactions in automobile, petroleum and energy industries. During the reactions, Pt is exposed to severe conditions, for example, heat and impurities, that cause Pt agglomeration and poisoning, respectively, resulting in activity/stability decrease. Here, perovskite materials are designed with Pt for significant catalytic properties through novel doping and exsolution methods.
Perovskite structured materials (ABO₃) are selected because these are basically stable at heat and redox environments with coke/sulfur resistances at the catalytic or electrochemical conditions. When perovskite oxides are employed as supporting frameworks, certain catalysts like Pt can be incorporated as cations on the B site of the perovskite lattice under oxidizing conditions (doping). By tailoring the stoichiometry of the doped perovskite materials, the dopants can be partly exsolved as nanoparticles (NP) on subsequent reductions, which provides the possibility of the in situ growth of NP (emergence). This method can improve the catalytic property of Pt by less loading, proper size, high dispersion, unique active sites and strong bonding structure with the perovskite.
Because only a few studies have been carried out due to the difficulty in the handling of Pt, the goal is to develop an innovative Pt perovskite catalyst to use in various catalytic applications.Title redactedZhang, Xiaotonghttps://hdl.handle.net/10023/292612024-02-17T03:06:14Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZZhang, XiaotongAbstract redactedDesign and development of a deoxyfluorination method using transition metal fluoridesSood, D. Eilidhhttps://hdl.handle.net/10023/292552024-02-15T12:00:22Z2020-12-01T00:00:00ZThe installation of a C–F bond in organic molecules is of significant importance to the scientific community due to its ability to modulate a compound’s physicochemical properties. For this reason, organofluorine compounds are valuable and widespread in the medicinal, agrochemical, and material industries.
Accordingly, research into developing new methods of C–F bond formation is a fast-paced field. A popular way of installing C(sp³)–F bonds is by deoxyfluorination whereby alcohols are converted to the corresponding fluorides. This particular transformation is attractive due to the fact that alcohols are readily available and inexpensive starting materials, and the reaction can proceed in a stereospecific manner. There have been a vast range of bespoke deoxyfluorination reagents which have been designed to facilitate this reaction, and whilst they are effective, they often have drawbacks associated with them such as cost and stability.
Of particular interest with regards to C–F bond formation is the use of metal fluorides. This poses a major challenge to organic chemists as the inherent properties of metal fluorides render them difficult to utilise as the fluoride is not easily accessible. Whilst this is an underdeveloped field, recently strategies are emerging which successfully aid the poor reactivity of metal fluorides such as hydrogen bonding catalysis, allowing them to successfully participate in fluorination reactions.
Enclosed is the development of a stereospecific deoxyfluorination reaction using CuF₂ enabled by a Lewis base activating group. The reaction design means that through a ligation approach, the inherent properties of metal fluorides can be circumvented which in turn allows for the chelate-directed delivery of fluoride. Ultimately, the development of this methodology and its generality towards a wide range of alcohol substrates will be discussed. In order to showcase the utility of this strategy, the translation of the system into a ¹⁸F-radiolabelling protocol is demonstrated.
2020-12-01T00:00:00ZSood, D. EilidhThe installation of a C–F bond in organic molecules is of significant importance to the scientific community due to its ability to modulate a compound’s physicochemical properties. For this reason, organofluorine compounds are valuable and widespread in the medicinal, agrochemical, and material industries.
Accordingly, research into developing new methods of C–F bond formation is a fast-paced field. A popular way of installing C(sp³)–F bonds is by deoxyfluorination whereby alcohols are converted to the corresponding fluorides. This particular transformation is attractive due to the fact that alcohols are readily available and inexpensive starting materials, and the reaction can proceed in a stereospecific manner. There have been a vast range of bespoke deoxyfluorination reagents which have been designed to facilitate this reaction, and whilst they are effective, they often have drawbacks associated with them such as cost and stability.
Of particular interest with regards to C–F bond formation is the use of metal fluorides. This poses a major challenge to organic chemists as the inherent properties of metal fluorides render them difficult to utilise as the fluoride is not easily accessible. Whilst this is an underdeveloped field, recently strategies are emerging which successfully aid the poor reactivity of metal fluorides such as hydrogen bonding catalysis, allowing them to successfully participate in fluorination reactions.
Enclosed is the development of a stereospecific deoxyfluorination reaction using CuF₂ enabled by a Lewis base activating group. The reaction design means that through a ligation approach, the inherent properties of metal fluorides can be circumvented which in turn allows for the chelate-directed delivery of fluoride. Ultimately, the development of this methodology and its generality towards a wide range of alcohol substrates will be discussed. In order to showcase the utility of this strategy, the translation of the system into a ¹⁸F-radiolabelling protocol is demonstrated.Novel magnetic materials with chemically-tailorable interactionsBradford, Alasdair Josephhttps://hdl.handle.net/10023/292202024-02-15T23:23:13Z2024-06-13T00:00:00ZThe investigation of compound KFe(C₂O₄)F was the impetus for this work as it was found to have interesting frustrated magnetic properties and became the first member of a family of transition metal oxalate fluorides which could be chemically tailored by cation substitution. Work to expand this family was undertaken to determine whether any other members exhibited novel magnetic properties. Depending on the cations and transition metals used, compounds with two distinct chemical formulae were synthesised; AM(C₂O₄)F and A₂M₂(C₂O₄)F₄ (A = K+, Rb+, Cs+, NH₄+; M = Mn²+, Fe²+, Co²+). Six compounds were isolated with the AM(C₂O₄)F formula; (NH₄)Mn(C₂O₄)F, KCo(C₂O₄)F, CsCo(C₂O₄)F, CsFe(C₂O₄)F, (NH₄)Fe(C₂O₄)F, and RbFe(C₂O₄)F while a further two were represented by the formula A2M2(C₂O₄)F₄; Cs₂Mn₂(C₂O₄)F₄ and (NH₄)₂Co₂(C₂O₄)F₄.
Through powder and single crystal X-ray diffraction, the AM(C₂O₄)F compounds could be divided into those with Pmmm space group symmetry [CsCo(C₂O₄)F and CsFe(C₂O₄)F], those with Pmc21 space group symmetry [(NH4)Mn(C₂O₄)F and RbFe(C₂O₄)F] and those with Cmc2₁ space group symmetry [KCo(C₂O₄)F and (NH4)Fe(C₂O₄)F]. A₂M₂(C₂O₄)F₄ compounds [Cs₂Mn₂(C₂O₄)F₄ and (NH₄)₂Co₂(C₂O₄)F₄] were found to crystalise with Cmmm space group symmetry.
The magnetic properties of all eight compounds were investigated initially by SQUID magnetometry, followed by elastic neutron diffraction to determine their magnetic ordering and structure. Additionally; CsCo(C₂O₄)F, CsFe(C₂O₄)F, Cs2Mn₂(C₂O₄)F₄ and (NH₄)₂Co₂(C₂O₄)F₄ were further investigated by µSR to probe spin behaviour over longer timescales. Neutron spectroscopy measurements were also taken for CsCo(C₂O₄)F and CsFe(C₂O₄)F to search for magnon excitations across temperature and energy ranges.
2024-06-13T00:00:00ZBradford, Alasdair JosephThe investigation of compound KFe(C₂O₄)F was the impetus for this work as it was found to have interesting frustrated magnetic properties and became the first member of a family of transition metal oxalate fluorides which could be chemically tailored by cation substitution. Work to expand this family was undertaken to determine whether any other members exhibited novel magnetic properties. Depending on the cations and transition metals used, compounds with two distinct chemical formulae were synthesised; AM(C₂O₄)F and A₂M₂(C₂O₄)F₄ (A = K+, Rb+, Cs+, NH₄+; M = Mn²+, Fe²+, Co²+). Six compounds were isolated with the AM(C₂O₄)F formula; (NH₄)Mn(C₂O₄)F, KCo(C₂O₄)F, CsCo(C₂O₄)F, CsFe(C₂O₄)F, (NH₄)Fe(C₂O₄)F, and RbFe(C₂O₄)F while a further two were represented by the formula A2M2(C₂O₄)F₄; Cs₂Mn₂(C₂O₄)F₄ and (NH₄)₂Co₂(C₂O₄)F₄.
Through powder and single crystal X-ray diffraction, the AM(C₂O₄)F compounds could be divided into those with Pmmm space group symmetry [CsCo(C₂O₄)F and CsFe(C₂O₄)F], those with Pmc21 space group symmetry [(NH4)Mn(C₂O₄)F and RbFe(C₂O₄)F] and those with Cmc2₁ space group symmetry [KCo(C₂O₄)F and (NH4)Fe(C₂O₄)F]. A₂M₂(C₂O₄)F₄ compounds [Cs₂Mn₂(C₂O₄)F₄ and (NH₄)₂Co₂(C₂O₄)F₄] were found to crystalise with Cmmm space group symmetry.
The magnetic properties of all eight compounds were investigated initially by SQUID magnetometry, followed by elastic neutron diffraction to determine their magnetic ordering and structure. Additionally; CsCo(C₂O₄)F, CsFe(C₂O₄)F, Cs2Mn₂(C₂O₄)F₄ and (NH₄)₂Co₂(C₂O₄)F₄ were further investigated by µSR to probe spin behaviour over longer timescales. Neutron spectroscopy measurements were also taken for CsCo(C₂O₄)F and CsFe(C₂O₄)F to search for magnon excitations across temperature and energy ranges.Methods for C-C and C-N bond formation using earth-abundant metalsWest, Matthewhttps://hdl.handle.net/10023/291452024-02-05T10:11:38Z2020-07-29T00:00:00ZThe formation of C–C and C–N bonds via transition metal catalysis is important in both academia and industry. Traditionally, both these fields have been dominated by the use of precious metal catalysts, with two of the most prominent reactions being the Suzuki– Miyaura cross-coupling (C–C) and the Buchwald–Hartwig amination (C–N), both palladium-catalysed processes. The use of earth-abundant metals in C–C and C–N formation could increase the economy and sustainability of such processes, whilst also introducing potential alternative reactivity.
The Suzuki–Miyaura cross-coupling is an extremely popular method of C–C bond formation in industry.¹ The vast majority of investigation into this reaction concerns solely the palladium-catalysed process, however, the more abundant group 10 metal Ni has been shown to be proficient in this process, while also displaying access to an increased scope of electrophiles. Enclosed is a comparison of a nickel and palladium Suzuki–Miyaura cross-coupling using a comparable ligand system. The practicalities of changing to a nickel-catalysed system are discussed, as well as insights into mechanistic variances between the two systems.
The Chan-Lam amination is a copper promoted cross-coupling of amines and organoborons. Recently, there has been important disocoveries into the mechanism of the amination.² The following study discusses the serendipitous discovery of a debenzylative Chan–Lam amination. This novel transformation was investigated, examining the scope of reactivity, whilst also considering the mechanistic pathway via which the reaction proceeds.
The use of boron protecting groups is well known in the Suzuki–Miyaura cross-coupling,³ but not as well explored in the Chan-Lam amination. The following study demonstrates the use of MIDA boronates in the Chan-Lam amination. The methodology attempts to access products not currently available using Chan-Lam aminations and also explores the difficulties of using the MIDA boronates in these systems.
2020-07-29T00:00:00ZWest, MatthewThe formation of C–C and C–N bonds via transition metal catalysis is important in both academia and industry. Traditionally, both these fields have been dominated by the use of precious metal catalysts, with two of the most prominent reactions being the Suzuki– Miyaura cross-coupling (C–C) and the Buchwald–Hartwig amination (C–N), both palladium-catalysed processes. The use of earth-abundant metals in C–C and C–N formation could increase the economy and sustainability of such processes, whilst also introducing potential alternative reactivity.
The Suzuki–Miyaura cross-coupling is an extremely popular method of C–C bond formation in industry.¹ The vast majority of investigation into this reaction concerns solely the palladium-catalysed process, however, the more abundant group 10 metal Ni has been shown to be proficient in this process, while also displaying access to an increased scope of electrophiles. Enclosed is a comparison of a nickel and palladium Suzuki–Miyaura cross-coupling using a comparable ligand system. The practicalities of changing to a nickel-catalysed system are discussed, as well as insights into mechanistic variances between the two systems.
The Chan-Lam amination is a copper promoted cross-coupling of amines and organoborons. Recently, there has been important disocoveries into the mechanism of the amination.² The following study discusses the serendipitous discovery of a debenzylative Chan–Lam amination. This novel transformation was investigated, examining the scope of reactivity, whilst also considering the mechanistic pathway via which the reaction proceeds.
The use of boron protecting groups is well known in the Suzuki–Miyaura cross-coupling,³ but not as well explored in the Chan-Lam amination. The following study demonstrates the use of MIDA boronates in the Chan-Lam amination. The methodology attempts to access products not currently available using Chan-Lam aminations and also explores the difficulties of using the MIDA boronates in these systems.Title redactedMcArdle, Timhttps://hdl.handle.net/10023/291432024-02-10T03:06:05Z2022-06-15T00:00:00ZAbstract redacted
2022-06-15T00:00:00ZMcArdle, TimAbstract redactedSynthesis, properties and applications of all-cis-pentafluorocyclohexane 'Janus' ring building blocksClark, Joshuahttps://hdl.handle.net/10023/291232024-02-01T22:34:34Z2022-06-15T00:00:00ZStrategically fluorinated compounds such as the all-cis-pentafluorocyclohexane ‘Janus’ rings, the subject of this research, can have strong molecular dipole moments because the electronegative fluorines polarise the geminal hydrogens rendering them electropositive.
In Chapter 1, a general discussion of the dominant interactions associated with organofluorine compounds is given. This is followed by an examination of the variety of fluorination methods available. The role of fluorine in medicinal chemistry is explored including in positron emission tomography (PET). A summary of previous work from the St Andrews group provides the contextual basis on which the following chapters build.
Chapter 2 explores a recently reported Rh-catalysed hydrogenation reaction of fluoroarenes to access all-cis-fluorocyclohexanes in excellent diastereoselectivity. The scope of this reaction is expanded to generate novel cyclohexane products such as alcohol 2.47 and methyl ester 2.60. Derivatisation of these products has furnished a library of all-cis-pentafluorocyclohexane building blocks for further study. These include alkyl bromide 2.82, organoazide 2.83 and aldehyde 2.87.
In Chapter 3, the elaboration of these building blocks to higher order molecular structures is explored. Ugi 4-component reactions (Ugi-4CR) with aldehyde 2.87 provide combinatorial access to medicinally relevant bis-amides 3.20-3.27. The Ugi-4CR, optimised by microwave assistance, can be completed within 45 mins. Using an HPLC method the Log P of three of these Ugi products (3.23, 3.25 and 3.27) was measured and in each case the Log P value reduced relative to phenyl ring analogues. This finding suggests a potential application of the ‘Janus’ ring as an arene isostere in medicinal chemistry. Other methods of elaboration explored in Chapter 3 include amide coupling, Wittig and CuAAC ‘click’ reactions.
Chapter 4 reports the preparation of ‘Janus’ ring bearing novel amphiphiles, the long chain carboxylic acid 4.1 and alcohol 4.2 as well as analogous hydrocarbon reference compounds 4.4 and 4.5. A Langmuir isotherm study examined the influence of the ring system on phase behaviour at the air-water interface. Evidence is presented of molecular self-assembly for the long chain 4.1 and 4.2, unlike the classical behaviour observed for the hydrocarbon counterparts 4.4 and 4.5. This analysis is supported by a thorough examination of X-ray crystal structures and presents a platform for the further development of the ‘Janus’ ring motif for supramolecular chemistry.
Finally, Chapter 5 summarises the findings of the previous chapters and explores possible avenues for future work such as the development of a ‘pull-down’ assay using biotinylated affinity probes 5.1 and 5.2 to better understand interactions between the ‘Janus’ ring and proteins of interest.
2022-06-15T00:00:00ZClark, JoshuaStrategically fluorinated compounds such as the all-cis-pentafluorocyclohexane ‘Janus’ rings, the subject of this research, can have strong molecular dipole moments because the electronegative fluorines polarise the geminal hydrogens rendering them electropositive.
In Chapter 1, a general discussion of the dominant interactions associated with organofluorine compounds is given. This is followed by an examination of the variety of fluorination methods available. The role of fluorine in medicinal chemistry is explored including in positron emission tomography (PET). A summary of previous work from the St Andrews group provides the contextual basis on which the following chapters build.
Chapter 2 explores a recently reported Rh-catalysed hydrogenation reaction of fluoroarenes to access all-cis-fluorocyclohexanes in excellent diastereoselectivity. The scope of this reaction is expanded to generate novel cyclohexane products such as alcohol 2.47 and methyl ester 2.60. Derivatisation of these products has furnished a library of all-cis-pentafluorocyclohexane building blocks for further study. These include alkyl bromide 2.82, organoazide 2.83 and aldehyde 2.87.
In Chapter 3, the elaboration of these building blocks to higher order molecular structures is explored. Ugi 4-component reactions (Ugi-4CR) with aldehyde 2.87 provide combinatorial access to medicinally relevant bis-amides 3.20-3.27. The Ugi-4CR, optimised by microwave assistance, can be completed within 45 mins. Using an HPLC method the Log P of three of these Ugi products (3.23, 3.25 and 3.27) was measured and in each case the Log P value reduced relative to phenyl ring analogues. This finding suggests a potential application of the ‘Janus’ ring as an arene isostere in medicinal chemistry. Other methods of elaboration explored in Chapter 3 include amide coupling, Wittig and CuAAC ‘click’ reactions.
Chapter 4 reports the preparation of ‘Janus’ ring bearing novel amphiphiles, the long chain carboxylic acid 4.1 and alcohol 4.2 as well as analogous hydrocarbon reference compounds 4.4 and 4.5. A Langmuir isotherm study examined the influence of the ring system on phase behaviour at the air-water interface. Evidence is presented of molecular self-assembly for the long chain 4.1 and 4.2, unlike the classical behaviour observed for the hydrocarbon counterparts 4.4 and 4.5. This analysis is supported by a thorough examination of X-ray crystal structures and presents a platform for the further development of the ‘Janus’ ring motif for supramolecular chemistry.
Finally, Chapter 5 summarises the findings of the previous chapters and explores possible avenues for future work such as the development of a ‘pull-down’ assay using biotinylated affinity probes 5.1 and 5.2 to better understand interactions between the ‘Janus’ ring and proteins of interest.Chiral phosphoric acid-catalyzed asymmetric protonation reactions of vinylheteroarylsAshford, Matthewhttps://hdl.handle.net/10023/291212024-02-01T03:01:09Z2022-06-15T00:00:00ZThis thesis describes investigations into the chiral phosphoric acid-catalyzed aza-Michael addition-asymmetric protonation between arylamines and various α-substituted vinylheterocycles.
Initially, research focused on the development of optimal reaction conditions for the aza-Michael addition-asymmetric protonation reaction of arylamines and fluorovinylheterocycles, furnishing heterocyclic phenethylamine products containing benzylic stereocentres with a carbon-fluorine bond in good yields (up to 95%) and enantioselectivity (up to >99:1 e.r.). Investigation into the asymmetric protonation step was carried out through DFT calculations and kinetic experiments, this provided evidence for a stereocontrolled proton transfer from catalyst to substrate. Additionally, the conformation of the heterocyclic phenethylamine products was explored through DFT calculations and XRD.
Chlorovinylheterocycles were also investigated within the aza-Michael addition- asymmetric protonation reaction, furnishing heterocyclic phenethylamine products containing benzylic stereocentres with a carbon-chlorine bond in good yields (up to 99%) and enantioselectivity (up to 99:1 e.r.). Development of a one-pot aza-Michael addition- asymmetric protonation-ring closure reaction was also carried out to furnish chiral heterocyclic aziridines in good yields (up to 81%) and enantioselectivity (up to 97:3 e.r.). Product derivatization of the chiral heterocyclic aziridines furnished chiral vicinal diamines in good yields (up to 84% yield) and enantioselectivity (up to 96:4 e.r.). Catalyst variation experiments showed the importance of steric interactions from the catalyst
alkyl groups in enforcing high enantioselectivity.
2022-06-15T00:00:00ZAshford, MatthewThis thesis describes investigations into the chiral phosphoric acid-catalyzed aza-Michael addition-asymmetric protonation between arylamines and various α-substituted vinylheterocycles.
Initially, research focused on the development of optimal reaction conditions for the aza-Michael addition-asymmetric protonation reaction of arylamines and fluorovinylheterocycles, furnishing heterocyclic phenethylamine products containing benzylic stereocentres with a carbon-fluorine bond in good yields (up to 95%) and enantioselectivity (up to >99:1 e.r.). Investigation into the asymmetric protonation step was carried out through DFT calculations and kinetic experiments, this provided evidence for a stereocontrolled proton transfer from catalyst to substrate. Additionally, the conformation of the heterocyclic phenethylamine products was explored through DFT calculations and XRD.
Chlorovinylheterocycles were also investigated within the aza-Michael addition- asymmetric protonation reaction, furnishing heterocyclic phenethylamine products containing benzylic stereocentres with a carbon-chlorine bond in good yields (up to 99%) and enantioselectivity (up to 99:1 e.r.). Development of a one-pot aza-Michael addition- asymmetric protonation-ring closure reaction was also carried out to furnish chiral heterocyclic aziridines in good yields (up to 81%) and enantioselectivity (up to 97:3 e.r.). Product derivatization of the chiral heterocyclic aziridines furnished chiral vicinal diamines in good yields (up to 84% yield) and enantioselectivity (up to 96:4 e.r.). Catalyst variation experiments showed the importance of steric interactions from the catalyst
alkyl groups in enforcing high enantioselectivity.MOF-based membranes for challenging gas separationsJia, Qianhttps://hdl.handle.net/10023/290292024-02-15T03:07:41Z2024-06-13T00:00:00ZMetal-organic framework materials (MOFs) have been extensively studied as adsorbents for carbon capture applications over past decades. However, when it comes to MOF-based membranes for CO₂ separation, factors that determine membrane performance are not limited to CO₂ adsorption capacity. Especially for mixed matrix membranes, other factors, such as MOF morphology, pore structure, and its compatibility with polymer materials are also of importance and should be considered in membrane design. The relevant background and literature review about the-state-of-the-art technology are provided in Chapter 1. In according to current research, various MOF materials with distinct properties have been applied for membrane-based gas separation in this PhD study, and their performance is discussed in Chapters 4 to 7.
In Chapter 4, two types of pure MOF membranes, crystalline and glassy, are introduced, however, they were difficult to work with and their membrane separation performance was not promising. Chapters 5 to 7 discuss the performance of MOFs as fillers in mixed matrix polymer membranes. MOFs were incorporated into two types of polymer at different loadings, namely PEBAX MH1657 and Matrimid®5218. The MOF materials can be classified into three types in terms of their morphology including nanoparticles (Chapter 5), nanoplates (Chapter 6) and nanosheets (Chapter 7). The incorporation of different MOF fillers generally achieved improvements in both gas permeability and some showed improvements in selectivity. A general conclusion is drawn in Chapter 8. In addition, the methodologies of MOF material and membrane preparation as well as material characterisation techniques are introduced in Chapter 3.
2024-06-13T00:00:00ZJia, QianMetal-organic framework materials (MOFs) have been extensively studied as adsorbents for carbon capture applications over past decades. However, when it comes to MOF-based membranes for CO₂ separation, factors that determine membrane performance are not limited to CO₂ adsorption capacity. Especially for mixed matrix membranes, other factors, such as MOF morphology, pore structure, and its compatibility with polymer materials are also of importance and should be considered in membrane design. The relevant background and literature review about the-state-of-the-art technology are provided in Chapter 1. In according to current research, various MOF materials with distinct properties have been applied for membrane-based gas separation in this PhD study, and their performance is discussed in Chapters 4 to 7.
In Chapter 4, two types of pure MOF membranes, crystalline and glassy, are introduced, however, they were difficult to work with and their membrane separation performance was not promising. Chapters 5 to 7 discuss the performance of MOFs as fillers in mixed matrix polymer membranes. MOFs were incorporated into two types of polymer at different loadings, namely PEBAX MH1657 and Matrimid®5218. The MOF materials can be classified into three types in terms of their morphology including nanoparticles (Chapter 5), nanoplates (Chapter 6) and nanosheets (Chapter 7). The incorporation of different MOF fillers generally achieved improvements in both gas permeability and some showed improvements in selectivity. A general conclusion is drawn in Chapter 8. In addition, the methodologies of MOF material and membrane preparation as well as material characterisation techniques are introduced in Chapter 3.Title redactedDuan, Zhuanhttps://hdl.handle.net/10023/290162024-01-17T03:09:03Z2024-06-13T00:00:00ZAbstract redacted
2024-06-13T00:00:00ZDuan, ZhuanAbstract redactedStudies of lithium-silicon negative electrode materials for batteriesAzad, Atiahttps://hdl.handle.net/10023/288572024-02-09T15:24:54Z2024-06-13T00:00:00ZSilicon is a promising negative electrode material for lithium-ion batteries because of its high specific capacity which is ten times higher than graphite. Lithium silicides are also the negative electrode material for thermal batteries. As a result, lithium silicides are of significant interest to the battery community. There are four thermodynamically stable phases in the lithium-silicon system: Li₂₁Si₅, Li₁₃Si₄, Li₇Si₃, Li₁₂Si₇ and this was determined electrochemically. The coulometric titration curve for lithium silicides was obtained at 415°C by Wen and Huggins. This work collected electrochemical data on lithium silicides as the negative electrode materials for thermal batteries before carrying out neutron diffraction on lithium-silicon phases. Galvanostatic discharges of FeS₂/LiCl-KCl/Li-Si cells were carried out to identify the voltage plateaux. Payne et al observed that no new lithium-silicon phases formed during the discharge of the thermal batteries with NiS₂/Li₁₃Si₄ and CoS₂/Li₁₃Si₄ chemistries. The question remained if a loss in crystallinity occurred due to Li₁₃Si₄ becoming amorphous during lithium removal at high temperature. This work studied if high temperature amorphisation occurs in Li₁₃Si₄ and Li₇Si₃ phases because electrochemically driven amorphisation was seen in the silicon electrode in lithium-ion cells at room temperature. The Li-Si phases were probed at room temperature and at high temperature (500°C). The thermal expansion coefficients were obtained from the neutron data. The samples retained crystallinity and did not become amorphous at high temperature. Both phases were remarkably stable at high temperature. The second part of this work studied the silicon clusters that exist within lithium silicides. The silicon clusters, which behave like molecules, likely control the electrochemistry of the batteries. Structural, magnetic and electronic transitions of the lithium silicides were investigated to find which temperature points to collect longer and good quality structural information with total scattering neutron diffraction.
2024-06-13T00:00:00ZAzad, AtiaSilicon is a promising negative electrode material for lithium-ion batteries because of its high specific capacity which is ten times higher than graphite. Lithium silicides are also the negative electrode material for thermal batteries. As a result, lithium silicides are of significant interest to the battery community. There are four thermodynamically stable phases in the lithium-silicon system: Li₂₁Si₅, Li₁₃Si₄, Li₇Si₃, Li₁₂Si₇ and this was determined electrochemically. The coulometric titration curve for lithium silicides was obtained at 415°C by Wen and Huggins. This work collected electrochemical data on lithium silicides as the negative electrode materials for thermal batteries before carrying out neutron diffraction on lithium-silicon phases. Galvanostatic discharges of FeS₂/LiCl-KCl/Li-Si cells were carried out to identify the voltage plateaux. Payne et al observed that no new lithium-silicon phases formed during the discharge of the thermal batteries with NiS₂/Li₁₃Si₄ and CoS₂/Li₁₃Si₄ chemistries. The question remained if a loss in crystallinity occurred due to Li₁₃Si₄ becoming amorphous during lithium removal at high temperature. This work studied if high temperature amorphisation occurs in Li₁₃Si₄ and Li₇Si₃ phases because electrochemically driven amorphisation was seen in the silicon electrode in lithium-ion cells at room temperature. The Li-Si phases were probed at room temperature and at high temperature (500°C). The thermal expansion coefficients were obtained from the neutron data. The samples retained crystallinity and did not become amorphous at high temperature. Both phases were remarkably stable at high temperature. The second part of this work studied the silicon clusters that exist within lithium silicides. The silicon clusters, which behave like molecules, likely control the electrochemistry of the batteries. Structural, magnetic and electronic transitions of the lithium silicides were investigated to find which temperature points to collect longer and good quality structural information with total scattering neutron diffraction.Clean up of bleed air contaminationAftab, Sadafhttps://hdl.handle.net/10023/287682023-11-28T03:02:16Z2020-07-29T00:00:00ZTo compensate for the low temperature and pressure at high altitude, the air provided to the cabin of the aircraft is drawn from the jet engine. This is known as bleed air which provides heat and pressurises the cabin and flight deck. As the air passes the engine, any minor mechanical faults can cause leakage of engine oil into the stream of air being fed into the cabin which can contaminate the air. There is growing evidence to suggest that this cabin air contamination in aircrafts is causing illness in passengers and this is accompanied by a concern that aviation safety regulators are not taking preventative actions.
The focus of this work was to develop a catalyst for bleed air contamination. For this, stainless steel 314 and 316 foams were modified and tested for the oxidation of known contaminants. The oxidised foam possessed had chemical composition of spinel oxides therefore, spinel oxides were also synthesised, reduced and etched during this work and were then tested. Stainless steel foam was an ideal candidate for this process as it can be used as a catalyst itself or act as a support to impregnate other catalytically active species on it. Spinel oxides also possess good catalytic capabilities. The main focus of the work was toluene as it is not only a contaminant in the cabin air but is also found in many industrial waste streams. It is also a model volatile organic compound therefore the catalytic system developed can be used in more than one application. Another contaminant studied was ethyl acetate which has been tested due to being present in the cabin air in the past.
Raw SS 314/316 foams were modified via oxidation and dip coating to be investigated for the oxidation of toluene/ethyl acetate in to CO₂ (g) and H₂O (v) in a lab scale rig at temperatures between 200 and 500 °C. MnFeCrO₄ and MnNiCrO₄ spinels were synthesised using solution combustion method and reduced at different temperatures. The reduced spinels were tested for oxidation of toluene. The results show that the impregnated SS 316 foams have higher selectivity towards production of CO₂ (g) at lower temperatures compared to SS 314 foams and spinels.
2020-07-29T00:00:00ZAftab, SadafTo compensate for the low temperature and pressure at high altitude, the air provided to the cabin of the aircraft is drawn from the jet engine. This is known as bleed air which provides heat and pressurises the cabin and flight deck. As the air passes the engine, any minor mechanical faults can cause leakage of engine oil into the stream of air being fed into the cabin which can contaminate the air. There is growing evidence to suggest that this cabin air contamination in aircrafts is causing illness in passengers and this is accompanied by a concern that aviation safety regulators are not taking preventative actions.
The focus of this work was to develop a catalyst for bleed air contamination. For this, stainless steel 314 and 316 foams were modified and tested for the oxidation of known contaminants. The oxidised foam possessed had chemical composition of spinel oxides therefore, spinel oxides were also synthesised, reduced and etched during this work and were then tested. Stainless steel foam was an ideal candidate for this process as it can be used as a catalyst itself or act as a support to impregnate other catalytically active species on it. Spinel oxides also possess good catalytic capabilities. The main focus of the work was toluene as it is not only a contaminant in the cabin air but is also found in many industrial waste streams. It is also a model volatile organic compound therefore the catalytic system developed can be used in more than one application. Another contaminant studied was ethyl acetate which has been tested due to being present in the cabin air in the past.
Raw SS 314/316 foams were modified via oxidation and dip coating to be investigated for the oxidation of toluene/ethyl acetate in to CO₂ (g) and H₂O (v) in a lab scale rig at temperatures between 200 and 500 °C. MnFeCrO₄ and MnNiCrO₄ spinels were synthesised using solution combustion method and reduced at different temperatures. The reduced spinels were tested for oxidation of toluene. The results show that the impregnated SS 316 foams have higher selectivity towards production of CO₂ (g) at lower temperatures compared to SS 314 foams and spinels.Exploration of halogenases and chitinases for the production of halogenated compounds and the remediation of chitin-containing wasteDhaliwal, Jagwinderhttps://hdl.handle.net/10023/286832023-11-14T03:02:25Z2024-06-13T00:00:00ZThis work aims to tackle two different subject matters with the utilisation of enzymes. The first part aims to illustrate the potential of flavin-dependent halogenases when applied to the synthesis of halogenated organic molecules, which have become important tools in the pharmaceutical and agricultural industries. Here we use a combination of in silico methods to identify five potential FDHs and subsequently designed and generated constructs for testing. Large-scale production and purification was carried out for three candidates which were subsequently tested in vitro using a substrate library. Initial results suggest that there is a degree of halogenation observed even in reactions which did not contain halogenase. These findings have now also been observed by others. Subsequent work with one of the enzymes showed that it was capable of halogenating several substrates with good conversion under modified conditions.
Part two aims to tackle the ongoing problem of seafood waste, which is often discarded into the ocean, onto beaches or burned. Chitinases are enzymes which are capable of breaking down the chitin matrix and could be applied to remediating such waste products to produce value-added products. Here we identify a chitinase from the mosquito parasite, Crithidia fasciculata. We then sought to test the ability of this chitinase (CfCHT1) to break down chitin and its analogues. We found CfCHT1 to be active on short oligomers, but unable to break down colloidal chitin, precluding its use for degrading larger polymeric units of chitin, as found in seafood waste. Nevertheless, we determined that CfCHT1 is primarily an endochitinase, but also possesses a small amount of exochitinase activity. We also tested its optimum pH, temperature and stability to pH and temperature. Finally, we attempted to obtain crystallographic data to aid our understanding of CfCHT1. Moreover, we believe that CfCHT1 may not be a true chitinase.
2024-06-13T00:00:00ZDhaliwal, JagwinderThis work aims to tackle two different subject matters with the utilisation of enzymes. The first part aims to illustrate the potential of flavin-dependent halogenases when applied to the synthesis of halogenated organic molecules, which have become important tools in the pharmaceutical and agricultural industries. Here we use a combination of in silico methods to identify five potential FDHs and subsequently designed and generated constructs for testing. Large-scale production and purification was carried out for three candidates which were subsequently tested in vitro using a substrate library. Initial results suggest that there is a degree of halogenation observed even in reactions which did not contain halogenase. These findings have now also been observed by others. Subsequent work with one of the enzymes showed that it was capable of halogenating several substrates with good conversion under modified conditions.
Part two aims to tackle the ongoing problem of seafood waste, which is often discarded into the ocean, onto beaches or burned. Chitinases are enzymes which are capable of breaking down the chitin matrix and could be applied to remediating such waste products to produce value-added products. Here we identify a chitinase from the mosquito parasite, Crithidia fasciculata. We then sought to test the ability of this chitinase (CfCHT1) to break down chitin and its analogues. We found CfCHT1 to be active on short oligomers, but unable to break down colloidal chitin, precluding its use for degrading larger polymeric units of chitin, as found in seafood waste. Nevertheless, we determined that CfCHT1 is primarily an endochitinase, but also possesses a small amount of exochitinase activity. We also tested its optimum pH, temperature and stability to pH and temperature. Finally, we attempted to obtain crystallographic data to aid our understanding of CfCHT1. Moreover, we believe that CfCHT1 may not be a true chitinase.Designed synthesis and structural investigation of novel zeolites in the ABC-6 familyChitac, Ruxandra Georgianahttps://hdl.handle.net/10023/286592023-11-13T16:57:45Z2023-11-29T00:00:00ZAbstract redacted
2023-11-29T00:00:00ZChitac, Ruxandra GeorgianaAbstract redactedDesign and synthesis of red thermally activated delayed fluorescence emitters for OLEDs, sensors and bioimagingSi, Changfenghttps://hdl.handle.net/10023/286292023-11-24T15:11:54Z2023-11-29T00:00:00ZDeveloping efficient red thermally activated delayed fluorescence (TADF) emitters remains a formidable challenge due to their low photoluminescence quantum yield governed by the energy-gap law. This thesis concerns the study of orange-to-red TADF materials, focusing on their molecular design, synthesis and photophysics. In addition to OLEDs, these materials were employed as sensors and bioimaging reagents.
Chapter 1 introduces fundamental principles of photoluminescence, electroluminescence, and provides a review of red TADF emitters for OLEDs and TADF emitters for bioimaging.
Chapter 2 documents the relationship between different N-doped polycyclic aromatic hydrocarbons (PAH)-acceptor compounds (DMACBP, DMACPyBP, DMACBPN and DMACPyBPN), their photophysics and OLED performance.
Chapter 3 focuses on a molecular design strategy that combines a p-conjugated acceptors with a TPA donor. By modulating the solid-state solvatochromism and adjusting the p-p stacking interactions, a deep red emission was obtained from both the TPAPyBPN-doped films and its OLED. Furthermore, we demonstrated the first TADF optical sensor for ZnCl₂ based on TPAPyBP.
Chapter 4 explores four new yellow-to-red TADF dendrimer emitters, which were designed to be solution processable. We systematically investigated the effect of substitution position and the strength of the donors on the optoelectronic properties of these four dendrimers. Finally, we employed these emitters in solution-processed OLEDs.
Chapter 5 continues the work on TADF dendrimer emitters by investigating the effect of extending the p-conjugation of the acceptor on the photophsics of the compound. 2GCzBPPZ, with a much larger planarity and p-conjugation acceptor, shows unusual dual emission that is both concentration-dependent and temperature-dependent in solution. 2GCzBPPZ is the first small molecule TADF compound used for colorimetric temperature sensing.
Chapter 6 presents three tetra(donor)-acceptor compounds TCzPhCor, TDMACPhCor, and TPXZPhCor employing corannulene, a curved PAH, as the acceptor. These three emitters exhibit room-temperature phosphorescence from different excited triplet states. While TPXZPhCor doped film can act as an optical temperature sensor in the range from 77 K to 298 K. We also fabricated solution-processed afterglow OLEDs using TPXZPhCor.
Chapter 7 explores the use of D-A TADF emitters in bioimaging. We discussed two types of water-soluble materials: nanoparticles and water-soluble sodium-salt emitters. We also document our first attempt to study these compounds in vitro.
2023-11-29T00:00:00ZSi, ChangfengDeveloping efficient red thermally activated delayed fluorescence (TADF) emitters remains a formidable challenge due to their low photoluminescence quantum yield governed by the energy-gap law. This thesis concerns the study of orange-to-red TADF materials, focusing on their molecular design, synthesis and photophysics. In addition to OLEDs, these materials were employed as sensors and bioimaging reagents.
Chapter 1 introduces fundamental principles of photoluminescence, electroluminescence, and provides a review of red TADF emitters for OLEDs and TADF emitters for bioimaging.
Chapter 2 documents the relationship between different N-doped polycyclic aromatic hydrocarbons (PAH)-acceptor compounds (DMACBP, DMACPyBP, DMACBPN and DMACPyBPN), their photophysics and OLED performance.
Chapter 3 focuses on a molecular design strategy that combines a p-conjugated acceptors with a TPA donor. By modulating the solid-state solvatochromism and adjusting the p-p stacking interactions, a deep red emission was obtained from both the TPAPyBPN-doped films and its OLED. Furthermore, we demonstrated the first TADF optical sensor for ZnCl₂ based on TPAPyBP.
Chapter 4 explores four new yellow-to-red TADF dendrimer emitters, which were designed to be solution processable. We systematically investigated the effect of substitution position and the strength of the donors on the optoelectronic properties of these four dendrimers. Finally, we employed these emitters in solution-processed OLEDs.
Chapter 5 continues the work on TADF dendrimer emitters by investigating the effect of extending the p-conjugation of the acceptor on the photophsics of the compound. 2GCzBPPZ, with a much larger planarity and p-conjugation acceptor, shows unusual dual emission that is both concentration-dependent and temperature-dependent in solution. 2GCzBPPZ is the first small molecule TADF compound used for colorimetric temperature sensing.
Chapter 6 presents three tetra(donor)-acceptor compounds TCzPhCor, TDMACPhCor, and TPXZPhCor employing corannulene, a curved PAH, as the acceptor. These three emitters exhibit room-temperature phosphorescence from different excited triplet states. While TPXZPhCor doped film can act as an optical temperature sensor in the range from 77 K to 298 K. We also fabricated solution-processed afterglow OLEDs using TPXZPhCor.
Chapter 7 explores the use of D-A TADF emitters in bioimaging. We discussed two types of water-soluble materials: nanoparticles and water-soluble sodium-salt emitters. We also document our first attempt to study these compounds in vitro.Computational insights into catalytic mechanism and thermostability of the enzyme Is-PETaseShrimpton-Phoenix, Eugenehttps://hdl.handle.net/10023/285922024-03-04T11:45:04Z2023-11-29T00:00:00ZThe field of study surrounding the PETase class of enzymes has gained a great deal of popularity in
the past five years. PETases are enzymes capable of degrading poly(ethylene) terephthalate and
presents an opportunity to bioanalytically recycle this common pollutant. The most extensively
researched PETase is the enzyme Is-PETase, which originates from the organism Idonella
sakaiensis and was discovered near a recycling plant in 2016. To further the utility of Is-PETase in
the industrial recycling of poly(ethylene) terephthalate, improvements in desirable properties
such as catalytic rate and thermostability must be achieved via introduction of amino-acid
substitutions to the enzyme.
In order to further improve the activity of Is-PETase, it would be informative to have a deeper
understanding of its catalytic mechanism. To this end, we have investigated the catalytic
mechanism of the degradation of poly(ethylene) terephthalate via Is-PETase. We applied hybrid
quantum mechanical/ molecular mechanical to generate several independent reaction profiles.
From these reaction profiles we have concluded that this reaction proceeds with an overall
activation barrier of 35.6 kJ mol-1
. This relatively low activation barrier suggests that the ‘true’
rate-limiting step for this reaction is a physical process such as substrate binding or product
dissociation. Our calculations provide preliminary evidence for the product dissociation step being
rate-limiting.
We have also investigated modifications to wild-type Is-PETase that contribute to the enzyme’s
thermostability. We have created our own mutant of Is-PETase, DISU-PETase, through the in silico
introduction of a novel disulfide bond. We generated reaction profiles for DISU-PETase using the
same quantum mechanical/ molecular mechanical techniques as applied to wild-type Is-PETase.
We found that introduction of the novel disulfide bond in DISU-PETase had no adverse effect upon
the reaction profile of the degradation of poly(ethylene) terephthalate. We have also applied
molecular dynamics techniques to investigate the intramolecular interactions that contribute
toward the thermostability of the most highly active variants of Is-PETase in the literature.
We have also used our quantum mechanical/ molecular mechanical techniques to generate
reaction profiles for the degradation of an alternate substrate, poly(ethylene) furanoate via wildtype Is-PETase.
2023-11-29T00:00:00ZShrimpton-Phoenix, EugeneThe field of study surrounding the PETase class of enzymes has gained a great deal of popularity in
the past five years. PETases are enzymes capable of degrading poly(ethylene) terephthalate and
presents an opportunity to bioanalytically recycle this common pollutant. The most extensively
researched PETase is the enzyme Is-PETase, which originates from the organism Idonella
sakaiensis and was discovered near a recycling plant in 2016. To further the utility of Is-PETase in
the industrial recycling of poly(ethylene) terephthalate, improvements in desirable properties
such as catalytic rate and thermostability must be achieved via introduction of amino-acid
substitutions to the enzyme.
In order to further improve the activity of Is-PETase, it would be informative to have a deeper
understanding of its catalytic mechanism. To this end, we have investigated the catalytic
mechanism of the degradation of poly(ethylene) terephthalate via Is-PETase. We applied hybrid
quantum mechanical/ molecular mechanical to generate several independent reaction profiles.
From these reaction profiles we have concluded that this reaction proceeds with an overall
activation barrier of 35.6 kJ mol-1
. This relatively low activation barrier suggests that the ‘true’
rate-limiting step for this reaction is a physical process such as substrate binding or product
dissociation. Our calculations provide preliminary evidence for the product dissociation step being
rate-limiting.
We have also investigated modifications to wild-type Is-PETase that contribute to the enzyme’s
thermostability. We have created our own mutant of Is-PETase, DISU-PETase, through the in silico
introduction of a novel disulfide bond. We generated reaction profiles for DISU-PETase using the
same quantum mechanical/ molecular mechanical techniques as applied to wild-type Is-PETase.
We found that introduction of the novel disulfide bond in DISU-PETase had no adverse effect upon
the reaction profile of the degradation of poly(ethylene) terephthalate. We have also applied
molecular dynamics techniques to investigate the intramolecular interactions that contribute
toward the thermostability of the most highly active variants of Is-PETase in the literature.
We have also used our quantum mechanical/ molecular mechanical techniques to generate
reaction profiles for the degradation of an alternate substrate, poly(ethylene) furanoate via wildtype Is-PETase.Photocatalytic C(sp³)–C(sp²) radical-polar crossover cross-coupling of styrenyl boronic acidsBrals, Jeremyhttps://hdl.handle.net/10023/285842023-10-30T10:09:38Z2023-11-29T00:00:00ZOrganoboron reagents are widely used in organic chemistry due to their versatile reactivity, ubiquity, stability, and low cost. They are commonly employed as coupling partners in cross-coupling reactions, such as the Pd-catalysed Suzuki-Miyaura reaction, which is responsible for 40% of C–C bond formation reactions in the pharmaceutical industry. However, with the development of the photoredox chemistry over the last 15 years, radical-mediated cross-coupling reactions have flourished. Radicals are now easily made from cheap-commercially-available or easy-to-make precursors using visible light irradiation. They can then further react with numerous different coupling partners leading to an extensive range of new cross coupling opportunities, without the requirement for a photocatalyst in some cases. Organoborons have mostly been employed as radical precursors but their use as coupling partners has increased over the past few years.
N-(Acyloxy)phthalimides (NHPI) esters, a class of redox activated ester species, are widely used as alkyl radical precursors owing to their bench-stability and ease of access. Single electron transfer (SET) affords the desired radical through decarboxylation. In this work, we disclose a new method for C–C bond formation between a styrenyl boronic acid and NHPI ester under Ru-mediated photocatalysis. The reaction proceeds smoothly within three hours under blue LED irradiation and affords the desired products in good to excellent yields. The radical addition undergoes unusual polarity-mismatched Giese-type addition to the organoboron coupling partner. A radical polar crossover reaction requires the presence of a redox-active additive to enable the desired bond formation to occur, and proceeds via an unusual boronic acid priming event. This thesis will describe the development and application of this reaction.
2023-11-29T00:00:00ZBrals, JeremyOrganoboron reagents are widely used in organic chemistry due to their versatile reactivity, ubiquity, stability, and low cost. They are commonly employed as coupling partners in cross-coupling reactions, such as the Pd-catalysed Suzuki-Miyaura reaction, which is responsible for 40% of C–C bond formation reactions in the pharmaceutical industry. However, with the development of the photoredox chemistry over the last 15 years, radical-mediated cross-coupling reactions have flourished. Radicals are now easily made from cheap-commercially-available or easy-to-make precursors using visible light irradiation. They can then further react with numerous different coupling partners leading to an extensive range of new cross coupling opportunities, without the requirement for a photocatalyst in some cases. Organoborons have mostly been employed as radical precursors but their use as coupling partners has increased over the past few years.
N-(Acyloxy)phthalimides (NHPI) esters, a class of redox activated ester species, are widely used as alkyl radical precursors owing to their bench-stability and ease of access. Single electron transfer (SET) affords the desired radical through decarboxylation. In this work, we disclose a new method for C–C bond formation between a styrenyl boronic acid and NHPI ester under Ru-mediated photocatalysis. The reaction proceeds smoothly within three hours under blue LED irradiation and affords the desired products in good to excellent yields. The radical addition undergoes unusual polarity-mismatched Giese-type addition to the organoboron coupling partner. A radical polar crossover reaction requires the presence of a redox-active additive to enable the desired bond formation to occur, and proceeds via an unusual boronic acid priming event. This thesis will describe the development and application of this reaction.Isothiourea-catalyzed enantioselective reactions of imines with α,β-unsaturated esters employing α,β- unsaturated acyl ammonium intermediatesLapetaje, Jersonhttps://hdl.handle.net/10023/285642023-10-26T02:01:35Z2023-11-29T00:00:00ZThe use of isothioureas as Lewis base organocatalysts has been widely studied by the Smith group and shown to be effective in various Michael addition and annulation reactions, which is associated with the formation of the reactive α,β-unsaturated acyl ammonium intermediates. To further explore the reactivity of these reactive intermediates, this research project focuses on employing α,β-unsaturated acyl ammonium intermediates to perform various reactions such as (i) aza-Michael addition reactions, (ii) Michael addition reactions, and (iii) a Michael- addition-cyclisation-lactonisation cascade reactions using imines and other imine derivatives as nucleophiles to access a range of chiral compounds with important structural motifs (e.g. β-amino acids, γ-imino esters and amides, γ-lactam compounds, and pyrrolidine compounds) in high enantio- and diastereoselectivity.
In this work, successful protocols for the highly selective aza-Michael addition reaction and Michael addition reaction of imine nucleophiles to α,β-unsaturated ester substrates were established to obtain various β-imino esters, β-imino amides, various γ-imino amide and ester products via the access of the reactive α,β-unsaturated acyl ammonium intermediate using an enantiopure isothiourea organocatalyst showing moderate to excellent yield (20% – 81%) and enantio- and diastereoselectivity ((<97:3 er, <96:4 dr). A proof of concept for the highly enantio- and diastereoselective formation of a chromeno-pyrrolidine product was highlighted from the reaction of a Schiff base and α,β-unsaturated ester substrate using isothiourea organocatalyst showing moderate yield (48% yield) but with excellent selectivity (99:1 er, >99:1 dr). The reaction was deduced to follow a highly stereoselective Michael addition, followed by a 5-endo-trig cyclization reaction to generate the pyrrolidine core, and a subsequent lactonization reaction to form the chromeno-pyrrolidine product in excellent enantio- and diastereoselectivity.
2023-11-29T00:00:00ZLapetaje, JersonThe use of isothioureas as Lewis base organocatalysts has been widely studied by the Smith group and shown to be effective in various Michael addition and annulation reactions, which is associated with the formation of the reactive α,β-unsaturated acyl ammonium intermediates. To further explore the reactivity of these reactive intermediates, this research project focuses on employing α,β-unsaturated acyl ammonium intermediates to perform various reactions such as (i) aza-Michael addition reactions, (ii) Michael addition reactions, and (iii) a Michael- addition-cyclisation-lactonisation cascade reactions using imines and other imine derivatives as nucleophiles to access a range of chiral compounds with important structural motifs (e.g. β-amino acids, γ-imino esters and amides, γ-lactam compounds, and pyrrolidine compounds) in high enantio- and diastereoselectivity.
In this work, successful protocols for the highly selective aza-Michael addition reaction and Michael addition reaction of imine nucleophiles to α,β-unsaturated ester substrates were established to obtain various β-imino esters, β-imino amides, various γ-imino amide and ester products via the access of the reactive α,β-unsaturated acyl ammonium intermediate using an enantiopure isothiourea organocatalyst showing moderate to excellent yield (20% – 81%) and enantio- and diastereoselectivity ((<97:3 er, <96:4 dr). A proof of concept for the highly enantio- and diastereoselective formation of a chromeno-pyrrolidine product was highlighted from the reaction of a Schiff base and α,β-unsaturated ester substrate using isothiourea organocatalyst showing moderate yield (48% yield) but with excellent selectivity (99:1 er, >99:1 dr). The reaction was deduced to follow a highly stereoselective Michael addition, followed by a 5-endo-trig cyclization reaction to generate the pyrrolidine core, and a subsequent lactonization reaction to form the chromeno-pyrrolidine product in excellent enantio- and diastereoselectivity.Enantioselective fluorination of bioactive amines and succinic acids for selected bioassaysRenault, Yohann Jean Gilleshttps://hdl.handle.net/10023/283962023-09-16T02:05:58Z2023-11-29T00:00:00ZSince its isolation by Henri Moissan in 1886, fluorine has garnered a growing interest within many fields of chemistry. This attention is a result of the unique properties of fluorine, explained by it being the most electronegative element in the Periodic Table. Chapter I introduces the principal characteristics of fluoro-compounds. A description of the different synthetic processes that have been developed to afford fluoro-organic molecules is then detailed. Finally, a brief history of fluoro-containing drugs is reviewed,
including the impact of fluorine regarding essential parameters that are necessary in their design, such as lipophilicity, acidity, and hydrogen bonding. Chapter II gives an overview of the three different methodologies of enantioselective α fluorination of aldehydes that were developed in 2005. This is followed by development of a new approach to the determination of enantiomeric ratios (er) of fluoro-amines using ¹⁹F{¹H}-NMR. Finally, the optimisation of α-fluorination of aldehydes toward the synthesis of the fluoro-bioactives will be explored in this chapter. Chapter III focuses on GABA, the principal neurotransmitter inhibitor of the central nervous system, detailing its mode of action and its importance in treating many diseases,alongside its existing analogues. This chapter includes a shorter enantioselective synthesis of 3-F-GABA developing from previous synthesis. Chapter IV explores calcium-sensing receptors (CaSR), their existing modulators and previous enantioselective synthesis of F-cinacalcet. An optimised α-fluorination of aldehydes is explored towards a 2 step 1 pot synthesis of F-cinacalcet ((ꟳS,R)-269, (ꟳR,R)-269) and other fluoro allosteric modulators ((ꟳS,R)-280, (ꟳR,R)-280, (ꟳS,R)-281, (ꟳR,R)-281, (ꟳS,R)-286, (ꟳR,R)-286). The potency of these new F-cinacalcet analogues is assessed in a CaSR bioassay giving an insight into the active molecular conformation. Chapter V gives a general introduction to the importance of isocitrate lyase (ICL) as a drug target for tuberculosis (TB). The design and synthesis of 4 fluoro-succinic acids (S)-315, (R)-315, 316 and 317 as potential ICL inhibitors is achieved. Finally, a ICL bioassay with (S)-315, (R)-315, and 316 is utilised to assess their mode of action.
2023-11-29T00:00:00ZRenault, Yohann Jean GillesSince its isolation by Henri Moissan in 1886, fluorine has garnered a growing interest within many fields of chemistry. This attention is a result of the unique properties of fluorine, explained by it being the most electronegative element in the Periodic Table. Chapter I introduces the principal characteristics of fluoro-compounds. A description of the different synthetic processes that have been developed to afford fluoro-organic molecules is then detailed. Finally, a brief history of fluoro-containing drugs is reviewed,
including the impact of fluorine regarding essential parameters that are necessary in their design, such as lipophilicity, acidity, and hydrogen bonding. Chapter II gives an overview of the three different methodologies of enantioselective α fluorination of aldehydes that were developed in 2005. This is followed by development of a new approach to the determination of enantiomeric ratios (er) of fluoro-amines using ¹⁹F{¹H}-NMR. Finally, the optimisation of α-fluorination of aldehydes toward the synthesis of the fluoro-bioactives will be explored in this chapter. Chapter III focuses on GABA, the principal neurotransmitter inhibitor of the central nervous system, detailing its mode of action and its importance in treating many diseases,alongside its existing analogues. This chapter includes a shorter enantioselective synthesis of 3-F-GABA developing from previous synthesis. Chapter IV explores calcium-sensing receptors (CaSR), their existing modulators and previous enantioselective synthesis of F-cinacalcet. An optimised α-fluorination of aldehydes is explored towards a 2 step 1 pot synthesis of F-cinacalcet ((ꟳS,R)-269, (ꟳR,R)-269) and other fluoro allosteric modulators ((ꟳS,R)-280, (ꟳR,R)-280, (ꟳS,R)-281, (ꟳR,R)-281, (ꟳS,R)-286, (ꟳR,R)-286). The potency of these new F-cinacalcet analogues is assessed in a CaSR bioassay giving an insight into the active molecular conformation. Chapter V gives a general introduction to the importance of isocitrate lyase (ICL) as a drug target for tuberculosis (TB). The design and synthesis of 4 fluoro-succinic acids (S)-315, (R)-315, 316 and 317 as potential ICL inhibitors is achieved. Finally, a ICL bioassay with (S)-315, (R)-315, and 316 is utilised to assess their mode of action.Mechanochemistry for sustainable synthesis of framework materialsRainer, Daniel Nikolaushttps://hdl.handle.net/10023/283302024-03-16T03:02:36Z2022-06-15T00:00:00ZThe following work presents the successful application of mechanochemical methods in the synthesis of framework materials, namely zeolites and sodium carboxylate coordination polymers. Common benefits of employing mechanical forces to aid and cause chemical reactions are typically decreased reaction times, lower amounts or avoidance of solvents, and highly efficient reactions, leading to overall more sustainable processes.
A mechanochemically aided hydrolysis protocol for the second step of the ADOR (Assembly-Disassembly-Organisation-Reassembly) process was devised using zeolites with UTL framework as parent material. In contrast to conventional disassembly, which relies on the reaction occurring in solution at elevated temperatures, the use of a rotary ball mill allows for significant reduction of employed liquids (water or hydrochloric acid) and completion can be achieved on much shorter time scales. This reaction setup minimises waste production and requires lower energy input. Obtained intermediate zeolite phases can be reassembled into known daughter zeolites with *PCS, OKO, and PCR frameworks. The developed protocol and its low volumetric requirements for the hydrolytic reagent are not only beneficial from a purely synthetic point of view but could be applied successfully in the enrichment of product zeolite phases with the NMR active isotope 17O. Such enrichment procedures are typically time and energy consuming as well as carrying a high financial burden due to the low natural abundance of this isotope,
which necessitates enrichment procedures in the first place.
Several of the more complex zeolite frameworks are only obtainable as germanosilicate variant, suffering from the comparatively high cost of germanium reagents compared to silicon or aluminium analogues. In an attempt to extend the scope of the solvent-free route for zeolite synthesis, mechanochemical treatment of starting materials prior to the crystallisation reaction was performed, targeting four different frameworks. Reproducing literature reports, zeolites with ITH structure could be obtained. Further, materials with UOV structure were targeted, but instead yielding structurally related BEC zeolites. Synthesis of UTL was so far unsuccessful, but experiments additionally using seed crystals of the desired phase showed some preliminary success. Finally, pure silica and germanosilicate materials with ISV framework were synthesised for the first time using a solvent-free approach.
Sodium carboxylates, members of the class of framework materials called coordination polymers, are promising candidates for organic-based anodes of sodium ion batteries, but face difficulties in large scale production. A mechanochemical synthesis route for sodium carboxylates using several, chemically varied organic carboxylic acids and the environmentally benign sodium acetate as source for the alkali metal, has been developed to alleviate most of these concerns. Produced materials show electrochemical
performance on par with compounds obtained through conventional solution-based synthesis, with improved reaction conditions, avoidance of solvent and thus reduced waste.
2022-06-15T00:00:00ZRainer, Daniel NikolausThe following work presents the successful application of mechanochemical methods in the synthesis of framework materials, namely zeolites and sodium carboxylate coordination polymers. Common benefits of employing mechanical forces to aid and cause chemical reactions are typically decreased reaction times, lower amounts or avoidance of solvents, and highly efficient reactions, leading to overall more sustainable processes.
A mechanochemically aided hydrolysis protocol for the second step of the ADOR (Assembly-Disassembly-Organisation-Reassembly) process was devised using zeolites with UTL framework as parent material. In contrast to conventional disassembly, which relies on the reaction occurring in solution at elevated temperatures, the use of a rotary ball mill allows for significant reduction of employed liquids (water or hydrochloric acid) and completion can be achieved on much shorter time scales. This reaction setup minimises waste production and requires lower energy input. Obtained intermediate zeolite phases can be reassembled into known daughter zeolites with *PCS, OKO, and PCR frameworks. The developed protocol and its low volumetric requirements for the hydrolytic reagent are not only beneficial from a purely synthetic point of view but could be applied successfully in the enrichment of product zeolite phases with the NMR active isotope 17O. Such enrichment procedures are typically time and energy consuming as well as carrying a high financial burden due to the low natural abundance of this isotope,
which necessitates enrichment procedures in the first place.
Several of the more complex zeolite frameworks are only obtainable as germanosilicate variant, suffering from the comparatively high cost of germanium reagents compared to silicon or aluminium analogues. In an attempt to extend the scope of the solvent-free route for zeolite synthesis, mechanochemical treatment of starting materials prior to the crystallisation reaction was performed, targeting four different frameworks. Reproducing literature reports, zeolites with ITH structure could be obtained. Further, materials with UOV structure were targeted, but instead yielding structurally related BEC zeolites. Synthesis of UTL was so far unsuccessful, but experiments additionally using seed crystals of the desired phase showed some preliminary success. Finally, pure silica and germanosilicate materials with ISV framework were synthesised for the first time using a solvent-free approach.
Sodium carboxylates, members of the class of framework materials called coordination polymers, are promising candidates for organic-based anodes of sodium ion batteries, but face difficulties in large scale production. A mechanochemical synthesis route for sodium carboxylates using several, chemically varied organic carboxylic acids and the environmentally benign sodium acetate as source for the alkali metal, has been developed to alleviate most of these concerns. Produced materials show electrochemical
performance on par with compounds obtained through conventional solution-based synthesis, with improved reaction conditions, avoidance of solvent and thus reduced waste.Photocatalytic oxidation of glucose and cellulose to valuable chemicals and hydrogenGkoulemani, Nikolettahttps://hdl.handle.net/10023/282212023-09-04T09:50:24Z2023-11-29T00:00:00ZUtilization of biomass is promising in the process of shifting from fossil fuels usage and evolving technologies implementation. Also, through the mild conditions required for the heterogeneous photocatalysis of cellulose and glucose, various products including organic acids, sugar alcohols, oligosaccharides, and H₂ can be produced.
The photocatalytic conversion of glucose was studied under aerobic (atm P), anaerobic (vacuum), inert (Ar) atmosphere and varying irradiation. TiO₂ was the main photocatalyst with Fe₂O₃, Pt, and g-C₃N₄ as co-catalysts. The Fe₂O₃ containing catalysts increased glucose conversion compared to bare TiO₂, Pt containing catalysts increased H₂ production, and g-C₃N₄ containing catalysts showed poor overall performance.
A photoreactor with internal irradiation was designed and developed to monitor and control multiple conditions of the photocatalytic testing and achieve simultaneous gas and liquid products analysis. While the analysis of sugars was conducted mainly via HPLC, study of these molecules and development of sugar mixtures analysis was conducted additionally via Raman spectroscopy, providing a quick, cost effective and non destructive alternative.
Characterisation of the synthesized catalysts was conducted via multiple analytical techniques, defining the crystal phases, optical behaviour, morphology, and participating phases. Fe₂O₃ increased the visible light absorption of the catalysts, while preserving the properties of TiO₂. High dispersion of the Fe₂O₃ phase was achieved upon addition in low percentages. The Pt/TiO₂ catalysts also showed high dispersion of the metal on the support, while preserving the surface area of TiO₂. The Fe₂O₃/g-C₃N₄-TiO₂ catalysts showed poor homogeneity across the material.
Cellulose was characterised regarding the particle size, morphology, and crystalline index. Pre-treatment of cellulose was conducted through ball milling, promoting interaction with the catalyst, which was investigated through multiple techniques. Results of cellulose photocatalytic testing showed H₂ evolution and production of various liquid products. Using the developed photoreactor both gas and liquid products were successfully recorded through chromatographic analysis.
2023-11-29T00:00:00ZGkoulemani, NikolettaUtilization of biomass is promising in the process of shifting from fossil fuels usage and evolving technologies implementation. Also, through the mild conditions required for the heterogeneous photocatalysis of cellulose and glucose, various products including organic acids, sugar alcohols, oligosaccharides, and H₂ can be produced.
The photocatalytic conversion of glucose was studied under aerobic (atm P), anaerobic (vacuum), inert (Ar) atmosphere and varying irradiation. TiO₂ was the main photocatalyst with Fe₂O₃, Pt, and g-C₃N₄ as co-catalysts. The Fe₂O₃ containing catalysts increased glucose conversion compared to bare TiO₂, Pt containing catalysts increased H₂ production, and g-C₃N₄ containing catalysts showed poor overall performance.
A photoreactor with internal irradiation was designed and developed to monitor and control multiple conditions of the photocatalytic testing and achieve simultaneous gas and liquid products analysis. While the analysis of sugars was conducted mainly via HPLC, study of these molecules and development of sugar mixtures analysis was conducted additionally via Raman spectroscopy, providing a quick, cost effective and non destructive alternative.
Characterisation of the synthesized catalysts was conducted via multiple analytical techniques, defining the crystal phases, optical behaviour, morphology, and participating phases. Fe₂O₃ increased the visible light absorption of the catalysts, while preserving the properties of TiO₂. High dispersion of the Fe₂O₃ phase was achieved upon addition in low percentages. The Pt/TiO₂ catalysts also showed high dispersion of the metal on the support, while preserving the surface area of TiO₂. The Fe₂O₃/g-C₃N₄-TiO₂ catalysts showed poor homogeneity across the material.
Cellulose was characterised regarding the particle size, morphology, and crystalline index. Pre-treatment of cellulose was conducted through ball milling, promoting interaction with the catalyst, which was investigated through multiple techniques. Results of cellulose photocatalytic testing showed H₂ evolution and production of various liquid products. Using the developed photoreactor both gas and liquid products were successfully recorded through chromatographic analysis.Switchable control of nanoparticle surface accessibility using dynamic covalent chemistryHowe, Edward Jameshttps://hdl.handle.net/10023/281912023-08-17T02:07:29Z2022-06-15T00:00:00ZMetal nanoparticles have exciting potential as catalysts for several chemical transformations, often displaying unique reactivity that is unprecedented by the analogous bulk material or organometallic complexes. In contrast to established substrate-supported nanoparticle catalysts, colloidally stable nanoparticles present opportunities for rational optimisation of catalytic activities by combining favourable features of both homogeneous and heterogeneous catalysts. However, achieving high colloidal stability, which requires a surface-passivating coating, while allowing easy access to catalytic sites on the nanoparticle surface remains a key unmet challenge. Some existing strategies rely on mixed monolayers of strong and weakly bound surface ligands, with no clear route to achieving high stability and high reactivity simultaneously; other approaches use ligands with complicated and synthetically demanding structures. Recently, dynamic covalent hydrazone exchange performed within a nanoparticle-bound monolayer has been used to reversibly control nanoparticle properties. This thesis presents the application of dynamically exchangeable steric bulk at the periphery of nanoparticle-bound monolayers to facilitate accessibility to the nanoparticle core without compromising colloidal stability. A series of nanoparticles stabilised by hydrazone-functionalised ligands of differing steric bulk have been synthesised to understand the relationship between ligand peripheral steric bulk and monolayer density. The results reflect the difficulty in deconvoluting the cause and effect of several inter-related factors, primarily the impact of ligand steric bulk on nanoparticle colloidal stability and how this impacts monolayer density. In general, when the density of nanoparticle-bound monolayers is at saturation for a given ligand, nanoparticles bound with sterically bulky ligands consistently have lower monolayer densities compared to nanoparticles coated with less bulky ligands. A method has also been developed to assess the accessibility to nanoparticles surfaces. Using dithiothreitol to displace nanoparticle-bound ligands results in aggregation, which can be monitored using UV-vis spectroscopy. The rate of dithiothreitol-induced nanoparticle aggregation is affected by both monolayer density and the ligand peripheral steric bulk. In general, nanoparticles with dense monolayers showed slow rates of dithiothreitol-induced aggregation. By exploiting the dynamic nature of the hydrazone bond, the monolayer periphery can be tuned via the exchange of aldehydes with differing sizes. The consequent effects on surface accessibility were investigated, revealing that decreasing the steric bulk at the monolayer periphery results in greater accessibility to the nanoparticle core surface. The impact of changing monolayer peripheral bulk on nanoparticle catalytic activity was also investigated. Catalytic activity was generally higher for mixed-ligand monolayer-stabilised nanoparticles with a high proportion of less sterically bulky peripheral units. However, issues maintaining colloidal stability during the catalytic reactions investigated are still to be solved.
2022-06-15T00:00:00ZHowe, Edward JamesMetal nanoparticles have exciting potential as catalysts for several chemical transformations, often displaying unique reactivity that is unprecedented by the analogous bulk material or organometallic complexes. In contrast to established substrate-supported nanoparticle catalysts, colloidally stable nanoparticles present opportunities for rational optimisation of catalytic activities by combining favourable features of both homogeneous and heterogeneous catalysts. However, achieving high colloidal stability, which requires a surface-passivating coating, while allowing easy access to catalytic sites on the nanoparticle surface remains a key unmet challenge. Some existing strategies rely on mixed monolayers of strong and weakly bound surface ligands, with no clear route to achieving high stability and high reactivity simultaneously; other approaches use ligands with complicated and synthetically demanding structures. Recently, dynamic covalent hydrazone exchange performed within a nanoparticle-bound monolayer has been used to reversibly control nanoparticle properties. This thesis presents the application of dynamically exchangeable steric bulk at the periphery of nanoparticle-bound monolayers to facilitate accessibility to the nanoparticle core without compromising colloidal stability. A series of nanoparticles stabilised by hydrazone-functionalised ligands of differing steric bulk have been synthesised to understand the relationship between ligand peripheral steric bulk and monolayer density. The results reflect the difficulty in deconvoluting the cause and effect of several inter-related factors, primarily the impact of ligand steric bulk on nanoparticle colloidal stability and how this impacts monolayer density. In general, when the density of nanoparticle-bound monolayers is at saturation for a given ligand, nanoparticles bound with sterically bulky ligands consistently have lower monolayer densities compared to nanoparticles coated with less bulky ligands. A method has also been developed to assess the accessibility to nanoparticles surfaces. Using dithiothreitol to displace nanoparticle-bound ligands results in aggregation, which can be monitored using UV-vis spectroscopy. The rate of dithiothreitol-induced nanoparticle aggregation is affected by both monolayer density and the ligand peripheral steric bulk. In general, nanoparticles with dense monolayers showed slow rates of dithiothreitol-induced aggregation. By exploiting the dynamic nature of the hydrazone bond, the monolayer periphery can be tuned via the exchange of aldehydes with differing sizes. The consequent effects on surface accessibility were investigated, revealing that decreasing the steric bulk at the monolayer periphery results in greater accessibility to the nanoparticle core surface. The impact of changing monolayer peripheral bulk on nanoparticle catalytic activity was also investigated. Catalytic activity was generally higher for mixed-ligand monolayer-stabilised nanoparticles with a high proportion of less sterically bulky peripheral units. However, issues maintaining colloidal stability during the catalytic reactions investigated are still to be solved.Integrating photoelectrochemical charging into lithium batteries for use as a single multifunctional deviceTupberg, Chayopashttps://hdl.handle.net/10023/281152023-08-20T02:05:46Z2023-11-29T00:00:00ZSolar energy is a promising renewable energy resource. The energy from the sun is typically converted by solar cells and collected into a battery in the form of chemicals. It requires at least two devices for energy conversion and storage. Rechargeable lithium-ion batteries are widely used nowadays because of their high energy density. Lithium manganese oxide, particularly LiMn₂O₄, is commonly used as positive electrodes for lithium batteries. Due to its semiconducting property, it is intriguing to integrate photoelectrochemical charging into lithium-ion batteries for use as a single multifunctional device. Lithium manganospinel was synthesised using sol- gel methods. The effects of calcination temperatures and the molar ratio of Li/Mn defined the lithium manganospinels in the binary LiMn₂O₄–Li₂Mn₄O₉ and the ternary LiMn₂O₄–Li₂Mn₄O₉–Li₄Mn₅O₁₂ systems. To allow the light transmission to interact with LiMn₂O₄ at the electrode/electrolyte interface, LiMn₂O₄ was prepared by spin-coating on a transparent conducting oxide-coated glass substrate. The sol-gel method using methanol as a solvent provided a homogeneous and good-quality film. The film of pure defect spinel Li₀.₉₅₅Mn₁.₉₁₀O₄ calcined at 400 ̊C was mainly studied in this work. The 200 nm thick Li₀.₉₅₅Mn₁.₉₁₀O₄ film coated on F-doped SnO₂ glass substrate possessed a band gap energy of 2.7 eV. Photoelectrochemical cells were built to test the films of Li₀.₉₅₅Mn₁.₉₁₀O₄ in LiNO₃ solution as an aqueous electrolyte and 1 M LiPF₆ in EC/DEC (1:1 w/w) as a non-aqueous electrolyte. The cells were designed to allow UV light to pass through the cells for photoelectrochemical measurement. Cyclic voltammetry, chronopotentiometry, chronoamperometry, and open-circuit potential measurements were carried out to study and understand the photoelectrochemical properties of the films. The results reveal that light irradiation on the cell facilitated the generation of electrons and holes. The findings showed an increase in current and a decrease in potential with light irradiation. Photoelectrochemical responses of the Li₀.₉₅₅Mn₁.₉₁₀O₄ film at a potential of 2.6 V and 3.7 V (vs Li/Li+) corresponded to lithium insertion/extraction at octahedral and tetrahedral sites, respectively. The mechanisms in the photoelectrochemical process were proposed, which agree with the electrochemical results.
2023-11-29T00:00:00ZTupberg, ChayopasSolar energy is a promising renewable energy resource. The energy from the sun is typically converted by solar cells and collected into a battery in the form of chemicals. It requires at least two devices for energy conversion and storage. Rechargeable lithium-ion batteries are widely used nowadays because of their high energy density. Lithium manganese oxide, particularly LiMn₂O₄, is commonly used as positive electrodes for lithium batteries. Due to its semiconducting property, it is intriguing to integrate photoelectrochemical charging into lithium-ion batteries for use as a single multifunctional device. Lithium manganospinel was synthesised using sol- gel methods. The effects of calcination temperatures and the molar ratio of Li/Mn defined the lithium manganospinels in the binary LiMn₂O₄–Li₂Mn₄O₉ and the ternary LiMn₂O₄–Li₂Mn₄O₉–Li₄Mn₅O₁₂ systems. To allow the light transmission to interact with LiMn₂O₄ at the electrode/electrolyte interface, LiMn₂O₄ was prepared by spin-coating on a transparent conducting oxide-coated glass substrate. The sol-gel method using methanol as a solvent provided a homogeneous and good-quality film. The film of pure defect spinel Li₀.₉₅₅Mn₁.₉₁₀O₄ calcined at 400 ̊C was mainly studied in this work. The 200 nm thick Li₀.₉₅₅Mn₁.₉₁₀O₄ film coated on F-doped SnO₂ glass substrate possessed a band gap energy of 2.7 eV. Photoelectrochemical cells were built to test the films of Li₀.₉₅₅Mn₁.₉₁₀O₄ in LiNO₃ solution as an aqueous electrolyte and 1 M LiPF₆ in EC/DEC (1:1 w/w) as a non-aqueous electrolyte. The cells were designed to allow UV light to pass through the cells for photoelectrochemical measurement. Cyclic voltammetry, chronopotentiometry, chronoamperometry, and open-circuit potential measurements were carried out to study and understand the photoelectrochemical properties of the films. The results reveal that light irradiation on the cell facilitated the generation of electrons and holes. The findings showed an increase in current and a decrease in potential with light irradiation. Photoelectrochemical responses of the Li₀.₉₅₅Mn₁.₉₁₀O₄ film at a potential of 2.6 V and 3.7 V (vs Li/Li+) corresponded to lithium insertion/extraction at octahedral and tetrahedral sites, respectively. The mechanisms in the photoelectrochemical process were proposed, which agree with the electrochemical results.Synthesis of peri-substituted acenaphthenes for carbon-heteroatom couplingKerr, Hannahhttps://hdl.handle.net/10023/281032023-08-05T02:01:29Z2023-11-29T00:00:00ZThe work presented in this thesis is an extension to the work started around peri¬-substituted acenaphthenes for carbon-heteroatom coupling, an expansion to dehydrocoupling and dealkacoupling (H–H and C–H bond formation). This thesis explores the synthesis of several classes of peri-substituted heteroatom species and investigates how the internal strain within the acenaphthene molecule is the catalyst for intermolecular coupling reaction tested under various conditions.
The main focus of this thesis is the synthesis of peri-substituted acenaphthenes of phosphinous thioesters, using a range of alkyl, cyclic and dialkyl thiols. These underwent the coupling reaction under various reaction conditions; thermal, radical initiator with AIBN and under UV irradiation. Addition of a radical initiator indicates that the mechanism of the coupling reaction is indeed radical. This completed the sulfur series, allowing for comparison not only structurally but also with regards to the coupling reaction. These compounds demonstrate that C–S coupling is viable, although these compounds are sensitive to both air and moisture.
This concept was extended to C–N heteroatom coupling, where a series of novel peri-substituted species were synthesised and where possible, structurally authenticated using single crystal X-ray diffraction. These were also subjected to the coupling reaction under both thermal and radical initiator conditions. However, unlike the sulfur series the nitrogen compounds do not couple under radical initiator conditions but do under thermal, indicating a higher activation barrier confirmed by computational calculations. Using one of the nitrogen compounds, the use of acenaphthene amines as a ligand for metal complexes was studied, allowing us to investigate the change in coupling constants between the two peri-atoms.
Finally, additional bis(phosphino) monoxides were synthesised to extended the current class of compounds. These species were subjected to the coupling reaction under thermal, radial initiator and UV irradiation, with thermal conditions showing the most promise.
2023-11-29T00:00:00ZKerr, HannahThe work presented in this thesis is an extension to the work started around peri¬-substituted acenaphthenes for carbon-heteroatom coupling, an expansion to dehydrocoupling and dealkacoupling (H–H and C–H bond formation). This thesis explores the synthesis of several classes of peri-substituted heteroatom species and investigates how the internal strain within the acenaphthene molecule is the catalyst for intermolecular coupling reaction tested under various conditions.
The main focus of this thesis is the synthesis of peri-substituted acenaphthenes of phosphinous thioesters, using a range of alkyl, cyclic and dialkyl thiols. These underwent the coupling reaction under various reaction conditions; thermal, radical initiator with AIBN and under UV irradiation. Addition of a radical initiator indicates that the mechanism of the coupling reaction is indeed radical. This completed the sulfur series, allowing for comparison not only structurally but also with regards to the coupling reaction. These compounds demonstrate that C–S coupling is viable, although these compounds are sensitive to both air and moisture.
This concept was extended to C–N heteroatom coupling, where a series of novel peri-substituted species were synthesised and where possible, structurally authenticated using single crystal X-ray diffraction. These were also subjected to the coupling reaction under both thermal and radical initiator conditions. However, unlike the sulfur series the nitrogen compounds do not couple under radical initiator conditions but do under thermal, indicating a higher activation barrier confirmed by computational calculations. Using one of the nitrogen compounds, the use of acenaphthene amines as a ligand for metal complexes was studied, allowing us to investigate the change in coupling constants between the two peri-atoms.
Finally, additional bis(phosphino) monoxides were synthesised to extended the current class of compounds. These species were subjected to the coupling reaction under thermal, radial initiator and UV irradiation, with thermal conditions showing the most promise.Solid-state NMR investigation of disordered metal-organic frameworksDavis, Zachary Harryhttps://hdl.handle.net/10023/279342023-07-13T02:06:09Z2023-11-29T00:00:00ZThis thesis focuses on synthetic studies for isotopic enrichment and characterisation using solid-state nuclear magnetic resonance (NMR) spectroscopy of metal-organic frameworks (MOFs). These materials, composed of metal cations and organic linkers, form porous structures which have a wide range of applications, and there is an increasing need to understand their structure-property relationships. Solid-state NMR spectroscopy, with its sensitivity to the local, atomic-scale environment makes it a powerful technique for the study of disordered materials. Combined with density functional theory (DFT) calculations, powder X-ray diffraction (PXRD), electron microscopy and energy dispersive X-ray (EDX) spectroscopy detailed structural information on these materials can be obtained. The low natural abundance of ¹⁷O (0.037%) hinders routine study of MOFs by ¹⁷O NMR spectroscopy and thus several methods for cost-effective and atom-efficient ¹⁷O isotopic enrichment of MOFs have been explored both during and post synthesis including dry-gel conversion (DGC), hydrothermal exchange and slurrying. Firstly, the breathing behaviour of mixed-metal MIL-53 is explored. ¹⁷O enrichment of these materials allows for high-resolution ¹⁷O NMR spectra to be acquired which indicate the types of pore forms adopted depending on composition and provides information on the cation distribution. DFT calculations help to better understand the energetic preferences for different cation arrangements and compositions. Secondly, post-synthetic ion-exchange methods are investigated as an alternative route to the synthesis of mixed-metal MOFs. By controlling when and how ¹⁷O enrichment occurs detailed information on the structure and metal distribution of (Al,Ga)-MIL-53 materials can be obtained using ¹⁷O NMR spectroscopy. An initial study of Al³⁺ exchange into Sc₂BDC₃ is also explored. Finally, anionic substitution at the secondary-building unit (SBU) of GUF-1 and Sc-fumarate is investigated. Here ¹³C NMR spectroscopy provides bulk measurements of the amount of μ₂-OCH₃⁻ exchange taking place under different temperature and pressure conditions, supported by ²H NMR spectroscopy and 2D correlation experiments.
2023-11-29T00:00:00ZDavis, Zachary HarryThis thesis focuses on synthetic studies for isotopic enrichment and characterisation using solid-state nuclear magnetic resonance (NMR) spectroscopy of metal-organic frameworks (MOFs). These materials, composed of metal cations and organic linkers, form porous structures which have a wide range of applications, and there is an increasing need to understand their structure-property relationships. Solid-state NMR spectroscopy, with its sensitivity to the local, atomic-scale environment makes it a powerful technique for the study of disordered materials. Combined with density functional theory (DFT) calculations, powder X-ray diffraction (PXRD), electron microscopy and energy dispersive X-ray (EDX) spectroscopy detailed structural information on these materials can be obtained. The low natural abundance of ¹⁷O (0.037%) hinders routine study of MOFs by ¹⁷O NMR spectroscopy and thus several methods for cost-effective and atom-efficient ¹⁷O isotopic enrichment of MOFs have been explored both during and post synthesis including dry-gel conversion (DGC), hydrothermal exchange and slurrying. Firstly, the breathing behaviour of mixed-metal MIL-53 is explored. ¹⁷O enrichment of these materials allows for high-resolution ¹⁷O NMR spectra to be acquired which indicate the types of pore forms adopted depending on composition and provides information on the cation distribution. DFT calculations help to better understand the energetic preferences for different cation arrangements and compositions. Secondly, post-synthetic ion-exchange methods are investigated as an alternative route to the synthesis of mixed-metal MOFs. By controlling when and how ¹⁷O enrichment occurs detailed information on the structure and metal distribution of (Al,Ga)-MIL-53 materials can be obtained using ¹⁷O NMR spectroscopy. An initial study of Al³⁺ exchange into Sc₂BDC₃ is also explored. Finally, anionic substitution at the secondary-building unit (SBU) of GUF-1 and Sc-fumarate is investigated. Here ¹³C NMR spectroscopy provides bulk measurements of the amount of μ₂-OCH₃⁻ exchange taking place under different temperature and pressure conditions, supported by ²H NMR spectroscopy and 2D correlation experiments.Gifts from nature : genomic and metabolomic approaches to natural product discovery from cyanobacteria and actinomycetesFerrinho, Scarlethttps://hdl.handle.net/10023/278982023-07-07T02:06:18Z2023-11-29T00:00:00ZCyanobacteria represent a treasure trove of uncovered natural products (NPs) and unbeknown biosynthetic machinery. Currently the exponential rise in genome sequencing of cyanobacteria and other organisms has revealed a wealth of biosynthetic gene clusters, many of which cannot be linked to a NP.
This work describes the investigation of cyanobacterial strains for the presence of non-ribosomal peptide synthase (NRPS) and polyketide synthase (PKS) genes screened by PCR and Sanger sequencing. In addition to whole genome sequencing (WGS) using Illumina and Oxford Nanopore was undertaken of selected strains. Bioinformatic tools were used to detect biosynthetic gene clusters (BGCs) and identify regions of interest. Furthermore, publicly available data, in the form of publications and nucleotide data from genome assemblies was gathered to form several datasets to analyse and link cyanobacterial metabolites to their genomes, and to uncover the diversity of cyanobacterial NPs.
Recent development has been undergoing to establish heterologous expression tools for cyanobacteria. Currently only a dozen cyanobacterial natural products have been heterologously expressed, this work details the heterologous expression of a ribosomally synthesised and post-translationally modified peptide (RiPP) named viridisamide A from Oscillatoria nigro-viridis PCC 7112 using the DiPaC method. This thesis also describes the use of this method for the cloning of the Fischerazole BGC from Fischerella sp. 9431.
Furthermore, the NP cyclomarin A, a marine natural product from an actinomycetes rather than a cyanobacterium, which possesses potent bioactivities against both tuberculosis and malaria was investigated. Here precursor directed biosynthesis of the fermented strain Streptomyces sp. BCC41611 was used to created halogenated cyclomarin variants. In addition, synthetic chemistry methods were used to functionalise the epoxide of the biosynthesised NP by azidolysis and copper(I) catalysed alkyne-azide cycloaddition.
Lastly, the halogenase VirX1 from the cyanophage syn10 was studied. This phage infects the marine cyanobacterial genera Synechococcus and Prochlorococcus which are responsible for over a quarter of global photosynthesis. Here, the halogenase was investigated in order to attempt to uncover its natural substrates.
2023-11-29T00:00:00ZFerrinho, ScarletCyanobacteria represent a treasure trove of uncovered natural products (NPs) and unbeknown biosynthetic machinery. Currently the exponential rise in genome sequencing of cyanobacteria and other organisms has revealed a wealth of biosynthetic gene clusters, many of which cannot be linked to a NP.
This work describes the investigation of cyanobacterial strains for the presence of non-ribosomal peptide synthase (NRPS) and polyketide synthase (PKS) genes screened by PCR and Sanger sequencing. In addition to whole genome sequencing (WGS) using Illumina and Oxford Nanopore was undertaken of selected strains. Bioinformatic tools were used to detect biosynthetic gene clusters (BGCs) and identify regions of interest. Furthermore, publicly available data, in the form of publications and nucleotide data from genome assemblies was gathered to form several datasets to analyse and link cyanobacterial metabolites to their genomes, and to uncover the diversity of cyanobacterial NPs.
Recent development has been undergoing to establish heterologous expression tools for cyanobacteria. Currently only a dozen cyanobacterial natural products have been heterologously expressed, this work details the heterologous expression of a ribosomally synthesised and post-translationally modified peptide (RiPP) named viridisamide A from Oscillatoria nigro-viridis PCC 7112 using the DiPaC method. This thesis also describes the use of this method for the cloning of the Fischerazole BGC from Fischerella sp. 9431.
Furthermore, the NP cyclomarin A, a marine natural product from an actinomycetes rather than a cyanobacterium, which possesses potent bioactivities against both tuberculosis and malaria was investigated. Here precursor directed biosynthesis of the fermented strain Streptomyces sp. BCC41611 was used to created halogenated cyclomarin variants. In addition, synthetic chemistry methods were used to functionalise the epoxide of the biosynthesised NP by azidolysis and copper(I) catalysed alkyne-azide cycloaddition.
Lastly, the halogenase VirX1 from the cyanophage syn10 was studied. This phage infects the marine cyanobacterial genera Synechococcus and Prochlorococcus which are responsible for over a quarter of global photosynthesis. Here, the halogenase was investigated in order to attempt to uncover its natural substrates.Electrochemical evaluation using alternative fuel electrode materials for syngas production via high temperature CO₂/H₂O co-electrolysisHeringer Boucas, Marianahttps://hdl.handle.net/10023/278932023-07-06T02:06:33Z2023-11-29T00:00:00ZThis Project was focused on the electrochemical evaluation of alternative Fuel Electrode (FE) materials for syngas production under HT H₂O/CO₂ co-electrolysis. The use of AC Impedance and I-V curve measurements on solid oxide electrolyser cells
were crucial for the investigation. Optimization of the FE applied, by mainly identifying the case exhibiting the lowest polarisation resistance (Rp) value, and comparison between the three different materials utilized, were also part of the Project’s scope.
The first FE material applied was the state-of-art Ni-YSZ leading on to La₀.₄₃Ca₀.₃₇Ni₀.₀₆Ti₀.₉₄O₃-δ (LCNT) and La₀.₅₂Sr₀.₂₈Ni₀.₀₆Ti₀.₉₄94₃-δ (LSNT) perovskites oxides. The motivation for investigating LCNT was based on literature and good results obtained within Prof. JTSI group at University of St. Andrews. Stability tests, different temperatures, voltages, flow rates and gas compositions (varying %H₂O, %CO₂, %H₂) were examined. The evaluation of LSNT material was part of a collaboration work with Dr. Sanchez mostly aiming the comparison with LCNT performance under similar conditions.
When cells were supplied with 0%H₂O, Rp values were substantially greater indicating that for a reasonable performance at least 3%H₂O is necessary. However, when only 3%H₂O was utilized under zero or low %CO₂ cells starved. The presence of
50%H₂O extinguished such problems and led to lower Rp values when applying both Ni and LCNT. In addition, higher CO₂ content led to lower electrode resistance in all cases studied.
Both perovskites displayed the lowest Rp values under 50%H₂O:0%H₂, whereas Ni-YSZ, due to its redox instability, exhibited very high Rp figures under 0%H₂, confirming the mandatory use of safe gas when applying Ni cermet. It displayed the
lowest Rp values under 15%H₂.
To summarize, LCNT proved to be an outstanding replacement for Ni cermet exhibiting good stability and performance with low Rp values under several different conditions especially when operating in the absence of H₂.
2023-11-29T00:00:00ZHeringer Boucas, MarianaThis Project was focused on the electrochemical evaluation of alternative Fuel Electrode (FE) materials for syngas production under HT H₂O/CO₂ co-electrolysis. The use of AC Impedance and I-V curve measurements on solid oxide electrolyser cells
were crucial for the investigation. Optimization of the FE applied, by mainly identifying the case exhibiting the lowest polarisation resistance (Rp) value, and comparison between the three different materials utilized, were also part of the Project’s scope.
The first FE material applied was the state-of-art Ni-YSZ leading on to La₀.₄₃Ca₀.₃₇Ni₀.₀₆Ti₀.₉₄O₃-δ (LCNT) and La₀.₅₂Sr₀.₂₈Ni₀.₀₆Ti₀.₉₄94₃-δ (LSNT) perovskites oxides. The motivation for investigating LCNT was based on literature and good results obtained within Prof. JTSI group at University of St. Andrews. Stability tests, different temperatures, voltages, flow rates and gas compositions (varying %H₂O, %CO₂, %H₂) were examined. The evaluation of LSNT material was part of a collaboration work with Dr. Sanchez mostly aiming the comparison with LCNT performance under similar conditions.
When cells were supplied with 0%H₂O, Rp values were substantially greater indicating that for a reasonable performance at least 3%H₂O is necessary. However, when only 3%H₂O was utilized under zero or low %CO₂ cells starved. The presence of
50%H₂O extinguished such problems and led to lower Rp values when applying both Ni and LCNT. In addition, higher CO₂ content led to lower electrode resistance in all cases studied.
Both perovskites displayed the lowest Rp values under 50%H₂O:0%H₂, whereas Ni-YSZ, due to its redox instability, exhibited very high Rp figures under 0%H₂, confirming the mandatory use of safe gas when applying Ni cermet. It displayed the
lowest Rp values under 15%H₂.
To summarize, LCNT proved to be an outstanding replacement for Ni cermet exhibiting good stability and performance with low Rp values under several different conditions especially when operating in the absence of H₂.Development of ligands and methodologies for the manganese-catalysed reduction of carbonyl compoundsOates, Conorhttps://hdl.handle.net/10023/278902023-07-06T02:04:50Z2023-11-29T00:00:00ZAbstract redacted
2023-11-29T00:00:00ZOates, ConorAbstract redactedInvestigation of metal nanoparticles exsolved from perovskite titanateMa, Penghttps://hdl.handle.net/10023/278692023-08-07T08:58:09Z2022-11-29T00:00:00ZNowadays, the energy and environment have become the restrictions to the development of human society. To solve the crisis coming from energy and environment, nanoparticles play a dominant role as the catalysts. However, traditional catalysts are easy to agglomerate to decrease their properties under high working temperatures. As a promising method to prepare nanoparticles, a new strategy, called exsolution, was proposed and has obtained much attention in many fields in catalysis and energy conversion and storage field due to the nanoparticles with the well-anchored and strained socketed structure.
This thesis illustrates the fundamental properties by doping different transition metals into the B-site of the perovskite. The parameters of the unit cells matched very well with the ionic radii of dopants. The corresponding nanoparticles exsolved successfully after the reduction post-treatments.
In particular, the thesis demonstrates the effects of reducing temperature and holding time on exsolution. In the exploration of the behaviours of exsolved nanoparticles after the redox experiments, it was found that the population and size of nanoparticles exsolved at lower temperatures were more sensitive than those exsolved at high temperatures.
The evolution of nanoparticles with different ratio of Ni and Co after CO oxidation experiments with different CO partial pressure was explored. As the loading of Co increases, the shape of the nanoparticles oxidized in CO oxidation experiments transformed from spherical to cubic, while the elemental distribution was still homogenous.
The thesis also explores the exsolution of small-sized metallic Cu nanoparticles from single-phase perovskite. We show that this is possible by selecting the suitable Cu precursor and control the parameters of the preparation to achieve Cu exsolution and its practical utility by preparing a nanostructured Cu metal catalyst which rival conventionally prepared Cu-based samples applied for CO oxidation. The catalytic properties of perovskite with exsolved nanoparticles can be tailored by doping Fe and Zn due to the synergistic effect.
2022-11-29T00:00:00ZMa, PengNowadays, the energy and environment have become the restrictions to the development of human society. To solve the crisis coming from energy and environment, nanoparticles play a dominant role as the catalysts. However, traditional catalysts are easy to agglomerate to decrease their properties under high working temperatures. As a promising method to prepare nanoparticles, a new strategy, called exsolution, was proposed and has obtained much attention in many fields in catalysis and energy conversion and storage field due to the nanoparticles with the well-anchored and strained socketed structure.
This thesis illustrates the fundamental properties by doping different transition metals into the B-site of the perovskite. The parameters of the unit cells matched very well with the ionic radii of dopants. The corresponding nanoparticles exsolved successfully after the reduction post-treatments.
In particular, the thesis demonstrates the effects of reducing temperature and holding time on exsolution. In the exploration of the behaviours of exsolved nanoparticles after the redox experiments, it was found that the population and size of nanoparticles exsolved at lower temperatures were more sensitive than those exsolved at high temperatures.
The evolution of nanoparticles with different ratio of Ni and Co after CO oxidation experiments with different CO partial pressure was explored. As the loading of Co increases, the shape of the nanoparticles oxidized in CO oxidation experiments transformed from spherical to cubic, while the elemental distribution was still homogenous.
The thesis also explores the exsolution of small-sized metallic Cu nanoparticles from single-phase perovskite. We show that this is possible by selecting the suitable Cu precursor and control the parameters of the preparation to achieve Cu exsolution and its practical utility by preparing a nanostructured Cu metal catalyst which rival conventionally prepared Cu-based samples applied for CO oxidation. The catalytic properties of perovskite with exsolved nanoparticles can be tailored by doping Fe and Zn due to the synergistic effect.Stable metal organic frameworks for the catalytic destruction of chemical warfare agentsElliott, Carolinehttps://hdl.handle.net/10023/278642023-07-01T02:02:48Z2023-11-29T00:00:00ZThe work described within this Thesis has focused on the preparation and characterisation of metal-organic frameworks (MOFs) as catalysts for the hydrolysis of the nerve agent simulant dimethyl 4-nitrophenyl phosphate (DMNP).
Mixed-metal MOFs were explored for this application using a combination of zirconium and hafnium in known MOFs in order to investigate the role of Lewis-acidity on catalysis. A series of mixed-metal MOFs were prepared and successfully catalysed the hydrolysis of DMNP. For UiO-66 and NU-1000 the highest rates were seen for the Zr 100% samples. For MOF-808 the most successful catalyst was found to be the Zr 33% Hf 66% sample. Further investigations compared properties of each sample and concluded that a change in Lewis-acidity plays a role in the catalytic activity, despite differences in material characteristics.
Mixed-linker MOFs were also investigated through the addition of di-topic linkers to a MOF-808 synthesis. For each sample, ca. 10\% of a chosen di-topic linker, as a proportion of linker present, was incorporated into the MOF-808 structure. Further investigations using the 5-amino isophthalic acid di-topic linker found up to 25% of 5-amino isophthalic acid could be incorporated into MOF-808. All samples successfully hydrolysed DMNP, with the 20% 5-amino isophthalic acid MOF-808 sample giving the highest rate and out-performing the parent MOF-808 sample.
Investigations into preparing MOF-composite materials were also carried out. This focused on incorporating MOF-808 into the materials PET, cotton, silk and nylon, using a range of synthesis methods. Loading estimates were calculated through q-NMR measurements. All materials saw MOF-808 successfully deposited on the surface, with the exception of one sample. All materials tested as catalysts for the hydrolysis of DMNP outperformed the blank samples. MOF-808 had therefore retained catalytic properties within the composite material. The hydrothermal synthesis method using PET displayed the highest initial rate for all composite materials prepared.
2023-11-29T00:00:00ZElliott, CarolineThe work described within this Thesis has focused on the preparation and characterisation of metal-organic frameworks (MOFs) as catalysts for the hydrolysis of the nerve agent simulant dimethyl 4-nitrophenyl phosphate (DMNP).
Mixed-metal MOFs were explored for this application using a combination of zirconium and hafnium in known MOFs in order to investigate the role of Lewis-acidity on catalysis. A series of mixed-metal MOFs were prepared and successfully catalysed the hydrolysis of DMNP. For UiO-66 and NU-1000 the highest rates were seen for the Zr 100% samples. For MOF-808 the most successful catalyst was found to be the Zr 33% Hf 66% sample. Further investigations compared properties of each sample and concluded that a change in Lewis-acidity plays a role in the catalytic activity, despite differences in material characteristics.
Mixed-linker MOFs were also investigated through the addition of di-topic linkers to a MOF-808 synthesis. For each sample, ca. 10\% of a chosen di-topic linker, as a proportion of linker present, was incorporated into the MOF-808 structure. Further investigations using the 5-amino isophthalic acid di-topic linker found up to 25% of 5-amino isophthalic acid could be incorporated into MOF-808. All samples successfully hydrolysed DMNP, with the 20% 5-amino isophthalic acid MOF-808 sample giving the highest rate and out-performing the parent MOF-808 sample.
Investigations into preparing MOF-composite materials were also carried out. This focused on incorporating MOF-808 into the materials PET, cotton, silk and nylon, using a range of synthesis methods. Loading estimates were calculated through q-NMR measurements. All materials saw MOF-808 successfully deposited on the surface, with the exception of one sample. All materials tested as catalysts for the hydrolysis of DMNP outperformed the blank samples. MOF-808 had therefore retained catalytic properties within the composite material. The hydrothermal synthesis method using PET displayed the highest initial rate for all composite materials prepared.The development of fuel electrodes for high temperature solid oxide cellsZhang, Nuoxihttps://hdl.handle.net/10023/278132023-06-28T02:07:16Z2022-11-29T00:00:00ZOur energetic matrix is currently based on finite fossil fuels, leading to climate change and increasing hazardous air pollutants. Nevertheless, solid oxide cells have emerged as a feasible and profitable route for energy generation. Solid oxide electrolysis cells can convert the excess electrical energy into chemical energy, thereby decoupling the transport fuels and chemicals production from today’s fossil fuels, while solid oxide fuel cells can convert chemical energy back into electricity, thus balancing energy availability and demand.
Solid oxide electrolysis cells afford an opportunity for upgrading biogas through the internal dry reforming of biogas and carbon dioxide electrolysis, producing hydrogen and carbon monoxide. Solid oxide electrolysis cells with conventional Ni-YSZ cermet fuel electrode and yttria stabilized zirconia electrolyte were constructed and tested on the direct feed of simulated biogas mixture (i.e. CH₄/CO₂ = 60/40, 50/50 and 40/60) at 850 °C. Cell performance and outlet gases measurements were carried out under open-circuit and closed-circuit conditions. The current densities at 1.8 V are -0.448, -0.678 and -0.876 A cm⁻² for the gas mixtures of CH₄/CO₂= 60/40, 50/50 and 40/60, respectively. The short term durability tests were performed in these three gas mixtures at 850 °C and 1.4 V. The cell fed with high CO₂ content demonstrates stable performance. No carbon deposition was observed on the Ni-YSZ fuel electrode surface, which might be due to not reaching the thermodynamic equilibrium and the reverse Boudouard reaction.
Nonstoichiometric perovskites with active metal nanoparticles exsolved on the surface have been proposed as the promising fuel electrode in solid oxide cells. Here, La₀.₄₀Ca₀.₄₀TiO₃ and La₀.₄₃Ca₀.₃₇M𝑥Ti₁-𝑥O₃-γ (M = Ni₀.₀₅, Ni₀.₁₀, Mn₀.₁₀, Co₀.₁₀, Ni₀.₀₅Mn₀.₀₅, and Ni₀.₀₅Co₀.₀₅) perovskite oxides were synthesized. The in-situ exsolution of Ni, Co and NiCo metal nanoparticles from the perovskite oxide parents was successfully according to the X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The results demonstrate that the exsolved metal nanoparticles can enhance the electrical conductivity, catalytic activity toward the hydrogen oxidation end carbon dioxide reduction. The cell performance can be improved by employing high voltage electrochemical reduction and extending the electrochemical reduction time. The best cell performance in 3% H₂O/H₂ was achieved by La₀.₄₃Ca₀.₃₇Ni₀.₁₀Ti₀.₉₀O₃-γ, exhibiting the maximum power density of 1.50 W cm⁻² at 900 °C. La₀.₄₃Ca₀.₃₇Co₀.₁₀Ti₀.₉O₃-γ based solid oxide electrolysis cell displays the highest current density of 0.856 A cm⁻² at 1.4 V.
2022-11-29T00:00:00ZZhang, NuoxiOur energetic matrix is currently based on finite fossil fuels, leading to climate change and increasing hazardous air pollutants. Nevertheless, solid oxide cells have emerged as a feasible and profitable route for energy generation. Solid oxide electrolysis cells can convert the excess electrical energy into chemical energy, thereby decoupling the transport fuels and chemicals production from today’s fossil fuels, while solid oxide fuel cells can convert chemical energy back into electricity, thus balancing energy availability and demand.
Solid oxide electrolysis cells afford an opportunity for upgrading biogas through the internal dry reforming of biogas and carbon dioxide electrolysis, producing hydrogen and carbon monoxide. Solid oxide electrolysis cells with conventional Ni-YSZ cermet fuel electrode and yttria stabilized zirconia electrolyte were constructed and tested on the direct feed of simulated biogas mixture (i.e. CH₄/CO₂ = 60/40, 50/50 and 40/60) at 850 °C. Cell performance and outlet gases measurements were carried out under open-circuit and closed-circuit conditions. The current densities at 1.8 V are -0.448, -0.678 and -0.876 A cm⁻² for the gas mixtures of CH₄/CO₂= 60/40, 50/50 and 40/60, respectively. The short term durability tests were performed in these three gas mixtures at 850 °C and 1.4 V. The cell fed with high CO₂ content demonstrates stable performance. No carbon deposition was observed on the Ni-YSZ fuel electrode surface, which might be due to not reaching the thermodynamic equilibrium and the reverse Boudouard reaction.
Nonstoichiometric perovskites with active metal nanoparticles exsolved on the surface have been proposed as the promising fuel electrode in solid oxide cells. Here, La₀.₄₀Ca₀.₄₀TiO₃ and La₀.₄₃Ca₀.₃₇M𝑥Ti₁-𝑥O₃-γ (M = Ni₀.₀₅, Ni₀.₁₀, Mn₀.₁₀, Co₀.₁₀, Ni₀.₀₅Mn₀.₀₅, and Ni₀.₀₅Co₀.₀₅) perovskite oxides were synthesized. The in-situ exsolution of Ni, Co and NiCo metal nanoparticles from the perovskite oxide parents was successfully according to the X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The results demonstrate that the exsolved metal nanoparticles can enhance the electrical conductivity, catalytic activity toward the hydrogen oxidation end carbon dioxide reduction. The cell performance can be improved by employing high voltage electrochemical reduction and extending the electrochemical reduction time. The best cell performance in 3% H₂O/H₂ was achieved by La₀.₄₃Ca₀.₃₇Ni₀.₁₀Ti₀.₉₀O₃-γ, exhibiting the maximum power density of 1.50 W cm⁻² at 900 °C. La₀.₄₃Ca₀.₃₇Co₀.₁₀Ti₀.₉O₃-γ based solid oxide electrolysis cell displays the highest current density of 0.856 A cm⁻² at 1.4 V.Title redactedMoloney, Markhttps://hdl.handle.net/10023/278092023-06-28T02:02:43Z2022-11-29T00:00:00ZAbstract redacted
2022-11-29T00:00:00ZMoloney, MarkAbstract redactedTitle redactedLynard, Oliverhttps://hdl.handle.net/10023/277992023-06-20T02:04:46Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZLynard, OliverAbstract redactedEvaluation of MR-TADF compounds as photocatalysts and their application in NHC/photoredox catalysisPrentice, Callumhttps://hdl.handle.net/10023/277942023-10-19T10:18:26Z2023-11-29T00:00:00ZThis thesis concerns the study of TADF and MR-TADF compounds for use as photocatalysts, with a focus on their application in Lewis base/photoredox dual catalysis.
Chapter 1 introduces the important concepts that are key to understanding both TADF photocatalysis and Lewis base catalysis as well as a literature survey of these areas of research.
Chapter 2 describes the synthesis and investigation of a bifunctional material that contains distinct isothiourea (ITU) and TADF moieties. Disappointingly, when incorporated into the same molecule, the two components proved to be incompatible due to oxidation of the Lewis basic ITU. Further investigations into ITU/photoredox dual catalysis using distinct ITU catalysts and photocatalysts also pointed to an issue of incompatibility due to the low oxidation potential of ITU catalysts. However, subsequent investigations by others¹,² showed that this catalytic system can be utilised effectively if a suitable radical precursor is identified that can be oxidised more easily than the ITU catalyst.
Chapter 3 investigates the benefits of using MR-TADF compounds DiKTa and Mes₃DiKTa as photocatalysts in a series of standard photocatalytic reactions using 4CzIPN as a benchmark for comparison. These reactions included reductive quenching reactions, oxidative quenching reactions, Dexter energy transfer (DET) reactions and dual catalytic reactions. Further comparisons were made through the analysis of the rates of reaction using the three different catalysts in a standard oxidative quenching reaction using an in-situ NMR technique.
Chapter 4 applies the knowledge gained in chapter 3 to a new NHC/photoredox catalysed synthesis of 1,4-diketones via a three-component radical relay reaction. The optimized conditions combined aroyl fluorides, α-ketoacids and styrenes in the presence of DiKTa and an NHC catalyst. Subsequent investigation of the scope was achieved by varying the substituents of each starting material. A mechanism is proposed and supported through Stern-Volmer analysis.
Chapter 5 explores the application of benzophenone as a DET photocatalyst in the key [2+2] photochemical cycloaddition step in the synthesis of dimethyl cubane-1,4-dicarboxylate. This allowed for the use of significantly lower energy light (λexc = 390 nm) than previously reported (λexc = 311 nm).³; References
1. R. del Río-Rodríguez, M. T. Westwood, M. Sicignano, M. Juhl, J. A. Fernández-Salas, J. Alemán and A. D. Smith, Chem. Commun., 2022, 58, 7277–7280.
2. W. C. Hartley, F. Schiel, E. Ermini and P. Melchiorre, Angew. Chem. Int. Ed., 2022, 61, e202204735.
3. D. E. Collin, E. H. Jackman, N. Jouandon, W. Sun, M. E. Light, D. C. Harrowven and B. Linclau, Synthesis, 2021, 53, 1307–1314.
2023-11-29T00:00:00ZPrentice, CallumThis thesis concerns the study of TADF and MR-TADF compounds for use as photocatalysts, with a focus on their application in Lewis base/photoredox dual catalysis.
Chapter 1 introduces the important concepts that are key to understanding both TADF photocatalysis and Lewis base catalysis as well as a literature survey of these areas of research.
Chapter 2 describes the synthesis and investigation of a bifunctional material that contains distinct isothiourea (ITU) and TADF moieties. Disappointingly, when incorporated into the same molecule, the two components proved to be incompatible due to oxidation of the Lewis basic ITU. Further investigations into ITU/photoredox dual catalysis using distinct ITU catalysts and photocatalysts also pointed to an issue of incompatibility due to the low oxidation potential of ITU catalysts. However, subsequent investigations by others¹,² showed that this catalytic system can be utilised effectively if a suitable radical precursor is identified that can be oxidised more easily than the ITU catalyst.
Chapter 3 investigates the benefits of using MR-TADF compounds DiKTa and Mes₃DiKTa as photocatalysts in a series of standard photocatalytic reactions using 4CzIPN as a benchmark for comparison. These reactions included reductive quenching reactions, oxidative quenching reactions, Dexter energy transfer (DET) reactions and dual catalytic reactions. Further comparisons were made through the analysis of the rates of reaction using the three different catalysts in a standard oxidative quenching reaction using an in-situ NMR technique.
Chapter 4 applies the knowledge gained in chapter 3 to a new NHC/photoredox catalysed synthesis of 1,4-diketones via a three-component radical relay reaction. The optimized conditions combined aroyl fluorides, α-ketoacids and styrenes in the presence of DiKTa and an NHC catalyst. Subsequent investigation of the scope was achieved by varying the substituents of each starting material. A mechanism is proposed and supported through Stern-Volmer analysis.
Chapter 5 explores the application of benzophenone as a DET photocatalyst in the key [2+2] photochemical cycloaddition step in the synthesis of dimethyl cubane-1,4-dicarboxylate. This allowed for the use of significantly lower energy light (λexc = 390 nm) than previously reported (λexc = 311 nm).³
References
1. R. del Río-Rodríguez, M. T. Westwood, M. Sicignano, M. Juhl, J. A. Fernández-Salas, J. Alemán and A. D. Smith, Chem. Commun., 2022, 58, 7277–7280.
2. W. C. Hartley, F. Schiel, E. Ermini and P. Melchiorre, Angew. Chem. Int. Ed., 2022, 61, e202204735.
3. D. E. Collin, E. H. Jackman, N. Jouandon, W. Sun, M. E. Light, D. C. Harrowven and B. Linclau, Synthesis, 2021, 53, 1307–1314.Enantioselective isothiourea catalysis via C(1)-ammonium enolate intermediates : applications and mechanistic studiesMcLaughlin, Calumhttps://hdl.handle.net/10023/277822023-06-19T12:40:31Z2021-06-30T00:00:00Z; The absolute stereochemistry of organic compounds can have a profound influence on the conformation, properties, and function of molecules. Therefore, sustainable synthetic methods that enable the catalytic, stereoselective preparation of enantioenriched compounds is a central research goal in chemistry.
Catalytically generated C(1)-ammonium enolate intermediates, derived from chiral tertiary amine Lewis base catalysts such as isothioureas, have emerged as synthetically useful intermediates for the enantioselective synthesis of α-functionalised carbonyl compounds at the carboxylic acid oxidation level, motifs that are found in many biologically relevant molecules. Despite the widespread application of C(1)-ammonium enolates in the synthesis of chiral heterocycles, there is typically a requirement for relatively high catalyst loadings, stoichiometric additives and/or auxiliary base for effective reactivity in the formation of acyclic α-functionalised products. In addition, a fundamental mechanistic understanding of these processes, governed by intermolecular catalyst turnover via an aryloxide, remains elusive and compatible electrophiles are limited to alkene and carbonyl derivatives.
The research goals of this thesis targeted the development of novel methodologies in isothiourea catalysis via C(1)-ammonium enolates using aryloxide catalyst turnover in reaction with alternative electrophiles, specifically looking to address the previous limitations of sustainability and mechanistic understanding (Scheme I). Herein, we report the base-free enantioselective α-functionalisation of esters via a Michael addition reaction of aryl esters to vinyl bis-sulfones enabled by a multifunctional aryloxide (Chapter 2). Using ¹⁹F{¹H} NMR reaction monitoring, a thorough mechanistic investigation was carried out to interrogate this methodology, enabling a large amount of mechanistic information to be collected, including elucidation of the turnover limiting step (Chapter 3). We also report the regio-, diastereo- and enantioselective dearomatisation of pyridinium salts using isothiourea catalysis via C(1)-ammonium enolate intermediates for the synthesis of 1,4-dihydropyridine heterocyclic motifs (Chapter 4). An enantioselective nucleophilic aromatic substitution protocol was also targeted, however, attempts to render both inter- and intramolecular variations of this transformation enantioselective proved challenging (Chapter 5).
2021-06-30T00:00:00ZMcLaughlin, CalumThe absolute stereochemistry of organic compounds can have a profound influence on the conformation, properties, and function of molecules. Therefore, sustainable synthetic methods that enable the catalytic, stereoselective preparation of enantioenriched compounds is a central research goal in chemistry.
Catalytically generated C(1)-ammonium enolate intermediates, derived from chiral tertiary amine Lewis base catalysts such as isothioureas, have emerged as synthetically useful intermediates for the enantioselective synthesis of α-functionalised carbonyl compounds at the carboxylic acid oxidation level, motifs that are found in many biologically relevant molecules. Despite the widespread application of C(1)-ammonium enolates in the synthesis of chiral heterocycles, there is typically a requirement for relatively high catalyst loadings, stoichiometric additives and/or auxiliary base for effective reactivity in the formation of acyclic α-functionalised products. In addition, a fundamental mechanistic understanding of these processes, governed by intermolecular catalyst turnover via an aryloxide, remains elusive and compatible electrophiles are limited to alkene and carbonyl derivatives.
The research goals of this thesis targeted the development of novel methodologies in isothiourea catalysis via C(1)-ammonium enolates using aryloxide catalyst turnover in reaction with alternative electrophiles, specifically looking to address the previous limitations of sustainability and mechanistic understanding (Scheme I). Herein, we report the base-free enantioselective α-functionalisation of esters via a Michael addition reaction of aryl esters to vinyl bis-sulfones enabled by a multifunctional aryloxide (Chapter 2). Using ¹⁹F{¹H} NMR reaction monitoring, a thorough mechanistic investigation was carried out to interrogate this methodology, enabling a large amount of mechanistic information to be collected, including elucidation of the turnover limiting step (Chapter 3). We also report the regio-, diastereo- and enantioselective dearomatisation of pyridinium salts using isothiourea catalysis via C(1)-ammonium enolate intermediates for the synthesis of 1,4-dihydropyridine heterocyclic motifs (Chapter 4). An enantioselective nucleophilic aromatic substitution protocol was also targeted, however, attempts to render both inter- and intramolecular variations of this transformation enantioselective proved challenging (Chapter 5).Investigation of copper and silver surfaces functionalised by N-heterocyclic moleculesAngove, Eloisehttps://hdl.handle.net/10023/277362023-06-06T15:31:54Z2023-11-29T00:00:00ZTo bestow particular properties on a metal surface, organic molecules can be used, amongst them N-heterocyclic molecules. In this study, N-heterocyclic molecules were deposited onto Ag(111) and Cu(111) surfaces in an ultra-high vacuum environment and analysed using complementary surface sensitive techniques and computational methods. Scanning tunnelling microscopy (STM) was utilized to observe the topography of the self-assembled monolayers, high-resolution electron energy loss spectroscopy (HREELS) was used to measure the vibrational frequencies of the adsorbed layers, temperature-programmed desorption (TPD) mass spectrometry was used to study the desorption trends of the overlayers; additionally, density functional theory calculations were implemented for deriving the adsorption geometry of the film. This study shows that, by varying the preparation conditions, the self-assembled monolayers of N-heterocyclic molecules can form different structures. For the initial adsorption of benzotriazole (BTAH) on Cu(111) new structures were observed dissimilar to the previously seen hexagonal phase. Additional structures were observed upon exposing an oxidised Cu(111) surface to BTAH resulting in hexagonal structures referred to as the “daisies” and “roses” phase. Through HREELS and STM analysis it was suggested that the BTAH reduces the oxidised surface and passivates the surface forming a protective film. Similar observations were made for a benzannulated N-heterocyclic carbene (NHCDBZ) on an oxidised Ag(111) surface through TPD and HREELS measurements with implication of a urea type by-product. In the case of the initial adsorption of NHCDBZ, the change in substituent geometry upon adsorption to Cu(111) and Ag(111) further supports the intrinsic role of the benzyl substituents in the structure of the self-assembled monolayer. The NHCDBZ film on Ag(111) shows promise as a corrosion inhibitor and also as a chemical etchant. The porous nature of the NHCDBZ on Cu(111) Kagome-like lattice offers possibilities in other fields such as catalyst research and nano electronic applications.
2023-11-29T00:00:00ZAngove, EloiseTo bestow particular properties on a metal surface, organic molecules can be used, amongst them N-heterocyclic molecules. In this study, N-heterocyclic molecules were deposited onto Ag(111) and Cu(111) surfaces in an ultra-high vacuum environment and analysed using complementary surface sensitive techniques and computational methods. Scanning tunnelling microscopy (STM) was utilized to observe the topography of the self-assembled monolayers, high-resolution electron energy loss spectroscopy (HREELS) was used to measure the vibrational frequencies of the adsorbed layers, temperature-programmed desorption (TPD) mass spectrometry was used to study the desorption trends of the overlayers; additionally, density functional theory calculations were implemented for deriving the adsorption geometry of the film. This study shows that, by varying the preparation conditions, the self-assembled monolayers of N-heterocyclic molecules can form different structures. For the initial adsorption of benzotriazole (BTAH) on Cu(111) new structures were observed dissimilar to the previously seen hexagonal phase. Additional structures were observed upon exposing an oxidised Cu(111) surface to BTAH resulting in hexagonal structures referred to as the “daisies” and “roses” phase. Through HREELS and STM analysis it was suggested that the BTAH reduces the oxidised surface and passivates the surface forming a protective film. Similar observations were made for a benzannulated N-heterocyclic carbene (NHCDBZ) on an oxidised Ag(111) surface through TPD and HREELS measurements with implication of a urea type by-product. In the case of the initial adsorption of NHCDBZ, the change in substituent geometry upon adsorption to Cu(111) and Ag(111) further supports the intrinsic role of the benzyl substituents in the structure of the self-assembled monolayer. The NHCDBZ film on Ag(111) shows promise as a corrosion inhibitor and also as a chemical etchant. The porous nature of the NHCDBZ on Cu(111) Kagome-like lattice offers possibilities in other fields such as catalyst research and nano electronic applications.Title redactedLiu, Chenchenghttps://hdl.handle.net/10023/276722023-06-20T15:47:53Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZLiu, ChenchengAbstract redactedDevelopment of a BMIDA Larock reaction and its application in total synthesisBell, George Edwardhttps://hdl.handle.net/10023/276612023-06-16T20:52:30Z2023-06-14T00:00:00ZIndoles are ubiquitous in natural products and in pharmaceuticals. Methods for their synthesis range from the classic Fischer synthesis to more modern, transition metal-catalysed reactions. One such method of indole synthesis is the Larock reaction, where a 2-haloaniline (usually iodoaniline, although recently, Larock reactions using bromo- and chloro-anilines have been disclosed) reacts with an internal alkyne, in the presence of Pd catalyst and a base (a chloride additive is often beneficial) to give a 2,3-disubtituted indole. A key feature of the Larock indole synthesis is its excellent regioselectivity, if one of the groups on the alkyne is larger than the other. Work in this thesis concerns the Larock reaction of 2-iodoanilines and borylated alkynes to form 2,3-difunctionalised indoles bearing a useful synthetic linchpin, N-methyliminodiacetic acid boronic ester (BMIDA), at the 2-position. The second chapter of this thesis concerns the optimisation of this so-called BMIDA Larock reaction on a model substrate. These optimised conditions would be used to create a variety of indoles bearing varied functionality about the benzenoid core of the indole and at the C-3 of the indole, all with a BMIDA group at C-2 which is amenable to Suzuki-Miyaura cross-coupling. It was found that two sets of conditions would be required depending on whether the carbon attached to the C-3 of the indole product would be sp2 or sp3. It was discovered that the relatively bulky BMIDA group was large enough to leverage the regioselectivity of the Larock reaction, resulting in the BMIDA group being reliably placed at the C-2 of the indole products. The third chapter involves using this developed methodology in the total synthesis of indole alkaloids. Initially, three alkaloids were targeted, each of which were proposed to be made in just several steps from a common intermediate. However, two of these failed due to the inability to form a macrocycle in one, and unexpected reactivity during a ring-closing step in the other. The third alkaloid, Goniomitine, was successfully synthesised.
2023-06-14T00:00:00ZBell, George EdwardIndoles are ubiquitous in natural products and in pharmaceuticals. Methods for their synthesis range from the classic Fischer synthesis to more modern, transition metal-catalysed reactions. One such method of indole synthesis is the Larock reaction, where a 2-haloaniline (usually iodoaniline, although recently, Larock reactions using bromo- and chloro-anilines have been disclosed) reacts with an internal alkyne, in the presence of Pd catalyst and a base (a chloride additive is often beneficial) to give a 2,3-disubtituted indole. A key feature of the Larock indole synthesis is its excellent regioselectivity, if one of the groups on the alkyne is larger than the other. Work in this thesis concerns the Larock reaction of 2-iodoanilines and borylated alkynes to form 2,3-difunctionalised indoles bearing a useful synthetic linchpin, N-methyliminodiacetic acid boronic ester (BMIDA), at the 2-position. The second chapter of this thesis concerns the optimisation of this so-called BMIDA Larock reaction on a model substrate. These optimised conditions would be used to create a variety of indoles bearing varied functionality about the benzenoid core of the indole and at the C-3 of the indole, all with a BMIDA group at C-2 which is amenable to Suzuki-Miyaura cross-coupling. It was found that two sets of conditions would be required depending on whether the carbon attached to the C-3 of the indole product would be sp2 or sp3. It was discovered that the relatively bulky BMIDA group was large enough to leverage the regioselectivity of the Larock reaction, resulting in the BMIDA group being reliably placed at the C-2 of the indole products. The third chapter involves using this developed methodology in the total synthesis of indole alkaloids. Initially, three alkaloids were targeted, each of which were proposed to be made in just several steps from a common intermediate. However, two of these failed due to the inability to form a macrocycle in one, and unexpected reactivity during a ring-closing step in the other. The third alkaloid, Goniomitine, was successfully synthesised.To bind or not to bind - dissociation equilibria studied by pulse dipolar EPRWort, Joshuahttps://hdl.handle.net/10023/276152023-06-21T11:11:57Z2022-06-15T00:00:00ZPulse dipolar EPR is an appealing strategy for structural characterisation of complex systems in solution that complements other biophysical techniques. Significantly, the emergence of genetically encoded self-assembling spin labels exploiting exogenously introduced double-histidine motifs in conjunction with Cull chelates offers high precision distance determination in systems non-permissive to thiol- directed spin labelling. However, the non‐covalent CuII coordination approach is vulnerable to low binding‐affinity. Here, an approach is outlined where dissociation constants (KD) are investigated directly from the modulation depths of relaxation‐induced dipolar modulation enhancement (RIDME) EPR experiments applied to the model protein Streptococcus sp. group G. protein G, B1 domain (GB1). This reveals low‐ to sub‐μM CuII-chelate KDS under RIDME conditions at cryogenic temperatures. We show the feasibility of exploiting the double‐histidine motif for EPR applications even at sub‐μM protein concentrations in orthogonally labelled CuII–nitroxide systems.
Additionally, modulation depth quantitation in CuII–CuII RIDME to simultaneously estimate a pair of non- identical independent KDS is addressed. Furthermore, we develop a general speciation model to optimise CuII labelling efficiency, depending upon pairs of identical or disparate KDS and total label concentration. We find the KD estimates are in excellent agreement with previously determined values. We also investigated the vulnerability of binding to both competition from adventitious divalent metal ions, and pH sensitivity. A combination of room-temperature isothermal titration calorimetry (ITC) and CuII-nitroxide RIDME measurements are applied to GB1. Results demonstrate double-histidine spin labelling using CuII-nitrilotriacetic acid (CuII-NTA) is robust against the competitor ligand ZnII-NTA at >1000-fold excess, and high nM binding affinity is retained at acidic and basic pH, despite room-
temperature behaviour suggesting a stronger dependence.
.
2022-06-15T00:00:00ZWort, JoshuaPulse dipolar EPR is an appealing strategy for structural characterisation of complex systems in solution that complements other biophysical techniques. Significantly, the emergence of genetically encoded self-assembling spin labels exploiting exogenously introduced double-histidine motifs in conjunction with Cull chelates offers high precision distance determination in systems non-permissive to thiol- directed spin labelling. However, the non‐covalent CuII coordination approach is vulnerable to low binding‐affinity. Here, an approach is outlined where dissociation constants (KD) are investigated directly from the modulation depths of relaxation‐induced dipolar modulation enhancement (RIDME) EPR experiments applied to the model protein Streptococcus sp. group G. protein G, B1 domain (GB1). This reveals low‐ to sub‐μM CuII-chelate KDS under RIDME conditions at cryogenic temperatures. We show the feasibility of exploiting the double‐histidine motif for EPR applications even at sub‐μM protein concentrations in orthogonally labelled CuII–nitroxide systems.
Additionally, modulation depth quantitation in CuII–CuII RIDME to simultaneously estimate a pair of non- identical independent KDS is addressed. Furthermore, we develop a general speciation model to optimise CuII labelling efficiency, depending upon pairs of identical or disparate KDS and total label concentration. We find the KD estimates are in excellent agreement with previously determined values. We also investigated the vulnerability of binding to both competition from adventitious divalent metal ions, and pH sensitivity. A combination of room-temperature isothermal titration calorimetry (ITC) and CuII-nitroxide RIDME measurements are applied to GB1. Results demonstrate double-histidine spin labelling using CuII-nitrilotriacetic acid (CuII-NTA) is robust against the competitor ligand ZnII-NTA at >1000-fold excess, and high nM binding affinity is retained at acidic and basic pH, despite room-
temperature behaviour suggesting a stronger dependence.
.Title redactedIrvine, Matthewhttps://hdl.handle.net/10023/275982023-06-28T21:03:08Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZIrvine, MatthewAbstract redactedMulti-purpose PVX : presentation and expression of enzymes and VLPsBurnett, David Alexanderhttps://hdl.handle.net/10023/275942023-05-24T02:08:00Z2023-06-14T00:00:00ZViral nanoparticles represent ideal nanomaterials, they replicate to high numbers, self-assemble into defined structures, and have many options for functionalisation. Presentation of heterologous peptides and proteins on the surface of nanoparticles is an area of growing research interest with far-ranging applications from vaccines to biocatalysts. Plant viral particles represent ideal candidates for this purpose as they are non-infectious to humans, replicate to extremely high titres and can be produced relatively cheaply. This study aims to investigate the potential of Potato virus X (PVX) as a platform for the presentation of enzymes in order to generate catalytically active nanoparticles. Presentation of enzymes on nanoparticles has the potential to increase the stability, reusability, and reaction rate of presented enzymes. This thesis also aims to investigate the ability of PVX to provide whole plant systemic overexpression of heterologous proteins and viral like particles. The knowledge gained is important to further development of plant viral nanoparticles as a technology and to the utilisation of PVX as a nanomaterial.
2023-06-14T00:00:00ZBurnett, David AlexanderViral nanoparticles represent ideal nanomaterials, they replicate to high numbers, self-assemble into defined structures, and have many options for functionalisation. Presentation of heterologous peptides and proteins on the surface of nanoparticles is an area of growing research interest with far-ranging applications from vaccines to biocatalysts. Plant viral particles represent ideal candidates for this purpose as they are non-infectious to humans, replicate to extremely high titres and can be produced relatively cheaply. This study aims to investigate the potential of Potato virus X (PVX) as a platform for the presentation of enzymes in order to generate catalytically active nanoparticles. Presentation of enzymes on nanoparticles has the potential to increase the stability, reusability, and reaction rate of presented enzymes. This thesis also aims to investigate the ability of PVX to provide whole plant systemic overexpression of heterologous proteins and viral like particles. The knowledge gained is important to further development of plant viral nanoparticles as a technology and to the utilisation of PVX as a nanomaterial.Title redactedSchindler, Nitihttps://hdl.handle.net/10023/275912023-05-12T02:07:07Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZSchindler, NitiAbstract redactedExploring the properties of selectively fluorinated Janus cyclohexane ringsYu, Cihanghttps://hdl.handle.net/10023/275692023-05-12T21:48:31Z2023-06-14T00:00:00ZJanus face fluorocycloalkanes (JFC) represent a novel subject of study. The fluorinated electronegative face and the hydrogenated electropositive face of the rings create an extraordinarily high dipole moment which induces facial polarity. This thesis carries out various studies on this new class of compound.
In Chapter 1, a discussion of the background and general interest in fluorine chemistry is given. The role of fluorine in pharmaceutical chemistry is demonstrated. The most recent studies on the JFC are summarised and discussed, including their preparation and applications in ionic binding, supramolecular chemistry, and biological chemistry.
In Chapter 2, a recently reported stereoselective Rh-catalysed hydrogenation was further explored, and its substrate scope was extended to aryl–CF₃ to deliver facially polarised CF₃–cyclohexane motifs in high diastereoselectivity. The direct preparation of CF₃–containing cyclohexanes form a library of stereoselective motifs for further studies.
In Chapter 3, the study of facially polar CF₃–cyclohexane was extended to the preparation, properties and physiochemistry of all-cis-multi-CF₃ cyclohexanes with between 3 and 6 substituent CF₃ groups. The prepared all-cis-hexakis-CF₃–cyclohexane has a high barrier to ring inversion (27 kcal mol⁻¹), more than twice that of cyclohexane. This ring also coordinates chloride (Cl-) ion to the hydrogen face with a modest affinity constant (K = 10³ M⁻¹).
In Chapter 4, the surface behaviour of the all-cis-hexafluorocyclohexane was studied on HOPG and gold surfaces. The reactivity of JFCs was studied, and a number of functional groups were installed onto the ring. of A novel amino acid of with a JFC side chain was prepared and incorporated into peptide synthesis.
In Chapter 5, trifluoro substituted cyclohexanes were prepared. An unexpected triaxial preference was found in all-cis-1,3,5-trifluorocyclohexane and some of its derivatives. The conformational preferences of these derivatives were also investigated.
In Chapter 6, the JFC motifs were transformed into multi-dentate supramolecular architectures. The proposed frameworks were synthesized in modular approaches. The crystal structure of a number of the building blocks were demonstrated with voids in their supramolecular architectures.
2023-06-14T00:00:00ZYu, CihangJanus face fluorocycloalkanes (JFC) represent a novel subject of study. The fluorinated electronegative face and the hydrogenated electropositive face of the rings create an extraordinarily high dipole moment which induces facial polarity. This thesis carries out various studies on this new class of compound.
In Chapter 1, a discussion of the background and general interest in fluorine chemistry is given. The role of fluorine in pharmaceutical chemistry is demonstrated. The most recent studies on the JFC are summarised and discussed, including their preparation and applications in ionic binding, supramolecular chemistry, and biological chemistry.
In Chapter 2, a recently reported stereoselective Rh-catalysed hydrogenation was further explored, and its substrate scope was extended to aryl–CF₃ to deliver facially polarised CF₃–cyclohexane motifs in high diastereoselectivity. The direct preparation of CF₃–containing cyclohexanes form a library of stereoselective motifs for further studies.
In Chapter 3, the study of facially polar CF₃–cyclohexane was extended to the preparation, properties and physiochemistry of all-cis-multi-CF₃ cyclohexanes with between 3 and 6 substituent CF₃ groups. The prepared all-cis-hexakis-CF₃–cyclohexane has a high barrier to ring inversion (27 kcal mol⁻¹), more than twice that of cyclohexane. This ring also coordinates chloride (Cl-) ion to the hydrogen face with a modest affinity constant (K = 10³ M⁻¹).
In Chapter 4, the surface behaviour of the all-cis-hexafluorocyclohexane was studied on HOPG and gold surfaces. The reactivity of JFCs was studied, and a number of functional groups were installed onto the ring. of A novel amino acid of with a JFC side chain was prepared and incorporated into peptide synthesis.
In Chapter 5, trifluoro substituted cyclohexanes were prepared. An unexpected triaxial preference was found in all-cis-1,3,5-trifluorocyclohexane and some of its derivatives. The conformational preferences of these derivatives were also investigated.
In Chapter 6, the JFC motifs were transformed into multi-dentate supramolecular architectures. The proposed frameworks were synthesized in modular approaches. The crystal structure of a number of the building blocks were demonstrated with voids in their supramolecular architectures.Broadening the scope and reactivity of C(1)-ammonium enolates to synthesise alpha-amino acid derivativesCraik, Rebeccahttps://hdl.handle.net/10023/275532023-10-26T08:08:33Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZCraik, RebeccaAbstract redactedAdvanced biomolecular applications of electron paramagnetic resonance spectroscopyRemmel, Laurahttps://hdl.handle.net/10023/274862023-05-23T09:19:25Z2023-06-14T00:00:00ZThe understanding of the structures, interactions, and functions of biological systems as well as their impact on health and disease is of fundamental importance. Electron paramagnetic resonance (EPR) spectroscopy has become a powerful tool for the investigation of structures and interactions of various systems. If not intrinsically present in the biological system paramagnetic centres can be introduced into the system of interest via site directed spin labelling (SDSL) to enable the use of EPR methods. Pulsed electron-electron double resonance (PELDOR) as well as relaxation-induced dipolar relaxation enhancement (RIDME) measurements exploit the dipole-dipole coupling between paramagnetic centres. Both methods have been used to investigate the distances between two spin labels, giving valuable insight into the structure of the biological systems investigated as well as sparse long-distance restrains used for structure refinement. PELDOR has in addition been used to determine the number of interacting spins, concluding to the number of interacting molecules. In combination with computational methods for structure prediction this opens a wide range of methods for the investigation and understanding of biological structures and structural transitions. The self-multimerisation of a single stranded DNA binding protein could be shown by PELDOR measurements and the flexibility of the system was validated by computational structure prediction. In another project good insight into the tertiary structure of the M3 protein could be gained using a combined approach of computational structure prediction, PELDOR, and RIDME measurements. ¹⁹F electron-nuclear double resonance (ENDOR) measurements enable the investigation of distances between a nitroxide spin label and a ¹⁹F nucleus. The investigation of a fluoride sensing riboswitch by nuclear magnetic resonance (NMR) spectroscopy and PELDOR showing a fluoride-free, a magnesium-stabilised and a fluoride-bound form is shown and an approach for the determination of the fluoride position in the solution structure based on ¹⁹F ENDOR measurements is introduced.
2023-06-14T00:00:00ZRemmel, LauraThe understanding of the structures, interactions, and functions of biological systems as well as their impact on health and disease is of fundamental importance. Electron paramagnetic resonance (EPR) spectroscopy has become a powerful tool for the investigation of structures and interactions of various systems. If not intrinsically present in the biological system paramagnetic centres can be introduced into the system of interest via site directed spin labelling (SDSL) to enable the use of EPR methods. Pulsed electron-electron double resonance (PELDOR) as well as relaxation-induced dipolar relaxation enhancement (RIDME) measurements exploit the dipole-dipole coupling between paramagnetic centres. Both methods have been used to investigate the distances between two spin labels, giving valuable insight into the structure of the biological systems investigated as well as sparse long-distance restrains used for structure refinement. PELDOR has in addition been used to determine the number of interacting spins, concluding to the number of interacting molecules. In combination with computational methods for structure prediction this opens a wide range of methods for the investigation and understanding of biological structures and structural transitions. The self-multimerisation of a single stranded DNA binding protein could be shown by PELDOR measurements and the flexibility of the system was validated by computational structure prediction. In another project good insight into the tertiary structure of the M3 protein could be gained using a combined approach of computational structure prediction, PELDOR, and RIDME measurements. ¹⁹F electron-nuclear double resonance (ENDOR) measurements enable the investigation of distances between a nitroxide spin label and a ¹⁹F nucleus. The investigation of a fluoride sensing riboswitch by nuclear magnetic resonance (NMR) spectroscopy and PELDOR showing a fluoride-free, a magnesium-stabilised and a fluoride-bound form is shown and an approach for the determination of the fluoride position in the solution structure based on ¹⁹F ENDOR measurements is introduced.Growth speeds and growth modes of sodium chloride : a quantitative two-dimensional phase-field studyTan, Chao Dunhttps://hdl.handle.net/10023/274252023-04-22T02:01:46Z2023-06-14T00:00:00ZThe understanding of crystal growth is beneficial to many different sectors, such as crystal engineering, drug manufacturing and life sciences. This phenomenon can be studied computationally on the molecular level, providing insights into the atomistic interactions of growth particles occurring at the solid-liquid interface. However, a significant amount of effort is often required to reveal information on spatial and temporal scales that are relevant in crystal growth experiments that are (usually) mesoscopic in nature. The Phase-field (PF) approach is a phenomenological model that can simulate, efficiently, the evolution of microstructures on length and time scales that are directly comparable to experiments but not many quantitative studies of precipitation crystal growth using the PF method are reported in the literature.
In this study, the precipitation PF model was employed to simulate and investigate, quantitatively, the crystal growth of sodium chloride, NaCl, in supersaturated solutions. More specifically, the accuracy of the model over a wide range of time scales is revealed by comparing the one-dimensional growth speeds of NaCl (simulated over periods of a few milliseconds up to several minutes) with experimental results from the literature. In addition, by simulating two-dimensional growth using circular crystals of different radii, it is shown that the PF model can be used to demonstrate the influence of curvature of a crystal surface on the growth speed. Lastly, by simulating anisotropic crystal growth of NaCl in two dimensions for a range of concentrations, the model predicted the transition from compact to non-compact growth to occur at a supersaturation coefficient of ~1.4, which is in good agreement with experimental observations of NaCl grown in microchannels.
The work described in this thesis demonstrates that the PF model can provide information about crystal growth on length and time scales that are not easily accessible with molecular methods.
2023-06-14T00:00:00ZTan, Chao DunThe understanding of crystal growth is beneficial to many different sectors, such as crystal engineering, drug manufacturing and life sciences. This phenomenon can be studied computationally on the molecular level, providing insights into the atomistic interactions of growth particles occurring at the solid-liquid interface. However, a significant amount of effort is often required to reveal information on spatial and temporal scales that are relevant in crystal growth experiments that are (usually) mesoscopic in nature. The Phase-field (PF) approach is a phenomenological model that can simulate, efficiently, the evolution of microstructures on length and time scales that are directly comparable to experiments but not many quantitative studies of precipitation crystal growth using the PF method are reported in the literature.
In this study, the precipitation PF model was employed to simulate and investigate, quantitatively, the crystal growth of sodium chloride, NaCl, in supersaturated solutions. More specifically, the accuracy of the model over a wide range of time scales is revealed by comparing the one-dimensional growth speeds of NaCl (simulated over periods of a few milliseconds up to several minutes) with experimental results from the literature. In addition, by simulating two-dimensional growth using circular crystals of different radii, it is shown that the PF model can be used to demonstrate the influence of curvature of a crystal surface on the growth speed. Lastly, by simulating anisotropic crystal growth of NaCl in two dimensions for a range of concentrations, the model predicted the transition from compact to non-compact growth to occur at a supersaturation coefficient of ~1.4, which is in good agreement with experimental observations of NaCl grown in microchannels.
The work described in this thesis demonstrates that the PF model can provide information about crystal growth on length and time scales that are not easily accessible with molecular methods.Peri-substituted phosphorus-selenium and -tin acenaphthenes : syntheses, reactivities and radical speciesZhang, Lu-Taohttps://hdl.handle.net/10023/274202024-02-15T16:55:57Z2021-06-30T00:00:00ZThe investigation of 𝘱𝘦𝘳𝘪-substitution has yielded fascinating approaches to unusual chemical bonds and interactions involving two or more atoms forced to close proximity. In this thesis, we discuss the syntheses and reactivities of a series of 𝘱𝘦𝘳𝘪-substituted P-Se and P-Sn species. Several dialkylphosphino-arylselanyl acenaphthenes Acenap (P𝘪Pr₂)(SeAr) (Ar = Mes, TRIP, Mes*), along with their transition metal complexes [M(Acenap(P𝘪Pr₂)(SeAr))ₙ] (M = Mo, Pd, Hg, Ag), have been prepared. Crystal structures and NMR properties (e.g. 𝘑MP and 𝘑MSe couplings) of these compounds have also been examined. We aimed to develop stable 𝘱𝘦𝘳𝘪-substituted systems that contain a captodative P-Se hemibond (2c-3e bond). We used P-Se acenaphthenes as radical candidates, investigating potential single-electron oxidation reactions with nitrosonium and silver (I) salts, expecting the formation of respective radical cations. The -P𝘪Pr₂ substituent is strongly electron-donating, and the bulky -SeAr groups are relatively electron-withdrawing. Therefore, the two captodative motifs were expected to form a stable P-Se hemibond. The stability of the radical centre was expected to be increased by steric shielding from the vicinal bulky arylselanyl groups and the presence of a large AI(ORꟳ)₄ weakly coordinated anion. The redox properties of the phosphine-selanes have been tested via electrochemical methods (e.g., cyclic voltammetry). The products of the potential single-electron oxidation reactions have been characterised by EPR spectroscopy. Despite all our efforts, the isolation of the desired cation radicals was not successful. In a separate project, we have investigated P-Sn acenaphthenes Acenap (P𝘪Pr₂)(SnHR₂) (R=Me, Ph) to get insight into their potential use as C-H coupling precursors. We have shown that the thermally induced reaction of these generates a phosphine-stabilised stannylene via elimination of benzene. Our observations have been supported by NMR spectroscopy; also, a gas trapping experiment indicates that benzene is formed as one of the products from fermal decomposition.
2021-06-30T00:00:00ZZhang, Lu-TaoThe investigation of 𝘱𝘦𝘳𝘪-substitution has yielded fascinating approaches to unusual chemical bonds and interactions involving two or more atoms forced to close proximity. In this thesis, we discuss the syntheses and reactivities of a series of 𝘱𝘦𝘳𝘪-substituted P-Se and P-Sn species. Several dialkylphosphino-arylselanyl acenaphthenes Acenap (P𝘪Pr₂)(SeAr) (Ar = Mes, TRIP, Mes*), along with their transition metal complexes [M(Acenap(P𝘪Pr₂)(SeAr))ₙ] (M = Mo, Pd, Hg, Ag), have been prepared. Crystal structures and NMR properties (e.g. 𝘑MP and 𝘑MSe couplings) of these compounds have also been examined. We aimed to develop stable 𝘱𝘦𝘳𝘪-substituted systems that contain a captodative P-Se hemibond (2c-3e bond). We used P-Se acenaphthenes as radical candidates, investigating potential single-electron oxidation reactions with nitrosonium and silver (I) salts, expecting the formation of respective radical cations. The -P𝘪Pr₂ substituent is strongly electron-donating, and the bulky -SeAr groups are relatively electron-withdrawing. Therefore, the two captodative motifs were expected to form a stable P-Se hemibond. The stability of the radical centre was expected to be increased by steric shielding from the vicinal bulky arylselanyl groups and the presence of a large AI(ORꟳ)₄ weakly coordinated anion. The redox properties of the phosphine-selanes have been tested via electrochemical methods (e.g., cyclic voltammetry). The products of the potential single-electron oxidation reactions have been characterised by EPR spectroscopy. Despite all our efforts, the isolation of the desired cation radicals was not successful. In a separate project, we have investigated P-Sn acenaphthenes Acenap (P𝘪Pr₂)(SnHR₂) (R=Me, Ph) to get insight into their potential use as C-H coupling precursors. We have shown that the thermally induced reaction of these generates a phosphine-stabilised stannylene via elimination of benzene. Our observations have been supported by NMR spectroscopy; also, a gas trapping experiment indicates that benzene is formed as one of the products from fermal decomposition.Title redactedTurner, Callum Alexanderhttps://hdl.handle.net/10023/273962023-07-01T02:02:44Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZTurner, Callum AlexanderAbstract redactedDesign and synthesis of triazine-based blue and oriented TADF emitters for high-efficiency OLEDsCrovini, Ettorehttps://hdl.handle.net/10023/273952024-03-23T03:11:57Z2023-06-14T00:00:00ZThis thesis focuses on the design, synthesis, characterization and OLED fabrication and testing of TADF emitters, with a particular emphasis on trying to achieve high horizontal orientation of their TDM. Chapter 1 explains the basic concepts behind light-matter interaction, photoluminescence, and electroluminescence, focusing on TADF materials and their use in OLEDs. An in-depth explanation of the outcoupling effect will be given, with a discussion of several literature-known strategies to achieve optimal orientation of the emitter in the OLED stack. Chapter 2 focuses on a highly oriented TADF emitter, ICzTRZ. The theoretical and optoelectronic properties and TDM orientation of the material were studied, with its most interesting feature being the nearly completely horizontal orientation of the TDM in the film. OLED performance is then discussed. Chapter 3 describes a study to try and enhance the efficiency of ICzTRZ by adopting a twin-emitter design strategy, with DICzTRZ. Due to its high molecular weight, we hypothesize that DICzTRZ could also maintain horizontal orientation in solution-processed films. Chapter 4 concludes the work on the ICz family, with a study on how the horizontal orientation of ICzTRZ derivates changes when the position and the number of tert-butyl groups on the material are modified. In Chapter 5, the knowledge gathered from the previous study on the ICz series is applied to the known randomly oriented emitter DMAC-TRZ, to try in achieving horizontal orientation of the material and therefore generate an improvement in the device efficiency. Chapter 6 continues the work on DMAC-TRZ by investigating the effect that a heteroaromatic bridge has on the photophysics of the emitter. Chapter 7 summarizes and compares the results from Chapters 2-6. A discussion of the future work and outlooks of these projects is also presented.
2023-06-14T00:00:00ZCrovini, EttoreThis thesis focuses on the design, synthesis, characterization and OLED fabrication and testing of TADF emitters, with a particular emphasis on trying to achieve high horizontal orientation of their TDM. Chapter 1 explains the basic concepts behind light-matter interaction, photoluminescence, and electroluminescence, focusing on TADF materials and their use in OLEDs. An in-depth explanation of the outcoupling effect will be given, with a discussion of several literature-known strategies to achieve optimal orientation of the emitter in the OLED stack. Chapter 2 focuses on a highly oriented TADF emitter, ICzTRZ. The theoretical and optoelectronic properties and TDM orientation of the material were studied, with its most interesting feature being the nearly completely horizontal orientation of the TDM in the film. OLED performance is then discussed. Chapter 3 describes a study to try and enhance the efficiency of ICzTRZ by adopting a twin-emitter design strategy, with DICzTRZ. Due to its high molecular weight, we hypothesize that DICzTRZ could also maintain horizontal orientation in solution-processed films. Chapter 4 concludes the work on the ICz family, with a study on how the horizontal orientation of ICzTRZ derivates changes when the position and the number of tert-butyl groups on the material are modified. In Chapter 5, the knowledge gathered from the previous study on the ICz series is applied to the known randomly oriented emitter DMAC-TRZ, to try in achieving horizontal orientation of the material and therefore generate an improvement in the device efficiency. Chapter 6 continues the work on DMAC-TRZ by investigating the effect that a heteroaromatic bridge has on the photophysics of the emitter. Chapter 7 summarizes and compares the results from Chapters 2-6. A discussion of the future work and outlooks of these projects is also presented.Synthesis of chiral nitrogen heterocycles using hydroformylation – cyclisation reactionsJeffrey, Ninahttps://hdl.handle.net/10023/273812023-11-30T03:03:43Z2022-11-29T00:00:00ZThis thesis concerns the investigation of hydroformylation-cyclisation reactions for the synthesis of chiral, saturated nitrogen heterocycles. The first chapter is a literature review that details the work that has previously been carried out in this area, much of which is focussed on linear regioselective hydroformylation reactions and hence these do not include any introduction of enantioselectivity from the hydroformylation reaction. A few examples use dual catalysts in order to refine the enantiomeric excess after the hydroformylation step, but the examples that introduce enantioselectivity in the hydroformylation step are recent ones and are primarily from the Zhang group and the Clarke group. These are discussed in the most detail. The second chapter is a discussion of the experimental work on the use of hydroformylation-cyclisation reactions with a Rh/ BOBPHOS catalyst for the synthesis of piperidines. Here it is established that the use of BOBPHOS is necessary for obtaining high branched regioselectivity as well as high enantioselectivity with these unbiased substrates. It is also clearly presented that the use of a sulfonamide protecting group on the nitrogen is key to balancing the nucleophilicity of the nitrogen lone pair with the stability of the hemi-aminal intermediate, which can then be reduced in a one-pot procedure to the piperidine. Expansion of this methodology to substituted piperidines is also discussed. The third chapter focusses on the formation of 3-methylpyrrolidine through hydroformylation-cyclisation to form the tosyl-protected derivative, followed by a one-pot reduction and subsequent isolation from the crude reaction mixture. Deprotection of such a small, volatile amine as well as measurement of the enantiomeric excess proved challenging and that is also discussed here. Preliminary steps for extending the reactivity of this methodology for the synthesis of an ant venom component, Leptothoracine, through a second HAM reaction of a 1,1-disubstituted alkene are also presented. The fourth chapter summarises the main outcomes of these results and contextualises the advances that have been made, whilst the final chapter contains the experimental procedures and compound data. Two appendixes are also included: the first describing palladium-catalysed carbonylation reactions for the synthesis of pyrrolidinones and piperidinones; the second appendix contains data for selected key compounds whose synthesis has been discussed within this thesis.
2022-11-29T00:00:00ZJeffrey, NinaThis thesis concerns the investigation of hydroformylation-cyclisation reactions for the synthesis of chiral, saturated nitrogen heterocycles. The first chapter is a literature review that details the work that has previously been carried out in this area, much of which is focussed on linear regioselective hydroformylation reactions and hence these do not include any introduction of enantioselectivity from the hydroformylation reaction. A few examples use dual catalysts in order to refine the enantiomeric excess after the hydroformylation step, but the examples that introduce enantioselectivity in the hydroformylation step are recent ones and are primarily from the Zhang group and the Clarke group. These are discussed in the most detail. The second chapter is a discussion of the experimental work on the use of hydroformylation-cyclisation reactions with a Rh/ BOBPHOS catalyst for the synthesis of piperidines. Here it is established that the use of BOBPHOS is necessary for obtaining high branched regioselectivity as well as high enantioselectivity with these unbiased substrates. It is also clearly presented that the use of a sulfonamide protecting group on the nitrogen is key to balancing the nucleophilicity of the nitrogen lone pair with the stability of the hemi-aminal intermediate, which can then be reduced in a one-pot procedure to the piperidine. Expansion of this methodology to substituted piperidines is also discussed. The third chapter focusses on the formation of 3-methylpyrrolidine through hydroformylation-cyclisation to form the tosyl-protected derivative, followed by a one-pot reduction and subsequent isolation from the crude reaction mixture. Deprotection of such a small, volatile amine as well as measurement of the enantiomeric excess proved challenging and that is also discussed here. Preliminary steps for extending the reactivity of this methodology for the synthesis of an ant venom component, Leptothoracine, through a second HAM reaction of a 1,1-disubstituted alkene are also presented. The fourth chapter summarises the main outcomes of these results and contextualises the advances that have been made, whilst the final chapter contains the experimental procedures and compound data. Two appendixes are also included: the first describing palladium-catalysed carbonylation reactions for the synthesis of pyrrolidinones and piperidinones; the second appendix contains data for selected key compounds whose synthesis has been discussed within this thesis.Probing the structure and reactivity of zeolites in their interactions with waterRice, Cameron Markhttps://hdl.handle.net/10023/273132024-01-22T10:54:41Z2022-11-29T00:00:00ZThe work presented in this thesis has been performed to increase the understanding of the interactions of zeolites with water, under a range of reaction conditions. The systems studied have been selected on the basis of their known hydrolytic instability or as model systems for which new avenues for hydrolytic instability can more easily be followed. The focus of research detailed in this thesis is split into three main sections. The mechanism of the ADOR (Assembly, Disassembly, Organisation, Reassembly) process for the synthesis of new zeolites from germanosilicate UTL is probed to deepen the understanding of the intermediate species formed and how the local structure and long-range order of the products are affected by reaction variables. Subsequently, the CHA framework has been selected as a model system for the study of a newly-identified bond lability exhibited by some non-‘ADORable’ aluminosilicate zeolite materials. To further aid characterisation and understanding of this lability, a series of inter-zeolite transformations from the FAU to CHA framework have been adapted to allow ¹⁷O enrichment and ¹⁷O NMR spectroscopic investigation, to characterise and identify key intermediate and framework species. The complexity and high structural disorder of the materials studied in this work mean that a multivariate approach to characterisation and analysis is required. Pri- marily, solid-state NMR spectroscopy and powder X-ray diffraction have been used to characterise the materials, elucidating differences between their local structure and long-range order. In addition, energy-dispersive X-ray spectroscopy, scanning electron microscopy, thermogravimetric analysis and density functional theory calculations have also been used to further aid characterisation and understanding of these complex systems. Results presented demonstrate that both zeolites and water interact strongly with one another when combined. Zeolites and water are found to be reactive even under mild conditions, e.g. room temperatures, where ¹⁷O NMR spectroscopy has shown the rapid exchange of H₂¹⁷O oxygen into the frameworks of UTL, CHA and FAU zeolites, by resolving signals attributed to framework zeolite linkages. Whilst favourable under ambient conditions, these bond lability processes are also found to be selective, with observed enrichment found to differ between frameworks with different topologies, com- positions and extraframework cations. In some cases, observed exchange of framework oxygen species has been attributed in part to the defective nature of zeolite frameworks. A further mechanistic explanation for the enrichment of zeolites for which the structure is not thought to be defective has also been predicted by collaborators using molecular dynamics. Whilst this mechanism may explain the facile bond lability seen for CHA frameworks, its widespread applicability to other zeolite frameworks that show rapid exchange of framework oxygen with that in water is not known. Water is also found to interact strongly with zeolite frameworks undergoing structural transformations, such as during the ADOR process or during post-synthetic transformations. Here, under the elevated temperatures of reaction conditions, ¹⁷O supplied from H₂¹⁷O reagent has been shown to be incorporated into the structure of zeolite frameworks, especially in regions considered non-reactive within the reaction. These results demonstrate that both zeolites and water interact and react when combined and provide further evidence to the contrary that zeolites are perceived as static, inert scaffolds. The findings have potential implications for the commercial uses of zeolites, where a balance between framework stability and flexibility is important.
2022-11-29T00:00:00ZRice, Cameron MarkThe work presented in this thesis has been performed to increase the understanding of the interactions of zeolites with water, under a range of reaction conditions. The systems studied have been selected on the basis of their known hydrolytic instability or as model systems for which new avenues for hydrolytic instability can more easily be followed. The focus of research detailed in this thesis is split into three main sections. The mechanism of the ADOR (Assembly, Disassembly, Organisation, Reassembly) process for the synthesis of new zeolites from germanosilicate UTL is probed to deepen the understanding of the intermediate species formed and how the local structure and long-range order of the products are affected by reaction variables. Subsequently, the CHA framework has been selected as a model system for the study of a newly-identified bond lability exhibited by some non-‘ADORable’ aluminosilicate zeolite materials. To further aid characterisation and understanding of this lability, a series of inter-zeolite transformations from the FAU to CHA framework have been adapted to allow ¹⁷O enrichment and ¹⁷O NMR spectroscopic investigation, to characterise and identify key intermediate and framework species. The complexity and high structural disorder of the materials studied in this work mean that a multivariate approach to characterisation and analysis is required. Pri- marily, solid-state NMR spectroscopy and powder X-ray diffraction have been used to characterise the materials, elucidating differences between their local structure and long-range order. In addition, energy-dispersive X-ray spectroscopy, scanning electron microscopy, thermogravimetric analysis and density functional theory calculations have also been used to further aid characterisation and understanding of these complex systems. Results presented demonstrate that both zeolites and water interact strongly with one another when combined. Zeolites and water are found to be reactive even under mild conditions, e.g. room temperatures, where ¹⁷O NMR spectroscopy has shown the rapid exchange of H₂¹⁷O oxygen into the frameworks of UTL, CHA and FAU zeolites, by resolving signals attributed to framework zeolite linkages. Whilst favourable under ambient conditions, these bond lability processes are also found to be selective, with observed enrichment found to differ between frameworks with different topologies, com- positions and extraframework cations. In some cases, observed exchange of framework oxygen species has been attributed in part to the defective nature of zeolite frameworks. A further mechanistic explanation for the enrichment of zeolites for which the structure is not thought to be defective has also been predicted by collaborators using molecular dynamics. Whilst this mechanism may explain the facile bond lability seen for CHA frameworks, its widespread applicability to other zeolite frameworks that show rapid exchange of framework oxygen with that in water is not known. Water is also found to interact strongly with zeolite frameworks undergoing structural transformations, such as during the ADOR process or during post-synthetic transformations. Here, under the elevated temperatures of reaction conditions, ¹⁷O supplied from H₂¹⁷O reagent has been shown to be incorporated into the structure of zeolite frameworks, especially in regions considered non-reactive within the reaction. These results demonstrate that both zeolites and water interact and react when combined and provide further evidence to the contrary that zeolites are perceived as static, inert scaffolds. The findings have potential implications for the commercial uses of zeolites, where a balance between framework stability and flexibility is important.Dynamic covalent functionalisation and assembly of boronic acid nanoparticlesPoss, Guillaumehttps://hdl.handle.net/10023/272982024-01-09T03:07:00Z2022-06-15T00:00:00ZThe rapid development in the synthesis and understanding of the properties of various types of nanoparticles has produced a plethora of potential building blocks. In attempts to exploit these novel species, several groups investigated methods to control their assembly and subsequent integration in technological devices. Almost 30 years after the first investigations, a lack of generalisable methods and understanding of the aggregation process still hampers the development of the field. Among lessons learnt from the large number of reports, reversibility of bond forming during the nanoparticle assembly is one crucial requirement. DNA-functionalised nanoparticles have established themselves as the state-of-the-art building blocks for the construction of nanoparticle superlattices. With the inherent limitations of this strategy, dynamic covalent chemistry-enabled gold nanoparticles featuring boronic acid-terminated ligands emerged as an alternative for the elaboration of responsive and robust nanoparticle-based assembled materials. Current limits of the system are moderate affinity for the biscatechol linkers used to connect boronic acid-functionalised nanoparticles and the requirement for high concentrations of tertiary amine based for a consistent reactivity. This thesis aims to improve on the first generation of boronic acid-functionalised nanoparticles and present a step-wise approach to meet this goal. The reactivity of boronic acids with a series of binding partners in non-aqueous media revealed how adjusting the concentration of tertiary amine base to the chosen binding partner allows for the tuning of the association constant for boronate esters over five orders of magnitude. This understanding was exploited to create a molecular switch in which the selectivity of a boronic acid for a catechol or salicylic acid is controlled by the controlled by the concentration of base and that can be actuated several times with high fidelity. These results have directed the next step of the creation of a second generation boronic acid ligand by replacing the arylboronic acid fragment of the original design with a new that forms more stable boronate esters. Subsequently, nanoparticles of different sizes bearing the new ligand were prepared with good size dispersity. The identification of a side-reaction during the nanoparticle synthesis oxidising the boronic acid to phenol motivated an optimisation of the reaction conditions to obtain single-ligand nanoparticles. A systematic comparison of the first- and second-generation nanoparticles was performed to understand the influence of the confinement of the boronic acids on their reactivity. Unexpectedly, these measurements suggest that salicylic acid ester formation is more inhibited than catechol ester formation on nanoparticle compared to their molecular counterparts and that the original nanoparticle design stabilises boronate esters better than the new one. Nevertheless, the general boronate ester stability trend relative to the concentration of base is verified on nanoparticles and a similar selectivity switch for catechol or salicylic acid binding could be created. These measurements finally helped set conditions that should facilitate boronate ester-directed nanoparticle assembly while minimising the base-catalysed degradation of the linkers. Catechol and salicylic acid-based bifunctional linkers were used to aggregate nanoparticles via boronate ester formation. to form similar assemblies to the first generation despite proceeding with slower kinetics. Under supposedly optimised conditions, second generation nanoparticles did not form extended insoluble networks, but smaller colloidally stable structures. Exploiting the reversibility of boronate ester formation, several stimuli could be applied to disassemble them and return colloidally stable isolated nanoparticles.
2022-06-15T00:00:00ZPoss, GuillaumeThe rapid development in the synthesis and understanding of the properties of various types of nanoparticles has produced a plethora of potential building blocks. In attempts to exploit these novel species, several groups investigated methods to control their assembly and subsequent integration in technological devices. Almost 30 years after the first investigations, a lack of generalisable methods and understanding of the aggregation process still hampers the development of the field. Among lessons learnt from the large number of reports, reversibility of bond forming during the nanoparticle assembly is one crucial requirement. DNA-functionalised nanoparticles have established themselves as the state-of-the-art building blocks for the construction of nanoparticle superlattices. With the inherent limitations of this strategy, dynamic covalent chemistry-enabled gold nanoparticles featuring boronic acid-terminated ligands emerged as an alternative for the elaboration of responsive and robust nanoparticle-based assembled materials. Current limits of the system are moderate affinity for the biscatechol linkers used to connect boronic acid-functionalised nanoparticles and the requirement for high concentrations of tertiary amine based for a consistent reactivity. This thesis aims to improve on the first generation of boronic acid-functionalised nanoparticles and present a step-wise approach to meet this goal. The reactivity of boronic acids with a series of binding partners in non-aqueous media revealed how adjusting the concentration of tertiary amine base to the chosen binding partner allows for the tuning of the association constant for boronate esters over five orders of magnitude. This understanding was exploited to create a molecular switch in which the selectivity of a boronic acid for a catechol or salicylic acid is controlled by the controlled by the concentration of base and that can be actuated several times with high fidelity. These results have directed the next step of the creation of a second generation boronic acid ligand by replacing the arylboronic acid fragment of the original design with a new that forms more stable boronate esters. Subsequently, nanoparticles of different sizes bearing the new ligand were prepared with good size dispersity. The identification of a side-reaction during the nanoparticle synthesis oxidising the boronic acid to phenol motivated an optimisation of the reaction conditions to obtain single-ligand nanoparticles. A systematic comparison of the first- and second-generation nanoparticles was performed to understand the influence of the confinement of the boronic acids on their reactivity. Unexpectedly, these measurements suggest that salicylic acid ester formation is more inhibited than catechol ester formation on nanoparticle compared to their molecular counterparts and that the original nanoparticle design stabilises boronate esters better than the new one. Nevertheless, the general boronate ester stability trend relative to the concentration of base is verified on nanoparticles and a similar selectivity switch for catechol or salicylic acid binding could be created. These measurements finally helped set conditions that should facilitate boronate ester-directed nanoparticle assembly while minimising the base-catalysed degradation of the linkers. Catechol and salicylic acid-based bifunctional linkers were used to aggregate nanoparticles via boronate ester formation. to form similar assemblies to the first generation despite proceeding with slower kinetics. Under supposedly optimised conditions, second generation nanoparticles did not form extended insoluble networks, but smaller colloidally stable structures. Exploiting the reversibility of boronate ester formation, several stimuli could be applied to disassemble them and return colloidally stable isolated nanoparticles.Adventures in poisoning parasites : chemical and biochemical investigations into the mode of action of novel anti-parasitic compounds against the kinetoplastid parasitesWoods, Rebecca Emilyhttps://hdl.handle.net/10023/272922023-04-19T08:23:37Z2023-06-14T00:00:00ZA library series of analogues of the natural product fumagillin suitable for photoaffinity labelling were prepared by Rodrigo Pierre and subjected to photoaffinity labelling studies by Dr Tulloch and myself against Trypanosoma brucei. These identified Methionine aminopeptidase 2 and another, as yet unknown molecular target. Investigations were undertaken to validate if this target was 3-methylglutaconyl coenzyme A hydratase (3-MGCoA-H) as suggested by immobilised drug affinity chromatography. These investigations involved the generation of an overexpression cell line and the recombinant expression and purification of the protein.
A series of N⁴-benzyl, N²-Phenyl quinazoline diamines were designed and synthesised to uncover structure activity relationships to inform the design of photoaffinity labelling probes. These compounds were found to be potent and selective in Leishmania major. A photoaffinity labelling probe and controls were designed and synthesised from the original SAR. Owing to a significant loss of potency against L. major, initial photoaffinity labelling studies were undertaken in Trypanosoma brucei, revealing several potential target proteins. A library of triphenylphosphonium and tributylphosphonium salts were assessed for their activity against Trypanosoma brucei, Trypanosoma cruzi and Leishmania major. A significant quantity of these compounds were found be potent or very potent against T. brucei and selective with respect to HeLa. The compounds were subjected to synergy studies and phenotypic screening of the KN morphologies and mitochondrial staining.
2023-06-14T00:00:00ZWoods, Rebecca EmilyA library series of analogues of the natural product fumagillin suitable for photoaffinity labelling were prepared by Rodrigo Pierre and subjected to photoaffinity labelling studies by Dr Tulloch and myself against Trypanosoma brucei. These identified Methionine aminopeptidase 2 and another, as yet unknown molecular target. Investigations were undertaken to validate if this target was 3-methylglutaconyl coenzyme A hydratase (3-MGCoA-H) as suggested by immobilised drug affinity chromatography. These investigations involved the generation of an overexpression cell line and the recombinant expression and purification of the protein.
A series of N⁴-benzyl, N²-Phenyl quinazoline diamines were designed and synthesised to uncover structure activity relationships to inform the design of photoaffinity labelling probes. These compounds were found to be potent and selective in Leishmania major. A photoaffinity labelling probe and controls were designed and synthesised from the original SAR. Owing to a significant loss of potency against L. major, initial photoaffinity labelling studies were undertaken in Trypanosoma brucei, revealing several potential target proteins. A library of triphenylphosphonium and tributylphosphonium salts were assessed for their activity against Trypanosoma brucei, Trypanosoma cruzi and Leishmania major. A significant quantity of these compounds were found be potent or very potent against T. brucei and selective with respect to HeLa. The compounds were subjected to synergy studies and phenotypic screening of the KN morphologies and mitochondrial staining.Synthesis and characterisation of the geometric ferroelectric LaTaO₄Howieson, Grant Williamhttps://hdl.handle.net/10023/272732023-11-14T03:06:23Z2022-06-15T00:00:00ZLaTaO₄ is one of very few reported n=2 Carpy-Galy oxides. It is isostructural to the BaMF₄ fluorides which were subject of much prior study due to their ferroelectric and multiferroic properties. Previous studies of LaTaO₄ have been consistent in their conclusion that it can adopt either a low temperature non-polar monoclinic, or high temperature polar orthorhombic phase, with the monoclinic – orthorhombic transition temperature (Tₘ₋ₒ) being dependent on the preparation method. Recent studies, however, have reported an unidentified dielectric anomaly in the orthorhombic phase which alludes to an additional subtle structural transition above Tₘ₋ₒ.
Powder neutron (PND) and electron diffraction studies have revealed that the previously unidentified dielectric anomaly denotes a transition between an incommensurately modulated and unmodulated orthorhombic (Cmc2₁) structure at ~503 K. The phase transition sequence is re-investigated in light of this new modulated phase, with resonant ultrasound (RUS) and Raman spectroscopy being utilised to elucidate the dynamics of transition and show the incommensurate – commensurate transition to be unusually 1ˢᵗ order, but nearly continuous (tri-critical).
Refinement of PND data in the Cmc2₁(α00)0s0 superspace group, indicates a modulation wavevector q = (0.456 0 0) at 483 K. The modulation arises from a variation in La³⁺ positions and octahedral tilts which propagate along the polar a-axis and is speculated to arise as a mechanism to improve overall bonding environment of La³⁺. Electron microscopy reveals that the modulation arises from partially ordered sub-units, which are 2.5× and 3× expansions of the original orthorhombic cell. A model has been constructed which combines the local structural origin with the observed macroscopic modulation, where sub-units partially order with an average periodicity of ~11a (~0.456 a*).
Previous studies report a relationship between the stability of each phase of LaTaO₄ and A-cation size. To explore the possibility that the modulation arises purely by an A-cation size effect, the series La₁₋ₓLnₓTaO₄ is synthesized, where Ln = Ce³⁺, Pr³⁺ and Nd³⁺ (0 ≤ x ≤ 0.3). Doping with these isovalent cations shows a general trend of stabilisation of the low temperature phases with decreasing average A-cation radii; the effect is amplified in Ce³⁺-doped samples and preliminary analysis suggests that this is due to a mix of oxidation states and the associated inter- and de-intercalation of interstitial oxygens during thermal cycling.
2022-06-15T00:00:00ZHowieson, Grant WilliamLaTaO₄ is one of very few reported n=2 Carpy-Galy oxides. It is isostructural to the BaMF₄ fluorides which were subject of much prior study due to their ferroelectric and multiferroic properties. Previous studies of LaTaO₄ have been consistent in their conclusion that it can adopt either a low temperature non-polar monoclinic, or high temperature polar orthorhombic phase, with the monoclinic – orthorhombic transition temperature (Tₘ₋ₒ) being dependent on the preparation method. Recent studies, however, have reported an unidentified dielectric anomaly in the orthorhombic phase which alludes to an additional subtle structural transition above Tₘ₋ₒ.
Powder neutron (PND) and electron diffraction studies have revealed that the previously unidentified dielectric anomaly denotes a transition between an incommensurately modulated and unmodulated orthorhombic (Cmc2₁) structure at ~503 K. The phase transition sequence is re-investigated in light of this new modulated phase, with resonant ultrasound (RUS) and Raman spectroscopy being utilised to elucidate the dynamics of transition and show the incommensurate – commensurate transition to be unusually 1ˢᵗ order, but nearly continuous (tri-critical).
Refinement of PND data in the Cmc2₁(α00)0s0 superspace group, indicates a modulation wavevector q = (0.456 0 0) at 483 K. The modulation arises from a variation in La³⁺ positions and octahedral tilts which propagate along the polar a-axis and is speculated to arise as a mechanism to improve overall bonding environment of La³⁺. Electron microscopy reveals that the modulation arises from partially ordered sub-units, which are 2.5× and 3× expansions of the original orthorhombic cell. A model has been constructed which combines the local structural origin with the observed macroscopic modulation, where sub-units partially order with an average periodicity of ~11a (~0.456 a*).
Previous studies report a relationship between the stability of each phase of LaTaO₄ and A-cation size. To explore the possibility that the modulation arises purely by an A-cation size effect, the series La₁₋ₓLnₓTaO₄ is synthesized, where Ln = Ce³⁺, Pr³⁺ and Nd³⁺ (0 ≤ x ≤ 0.3). Doping with these isovalent cations shows a general trend of stabilisation of the low temperature phases with decreasing average A-cation radii; the effect is amplified in Ce³⁺-doped samples and preliminary analysis suggests that this is due to a mix of oxidation states and the associated inter- and de-intercalation of interstitial oxygens during thermal cycling.Title redactedde Vere-Tucker, Matthewhttps://hdl.handle.net/10023/272222023-06-30T14:05:55Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00Zde Vere-Tucker, MatthewAbstract redactedA single molecule spectroscopy approach towards understanding the structure of catalytically active sitesAnetts, Simon Royhttps://hdl.handle.net/10023/272172023-08-24T10:31:08Z2023-06-14T00:00:00ZThe work presented in this thesis has been performed with the aim of increasing our understanding of relationships between the structure of an adsorption site and the extent of adsorbate activation, a key step in catalytic processes. Unravelling such structure-performance relationships is often hindered by the complex structures displayed by heterogeneous catalysts; they can be multiphasic and are typically dynamic in nature with respect to structure, composition and local electronic environment. A reactive surface can be comprised of many step edges, kinks and defect sites, but only a small portion of this rich structural diversity may be responsible for catalytic activity. The challenges associated with identifying the structure of active sites can be simplified through the interrogation of single crystal surfaces, for which structural complexity is greatly reduced. By using a low temperature, ultra-high vacuum scanning tunnelling microscope (LT-UHV-STM), individual surface sites of interest can be identified and investigated on an atomic scale. The application of STM-inelastic electron tunnelling spectroscopy (STM-IETS) and scanning tunnelling spectroscopy (STS), allows the bond strength, and therefore the extent of adsorbate activation to be studied at surface sites of differing geometric and electronic structure. The work described in this thesis has focussed on the development of STM-IETS and STS to investigate the interaction of carbon monoxide (CO) with Cu-based surfaces. CO is an ideal probe molecule given the sensitivity of its vibrational frequency to local structure and its use as a C₁ building block in chemical processes. On Cu(110), adsorbed CO forms one-dimensional structures where the nearest neighbour sites are occupied in the [001] direction. The vibrational frequency of adsorbed CO is highly dependent on the CO coverage. A CO molecule with one of its nearest neighbour sites occupied by CO (a CO adsorption dimer) exhibits an increased C-O bond strength (higher frequency) relative to a terrace monomer. This is assigned to dipole-dipole coupling effects between neighbouring molecules. Conversely, the CO bond is weakened compared to a terrace monomer, when two nearest neighbour sites of the adsorbate are also occupied (a CO adsorption trimer). This is attributed to chemical effects that cause a broadening of the CO 2π* orbital and its increased occupancy. Further investigations have explored the effects of the structure of adsorption site on the CO bond strength. CO adsorbed at the lower [001] aligned Cu(110) step edge sites, exhibits lower CO stretching frequency when compared to CO adsorbed at the upper edge sites. This can again be attributed to changes in the occupancy of the antibonding 2π* orbital that is driven in this case by a substantial difference in electron density associated with these adsorption sites. The aforementioned studies have been extended to investigations of Co, a metal upon which CO activation is of great interest. Given the complexities of preparing Co single crystals, a model surface was formed by depositing Co on Cu(110). When deposition is performed in the presence of CO, a novel CoCu(110) alloy is formed in which two-atom wide Co structures aligned in the [001] direction are embedded in the first layer of the Cu(110) surface. When CO is adsorbed between the linear arrangements of Co atoms, there is a far greater activation of the CO bond relative to the Cu(110) surface. The results demonstrate the broad application of the STM-IETS approach to studying complex surfaces and the ability to provide deeper insights into data that is traditionally generated using techniques that provide a macroscopic picture of a surface.
2023-06-14T00:00:00ZAnetts, Simon RoyThe work presented in this thesis has been performed with the aim of increasing our understanding of relationships between the structure of an adsorption site and the extent of adsorbate activation, a key step in catalytic processes. Unravelling such structure-performance relationships is often hindered by the complex structures displayed by heterogeneous catalysts; they can be multiphasic and are typically dynamic in nature with respect to structure, composition and local electronic environment. A reactive surface can be comprised of many step edges, kinks and defect sites, but only a small portion of this rich structural diversity may be responsible for catalytic activity. The challenges associated with identifying the structure of active sites can be simplified through the interrogation of single crystal surfaces, for which structural complexity is greatly reduced. By using a low temperature, ultra-high vacuum scanning tunnelling microscope (LT-UHV-STM), individual surface sites of interest can be identified and investigated on an atomic scale. The application of STM-inelastic electron tunnelling spectroscopy (STM-IETS) and scanning tunnelling spectroscopy (STS), allows the bond strength, and therefore the extent of adsorbate activation to be studied at surface sites of differing geometric and electronic structure. The work described in this thesis has focussed on the development of STM-IETS and STS to investigate the interaction of carbon monoxide (CO) with Cu-based surfaces. CO is an ideal probe molecule given the sensitivity of its vibrational frequency to local structure and its use as a C₁ building block in chemical processes. On Cu(110), adsorbed CO forms one-dimensional structures where the nearest neighbour sites are occupied in the [001] direction. The vibrational frequency of adsorbed CO is highly dependent on the CO coverage. A CO molecule with one of its nearest neighbour sites occupied by CO (a CO adsorption dimer) exhibits an increased C-O bond strength (higher frequency) relative to a terrace monomer. This is assigned to dipole-dipole coupling effects between neighbouring molecules. Conversely, the CO bond is weakened compared to a terrace monomer, when two nearest neighbour sites of the adsorbate are also occupied (a CO adsorption trimer). This is attributed to chemical effects that cause a broadening of the CO 2π* orbital and its increased occupancy. Further investigations have explored the effects of the structure of adsorption site on the CO bond strength. CO adsorbed at the lower [001] aligned Cu(110) step edge sites, exhibits lower CO stretching frequency when compared to CO adsorbed at the upper edge sites. This can again be attributed to changes in the occupancy of the antibonding 2π* orbital that is driven in this case by a substantial difference in electron density associated with these adsorption sites. The aforementioned studies have been extended to investigations of Co, a metal upon which CO activation is of great interest. Given the complexities of preparing Co single crystals, a model surface was formed by depositing Co on Cu(110). When deposition is performed in the presence of CO, a novel CoCu(110) alloy is formed in which two-atom wide Co structures aligned in the [001] direction are embedded in the first layer of the Cu(110) surface. When CO is adsorbed between the linear arrangements of Co atoms, there is a far greater activation of the CO bond relative to the Cu(110) surface. The results demonstrate the broad application of the STM-IETS approach to studying complex surfaces and the ability to provide deeper insights into data that is traditionally generated using techniques that provide a macroscopic picture of a surface.Evaluation of two- and three-coordinate copper(I) NHC complexes as photocatalystsHockin, Bryonyhttps://hdl.handle.net/10023/271132023-11-21T03:01:40Z2023-06-14T00:00:00ZThis thesis explores the design, synthesis, optoelectronic properties, and photocatalytic testing of copper(I) complexes with a two- or three-coordinate geometry bearing N-heterocyclic carbene ligands. Our design strategies aim to avoid the failings of four-coordinate copper(I) complexes which are prone to Jahn-Teller distortion in the excited state.
The first chapter provides an overview of the fundamental photophysical properties of transition metal complexes and an introduction to bimolecular energy and electron transfer processes. A mini-review of Earth-abundant photocatalysts is presented. Special attention will then be devoted to describing the design principles of copper(I) based photocatalysts (PCs). We begin by describing the photophysical and electrochemical properties of four-coordinate copper(I) complexes, followed by the design and applications of copper(I) complexes as PCs. Next, we
provide a summary of the development of two- and three-coordinate copper(I) complexes, describing their photophysical properties and applications.
Chapter 2 describes the synthesis, characterisation and optoelectronic properties of seven three-coordinate copper(I) N-heterocyclic carbene (NHC) complexes bearing N^N ligands, of the form of [Cu(IPr)(N^N)]PF₆ (where IPr is 1,3-Bis(2,6-diisopropylphenyl)imidazolium, and N^N is phen = 1,10-phenanthroline, bpy = 2,2’-bipyridine, dpa = 2,2’-dipyridylamine, mdpa = N-methyl-2,2’-dipyridylamine, dpym = di(pyridin-2-yl)methane, phdpym = 2,2'-(phenylmethylene)dipyridine, fludpym = 2,2'-(9H-fluorene-9,9-diyl)dipyridine). Six complexes
underwent successful preliminary photocatalytic testing in two mechanistically distinct photocatalysis reactions: an Atom Transfer Radical Addition (ATRA) photoinduced electron transfer (PET) reaction between an alkyl halide and an alkene; and photoinduced energy transfer (PEnT) reaction of a vinyl azide to a vinyl nitrene, which subsequently rearranges to form a pyrrole. The complex [Cu(IPr)(phen)]PF₆ performed best in the ATRA reaction (77% NMR yield) out of six complexes tested, while complex [Cu(IPr)(phdpym)]PF₆ performed best in the
PEnT reaction (59% NMR yield vs 66% obtained with [Cu(dmp)(BINAP)]BF₄).
Chapter 3 reports the synthesis, characterisation and optoelectronic properties of a series of three-coordinate copper(I) NHC complexes bearing a dpa ligand, of the form [Cu(NHC)(dpa)]PF₆. Three complexes underwent preliminary photocatalytic testing, however their performance as PCs was poor.
Chapter 4 reports the first example of a neutral linear two-coordinate Cu(I) complex Cu(IPrBIAN)(Cz) bearing an IPrBIAN NHC ligand, and after investigation of its optoelectronic properties, it was successfully applied as a PC in a proof-of-concept PET ATRA reaction (52% NMR yield). Cu(IPrBIAN)(Cz) also exhibited interesting dual emission properties in solution; this is seen as separate emission depending on excitation source for most solvents, and is especially strong in chloroform solution. The synthesis, characterisation, and optoelectronic
properties of further derivatives of this complex bearing 3,6-substituted carbazolate ligands were also investigated.
The final conclusions chapter summarises the results of each chapter and brings focus to the overarching aims and themes of the thesis. This chapter identifies key areas for future work in the field of two- and three-coordinate copper(I) complexes as photocatalysts, specifically the need to improve PC stability, investigate reaction mechanisms, and correlate structure-property relationships with photocatalytic performance. A need for standardisation of photocatalysis reaction set-ups is identified as a requirement for reproducibility of results within the field of photocatalysis.
2023-06-14T00:00:00ZHockin, BryonyThis thesis explores the design, synthesis, optoelectronic properties, and photocatalytic testing of copper(I) complexes with a two- or three-coordinate geometry bearing N-heterocyclic carbene ligands. Our design strategies aim to avoid the failings of four-coordinate copper(I) complexes which are prone to Jahn-Teller distortion in the excited state.
The first chapter provides an overview of the fundamental photophysical properties of transition metal complexes and an introduction to bimolecular energy and electron transfer processes. A mini-review of Earth-abundant photocatalysts is presented. Special attention will then be devoted to describing the design principles of copper(I) based photocatalysts (PCs). We begin by describing the photophysical and electrochemical properties of four-coordinate copper(I) complexes, followed by the design and applications of copper(I) complexes as PCs. Next, we
provide a summary of the development of two- and three-coordinate copper(I) complexes, describing their photophysical properties and applications.
Chapter 2 describes the synthesis, characterisation and optoelectronic properties of seven three-coordinate copper(I) N-heterocyclic carbene (NHC) complexes bearing N^N ligands, of the form of [Cu(IPr)(N^N)]PF₆ (where IPr is 1,3-Bis(2,6-diisopropylphenyl)imidazolium, and N^N is phen = 1,10-phenanthroline, bpy = 2,2’-bipyridine, dpa = 2,2’-dipyridylamine, mdpa = N-methyl-2,2’-dipyridylamine, dpym = di(pyridin-2-yl)methane, phdpym = 2,2'-(phenylmethylene)dipyridine, fludpym = 2,2'-(9H-fluorene-9,9-diyl)dipyridine). Six complexes
underwent successful preliminary photocatalytic testing in two mechanistically distinct photocatalysis reactions: an Atom Transfer Radical Addition (ATRA) photoinduced electron transfer (PET) reaction between an alkyl halide and an alkene; and photoinduced energy transfer (PEnT) reaction of a vinyl azide to a vinyl nitrene, which subsequently rearranges to form a pyrrole. The complex [Cu(IPr)(phen)]PF₆ performed best in the ATRA reaction (77% NMR yield) out of six complexes tested, while complex [Cu(IPr)(phdpym)]PF₆ performed best in the
PEnT reaction (59% NMR yield vs 66% obtained with [Cu(dmp)(BINAP)]BF₄).
Chapter 3 reports the synthesis, characterisation and optoelectronic properties of a series of three-coordinate copper(I) NHC complexes bearing a dpa ligand, of the form [Cu(NHC)(dpa)]PF₆. Three complexes underwent preliminary photocatalytic testing, however their performance as PCs was poor.
Chapter 4 reports the first example of a neutral linear two-coordinate Cu(I) complex Cu(IPrBIAN)(Cz) bearing an IPrBIAN NHC ligand, and after investigation of its optoelectronic properties, it was successfully applied as a PC in a proof-of-concept PET ATRA reaction (52% NMR yield). Cu(IPrBIAN)(Cz) also exhibited interesting dual emission properties in solution; this is seen as separate emission depending on excitation source for most solvents, and is especially strong in chloroform solution. The synthesis, characterisation, and optoelectronic
properties of further derivatives of this complex bearing 3,6-substituted carbazolate ligands were also investigated.
The final conclusions chapter summarises the results of each chapter and brings focus to the overarching aims and themes of the thesis. This chapter identifies key areas for future work in the field of two- and three-coordinate copper(I) complexes as photocatalysts, specifically the need to improve PC stability, investigate reaction mechanisms, and correlate structure-property relationships with photocatalytic performance. A need for standardisation of photocatalysis reaction set-ups is identified as a requirement for reproducibility of results within the field of photocatalysis.A study of copper and gold systems for the hydrogen-free hydrogenation of furfural to furfuryl alcoholMegginson, Roryhttps://hdl.handle.net/10023/270932023-12-02T03:09:19Z2022-11-18T00:00:00ZThe production of a new catalysts for the production of furfuryl alcohol from furfural is a topic of interest as it would alleviate the need for the use of a toxic copper chromate catalyst. A new coupled AuCu catalyst system has been developed for the conversion of furfural to furfuryl alcohol, using 2-butanol as a source of hydrogen atoms.
In this study the adsorption characteristics of 2-butanol and furfural will be studied on a number of Au Cu systems as well as the effect of alloying behaviour of Au and Cu has on the catalyst process.
Initial experiments were carried out on the formation of Cu multilayers on the Au (111) surface using scanning tunnelling microscopy (STM) and photoemission spectroscopy (PES). The structure and growth modes of the various layers. Experiments were carried out to attempt to form an alloy on the surface leading to the creation of a 1:1 ordered surface alloy.
The adsorption of 2-butanol and furfural was then studied on these multilayer and alloy systems using thermal desorption spectroscopy (TDS), high-resolution electronic energy loss spectroscopy (HREELS) and STM. The adsorption was also studied on the ordered alloy system.
The alloying behaviour of Au and Cu nanoparticles was studied on manufactured SiO₂ and CeO₂ films. The structure of the manufactured catalyst as well their behaviour with annealing was studied using atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS) and medium energy ion scattering (MEIS).
The adsorption behaviour of the 2-butanol and furfural was studied on catalyst provided by our collaborators at Herriot-Watt University using diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) as mass spectroscopy (MS) of the outflow gas.
2022-11-18T00:00:00ZMegginson, RoryThe production of a new catalysts for the production of furfuryl alcohol from furfural is a topic of interest as it would alleviate the need for the use of a toxic copper chromate catalyst. A new coupled AuCu catalyst system has been developed for the conversion of furfural to furfuryl alcohol, using 2-butanol as a source of hydrogen atoms.
In this study the adsorption characteristics of 2-butanol and furfural will be studied on a number of Au Cu systems as well as the effect of alloying behaviour of Au and Cu has on the catalyst process.
Initial experiments were carried out on the formation of Cu multilayers on the Au (111) surface using scanning tunnelling microscopy (STM) and photoemission spectroscopy (PES). The structure and growth modes of the various layers. Experiments were carried out to attempt to form an alloy on the surface leading to the creation of a 1:1 ordered surface alloy.
The adsorption of 2-butanol and furfural was then studied on these multilayer and alloy systems using thermal desorption spectroscopy (TDS), high-resolution electronic energy loss spectroscopy (HREELS) and STM. The adsorption was also studied on the ordered alloy system.
The alloying behaviour of Au and Cu nanoparticles was studied on manufactured SiO₂ and CeO₂ films. The structure of the manufactured catalyst as well their behaviour with annealing was studied using atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS) and medium energy ion scattering (MEIS).
The adsorption behaviour of the 2-butanol and furfural was studied on catalyst provided by our collaborators at Herriot-Watt University using diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) as mass spectroscopy (MS) of the outflow gas.Solid-state NMR studies of alumina-based catalysts and investigation of CPMAS experiments involving quadrupolar nucleiLégrády, Máté Bonifáchttps://hdl.handle.net/10023/270502024-01-06T03:07:24Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZLégrády, Máté BonifácAbstract redactedPerovskite nanofibers for electrochemical and catalysis applicationsXu, Minhttps://hdl.handle.net/10023/269722023-04-30T14:57:13Z2022-06-15T00:00:00ZThe ever increasing demand for renewable energy encourages people to search for technique creation. The development of efficient materials is of key importance for various reliable technologies, including catalysis, photocatalysis and energy conversion and storage (such as fuel cell, electrolyser and battery). Perovskite attracts much attention because of its versatility and flexibility. However, understanding the relationship among composition, structure (both morphological and crystal) of perovskite is still of a crucial role in tuning the properties of materials.
Fibre structure opens new scenarios for designing perovskite-based materials with intriguing properties in this work. This thesis explores the versatility of electrospinning with respect to fabricating various titanium perovskite fibre, from aristotype SrTiO₃ to A/B-site co-doping material. The perovskite fibres were employed in photocatalysis, CO oxidation and solid oxide cells.
In particular, this work demonstrates that the fibre structure offers a unique platform to observe the surface reconstruction. Besides, the grain-grain connected fiber structure sets a unique context for the cation ordering stabilisation. The continuous fibre structure also render a fast delivering pathway for the B-site cation diffusion. As demonstrated in this study, the exsolution of Ni-cation is faster in fibre structure than powder and bulk materials.
The synergetic effect of bi-metal exsolution was also investigated by introducing Fe and Co into the B-site of perovskite. Bi-metal doping was found to enhance the reducibility of the perovskite and facilitate the formation of alloy nanoparticles. Consequently, the egressed bimetallic nanoparticles contribute to an enhanced CO₂ electrolysis performance.
Furthermore, the interwoven fibres material provides space for reactant transport and acts well as a framework for Pt deposition. The reactive interaction between the Pt nanoparticles and the perovskite support facilitates the exsolution of Ni from the support. The exsolved Ni in turn prompts the in-situ formation of PtNi bimetallic nanoparticles. Controlling and understanding of the formation of the PtNi may inspire the development of a new driven force of exsolution. Moreover, the method developed in this study may be extended to other metals and supports.
2022-06-15T00:00:00ZXu, MinThe ever increasing demand for renewable energy encourages people to search for technique creation. The development of efficient materials is of key importance for various reliable technologies, including catalysis, photocatalysis and energy conversion and storage (such as fuel cell, electrolyser and battery). Perovskite attracts much attention because of its versatility and flexibility. However, understanding the relationship among composition, structure (both morphological and crystal) of perovskite is still of a crucial role in tuning the properties of materials.
Fibre structure opens new scenarios for designing perovskite-based materials with intriguing properties in this work. This thesis explores the versatility of electrospinning with respect to fabricating various titanium perovskite fibre, from aristotype SrTiO₃ to A/B-site co-doping material. The perovskite fibres were employed in photocatalysis, CO oxidation and solid oxide cells.
In particular, this work demonstrates that the fibre structure offers a unique platform to observe the surface reconstruction. Besides, the grain-grain connected fiber structure sets a unique context for the cation ordering stabilisation. The continuous fibre structure also render a fast delivering pathway for the B-site cation diffusion. As demonstrated in this study, the exsolution of Ni-cation is faster in fibre structure than powder and bulk materials.
The synergetic effect of bi-metal exsolution was also investigated by introducing Fe and Co into the B-site of perovskite. Bi-metal doping was found to enhance the reducibility of the perovskite and facilitate the formation of alloy nanoparticles. Consequently, the egressed bimetallic nanoparticles contribute to an enhanced CO₂ electrolysis performance.
Furthermore, the interwoven fibres material provides space for reactant transport and acts well as a framework for Pt deposition. The reactive interaction between the Pt nanoparticles and the perovskite support facilitates the exsolution of Ni from the support. The exsolved Ni in turn prompts the in-situ formation of PtNi bimetallic nanoparticles. Controlling and understanding of the formation of the PtNi may inspire the development of a new driven force of exsolution. Moreover, the method developed in this study may be extended to other metals and supports.Title redactedBurnett, Stuarthttps://hdl.handle.net/10023/269592023-06-28T22:20:20Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZBurnett, StuartAbstract redactedDeveloping and broadening the reactivity of C(1)-ammonium enolatesWang, Yihonghttps://hdl.handle.net/10023/269542023-02-11T03:06:29Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZWang, YihongAbstract redactedFatty acid metabolism in kinetoplastid parasites : from exploring the activity of Δ6-desaturase to building a PUFAs cell-factoryCerone, Michelahttps://hdl.handle.net/10023/269532023-10-19T02:06:17Z2023-06-14T00:00:00ZFatty acids (FAs) are exceptional biological and chemical molecules. Recently, the attention has been focused on ω-3 polyunsaturated fatty acids (PUFAs) for their benefit to human health. These cannot be produced by humans de novo and must be acquired from our diet. Consequently, their demand is constantly increasing and thus outstripping demand with the ever-decreasing availability of sources of ω-3 PUFAs, such as plant and marine ecosystems, because of agribusiness and climate change. Novel microbial techniques and chemical total synthesis to make high value PUFAs are often costly and challenging. Therefore, there is a constant need to meet the high demand of PUFAs via innovative and bio-sustainable methods. In this scenario, this project focused on formidable producers of PUFAs: kinetoplastid parasites. They possess a unique finely regulated machinery for the biosynthesis of PUFAs. Among those, Trypanosoma brucei and Crithidia fasciculata were chosen to study the activity of a putative Δ6-desaturase from T. brucei (Tb-Δ6), and its homolog in C. fasciculata (Cf-Δ6), via genetic manipulation and chemical alteration of the fat sources in the media. Particularly, T. brucei was used as model system to unveil novel information around the PUFA pathway in these pathogens, for which little is known. Particularly, it was shown that Tb-Δ6 is essential for cell growth in the procyclic and bloodstream forms of T. brucei, and that it works in the de novo synthesis of 22C PUFAs, by displaying an effect on the remodelling of the lipid pool that resembles changes in a life-cycle stage specific manner. C. fasciculata were used as a model system in which to produce PUFAs, by using it to build an innovative PUFAs cell-factory. By overexpressing either the desaturases Cf-Δ6 or Cf-Δ4, in conjunction with the elongase Cf-Elo4, significant amounts of useful ω-3 PUFAs were yielded, that could potentially be added to the food chain at a low-cost and via a bio-sustainable approach.
2023-06-14T00:00:00ZCerone, MichelaFatty acids (FAs) are exceptional biological and chemical molecules. Recently, the attention has been focused on ω-3 polyunsaturated fatty acids (PUFAs) for their benefit to human health. These cannot be produced by humans de novo and must be acquired from our diet. Consequently, their demand is constantly increasing and thus outstripping demand with the ever-decreasing availability of sources of ω-3 PUFAs, such as plant and marine ecosystems, because of agribusiness and climate change. Novel microbial techniques and chemical total synthesis to make high value PUFAs are often costly and challenging. Therefore, there is a constant need to meet the high demand of PUFAs via innovative and bio-sustainable methods. In this scenario, this project focused on formidable producers of PUFAs: kinetoplastid parasites. They possess a unique finely regulated machinery for the biosynthesis of PUFAs. Among those, Trypanosoma brucei and Crithidia fasciculata were chosen to study the activity of a putative Δ6-desaturase from T. brucei (Tb-Δ6), and its homolog in C. fasciculata (Cf-Δ6), via genetic manipulation and chemical alteration of the fat sources in the media. Particularly, T. brucei was used as model system to unveil novel information around the PUFA pathway in these pathogens, for which little is known. Particularly, it was shown that Tb-Δ6 is essential for cell growth in the procyclic and bloodstream forms of T. brucei, and that it works in the de novo synthesis of 22C PUFAs, by displaying an effect on the remodelling of the lipid pool that resembles changes in a life-cycle stage specific manner. C. fasciculata were used as a model system in which to produce PUFAs, by using it to build an innovative PUFAs cell-factory. By overexpressing either the desaturases Cf-Δ6 or Cf-Δ4, in conjunction with the elongase Cf-Elo4, significant amounts of useful ω-3 PUFAs were yielded, that could potentially be added to the food chain at a low-cost and via a bio-sustainable approach.Total synthesis and SAR of Alternaric acid towards the development of a new herbicidal leadIsrael, Eva M.https://hdl.handle.net/10023/268942023-04-30T22:26:59Z2022-11-29T00:00:00ZCrop protection is essential in agricultural chemistry to help farmers maintain a healthy and productive cropland. However, agrochemical research faces a constant need for innovation in crop protection to be able to meet the global requirement for food supplies. Over the years, fighting resistance against crop protection products has become one of the biggest challenges in the development of effective agrochemicals. As a result, there is a requirement for new agrochemicals exhibiting novel Modes of Action (MoA). Natural products are privileged scaffolds in agrochemistry, owing to their molecular complexity and rich bioactivity, which can leads to the discovery of novel MoA.
The natural product Alternaric acid, isolated from the phytopathogenic fungus Alternaria solani, has been identified as possessing herbicidal activity. As such, it represents an attractive herbicidal lead for the agrochemical industry. However, exploration of the potential of this target has remained undeveloped due to low accessibility and lack of Structure-Activity Relationship (SAR) data.
The research described in this thesis was conducted in collaboration with Syngenta. Herein, we report the development of a scalable and flexible synthetic route, which enabled the synthesis of significant quantities of Alternaric acid as well as a variety of analogues. Through biological evaluation of these compounds, SAR profiling of focused libraries identified a new class of small molecule leads, with enhanced herbicidal activity and developability. Additionally, MoA investigations have been conducted, suggesting that this new class of lead compounds is likely to exhibit a novel MoA, highlighting their potential for herbicidal discovery.
2022-11-29T00:00:00ZIsrael, Eva M.Crop protection is essential in agricultural chemistry to help farmers maintain a healthy and productive cropland. However, agrochemical research faces a constant need for innovation in crop protection to be able to meet the global requirement for food supplies. Over the years, fighting resistance against crop protection products has become one of the biggest challenges in the development of effective agrochemicals. As a result, there is a requirement for new agrochemicals exhibiting novel Modes of Action (MoA). Natural products are privileged scaffolds in agrochemistry, owing to their molecular complexity and rich bioactivity, which can leads to the discovery of novel MoA.
The natural product Alternaric acid, isolated from the phytopathogenic fungus Alternaria solani, has been identified as possessing herbicidal activity. As such, it represents an attractive herbicidal lead for the agrochemical industry. However, exploration of the potential of this target has remained undeveloped due to low accessibility and lack of Structure-Activity Relationship (SAR) data.
The research described in this thesis was conducted in collaboration with Syngenta. Herein, we report the development of a scalable and flexible synthetic route, which enabled the synthesis of significant quantities of Alternaric acid as well as a variety of analogues. Through biological evaluation of these compounds, SAR profiling of focused libraries identified a new class of small molecule leads, with enhanced herbicidal activity and developability. Additionally, MoA investigations have been conducted, suggesting that this new class of lead compounds is likely to exhibit a novel MoA, highlighting their potential for herbicidal discovery.The synthesis, structure and physical properties of layered hybrid copper (II) halide perovskitesHan, Cenghttps://hdl.handle.net/10023/268532023-12-21T15:17:11Z2023-06-14T00:00:00ZAbstract redacted
2023-06-14T00:00:00ZHan, CengAbstract redactedIsothiourea-catalysed acylative kinetic resolution of alcoholsQu, Shenhttps://hdl.handle.net/10023/265042022-11-29T03:02:26Z2022-11-29T00:00:00ZAbstract redacted
2022-11-29T00:00:00ZQu, ShenAbstract redactedNovel nanostructured materials for anodes in solid oxide fuel cellsLightfoot, Alison Emilyhttps://hdl.handle.net/10023/261462022-12-06T13:51:33Z2022-11-29T00:00:00ZMaterials for heterogenous catalysis as well as in anodes for solid oxide fuel cells are two innovative and relevant areas of research. The search for a replacement of traditional Ni-based anodes in solid oxide fuel cells has been an increasing area of study over the last 20 years. The use of template materials such as ordered mesoporous silica to provide higher surface area materials for heterogenous catalysis are also a hot topic. In this thesis nanocubic doped-ceria oxides (for anodes in SOFCS) and lanthanum ferrite (as a good catalyst for the oxidation of hydrocarbons), were synthesised and studied separately for their electrochemical, structural, and catalytic properties, respectively.
Three different nanocubic ceria candidate materials were synthesised and tested by impedance spectroscopy for their electrochemical properties (Nanocubic ceria, La-doped ceria, and Pr-doped ceria). These materials were studied to determine the effect of dopants and nanostructure of the material on the resistances and conductivities. The electrochemical studies, by impedance spectroscopy yielded that La-doped ceria has the lowest resistance of the three materials. Problems were encountered both with the testing apparatus, as well as the printing and durability of the ink electrodes and this area of research was not pursued further.
For the lanthanum ferrite (LFO) materials, different preparation methods were explored by using ordered mesoporous carbon (OMC) templates to nanocast 19 ordered mesoporous products with high surface areas and improved catalytic performance. The use of OMC templates is a novel, safer, and easier route for nanocasting than its ordered mesoporous silica (OMS) counterparts. The preparation methods included a citrate complexation method, two solid-liquid methods – one of which included the preparation of these materials with OMC templates calcined at different temperatures – and a vacuum impregnation method.
These materials were characterised using x-ray diffraction, transmission (and scanning transmission) electron microscopy, and nitrogen physisorption. They were evaluated catalytically by temperature programmed reduction and light-off experiments. The crystallite size, BET specific surface area, particle size, pore volume, pore diameter, degree of nanorod-like and ordered mesoporous structure, the reducibility, and light-off temperatures were obtained for each material.
The vacuum impregnation method was the most successful method out of the four tested, with the highest specific surface areas reported as well as the best catalytic activity for the oxidation of methane in light-off experiments. The citrate complexation method was ranked second behind this with high specific surface areas and improved catalytic activity. The solid-liquid methods reported the lowest surface areas and worst catalytic activity, as well as having high impurity phases in the final products.
2022-11-29T00:00:00ZLightfoot, Alison EmilyMaterials for heterogenous catalysis as well as in anodes for solid oxide fuel cells are two innovative and relevant areas of research. The search for a replacement of traditional Ni-based anodes in solid oxide fuel cells has been an increasing area of study over the last 20 years. The use of template materials such as ordered mesoporous silica to provide higher surface area materials for heterogenous catalysis are also a hot topic. In this thesis nanocubic doped-ceria oxides (for anodes in SOFCS) and lanthanum ferrite (as a good catalyst for the oxidation of hydrocarbons), were synthesised and studied separately for their electrochemical, structural, and catalytic properties, respectively.
Three different nanocubic ceria candidate materials were synthesised and tested by impedance spectroscopy for their electrochemical properties (Nanocubic ceria, La-doped ceria, and Pr-doped ceria). These materials were studied to determine the effect of dopants and nanostructure of the material on the resistances and conductivities. The electrochemical studies, by impedance spectroscopy yielded that La-doped ceria has the lowest resistance of the three materials. Problems were encountered both with the testing apparatus, as well as the printing and durability of the ink electrodes and this area of research was not pursued further.
For the lanthanum ferrite (LFO) materials, different preparation methods were explored by using ordered mesoporous carbon (OMC) templates to nanocast 19 ordered mesoporous products with high surface areas and improved catalytic performance. The use of OMC templates is a novel, safer, and easier route for nanocasting than its ordered mesoporous silica (OMS) counterparts. The preparation methods included a citrate complexation method, two solid-liquid methods – one of which included the preparation of these materials with OMC templates calcined at different temperatures – and a vacuum impregnation method.
These materials were characterised using x-ray diffraction, transmission (and scanning transmission) electron microscopy, and nitrogen physisorption. They were evaluated catalytically by temperature programmed reduction and light-off experiments. The crystallite size, BET specific surface area, particle size, pore volume, pore diameter, degree of nanorod-like and ordered mesoporous structure, the reducibility, and light-off temperatures were obtained for each material.
The vacuum impregnation method was the most successful method out of the four tested, with the highest specific surface areas reported as well as the best catalytic activity for the oxidation of methane in light-off experiments. The citrate complexation method was ranked second behind this with high specific surface areas and improved catalytic activity. The solid-liquid methods reported the lowest surface areas and worst catalytic activity, as well as having high impurity phases in the final products.Electron microscopic studies of novel crystal morphologies and related growth mechanismsSun, Weihaohttps://hdl.handle.net/10023/261272022-10-05T02:08:09Z2022-11-29T00:00:00ZThis project explores selected crystals with novel morphologies and corresponding growth mechanisms. Crystal samples from different growth stages are obtained by interrupting the reaction in order to study the growth mechanisms step by step. To achieve the characterisations of the crystals, electron microscopes and in-built electron spectroscopic techniques are the major implements. Together with electron microscopy, other techniques, such as X-ray diffraction and infrared spectroscopy, are also employed. Schematic visualisation is exploited to illustrate the formation mechanisms.
Copper pseudo-icosahedral crystals are prepared and studied. Polyvinylpyrrolidone-assisted growth route involving dual-step reduction and multiple intermediate phases is revealed. The attribute of pseudo-icosahedral is discussed morphologically. Using the same synthesis system but different reactant, Cu₂O spherulites are prepared. By examining the polarity of the spherulites and the feature of Cu₂O nanocrystallites in PVP matrix, the formation mechanism concerning intrinsic dipolar force is proposed.
Cs₄PbBr₆ rhombohedral crystals with embedded CsPbBr₃ nanocrystallites are produced via antisolvent preparation method. Despite the sensitivity to electron beam exposure, we manage to visualise the material using electron microscopy. With observed evidence of amorphous precursor, a formation mechanism associated with the precursor amorphous phase is proposed. Different antisolvents are tested on their effects of the morphology. Water triggered transformation of Cs₄PbBr₆ to CsPb₂Br₅ and CsPbBr₃ is realised.
Electron microscopic and spectroscopic information of Ti₃C₂Tₓ nanowire clusters synthesised at Beijing Normal University reveals the dimensional degradation mechanism. From the oxidation of layered Ti3C2Tₓ structure, interconnected Ti₃C₂O and Ti₃C₂ nanowires are produced.
We anticipate that this doctorate project can provide new perspectives in understanding non-classical crystal growth, set an example for the study of beam sensitive materials and inspire the morphology engineering of crystalline materials.
2022-11-29T00:00:00ZSun, WeihaoThis project explores selected crystals with novel morphologies and corresponding growth mechanisms. Crystal samples from different growth stages are obtained by interrupting the reaction in order to study the growth mechanisms step by step. To achieve the characterisations of the crystals, electron microscopes and in-built electron spectroscopic techniques are the major implements. Together with electron microscopy, other techniques, such as X-ray diffraction and infrared spectroscopy, are also employed. Schematic visualisation is exploited to illustrate the formation mechanisms.
Copper pseudo-icosahedral crystals are prepared and studied. Polyvinylpyrrolidone-assisted growth route involving dual-step reduction and multiple intermediate phases is revealed. The attribute of pseudo-icosahedral is discussed morphologically. Using the same synthesis system but different reactant, Cu₂O spherulites are prepared. By examining the polarity of the spherulites and the feature of Cu₂O nanocrystallites in PVP matrix, the formation mechanism concerning intrinsic dipolar force is proposed.
Cs₄PbBr₆ rhombohedral crystals with embedded CsPbBr₃ nanocrystallites are produced via antisolvent preparation method. Despite the sensitivity to electron beam exposure, we manage to visualise the material using electron microscopy. With observed evidence of amorphous precursor, a formation mechanism associated with the precursor amorphous phase is proposed. Different antisolvents are tested on their effects of the morphology. Water triggered transformation of Cs₄PbBr₆ to CsPb₂Br₅ and CsPbBr₃ is realised.
Electron microscopic and spectroscopic information of Ti₃C₂Tₓ nanowire clusters synthesised at Beijing Normal University reveals the dimensional degradation mechanism. From the oxidation of layered Ti3C2Tₓ structure, interconnected Ti₃C₂O and Ti₃C₂ nanowires are produced.
We anticipate that this doctorate project can provide new perspectives in understanding non-classical crystal growth, set an example for the study of beam sensitive materials and inspire the morphology engineering of crystalline materials.On the use of generating functions for topics in clustered networksMann, Peter Stephenhttps://hdl.handle.net/10023/259832022-09-10T02:03:16Z2022-06-15T00:00:00ZIn this thesis we relax the locally tree-like assumption of configuration model
random networks to examine the properties of clustering, and the effects
thereof, on bond percolation. We introduce an algorithmic enumeration
method to evaluate the probability that a vertex remains unattached to the giant
connected component during percolation. The properties of the non-giant,
finite components of clustered networks are also examined, along with the
degree correlations between subgraphs. In a second avenue of research, we
investigate the role of clustering on 2-strain epidemic processes under various
disease interaction schedules. We then examine an 𝑁-generation epidemic by
performing repeated percolation events.
2022-06-15T00:00:00ZMann, Peter StephenIn this thesis we relax the locally tree-like assumption of configuration model
random networks to examine the properties of clustering, and the effects
thereof, on bond percolation. We introduce an algorithmic enumeration
method to evaluate the probability that a vertex remains unattached to the giant
connected component during percolation. The properties of the non-giant,
finite components of clustered networks are also examined, along with the
degree correlations between subgraphs. In a second avenue of research, we
investigate the role of clustering on 2-strain epidemic processes under various
disease interaction schedules. We then examine an 𝑁-generation epidemic by
performing repeated percolation events.The development of SOFC with perovskite electrodes by co-sintering and co-casting methodNowicki, Kamilhttps://hdl.handle.net/10023/255202022-06-14T02:08:04Z2022-06-15T00:00:00ZThe Solid Oxide Fuel Cells (SOFCs) were produced with various geometries by tape casting and co-sintering. Tape casting is a cheap and easily scalable method employed on a large scale for thin layers preparation. In the project, a sequential casting technique was developed where all the function layers in SOFC assembly were cast on each other; co-casting gave a strong interface and reduced electrolyte thickness. Co-sintering further simplified cells manufacturing and reduced processing time and energy demand, making fuel cells more profitable and suitable for mass production. The crucial factor for co-sintering of various-material tapes is to ensure that they have close shrinkage profiles during the sintering step, which usually differ due to individual properties of ceramic materials and pore former’s concentration in the slurry. The minor differences create stress between layers, leading to delamination and cracks in the cell’s structure. By controlling the composition of the slurry, particle size distribution and sintering temperature, it was possible to produce a cell without any internal structural defects.
The developed method was used to produce SOFC with alternative SOFCRoll geometry and the small tubular cells. SOFCRoll gives the possibility to extend the surface area while keeping the volume low. Up to 27.75 cm² of surface area was incorporated in a spiral structure, with a volume of about 2.5 cm³, thus giving better applicability where size reduction is required and a more robust structure; however, the cell was suffered a performance loss due to complications with the current collection and gas distribution. The structure modification and co-sintering of the current collector with high Ni content into otherwise unavailable part of the cell allowed for optimal use of 12 cm² surface area in the smaller version of the cell. Tubular cells are known for their high mechanical and thermal resistance. Tubular cell's surface area was up to 7 cm², much lower than in SOFCRoll but more accessible for gas and current collector. The combination of a small tubular design with thermally and redox stable alternative perovskite fuel electrode gave a highly durable device; without noticeable degradation after testing in extreme conditions.
Through the project, composite electrodes were mainly used, co-cast, and co-sintered with electrolyte at 1350 °C. The state-of-art yttria-stabilised zirconia (Zr₀.₈₄Y₀.₁₆O₁.₉₂, YSZ) was used as the electrolyte, which offers good performance and commercial availability. The co-sintered active fuel electrode contained the nickel-doped lanthanum calcium titanate (La₀.₄₃Ca₀.₃₇Ni₀.₀₆Ti₀.₉₄O[sub](3-γ), LCNT) and YSZ. The co-sintered oxygen electrode was a composite of lanthanum strontium manganate ((La₀.₈Sr₀.₂)₀.₉₅MnO₃, LSM) and YSZ. LCNT belongs to the family of new alternative materials proposed to replace highly active but prone to degradation state-of-the-art Ni/YSZ composite. Thanks to its mixed ionic and electronic properties (MIEC) and the possibility of exsolving nickel nanoparticles on its surface, LCNT offers a high activity for hydrogen oxidation whilst possessing great thermal shock and redox resistance as a fully ceramic electrode.
Despite the successful co-sintering of the LCNT/YSZ fuel electrode and LSM/YSZ oxygen electrode into a SOFCRoll and tubular structure, due to limitations related to the sintering temperature and composition, electrodes showed a significant ohmic and polarisation resistance.
In the following experiment, the composite electrodes were replaced. For the development of the next generation of tubular cells, the active material was impregnated into a co-sintered porous YSZ backbone. For impregnated electrodes, LCNT was impregnated on a porous YSZ backbone for the fuel hydrogen side, while on the air electrode, a lanthanum strontium ferrite (La₀.₈Sr₀.₂FeO₃, LSF). The impregnated electrodes were sintered at a much lower temperature than in state-of-the-art methods, giving more active spatial microstructures with a large surface area. Using this technique in co-sintered cells simplified manufacturing and made a broader range of materials available.
This work contains complete procedures for producing SOFC with various designs, including planar, tubular, and SOFCRoll, by the outlined methods. In addition, it seeks to determine a mechanism of their functionality based on electrochemical tests and DRT analysis.
2022-06-15T00:00:00ZNowicki, KamilThe Solid Oxide Fuel Cells (SOFCs) were produced with various geometries by tape casting and co-sintering. Tape casting is a cheap and easily scalable method employed on a large scale for thin layers preparation. In the project, a sequential casting technique was developed where all the function layers in SOFC assembly were cast on each other; co-casting gave a strong interface and reduced electrolyte thickness. Co-sintering further simplified cells manufacturing and reduced processing time and energy demand, making fuel cells more profitable and suitable for mass production. The crucial factor for co-sintering of various-material tapes is to ensure that they have close shrinkage profiles during the sintering step, which usually differ due to individual properties of ceramic materials and pore former’s concentration in the slurry. The minor differences create stress between layers, leading to delamination and cracks in the cell’s structure. By controlling the composition of the slurry, particle size distribution and sintering temperature, it was possible to produce a cell without any internal structural defects.
The developed method was used to produce SOFC with alternative SOFCRoll geometry and the small tubular cells. SOFCRoll gives the possibility to extend the surface area while keeping the volume low. Up to 27.75 cm² of surface area was incorporated in a spiral structure, with a volume of about 2.5 cm³, thus giving better applicability where size reduction is required and a more robust structure; however, the cell was suffered a performance loss due to complications with the current collection and gas distribution. The structure modification and co-sintering of the current collector with high Ni content into otherwise unavailable part of the cell allowed for optimal use of 12 cm² surface area in the smaller version of the cell. Tubular cells are known for their high mechanical and thermal resistance. Tubular cell's surface area was up to 7 cm², much lower than in SOFCRoll but more accessible for gas and current collector. The combination of a small tubular design with thermally and redox stable alternative perovskite fuel electrode gave a highly durable device; without noticeable degradation after testing in extreme conditions.
Through the project, composite electrodes were mainly used, co-cast, and co-sintered with electrolyte at 1350 °C. The state-of-art yttria-stabilised zirconia (Zr₀.₈₄Y₀.₁₆O₁.₉₂, YSZ) was used as the electrolyte, which offers good performance and commercial availability. The co-sintered active fuel electrode contained the nickel-doped lanthanum calcium titanate (La₀.₄₃Ca₀.₃₇Ni₀.₀₆Ti₀.₉₄O[sub](3-γ), LCNT) and YSZ. The co-sintered oxygen electrode was a composite of lanthanum strontium manganate ((La₀.₈Sr₀.₂)₀.₉₅MnO₃, LSM) and YSZ. LCNT belongs to the family of new alternative materials proposed to replace highly active but prone to degradation state-of-the-art Ni/YSZ composite. Thanks to its mixed ionic and electronic properties (MIEC) and the possibility of exsolving nickel nanoparticles on its surface, LCNT offers a high activity for hydrogen oxidation whilst possessing great thermal shock and redox resistance as a fully ceramic electrode.
Despite the successful co-sintering of the LCNT/YSZ fuel electrode and LSM/YSZ oxygen electrode into a SOFCRoll and tubular structure, due to limitations related to the sintering temperature and composition, electrodes showed a significant ohmic and polarisation resistance.
In the following experiment, the composite electrodes were replaced. For the development of the next generation of tubular cells, the active material was impregnated into a co-sintered porous YSZ backbone. For impregnated electrodes, LCNT was impregnated on a porous YSZ backbone for the fuel hydrogen side, while on the air electrode, a lanthanum strontium ferrite (La₀.₈Sr₀.₂FeO₃, LSF). The impregnated electrodes were sintered at a much lower temperature than in state-of-the-art methods, giving more active spatial microstructures with a large surface area. Using this technique in co-sintered cells simplified manufacturing and made a broader range of materials available.
This work contains complete procedures for producing SOFC with various designs, including planar, tubular, and SOFCRoll, by the outlined methods. In addition, it seeks to determine a mechanism of their functionality based on electrochemical tests and DRT analysis.Insights into catalytic activities of noble transition metal complexes from quantum-chemical calculationsAhmad, Shahbazhttps://hdl.handle.net/10023/254532024-02-17T03:07:41Z2022-06-15T00:00:00ZHomogeneous catalysis at transition metal centres is an essential and ubiquitous tool for the regioselective direct synthesis of fine chemicals from abundant resources. Quantum chemical models are used to gain insights into mechanisms of homogeneous catalysis with organo-transition metal complexes. The resulting overall kinetic barriers and barriers at branching leading to different products can help in steric and electronic tuning of ligands at the metal centre to control chemo- and regioselectivities. This thesis presents computational investigations on detailed mechanisms of alkene and alkyne alkoxycarbonylation at palladium catalysts and ruthenium–catalysed selective reduction of cardanol derivatives via transfer hydrogenation using state-of-the-art Density Functional Theory (DFT).
We have explored catalytic methoxycarbonylation of ethene with a bidentate tertiary phosphine (DTBPX) and palladium. Out of three pathways, (i) carbomethoxy, (ii) ketene, and (iii) hydride-hydroxyalkylpalladium, the latter is the most plausible pathway with a computed selectivity of >99% towards the formation of methyl propanoate (MePro) and a reasonably low overall kinetic barrier of 17.8 kcal mol⁻¹. Consistent with experimental data, for a less bulky bidentate phosphine, the overall barrier increases to 30.1 kcal mol⁻¹.
We have revisited in situ base mechanism of alkyne alkoxycarbonylation via a Pd catalyst with hemilabile P,N-ligands (PyPPh₂, Py = 2-pyridyl). Newly characterised acryloyl and η³-propen-1-oyl intermediates readily undergo methanolysis. The new mechanism is consistent with experimental data in terms of ligand effects on the reaction rates and selectivities, where (6-Cl-Py)PPh₂ has been shown to improve both selectivity and turnover. We further have explored the formation of a highly stable π-allyl intermediate as the reason for catalyst poisoning due to the presence of propadiene in technical propyne. Predicted regioselectivities suggest that at least 11 % of propadiene should yield this π-allyl intermediate, which requires an insurmountable barrier of 25.8 kcal mol⁻¹ to proceed to the product via methanolysis. A new ligand, (6-Cl-3-Me-Py)PPh₂, is proposed, which is more tolerant to propadiene poisoning (as only 0.2% of propadiene gets trapped at the π-allyl complex) and tremendously active (as decreases the overall barrier to 9.1 kcal mol⁻¹).
Finally, we have calculated the complete pathway leading to the monoene cardanol at ruthenium–catalysed selective reduction of cardanol derivatives via transfer hydrogenation. The overall barrier of 29.2 kcal mol⁻¹ associated with the transfer hydrogenation leading to the monoene cardanol is surmountable under the elevated temperatures of the experiments (refluxing iso-propanol). The computed barrier of 46.6 kcal mol⁻¹ leading to a fully saturated cardanol product explains the 100% selectivity towards monoene cardanol.
2022-06-15T00:00:00ZAhmad, ShahbazHomogeneous catalysis at transition metal centres is an essential and ubiquitous tool for the regioselective direct synthesis of fine chemicals from abundant resources. Quantum chemical models are used to gain insights into mechanisms of homogeneous catalysis with organo-transition metal complexes. The resulting overall kinetic barriers and barriers at branching leading to different products can help in steric and electronic tuning of ligands at the metal centre to control chemo- and regioselectivities. This thesis presents computational investigations on detailed mechanisms of alkene and alkyne alkoxycarbonylation at palladium catalysts and ruthenium–catalysed selective reduction of cardanol derivatives via transfer hydrogenation using state-of-the-art Density Functional Theory (DFT).
We have explored catalytic methoxycarbonylation of ethene with a bidentate tertiary phosphine (DTBPX) and palladium. Out of three pathways, (i) carbomethoxy, (ii) ketene, and (iii) hydride-hydroxyalkylpalladium, the latter is the most plausible pathway with a computed selectivity of >99% towards the formation of methyl propanoate (MePro) and a reasonably low overall kinetic barrier of 17.8 kcal mol⁻¹. Consistent with experimental data, for a less bulky bidentate phosphine, the overall barrier increases to 30.1 kcal mol⁻¹.
We have revisited in situ base mechanism of alkyne alkoxycarbonylation via a Pd catalyst with hemilabile P,N-ligands (PyPPh₂, Py = 2-pyridyl). Newly characterised acryloyl and η³-propen-1-oyl intermediates readily undergo methanolysis. The new mechanism is consistent with experimental data in terms of ligand effects on the reaction rates and selectivities, where (6-Cl-Py)PPh₂ has been shown to improve both selectivity and turnover. We further have explored the formation of a highly stable π-allyl intermediate as the reason for catalyst poisoning due to the presence of propadiene in technical propyne. Predicted regioselectivities suggest that at least 11 % of propadiene should yield this π-allyl intermediate, which requires an insurmountable barrier of 25.8 kcal mol⁻¹ to proceed to the product via methanolysis. A new ligand, (6-Cl-3-Me-Py)PPh₂, is proposed, which is more tolerant to propadiene poisoning (as only 0.2% of propadiene gets trapped at the π-allyl complex) and tremendously active (as decreases the overall barrier to 9.1 kcal mol⁻¹).
Finally, we have calculated the complete pathway leading to the monoene cardanol at ruthenium–catalysed selective reduction of cardanol derivatives via transfer hydrogenation. The overall barrier of 29.2 kcal mol⁻¹ associated with the transfer hydrogenation leading to the monoene cardanol is surmountable under the elevated temperatures of the experiments (refluxing iso-propanol). The computed barrier of 46.6 kcal mol⁻¹ leading to a fully saturated cardanol product explains the 100% selectivity towards monoene cardanol.Chemical transformations of biomass-derived fractions : studies on lignin models and selected monosaccharidesXiao, Ganyuanhttps://hdl.handle.net/10023/253882023-06-22T15:21:43Z2022-06-15T00:00:00ZAbstract redacted
2022-06-15T00:00:00ZXiao, GanyuanAbstract redactedEnantioselective palladium and isothiourea dual catalysisBitai, Jacquelinehttps://hdl.handle.net/10023/253852024-02-28T03:02:12Z2022-06-15T00:00:00ZThis thesis details the development of dual catalytic processes involving achiral palladium and enantiopure isothiourea catalysts for the synthesis of enantioenriched and highly functionalised products. Taking inspiration from related literature examples demonstrating the compatibility of palladium and isothiourea catalysis, the extension of existing methodologies as well as the development of novel processes were investigated.
Based on the relay catalytic allylic amination/[2,3]-rearrangement protocol, previously developed in our group for the synthesis of enantioenriched α-amino ester derivatives, the scope and limitations of this process were probed. Initial studies aimed at identifying functional groups that could be tolerated in the relay catalysis. Electron-withdrawing amide substituents proved most promising and were explored in more depth to furnish enantioenriched α-amino ester derivatives featuring a 1,4-dicarbonyl motif.
As processes reported so far had focused on ammonium enolates as reaction partners, the range of reactivity modes accessible by isothiourea catalysis had not been fully exploited in dual catalytic methodologies. As such, the development of a cooperative palladium and isothiourea catalysis process employing α,β-unsaturated acyl ammonium intermediates was explored. This process furnishes enantioenriched cyclopentane products with up to four contiguous stereogenic centres with high stereoselectivity (up to 99:1 dr, up to 97:3 er). The scope and limitations of this process were probed, with subsequent derivatisation reactions demonstrating the synthetic utility of the products. In addition, a range of control experiments provided insight into the mechanism of this cooperative palladium and isothiourea catalysis.
2022-06-15T00:00:00ZBitai, JacquelineThis thesis details the development of dual catalytic processes involving achiral palladium and enantiopure isothiourea catalysts for the synthesis of enantioenriched and highly functionalised products. Taking inspiration from related literature examples demonstrating the compatibility of palladium and isothiourea catalysis, the extension of existing methodologies as well as the development of novel processes were investigated.
Based on the relay catalytic allylic amination/[2,3]-rearrangement protocol, previously developed in our group for the synthesis of enantioenriched α-amino ester derivatives, the scope and limitations of this process were probed. Initial studies aimed at identifying functional groups that could be tolerated in the relay catalysis. Electron-withdrawing amide substituents proved most promising and were explored in more depth to furnish enantioenriched α-amino ester derivatives featuring a 1,4-dicarbonyl motif.
As processes reported so far had focused on ammonium enolates as reaction partners, the range of reactivity modes accessible by isothiourea catalysis had not been fully exploited in dual catalytic methodologies. As such, the development of a cooperative palladium and isothiourea catalysis process employing α,β-unsaturated acyl ammonium intermediates was explored. This process furnishes enantioenriched cyclopentane products with up to four contiguous stereogenic centres with high stereoselectivity (up to 99:1 dr, up to 97:3 er). The scope and limitations of this process were probed, with subsequent derivatisation reactions demonstrating the synthetic utility of the products. In addition, a range of control experiments provided insight into the mechanism of this cooperative palladium and isothiourea catalysis.Title redactedInwood, Ryanhttps://hdl.handle.net/10023/253332023-06-22T09:44:33Z2022-06-15T00:00:00Z2022-06-15T00:00:00ZInwood, RyanDesign and synthesis of blue thermally activated delayed fluorescence emitters for organic light emitting diodesChen, Dongyanghttps://hdl.handle.net/10023/252712024-03-12T12:03:55Z2022-06-15T00:00:00ZThermally activated delayed fluorescence (TADF) has emerged as one of the most
promising and efficient approaches to realize highly efficient organic light-emitting diodes
(OLEDs). It took only several years for OLEDs using organic TADF emitters to reach
efficiencies comparable to phosphorescent OLEDs. Chapter 1 presents an overview of the
TADF mechanism and focuses more specifically on blue TADF emitter design and their use in
OLEDs. There is still room for improvement in terms of highly efficient deep-blue TADF
emitters. These include improving exciton lifetime and reducing exciton annihilation in device,
and optimizing the orientation of the transition dipole moment of the emitter to enhance light
out-coupling. This thesis is focused on blue TADF emitter design and makes efforts to address
these issues, and throughout the projects in this thesis, various design strategies are presented
to optimize blue TADF materials for OLED applications.
In Chapter 2, three TADF emitters each with a multichromphore structure are
presented. In Chapter 3, we explored the use of heteroaromatic bridges between donor and
acceptor units for efficient blue TADF emitter design and synthesized four TADF emitters based
on different heteroaromatic sulfones as acceptors. In Chapter 4, we synthesized two pyrazine-
based emitters bearing a mono and dipyrazine acceptors and di-tert-butylcarbazole as the donor,
and in Chapter 5, two pyridine-containing ambipolar hosts were designed and employed as the
host for yellow TADF OLEDs. In Chapter 6, to improve and control the orientation of TADF
emitters in solution-processed films we explored introducing mesogens onto to TADF emitter.
The compound DiKTaLC exhibits both TADF and liquid crystal character. The transition
dipole moment of the as-prepared spin-coated neat film of DiKTaLC shows preferential
horizontal orientation. In Chapter 7, we explored the possibility of using nanohoop structures
in terms of cycloparaphenylenes (CPPs) for TADF emitter design. The photophysical properties
of these materials are investigated, and state-of-the-art OLED performances are demonstrated.
2022-06-15T00:00:00ZChen, DongyangThermally activated delayed fluorescence (TADF) has emerged as one of the most
promising and efficient approaches to realize highly efficient organic light-emitting diodes
(OLEDs). It took only several years for OLEDs using organic TADF emitters to reach
efficiencies comparable to phosphorescent OLEDs. Chapter 1 presents an overview of the
TADF mechanism and focuses more specifically on blue TADF emitter design and their use in
OLEDs. There is still room for improvement in terms of highly efficient deep-blue TADF
emitters. These include improving exciton lifetime and reducing exciton annihilation in device,
and optimizing the orientation of the transition dipole moment of the emitter to enhance light
out-coupling. This thesis is focused on blue TADF emitter design and makes efforts to address
these issues, and throughout the projects in this thesis, various design strategies are presented
to optimize blue TADF materials for OLED applications.
In Chapter 2, three TADF emitters each with a multichromphore structure are
presented. In Chapter 3, we explored the use of heteroaromatic bridges between donor and
acceptor units for efficient blue TADF emitter design and synthesized four TADF emitters based
on different heteroaromatic sulfones as acceptors. In Chapter 4, we synthesized two pyrazine-
based emitters bearing a mono and dipyrazine acceptors and di-tert-butylcarbazole as the donor,
and in Chapter 5, two pyridine-containing ambipolar hosts were designed and employed as the
host for yellow TADF OLEDs. In Chapter 6, to improve and control the orientation of TADF
emitters in solution-processed films we explored introducing mesogens onto to TADF emitter.
The compound DiKTaLC exhibits both TADF and liquid crystal character. The transition
dipole moment of the as-prepared spin-coated neat film of DiKTaLC shows preferential
horizontal orientation. In Chapter 7, we explored the possibility of using nanohoop structures
in terms of cycloparaphenylenes (CPPs) for TADF emitter design. The photophysical properties
of these materials are investigated, and state-of-the-art OLED performances are demonstrated.Computational design, synthesis and optoelectronic characterisation of thermally activated delayed fluorescent materials : donor-acceptor and multi-resonance designsHall, David Luke Starkeyhttps://hdl.handle.net/10023/252612023-10-24T02:08:57Z2022-06-15T00:00:00ZThis thesis concerns the study of organic TADF materials, focussing on donor-acceptor (D-A TADF) and multi-resonance (MR-TADF) emitters. Materials were developed in silico, they were then synthesized, characterized and finally tested in OLED devices.
Chapter 1 introduces the various radiative decay pathways available in electronically excited molecules from photoluminescence and electroluminescence. D-A TADF and MR-TADF emitters are discussed in detail.
Chapter 2 introduces the background behind the computational methods undertaken. These include Hartree Fock, coupled cluster and DFT.
Chapter 3 investigates the impact of donor dendrons in the TADF emitter 2CzPN. Donor extension improves kRISC but at the expense of increasing non-radiative pathways.
Chapter 4 discloses a new acceptor unit, BImPy, which is coupled to phenoxazine as a donor, with TADF observed. The torsion angle within the acceptor was modulated as a function of N-substitution, with 4 emitters studied.
In Chapter 5 a computational investigation of a series of 14 literature D-A TADF emitters is undertaken, with calculated T₁, T₂, S₁, ΔE[sub](ST), ΔE[sub](ST2) and ΔE[sub](T2T1) along with S₁, T₁ and T₂ excited state natures from DFT compared with SCS-CC2, with M06-2X and CAM-B3LYP performing well.
Chapter 6 presents an accurate method for computational modelling of MR-TADF, SCS-CC2. This method is then used to design two new MR-TADF emitters which were synthesized and their optoelectronic properties evaluated with OLEDs fabricated.
In Chapter 7 the calculated S₁, T₁ and ΔE[sub](ST) of 35 literature MR-TADF emitters from SCS-CC2 and TD(A)-DFT are compared with experimental values, with SCS-CC2 performing well. Using SCS-CC2 the properties of MR-TADF emitters are discussed and further studies of related INVEST materials and D-A emitters that contain a MR-TADF acceptors are undertaken.
Chapter 8 presents a new class of MR-TADF emitter without acceptor units designed using SCS-CC2. Modest TADF in doped films and high performing hyperfluorescent OLEDs are presented.
2022-06-15T00:00:00ZHall, David Luke StarkeyThis thesis concerns the study of organic TADF materials, focussing on donor-acceptor (D-A TADF) and multi-resonance (MR-TADF) emitters. Materials were developed in silico, they were then synthesized, characterized and finally tested in OLED devices.
Chapter 1 introduces the various radiative decay pathways available in electronically excited molecules from photoluminescence and electroluminescence. D-A TADF and MR-TADF emitters are discussed in detail.
Chapter 2 introduces the background behind the computational methods undertaken. These include Hartree Fock, coupled cluster and DFT.
Chapter 3 investigates the impact of donor dendrons in the TADF emitter 2CzPN. Donor extension improves kRISC but at the expense of increasing non-radiative pathways.
Chapter 4 discloses a new acceptor unit, BImPy, which is coupled to phenoxazine as a donor, with TADF observed. The torsion angle within the acceptor was modulated as a function of N-substitution, with 4 emitters studied.
In Chapter 5 a computational investigation of a series of 14 literature D-A TADF emitters is undertaken, with calculated T₁, T₂, S₁, ΔE[sub](ST), ΔE[sub](ST2) and ΔE[sub](T2T1) along with S₁, T₁ and T₂ excited state natures from DFT compared with SCS-CC2, with M06-2X and CAM-B3LYP performing well.
Chapter 6 presents an accurate method for computational modelling of MR-TADF, SCS-CC2. This method is then used to design two new MR-TADF emitters which were synthesized and their optoelectronic properties evaluated with OLEDs fabricated.
In Chapter 7 the calculated S₁, T₁ and ΔE[sub](ST) of 35 literature MR-TADF emitters from SCS-CC2 and TD(A)-DFT are compared with experimental values, with SCS-CC2 performing well. Using SCS-CC2 the properties of MR-TADF emitters are discussed and further studies of related INVEST materials and D-A emitters that contain a MR-TADF acceptors are undertaken.
Chapter 8 presents a new class of MR-TADF emitter without acceptor units designed using SCS-CC2. Modest TADF in doped films and high performing hyperfluorescent OLEDs are presented.Towards self-catalytic dynamic covalent nanoparticlesSuo, Rongtianhttps://hdl.handle.net/10023/251892023-06-21T15:59:47Z2022-06-15T00:00:00ZMonolayer-stabilised nanoparticles have found applications in various areas due to their unique properties. Manipulation of the monolayer bound to the nanoparticle surface can be used to control and functionalise nanoparticles. Developing post-synthetic strategies for functionalising nanoparticle-bound monolayers are essential for virtually all applications. However, traditional established methods each have drawbacks. The Kay group has applied dynamic covalent chemistry to modify nanoparticle-bound molecules, which overcomes many of the disadvantages of traditional methods.
The reactivity of dynamic covalent reactions of nanoparticle-bound molecules can be affected by both external and intra-monolayer environments. In this thesis, stimuli-responsiveness and intra-monolayer catalysis of dynamic covalent exchange on nanoparticle-bound monolayer have been investigated. To achieve this, nanoparticles stabilised with an acetal functionalized monolayer were firstly prepared. The nanoparticle-bound acetal can be converted to aldehyde readily, and the conversion can be tracked in situ with NMR spectroscopy, enabling kinetics analysis of this process. Moreover, partial conversions form nanoparticle-bound acetal to aldehyde have been realized by stopping the conversion when the composition is as expected, as indicated by NMR spectroscopy. The ability to make mixed monolayer of acetal/aldehyde provides possibility to install both catalytic and exchangeable units on nanoparticles at controllable ratios.
Previously, kinetics of dynamic covalent exchange of hydrazones on nanoparticle-bound monolayers has been investigated. In this thesis, Hydrazones were introduced as exchangeable units to nanoparticle-bound monolayers by reacting nanoparticle-bound acetal/aldehyde with hydrazides. The conversion form acetal to hydrazone in the monolayer, being trackable by NMR spectroscopy, can be stopped at certain intermediate states to make mixed monolayers of acetal/hydrazone, providing possibility to install catalytic units starting from reactions with acetals in the mixed monolayers.
Imines can also be introduced to nanoparticle-bound monolayers as exchangeable units. Imines are usually more labile compared to hydrazones, and thus can be employed to demonstrate the adaptive features of dynamic covalent nanoparticles. Mixed nanoparticle-bound monolayer consists of two imines were produced be reacting nanoparticle-bound aldehyde with two amines with different nucleophilicity. Changing pH of the reaction solution can induce the constitutional reorganization of the mixed monolayer of two imines, which can be characterized in real-time by NMR spectroscopy.
Catalytic units may be installed to the nanoparticle-bound monolayer as a permanent component by reductive amination. Conditions for realisation of nanoparticle-bound have been investigated. Alcohols may also be introduced as a component to promote dynamic covalent reactions on the same monolayer. Therefore, alcohols were introduced to the monolayer by direct synthesis and kinetics of acetal hydrolysis were investigated. These are some preliminary explorations regarding self-catalytic dynamic covalent nanoparticles, but provide methodologies for further investigations.
2022-06-15T00:00:00ZSuo, RongtianMonolayer-stabilised nanoparticles have found applications in various areas due to their unique properties. Manipulation of the monolayer bound to the nanoparticle surface can be used to control and functionalise nanoparticles. Developing post-synthetic strategies for functionalising nanoparticle-bound monolayers are essential for virtually all applications. However, traditional established methods each have drawbacks. The Kay group has applied dynamic covalent chemistry to modify nanoparticle-bound molecules, which overcomes many of the disadvantages of traditional methods.
The reactivity of dynamic covalent reactions of nanoparticle-bound molecules can be affected by both external and intra-monolayer environments. In this thesis, stimuli-responsiveness and intra-monolayer catalysis of dynamic covalent exchange on nanoparticle-bound monolayer have been investigated. To achieve this, nanoparticles stabilised with an acetal functionalized monolayer were firstly prepared. The nanoparticle-bound acetal can be converted to aldehyde readily, and the conversion can be tracked in situ with NMR spectroscopy, enabling kinetics analysis of this process. Moreover, partial conversions form nanoparticle-bound acetal to aldehyde have been realized by stopping the conversion when the composition is as expected, as indicated by NMR spectroscopy. The ability to make mixed monolayer of acetal/aldehyde provides possibility to install both catalytic and exchangeable units on nanoparticles at controllable ratios.
Previously, kinetics of dynamic covalent exchange of hydrazones on nanoparticle-bound monolayers has been investigated. In this thesis, Hydrazones were introduced as exchangeable units to nanoparticle-bound monolayers by reacting nanoparticle-bound acetal/aldehyde with hydrazides. The conversion form acetal to hydrazone in the monolayer, being trackable by NMR spectroscopy, can be stopped at certain intermediate states to make mixed monolayers of acetal/hydrazone, providing possibility to install catalytic units starting from reactions with acetals in the mixed monolayers.
Imines can also be introduced to nanoparticle-bound monolayers as exchangeable units. Imines are usually more labile compared to hydrazones, and thus can be employed to demonstrate the adaptive features of dynamic covalent nanoparticles. Mixed nanoparticle-bound monolayer consists of two imines were produced be reacting nanoparticle-bound aldehyde with two amines with different nucleophilicity. Changing pH of the reaction solution can induce the constitutional reorganization of the mixed monolayer of two imines, which can be characterized in real-time by NMR spectroscopy.
Catalytic units may be installed to the nanoparticle-bound monolayer as a permanent component by reductive amination. Conditions for realisation of nanoparticle-bound have been investigated. Alcohols may also be introduced as a component to promote dynamic covalent reactions on the same monolayer. Therefore, alcohols were introduced to the monolayer by direct synthesis and kinetics of acetal hydrolysis were investigated. These are some preliminary explorations regarding self-catalytic dynamic covalent nanoparticles, but provide methodologies for further investigations.Exploring azetidinium as the A-site in organic-inorganic hybrid perovskitesTian, Jiyuhttps://hdl.handle.net/10023/247332022-11-03T03:06:33Z2021-11-30T00:00:00ZOrganic inorganic hybrid perovskites (OIHPs) have appealing optoelectronic properties.
As sample preparation is relatively straightforward, there are opportunities to investigate
novel compositions and structures. This thesis concerns the synthesis, structure and
optoelectrical properties of OIHPs with azetidinium as an A-site cation.
Azetidinium [(CH₂)₃NH₂⁺, Az] is a four-member ring ammonium, and its size is
calculated to be promising as an A-cation for OIHPs. A stable 6H hexagonal perovskite
AzPbBr₃ was synthesised and analysed, and its bandgap was determined to be 2.81 eV.
On cooling, AzPbBr₃ undergoes a symmetry lowering distortion which was identified by
variable temperature PXRD and dielectric spectroscopy. An anisotropic change in lattice
parameters on cooling marked a phase transition likely driven by the Pb⋯Pb repulsion in
the face sharing octahedra.
Compositional and structural analyses were performed on precipitation synthesised and
mechanosynthesised OIHPs Az₁₋ₓFAₓPbBr₃ and Az₁₋ₓMAₓPbBr₃ (0 ≤ x ≤ 1). For samples
obtained from precipitation synthesis, the actual FA% or MA% in the precipitate was
found to be less than the nominal composition in the reaction solution. No such mismatch
was found for mechanosynthesised samples. PXRD indicated partial solid solution
formation for Az-rich and MA- or FA-rich compositions, separated by an intermediate
two-phase region. The result suggests the extent of the solid solution of halide perovskites
is dependent only on the average A-cation size; the size mismatch is less of an influence.
This is in contrast to solid solution formation observed in oxide perovskites.
A tuneable bandgap was achieved ranging from 2.00 eV (AzPbI₃) to 3.41 eV (AzPbCl₃)
for the mixed halide perovskite AzPbBr₃₋ₓXₓ (X = Cl or I, 0 ≤ x ≤ 3). The structural
analyses revealed a complete 6H solid solution for AzPbBr₃₋ₓClₓ in comparison to the
structural progression from 6H, 4H to 9R polytypes, when varying the halide composition
from Br (x = 0) to I (x = 3) in AzPbBr₃₋ₓIₓ. A linear variation in unit cell volume as a
function of anion average radius was observed not only within the solid solution of each
polytype (following Vegard’s law) but continuously across all three polytypes.
Preliminary results on the synthesis and structural analysis indicate that Az₂PbBr₄ adopts
the 𝘯 = 1 Ruddlesden-Popper structure while azetidinium bismuth bromide has a 1D chain
structure. Detailed structural and optical analysis are planned in future projects.
2021-11-30T00:00:00ZTian, JiyuOrganic inorganic hybrid perovskites (OIHPs) have appealing optoelectronic properties.
As sample preparation is relatively straightforward, there are opportunities to investigate
novel compositions and structures. This thesis concerns the synthesis, structure and
optoelectrical properties of OIHPs with azetidinium as an A-site cation.
Azetidinium [(CH₂)₃NH₂⁺, Az] is a four-member ring ammonium, and its size is
calculated to be promising as an A-cation for OIHPs. A stable 6H hexagonal perovskite
AzPbBr₃ was synthesised and analysed, and its bandgap was determined to be 2.81 eV.
On cooling, AzPbBr₃ undergoes a symmetry lowering distortion which was identified by
variable temperature PXRD and dielectric spectroscopy. An anisotropic change in lattice
parameters on cooling marked a phase transition likely driven by the Pb⋯Pb repulsion in
the face sharing octahedra.
Compositional and structural analyses were performed on precipitation synthesised and
mechanosynthesised OIHPs Az₁₋ₓFAₓPbBr₃ and Az₁₋ₓMAₓPbBr₃ (0 ≤ x ≤ 1). For samples
obtained from precipitation synthesis, the actual FA% or MA% in the precipitate was
found to be less than the nominal composition in the reaction solution. No such mismatch
was found for mechanosynthesised samples. PXRD indicated partial solid solution
formation for Az-rich and MA- or FA-rich compositions, separated by an intermediate
two-phase region. The result suggests the extent of the solid solution of halide perovskites
is dependent only on the average A-cation size; the size mismatch is less of an influence.
This is in contrast to solid solution formation observed in oxide perovskites.
A tuneable bandgap was achieved ranging from 2.00 eV (AzPbI₃) to 3.41 eV (AzPbCl₃)
for the mixed halide perovskite AzPbBr₃₋ₓXₓ (X = Cl or I, 0 ≤ x ≤ 3). The structural
analyses revealed a complete 6H solid solution for AzPbBr₃₋ₓClₓ in comparison to the
structural progression from 6H, 4H to 9R polytypes, when varying the halide composition
from Br (x = 0) to I (x = 3) in AzPbBr₃₋ₓIₓ. A linear variation in unit cell volume as a
function of anion average radius was observed not only within the solid solution of each
polytype (following Vegard’s law) but continuously across all three polytypes.
Preliminary results on the synthesis and structural analysis indicate that Az₂PbBr₄ adopts
the 𝘯 = 1 Ruddlesden-Popper structure while azetidinium bismuth bromide has a 1D chain
structure. Detailed structural and optical analysis are planned in future projects.Photoredox catalysts based on earth-abundant metal complexesLi, Chenfeihttps://hdl.handle.net/10023/247172022-01-20T15:40:39Z2020-07-29T00:00:00ZPhotoredox catalysis have been developed since at least 1968 when the term of photoredox was first used. During the past 50 years or so, the scope of reactions catalysed by a photocatalyst has experienced a rapid expansion. Photocatalysis is now employed to synthesize a huge amount of different types of organic compounds. At the same time, studies about the reaction mechanism have also become more and more detailed and comprehensive. This thesis discussed design, synthesis and photophysical properties of earth-abundant metal complexes. It also explores photoredox catalytic reactions using these earth-abundant metal complexes.
In Chapter 1, an overview of the development of photoredox catalysis is given followed by an overview of the basics
of photophysics of 1ˢᵗ row transition metal complexes. Moreover, the different types of photocatalytic reactions and
the corresponding reaction mechanism behind them were discussed. The importance of mechanistic studies for
photocatalytic reactions and the methodology used for mechanistic studies are also addressed in Chapter 1. In
particular, the optoelectronic properties of photoactive earth-abundant complexes and the photocatalysis using
photocatalysts based on Copper(I) complexes are reviewed at the end of the Chapter 1.
In Chapter 2, the photophysics and electrochemistry of six sulfur-bridged luminescent copper(I) complexes are
explored. This chapter discusses the influence of sulfur oxidation state and substituents effect on the optoelectronic
properties of these copper(I) complexes. Furthermore, these complexes were identified as showing thermally
activated delayed fluorescence (TADF) and these complexes showed potential as solid-state emitters.
In Chapter 3, the synthesis and the photophysics of two dinuclear copper(I) complexes bearing pyrimidylimidazole
bridging ligand are described. The tetrahedral coordination sphere of each copper centre is completed through the
use of a bulky bisphosphine ligand, either POP or Xantphos. Temperature-dependant photophysical studies
demonstrated emission through a combination of phosphorescence and TADF from both complexes, and an intense emission (Φ[sub](PL) = 46%) was observed for a crystalline sample of one of the complexes reported. The photophysics of
these two complexes is very sensitive to the environment. Two polymorphs of one of the dinuclear complex were
isolated, and their photophysics is distinct. Upon grinding, the higher emission energy crystal could be converted to
the lower energy crystal.
In Chapter 4, the optoelectronic properties of a family of six structurally related heteroleptic copper(I) complexes of
the form of [Cu(N^N)(P^P)]⁺ bearing a 2,9-dimethyl-1,10-phenanthroline diimine (N^N) ligand and a series of
electronically tunable Xantphos (P^P) ligands were characterized. The reactivity of these complexes in the copperphotocatalyzed
Aza-Henry
reaction
of
N-phenyltetrahydroisoquinoline
was
evaluated,
while
the
related
excited
state
kinetics
were comprehensively studied. A combined study of structural modulation of copper(I) photocatalysts,
optoelectronic properties and photocatalytic reactivity resulted in a better understanding of the rational design of a
photocatalyst targeting complicated photocatalytic reactions.
In Chapter 5, two room-temperature luminescent cobalt(III) complexes were found to be powerful photo-oxidants and
were used as inexpensive photoredox catalysts for the regioselective mono-(trifluoromethylation) of polycyclic
aromatic hydrocarbons (PAHs) in good yields (ca. 40–58%). The reaction mechanism was comprehensively studied,
and an origin of the chemoselectivity was proposed.
2020-07-29T00:00:00ZLi, ChenfeiPhotoredox catalysis have been developed since at least 1968 when the term of photoredox was first used. During the past 50 years or so, the scope of reactions catalysed by a photocatalyst has experienced a rapid expansion. Photocatalysis is now employed to synthesize a huge amount of different types of organic compounds. At the same time, studies about the reaction mechanism have also become more and more detailed and comprehensive. This thesis discussed design, synthesis and photophysical properties of earth-abundant metal complexes. It also explores photoredox catalytic reactions using these earth-abundant metal complexes.
In Chapter 1, an overview of the development of photoredox catalysis is given followed by an overview of the basics
of photophysics of 1ˢᵗ row transition metal complexes. Moreover, the different types of photocatalytic reactions and
the corresponding reaction mechanism behind them were discussed. The importance of mechanistic studies for
photocatalytic reactions and the methodology used for mechanistic studies are also addressed in Chapter 1. In
particular, the optoelectronic properties of photoactive earth-abundant complexes and the photocatalysis using
photocatalysts based on Copper(I) complexes are reviewed at the end of the Chapter 1.
In Chapter 2, the photophysics and electrochemistry of six sulfur-bridged luminescent copper(I) complexes are
explored. This chapter discusses the influence of sulfur oxidation state and substituents effect on the optoelectronic
properties of these copper(I) complexes. Furthermore, these complexes were identified as showing thermally
activated delayed fluorescence (TADF) and these complexes showed potential as solid-state emitters.
In Chapter 3, the synthesis and the photophysics of two dinuclear copper(I) complexes bearing pyrimidylimidazole
bridging ligand are described. The tetrahedral coordination sphere of each copper centre is completed through the
use of a bulky bisphosphine ligand, either POP or Xantphos. Temperature-dependant photophysical studies
demonstrated emission through a combination of phosphorescence and TADF from both complexes, and an intense emission (Φ[sub](PL) = 46%) was observed for a crystalline sample of one of the complexes reported. The photophysics of
these two complexes is very sensitive to the environment. Two polymorphs of one of the dinuclear complex were
isolated, and their photophysics is distinct. Upon grinding, the higher emission energy crystal could be converted to
the lower energy crystal.
In Chapter 4, the optoelectronic properties of a family of six structurally related heteroleptic copper(I) complexes of
the form of [Cu(N^N)(P^P)]⁺ bearing a 2,9-dimethyl-1,10-phenanthroline diimine (N^N) ligand and a series of
electronically tunable Xantphos (P^P) ligands were characterized. The reactivity of these complexes in the copperphotocatalyzed
Aza-Henry
reaction
of
N-phenyltetrahydroisoquinoline
was
evaluated,
while
the
related
excited
state
kinetics
were comprehensively studied. A combined study of structural modulation of copper(I) photocatalysts,
optoelectronic properties and photocatalytic reactivity resulted in a better understanding of the rational design of a
photocatalyst targeting complicated photocatalytic reactions.
In Chapter 5, two room-temperature luminescent cobalt(III) complexes were found to be powerful photo-oxidants and
were used as inexpensive photoredox catalysts for the regioselective mono-(trifluoromethylation) of polycyclic
aromatic hydrocarbons (PAHs) in good yields (ca. 40–58%). The reaction mechanism was comprehensively studied,
and an origin of the chemoselectivity was proposed.Design of novel inhibitors of trypanosomatid parasitesZhang, Yahanhttps://hdl.handle.net/10023/244332021-12-01T03:08:57Z2021-11-30T00:00:00ZNeglected tropical diseases (NTDs) are a group of infectious diseases that are endemic in tropical and subtropical regions. The associated infectious agents include protozoa, bacteria, viruses, and helminth parasites. In particular, Human African Trypanosomiasis, Chagas disease and Leishmaniasis are responsible for high mortality and morbidity rates in developing countries. However, the current treatments for trypanosomiasis and leishmaniasis have severe side effects and can be lethal. Most of these treatments are antiquated, resulting in emerging drug resistance, and are difficult to administer (mostly by injection). Therefore, there is an urgent demand to find safer, cheaper, and more efficient alternatives to the existing drugs. Natural products play an important part in drug discovery, with more than 50 % of modern drugs being directly or indirectly derived from them. In particular, the natural product chamuvarinin was found to have potent activity against trypanosomatid parasites. In this project, we synthesized a series of chamuvarinin based analogues, aiming to expand the library of trypanosomatid inhibitors, and further exploring the structure-activity relationship (SAR).
2021-11-30T00:00:00ZZhang, YahanNeglected tropical diseases (NTDs) are a group of infectious diseases that are endemic in tropical and subtropical regions. The associated infectious agents include protozoa, bacteria, viruses, and helminth parasites. In particular, Human African Trypanosomiasis, Chagas disease and Leishmaniasis are responsible for high mortality and morbidity rates in developing countries. However, the current treatments for trypanosomiasis and leishmaniasis have severe side effects and can be lethal. Most of these treatments are antiquated, resulting in emerging drug resistance, and are difficult to administer (mostly by injection). Therefore, there is an urgent demand to find safer, cheaper, and more efficient alternatives to the existing drugs. Natural products play an important part in drug discovery, with more than 50 % of modern drugs being directly or indirectly derived from them. In particular, the natural product chamuvarinin was found to have potent activity against trypanosomatid parasites. In this project, we synthesized a series of chamuvarinin based analogues, aiming to expand the library of trypanosomatid inhibitors, and further exploring the structure-activity relationship (SAR).The synthesis, structures and physical properties of fluoride and oxalate based magnetic coordination polymersLi, Tenghttps://hdl.handle.net/10023/243122023-11-07T03:06:58Z2020-06-30T00:00:00Z; This thesis describes the crystal structures and physical properties of three types of organic-inorganic hybrid coordination polymers (CPs): organic-inorganic hybrid fluoride layered perovskites, oxalate fluoride CPs and metal(III)-fluoride compounds. Most of the compounds presented here were synthesised through hydrothermal and solvothermal reactions, except two metal(III)-fluoride compounds which were synthesised by a layered solution method. For the organic-inorganic hybrid layered perovskites, seven compounds are reported. The crystal structures are revealed by single crystal X-ray diffraction. The magnetic properties of some have also been characterised by SQUID magnetometry, and the results show the metal centres in all the compounds display antiferromagnetic interactions at high temperature. For the compounds (enH₂)MnF₄ (1) and (enH₂)CoF₄ (2), variable temperature crystal structure analysis has been carried by the powder synchrotron X-ray diffraction and powder neutron diffraction. The results of Rietveld refinements show no phase transition was observed for both compounds. The magnetic structure of 2 has also been determined from the neutron data, in which the interactions of Co remain antiferromagnetic, with the magnetic moment (Mx0, My0, Mz0) = (3.53, 0, 0.53) at 20 K. In addition, the crystal structures of two derived compounds are also presented in this section. For the oxalate fluoride compounds, nine crystal structures are also characterised by single crystal X-ray diffraction. The compounds are in the form of 1D or 2D magnetic structures which are constructed by the metal centres and versatile coordination modes of the oxalate ligands. Magnetic characterisations show nearly all the compounds display antiferromagnetic interactions at high temperature, which are all well fitted by the 1D Heisenberg model. The majority of the seven metal(III)-fluoride compounds contain monomeric units. However, two unusual layered structures, which may form part of a homologous series, have been discovered, and there are some relationships between the syntheses and structures which can be applied in more targeted work in the future.
2020-06-30T00:00:00ZLi, TengThis thesis describes the crystal structures and physical properties of three types of organic-inorganic hybrid coordination polymers (CPs): organic-inorganic hybrid fluoride layered perovskites, oxalate fluoride CPs and metal(III)-fluoride compounds. Most of the compounds presented here were synthesised through hydrothermal and solvothermal reactions, except two metal(III)-fluoride compounds which were synthesised by a layered solution method. For the organic-inorganic hybrid layered perovskites, seven compounds are reported. The crystal structures are revealed by single crystal X-ray diffraction. The magnetic properties of some have also been characterised by SQUID magnetometry, and the results show the metal centres in all the compounds display antiferromagnetic interactions at high temperature. For the compounds (enH₂)MnF₄ (1) and (enH₂)CoF₄ (2), variable temperature crystal structure analysis has been carried by the powder synchrotron X-ray diffraction and powder neutron diffraction. The results of Rietveld refinements show no phase transition was observed for both compounds. The magnetic structure of 2 has also been determined from the neutron data, in which the interactions of Co remain antiferromagnetic, with the magnetic moment (Mx0, My0, Mz0) = (3.53, 0, 0.53) at 20 K. In addition, the crystal structures of two derived compounds are also presented in this section. For the oxalate fluoride compounds, nine crystal structures are also characterised by single crystal X-ray diffraction. The compounds are in the form of 1D or 2D magnetic structures which are constructed by the metal centres and versatile coordination modes of the oxalate ligands. Magnetic characterisations show nearly all the compounds display antiferromagnetic interactions at high temperature, which are all well fitted by the 1D Heisenberg model. The majority of the seven metal(III)-fluoride compounds contain monomeric units. However, two unusual layered structures, which may form part of a homologous series, have been discovered, and there are some relationships between the syntheses and structures which can be applied in more targeted work in the future.Novel metal-organic frameworks and polymer formulations for biomedical applicationsVornholt, Simon Maximilianhttps://hdl.handle.net/10023/235662021-09-06T11:43:49Z2021-06-30T00:00:00ZThe research presented in this thesis aimed to develop new metal-organic framework (MOF) materials and MOF composites for biomedical applications.
New synthesis methods of CPO-27-M (M = Co, Mg, Ni, Zn) were explored with particular focus on the formation of single crystals. Low temperature syntheses showed formation of crystalline CPO-27-Zn down to 195 K. Single crystals of CPO-27-Mg and -Zn were afforded from a modulated solvothermal synthesis using salicylic acid, and an isomorph called UTSA-74 was obtained when benzoic acid was used. All three materials proved suitable for structural analysis through in-house single crystal X-ray diffraction (SXRD). The concept of modulation chemistry was employed to control the crystallite size and a novel mixed-linker synthesis approach yielded large single crystals of CPO-27-Ni. All materials displayed phase pure through PXRD, compositional analysis, TGA, and electron microscopy methods.
Large single crystals of CPO-27-Ni were used in synchrotron based in situ gas cell experiments to probe the adsorption of nitric oxide (NO). An efficient activation protocol was developed leading to a dehydrated structure after just 4 h. For the first time, single crystal structure models of CPO-27-Ni were presented of the as-synthesised, dehydrated, and subsequently NO loaded conformation.
A multifaceted study of the interactions between CPO-27-Ni and polyurethane (PU) was conducted to rationalise the NO release performance of composite films used as proxy for antibacterial coatings. From a range of MOF loadings (5, 10, 20, and 40 wt%) an optimal MOF loading of 10 wt% was identified, where highest amounts of NO with a potent bactericidal efficacy are released. Molecular dynamics simulations and FIB-SEM techniques revealed an excellent compatibility and connectivity between the MOF/PU interface. Reconstruction of the microstructure of a high MOF loading composite (40 wt%) showed that the MOF exhibits a highly connected network, which was proposed to contribute to a more tortuous gas transport. This also may be the reason for reduced NO efficiencies and tensile strengths seen in high MOF loading composites (20−40 wt%).
The Kolbe-Schmitt reaction was utilised for the synthesis of new functional linkers. Two methylated 4,6-dihydroxyisophthalic acids were obtained and used to generate new MOF materials for storage and release of NO. The 2,3-dihydroxyterephthalic acid linker was used to synthesise a new MOF system that has properties of isoreticular chemistry and is systematically named SIMOF-0, 1, 2, and 3 (St Andrews Isoreticular MOF). All four phases were characterised through SXRD. SIMOF-3 displayed an interesting, pillared crystal structure with indication of flexibility. A drug loading study using flutamide showed a prolonged release of the drug over the course of 72 h and solid-state NMR indicated that the drug may be adsorbed in the pore system of the MOF. SIMOF-1 was used as a precursor for other materials. In a ‘regeneration’ synthesis approach, a sample of SIMOF-1 was transformed to phase pure SIMOF-3.
2021-06-30T00:00:00ZVornholt, Simon MaximilianThe research presented in this thesis aimed to develop new metal-organic framework (MOF) materials and MOF composites for biomedical applications.
New synthesis methods of CPO-27-M (M = Co, Mg, Ni, Zn) were explored with particular focus on the formation of single crystals. Low temperature syntheses showed formation of crystalline CPO-27-Zn down to 195 K. Single crystals of CPO-27-Mg and -Zn were afforded from a modulated solvothermal synthesis using salicylic acid, and an isomorph called UTSA-74 was obtained when benzoic acid was used. All three materials proved suitable for structural analysis through in-house single crystal X-ray diffraction (SXRD). The concept of modulation chemistry was employed to control the crystallite size and a novel mixed-linker synthesis approach yielded large single crystals of CPO-27-Ni. All materials displayed phase pure through PXRD, compositional analysis, TGA, and electron microscopy methods.
Large single crystals of CPO-27-Ni were used in synchrotron based in situ gas cell experiments to probe the adsorption of nitric oxide (NO). An efficient activation protocol was developed leading to a dehydrated structure after just 4 h. For the first time, single crystal structure models of CPO-27-Ni were presented of the as-synthesised, dehydrated, and subsequently NO loaded conformation.
A multifaceted study of the interactions between CPO-27-Ni and polyurethane (PU) was conducted to rationalise the NO release performance of composite films used as proxy for antibacterial coatings. From a range of MOF loadings (5, 10, 20, and 40 wt%) an optimal MOF loading of 10 wt% was identified, where highest amounts of NO with a potent bactericidal efficacy are released. Molecular dynamics simulations and FIB-SEM techniques revealed an excellent compatibility and connectivity between the MOF/PU interface. Reconstruction of the microstructure of a high MOF loading composite (40 wt%) showed that the MOF exhibits a highly connected network, which was proposed to contribute to a more tortuous gas transport. This also may be the reason for reduced NO efficiencies and tensile strengths seen in high MOF loading composites (20−40 wt%).
The Kolbe-Schmitt reaction was utilised for the synthesis of new functional linkers. Two methylated 4,6-dihydroxyisophthalic acids were obtained and used to generate new MOF materials for storage and release of NO. The 2,3-dihydroxyterephthalic acid linker was used to synthesise a new MOF system that has properties of isoreticular chemistry and is systematically named SIMOF-0, 1, 2, and 3 (St Andrews Isoreticular MOF). All four phases were characterised through SXRD. SIMOF-3 displayed an interesting, pillared crystal structure with indication of flexibility. A drug loading study using flutamide showed a prolonged release of the drug over the course of 72 h and solid-state NMR indicated that the drug may be adsorbed in the pore system of the MOF. SIMOF-1 was used as a precursor for other materials. In a ‘regeneration’ synthesis approach, a sample of SIMOF-1 was transformed to phase pure SIMOF-3.Design and synthesis of novel synthetic and natural product inspired trypanosomatid inhibitorsFreire de Araujo Gouy, Rodrigo Pierrehttps://hdl.handle.net/10023/235332021-07-21T15:03:42Z2021-06-30T00:00:00ZChapter 1 – Introduction of neglected tropical diseases, their impact in our society, treatments,
and current challenges. We further explore how a limited understanding of these diseases
impedes their treatments. Identification of novel compounds and targets as well as
repurposing of previously developed promising drug candidates, may lead to improvement of
current treatments methods.
Chapter 2 – Nitro heteroaromatic compounds have demonstrated their potential through their
recurrent use as antiparasitic treatments. The novel series of nitro containing heteroaromatics
moieties presented in this work were designed to further explore their antiparasitic potential
and improve the series for the use in target identification studies.
Chapter 3 – Fumagillin, a natural product isolated from Aspergillus fumigatus, has recently
been found to be a promising antiparasitic drug candidate. Its target in mammalian cell lines
has been found to be the enzyme MetAP2, however its target in trypanosomatids parasite is
yet to be confirmed. In this chapter, we discuss the development of a new series of fumagillin
analogues with increased antiparasitic potential. The determined SAR is further applied in the
synthesis of probes for imaging and photo-affinity labelling suitable for target identification.
Chapter 4 – Summary of the synthesised compounds for both series and biological data
obtained throughout this work, and discussion of further work on both series towards novel
analogues with antiparasitic potential.
2021-06-30T00:00:00ZFreire de Araujo Gouy, Rodrigo PierreChapter 1 – Introduction of neglected tropical diseases, their impact in our society, treatments,
and current challenges. We further explore how a limited understanding of these diseases
impedes their treatments. Identification of novel compounds and targets as well as
repurposing of previously developed promising drug candidates, may lead to improvement of
current treatments methods.
Chapter 2 – Nitro heteroaromatic compounds have demonstrated their potential through their
recurrent use as antiparasitic treatments. The novel series of nitro containing heteroaromatics
moieties presented in this work were designed to further explore their antiparasitic potential
and improve the series for the use in target identification studies.
Chapter 3 – Fumagillin, a natural product isolated from Aspergillus fumigatus, has recently
been found to be a promising antiparasitic drug candidate. Its target in mammalian cell lines
has been found to be the enzyme MetAP2, however its target in trypanosomatids parasite is
yet to be confirmed. In this chapter, we discuss the development of a new series of fumagillin
analogues with increased antiparasitic potential. The determined SAR is further applied in the
synthesis of probes for imaging and photo-affinity labelling suitable for target identification.
Chapter 4 – Summary of the synthesised compounds for both series and biological data
obtained throughout this work, and discussion of further work on both series towards novel
analogues with antiparasitic potential.Exploring NMR parameters of paramagnetic Cu complexes using density functional theoryKe, Zhipenghttps://hdl.handle.net/10023/235072021-07-20T14:34:05Z2021-06-30T00:00:00ZIn this thesis, Density Functional Theory (DFT) methods have been validated to compute Nuclear Magnetic Resonance (NMR) chemical shifts for paramagnetic materials to complement solid-state NMR experiments carried out in the Ashbrook group. The materials studied include Cu phenolic oximes (which contain one paramagnetic centre), urea loaded Cu benzoate (containing two paramagnetic centres), and Metal-Organic Frameworks (MOFs) from the HKUST-1 and STAM families loaded with a variety of guest molecules (which have multiple paramagnetic centres). For Cu phenolic oximes, a combination of experiment and computation has revealed significant substituent effects on the ¹³C and ¹H chemical shifts. For urea loaded Cu benzoate, the observed δ (¹³C) values are reproduced reasonably well at the PBE0-⅓/II//PBE0-D3/AE1 level assuming a Boltzmann distribution between a diamagnetic open-shell singlet ground state (in a broken-symmetry Kohn-Sham DFT description) and an excited triplet state. Using the proposed assignments of the signals, the mean absolute deviation between the computed and observed ¹³C chemical shifts is below 30 ppm over a range of more than 1100 ppm. For HKUST-1 loaded with a variety of guests, a trimmed dimer (where three benzoate moieties of the dimer have been replaced with three acetate moieties) is shown to reproduce ¹³C chemical shifts for the carboxylate and benzoic carbons in the MOFs reasonably well at low computational cost. This reasonable accuracy can only be achieved after empirical scaling of the singlet-triplet energy gap (by factors close to 2). Molecular models with increasing numbers of dimer units (two or three joined by benzene linkers) have been validated against experimental ¹³C pNMR shifts for activated and hydrated MOFs in HKUST-1, STAM-1 and STAM-17. Using an appropriate selection of electronic states, calculations with lower scaling factors of the energy gaps between the spin states can fully reproduce the unusual temperature dependence of ¹³C shifts and substituent effects on these shifts in the STAM MOFs at the CAM-B3LYP/II//GFN2-xTB level.
2021-06-30T00:00:00ZKe, ZhipengIn this thesis, Density Functional Theory (DFT) methods have been validated to compute Nuclear Magnetic Resonance (NMR) chemical shifts for paramagnetic materials to complement solid-state NMR experiments carried out in the Ashbrook group. The materials studied include Cu phenolic oximes (which contain one paramagnetic centre), urea loaded Cu benzoate (containing two paramagnetic centres), and Metal-Organic Frameworks (MOFs) from the HKUST-1 and STAM families loaded with a variety of guest molecules (which have multiple paramagnetic centres). For Cu phenolic oximes, a combination of experiment and computation has revealed significant substituent effects on the ¹³C and ¹H chemical shifts. For urea loaded Cu benzoate, the observed δ (¹³C) values are reproduced reasonably well at the PBE0-⅓/II//PBE0-D3/AE1 level assuming a Boltzmann distribution between a diamagnetic open-shell singlet ground state (in a broken-symmetry Kohn-Sham DFT description) and an excited triplet state. Using the proposed assignments of the signals, the mean absolute deviation between the computed and observed ¹³C chemical shifts is below 30 ppm over a range of more than 1100 ppm. For HKUST-1 loaded with a variety of guests, a trimmed dimer (where three benzoate moieties of the dimer have been replaced with three acetate moieties) is shown to reproduce ¹³C chemical shifts for the carboxylate and benzoic carbons in the MOFs reasonably well at low computational cost. This reasonable accuracy can only be achieved after empirical scaling of the singlet-triplet energy gap (by factors close to 2). Molecular models with increasing numbers of dimer units (two or three joined by benzene linkers) have been validated against experimental ¹³C pNMR shifts for activated and hydrated MOFs in HKUST-1, STAM-1 and STAM-17. Using an appropriate selection of electronic states, calculations with lower scaling factors of the energy gaps between the spin states can fully reproduce the unusual temperature dependence of ¹³C shifts and substituent effects on these shifts in the STAM MOFs at the CAM-B3LYP/II//GFN2-xTB level.Development of cascade cross-coupling / Diels–Alder approaches for complex molecule synthesisCain, Davidhttps://hdl.handle.net/10023/232272023-05-06T02:06:29Z2021-06-30T00:00:00ZThe Diels–Alder (DA) reaction is an important and frequently used synthetic transformation in the formation of both complex building blocks and natural products. Significant attention has being invested in its utilisation within cascade events, primarily due to its ability to form six-membered rings with numerous contiguous stereocenters in a selective manner. Its combination with cross-coupling reactions has become an evolving field in accessing novel chemical space, by circumventing the need for handling potentially reactive diene intermediates. This thesis will begin with a discussion surrounding the multiple terminologies defining multi-step reactions, and provide examples focussing in the area involving cross-coupling/Diels-Alder reactions (CCDA).
The first chapter highlights the development of a cascade Suzuki–Miyaura/Diels–Alder (SM/DA) protocol, involving vinyl Bpin, a bi-functional entity (as nucleophile in the SM, and the dienophile in DA), in facilitating the overall transformation. A discussion involving its optimization is disclosed, alongside the challenges that were encountered and how these were overcome. The optimised conditions were applied to generate a range of borylated carbocylic products of varying complexity (17 examples). In this work the effect of the organoboron subtype on Diels-Alder regioselectivity was investigated and post-synthetic modifications were carried out on a model substrate. Lastly, the potential for a complementary Heck/Diels-Alder process was also assessed.
Having developed the SM/DA methodology, its application was envisaged as a key step in the divergent synthesis of Aspidosperma alkaloids in the second chapter. Despite these alkaloids being synthesized numerous times, due to their challenging structural topology and beneficial biological properties, there is a lack in Structure activity relationship (SAR) studies. The SM/DA protocol allows the rapid and efficient creation of an advanced skeletal framework in a single reaction, which can then be subjected to a series of simple chemical manipulations to furnish a common intermediate from which a natural product library can be generated. The optimization of pertinent steps in the synthesis are disclosed, along with interesting observations that were encountered.
2021-06-30T00:00:00ZCain, DavidThe Diels–Alder (DA) reaction is an important and frequently used synthetic transformation in the formation of both complex building blocks and natural products. Significant attention has being invested in its utilisation within cascade events, primarily due to its ability to form six-membered rings with numerous contiguous stereocenters in a selective manner. Its combination with cross-coupling reactions has become an evolving field in accessing novel chemical space, by circumventing the need for handling potentially reactive diene intermediates. This thesis will begin with a discussion surrounding the multiple terminologies defining multi-step reactions, and provide examples focussing in the area involving cross-coupling/Diels-Alder reactions (CCDA).
The first chapter highlights the development of a cascade Suzuki–Miyaura/Diels–Alder (SM/DA) protocol, involving vinyl Bpin, a bi-functional entity (as nucleophile in the SM, and the dienophile in DA), in facilitating the overall transformation. A discussion involving its optimization is disclosed, alongside the challenges that were encountered and how these were overcome. The optimised conditions were applied to generate a range of borylated carbocylic products of varying complexity (17 examples). In this work the effect of the organoboron subtype on Diels-Alder regioselectivity was investigated and post-synthetic modifications were carried out on a model substrate. Lastly, the potential for a complementary Heck/Diels-Alder process was also assessed.
Having developed the SM/DA methodology, its application was envisaged as a key step in the divergent synthesis of Aspidosperma alkaloids in the second chapter. Despite these alkaloids being synthesized numerous times, due to their challenging structural topology and beneficial biological properties, there is a lack in Structure activity relationship (SAR) studies. The SM/DA protocol allows the rapid and efficient creation of an advanced skeletal framework in a single reaction, which can then be subjected to a series of simple chemical manipulations to furnish a common intermediate from which a natural product library can be generated. The optimization of pertinent steps in the synthesis are disclosed, along with interesting observations that were encountered.New mixed anion frameworksLethbridge, Zoe A. D.https://hdl.handle.net/10023/229812021-06-11T09:42:18Z2002-01-01T00:00:00Z2002-01-01T00:00:00ZLethbridge, Zoe A. D.1, 2, 4 - triazines and 1, 2, 4, 5 - tetrazines as monomers for Diels-Alder polymerisationsBruce, Michael Johnhttps://hdl.handle.net/10023/225712021-10-05T11:40:16Z1995-01-01T00:00:00ZChapter 1 (Introduction) comprises a brief overview of the origins,
mechanism and scope of the Diels-Alder reaction. It deals with the three different Diels Alder reaction types and highlights the utilisation of the reaction in general terms for the
synthesis of aromatic and heteroaromatic ring systems. Particular attention has been
paid to the inverse electron-demand Diels-Alder reactions of nitrogen-containing
heterocycles, where aromatisation is brought about by the thermodynamically-driven
loss of molecular nitrogen, leading to both carbocyclic and heterocyclic ring systems.
Chapter 2 (Results and Discussion) develops the ideas formed in Chapter
1 to seek possible bis-dienes and bis-dienophiles for utilisation in polymer synthesis.
Attention has been concentrated on possible routes to bis-l,2,4-triazines and 1,2,4,5-
tetrazines, which are novel compounds, and on their possible use in both inter- and
intra-molecular Diels-Alder reactions.
A new method for the synthesis of bis-glyoxals involving the oxidation of the
corresponding diacetyl-aromatics using HBr/DMSO is the most reliable and is capable
of being scaled up without safety/environmental problems. The bis-glyoxals are then
readily convertible into 5,5'-linked bis-l,2,4-triazines which are potential bis-dienes for
Diels-Alder reactions. The attempted intermolecular reactions of the bis-triazines with a
range of diethynyl-aromatics have, however, proved unsuccessful so far. Attempts to
form bis-(o-ethynylphenols) for intramolecular Diels-Alder reactions after coupling to
bis-triazines have also been unsuccessful.
Several 5-(substituted phenyl)-1,2,4-triazines have also been formed, with the
intention of coupling these through the phenyl substituent to a central difunctional core.
Several 1,2,4,5-tetrazines have been formed with similar intent.
Chapter 3 (Experimental) details the synthetic procedures and the
Bibliography follows.
1995-01-01T00:00:00ZBruce, Michael JohnChapter 1 (Introduction) comprises a brief overview of the origins,
mechanism and scope of the Diels-Alder reaction. It deals with the three different Diels Alder reaction types and highlights the utilisation of the reaction in general terms for the
synthesis of aromatic and heteroaromatic ring systems. Particular attention has been
paid to the inverse electron-demand Diels-Alder reactions of nitrogen-containing
heterocycles, where aromatisation is brought about by the thermodynamically-driven
loss of molecular nitrogen, leading to both carbocyclic and heterocyclic ring systems.
Chapter 2 (Results and Discussion) develops the ideas formed in Chapter
1 to seek possible bis-dienes and bis-dienophiles for utilisation in polymer synthesis.
Attention has been concentrated on possible routes to bis-l,2,4-triazines and 1,2,4,5-
tetrazines, which are novel compounds, and on their possible use in both inter- and
intra-molecular Diels-Alder reactions.
A new method for the synthesis of bis-glyoxals involving the oxidation of the
corresponding diacetyl-aromatics using HBr/DMSO is the most reliable and is capable
of being scaled up without safety/environmental problems. The bis-glyoxals are then
readily convertible into 5,5'-linked bis-l,2,4-triazines which are potential bis-dienes for
Diels-Alder reactions. The attempted intermolecular reactions of the bis-triazines with a
range of diethynyl-aromatics have, however, proved unsuccessful so far. Attempts to
form bis-(o-ethynylphenols) for intramolecular Diels-Alder reactions after coupling to
bis-triazines have also been unsuccessful.
Several 5-(substituted phenyl)-1,2,4-triazines have also been formed, with the
intention of coupling these through the phenyl substituent to a central difunctional core.
Several 1,2,4,5-tetrazines have been formed with similar intent.
Chapter 3 (Experimental) details the synthetic procedures and the
Bibliography follows.The carbonylation of ammonia to ureaButler, David Charles Donnellhttps://hdl.handle.net/10023/220342022-04-15T10:34:33Z1997-01-01T00:00:00ZPresent industrial production of urea involves high temperature/ high pressure conversion of NH₃ and CO₂ via carbamate. There would be economic interest in a low-cost method for the manufacture of urea. One possible way of achieving this is by conversion of NH₃ and CO to urea with elimination of H₂, or H₂O. Although the thermodynamics of such a process are favourable, the reaction does not occur in the absence of catalyst due to the high energy barrier of activation. From what is already known about species which can lower this energy barrier, a mechanistic strategy has been devised to screen complexes which are active for the Water Gas Shift Reaction (WGSR) under basic conditions.
[M(CO)₆] (M = Cr, W), [Fe(CO)₅], K[Ru(HEDTA)Cl].2H₂O and [RhH(PR₃)₃] (R = PEt, PᶦPr) are known WGSR catalysts which do not catalyse the carbonylation of NH₃ to urea under conditions for which they are active for the WGSR, however, [Ru₃(CO)₁₂] is active for this reaction with methanol or ethanol as solvent. Conditions for optimum activity are T = 160°C CO charging pressure = 2-10 bar and [NH₃] = ca. 7 mol dm^-3. ¹H NMR, IR and electrospray mass spectroscopy were employed for carbonyl cluster identification, and species found to be present after catalysis include [HRu₃(CO)₁₁]⁻, [H₃ Ru₄(CO)₁₂]⁻, [H₂RU₄(CO)₁₂]²⁻, [Ru6C(CO)₁6]²⁻, [Ru6(CO)₁₈]²⁻, [Ru₄(CO)₁3]2 , [H₂Ru₃(NH)(CO)₉], [H₃ Ru₄(NH₂)(CO)₁₂], and some unidentified Ru₇ and Ru₈ monoanionic cluster species. [HRu₃(CO)₁₁]⁻ appears to be the most abundant species present in solution, both before, during (identified by high pressure IR spectroscopy), and after catalysis. Additionally, [HRu₃(CO)₁₁][NEt₄] catalyses the reaction as a starting material and so is thought to be the catalytic intermediate in the reaction with [Ru₃(CO)₁₂] as precursor.
The period of catalytic activity is short. Possible reasons for this include incorporation of NH₃ into formamide (effectively reducing [NH₃]), and the formation of a non-catalytic species, possibly a dianion such as [Ru₃(CO)n]²⁻, [Ru6C(CO)16]²⁻, or [H₂Ru₄(CO)₁₂]²⁻. V [RhHCl₂(PᶦPr₃)²] reacts with sodium amalgam in THF solution with trace H₂0 to form [RhH₂Cl(PᶦPr₃)²], which we have isolated. The crystal structure of a new polymorph of this complex is described. [RhH₂Cl(PᶦPr₃)²] can be used as an alternative route to make [RhH(PᶦPr₃)³], by the reaction with strong base in excess PᶦPr₃. [RhCl3.xH₂0] reacts with excess PᶦPr₃ in THF and in the presence of H₂0 under reflux to give [RhHCl3(PᶦPr₃)²][H PᶦPr₃], the crystal structure of which is described. In solution, at room temperature, it dissociates to [RhHCl₂(PᶦPr₃)²] and [CLH PᶦPr₃], and, on cooling, [RhHCl3(PᶦPr₃)²][H PᶦPr₃] can be observed in the 31P and low-field 'H NMR spectra. [RhH(PᶦPr₃)³] and [RhH₂Cl(PᶦPr₃)²] both react with NH₃ in THF solution to yield an unknown adduct thought to be [RhH₂(NH₂)(PᶦPr₃)²], Reaction with NH₃ is unprecedented for any complex of Rh and has possible mechanistic significance in the carbonylation of NH₃ to urea.
1997-01-01T00:00:00ZButler, David Charles DonnellPresent industrial production of urea involves high temperature/ high pressure conversion of NH₃ and CO₂ via carbamate. There would be economic interest in a low-cost method for the manufacture of urea. One possible way of achieving this is by conversion of NH₃ and CO to urea with elimination of H₂, or H₂O. Although the thermodynamics of such a process are favourable, the reaction does not occur in the absence of catalyst due to the high energy barrier of activation. From what is already known about species which can lower this energy barrier, a mechanistic strategy has been devised to screen complexes which are active for the Water Gas Shift Reaction (WGSR) under basic conditions.
[M(CO)₆] (M = Cr, W), [Fe(CO)₅], K[Ru(HEDTA)Cl].2H₂O and [RhH(PR₃)₃] (R = PEt, PᶦPr) are known WGSR catalysts which do not catalyse the carbonylation of NH₃ to urea under conditions for which they are active for the WGSR, however, [Ru₃(CO)₁₂] is active for this reaction with methanol or ethanol as solvent. Conditions for optimum activity are T = 160°C CO charging pressure = 2-10 bar and [NH₃] = ca. 7 mol dm^-3. ¹H NMR, IR and electrospray mass spectroscopy were employed for carbonyl cluster identification, and species found to be present after catalysis include [HRu₃(CO)₁₁]⁻, [H₃ Ru₄(CO)₁₂]⁻, [H₂RU₄(CO)₁₂]²⁻, [Ru6C(CO)₁6]²⁻, [Ru6(CO)₁₈]²⁻, [Ru₄(CO)₁3]2 , [H₂Ru₃(NH)(CO)₉], [H₃ Ru₄(NH₂)(CO)₁₂], and some unidentified Ru₇ and Ru₈ monoanionic cluster species. [HRu₃(CO)₁₁]⁻ appears to be the most abundant species present in solution, both before, during (identified by high pressure IR spectroscopy), and after catalysis. Additionally, [HRu₃(CO)₁₁][NEt₄] catalyses the reaction as a starting material and so is thought to be the catalytic intermediate in the reaction with [Ru₃(CO)₁₂] as precursor.
The period of catalytic activity is short. Possible reasons for this include incorporation of NH₃ into formamide (effectively reducing [NH₃]), and the formation of a non-catalytic species, possibly a dianion such as [Ru₃(CO)n]²⁻, [Ru6C(CO)16]²⁻, or [H₂Ru₄(CO)₁₂]²⁻. V [RhHCl₂(PᶦPr₃)²] reacts with sodium amalgam in THF solution with trace H₂0 to form [RhH₂Cl(PᶦPr₃)²], which we have isolated. The crystal structure of a new polymorph of this complex is described. [RhH₂Cl(PᶦPr₃)²] can be used as an alternative route to make [RhH(PᶦPr₃)³], by the reaction with strong base in excess PᶦPr₃. [RhCl3.xH₂0] reacts with excess PᶦPr₃ in THF and in the presence of H₂0 under reflux to give [RhHCl3(PᶦPr₃)²][H PᶦPr₃], the crystal structure of which is described. In solution, at room temperature, it dissociates to [RhHCl₂(PᶦPr₃)²] and [CLH PᶦPr₃], and, on cooling, [RhHCl3(PᶦPr₃)²][H PᶦPr₃] can be observed in the 31P and low-field 'H NMR spectra. [RhH(PᶦPr₃)³] and [RhH₂Cl(PᶦPr₃)²] both react with NH₃ in THF solution to yield an unknown adduct thought to be [RhH₂(NH₂)(PᶦPr₃)²], Reaction with NH₃ is unprecedented for any complex of Rh and has possible mechanistic significance in the carbonylation of NH₃ to urea.A study of reactions of tertiary phosphines with halogensBeaumont, David Michaelhttps://hdl.handle.net/10023/220302022-04-14T09:08:39Z1974-01-01T00:00:00Z1974-01-01T00:00:00ZBeaumont, David MichaelA combinatorial approach to glycotherapeutics : template synthesisGibson, Darrenhttps://hdl.handle.net/10023/220262022-04-13T16:00:03Z2001-01-01T00:00:00ZIn this thesis, general synthetic methods applicable to the development of carbohydrate mimetics were achieved. With such methodology in hand we turned to the development of inhibitor libraries for: a) Trypanosoma cruzi trans-sialidase, an essential enzyme involved in the onset of South American Chagas' disease. Octyl galactoside is recognised by the enzyme so chemical modifications of this structure would be possible. The synthesis of octyl 6- azido-6-deoxy galactoside has been achieved by using two different chemical methods.
b) E. coli 0157 (verotoxin) is a food poisoning toxin (Wishaw, central Scotland). The minimum active component for interaction of sugar and toxin is galabiose [αGal-(1-4)- βGal-(l-4)-OMe] In this thesis, the synthesis of galabiose and various galabiose template mimics are described. Modification of the galabiose structure at the 2 position (methoxycarbonylmethyl) and at the 6 position (amine) or both was successfully achieved. These structures are ready to be incorporated onto a solid-support or a dendrimer base for further evaluation. A small array of 6-amino functionalised galabiose compounds has been successfully achieved.
2001-01-01T00:00:00ZGibson, DarrenIn this thesis, general synthetic methods applicable to the development of carbohydrate mimetics were achieved. With such methodology in hand we turned to the development of inhibitor libraries for: a) Trypanosoma cruzi trans-sialidase, an essential enzyme involved in the onset of South American Chagas' disease. Octyl galactoside is recognised by the enzyme so chemical modifications of this structure would be possible. The synthesis of octyl 6- azido-6-deoxy galactoside has been achieved by using two different chemical methods.
b) E. coli 0157 (verotoxin) is a food poisoning toxin (Wishaw, central Scotland). The minimum active component for interaction of sugar and toxin is galabiose [αGal-(1-4)- βGal-(l-4)-OMe] In this thesis, the synthesis of galabiose and various galabiose template mimics are described. Modification of the galabiose structure at the 2 position (methoxycarbonylmethyl) and at the 6 position (amine) or both was successfully achieved. These structures are ready to be incorporated onto a solid-support or a dendrimer base for further evaluation. A small array of 6-amino functionalised galabiose compounds has been successfully achieved.The oxidation of chiral 2-thiazolines and thiazolidine-2-thionesArmstrong, David Philiphttps://hdl.handle.net/10023/220282022-05-10T10:02:13Z1991-01-01T00:00:00ZChiral 2-thiazolines with a variety of substituents at the 2- and 4-positions have been prepared starting from readily available enantiomerically pure aminoalcohols via intermediate 2-oxazolines or N-acylamino alcohols. The behaviour of these 2-thiazolines towards oxidation has been investigated in detail. Stable 2-thiazoline N-oxides, a previously unknown class of compounds, are formed with two oxidising agents: peroxytrifluoroacetic acid and dinitrogen tetroxide. A large number of other oxidising agents give mixtures of some or all of 2-thiazoline S,S-dioxides, aromatised thiazoles and both N-acylaminodisulphides and sulphonic acids apparently derived from initial hydrolytic ring-opening to the N-acylaminothiols followed by further oxidation. Conditions have not yet been developed to obtain the desired S,S-dioxides in pure form.
Potential applications of the 2-thiazoline N-oxides in asymmetric synthesis have been investigated. The compounds surprisingly do not undergo 1,3-dipolar cycloaddition with a wide variety of dipolarophiles. They do however transfer oxygen both to neutral acceptors such as styrene and to organolithium species such as LDA and phenyllithium. Other anions have given disappointing results but the use of the N-oxides as a chiral OH⁺ source merits further investigation.
A number of chiral thiazolidine-2-thiones have also been prepared from chiral aminoalcohols. Conditions have been developed for the efficient direct oxidation of these to the corresponding thiazolidin-2-one S,S-dioxides. A preliminary study of the thermal decomposition of one example showed this to proceed by a concerted fragmentation to give SO₂, an alkene and an isocyanate. This may be due in part to the bulky groups present at positions 3 and 4, and the prospects for elimination of only SO₂ to give β-lactams in cases with less bulky or interconnected groups look bright.
1991-01-01T00:00:00ZArmstrong, David PhilipChiral 2-thiazolines with a variety of substituents at the 2- and 4-positions have been prepared starting from readily available enantiomerically pure aminoalcohols via intermediate 2-oxazolines or N-acylamino alcohols. The behaviour of these 2-thiazolines towards oxidation has been investigated in detail. Stable 2-thiazoline N-oxides, a previously unknown class of compounds, are formed with two oxidising agents: peroxytrifluoroacetic acid and dinitrogen tetroxide. A large number of other oxidising agents give mixtures of some or all of 2-thiazoline S,S-dioxides, aromatised thiazoles and both N-acylaminodisulphides and sulphonic acids apparently derived from initial hydrolytic ring-opening to the N-acylaminothiols followed by further oxidation. Conditions have not yet been developed to obtain the desired S,S-dioxides in pure form.
Potential applications of the 2-thiazoline N-oxides in asymmetric synthesis have been investigated. The compounds surprisingly do not undergo 1,3-dipolar cycloaddition with a wide variety of dipolarophiles. They do however transfer oxygen both to neutral acceptors such as styrene and to organolithium species such as LDA and phenyllithium. Other anions have given disappointing results but the use of the N-oxides as a chiral OH⁺ source merits further investigation.
A number of chiral thiazolidine-2-thiones have also been prepared from chiral aminoalcohols. Conditions have been developed for the efficient direct oxidation of these to the corresponding thiazolidin-2-one S,S-dioxides. A preliminary study of the thermal decomposition of one example showed this to proceed by a concerted fragmentation to give SO₂, an alkene and an isocyanate. This may be due in part to the bulky groups present at positions 3 and 4, and the prospects for elimination of only SO₂ to give β-lactams in cases with less bulky or interconnected groups look bright.Rhodium catalysed hydroformylation of allyl alcohol with diphosphine ligandsWhite, Daniel Ferrier Sinclairhttps://hdl.handle.net/10023/220242022-04-13T14:25:39Z2001-01-01T00:00:00Z2001-01-01T00:00:00ZWhite, Daniel Ferrier SinclairBehaviour of small biomolecules on the Cu(110) surfaceFrankel, Danielhttps://hdl.handle.net/10023/220202022-04-12T08:36:37Z2002-01-01T00:00:00Z2002-01-01T00:00:00ZFrankel, DanielSynthetic studies on the small molecule tool (S)-(-)-blebbistatinLucas-Lopez, Cristinahttps://hdl.handle.net/10023/220182022-04-11T15:46:04Z2005-01-01T00:00:00ZSmall molecules that can perturb the function of a specific target protein are useful tools in basic cell biology research. Important areas in biology, such as cytokinesis (the last step in cell division), have not been extensively explored due to the lack of suitable small molecule tools that target their relevant proteins. Non-muscle myosin II has been identified as a protein component necessary for cell division. A recent programme focused on identifying novel inhibitors of non-muscle myosin II has been developed at Harvard University and screening of a commercially available compound library led to the discovery of the novel small molecule inhibitor, (-)-blebbistatin. This thesis describes an efficient and flexible synthetic approach to highly optically enriched (-)-blebbistatin. The bioactive compound is synthesised from 2-amino-5-methylbenzoic acid in a four step procedure. The key step is the asymmetric hydroxylation of a quinolone intermediate using the Davis oxaziridine methodology. For the first time, we have proved that the absolute stereochemistry of (-)-blebbistatin is S by X-ray analysis of a heavy atom containing analogue of blebbistatin. Subsequent studies on the core structure of blebbistatin show that it is possible through chemical modification to prepare analogues. Further biological testing of these compounds show which parts of (S)-(-)-blebbistatin are important to retain its inhibitory activity. In addition, it is shown that the incorporation of a nitro functional group into the blebbistatin core structure modifies its fluorescence properties. This is of importance since this analogue can therefore be used in fluorescence-based microscope imaging experiments on live cells where (-)-blebbistatin cannot.
2005-01-01T00:00:00ZLucas-Lopez, CristinaSmall molecules that can perturb the function of a specific target protein are useful tools in basic cell biology research. Important areas in biology, such as cytokinesis (the last step in cell division), have not been extensively explored due to the lack of suitable small molecule tools that target their relevant proteins. Non-muscle myosin II has been identified as a protein component necessary for cell division. A recent programme focused on identifying novel inhibitors of non-muscle myosin II has been developed at Harvard University and screening of a commercially available compound library led to the discovery of the novel small molecule inhibitor, (-)-blebbistatin. This thesis describes an efficient and flexible synthetic approach to highly optically enriched (-)-blebbistatin. The bioactive compound is synthesised from 2-amino-5-methylbenzoic acid in a four step procedure. The key step is the asymmetric hydroxylation of a quinolone intermediate using the Davis oxaziridine methodology. For the first time, we have proved that the absolute stereochemistry of (-)-blebbistatin is S by X-ray analysis of a heavy atom containing analogue of blebbistatin. Subsequent studies on the core structure of blebbistatin show that it is possible through chemical modification to prepare analogues. Further biological testing of these compounds show which parts of (S)-(-)-blebbistatin are important to retain its inhibitory activity. In addition, it is shown that the incorporation of a nitro functional group into the blebbistatin core structure modifies its fluorescence properties. This is of importance since this analogue can therefore be used in fluorescence-based microscope imaging experiments on live cells where (-)-blebbistatin cannot.Reactions of nitrogen oxides and oxygen with hydrocarbons over manganese and related oxidesFairbridge, Craig Williamhttps://hdl.handle.net/10023/220162022-04-05T09:27:04Z1981-01-01T00:00:00ZThe catalytic reactions of nitric oxide, nitrous oxide or oxygen with either ethane or 1-butene were studied. Manganese (III) oxide was evaluated as a catalyst for these reactions in a differential-reactor flow system operated at atmospheric pressure. This system allowed the kinetics of reaction to be calculated and kinetic modelling studies were used as an aid in determining reaction mechanisms.
Nitric oxide reacted in a complex sequence of steps beginning with an irreversible bimolecular reaction between adsorbed species on the catalyst surface. In the case of the reactions with ethane, each reactant was adsorbed on one surface site, while in reactions with 1-butene each was adsorbed on two sites. Nitrous oxide was one of the products of re¬ action when nitric oxide was a reactant. In reactions with nitrous oxide or oxygen, similar mechanisms operated and only the products of complete hydrocarbon oxidation were observed.
In all reactions, the manganese (III) oxide went through a phase change from the alpha to the gamma phase. A nitro or nitrate species appeared on the catalyst surface after reactions involving nitric oxide.
The effects of a series of oxide catalysts were observed on the nitrous oxide / 1-butene reaction. Reactivity decreased down the series:
CuO, Fe₂O₃, NiO Mn₂O₃, Cr₂O₃, TiO₂, Sc₂O₃, SnO, ZnO, V₂O₅, Al₂O₃.
The use of carbon fibres as catalyst supports or cocatalysts was assessed, and the kinetics of the oxygen / ethane and oxygen / 1-butene reactions over manganese oxide / carbon fibre were determined.
1981-01-01T00:00:00ZFairbridge, Craig WilliamThe catalytic reactions of nitric oxide, nitrous oxide or oxygen with either ethane or 1-butene were studied. Manganese (III) oxide was evaluated as a catalyst for these reactions in a differential-reactor flow system operated at atmospheric pressure. This system allowed the kinetics of reaction to be calculated and kinetic modelling studies were used as an aid in determining reaction mechanisms.
Nitric oxide reacted in a complex sequence of steps beginning with an irreversible bimolecular reaction between adsorbed species on the catalyst surface. In the case of the reactions with ethane, each reactant was adsorbed on one surface site, while in reactions with 1-butene each was adsorbed on two sites. Nitrous oxide was one of the products of re¬ action when nitric oxide was a reactant. In reactions with nitrous oxide or oxygen, similar mechanisms operated and only the products of complete hydrocarbon oxidation were observed.
In all reactions, the manganese (III) oxide went through a phase change from the alpha to the gamma phase. A nitro or nitrate species appeared on the catalyst surface after reactions involving nitric oxide.
The effects of a series of oxide catalysts were observed on the nitrous oxide / 1-butene reaction. Reactivity decreased down the series:
CuO, Fe₂O₃, NiO Mn₂O₃, Cr₂O₃, TiO₂, Sc₂O₃, SnO, ZnO, V₂O₅, Al₂O₃.
The use of carbon fibres as catalyst supports or cocatalysts was assessed, and the kinetics of the oxygen / ethane and oxygen / 1-butene reactions over manganese oxide / carbon fibre were determined.The characterisation of carbon fibre surfaces by electrochemical methodsStewart, Colin J. M.https://hdl.handle.net/10023/220082022-03-23T03:08:07Z1989-01-01T00:00:00ZThe possibility of surface characterisation of carbon fibres by electrochemical methods is investigated. A three electrode cell set-up is used and the carbon fibre electrode/solution electrolyte interface is studied. The interface is represented as an equivalent circuit of electrical components and the variation in the nature and value of these components is investigated for various high modulus fibres. Initial studies using non-sinusoidal techniques show that the simple equivalent circuit model, containing a solution resistance, a charge transfer resistance and a double layer capacitance, normally used for this type of cell is completely inadequate. It is not feasible to distinguish between fibres or even between different electrolyte solutions using these methods. However, it is shown that by applying an a.c. impedance technique coupled with equivalent circuit analysis developed by Boukamp it is possible to generate a more accurate representation of the fibre/solution interface. The new circuit contains additional elements such as an interfacial inductance and a constant phase diffusional element. By monitoring the d.c. polarisation potential dependence of these circuit components it is shown to be possible to distinguish between untreated and surface-treated fibres. However, it is not possible to distinguish between different batches of the same fibre. It is shown that galvanic oxidation of untreated fibres can be monitored by this method. The effects of time on oxidised fibres is also investigated.
1989-01-01T00:00:00ZStewart, Colin J. M.The possibility of surface characterisation of carbon fibres by electrochemical methods is investigated. A three electrode cell set-up is used and the carbon fibre electrode/solution electrolyte interface is studied. The interface is represented as an equivalent circuit of electrical components and the variation in the nature and value of these components is investigated for various high modulus fibres. Initial studies using non-sinusoidal techniques show that the simple equivalent circuit model, containing a solution resistance, a charge transfer resistance and a double layer capacitance, normally used for this type of cell is completely inadequate. It is not feasible to distinguish between fibres or even between different electrolyte solutions using these methods. However, it is shown that by applying an a.c. impedance technique coupled with equivalent circuit analysis developed by Boukamp it is possible to generate a more accurate representation of the fibre/solution interface. The new circuit contains additional elements such as an interfacial inductance and a constant phase diffusional element. By monitoring the d.c. polarisation potential dependence of these circuit components it is shown to be possible to distinguish between untreated and surface-treated fibres. However, it is not possible to distinguish between different batches of the same fibre. It is shown that galvanic oxidation of untreated fibres can be monitored by this method. The effects of time on oxidised fibres is also investigated.Photochemical electron transfer across surfactant vesicle bilayersGrubb, Colin Johnhttps://hdl.handle.net/10023/220052022-03-22T11:49:38Z1996-01-01T00:00:00ZDiethyl (BTDE) and dibutyl (BTDB) esters of 2,1,3-benzothiadiazole-4,7,- dicarboxylic acid are effective as combined chromophores and electron transfer catalysts in the photochemical transfer of electrons from suitable donors to anthraquinones. The less electron withdrawing nature of the ester groups than of -CN has improved the redox potential and by altering the nature of the ester R group, we can tailor other properties into the molecule such as increasing solubility in the lipophilic environment of the micellar core or vesicle bilayer by increasing the length of the R group.
The stability of the radical anions obtained by reduction decreases in the order BTDN⁻ >BTDE⁻ >BTDB ⁻; correlating inversely with their reducing power. The more transient nature of BTDB⁻ is compensated for by its more favourable redox, micellepartition and light absorption properties. The rate of onward electron transfer from all the radical anions is sufficient for it to dominate over the radical decomposition. The rate of electron transfer is the same for each chromophore and this is interpreted in terms of charge compensating diffusion of OH⁻ or H+ across the vesicle as being the overall rate determining process. Mechanistic studies have highlighted that transmembrane electron transfer is affected by the diffusion of the radical anion. Attempts will be made to couple the transmembrane electron transfer with the production of H₂.
Kinetic studies carried out on the electron transfer from MES to AQDS in a micellar system mediated by BTDB show that the reaction is first order in [BTDB], light intensity (with saturation at high I) and [MESH] at low concentration. It tends to zero order at higher [MESH] and is zero order in [AQDS] and [H+] between pH 6.5 and 10. A mechanism is proposed in which the BTDB acts as a chromophore and electron transfer catalyst and the rate determining step is transfer of the electron from BTDB⁻ to AQDS.
The system can be modified to allow transfer of electrons across a vesicle bilaycr constructed from simple surfactant molecules (DODAB). It is shown that the initial rate of electron transfer depends upon the overall surface area of the vesicle present in solution but that the yield is determined by the availability of MES⁻ within the inner water pools of the vesicles. For unilamellar vesicles, all of the MES⁻ present within them is available for reaction but for multilamellar vesicles only the MES⁻ within the outer bilayer is available.
Kinetic studies upon the vesicular system indicates similar results to those obtained in the micelles except that at higher BTDB concentration the reaction is zero order in all reagents except H+. This suggests that some process other than electron transfer must be rate determining. Since the rate increases with [H+], we assume that charge compensating flow of H+ across the vesicle bilayer is rate determining. Attempts to couple the transbilayer electron transfer to H₂ production were unsuccessful.
Studies were also carried out on benzofurazan-4,7-dicarbonitrile (BFDN) but it proved to be a less effective electron transfer agent in the micelle system than BTDN or BTDB and was ineffective for electron transfer across the vesicles. Some possible explanations for this behaviour are discussed.
1996-01-01T00:00:00ZGrubb, Colin JohnDiethyl (BTDE) and dibutyl (BTDB) esters of 2,1,3-benzothiadiazole-4,7,- dicarboxylic acid are effective as combined chromophores and electron transfer catalysts in the photochemical transfer of electrons from suitable donors to anthraquinones. The less electron withdrawing nature of the ester groups than of -CN has improved the redox potential and by altering the nature of the ester R group, we can tailor other properties into the molecule such as increasing solubility in the lipophilic environment of the micellar core or vesicle bilayer by increasing the length of the R group.
The stability of the radical anions obtained by reduction decreases in the order BTDN⁻ >BTDE⁻ >BTDB ⁻; correlating inversely with their reducing power. The more transient nature of BTDB⁻ is compensated for by its more favourable redox, micellepartition and light absorption properties. The rate of onward electron transfer from all the radical anions is sufficient for it to dominate over the radical decomposition. The rate of electron transfer is the same for each chromophore and this is interpreted in terms of charge compensating diffusion of OH⁻ or H+ across the vesicle as being the overall rate determining process. Mechanistic studies have highlighted that transmembrane electron transfer is affected by the diffusion of the radical anion. Attempts will be made to couple the transmembrane electron transfer with the production of H₂.
Kinetic studies carried out on the electron transfer from MES to AQDS in a micellar system mediated by BTDB show that the reaction is first order in [BTDB], light intensity (with saturation at high I) and [MESH] at low concentration. It tends to zero order at higher [MESH] and is zero order in [AQDS] and [H+] between pH 6.5 and 10. A mechanism is proposed in which the BTDB acts as a chromophore and electron transfer catalyst and the rate determining step is transfer of the electron from BTDB⁻ to AQDS.
The system can be modified to allow transfer of electrons across a vesicle bilaycr constructed from simple surfactant molecules (DODAB). It is shown that the initial rate of electron transfer depends upon the overall surface area of the vesicle present in solution but that the yield is determined by the availability of MES⁻ within the inner water pools of the vesicles. For unilamellar vesicles, all of the MES⁻ present within them is available for reaction but for multilamellar vesicles only the MES⁻ within the outer bilayer is available.
Kinetic studies upon the vesicular system indicates similar results to those obtained in the micelles except that at higher BTDB concentration the reaction is zero order in all reagents except H+. This suggests that some process other than electron transfer must be rate determining. Since the rate increases with [H+], we assume that charge compensating flow of H+ across the vesicle bilayer is rate determining. Attempts to couple the transbilayer electron transfer to H₂ production were unsuccessful.
Studies were also carried out on benzofurazan-4,7-dicarbonitrile (BFDN) but it proved to be a less effective electron transfer agent in the micelle system than BTDN or BTDB and was ineffective for electron transfer across the vesicles. Some possible explanations for this behaviour are discussed.Chalcogen-carbon-nitrogen rings, chains and coordination compoundsBurchell, Colin Jameshttps://hdl.handle.net/10023/220042022-03-22T11:25:27Z2005-01-01T00:00:00ZThis thesis describes the general area of chalcogen-carbon-nitrogen compounds. The first part of Chapter 1 provides an introduction to chalcogen donor ligands. The second part of Chapter 1 considers the literature reports on polythiocyanogen and related compounds. Chapter 2 details the synthesis and characterisation of a series of homoleptic, heteroleptic and dimeric cyanodithioimidocarbonate complexes prepared by the reaction of dipotassium cyanodithioimidocarbonate with the appropriate transition metal starting materials. Chapter 3 describes the synthesis and characterisation of the cyanodiselenoimidocarbonate complexes. In Chapter 4 we report a convenient one pot synthesis for the preparation of triselenocarbonate complexes. We have prepared mononuclear, binuclear and tetranuclear complexes of this ligand including the first crystallographically characterised example of a triselenocarbonate complex. In Chapter 5 we have prepared a series of 1,2,4- thiadiazole compounds for spectroscopic comparison with (SCN)ₓ. We also report the synthesis of model compounds for (SCN)ₓ composed of two 1,2,4- dithiazole rings linked by a sulfur bridge. Chapter 6 describes the synthesis and full characterisation of polythiocyanogen (SCN)ₓ the related small molecules Sₓ(CN)₂ (x = 1, 2, 3) and the selenium analogues. Using the data obtained and comparison with the 1,2,4-thiadiazole model compounds reported in Chapter 5 as well as literature compounds we have determined the structure of polythiocyanogen.
2005-01-01T00:00:00ZBurchell, Colin JamesThis thesis describes the general area of chalcogen-carbon-nitrogen compounds. The first part of Chapter 1 provides an introduction to chalcogen donor ligands. The second part of Chapter 1 considers the literature reports on polythiocyanogen and related compounds. Chapter 2 details the synthesis and characterisation of a series of homoleptic, heteroleptic and dimeric cyanodithioimidocarbonate complexes prepared by the reaction of dipotassium cyanodithioimidocarbonate with the appropriate transition metal starting materials. Chapter 3 describes the synthesis and characterisation of the cyanodiselenoimidocarbonate complexes. In Chapter 4 we report a convenient one pot synthesis for the preparation of triselenocarbonate complexes. We have prepared mononuclear, binuclear and tetranuclear complexes of this ligand including the first crystallographically characterised example of a triselenocarbonate complex. In Chapter 5 we have prepared a series of 1,2,4- thiadiazole compounds for spectroscopic comparison with (SCN)ₓ. We also report the synthesis of model compounds for (SCN)ₓ composed of two 1,2,4- dithiazole rings linked by a sulfur bridge. Chapter 6 describes the synthesis and full characterisation of polythiocyanogen (SCN)ₓ the related small molecules Sₓ(CN)₂ (x = 1, 2, 3) and the selenium analogues. Using the data obtained and comparison with the 1,2,4-thiadiazole model compounds reported in Chapter 5 as well as literature compounds we have determined the structure of polythiocyanogen.A study of the photochemical decomposition of polymethacrylatesSchoff, Clifford Kinghttps://hdl.handle.net/10023/220002022-03-21T12:19:07Z1970-01-01T00:00:00Z1970-01-01T00:00:00ZSchoff, Clifford KingA study of the oxidation of polymers using excited oxygen speciesRankin, Clive Tauntonhttps://hdl.handle.net/10023/220022022-03-22T10:53:11Z1972-01-01T00:00:00ZIn this thesis, the work is concerned with the effects of exposing various polymers, both in the solid state and in solution, to 'active' oxygen species. In this case the active species are mainly 1△g molecular oxygen and atomic oxygen produced by microwave discharge of molecular oxygen. The experimental work is in two parts, the first is concerned with solid phase reactions and the second with reactions in solution. The information derived may perhaps be used to elucidate the mechanisms by which polymers are oxidised, leading to a better understanding of polymer oxidations as a whole.
1972-01-01T00:00:00ZRankin, Clive TauntonIn this thesis, the work is concerned with the effects of exposing various polymers, both in the solid state and in solution, to 'active' oxygen species. In this case the active species are mainly 1△g molecular oxygen and atomic oxygen produced by microwave discharge of molecular oxygen. The experimental work is in two parts, the first is concerned with solid phase reactions and the second with reactions in solution. The information derived may perhaps be used to elucidate the mechanisms by which polymers are oxidised, leading to a better understanding of polymer oxidations as a whole.Biosynthesis and enzymology of fluorometabolite production in Streptomyces cattleyaSchaffrath, Christophhttps://hdl.handle.net/10023/219902022-03-10T15:06:18Z2003-01-01T00:00:00ZOrganofluorine compounds are very rare in nature when compared with other organohalogens and the way by which fluorine is inserted into these compounds was unknown before the investigations described in this thesis. The biochemical processes involved in fluoroacetate and 4-fluorothreonine formation in the actinomycete Streptomyces cattleya have been explored by using isotopic labelling approaches, enzymatic studies and protein purification.
The synthesis and feeding of [1-²H₁]-fluoroacetaldehyde to resting cells of S. cattleya proved that fluoroacetaldehyde is a common intermediate in fluorometabolite biosynthesis and is the direct precursor to 4-fluorothreonine. Isotopic labelling studies with [1,1-²H₂]- ethanolamine and [1,1-²H₂]- cysteamine demonstrated that such C-2 units are not involved in the biosynthesis of fluoroacetate and 4-fluorothreonine. Experiments with [2-²H, 2-¹⁸O]-glycerol showed that the C-2 oxygen of glycerol becomes incorporated into both fluorometabolites, whereas the deuterium is lost, probably during the in vivo formation of a carbonyl intermediate during glycolysis.
A threonine transaldolase was identified and partially purified from S. cattleya. The enzyme catalyses the formation of 4-fluorothreonine from fluoroacetaldehyde and L-threonine in a pyridoxal phosphate dependent process. Investigations into the mechanism of the transaldolase have been carried out using [1,2,2,2-²H₄]-acetaldehyde and [4,4,4-²H₃]-DL-threonine. The experiments have shown that the threonine transaldolase is a novel enzyme, which is distinct to other enzymes such as threonine aldolase or serine hydroxymethyltransferase, as glycine is not used as a substrate and only L-threonine is accepted.
The enzyme responsible for the formation of a C-F bond in S. cattleya was identified and purified to homogeneity. This fluorination enzyme, the first of its class, mediates a reaction between inorganic fluoride ion and S'-adenosyl-L-methionine to generate 5'- fluoro-5'-deoxyadenosine. The fluorinase enzyme was found to be a hexamer with a molecular mass of approximately 180-190 kDa.
2003-01-01T00:00:00ZSchaffrath, ChristophOrganofluorine compounds are very rare in nature when compared with other organohalogens and the way by which fluorine is inserted into these compounds was unknown before the investigations described in this thesis. The biochemical processes involved in fluoroacetate and 4-fluorothreonine formation in the actinomycete Streptomyces cattleya have been explored by using isotopic labelling approaches, enzymatic studies and protein purification.
The synthesis and feeding of [1-²H₁]-fluoroacetaldehyde to resting cells of S. cattleya proved that fluoroacetaldehyde is a common intermediate in fluorometabolite biosynthesis and is the direct precursor to 4-fluorothreonine. Isotopic labelling studies with [1,1-²H₂]- ethanolamine and [1,1-²H₂]- cysteamine demonstrated that such C-2 units are not involved in the biosynthesis of fluoroacetate and 4-fluorothreonine. Experiments with [2-²H, 2-¹⁸O]-glycerol showed that the C-2 oxygen of glycerol becomes incorporated into both fluorometabolites, whereas the deuterium is lost, probably during the in vivo formation of a carbonyl intermediate during glycolysis.
A threonine transaldolase was identified and partially purified from S. cattleya. The enzyme catalyses the formation of 4-fluorothreonine from fluoroacetaldehyde and L-threonine in a pyridoxal phosphate dependent process. Investigations into the mechanism of the transaldolase have been carried out using [1,2,2,2-²H₄]-acetaldehyde and [4,4,4-²H₃]-DL-threonine. The experiments have shown that the threonine transaldolase is a novel enzyme, which is distinct to other enzymes such as threonine aldolase or serine hydroxymethyltransferase, as glycine is not used as a substrate and only L-threonine is accepted.
The enzyme responsible for the formation of a C-F bond in S. cattleya was identified and purified to homogeneity. This fluorination enzyme, the first of its class, mediates a reaction between inorganic fluoride ion and S'-adenosyl-L-methionine to generate 5'- fluoro-5'-deoxyadenosine. The fluorinase enzyme was found to be a hexamer with a molecular mass of approximately 180-190 kDa.Quantum chemical studies of intermediates in nitrosamine carcinogenesisReynolds, Christopher Arthurhttps://hdl.handle.net/10023/219892022-03-10T14:31:57Z1986-01-01T00:00:00ZN-Nitrosamines are chemical compounds which are frequently carcinogenic. They may be formed from naturally occurring precursors under a variety of conditions. Despite much experimental study, many of these intermediates in nitrosamine carcinogenesis have not been identified; this thesis describes quantum chemical calculations on these intermediates.
The majority of the calculations have been performed using ab-initio self-consistent-field gradient techniques with a 4-21G split valence basis set. Some calculations have used polarised basis sets; estimates of the correlation energy have also been made. The strategy has been to locate stationary points on the potential energy surfaces for proposed intermediates; the calculation of energies of reaction and energy barriers has made a critical evaluation of alternative pathways possible. A large number of fully optimised ab-initio transition structures are reported.
The nitrosating agent in acidic solution - the nitrous acidium ion has never been observed. However, calculations show that it may exist as a number of different structures. The nitrosation of tertiary amines by the nitrous acidium ion is discussed. Enzymic activation of nitrosamines usually yields an α-hydroxynitrosamine; the calculations suggest that this decomposes either to the diazohydroxide or to the diazotate. The interconversion of monomethylnitrosamines and methyldiazohydroxides is studied. It is proposed that both the (V-hydroxynitrosamines and the diazohydroxides may have sufficient stability to diffuse across the cell. The nature of the alkylating agent is discussed and reasons for reconsidering the diazoalkane are presented. Acid catalysis may be important in the formation of the diazohydroxide. Experiments are suggested which may shed light upon the nature of the alkylating agent.
1986-01-01T00:00:00ZReynolds, Christopher ArthurN-Nitrosamines are chemical compounds which are frequently carcinogenic. They may be formed from naturally occurring precursors under a variety of conditions. Despite much experimental study, many of these intermediates in nitrosamine carcinogenesis have not been identified; this thesis describes quantum chemical calculations on these intermediates.
The majority of the calculations have been performed using ab-initio self-consistent-field gradient techniques with a 4-21G split valence basis set. Some calculations have used polarised basis sets; estimates of the correlation energy have also been made. The strategy has been to locate stationary points on the potential energy surfaces for proposed intermediates; the calculation of energies of reaction and energy barriers has made a critical evaluation of alternative pathways possible. A large number of fully optimised ab-initio transition structures are reported.
The nitrosating agent in acidic solution - the nitrous acidium ion has never been observed. However, calculations show that it may exist as a number of different structures. The nitrosation of tertiary amines by the nitrous acidium ion is discussed. Enzymic activation of nitrosamines usually yields an α-hydroxynitrosamine; the calculations suggest that this decomposes either to the diazohydroxide or to the diazotate. The interconversion of monomethylnitrosamines and methyldiazohydroxides is studied. It is proposed that both the (V-hydroxynitrosamines and the diazohydroxides may have sufficient stability to diffuse across the cell. The nature of the alkylating agent is discussed and reasons for reconsidering the diazoalkane are presented. Acid catalysis may be important in the formation of the diazohydroxide. Experiments are suggested which may shed light upon the nature of the alkylating agent.Synthesis and characterisation of porous polymersLove, Christopher Jameshttps://hdl.handle.net/10023/219862022-03-09T11:45:15Z2003-01-01T00:00:00ZHighly porous silsesquioxane based copolymers, deriving from vinyl and hydridosilsesquioxane monomers, have been synthesised. These materials have been characterised in order to determine their chemical structure, with particular emphasis upon the surface area and porosity. A number of slight variations to the composition has also been considered, showing similar physical properties to those prepared earlier. In most cases the materials produced are observed to be highly porous, with surface areas typically around 500m²/g. Additionally the thermal behaviour was investigated, with the copolymers seen to start breaking down at temperatures over 150°C.
Subsequently these silsesquioxane copolymers have been used as supports for a number of different transition metal species. This was achieved by means of opening the silsesquioxane ring structure in the presence of a base, before insertion of chlorine containing complexes of titanium, zirconium, molybdenum or cobalt. The porosity of these was comparable to results prior to the insertion, with only a slight reduction in surface area.
The preparation of copolymers containing zirconium and cobalt species was also attempted by preparing monomeric silsesquioxanes possessing these metals, and then conducting the polymerisation. From this a zirconium containing porous polymer was successfully prepared.
Extended x-ray absorption fine structure (EXAFS) was used to determine the structure of the metal containing species, and results compared with samples with the metal species having been inserted in monomelic species. From this data a number of likely structures for these materials was proposed.
2003-01-01T00:00:00ZLove, Christopher JamesHighly porous silsesquioxane based copolymers, deriving from vinyl and hydridosilsesquioxane monomers, have been synthesised. These materials have been characterised in order to determine their chemical structure, with particular emphasis upon the surface area and porosity. A number of slight variations to the composition has also been considered, showing similar physical properties to those prepared earlier. In most cases the materials produced are observed to be highly porous, with surface areas typically around 500m²/g. Additionally the thermal behaviour was investigated, with the copolymers seen to start breaking down at temperatures over 150°C.
Subsequently these silsesquioxane copolymers have been used as supports for a number of different transition metal species. This was achieved by means of opening the silsesquioxane ring structure in the presence of a base, before insertion of chlorine containing complexes of titanium, zirconium, molybdenum or cobalt. The porosity of these was comparable to results prior to the insertion, with only a slight reduction in surface area.
The preparation of copolymers containing zirconium and cobalt species was also attempted by preparing monomeric silsesquioxanes possessing these metals, and then conducting the polymerisation. From this a zirconium containing porous polymer was successfully prepared.
Extended x-ray absorption fine structure (EXAFS) was used to determine the structure of the metal containing species, and results compared with samples with the metal species having been inserted in monomelic species. From this data a number of likely structures for these materials was proposed.Hydrogen bonding in sterically-hindered ferrocenes and related systemsZakaria, Choudhury M.https://hdl.handle.net/10023/219762022-03-08T12:56:32Z1995-01-01T00:00:00ZThe aims of this project are the synthesis and characterisation of new types of chemical structure containing the electroactive ferrocene nucleus. There are three main strands to this work: (i) coupling reactions of ferrocenes, using Wittig reactions and other coupling reagents, to form electroactive oligomers and polymers; (ii) the design of host molecules for the formation of inclusion compounds; and (iii) the design of new electroactive ligands for metal complexation.
1995-01-01T00:00:00ZZakaria, Choudhury M.The aims of this project are the synthesis and characterisation of new types of chemical structure containing the electroactive ferrocene nucleus. There are three main strands to this work: (i) coupling reactions of ferrocenes, using Wittig reactions and other coupling reagents, to form electroactive oligomers and polymers; (ii) the design of host molecules for the formation of inclusion compounds; and (iii) the design of new electroactive ligands for metal complexation.Chlorination of quinoxalino[2,3-c]cinnolines : mechanistic studiesWhite, Charles Richardhttps://hdl.handle.net/10023/219702022-03-08T11:28:30Z1996-01-01T00:00:00ZSection 1 (Introduction) gives a brief outline of some cyanide-induced cyclisation reactions of ortho-substituted nitrobenzene derivatives, and the proposed mechanism for the cyclisation of N-(o-nitrobenzylidene)-o-phenylenediamines to quinoxalino[2,3-c]cinnolines. An overview of the mechanism for the chlorination of the quinoxalinocinnoline ring and the reasoning behind the hypothesis is also given, as are the aims of the project.
Section 2 (Results and Discussion) develops the mechanistic ideas outlined in Section 1 relating to the chlorination reaction, and attempts to divert the course of this reaction by hindering the protonation of the quinoxalinocinnoline at the preferred location. Chlorination of l-methylquinoxalino-[2,3-c]cinnoline, however, still follows the usual pathway, although the reaction is both slow and incomplete. These results therefore support the previous proposal that protonation occurs preferentially at N-12. Attempts to synthesise the analogous ring system in which N-12 is lacking have so far met with no success.
Section 3 (Experimental) details the synthetic procedures used and this is followed by the Bibliography.
1996-01-01T00:00:00ZWhite, Charles RichardSection 1 (Introduction) gives a brief outline of some cyanide-induced cyclisation reactions of ortho-substituted nitrobenzene derivatives, and the proposed mechanism for the cyclisation of N-(o-nitrobenzylidene)-o-phenylenediamines to quinoxalino[2,3-c]cinnolines. An overview of the mechanism for the chlorination of the quinoxalinocinnoline ring and the reasoning behind the hypothesis is also given, as are the aims of the project.
Section 2 (Results and Discussion) develops the mechanistic ideas outlined in Section 1 relating to the chlorination reaction, and attempts to divert the course of this reaction by hindering the protonation of the quinoxalinocinnoline at the preferred location. Chlorination of l-methylquinoxalino-[2,3-c]cinnoline, however, still follows the usual pathway, although the reaction is both slow and incomplete. These results therefore support the previous proposal that protonation occurs preferentially at N-12. Attempts to synthesise the analogous ring system in which N-12 is lacking have so far met with no success.
Section 3 (Experimental) details the synthetic procedures used and this is followed by the Bibliography.Synthetic studies on some fatty acidsBaker, Charles Derekhttps://hdl.handle.net/10023/219642022-03-01T12:03:55Z1961-01-01T00:00:00ZPart 1 – Synthesis of some Monoethenoid Acids with Potential Essential Fatty Acid Activity.
The cis-isomers of the four acids, teradec-8-enoic, hexadeco-10-enoic, octadic-12-enoic and cicos-14-enoic have been synthesised via the corresponding acetylenic acids.
Part II – Configuration of Natural 9-hydroxyoctadecanoic Acid.
9D-Hydroxyoctadecanoic acid has been synthesised and found to possess no measurable optical activity. It is suggested, on the evidence of a mixed melting point, that the natural acid has the d-configuration.
Part III – Synthetic studies on 6,8-Dihydroxyoctanoic Acid.
Two synthetic routes to 6,8-dihydroxyoctanoic acid have been examined. Both were eventually abandoned.
1961-01-01T00:00:00ZBaker, Charles DerekPart 1 – Synthesis of some Monoethenoid Acids with Potential Essential Fatty Acid Activity.
The cis-isomers of the four acids, teradec-8-enoic, hexadeco-10-enoic, octadic-12-enoic and cicos-14-enoic have been synthesised via the corresponding acetylenic acids.
Part II – Configuration of Natural 9-hydroxyoctadecanoic Acid.
9D-Hydroxyoctadecanoic acid has been synthesised and found to possess no measurable optical activity. It is suggested, on the evidence of a mixed melting point, that the natural acid has the d-configuration.
Part III – Synthetic studies on 6,8-Dihydroxyoctanoic Acid.
Two synthetic routes to 6,8-dihydroxyoctanoic acid have been examined. Both were eventually abandoned.Investigation of the chemistry of phosphorus fluoridesBarlow, Charles Georgehttps://hdl.handle.net/10023/219652022-03-01T12:19:04Z1967-01-01T00:00:00Z1967-01-01T00:00:00ZBarlow, Charles GeorgeThe C-F bond as a tool in predicting the conformational preference of organic moleculesBriggs, Caroline R. S.https://hdl.handle.net/10023/219452022-02-24T11:27:44Z2003-01-01T00:00:00ZChapter One highlights the history and development of organofluorine chemistry. Later sections highlight the introduction of fluorine into organic molecules as an important tool in modifying their physical, chemical and biological properties. The significance of fluorine substitution is further explored by exemplifying its role in medicinal chemistry.
Chapter Two introduces the importance of stereoelectronic effects on the conformational preference of organic molecules. The implications of the gauche effect and, in particular, the fluorine-gauche effect are discussed.
Chapter Three presents results which demonstrate the influence of the C-F bond in the β- fluoroamide gauche effect and an α -fluoroamide cis effect. The presence of a fluorine atom (β-to an ester oxygen also reveals the influence of a (β -fluoroester) gauche effect.
Chapter Four presents ab initio calculations used to investigate the gauche effect in protonated 2-fluoroethanol and 2-fluoroethylamine. It is noted that the (β-fluoroethylammonium ion is the largest conformational gauche preference yet measured whereas its neutral counterpart, fluoroethylamine, does not exhibit a measurable gauche preference.
2003-01-01T00:00:00ZBriggs, Caroline R. S.Chapter One highlights the history and development of organofluorine chemistry. Later sections highlight the introduction of fluorine into organic molecules as an important tool in modifying their physical, chemical and biological properties. The significance of fluorine substitution is further explored by exemplifying its role in medicinal chemistry.
Chapter Two introduces the importance of stereoelectronic effects on the conformational preference of organic molecules. The implications of the gauche effect and, in particular, the fluorine-gauche effect are discussed.
Chapter Three presents results which demonstrate the influence of the C-F bond in the β- fluoroamide gauche effect and an α -fluoroamide cis effect. The presence of a fluorine atom (β-to an ester oxygen also reveals the influence of a (β -fluoroester) gauche effect.
Chapter Four presents ab initio calculations used to investigate the gauche effect in protonated 2-fluoroethanol and 2-fluoroethylamine. It is noted that the (β-fluoroethylammonium ion is the largest conformational gauche preference yet measured whereas its neutral counterpart, fluoroethylamine, does not exhibit a measurable gauche preference.Chemical manipulation of polyhedral oligomeric silsesquioxanes for the synthesis of modular materials and catalystsManson, Brucehttps://hdl.handle.net/10023/219382022-02-23T16:10:16Z2003-01-01T00:00:00ZA study has been undertaken to investigate the chemical modification of near cubic polyhedral oligomeric silsesquioxanes (POSS) of the general formula [RSi03/2]8 to produce molecular building blocks suitable for the preparation of microporous modular solids with engineered properties. Several approaches have been taken in an effort to prepare octa-fiinctional POSS suitable for self-assembly resulting in the synthesis of new benzoic acid functionalised POSS and, preliminary analysis suggests, two new highly functionalised pyridine bearing POSS. Studies into the use of Heck type arylation, the Gabriel synthesis and thyl radical reactions to modify functionalised POSS have also been undertaken with a view to identifying new synthetic routes to functionalised POSS.
During efforts to investigate the requirements for the preparation of porous materials from POSS, several new copolymers were prepared through hydrosilylation of POSS only and POSS-spacer mixtures. Three of these copolymers are porous in nature and have high surface areas measuring several hundred meters square per gram. Acid cleavage has been used to alter the form of one of these copolymers by, it is suggested, opening individual POSS within the structure of the material. This demonstrates that it is possible to modify linked POSS molecules in a manner and may provide a route to catalytic materials from POSS copolymers and, potentially, extended networks of POSS.
2003-01-01T00:00:00ZManson, BruceA study has been undertaken to investigate the chemical modification of near cubic polyhedral oligomeric silsesquioxanes (POSS) of the general formula [RSi03/2]8 to produce molecular building blocks suitable for the preparation of microporous modular solids with engineered properties. Several approaches have been taken in an effort to prepare octa-fiinctional POSS suitable for self-assembly resulting in the synthesis of new benzoic acid functionalised POSS and, preliminary analysis suggests, two new highly functionalised pyridine bearing POSS. Studies into the use of Heck type arylation, the Gabriel synthesis and thyl radical reactions to modify functionalised POSS have also been undertaken with a view to identifying new synthetic routes to functionalised POSS.
During efforts to investigate the requirements for the preparation of porous materials from POSS, several new copolymers were prepared through hydrosilylation of POSS only and POSS-spacer mixtures. Three of these copolymers are porous in nature and have high surface areas measuring several hundred meters square per gram. Acid cleavage has been used to alter the form of one of these copolymers by, it is suggested, opening individual POSS within the structure of the material. This demonstrates that it is possible to modify linked POSS molecules in a manner and may provide a route to catalytic materials from POSS copolymers and, potentially, extended networks of POSS.Ab initio SCF-MO calculations on linear triatomic moleculesWishart, B.J.https://hdl.handle.net/10023/219272022-02-01T11:25:13Z1981-01-01T00:00:00ZSingle configuration wave functions for the ground states of several small species have been calculated – 0CC ³Σ⁻ ; CNC ²π ; NCO ²π ; NC ²Σ⁺ ; PC ²Σ⁺ ; OBO ²π Extended, Slater function basis sets were used in these calculations, allowing the wave functions so calculated to approach the Hartree-Fock limit. One-electron properties have been calculated for the species; and, where possible, compared with the experimental results. Conclusions are drawn that the near Hartree-Fock wave function gives good predictions of one-electron properties. These investigations were continued for species containing second-row atoms – SCC ³Σ⁻ ; PCC ²π ; SCN ²π ; PC ²Σ⁺ The single configuration approximation has been used in the calculation of wave functions for excited states of some of these species - OCC; HCC; HNC; NCO; CNC. Conclusions are drawn that the single configuration wave function is not an adequate model of excited states. For the ground state species, HBO, a configuration interaction investigation was undertaken.
1981-01-01T00:00:00ZWishart, B.J.Single configuration wave functions for the ground states of several small species have been calculated – 0CC ³Σ⁻ ; CNC ²π ; NCO ²π ; NC ²Σ⁺ ; PC ²Σ⁺ ; OBO ²π Extended, Slater function basis sets were used in these calculations, allowing the wave functions so calculated to approach the Hartree-Fock limit. One-electron properties have been calculated for the species; and, where possible, compared with the experimental results. Conclusions are drawn that the near Hartree-Fock wave function gives good predictions of one-electron properties. These investigations were continued for species containing second-row atoms – SCC ³Σ⁻ ; PCC ²π ; SCN ²π ; PC ²Σ⁺ The single configuration approximation has been used in the calculation of wave functions for excited states of some of these species - OCC; HCC; HNC; NCO; CNC. Conclusions are drawn that the single configuration wave function is not an adequate model of excited states. For the ground state species, HBO, a configuration interaction investigation was undertaken.Thermodynamics of concentrated aqueous solutions of halide mixturesGilchrist Belmar, Maria Antonietahttps://hdl.handle.net/10023/219162022-01-31T11:09:37Z1978-01-01T00:00:00ZThe object of this work was mainly the adaptation to other partial molar quantities of the method which KcKay and Perring developed for the activity coefficients of solute components in mixed solutions. Equations were deduced which permit the calculation of the partial molar enthalpy of each solute component of a ternary mixed electrolyte solution, at constant partial molar enthalpy of water, and at constant total molality. Similar relations for the partial molar heat capacities were also developed. The system sodium chloride-calcium chloride-water, due to its important role in natural salt deposits, was chosen to investigate the utility of applying these equations. The calorirnetric study of this system was carried out and the partial molar enthalpies of both solutes, sodium chloride and calcium chloride, were determined by the new method. The calorimetric data of the systems sodium chloride- magnesium chloride-water and calcium chloride-magnesium chloridewater were also obtained and in this work the possibility of their treatment by either of the two new adaptions of the McKay-Perring methods is discussed.
To appreciate the differences with temperature of the activity coefficients of the components of the systems under investigation, isopiestic measurements were made on the systems sodium chloride-calcium chloride-water, and calcium chloride-magnesium chloride-water, at 45 °C. The activity coefficients were computed ty the McKay-Perring method. Comparison between the calorimetric and the isopiestic results shows that, since the observed changes in log Y+ with temperature are in any case very small and depend upon a difference between two large quantities, it seems most probable that the enthalpies of dilution give a much more reliable estimate of the small variation in log Y+ to be expected over a moderate temperature range.
1978-01-01T00:00:00ZGilchrist Belmar, Maria AntonietaThe object of this work was mainly the adaptation to other partial molar quantities of the method which KcKay and Perring developed for the activity coefficients of solute components in mixed solutions. Equations were deduced which permit the calculation of the partial molar enthalpy of each solute component of a ternary mixed electrolyte solution, at constant partial molar enthalpy of water, and at constant total molality. Similar relations for the partial molar heat capacities were also developed. The system sodium chloride-calcium chloride-water, due to its important role in natural salt deposits, was chosen to investigate the utility of applying these equations. The calorirnetric study of this system was carried out and the partial molar enthalpies of both solutes, sodium chloride and calcium chloride, were determined by the new method. The calorimetric data of the systems sodium chloride- magnesium chloride-water and calcium chloride-magnesium chloridewater were also obtained and in this work the possibility of their treatment by either of the two new adaptions of the McKay-Perring methods is discussed.
To appreciate the differences with temperature of the activity coefficients of the components of the systems under investigation, isopiestic measurements were made on the systems sodium chloride-calcium chloride-water, and calcium chloride-magnesium chloride-water, at 45 °C. The activity coefficients were computed ty the McKay-Perring method. Comparison between the calorimetric and the isopiestic results shows that, since the observed changes in log Y+ with temperature are in any case very small and depend upon a difference between two large quantities, it seems most probable that the enthalpies of dilution give a much more reliable estimate of the small variation in log Y+ to be expected over a moderate temperature range.Photophysical studies of polymersRudkin, Arthur Laurencehttps://hdl.handle.net/10023/219072022-01-07T11:41:05Z1976-01-01T00:00:00ZOne means of stabilising a polymer against irradiation involves energy transfer between a fluorescent polymer (donor) and a photostabiliser (acceptor) which removes some of the absorbed energy from the polymer. Polymers examined for this purpose were mainly conjugated derivatives of polystyrene and poly(vinylchloride). The dependence of donor emission on concentration of acceptor has been used to evaluate a transfer distance from donor to acceptor in fluid and rigid media. Polarisation measurements on thin films demonstrate that transfer is a long-range intermolecular process with no down chain migration of energy prior to transfer. Rotational Brownian motion in styrene copolymers has been studied in solution by fluorescence quenching and polarisation to determine relaxation times for the emitting species. Variable temperature work on fluorescence has highlighted the effect of chain mobility on emission spectra while a novel method for measuring diffusion coefficients has been proposed. Photodegradation of thin polymer films has been followed under accelerated weathering conditions using a medium pressure arc with a pyrex filter. The results reveal a subtle correlation between structure and reactivity. As an extension, polymer and acceptor have been simultaneously irradiated to examine the stabilising effect of the acceptor.
1976-01-01T00:00:00ZRudkin, Arthur LaurenceOne means of stabilising a polymer against irradiation involves energy transfer between a fluorescent polymer (donor) and a photostabiliser (acceptor) which removes some of the absorbed energy from the polymer. Polymers examined for this purpose were mainly conjugated derivatives of polystyrene and poly(vinylchloride). The dependence of donor emission on concentration of acceptor has been used to evaluate a transfer distance from donor to acceptor in fluid and rigid media. Polarisation measurements on thin films demonstrate that transfer is a long-range intermolecular process with no down chain migration of energy prior to transfer. Rotational Brownian motion in styrene copolymers has been studied in solution by fluorescence quenching and polarisation to determine relaxation times for the emitting species. Variable temperature work on fluorescence has highlighted the effect of chain mobility on emission spectra while a novel method for measuring diffusion coefficients has been proposed. Photodegradation of thin polymer films has been followed under accelerated weathering conditions using a medium pressure arc with a pyrex filter. The results reveal a subtle correlation between structure and reactivity. As an extension, polymer and acceptor have been simultaneously irradiated to examine the stabilising effect of the acceptor.Amidocyclohexadienes in synthesis of biologically active compoundsBella, Antonio Francohttps://hdl.handle.net/10023/219012022-01-06T17:02:22Z2003-01-01T00:00:00ZA summary of tin hydride mediated reactions in generating radicals in organic synthesis is presented, together with some of the many alternative methods available for conducting radical reactions. Particular attention has been given to the development of tin-free organic radical precursors. This is followed by three chapters describing research on the use of pro-aromatic 1-carbamoyl-l-methylcyclohexa-2,5-dienes as free-radical precursors.
A variety of 1 -carbamoyl-l-methylcyclohexa-2,5-dienes, TV-benzyl protected-amide, free-radical precursors have been prepared and utilised in subsequent experiments. EPR studies confirmed the formation of the delocalised cyclohexadienyl radical at low temperatures. At higher temperatures cyclohexadienyl radicals underwent homolysis with release of the associated aminoacyl (carbamoyl) radicals. Measurement of radical concentrations in DTBP solution from the aquired EPR spectra allowed us to calculate the rates of dissociation for several of these aminoacyl radicals. We concluded that the dissociations of cyclohexadienyl radicals, and the carbamoyl radical cyclisations, were both fast enough for chain propagation to be sustained.
The formation of pyrrolidin-2-ones was tested by examining the decomposition of but3-enyl amides induced thermally with dibenzoyl peroxide. 3-Alkyl-TVbenzylpyrrolidin-2-ones were obtained in moderate yields, along with significant amounts of the corresponding formamides. Reactions with other initiators, including photochemical processes with di-/-butyl peroxide, showed no significant advantage. A cyclohexadienyl amide containing bis-methyl substitution of the butenyl chain was prepared; in the hope that ring closure of the carbamoyl radical would be more efficient because of a Thorpe-Ingold effect. In practice, the yield of the corresponding pyrrolidinone was a disappointing 20 %. Evidence from characterisation of byproducts suggested that radical-radical reactions were important.
The use of cyclohexadienyl amides for the preparation of (β-lactams was also investigated. The cinnamyl-substituted amide 144 (Chapter 3) was chosen because the phenyl substituent confers resonance stabilisation on the cyclised radical and hence should expedite the 4-exo-cyclisation step. However, as an additional consequence of this resonance stabilisation the hydrogen-atom abstraction step was disfavoured. The thermal and photochemical reactions gave the corresponding azetidin-2-one, in low yields. Addition of a good H-atom donor enabled the ring closed benzyl type radical to be trapped. Reactions initiated with di-/-butyl peroxyoxalate, including 1.2 mol equiv. of methyl thioglycolate (RSH) produced 1,3-dibenzylazetidinone (148, Chapter 3) in increased yields. When a catalytic amount of RSH was employed, the (3- lactam yield increased, but radical-radical reactions again became important. Use of lauroyl peroxide as initiator, in concert with 1 equiv. of RSH, led to a greatly improved (3-lactam yield. It is likely that polarity reversal catalysis played a part in enhancing the yield of (3-lactam. The azetidinylbenzyl radical is resonance stabilised and nucleophilic. Hence a polar effect favoured hydrogen-abstraction from the electronegative RSH. The electrophilic thiyl radical (RS*) generated in this way, in turn, abstracted more readily from the cyclohexadienyl site thus regenerating RSH and continuing the chain. In the lauroyl peroxide initiated reactions, products derived from the initiator included undecane and docosane which significantly increased the viscosity of the reaction medium thus slowing radical-radical reactions which are normally diffusion controlled.
Overall, the induced carbamoyl-cyclohexadiene decompositions represent novel, comparatively 'clean', tin-free radical routes that are applicable for the preparation of a range of lactams from secondary amine starting materials. Inclusion of methyl thioglycolate in the reaction medium leads to increased lactam yields. Cyclisation onto an oxime ether C=N double bond was faster and more efficient, and the product heterocycles contain N-functionality at C(3), exactly as required in many antibiotics. Amidocyclohexadiene precursors containing oxime ether functionality were therefore designed and assembled. The radical-induced decompositions were studied by EPR spectroscopy which showed the expected cyclohexadienyl radicals at low temperatures. At higher temperatures, alkoxyaminyl radicals were also observed.
Cyclisations of the corresponding carbamoyl radicals were so fast that they were not observable by EPR spectra. When reactions were carried out preparatively, amino benzopyrrolidinone derivatives were isolated in good yields. Addition of methyl thioglycolate in dilauroyl peroxide mediated radical reactions, again improved product yields. An elegant use of O-trityl oxime ethers, in which the oxime functionality was ultimately regenerated had attracted our attention. We sought to adapt this tactic to our system and, accordingly, we prepared an O-trityl oxime ether substituted cyclohexadienecarboxamide precursor. The standard initiation followed by (3-scission of the cyclohexadienyl radical, produced the corresponding carbamoyl radical which ring closed to yield the alkoxyaminyl radical. However, the reaction took a novel route because trityl alkoxyaminyl radicals containing O-trityl moiety, underwent a second [3- scission to extrude the highly stabilised trityl radical with production of a nitrosocompound.
The use of our strategy was planned for a tin-free, radical-mediated synthesis of benzepril (ACE inhibitor). 7-exo-ring closure onto the oxime ether radical acceptor would be sufficiently rapid to facilitate the otherwise difficult ring closure. Carbamoyl radical released from a specifically designed 1-methylcyclohexadiene carboxamide containing O-trityl oxime ether moiety would undergo 7-exo-cyclisation to afford the desired 7-membered lactam oxime ether (tautomer of the corresponding nitrosocompound). Due to time limitations, work in this area could not be completed but this remains a promising avenue for future work.
2003-01-01T00:00:00ZBella, Antonio FrancoA summary of tin hydride mediated reactions in generating radicals in organic synthesis is presented, together with some of the many alternative methods available for conducting radical reactions. Particular attention has been given to the development of tin-free organic radical precursors. This is followed by three chapters describing research on the use of pro-aromatic 1-carbamoyl-l-methylcyclohexa-2,5-dienes as free-radical precursors.
A variety of 1 -carbamoyl-l-methylcyclohexa-2,5-dienes, TV-benzyl protected-amide, free-radical precursors have been prepared and utilised in subsequent experiments. EPR studies confirmed the formation of the delocalised cyclohexadienyl radical at low temperatures. At higher temperatures cyclohexadienyl radicals underwent homolysis with release of the associated aminoacyl (carbamoyl) radicals. Measurement of radical concentrations in DTBP solution from the aquired EPR spectra allowed us to calculate the rates of dissociation for several of these aminoacyl radicals. We concluded that the dissociations of cyclohexadienyl radicals, and the carbamoyl radical cyclisations, were both fast enough for chain propagation to be sustained.
The formation of pyrrolidin-2-ones was tested by examining the decomposition of but3-enyl amides induced thermally with dibenzoyl peroxide. 3-Alkyl-TVbenzylpyrrolidin-2-ones were obtained in moderate yields, along with significant amounts of the corresponding formamides. Reactions with other initiators, including photochemical processes with di-/-butyl peroxide, showed no significant advantage. A cyclohexadienyl amide containing bis-methyl substitution of the butenyl chain was prepared; in the hope that ring closure of the carbamoyl radical would be more efficient because of a Thorpe-Ingold effect. In practice, the yield of the corresponding pyrrolidinone was a disappointing 20 %. Evidence from characterisation of byproducts suggested that radical-radical reactions were important.
The use of cyclohexadienyl amides for the preparation of (β-lactams was also investigated. The cinnamyl-substituted amide 144 (Chapter 3) was chosen because the phenyl substituent confers resonance stabilisation on the cyclised radical and hence should expedite the 4-exo-cyclisation step. However, as an additional consequence of this resonance stabilisation the hydrogen-atom abstraction step was disfavoured. The thermal and photochemical reactions gave the corresponding azetidin-2-one, in low yields. Addition of a good H-atom donor enabled the ring closed benzyl type radical to be trapped. Reactions initiated with di-/-butyl peroxyoxalate, including 1.2 mol equiv. of methyl thioglycolate (RSH) produced 1,3-dibenzylazetidinone (148, Chapter 3) in increased yields. When a catalytic amount of RSH was employed, the (3- lactam yield increased, but radical-radical reactions again became important. Use of lauroyl peroxide as initiator, in concert with 1 equiv. of RSH, led to a greatly improved (3-lactam yield. It is likely that polarity reversal catalysis played a part in enhancing the yield of (3-lactam. The azetidinylbenzyl radical is resonance stabilised and nucleophilic. Hence a polar effect favoured hydrogen-abstraction from the electronegative RSH. The electrophilic thiyl radical (RS*) generated in this way, in turn, abstracted more readily from the cyclohexadienyl site thus regenerating RSH and continuing the chain. In the lauroyl peroxide initiated reactions, products derived from the initiator included undecane and docosane which significantly increased the viscosity of the reaction medium thus slowing radical-radical reactions which are normally diffusion controlled.
Overall, the induced carbamoyl-cyclohexadiene decompositions represent novel, comparatively 'clean', tin-free radical routes that are applicable for the preparation of a range of lactams from secondary amine starting materials. Inclusion of methyl thioglycolate in the reaction medium leads to increased lactam yields. Cyclisation onto an oxime ether C=N double bond was faster and more efficient, and the product heterocycles contain N-functionality at C(3), exactly as required in many antibiotics. Amidocyclohexadiene precursors containing oxime ether functionality were therefore designed and assembled. The radical-induced decompositions were studied by EPR spectroscopy which showed the expected cyclohexadienyl radicals at low temperatures. At higher temperatures, alkoxyaminyl radicals were also observed.
Cyclisations of the corresponding carbamoyl radicals were so fast that they were not observable by EPR spectra. When reactions were carried out preparatively, amino benzopyrrolidinone derivatives were isolated in good yields. Addition of methyl thioglycolate in dilauroyl peroxide mediated radical reactions, again improved product yields. An elegant use of O-trityl oxime ethers, in which the oxime functionality was ultimately regenerated had attracted our attention. We sought to adapt this tactic to our system and, accordingly, we prepared an O-trityl oxime ether substituted cyclohexadienecarboxamide precursor. The standard initiation followed by (3-scission of the cyclohexadienyl radical, produced the corresponding carbamoyl radical which ring closed to yield the alkoxyaminyl radical. However, the reaction took a novel route because trityl alkoxyaminyl radicals containing O-trityl moiety, underwent a second [3- scission to extrude the highly stabilised trityl radical with production of a nitrosocompound.
The use of our strategy was planned for a tin-free, radical-mediated synthesis of benzepril (ACE inhibitor). 7-exo-ring closure onto the oxime ether radical acceptor would be sufficiently rapid to facilitate the otherwise difficult ring closure. Carbamoyl radical released from a specifically designed 1-methylcyclohexadiene carboxamide containing O-trityl oxime ether moiety would undergo 7-exo-cyclisation to afford the desired 7-membered lactam oxime ether (tautomer of the corresponding nitrosocompound). Due to time limitations, work in this area could not be completed but this remains a promising avenue for future work.Substitution reactions of arylated oxadiazoles and related compoundsSagar, Anthony John Granthttps://hdl.handle.net/10023/218982022-01-06T10:22:02Z1978-01-01T00:00:00ZThe nitrations of 2,5-diphenyl-1,3,4-oxadiazole and 2,5-diphenyloxazole are investigated. Previously, there have been problems associated with the separation of isomeric products in such reactions. We have developed separation methods for the products by using high performance liquid chromatography.
In the nitration of 2,5-diphenyl-1,3,4-oxadiazole, considerable variations in the isomer ratios are found when the acid strength of the nitrating medium is altered. In fuming nitric acid alone the orientation is mainly para/meta but with fuming nitric acid in concentrated sulphuric acid a large enhancement in meta-orientation occurs. With nitronium tetrafluoroborate an enhancement in ortho-substitution is found.
In an attempt to explain these results 2-nitrophenyl-5-phenyl-1,3,4-oxadiazole isomers were nitrated under the same conditions as above. With fuming.nitric acid the three mono-nitro isomers give approximately 45% para-substitution. With fuming nitric acid in sulphuric acid the p:m:o ratio is approximately 1:3:1. With nitronium tetrafluoroborate there is a large increase in ortho -substitution.
The first and second nitrations were found to be consecutive for the nitration in fuming nitric acid and p:m:o ratios for the first nitration are calculated.
Possible reasons for the variations in isomer ratios are discussed. It is proposed that the oxadiazole ring is protonated in concentrated sulphuric acid and that the enhancement in meta-nitration in the second nitration is due to a positive pole effect. It is proposed that N-nitration accounts for the enhancement in ortho-nitration in nitronium tetrafluoroborate. Analogous systems do not provide a good comparison e.g. 2,5-diphenyloxazole gives mainly parasubstitution.
The brominations of some 2,5-diphenyl-1,3,4- oxadiazoles, in oleum, are investigated. The products were identified by hydrolysis of the brominated oxadiazole and inspection of the esterified hydrolysis product by h.p.l.c. Most of the esters were found to contain a bromine atom in the meta-position. Mono- , di-, tri-,tetra-and pentabromo species were identified by mass spectroscopy.
1978-01-01T00:00:00ZSagar, Anthony John GrantThe nitrations of 2,5-diphenyl-1,3,4-oxadiazole and 2,5-diphenyloxazole are investigated. Previously, there have been problems associated with the separation of isomeric products in such reactions. We have developed separation methods for the products by using high performance liquid chromatography.
In the nitration of 2,5-diphenyl-1,3,4-oxadiazole, considerable variations in the isomer ratios are found when the acid strength of the nitrating medium is altered. In fuming nitric acid alone the orientation is mainly para/meta but with fuming nitric acid in concentrated sulphuric acid a large enhancement in meta-orientation occurs. With nitronium tetrafluoroborate an enhancement in ortho-substitution is found.
In an attempt to explain these results 2-nitrophenyl-5-phenyl-1,3,4-oxadiazole isomers were nitrated under the same conditions as above. With fuming.nitric acid the three mono-nitro isomers give approximately 45% para-substitution. With fuming nitric acid in sulphuric acid the p:m:o ratio is approximately 1:3:1. With nitronium tetrafluoroborate there is a large increase in ortho -substitution.
The first and second nitrations were found to be consecutive for the nitration in fuming nitric acid and p:m:o ratios for the first nitration are calculated.
Possible reasons for the variations in isomer ratios are discussed. It is proposed that the oxadiazole ring is protonated in concentrated sulphuric acid and that the enhancement in meta-nitration in the second nitration is due to a positive pole effect. It is proposed that N-nitration accounts for the enhancement in ortho-nitration in nitronium tetrafluoroborate. Analogous systems do not provide a good comparison e.g. 2,5-diphenyloxazole gives mainly parasubstitution.
The brominations of some 2,5-diphenyl-1,3,4- oxadiazoles, in oleum, are investigated. The products were identified by hydrolysis of the brominated oxadiazole and inspection of the esterified hydrolysis product by h.p.l.c. Most of the esters were found to contain a bromine atom in the meta-position. Mono- , di-, tri-,tetra-and pentabromo species were identified by mass spectroscopy.Investigation of sodium nitroprusside and its ruthenium analoguesBarclay, Anne E.https://hdl.handle.net/10023/218912022-01-05T09:39:37Z1988-01-01T00:00:00ZThis thesis describes the work conducted in two main areas - one concerning sodium nitroprusside, and the second concerning its ruthenium analogues. The first chapter is a general introduction to the historical background to the work. Chapter II reports the experimental work concerning the reactions of sodium nitroprusside with various amines and the conclusions drawn from this and earlier work with other compounds concerning the in vivo reaction when nitroprusside is employed as a hypotensive agent. Chapter III discusses the decomposition of nitroprusside and examines various detection methods for cyanide and thiocyanate; the effect of the enzyme rhodanese on the compound is also studied. Chapter IV is a review of the structure and bonding of nitrosyl complexes of ruthenium, a brief look at their reactions is also presented. Chapter V describes the preparation of sodium pentacyanonitrosyruthenate(II) , its physical properties and a mechanistic study of its reactions with hydroxide, sulphide, amines and carbanions; comparison to the iron analogue nitroprusside is made where appropriate. Chapter VI describes the preparation of sodium pentachloronitrosylruthenate(II), its physical properties and chemical reactions. The results from clinical tests of this and the pentacyanonitrosyl complex are reported.
1988-01-01T00:00:00ZBarclay, Anne E.This thesis describes the work conducted in two main areas - one concerning sodium nitroprusside, and the second concerning its ruthenium analogues. The first chapter is a general introduction to the historical background to the work. Chapter II reports the experimental work concerning the reactions of sodium nitroprusside with various amines and the conclusions drawn from this and earlier work with other compounds concerning the in vivo reaction when nitroprusside is employed as a hypotensive agent. Chapter III discusses the decomposition of nitroprusside and examines various detection methods for cyanide and thiocyanate; the effect of the enzyme rhodanese on the compound is also studied. Chapter IV is a review of the structure and bonding of nitrosyl complexes of ruthenium, a brief look at their reactions is also presented. Chapter V describes the preparation of sodium pentacyanonitrosyruthenate(II) , its physical properties and a mechanistic study of its reactions with hydroxide, sulphide, amines and carbanions; comparison to the iron analogue nitroprusside is made where appropriate. Chapter VI describes the preparation of sodium pentachloronitrosylruthenate(II), its physical properties and chemical reactions. The results from clinical tests of this and the pentacyanonitrosyl complex are reported.Studies on alkylresorcinols and novel analoguesTalbot, Anna Elizabethhttps://hdl.handle.net/10023/218892021-11-24T12:41:35Z2006-01-01T00:00:00ZAlkylresorcinols such as 1,3-dihydroxy-5-alkylbenzenes have been found to have a number of biological activites including antiparasitic, cytotoxic, fungicidal and bacteriocidal properties that act against various pathogens. These resorcinols have been found to be present and have been isolated from a range of plants in the Ancircardiaceae Ginkgoaceae and Graminae families.
Alkylresorcinols have previously been synthesised by various routes, with the attachment of the side chain being the most challenging aspect of the synthesis. For comprehensive studies on their structure-activity relationships, an efficient synthetic route therefore needs to be found. Alkylresorcinols were to be used as standards in GC-MS and LC-MS based analytical methods for the detection and quantification of alkylresorcinols in human fluids. Carboxyalkylresorcinols were required for the development of new automated immunoassays of alkylresorcinols from biological samples.
The work towards the synthesis of a number of novel analogues of resorcinol was achieved, namely 15-(3',5'-dihydroxyphenyl)pentadecane via a Suzuki coupling reaction; 16-(3',5'-dihydroxyphenyl)hexadecanoic acid via an iron(III) catalysed carbon-carbon coupling reaction employing a grignard reagent; 16-(3',5'-dihydroxyphenyl)hexadecane, 17-(3' ,5' -dihydroxyphenyl)heptadecanoic acid, 21 -(3',5'-dihydroxyphenyl)henicosanoic acid and 19-(3',5'-dihydroxyphenyl)nonadecanoic acid employing standard conditions of Wittig reactions.
2006-01-01T00:00:00ZTalbot, Anna ElizabethAlkylresorcinols such as 1,3-dihydroxy-5-alkylbenzenes have been found to have a number of biological activites including antiparasitic, cytotoxic, fungicidal and bacteriocidal properties that act against various pathogens. These resorcinols have been found to be present and have been isolated from a range of plants in the Ancircardiaceae Ginkgoaceae and Graminae families.
Alkylresorcinols have previously been synthesised by various routes, with the attachment of the side chain being the most challenging aspect of the synthesis. For comprehensive studies on their structure-activity relationships, an efficient synthetic route therefore needs to be found. Alkylresorcinols were to be used as standards in GC-MS and LC-MS based analytical methods for the detection and quantification of alkylresorcinols in human fluids. Carboxyalkylresorcinols were required for the development of new automated immunoassays of alkylresorcinols from biological samples.
The work towards the synthesis of a number of novel analogues of resorcinol was achieved, namely 15-(3',5'-dihydroxyphenyl)pentadecane via a Suzuki coupling reaction; 16-(3',5'-dihydroxyphenyl)hexadecanoic acid via an iron(III) catalysed carbon-carbon coupling reaction employing a grignard reagent; 16-(3',5'-dihydroxyphenyl)hexadecane, 17-(3' ,5' -dihydroxyphenyl)heptadecanoic acid, 21 -(3',5'-dihydroxyphenyl)henicosanoic acid and 19-(3',5'-dihydroxyphenyl)nonadecanoic acid employing standard conditions of Wittig reactions.Niobium based materials for use as current collectors in the anode of solid oxide fuel cellsLashtabeg, Annahttps://hdl.handle.net/10023/218862021-11-24T10:17:21Z2004-01-01T00:00:00ZIn this work I present the results of my studies on a series of reduced niobium based rutile structures: Nb₂TiO₇ doped with Fe and Zr, Ti₁₋₂ₓCrₓNbₓO₂ solid solution series. Strontium niobates of the stoichiometry Sr₄Nb₂O₉, Sr₂Nb₂O₇, Sr₂Nb₂O₆ and their reduced phases were also investigated, along with CaNb₂O₆ and BaNb₂O₆.
Thermal expansion and electronic conductivity of these materials were investigated under oxidising and reducing conditions. Nb₂TiO₇ goes to rutile structure Nb ₁.₃₃Ti₀.₆₇O₄ under reducing conditions, and this has the highest conductivity of all materials investigated at 300 Scm⁻¹ at 900°C with p(O₂)=10⁻²⁰ atm, but the lowest thermal expansion of 3.00±0.05x10⁻⁶ K⁻¹ (100°C-900°C), which is incompatible with the thermal expansion coefficient of the Ni/YSZ anode in the solid oxide fuel cell of 10.3x10⁻⁶ K⁻¹. Doping Nb ₁.₃₃Ti₀.₆₇O₄ decreases its conductivity, but increases its thermal expansion to a maximum of 6.3x10⁻⁶ K⁻¹ for Nb₁.₃₄₇Ti₀.₆₃₉Fe₀.₀₀₁₄O₄.
The Ti₁₋₂ₓCrₓNbₓO₂ solid solution series shows a maximum thermal expansion of 8.5x10⁻⁶ K⁻¹ for x=0.1 which then drops with increasing x to 5.6x10⁻⁶ K⁻¹ for x=0.5. The conductivity of these samples, however, reaches a maximum of ~20Scm⁻¹ at p(O₂)=10⁻²⁰ atm at 900°C for x=0.1-0.3, then drops to ~10 Scm⁻¹ for x=0.4 and -6 Scm⁻¹ for x=0.5.
Sr₄Nb₂O₉, Sr₂Nb₂O₇, SrNb₂O₆, CaNb₂O₆, and BaNb₂O₆, all show fairly poor electronic conductivities in air and 5%H₂/Ar (p(O₂)=10⁻²⁰ atm) at 900°C which make them unsuitable for use in the anode of the SOFC. Structurally they are very stable to reducing conditions up to 1200°-1300°C in 5% H₂/Ar compared to Nb₂TiO₇ whose structure changes to rutile upon reduction.
In the systems studied, there are two types of conductivity that dominate. BaNb₂O₆ or Sr₂Nb₂O₇ show a linear dependence over the p(O₂) range with simple defect equilibrium and fair kinetics. The rutile Ti₁₋₂ₓCrₓNbₓO₂ series, on the other hand, shows complex phase transitions throughout the p(O₂) range with kinetically limited reduction.
2004-01-01T00:00:00ZLashtabeg, AnnaIn this work I present the results of my studies on a series of reduced niobium based rutile structures: Nb₂TiO₇ doped with Fe and Zr, Ti₁₋₂ₓCrₓNbₓO₂ solid solution series. Strontium niobates of the stoichiometry Sr₄Nb₂O₉, Sr₂Nb₂O₇, Sr₂Nb₂O₆ and their reduced phases were also investigated, along with CaNb₂O₆ and BaNb₂O₆.
Thermal expansion and electronic conductivity of these materials were investigated under oxidising and reducing conditions. Nb₂TiO₇ goes to rutile structure Nb ₁.₃₃Ti₀.₆₇O₄ under reducing conditions, and this has the highest conductivity of all materials investigated at 300 Scm⁻¹ at 900°C with p(O₂)=10⁻²⁰ atm, but the lowest thermal expansion of 3.00±0.05x10⁻⁶ K⁻¹ (100°C-900°C), which is incompatible with the thermal expansion coefficient of the Ni/YSZ anode in the solid oxide fuel cell of 10.3x10⁻⁶ K⁻¹. Doping Nb ₁.₃₃Ti₀.₆₇O₄ decreases its conductivity, but increases its thermal expansion to a maximum of 6.3x10⁻⁶ K⁻¹ for Nb₁.₃₄₇Ti₀.₆₃₉Fe₀.₀₀₁₄O₄.
The Ti₁₋₂ₓCrₓNbₓO₂ solid solution series shows a maximum thermal expansion of 8.5x10⁻⁶ K⁻¹ for x=0.1 which then drops with increasing x to 5.6x10⁻⁶ K⁻¹ for x=0.5. The conductivity of these samples, however, reaches a maximum of ~20Scm⁻¹ at p(O₂)=10⁻²⁰ atm at 900°C for x=0.1-0.3, then drops to ~10 Scm⁻¹ for x=0.4 and -6 Scm⁻¹ for x=0.5.
Sr₄Nb₂O₉, Sr₂Nb₂O₇, SrNb₂O₆, CaNb₂O₆, and BaNb₂O₆, all show fairly poor electronic conductivities in air and 5%H₂/Ar (p(O₂)=10⁻²⁰ atm) at 900°C which make them unsuitable for use in the anode of the SOFC. Structurally they are very stable to reducing conditions up to 1200°-1300°C in 5% H₂/Ar compared to Nb₂TiO₇ whose structure changes to rutile upon reduction.
In the systems studied, there are two types of conductivity that dominate. BaNb₂O₆ or Sr₂Nb₂O₇ show a linear dependence over the p(O₂) range with simple defect equilibrium and fair kinetics. The rutile Ti₁₋₂ₓCrₓNbₓO₂ series, on the other hand, shows complex phase transitions throughout the p(O₂) range with kinetically limited reduction.Some aspects of phosphorus halide chemistryMacPherson, Angus Iain Thomsonhttps://hdl.handle.net/10023/218822021-11-17T10:43:34Z1970-01-01T00:00:00Z1970-01-01T00:00:00ZMacPherson, Angus Iain Thomson2, 3 - dihydro - 1, 4 - diazepinesGorringe, Anita Michaellehttps://hdl.handle.net/10023/218842021-11-17T11:23:38Z1968-01-01T00:00:00Z1968-01-01T00:00:00ZGorringe, Anita MichaelleThe surface Raman spectroscopy of polymer-modified electrodesTaylor, Andrew Peterhttps://hdl.handle.net/10023/218752021-11-16T16:59:46Z1996-01-01T00:00:00ZApplications of surface-enhanced Raman spectroscopies and the quartz crystal microbalance to electrode interfaces, especially polymer-modified electrodes, are investigated. The quartz crystal microbalance is used to investigate the adsorption of pyridine at electrochemically roughened silver electrodes from aqueous chloride electrolyte, using conditions comparable to those used in SERS studies. During roughening in aqueous chloride solution, delays seen between the onset of oxidation and reduction at the Ag surface and the commencement of frequency decrease and increase, respectively, are explained by release of trapped species upon initial formation of the AgCl layer and then re-trapping upon reduction. At anodic limits of +0.25 V and above, the reduction proceeds in two steps representing the reduction of two separate silver chloride phases. Below the silver oxidation potential corrosion inhibition of the silver surface by pyridine leads to a lower hysteresis between cathodic and anodic sweeps in the frequency vs potential plots when the heterocycle is present in solution. The most intense pyridine SERS spectra occur at potentials where the frequency of the quartz crystal is highest, suggesting that adsorption of the organic species leads to break-down of long-range viscous coupling of solvent to the surface via hydrogen-bonding interactions. Full assignments of the SERS spectrum of pyridine-d₅ are reported.
SERS spectra of 4-vinyl pyridine and poly(4-vinyl)pyridine at the silver electrode are reported and assigned. At negative potentials free-radical polymerization of the monomer and short-chain polymers can be initiated by H*. When dissolved oxygen is present, surface bound and organic peroxides may also be formed and bands due to these are assigned. SERRS spectra of [PVP-M(bpy) ₂Cl]Cl (M = Ru or Os) adsorbed layers show typical 2,2'-bipyridine dominated spectra at Ag. Small changes in band positions due the oxidation of Os(II) to Os(III) were observed at a gold electrode for the 1400 -1700 cm⁻ ¹ region.
The metallopolymers are used as model systems for the quantification of the SERRS signal in polymer-modified electrodes, plots for intensity vs surface coverage of metal centres being obtained as a function of loading (py:M ratio) at a constant deposition mass and as a function of deposition mass at a constant loading. At very low surface coverages the attenuation adjusted intensity can be modelled as a Freundlich isotherm with I = 1.41c ⁰.³⁷ (c = the concentration, in moldm⁻³, of Ru centres in the film). At higher coverages surface plasmon damping and the increasing importance of resonance Raman scattering lead to substantial deviation from this equation. The potential of SERS for obtaining partition coefficients and diffusion coefficients of ions into polymer films is considered.
A series of Crᴵᴵᴵ(bpy)₂(L)(L') {L = OH, L' = OH₂ monomer and dimer; L = L' = CI; and L = poly(acrylic acid), no L') complexes are studied at glassy carbon by cyclic voltammetry and at silver by SERRS. Slow electron transfer in the reduction of Cr(III) to Cr(II) means that reduction waves are only observed for adsorbed species. The reduced species undergo ligand substitution reactions, and at a PVP modified electrode the dichloride can be reductively electrolyzed to form [(PVP)₂-Cr(bpy)₂]³⁺ (E0j/2 = -0.32 V vs SCE). Surface Raman spectra of the reduced complexes are thought to be in resonance with a broad ligand 𝜋7 𝜋10* transition of the bipyridine radical anion, resulting in spectra which indicate that the electron is localized on one bipyridine. The aquahydroxo complexes, which have an initial 2+ charge per Cr centre, adsorb strongly at the Ag surface, as evidenced by a broad Cr-0 vibration at around 550 cm-1 and by the fact that they stabilize the surface against chloride desorption and therefore show intense SERRS spectra at -1.1 V vs Ag / AgCl. The dichloro and poly(acrylic acid) complexes, which have an initial 1+ charge, do not show similar stabilization of SERRS sites.
1996-01-01T00:00:00ZTaylor, Andrew PeterApplications of surface-enhanced Raman spectroscopies and the quartz crystal microbalance to electrode interfaces, especially polymer-modified electrodes, are investigated. The quartz crystal microbalance is used to investigate the adsorption of pyridine at electrochemically roughened silver electrodes from aqueous chloride electrolyte, using conditions comparable to those used in SERS studies. During roughening in aqueous chloride solution, delays seen between the onset of oxidation and reduction at the Ag surface and the commencement of frequency decrease and increase, respectively, are explained by release of trapped species upon initial formation of the AgCl layer and then re-trapping upon reduction. At anodic limits of +0.25 V and above, the reduction proceeds in two steps representing the reduction of two separate silver chloride phases. Below the silver oxidation potential corrosion inhibition of the silver surface by pyridine leads to a lower hysteresis between cathodic and anodic sweeps in the frequency vs potential plots when the heterocycle is present in solution. The most intense pyridine SERS spectra occur at potentials where the frequency of the quartz crystal is highest, suggesting that adsorption of the organic species leads to break-down of long-range viscous coupling of solvent to the surface via hydrogen-bonding interactions. Full assignments of the SERS spectrum of pyridine-d₅ are reported.
SERS spectra of 4-vinyl pyridine and poly(4-vinyl)pyridine at the silver electrode are reported and assigned. At negative potentials free-radical polymerization of the monomer and short-chain polymers can be initiated by H*. When dissolved oxygen is present, surface bound and organic peroxides may also be formed and bands due to these are assigned. SERRS spectra of [PVP-M(bpy) ₂Cl]Cl (M = Ru or Os) adsorbed layers show typical 2,2'-bipyridine dominated spectra at Ag. Small changes in band positions due the oxidation of Os(II) to Os(III) were observed at a gold electrode for the 1400 -1700 cm⁻ ¹ region.
The metallopolymers are used as model systems for the quantification of the SERRS signal in polymer-modified electrodes, plots for intensity vs surface coverage of metal centres being obtained as a function of loading (py:M ratio) at a constant deposition mass and as a function of deposition mass at a constant loading. At very low surface coverages the attenuation adjusted intensity can be modelled as a Freundlich isotherm with I = 1.41c ⁰.³⁷ (c = the concentration, in moldm⁻³, of Ru centres in the film). At higher coverages surface plasmon damping and the increasing importance of resonance Raman scattering lead to substantial deviation from this equation. The potential of SERS for obtaining partition coefficients and diffusion coefficients of ions into polymer films is considered.
A series of Crᴵᴵᴵ(bpy)₂(L)(L') {L = OH, L' = OH₂ monomer and dimer; L = L' = CI; and L = poly(acrylic acid), no L') complexes are studied at glassy carbon by cyclic voltammetry and at silver by SERRS. Slow electron transfer in the reduction of Cr(III) to Cr(II) means that reduction waves are only observed for adsorbed species. The reduced species undergo ligand substitution reactions, and at a PVP modified electrode the dichloride can be reductively electrolyzed to form [(PVP)₂-Cr(bpy)₂]³⁺ (E0j/2 = -0.32 V vs SCE). Surface Raman spectra of the reduced complexes are thought to be in resonance with a broad ligand 𝜋7 𝜋10* transition of the bipyridine radical anion, resulting in spectra which indicate that the electron is localized on one bipyridine. The aquahydroxo complexes, which have an initial 2+ charge per Cr centre, adsorb strongly at the Ag surface, as evidenced by a broad Cr-0 vibration at around 550 cm-1 and by the fact that they stabilize the surface against chloride desorption and therefore show intense SERRS spectra at -1.1 V vs Ag / AgCl. The dichloro and poly(acrylic acid) complexes, which have an initial 1+ charge, do not show similar stabilization of SERRS sites.New free-radical precursors and pathwaysMcCarroll, Andrew J.https://hdl.handle.net/10023/218682021-11-15T16:30:17Z2000-01-01T00:00:00ZA method of cataloguing sequential radical reactions according to the individual processes taking place has been described. The system has been used to illustrate the range and power of radical reactions in synthesis, in particular emphasising cascade reactions mediated by reagents that do not contain toxic tin. Of primary consideration were consecutive intramolecular processes, but annulation reactions, in which intermolecular additions precede cyclisations, were also discussed.
An EPR and product analysis investigation into the radical reactions of aryl aldoxime esters and ethers is described. O-acyl derivatives of benzaldoxime, 2,4-dimethoxybenzaldoxime and 2,4,6-trimethoxybenzaldoxime underwent direct cleavage of the N-O bond on photolysis, forming an iminyl radical and an alkyl radical via decarboxylation. Synthesis of these precursors from the corresponding carboxylic acid was high yielding, and purification was usually simple. The radicals produced by this method underwent cyclisation when appropriate unsaturation was present. Use of carbon tetrachloride as solvent enabled synthesis of chlorinated products. We have shown that p-methoxyacetophenone acts as a sensitiser in these reactions. The formation of iminyl radicals enabled g-factors of alkyl radicals to be calculated simply in EPR experiments, while not interfering with the main spectrum. Cleavage of the N-O bond in O-alkyl arylaldoximes was much less efficient, and cannot be used as a synthetic method. Radical addition to the iminyl double bond was a more efficient process.
The ability of cyclohexadienones to act as radical precursors was investigated. Preparations of suitable precursors were not efficient enough to enable the technique to be synthetically useful. 2-Allyl-2,4,6-trimethylcyclohexa-3,5-dien-l-one, 10a, and 4-allyl-2,4,6-trimethylcyclohexa-2,5-dien-l-one, 11a, expelled the allyl radical on reaction with the trimethylstannyl radical, as evidenced by EPR spectroscopy. 2-Benzyl-2,4,6 trimethylcyclohexa-3,5-dien-l-one 10b acted as a precursor to the benzyl radical, and toluene product was identified by GC/MS analysis.
Samarium(II) iodide was shown to be a suitable reagent for performing radical annulation reactions. The cyclopentenol derivatives obtained in this study readily dehydrated, and in at least one case underwent thermal rearrangement. Tin based methods were shown to be much less suitable for annulations, while manganese(III) picolinate based annulations were not investigated due to low yielding precursor preparations.
Radicals containing a boronic ester group have been characterised by EPR spectroscopy. The boronic ester group was shown to provide little stabilisation to an adjacent radical centre. The barrier to rotation around the C-B bond in unsymmetric radical 5b was determined as 2.9 ± 0.7 kcal mob1. Hydrogen abstraction from methylboronic ester 8 by the t-butoxyl radical was shown to not be facile, and homolytic substitution was competitive. Addition to vinylboronic ester 12 by nucleophilic radicals was efficient under EPR conditions. P-Bromoboronic esters are susceptible to homolytic substitution at the boron centre under certain conditions. At lower temperatures, bromine abstraction occurs readily.
2000-01-01T00:00:00ZMcCarroll, Andrew J.A method of cataloguing sequential radical reactions according to the individual processes taking place has been described. The system has been used to illustrate the range and power of radical reactions in synthesis, in particular emphasising cascade reactions mediated by reagents that do not contain toxic tin. Of primary consideration were consecutive intramolecular processes, but annulation reactions, in which intermolecular additions precede cyclisations, were also discussed.
An EPR and product analysis investigation into the radical reactions of aryl aldoxime esters and ethers is described. O-acyl derivatives of benzaldoxime, 2,4-dimethoxybenzaldoxime and 2,4,6-trimethoxybenzaldoxime underwent direct cleavage of the N-O bond on photolysis, forming an iminyl radical and an alkyl radical via decarboxylation. Synthesis of these precursors from the corresponding carboxylic acid was high yielding, and purification was usually simple. The radicals produced by this method underwent cyclisation when appropriate unsaturation was present. Use of carbon tetrachloride as solvent enabled synthesis of chlorinated products. We have shown that p-methoxyacetophenone acts as a sensitiser in these reactions. The formation of iminyl radicals enabled g-factors of alkyl radicals to be calculated simply in EPR experiments, while not interfering with the main spectrum. Cleavage of the N-O bond in O-alkyl arylaldoximes was much less efficient, and cannot be used as a synthetic method. Radical addition to the iminyl double bond was a more efficient process.
The ability of cyclohexadienones to act as radical precursors was investigated. Preparations of suitable precursors were not efficient enough to enable the technique to be synthetically useful. 2-Allyl-2,4,6-trimethylcyclohexa-3,5-dien-l-one, 10a, and 4-allyl-2,4,6-trimethylcyclohexa-2,5-dien-l-one, 11a, expelled the allyl radical on reaction with the trimethylstannyl radical, as evidenced by EPR spectroscopy. 2-Benzyl-2,4,6 trimethylcyclohexa-3,5-dien-l-one 10b acted as a precursor to the benzyl radical, and toluene product was identified by GC/MS analysis.
Samarium(II) iodide was shown to be a suitable reagent for performing radical annulation reactions. The cyclopentenol derivatives obtained in this study readily dehydrated, and in at least one case underwent thermal rearrangement. Tin based methods were shown to be much less suitable for annulations, while manganese(III) picolinate based annulations were not investigated due to low yielding precursor preparations.
Radicals containing a boronic ester group have been characterised by EPR spectroscopy. The boronic ester group was shown to provide little stabilisation to an adjacent radical centre. The barrier to rotation around the C-B bond in unsymmetric radical 5b was determined as 2.9 ± 0.7 kcal mob1. Hydrogen abstraction from methylboronic ester 8 by the t-butoxyl radical was shown to not be facile, and homolytic substitution was competitive. Addition to vinylboronic ester 12 by nucleophilic radicals was efficient under EPR conditions. P-Bromoboronic esters are susceptible to homolytic substitution at the boron centre under certain conditions. At lower temperatures, bromine abstraction occurs readily.Free radical rearrangements in synthesisHindson, Andrew Charleshttps://hdl.handle.net/10023/218652021-10-28T15:52:56Z1993-01-01T00:00:00ZIn chapter 1, the syntheses of a number of 2,2- disubstituted 4,7- dihydro-l,3-dioxepins are described, together with EPR studies on the radicals derived from these compounds. In the case of 2-bromomethyl-2- phenyl-4,7-dihydro-l,3-dioxepin, bromine abstraction was achieved with tin radicals to yield a CH₂. rotor type radical. This radical was studied by EPR spectroscopy and an exchange broadening process was observed. The experimental spectra were computer simulated in order to obtain the best fit rate constants and hence calculate the activation energy for rotation of the CH₂. group, which was found to be 7.7 kcal mol⁻¹. The transannular cyclisation of this compound was investigated, using the Bu₃SnH reduction method, the product proportions being measured by g.c. analysis. The rate constant and activation energy for the cyclisation were calculated to be kc₍₂₉₈₎ = 4.9 x 10^5 s⁻¹, Eₐ= 9.02 kcal mol⁻¹. The hydrolysis reaction of the bicyclic ketal produced by cyclisation, l-phenyl-2,7-dioxabicyclo[3.2.1]octane was investigated. EPR studies were carried out on the allyl type radicals formed by hydrogen abstraction from the C(4) or C(7) positions on the 1,3-dioxepin molecules. In the case of the 2,2-dimethyl-, and 2,2-diethyl-1,3-dioxepins, the exchange broadening process observed ( due to conformational changes in the ring ) was computer simulated and the activation energies for ring inversion were calculated to be 8.1 kcal mol⁻¹, and 6.1 kcal mol⁻¹respectively for the two compounds.
Chapter 2 reports the syntheses of some 2,2-disubstituted 4,7-dihydro-1.3-dithiepins. Several of these compounds were studied by EPR in the presence of t-BuO. radicals. The expected allyl type radical (analogous to that of the 1,3-dioxepins) was not observed. Instead another radical of a secondary nature was found to be present, formed either by rearrangement of the dithiepin molecule, or by some decomposition process. Some photolysis / product analysis type reactions were carried out on the dithiepins using GC / MS to identify the fragmentation products of these molecules.
Chapter 3 describes the EPR, photolysis, and bromination studies on three cyclic epoxides - cyclopentene oxide, cyclohexene oxide, and cyclo-octene oxide. Photolysis reactions were performed in the presence of CCl₃Br and di-tert butyl peroxide, and brominations involved NBS and Br₂/CCl₄ The products were analysed by GC/MS.
Chapter 4 describes the examination of " interior chain extension " type reactions, and the EPR study of a number of cyclopropane derivatives, together with the reactions of selected compounds with the radical precursors NBS and (Me₃Si₂)NBr.
1993-01-01T00:00:00ZHindson, Andrew CharlesIn chapter 1, the syntheses of a number of 2,2- disubstituted 4,7- dihydro-l,3-dioxepins are described, together with EPR studies on the radicals derived from these compounds. In the case of 2-bromomethyl-2- phenyl-4,7-dihydro-l,3-dioxepin, bromine abstraction was achieved with tin radicals to yield a CH₂. rotor type radical. This radical was studied by EPR spectroscopy and an exchange broadening process was observed. The experimental spectra were computer simulated in order to obtain the best fit rate constants and hence calculate the activation energy for rotation of the CH₂. group, which was found to be 7.7 kcal mol⁻¹. The transannular cyclisation of this compound was investigated, using the Bu₃SnH reduction method, the product proportions being measured by g.c. analysis. The rate constant and activation energy for the cyclisation were calculated to be kc₍₂₉₈₎ = 4.9 x 10^5 s⁻¹, Eₐ= 9.02 kcal mol⁻¹. The hydrolysis reaction of the bicyclic ketal produced by cyclisation, l-phenyl-2,7-dioxabicyclo[3.2.1]octane was investigated. EPR studies were carried out on the allyl type radicals formed by hydrogen abstraction from the C(4) or C(7) positions on the 1,3-dioxepin molecules. In the case of the 2,2-dimethyl-, and 2,2-diethyl-1,3-dioxepins, the exchange broadening process observed ( due to conformational changes in the ring ) was computer simulated and the activation energies for ring inversion were calculated to be 8.1 kcal mol⁻¹, and 6.1 kcal mol⁻¹respectively for the two compounds.
Chapter 2 reports the syntheses of some 2,2-disubstituted 4,7-dihydro-1.3-dithiepins. Several of these compounds were studied by EPR in the presence of t-BuO. radicals. The expected allyl type radical (analogous to that of the 1,3-dioxepins) was not observed. Instead another radical of a secondary nature was found to be present, formed either by rearrangement of the dithiepin molecule, or by some decomposition process. Some photolysis / product analysis type reactions were carried out on the dithiepins using GC / MS to identify the fragmentation products of these molecules.
Chapter 3 describes the EPR, photolysis, and bromination studies on three cyclic epoxides - cyclopentene oxide, cyclohexene oxide, and cyclo-octene oxide. Photolysis reactions were performed in the presence of CCl₃Br and di-tert butyl peroxide, and brominations involved NBS and Br₂/CCl₄ The products were analysed by GC/MS.
Chapter 4 describes the examination of " interior chain extension " type reactions, and the EPR study of a number of cyclopropane derivatives, together with the reactions of selected compounds with the radical precursors NBS and (Me₃Si₂)NBr.Synthetic and kinetic studies of macrocyclic metal complexesDanby, Andrew Markhttps://hdl.handle.net/10023/218632021-10-28T14:45:57Z1996-01-01T00:00:00ZThe chemistry of a series of pentaaza and hexaaza macrocycles formed by the metal directed condensation of formaldehyde, diamines and primary amines has been investigated. Structural studies were carried out and the results used to determine the extent of any long range interactions between the coordinated metal ion and non-coordinating amino groups. The effect of the uncoordinated tertiary amine on the square planar-octahedral spin equilibria was also studied. Chapter 2 investigates kinetic aspects of the chemistry of binuclear complexes of hexaaza macrocycles. The acid catalysed metal dissociation reactions of the copper(II) complexes of three ligands were studied. It was found that the two metal centres in such complexes act independently of each other. Activation parameters for the metal dissociation reactions have been determined.
Chapter 3 discusses cobalt(III) complexes of the tetraaza macrocycle [15]aneN₄. Kinetic and mechanistic studies have been carried out to study the decarboxylation reaction of [Co([15]aneN ₄)(CO₃)]⁺. A mechanism for this reaction is described. The kinetics ofthe hydrolysis of [Co([15]aneN₄)Cl₂]⁺ have also been investigated. The ring closure reactions of a linear β-aminoketone copper(II) complex to form the macrocyclic complex [Cu(trans[14]dieneN₄)]²⁺ have been studied kinetically. A mechanism involving an intramolecular reaction with a coordinated hydroxide group has been proposed. Attempts to synthesise macrocyclic tetraamide complexes via a literature method are described Evidence is presented which suggests that the preparation of such complexes by metal template directed condensation of diacids and diamines is not viable and this view has been confirmed by crystallographic studies.
1996-01-01T00:00:00ZDanby, Andrew MarkThe chemistry of a series of pentaaza and hexaaza macrocycles formed by the metal directed condensation of formaldehyde, diamines and primary amines has been investigated. Structural studies were carried out and the results used to determine the extent of any long range interactions between the coordinated metal ion and non-coordinating amino groups. The effect of the uncoordinated tertiary amine on the square planar-octahedral spin equilibria was also studied. Chapter 2 investigates kinetic aspects of the chemistry of binuclear complexes of hexaaza macrocycles. The acid catalysed metal dissociation reactions of the copper(II) complexes of three ligands were studied. It was found that the two metal centres in such complexes act independently of each other. Activation parameters for the metal dissociation reactions have been determined.
Chapter 3 discusses cobalt(III) complexes of the tetraaza macrocycle [15]aneN₄. Kinetic and mechanistic studies have been carried out to study the decarboxylation reaction of [Co([15]aneN ₄)(CO₃)]⁺. A mechanism for this reaction is described. The kinetics ofthe hydrolysis of [Co([15]aneN₄)Cl₂]⁺ have also been investigated. The ring closure reactions of a linear β-aminoketone copper(II) complex to form the macrocyclic complex [Cu(trans[14]dieneN₄)]²⁺ have been studied kinetically. A mechanism involving an intramolecular reaction with a coordinated hydroxide group has been proposed. Attempts to synthesise macrocyclic tetraamide complexes via a literature method are described Evidence is presented which suggests that the preparation of such complexes by metal template directed condensation of diacids and diamines is not viable and this view has been confirmed by crystallographic studies.Kinetics and mechanisms of some free radical reactionsEl-Soueni, Amr Kamal El-Dinehttps://hdl.handle.net/10023/218582021-10-29T02:08:22Z1979-01-01T00:00:00ZThis thesis consists of four parts. The main two parts provide more kinetic data on free radical addition reactions. This data is used to extend existing theories. The data obtained in the first part filled an important gap in kinetic data for radical addition reactions. These data of perfluoro-ethyl radical addition to ethylene and fluoro-ethylenes provided data for an increasing branching in the series CF₃., CF₃CF₂, (CF₃)₂CF. and (CF₃)₃C. Radicals and in addition for an increasing chain length in the series CF₃ ., CF₃CF₂. CF₃CF₂CF₂, and CF₃(CF₂)₂CF₂.radicals. The new data followed the sequence expected and established that the reson¬ ance stabilisation of the adduct radical in radical addition reactions to olefins is of minor importance. Instead there is a complex interplay of polar, steric and bond strength terms, all of which are necessarily inter-related in governing the rate and orientation of free radical addition reactions. The second part involved the addition of trifluoromethyl radicals to acetylene, alkyl and fluoroalkyl substituted acetylenes. The results showed similarity in the rates and orientation of addition to acetylenes and the corresponding sub¬ stituted ethylenes. This reveals that the substituents have very similar effects on the reactivity of the double and triple bonds. On the other hand, the Arrhenius parameters were significantly higher for the addition to acetylenes compared to the addition to ethylenes. This confirmed the transition theory predictions. The work also offers a study of the stereospecificity of the addition reaction with acetylenes. The third part involves the addition of trifluoromethyl radicals to 1,3-butadiene, isoprene, trans-piperylene and vinyl acetylene. The stereospecificity of the addition reaction with 1, 3-butadiene was studied.
The fourth part deals with the topic "homosolvolysis", a study of the homolysis of carbon-halogen, carbon-metal, metal-metal and metal-halogen bonds using di-t-butylnitroxide and 2,2,5,5-tetramethylpyrrolydine nitroxide as solvents.
1979-01-01T00:00:00ZEl-Soueni, Amr Kamal El-DineThis thesis consists of four parts. The main two parts provide more kinetic data on free radical addition reactions. This data is used to extend existing theories. The data obtained in the first part filled an important gap in kinetic data for radical addition reactions. These data of perfluoro-ethyl radical addition to ethylene and fluoro-ethylenes provided data for an increasing branching in the series CF₃., CF₃CF₂, (CF₃)₂CF. and (CF₃)₃C. Radicals and in addition for an increasing chain length in the series CF₃ ., CF₃CF₂. CF₃CF₂CF₂, and CF₃(CF₂)₂CF₂.radicals. The new data followed the sequence expected and established that the reson¬ ance stabilisation of the adduct radical in radical addition reactions to olefins is of minor importance. Instead there is a complex interplay of polar, steric and bond strength terms, all of which are necessarily inter-related in governing the rate and orientation of free radical addition reactions. The second part involved the addition of trifluoromethyl radicals to acetylene, alkyl and fluoroalkyl substituted acetylenes. The results showed similarity in the rates and orientation of addition to acetylenes and the corresponding sub¬ stituted ethylenes. This reveals that the substituents have very similar effects on the reactivity of the double and triple bonds. On the other hand, the Arrhenius parameters were significantly higher for the addition to acetylenes compared to the addition to ethylenes. This confirmed the transition theory predictions. The work also offers a study of the stereospecificity of the addition reaction with acetylenes. The third part involves the addition of trifluoromethyl radicals to 1,3-butadiene, isoprene, trans-piperylene and vinyl acetylene. The stereospecificity of the addition reaction with 1, 3-butadiene was studied.
The fourth part deals with the topic "homosolvolysis", a study of the homolysis of carbon-halogen, carbon-metal, metal-metal and metal-halogen bonds using di-t-butylnitroxide and 2,2,5,5-tetramethylpyrrolydine nitroxide as solvents.A study of halogen adducts of some arsinesMahomedy, Amina Y.https://hdl.handle.net/10023/218562021-10-28T09:08:58Z1978-01-01T00:00:00Z1978-01-01T00:00:00ZMahomedy, Amina Y.Synthetic studies towards a nodularin based analogue as a potential protein phosphatase inhibitorMehrotra, Amit Prataphttps://hdl.handle.net/10023/218572021-10-28T09:29:17Z1995-01-01T00:00:00ZThe microcystins and nodularins, cyclic isohepta- and isopentapeptides, respectively, are potent inhibitors of the serine/threonine protein phosphatase enzymes 1 (PP1) and 2A (PP2A). They have been shown to form covalent adducts with the enzymes and are known to be potent hepatotoxins and liver tumour promoters. These cyclic peptides possess both dehydroamino acid and Adda residues which could potentially form covalent bonds with proteins. The possibility that the dehydroamino acid moiety is the reactive group in inhibition has been excluded by showing that the reduced analogue (dihydromicrocystin-LR) is fully active as an inhibitor. This indicates that the Adda residue is the site at which covalent bond formation with the proteins occurs. In order to investigate the mode of inhibition, the potential inhibitor (33) (cyclo(Gly-(R)-isoAsp-(S)-Phe-"Adda"-(R)-isoGlu) was designed and its synthesis was contemplated. (3-Alanine was used as a model for the "Adda" residue in order to optimise the conditions for cyclisation. The isopentapeptide (65) [Cbz- (R)-Asp-α-(OCH3)-B-(S)-Phe-B-Ala-(R)-Glu-α-(OCH3)-y-Gly-OBzl] was synthesised, from (2R)-aspartic acid and the readily available Boc-(2R)-Glu-a-(OH)-y-OBzl. The overall synthesis required 15 steps and was achieved in 17.5% yield. Simultaneous N- and C-terminal deprotection using catalytic hydrogenation gave deprotected peptide (108). All attempts to cyclise this peptide using the commonly employed protocols (DPPA, EDCI and TBTU etc.) failed. Molecular modelling showed that the two ends of peptide (108) could not approach in the correct orientation to allow ring closure. As a result of modelling studies the isopentapeptide (110) containing sarcosine in place of glycine was prepared. Modelling studies predict that ring closure of this peptide could be achieved (after deprotection). The B-amino acid diene (3S)-methyl-3-(N)-9'-phenylfluoren-9'-yl-6-methyl-nona-4,6-dienoate (107) was used as an analogue for the Adda residue of the microcystins/nodularins. The diene was formed from the suitably protected aspartic acid α-aldehyde (106) using Wittig chemistry. The α-aldehyde (106) was prepared by Dess-Martin periodinane oxidation of the corresponding α-hydroxymethyl alcohol (103). Thus, a pentapeptide containing a hydroxymethyl group has been prepared, which can be elaborated to the diene, after successful ring closure to give our potential inhibitor (33). Owing to time constraints, it was not possible to complete the cyclisation. If cyclisation of these new peptides can not be achieved by standard methods, the use of a free radical mediated macrocyclisation may offer a solution. This is currently under investigation by others in the group.
1995-01-01T00:00:00ZMehrotra, Amit PratapThe microcystins and nodularins, cyclic isohepta- and isopentapeptides, respectively, are potent inhibitors of the serine/threonine protein phosphatase enzymes 1 (PP1) and 2A (PP2A). They have been shown to form covalent adducts with the enzymes and are known to be potent hepatotoxins and liver tumour promoters. These cyclic peptides possess both dehydroamino acid and Adda residues which could potentially form covalent bonds with proteins. The possibility that the dehydroamino acid moiety is the reactive group in inhibition has been excluded by showing that the reduced analogue (dihydromicrocystin-LR) is fully active as an inhibitor. This indicates that the Adda residue is the site at which covalent bond formation with the proteins occurs. In order to investigate the mode of inhibition, the potential inhibitor (33) (cyclo(Gly-(R)-isoAsp-(S)-Phe-"Adda"-(R)-isoGlu) was designed and its synthesis was contemplated. (3-Alanine was used as a model for the "Adda" residue in order to optimise the conditions for cyclisation. The isopentapeptide (65) [Cbz- (R)-Asp-α-(OCH3)-B-(S)-Phe-B-Ala-(R)-Glu-α-(OCH3)-y-Gly-OBzl] was synthesised, from (2R)-aspartic acid and the readily available Boc-(2R)-Glu-a-(OH)-y-OBzl. The overall synthesis required 15 steps and was achieved in 17.5% yield. Simultaneous N- and C-terminal deprotection using catalytic hydrogenation gave deprotected peptide (108). All attempts to cyclise this peptide using the commonly employed protocols (DPPA, EDCI and TBTU etc.) failed. Molecular modelling showed that the two ends of peptide (108) could not approach in the correct orientation to allow ring closure. As a result of modelling studies the isopentapeptide (110) containing sarcosine in place of glycine was prepared. Modelling studies predict that ring closure of this peptide could be achieved (after deprotection). The B-amino acid diene (3S)-methyl-3-(N)-9'-phenylfluoren-9'-yl-6-methyl-nona-4,6-dienoate (107) was used as an analogue for the Adda residue of the microcystins/nodularins. The diene was formed from the suitably protected aspartic acid α-aldehyde (106) using Wittig chemistry. The α-aldehyde (106) was prepared by Dess-Martin periodinane oxidation of the corresponding α-hydroxymethyl alcohol (103). Thus, a pentapeptide containing a hydroxymethyl group has been prepared, which can be elaborated to the diene, after successful ring closure to give our potential inhibitor (33). Owing to time constraints, it was not possible to complete the cyclisation. If cyclisation of these new peptides can not be achieved by standard methods, the use of a free radical mediated macrocyclisation may offer a solution. This is currently under investigation by others in the group.Electrochemical reduction of carbon dioxide catalysed by nickel macrocyclic complexesDe Alwis, Dandeniyage Chanaka Lalindrahttps://hdl.handle.net/10023/218532021-10-28T08:25:18Z1999-01-01T00:00:00ZThe efficiency of the reduction of carbon dioxide catalysed by 1,4,8,11- tetraazacyclotetradecane nickel(II) (nickel cyclam) at a mercury electrode depends on the pH, temperature and the type of electrolyte. The use of non-aqueous solvents increases the catalytic current as a result of the greater solubility of carbon dioxide. Addition of alkali and alkaline earth metal cations also enhances the efficiency of the catalyst. Nickel cyclam exists in the form of five configurational isomers in aqueous solvents. Among these isomers the trans-III form displays the highest activity towards carbon dioxide reduction. This discrepancy in the catalytic activity was shown to be due to the extent of adsorption of each isomer. At a glassy carbon electrode in acetonitrile/water the catalysis occurs in solution whereas it is a surface confined process at the mercury electrode. The reduction products were analysed using gas chromatography, electron spray mass spectrometry and rotating ring disc electrode techniques. Carbon monoxide is the sole reduction product at the mercury electrode while both carbon monoxide (at -1.7 V) and oxalic acid (at —1.5 V) are produced at the glassy carbon electrode depending on the applied potential. The catalytic current measured using pentaaza and hexaaza macrocyclic complexes as catalysts was enhanced with simple alkyl, hydroxyethyl and aminoalkyl pendant arms. This enhancement of the catalytic current is probably due to formation of hydrogen bonds between the coordinated carbon dioxide and either the pendant arm or the non-coordinated tertiary nitrogen atom. Pentaaza macrocyclic complexes display a greater catalytic current than the hexaazamacrocyclic complexes, but the latter reduce carbon dioxide at less negative potentials. Pendant arms with large aromatic or sulphur-containing groups produced lower currents due to competitive adsorption. Cyclic voltammetry of two series of binuclear macrocyclic nickel(II) complexes with varying lengths of the chain linking the two macrocyclic showed that the two nickel sites in the binuclear complexes behave independently with the currents corresponding to the simultaneous transfer of two electrons. The redox potentials are remarkably constant along this series but the peak separations increase, reflecting slower electron transfer. The catalytic currents are about half those of the mononuclear complex; this is proposed to be due to steric constraints allowing strong interaction of only one nickel centre of the binuclear complex on the surface. The catalytic currents increased slightly as the linking chain length increased, reflecting some relaxation of the stereochemical constraints accompanying the adsorption of both nickel centres. Comparative investigations of cobalt and nickel macrocyclic complexes as photocatalysts with the ruthenium tris(bipyridyl) sensitiser indicate that the nickel complexes do not give detectable amounts of carbon monoxide and also inhibit hydrogen evolution from the reaction mixture.
1999-01-01T00:00:00ZDe Alwis, Dandeniyage Chanaka LalindraThe efficiency of the reduction of carbon dioxide catalysed by 1,4,8,11- tetraazacyclotetradecane nickel(II) (nickel cyclam) at a mercury electrode depends on the pH, temperature and the type of electrolyte. The use of non-aqueous solvents increases the catalytic current as a result of the greater solubility of carbon dioxide. Addition of alkali and alkaline earth metal cations also enhances the efficiency of the catalyst. Nickel cyclam exists in the form of five configurational isomers in aqueous solvents. Among these isomers the trans-III form displays the highest activity towards carbon dioxide reduction. This discrepancy in the catalytic activity was shown to be due to the extent of adsorption of each isomer. At a glassy carbon electrode in acetonitrile/water the catalysis occurs in solution whereas it is a surface confined process at the mercury electrode. The reduction products were analysed using gas chromatography, electron spray mass spectrometry and rotating ring disc electrode techniques. Carbon monoxide is the sole reduction product at the mercury electrode while both carbon monoxide (at -1.7 V) and oxalic acid (at —1.5 V) are produced at the glassy carbon electrode depending on the applied potential. The catalytic current measured using pentaaza and hexaaza macrocyclic complexes as catalysts was enhanced with simple alkyl, hydroxyethyl and aminoalkyl pendant arms. This enhancement of the catalytic current is probably due to formation of hydrogen bonds between the coordinated carbon dioxide and either the pendant arm or the non-coordinated tertiary nitrogen atom. Pentaaza macrocyclic complexes display a greater catalytic current than the hexaazamacrocyclic complexes, but the latter reduce carbon dioxide at less negative potentials. Pendant arms with large aromatic or sulphur-containing groups produced lower currents due to competitive adsorption. Cyclic voltammetry of two series of binuclear macrocyclic nickel(II) complexes with varying lengths of the chain linking the two macrocyclic showed that the two nickel sites in the binuclear complexes behave independently with the currents corresponding to the simultaneous transfer of two electrons. The redox potentials are remarkably constant along this series but the peak separations increase, reflecting slower electron transfer. The catalytic currents are about half those of the mononuclear complex; this is proposed to be due to steric constraints allowing strong interaction of only one nickel centre of the binuclear complex on the surface. The catalytic currents increased slightly as the linking chain length increased, reflecting some relaxation of the stereochemical constraints accompanying the adsorption of both nickel centres. Comparative investigations of cobalt and nickel macrocyclic complexes as photocatalysts with the ruthenium tris(bipyridyl) sensitiser indicate that the nickel complexes do not give detectable amounts of carbon monoxide and also inhibit hydrogen evolution from the reaction mixture.Microcomputer based instrumentation : applications in fluorescence spectroscopyCairns, Alistair Jameshttps://hdl.handle.net/10023/218472021-10-28T02:06:04Z1983-01-01T00:00:00ZThis thesis is largely concerned with two specific applications of microprocessor technology in chemical instrumentation. The hardware and software aspects of the design and construction of a control system, based on a NASCOM 2 microcomputer, for an extensively modified Perkin Elmer model MPF-44A spectrofluorimeter are described. The modified instrument is capable of recording excitation and background corrected spectra, and signal averaging. In addition, it allows three-dimensional spectra to be recorded. Data may be transferred to a mainframe computer for graphical presentation and long term storage. The sensitivity and versatility of the original instrument are markedly enhanced. Spectra of the M3+ ions of the lanthanide elements europium, terbium and samarium in solution are reported. The second application is the development of a versatile microprocessor based instrument which can act as a datalogger or signal averager. With this general purpose device, voltage data can be acquired and stored under a wide range of conditions and can be output in either digital or analogue form. The author's contribution to this project is largely concerned with the design of the instrument logic and the development of a machine code control program.
1983-01-01T00:00:00ZCairns, Alistair JamesThis thesis is largely concerned with two specific applications of microprocessor technology in chemical instrumentation. The hardware and software aspects of the design and construction of a control system, based on a NASCOM 2 microcomputer, for an extensively modified Perkin Elmer model MPF-44A spectrofluorimeter are described. The modified instrument is capable of recording excitation and background corrected spectra, and signal averaging. In addition, it allows three-dimensional spectra to be recorded. Data may be transferred to a mainframe computer for graphical presentation and long term storage. The sensitivity and versatility of the original instrument are markedly enhanced. Spectra of the M3+ ions of the lanthanide elements europium, terbium and samarium in solution are reported. The second application is the development of a versatile microprocessor based instrument which can act as a datalogger or signal averager. With this general purpose device, voltage data can be acquired and stored under a wide range of conditions and can be output in either digital or analogue form. The author's contribution to this project is largely concerned with the design of the instrument logic and the development of a machine code control program.Layered lithium manganese oxide cathodesPaterson, Allan J.https://hdl.handle.net/10023/218492021-10-27T11:16:10Z2003-01-01T00:00:00ZThe synthesis, characterisation and electrochemical performance of layered lithium manganese oxide materials have been investigated in terms of their application as an intercalation cathode in rechargeable lithium batteries. Non-stoichiometric LiₓMnᵧO₂, stoichiometric LiMnO₂ (α-NaFeO₂ type) with doped forms, LiₓMn₁₋ᵧMeᵧO₂ and LiMn₁₋ᵧMeᵧO₂ (where Me = Al, Mg, Li, Ni, Co), were prepared by solid-state and solution synthesis routes coupled with ion exchange from sodium precursors. These materials were investigated by X-ray and neutron powder diffraction, as well as chemical and compositional analysis, SEM, TEM, surface area and galvanostatic cycling measurements.
The structure and performance of non-stoichiometric materials is highly dependant on the synthesis conditions and ion exchange process which determine the defect chemistry. LiₓMnᵧO₂ exhibits high capacities, 190mAhg⁻¹ at a rate of 25mAg⁻¹ (C/8) with good retention of this capacity (fade rate of ~0.1% per cycle). However, performance is hindered by a first cycle charge capacity which is less than the subsequent discharge. This is a problem for lithium ion cells which require a slight excess of Li on the first charge to form the SEI layer on the carbon anode.
The performance of LiMnO₂ is less dependant on synthesis conditions, exhibiting high discharge capacities, ~200mAhg⁻¹at 25mAg⁻¹with minimal fade rate and essentially theoretical charge capacity on the first cycle. Doping of layered materials was found to result in a reduction in the initial dip and rise in capacity over the first few cycles, improved rate capability and first cycle efficiency for non-stoichiometric materials as well as higher overall capacity >200mAhg⁻¹. Structural transformation from a layered to spinel-like configuration on cycling has been investigated. Performance of the spinel-like material formed in situ is markedly superior to directly prepared spinels, being attributed to the formation of a nanostructure able to accommodate the lattice strain caused by the Jahn-Teller distortion. Ball milling and variation in carbon and Kynar concentration were investigated as well as the possibility of electrodes containing both stoichiometric and non-stoichiometric components, to permit an excess of charge capacity on the first cycle in order to accommodate the irreversible losses due to SEI surface layer formation when cycling against a carbon based anode.
2003-01-01T00:00:00ZPaterson, Allan J.The synthesis, characterisation and electrochemical performance of layered lithium manganese oxide materials have been investigated in terms of their application as an intercalation cathode in rechargeable lithium batteries. Non-stoichiometric LiₓMnᵧO₂, stoichiometric LiMnO₂ (α-NaFeO₂ type) with doped forms, LiₓMn₁₋ᵧMeᵧO₂ and LiMn₁₋ᵧMeᵧO₂ (where Me = Al, Mg, Li, Ni, Co), were prepared by solid-state and solution synthesis routes coupled with ion exchange from sodium precursors. These materials were investigated by X-ray and neutron powder diffraction, as well as chemical and compositional analysis, SEM, TEM, surface area and galvanostatic cycling measurements.
The structure and performance of non-stoichiometric materials is highly dependant on the synthesis conditions and ion exchange process which determine the defect chemistry. LiₓMnᵧO₂ exhibits high capacities, 190mAhg⁻¹ at a rate of 25mAg⁻¹ (C/8) with good retention of this capacity (fade rate of ~0.1% per cycle). However, performance is hindered by a first cycle charge capacity which is less than the subsequent discharge. This is a problem for lithium ion cells which require a slight excess of Li on the first charge to form the SEI layer on the carbon anode.
The performance of LiMnO₂ is less dependant on synthesis conditions, exhibiting high discharge capacities, ~200mAhg⁻¹at 25mAg⁻¹with minimal fade rate and essentially theoretical charge capacity on the first cycle. Doping of layered materials was found to result in a reduction in the initial dip and rise in capacity over the first few cycles, improved rate capability and first cycle efficiency for non-stoichiometric materials as well as higher overall capacity >200mAhg⁻¹. Structural transformation from a layered to spinel-like configuration on cycling has been investigated. Performance of the spinel-like material formed in situ is markedly superior to directly prepared spinels, being attributed to the formation of a nanostructure able to accommodate the lattice strain caused by the Jahn-Teller distortion. Ball milling and variation in carbon and Kynar concentration were investigated as well as the possibility of electrodes containing both stoichiometric and non-stoichiometric components, to permit an excess of charge capacity on the first cycle in order to accommodate the irreversible losses due to SEI surface layer formation when cycling against a carbon based anode.Solid state NMR investigations of crystalline organic inclusion compoundsMahdyarfar, Alihttps://hdl.handle.net/10023/218412021-10-26T09:06:46Z1994-01-01T00:00:00ZThe work presented here is concerned with structural and dynamic investigations of crystalline organic inclusion compounds primarily using high-resolution solid state NMR spectroscopy. The focus has been on two types of host systems; urea and tri-ortho-thyirrotide (TOT). High-resolution solid state ¹³C NMR spectra of 1-haloalkane/urea inclusion compounds indicate the existence of two different interactions between end-groups of these guest molecules. This conclusion is derived from the presence of the two signals due to the related end-groups. The chemical shift variation of these signals as a function of the chain length of haloalkanes is reported. A noticeable trend is observed for some of these guest molecules. The areas under these signals are related to the relative numbers of these two interactions. However mathematical analysis shows that it is not possible to derive intrinsic interactions between the end-groups from measurements on these inclusion compounds. It is shown that such information can be obtained via measurement on inclusion compounds containing two types of guest molecules, and then applying the standard results of a Markov chain on these measurements. The migration of the potential guest molecules from the external liquid phase into the tunnel structure of urea inclusion compounds is reported by solid state ¹³C NMR spectroscopy. Several evidence is presented to support the exchange mechanism for this observation. The dynamics of deuterated benzene and pyridine in their TOT inclusion compounds is investigated by variable temperature ²H NMR. These guest molecules are undergoing well defined motion in the solid cage structure. The detailed mechanism of their motions is investigated using computer simulation of the spectra.
1994-01-01T00:00:00ZMahdyarfar, AliThe work presented here is concerned with structural and dynamic investigations of crystalline organic inclusion compounds primarily using high-resolution solid state NMR spectroscopy. The focus has been on two types of host systems; urea and tri-ortho-thyirrotide (TOT). High-resolution solid state ¹³C NMR spectra of 1-haloalkane/urea inclusion compounds indicate the existence of two different interactions between end-groups of these guest molecules. This conclusion is derived from the presence of the two signals due to the related end-groups. The chemical shift variation of these signals as a function of the chain length of haloalkanes is reported. A noticeable trend is observed for some of these guest molecules. The areas under these signals are related to the relative numbers of these two interactions. However mathematical analysis shows that it is not possible to derive intrinsic interactions between the end-groups from measurements on these inclusion compounds. It is shown that such information can be obtained via measurement on inclusion compounds containing two types of guest molecules, and then applying the standard results of a Markov chain on these measurements. The migration of the potential guest molecules from the external liquid phase into the tunnel structure of urea inclusion compounds is reported by solid state ¹³C NMR spectroscopy. Several evidence is presented to support the exchange mechanism for this observation. The dynamics of deuterated benzene and pyridine in their TOT inclusion compounds is investigated by variable temperature ²H NMR. These guest molecules are undergoing well defined motion in the solid cage structure. The detailed mechanism of their motions is investigated using computer simulation of the spectra.Enzyme-catalysed carbohydrate biosynthesis and modificationMerkel, Alexandra B.https://hdl.handle.net/10023/218372021-10-25T14:10:05Z2005-01-01T00:00:00ZGlycopeptides are regarded as the last line of defence antibiotics. Since their peptide backbone has no biological activity, these compounds depend on attached carbohydrates for their antibacterial potency, as well as for their selectivity and specificity. In Amycolatopsis orientalis, five enzymes are responsible for the synthesis of the L-epivancosamine deoxysugar from dTDP-glucose in the chloroeremomycin biosynthesis. This thesis discusses the structural characterisation of two of these enzymes: EvaD, a 5-epimerase; and EvaA, a 2,3-dehydratase. Structural data on EvaD crystals have been obtained to 1.5Å resolution for apo- and to 1.4Å resolution for a dTMP co-complex. The M131F/L135A mutant of EvaD was also crystallised and data to 2.lÅ collected. Kinetic analysis and deuterium incorporation studies with wild-type and mutant EvaD allowed the identification of all residues involved in catalysis and showed that this enzyme is naturally a mono-epimerase, despite being structurally similar to RmlC-type epimerases. The main reason for this anomaly is the orientation of the catalytic acid, Tyr133. EvaA and several homologues from other Actinomycetales have been cloned, expressed and purified; and the activity of EvaA has been confirmed. Initial crystallisation conditions have been identified for EvaA, but no diffraction has been obtained. A second part of this thesis deals with the investigations into the reaction mechanism of KDPG aldolase from E. coli. This enzyme is useful for the enzymatic synthesis of C-C bonds; however, its substrate profile is too limited for chemical synthesis. To engineer this enzyme to accept non-natural substrates, the reaction mechanism and basis for selectivity have to be understood. Prior to this study, the aldolase had been crystallised, but citrate contained in these conditions bound to the active site preventing co-crystallisation and soaking experiments. Several new crystal forms without citrate were identified facilitating substrate soaks; however, no clear results were obtained.
2005-01-01T00:00:00ZMerkel, Alexandra B.Glycopeptides are regarded as the last line of defence antibiotics. Since their peptide backbone has no biological activity, these compounds depend on attached carbohydrates for their antibacterial potency, as well as for their selectivity and specificity. In Amycolatopsis orientalis, five enzymes are responsible for the synthesis of the L-epivancosamine deoxysugar from dTDP-glucose in the chloroeremomycin biosynthesis. This thesis discusses the structural characterisation of two of these enzymes: EvaD, a 5-epimerase; and EvaA, a 2,3-dehydratase. Structural data on EvaD crystals have been obtained to 1.5Å resolution for apo- and to 1.4Å resolution for a dTMP co-complex. The M131F/L135A mutant of EvaD was also crystallised and data to 2.lÅ collected. Kinetic analysis and deuterium incorporation studies with wild-type and mutant EvaD allowed the identification of all residues involved in catalysis and showed that this enzyme is naturally a mono-epimerase, despite being structurally similar to RmlC-type epimerases. The main reason for this anomaly is the orientation of the catalytic acid, Tyr133. EvaA and several homologues from other Actinomycetales have been cloned, expressed and purified; and the activity of EvaA has been confirmed. Initial crystallisation conditions have been identified for EvaA, but no diffraction has been obtained. A second part of this thesis deals with the investigations into the reaction mechanism of KDPG aldolase from E. coli. This enzyme is useful for the enzymatic synthesis of C-C bonds; however, its substrate profile is too limited for chemical synthesis. To engineer this enzyme to accept non-natural substrates, the reaction mechanism and basis for selectivity have to be understood. Prior to this study, the aldolase had been crystallised, but citrate contained in these conditions bound to the active site preventing co-crystallisation and soaking experiments. Several new crystal forms without citrate were identified facilitating substrate soaks; however, no clear results were obtained.Polyaromatic molecules : structure and reactivity on copper single crystalsMcDowall, Alexander Josephhttps://hdl.handle.net/10023/218332021-10-25T11:50:59Z2004-01-01T00:00:00ZIn recent years there has been a significant interest in the use of polyaromatic molecules in (opto-) electronic devices. This family of molecules tends to be vibrantly coloured and have interesting optical and semiconductor properties hence a specific interest in display devices. In this thesis, thin films of organic polyaromatic molecules 3,4,9,10- perylenetetracarboxylic dianhydride (PTCDA), perylene and tetracene on copper single crystals were investigated. The molecules were deposited in Ultra High Vacuum (UHV) onto clean copper crystals under a number of different substrate conditions where they formed ordered thin films. The films were characterised using scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), thermal desorption, X-ray photoelectron spectroscopy (XPS) and vibrational spectroscopies, electron energy loss spectroscopy (EELS) and reflection/absorption infra-red spectroscopy (RAIRS). PTCDA, the most widely investigated of the molecules, was analysed on Cu(211) and (110) surfaces and was shown to have strong interactions with the copper rows of the substrates strongly influencing the structures formed. XPS results indicate a strong bond to the surface through loss of the anhydride oxygen atoms with subsequent layers physisorbed. On Cu(211) PTCDA formed a unit cell of a = 16.1 Å, b = 24. 1Å, β = 85°. On Cu(110), PTCDA forms a unit cell of a= 18.9 Å, b = 18.9 Å, β = 75°.
Perylene proved to be the most complex molecule with annealing of the initial monolayer vital in determining the structure of the subsequent layers. A highly ordered structure with molecular rows far larger than the terraces of the underlying copper could be formed after heating as opposed to a less ordered structure. The three thin film structures of perylene recorded were: α -phase: a = 11.0 Å, b = 11.0 Å, β = 77°, β -phase: a = 10.84Å, b = 10.84Å, β = 65° and γ-phase: a = 20.7 Å, b = 19.3 Å, β = 90° all of which are significantly different from the bulk crystal structures. Photoluminescence experiments show that the different multilayer structures lead to different wavelengths of emission due to different intermolecular interactions within the films. The recorded photon emission results from a excimer due to overlapping of π-orbitals in the novel crystal structure. Below two monolayers, no emission is recorded due to quenching by the substrate.
Tetracene forms only monolayers at room temperature. If cooled, multilayers can be formed. Two tetracene monolayer structures were observed, the first driven by interactions with the copper rows produced a centred 12 x 2 structure, and the second, formed by annealing the first, involved molecules which were close packed and interdigitated, giving a compressed primitive 6 x 1.83 structure.
2004-01-01T00:00:00ZMcDowall, Alexander JosephIn recent years there has been a significant interest in the use of polyaromatic molecules in (opto-) electronic devices. This family of molecules tends to be vibrantly coloured and have interesting optical and semiconductor properties hence a specific interest in display devices. In this thesis, thin films of organic polyaromatic molecules 3,4,9,10- perylenetetracarboxylic dianhydride (PTCDA), perylene and tetracene on copper single crystals were investigated. The molecules were deposited in Ultra High Vacuum (UHV) onto clean copper crystals under a number of different substrate conditions where they formed ordered thin films. The films were characterised using scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), thermal desorption, X-ray photoelectron spectroscopy (XPS) and vibrational spectroscopies, electron energy loss spectroscopy (EELS) and reflection/absorption infra-red spectroscopy (RAIRS). PTCDA, the most widely investigated of the molecules, was analysed on Cu(211) and (110) surfaces and was shown to have strong interactions with the copper rows of the substrates strongly influencing the structures formed. XPS results indicate a strong bond to the surface through loss of the anhydride oxygen atoms with subsequent layers physisorbed. On Cu(211) PTCDA formed a unit cell of a = 16.1 Å, b = 24. 1Å, β = 85°. On Cu(110), PTCDA forms a unit cell of a= 18.9 Å, b = 18.9 Å, β = 75°.
Perylene proved to be the most complex molecule with annealing of the initial monolayer vital in determining the structure of the subsequent layers. A highly ordered structure with molecular rows far larger than the terraces of the underlying copper could be formed after heating as opposed to a less ordered structure. The three thin film structures of perylene recorded were: α -phase: a = 11.0 Å, b = 11.0 Å, β = 77°, β -phase: a = 10.84Å, b = 10.84Å, β = 65° and γ-phase: a = 20.7 Å, b = 19.3 Å, β = 90° all of which are significantly different from the bulk crystal structures. Photoluminescence experiments show that the different multilayer structures lead to different wavelengths of emission due to different intermolecular interactions within the films. The recorded photon emission results from a excimer due to overlapping of π-orbitals in the novel crystal structure. Below two monolayers, no emission is recorded due to quenching by the substrate.
Tetracene forms only monolayers at room temperature. If cooled, multilayers can be formed. Two tetracene monolayer structures were observed, the first driven by interactions with the copper rows produced a centred 12 x 2 structure, and the second, formed by annealing the first, involved molecules which were close packed and interdigitated, giving a compressed primitive 6 x 1.83 structure.Studies of 2-AZA analogues of 1, 6, 6a λ⁴-trithiapentalenes : introduction of the =N-S unit into four-electron three-centre bonded structures and reactions of 1, 6, 6a λ⁴-trithiapentalenes with arenediazonium tetrafluoroboratesBriggs, Alexander Gibsonhttps://hdl.handle.net/10023/218302021-10-26T02:01:34Z1977-01-01T00:00:00ZThere is only one report in the literature of a structure of the trithiapentalene type containing the =N—S unit. We have 4 thionated 3,4-dimethyl - 1 - oxa - 6, 6aλ⁴. -di selena- 2 -azapentalene with phosphorus pentasulphide and obtained two products, 3,4- 4 dimethyl-1-thia-6, 6a λ⁴ -diselena-2-azapentalene and 3, 4-dimethyl-4 1, 6-dithia-6a λ⁴ - selena-2-azapentane, both new systems which contain this moiety. A third product from the same reaction was 3,4- dimethyl-1-oxa-6—thia-6a λ⁴ - selena-2-azapentalene, the first trithiapentalene analogue containing four different heteroatoms. An attempt to introduce the =N—S unit into 4, 5-dihydro-3H-benzo [cd ]-l-oxa-6, 6a λ⁴ -dithia-2-azapentalene by treatment with phosphorus pentasulphide was unsuccessful.
We have demonstrated that the very large increase in acidity of isothiazole-5-carboxaldoxime on methylation at N-2, which had been reported in the literature, is due to the formation of a stabilised bicyclic three-centre bonded structure on deprotonation of the resulting salt in solution. This investigation thus led to the isolation of 6-methyl- 1 -oxa- λ⁴ -thia-2, 6-diazapentalene, the first member of a new heterocyclic system. An attempt to introduce the =N—S unit into this product by thionation with phosphorus pentasulphide was precluded by the low yield in which this compound was obtained. Several other related compounds were also studied.
It has been suggested that the products from reactions of 4 l,6,6a λ⁴ -trithiapentalenes with arenediazonium electrophiles arise from two distinct mechanisms, one involving attack at C-3(4) and the other involving attack at S-1(6). We have provided further verification of the latter mechanism by obtaining S-arylation products from the reaction of 5-methyl(ene)- 1, 2-dithiole-3-thiones with arenediazonium tetrafluoroborates. We have also trapped a dithiolium salt intermediate from this type of reaction as 3-p-nitrophenylthio-5-t-butyl- 1, 2-dithiolium tetrafluoroborate.
1977-01-01T00:00:00ZBriggs, Alexander GibsonThere is only one report in the literature of a structure of the trithiapentalene type containing the =N—S unit. We have 4 thionated 3,4-dimethyl - 1 - oxa - 6, 6aλ⁴. -di selena- 2 -azapentalene with phosphorus pentasulphide and obtained two products, 3,4- 4 dimethyl-1-thia-6, 6a λ⁴ -diselena-2-azapentalene and 3, 4-dimethyl-4 1, 6-dithia-6a λ⁴ - selena-2-azapentane, both new systems which contain this moiety. A third product from the same reaction was 3,4- dimethyl-1-oxa-6—thia-6a λ⁴ - selena-2-azapentalene, the first trithiapentalene analogue containing four different heteroatoms. An attempt to introduce the =N—S unit into 4, 5-dihydro-3H-benzo [cd ]-l-oxa-6, 6a λ⁴ -dithia-2-azapentalene by treatment with phosphorus pentasulphide was unsuccessful.
We have demonstrated that the very large increase in acidity of isothiazole-5-carboxaldoxime on methylation at N-2, which had been reported in the literature, is due to the formation of a stabilised bicyclic three-centre bonded structure on deprotonation of the resulting salt in solution. This investigation thus led to the isolation of 6-methyl- 1 -oxa- λ⁴ -thia-2, 6-diazapentalene, the first member of a new heterocyclic system. An attempt to introduce the =N—S unit into this product by thionation with phosphorus pentasulphide was precluded by the low yield in which this compound was obtained. Several other related compounds were also studied.
It has been suggested that the products from reactions of 4 l,6,6a λ⁴ -trithiapentalenes with arenediazonium electrophiles arise from two distinct mechanisms, one involving attack at C-3(4) and the other involving attack at S-1(6). We have provided further verification of the latter mechanism by obtaining S-arylation products from the reaction of 5-methyl(ene)- 1, 2-dithiole-3-thiones with arenediazonium tetrafluoroborates. We have also trapped a dithiolium salt intermediate from this type of reaction as 3-p-nitrophenylthio-5-t-butyl- 1, 2-dithiolium tetrafluoroborate.On the equation of state of metals at low temperaturesIronside, Alexander Matherhttps://hdl.handle.net/10023/218312021-10-26T02:06:42Z1966-01-01T00:00:00Z1966-01-01T00:00:00ZIronside, Alexander MatherThe chemistry of simple alcohols, amino acids and nucleic acid bases on silicon substratesGómez, Alberto Lópezhttps://hdl.handle.net/10023/218282021-10-25T10:10:15Z2002-01-01T00:00:00ZThe interaction between organic molecules and silicon substrates has been investigated using several surface sensitive techniques. The studies of the competitive reactions between simple alcohols and water show that only isopropanol is able to passivate the surface and inhibit further adsorption of H2O. The reaction occurs through cleavage of OH bonds and the formation of Si-O linkages. At room temperature, the cleaved H atoms are kept at the surface through the formation of Si-H bonds. Unsaturated heterocyclic molecules like maleic anhydride react with the silicon surface through a 2+2-cycloaddition reaction and provide a well defined ordered template to achieve further film growth. Bifunctional molecules like glycine and 4-aminobenzoic acid react with the surface through the carboxylate group, leaving the amino group available for further film growth. Similarly to the alcohols, the reaction occurs through cleavage of OH bonds and formation of Si-O-C linkages. The presence of a surface modifier like Na, modifies the interaction of the carboxylate groups with the surface from unidentate to bidentate. This leads to the formation of an ordered layer with well-defined bonding sites. The study of the adsorption of uracil on Si(100)-2x1 showed that this molecule is able to form well ordered structures on the surface. The vibrational spectroscopy study indicated that only the enol tautomer of uracil is able to react with the surface.
2002-01-01T00:00:00ZGómez, Alberto LópezThe interaction between organic molecules and silicon substrates has been investigated using several surface sensitive techniques. The studies of the competitive reactions between simple alcohols and water show that only isopropanol is able to passivate the surface and inhibit further adsorption of H2O. The reaction occurs through cleavage of OH bonds and the formation of Si-O linkages. At room temperature, the cleaved H atoms are kept at the surface through the formation of Si-H bonds. Unsaturated heterocyclic molecules like maleic anhydride react with the silicon surface through a 2+2-cycloaddition reaction and provide a well defined ordered template to achieve further film growth. Bifunctional molecules like glycine and 4-aminobenzoic acid react with the surface through the carboxylate group, leaving the amino group available for further film growth. Similarly to the alcohols, the reaction occurs through cleavage of OH bonds and formation of Si-O-C linkages. The presence of a surface modifier like Na, modifies the interaction of the carboxylate groups with the surface from unidentate to bidentate. This leads to the formation of an ordered layer with well-defined bonding sites. The study of the adsorption of uracil on Si(100)-2x1 showed that this molecule is able to form well ordered structures on the surface. The vibrational spectroscopy study indicated that only the enol tautomer of uracil is able to react with the surface.Synthetic studies towards new pigmentsGarnett, Alasdair Nathanhttps://hdl.handle.net/10023/218222021-10-25T08:24:22Z1998-01-01T00:00:00ZPhthalate ester synthesis. An investigation into various methods of synthesising phthalate esters suitable as precursors for phthalocyanine and other pigment synthesis was conducted. This was achieved via thermal Diels-Alder reactions between 2-substituted furans and dimethyl acetylenedicarboxylate (DMAD), proceeding in high yield. Subsequent aromatisation of the resulting adducts by either sulphuric acid or low-valence titanium also proceeded in good yields. The phenols generated by the acid aromatisation were further reacted in high yields with a range of haloalkanes to form the expected aryl ethers.
Latent pigment investigation Work was also carried out on the synthesis of reversibly soluble "latent" DPP (1,4-diketo-pyrrolo[3,4-c]pyrrole) pigments. The aim was to synthesise a moiety that could be incorporated into a DPP pigment, increasing its solubility in various media. The solublised DPP pigment should then be treatable in situ to precipitate a considerably less soluble aromatic DPP pigment.
2X X-DPP-X Ar-DPP-Ar
It was necessary for the moiety X to be stable to the DPP forming conditions (1), but once it was incorporated into the soluble DPP it had to be easily converted without significant degradation to produce the less soluble aromatic DPP pigment under reasonably mild conditions (2). A variety of methods and moieties were investigated, the main efforts concentrating on two areas: heterobicycloheptadiene "norbornadiene" analogue containing groups, which could aromatise to phenyl-type groups under thermal conditions while extruding various gases, and upon both cis and trans-stilbenyl containing groups which could cyclise to planar phenanthryl groups under suitably oxidative photochemical conditions.
1998-01-01T00:00:00ZGarnett, Alasdair NathanPhthalate ester synthesis. An investigation into various methods of synthesising phthalate esters suitable as precursors for phthalocyanine and other pigment synthesis was conducted. This was achieved via thermal Diels-Alder reactions between 2-substituted furans and dimethyl acetylenedicarboxylate (DMAD), proceeding in high yield. Subsequent aromatisation of the resulting adducts by either sulphuric acid or low-valence titanium also proceeded in good yields. The phenols generated by the acid aromatisation were further reacted in high yields with a range of haloalkanes to form the expected aryl ethers.
Latent pigment investigation Work was also carried out on the synthesis of reversibly soluble "latent" DPP (1,4-diketo-pyrrolo[3,4-c]pyrrole) pigments. The aim was to synthesise a moiety that could be incorporated into a DPP pigment, increasing its solubility in various media. The solublised DPP pigment should then be treatable in situ to precipitate a considerably less soluble aromatic DPP pigment.
2X X-DPP-X Ar-DPP-Ar
It was necessary for the moiety X to be stable to the DPP forming conditions (1), but once it was incorporated into the soluble DPP it had to be easily converted without significant degradation to produce the less soluble aromatic DPP pigment under reasonably mild conditions (2). A variety of methods and moieties were investigated, the main efforts concentrating on two areas: heterobicycloheptadiene "norbornadiene" analogue containing groups, which could aromatise to phenyl-type groups under thermal conditions while extruding various gases, and upon both cis and trans-stilbenyl containing groups which could cyclise to planar phenanthryl groups under suitably oxidative photochemical conditions.Versatile pyrolitic synthesis of tetracyclic heteroaromatic compoundsGarnett, Alasdair N.https://hdl.handle.net/10023/218232021-10-25T08:36:20Z2001-01-01T00:00:00ZThe scope of a new synthetic method for tetracyclic heteroaromatic compounds involving flash vacuum pyrolysis of suitably functionalised phosphorus ylides has been examined in detail. The reaction involves generation of a C=C triple bond and an adjacent aryloxy or arylthio radical which cyclises to form a furan or thiophene ring and this is followed by a second cyclisation to form the tetracyclic product. A total of over sixty new stabilised ylides have been prepared and fully characterised and their pyrolysis has in most cases afforded the target heterocyclic products, many of which are the first examples of new ring systems. For the initial cyclisation, benzene, pyridine and naphthalene-containing systems worked well while for the second cyclisation benzene, thiophene, furan and naphthalene groups could be used. Use of thiophene systems in the initial cyclisation proved to be less successful but in the course of preparation of the necessary starting materials a new fundamental reaction of electron-rich thiophenemethanols was discovered. Preparation of specifically substituted tetracyclic products was also possible by starting from appropriate substituted precursors. The multitude of possible combinations of groups suggested a combinatorial approach and this was successfully achieved with three phosphonium salts and four acid chlorides being used to obtain a mixture of twelve ylides which was then pyrolysed to produce a "library" of twelve heterocyclic products. Ylides giving rise to two aryloxy or arylthio radical sites were also examined and these led to tetracyclic products with a different ring topology. In the course of this work an unexpected eight-step cascade reaction leading to the first benzothienylbenzofuran was discovered. Finally, the extension of the approach to bis(ylides) was examined in one case and this led to direct formation of a heptacyclic heterocyclic product.
2001-01-01T00:00:00ZGarnett, Alasdair N.The scope of a new synthetic method for tetracyclic heteroaromatic compounds involving flash vacuum pyrolysis of suitably functionalised phosphorus ylides has been examined in detail. The reaction involves generation of a C=C triple bond and an adjacent aryloxy or arylthio radical which cyclises to form a furan or thiophene ring and this is followed by a second cyclisation to form the tetracyclic product. A total of over sixty new stabilised ylides have been prepared and fully characterised and their pyrolysis has in most cases afforded the target heterocyclic products, many of which are the first examples of new ring systems. For the initial cyclisation, benzene, pyridine and naphthalene-containing systems worked well while for the second cyclisation benzene, thiophene, furan and naphthalene groups could be used. Use of thiophene systems in the initial cyclisation proved to be less successful but in the course of preparation of the necessary starting materials a new fundamental reaction of electron-rich thiophenemethanols was discovered. Preparation of specifically substituted tetracyclic products was also possible by starting from appropriate substituted precursors. The multitude of possible combinations of groups suggested a combinatorial approach and this was successfully achieved with three phosphonium salts and four acid chlorides being used to obtain a mixture of twelve ylides which was then pyrolysed to produce a "library" of twelve heterocyclic products. Ylides giving rise to two aryloxy or arylthio radical sites were also examined and these led to tetracyclic products with a different ring topology. In the course of this work an unexpected eight-step cascade reaction leading to the first benzothienylbenzofuran was discovered. Finally, the extension of the approach to bis(ylides) was examined in one case and this led to direct formation of a heptacyclic heterocyclic product.Electrochemistry of novel lithium salt complexes in non-aqueous poleyther and gel mediaChristie, Alasdair McCallhttps://hdl.handle.net/10023/218212021-10-23T02:02:29Z1995-01-01T00:00:00ZElectrochemical studies have been performed on some novel lithium salt complexes in polyether media, propylene carbonate and poly(methyl methacrylate) gels. The electrochemical performances of these electrolytes containing added ligands were assessed with particular attention given to their applicability to modern lithium rechargeable battery systems. Conductivity data was obtained for complexes of lithium hexafluorophosphate in non¬ aqueous polyether media and propylene carbonate over a wide range of concentration (10^-3 M to 1M) and analysed using the Fuoss-Kraus, Fuoss (1978) and Casteel-Amis methods. The electrolyte parameters, namely molar conductivity at infinite dilution, dissociation constants for ion-pairs and triple-ions, and maximum specific conductivities, have been obtained. These parameters, particularly at low salt concentration, have been interpreted in terms of ion-ion interactions. Kinetics and mechanisms for the electrodeposition of lithium from non-aqueous solvents and gel media were studied using chronoamperometric, cyclic voltammetric and chronopotentiometric methods at a microelectrode. Nucleation and crystal growth models have been proposed for each electrolyte. Exchange current densities, coulombic stripping efficiencies and lithium corrosion rates were evaluated.
1995-01-01T00:00:00ZChristie, Alasdair McCallElectrochemical studies have been performed on some novel lithium salt complexes in polyether media, propylene carbonate and poly(methyl methacrylate) gels. The electrochemical performances of these electrolytes containing added ligands were assessed with particular attention given to their applicability to modern lithium rechargeable battery systems. Conductivity data was obtained for complexes of lithium hexafluorophosphate in non¬ aqueous polyether media and propylene carbonate over a wide range of concentration (10^-3 M to 1M) and analysed using the Fuoss-Kraus, Fuoss (1978) and Casteel-Amis methods. The electrolyte parameters, namely molar conductivity at infinite dilution, dissociation constants for ion-pairs and triple-ions, and maximum specific conductivities, have been obtained. These parameters, particularly at low salt concentration, have been interpreted in terms of ion-ion interactions. Kinetics and mechanisms for the electrodeposition of lithium from non-aqueous solvents and gel media were studied using chronoamperometric, cyclic voltammetric and chronopotentiometric methods at a microelectrode. Nucleation and crystal growth models have been proposed for each electrolyte. Exchange current densities, coulombic stripping efficiencies and lithium corrosion rates were evaluated.Investigations into the polymerisation of hexachlorocylotriphosphazene and the depolymerisation of polydichlorophosphazeneWerninck, Alan Robert Scotthttps://hdl.handle.net/10023/218202021-10-22T11:52:45Z1969-01-01T00:00:00Z1969-01-01T00:00:00ZWerninck, Alan Robert ScottStructural studies of layered perovskitesSnedden, Alanhttps://hdl.handle.net/10023/218172021-10-22T11:03:35Z2004-01-01T00:00:00ZIn this work studies have been carried out into the structures of three families of layered perovskite using powder neutron diffraction. It is shown that Bi₅Ti₃FeO₁₅ exhibits only one high temperature phase transition, from A2₁am to I4/mmm. For another 4-layer Aurivillius phase, BaBi₄Ti₄O₁₅, the room temperature structure has been successfully refined in space group F2mm. Both of these results are in contradiction to earlier suggestions. La³+ doping into 2- and 3-layer structures was investigated in Bi₃₋ₓLaₓTiNbO₉ for 0 ≤ x ≤1 and Bi₄₋ₓLaₓTi₃O₁₂ for 0 ≤ x ≤ 2. The transition from polar to centrosymmetric has been examined and is in agreement with documented ferroelectric properties. The series Bi₂Sr₂2Ti₁₋ₓGaₓNb₂O₁₂₋ₓ/₂ and BaBi₄Ti₄₋ₓGaₓO₁₅₋ₓ/₂ were studied for x = 0.2, 0.5 and 1 using powder X-ray diffraction. The presence of a second phase, Bi₂O₃ was identified. The presence of this impurity would suggest that the main phases are unlikely to be oxide ion conductors, as previously suggested.
The structures of the 2-layer Dion-Jacobson phases CsBiNb₂O₇ and CsNdNb₂O₇ and the 4-layer CsBi₃Ti₄O₁₃ have been determined using space group P2₁am. The system of octahedral tilting within the perovskite blocks is analogous to that observed in the ferroelectric Aurivillius phases, though no ferroelectric behaviour has been observed. Contrasting behaviour has been found in the 3-layer phases CsA₂Ti₂NbO₁₀ (A = La, Nd, Bi), with the Nd and Bi phases adopting an orthorhombically distorted version (space group I2cm) of the parent tetragonal structure of the La derivative.
Atomistic calculations have been used to study the possibility of doping Me3+ (Me = Al, Ga, In) into BaBi₄Ti₄O₁₅ and BiTi₄O₁₂; these suggest the doping of In3+ into the [Bi₂O₂] layer as the most energetically favoured. The O position in the [Bi₂O₂] layer was given as the lowest energy site for oxygen vacancies, however, the possibility of oxygen migration in Bi₄Ti₃O₁₂ was found to be unfavourable. At the dilute limit La3+ doping was suggested to occur at the [Bi₂O₂] layer in Bi₄Ti₃ O₁₂.
2004-01-01T00:00:00ZSnedden, AlanIn this work studies have been carried out into the structures of three families of layered perovskite using powder neutron diffraction. It is shown that Bi₅Ti₃FeO₁₅ exhibits only one high temperature phase transition, from A2₁am to I4/mmm. For another 4-layer Aurivillius phase, BaBi₄Ti₄O₁₅, the room temperature structure has been successfully refined in space group F2mm. Both of these results are in contradiction to earlier suggestions. La³+ doping into 2- and 3-layer structures was investigated in Bi₃₋ₓLaₓTiNbO₉ for 0 ≤ x ≤1 and Bi₄₋ₓLaₓTi₃O₁₂ for 0 ≤ x ≤ 2. The transition from polar to centrosymmetric has been examined and is in agreement with documented ferroelectric properties. The series Bi₂Sr₂2Ti₁₋ₓGaₓNb₂O₁₂₋ₓ/₂ and BaBi₄Ti₄₋ₓGaₓO₁₅₋ₓ/₂ were studied for x = 0.2, 0.5 and 1 using powder X-ray diffraction. The presence of a second phase, Bi₂O₃ was identified. The presence of this impurity would suggest that the main phases are unlikely to be oxide ion conductors, as previously suggested.
The structures of the 2-layer Dion-Jacobson phases CsBiNb₂O₇ and CsNdNb₂O₇ and the 4-layer CsBi₃Ti₄O₁₃ have been determined using space group P2₁am. The system of octahedral tilting within the perovskite blocks is analogous to that observed in the ferroelectric Aurivillius phases, though no ferroelectric behaviour has been observed. Contrasting behaviour has been found in the 3-layer phases CsA₂Ti₂NbO₁₀ (A = La, Nd, Bi), with the Nd and Bi phases adopting an orthorhombically distorted version (space group I2cm) of the parent tetragonal structure of the La derivative.
Atomistic calculations have been used to study the possibility of doping Me3+ (Me = Al, Ga, In) into BaBi₄Ti₄O₁₅ and BiTi₄O₁₂; these suggest the doping of In3+ into the [Bi₂O₂] layer as the most energetically favoured. The O position in the [Bi₂O₂] layer was given as the lowest energy site for oxygen vacancies, however, the possibility of oxygen migration in Bi₄Ti₃O₁₂ was found to be unfavourable. At the dilute limit La3+ doping was suggested to occur at the [Bi₂O₂] layer in Bi₄Ti₃ O₁₂.A study of the photochemical decomposition of poly(isobutylmethacrylate)Torbet, Alanhttps://hdl.handle.net/10023/218182021-10-22T11:22:07Z1973-01-01T00:00:00ZThis present study was undertaken to obtain kinetic data on the photolytic decomposition of poly(isobutlyl-methacrylate) using a new technique of direct weight measurement during the reaction rather than the indirect pressure measurement systems previously used. The results obtained were used to fit the isobutyl ester into the pattern of information already obtained from the other members of the poly(alkylmethacrylate) series and in particular to determine whether a relationship existed between the Tg and the type of degradation reaction which occurs.
The use of an adapted thermobalance to continuously register weight changes during degradation had a considerable advantage in terms of throughput of data, but, although producing information consistent with that obtained using more traditional methods could not compare in accuracy. The inherent lack of sensitivity of the thermobalance system and the appearance of a previously unreported local pressure phenomenon called the "thrust" effect produced results whose calculated error margin could cast serious doubt upon conclusions drawn from data obtained from all types of thermobalance work.
The kinetic data obtained for poly(isobutylmethacrylate) indicated that the photodegradation reaction is random initiation followed by complete unzipping the overall Activation Energy for a sample of molecular weight 2. 71 x 10^6 being 42 kj mole^-1 and for a 5 -1 sample of molecular weight 3. 09 x 10^5 being 39 kJ mole^-1 Comparing these results with those obtained by Schoff¹⁰ for poly(ethyl) and methy-methacrylate) it is apparent that the reaction is not viscosity controlled because degradation takes place at temperatures well above the Tg and attempts to analyse the data using Schoffs equation proved unsuccessful.
1973-01-01T00:00:00ZTorbet, AlanThis present study was undertaken to obtain kinetic data on the photolytic decomposition of poly(isobutlyl-methacrylate) using a new technique of direct weight measurement during the reaction rather than the indirect pressure measurement systems previously used. The results obtained were used to fit the isobutyl ester into the pattern of information already obtained from the other members of the poly(alkylmethacrylate) series and in particular to determine whether a relationship existed between the Tg and the type of degradation reaction which occurs.
The use of an adapted thermobalance to continuously register weight changes during degradation had a considerable advantage in terms of throughput of data, but, although producing information consistent with that obtained using more traditional methods could not compare in accuracy. The inherent lack of sensitivity of the thermobalance system and the appearance of a previously unreported local pressure phenomenon called the "thrust" effect produced results whose calculated error margin could cast serious doubt upon conclusions drawn from data obtained from all types of thermobalance work.
The kinetic data obtained for poly(isobutylmethacrylate) indicated that the photodegradation reaction is random initiation followed by complete unzipping the overall Activation Energy for a sample of molecular weight 2. 71 x 10^6 being 42 kj mole^-1 and for a 5 -1 sample of molecular weight 3. 09 x 10^5 being 39 kJ mole^-1 Comparing these results with those obtained by Schoff¹⁰ for poly(ethyl) and methy-methacrylate) it is apparent that the reaction is not viscosity controlled because degradation takes place at temperatures well above the Tg and attempts to analyse the data using Schoffs equation proved unsuccessful.A study of ion-molecule reactions in the gas phase using a triple quadrupole mass spectrometerMitchell, Alan Lyallhttps://hdl.handle.net/10023/218132021-10-21T13:55:22Z1988-01-01T00:00:00ZA triple quadrupole mass spectrometer was used to study a number of different ion-molecule reactions. The TQMS is a relatively new device, and is ideally suited to the study of gaseous ion-molecule reactions. It avoids the major complication inherent in other techniques - namely, only one primary ion is ever present in the collision chamber. Consequently, the spectra which were obtained were much easier to interpret than before.
The initial experiments undertaken involved the use of two previously rarely used cationic species, CH⁺₃ and CH⁺₄ . These were reacted with n-, iso- and cyclo-alkanes, and the results showed that the two primary ionic species brought about ionisation of the collision molecules in different ways. Methane radical cation (CH⁺₄) effected ionisation by charge-transfer, whilst methyl cation (CH⁺₃) reacted via a hydride transfer, giving (M-1)+ ions. Thus ionised, we were then able to follow the breakdown of the collision molecules, producing fragmentation schemes for these species. Comparisons between the spectra for n-and iso- alkanes (using both primary ionic species), revealed that the (M-1)+ ions produced in the reactions with CH⁺₃ were in fact the same species. In other words, there is a structural rearrangement of the carbon skeleton before fragmentation. (No such rearrangement was observed for the M+ ions produced in CH⁺₄ ionisation).
The reaction of methyl and trideuteromethyl cations with ethyne produced an excess of the C₃H⁺₃ ion, which was shown to have the cyclopropenyl structure, rather than the propargyl structure.
The reactions of the fluoromethyl cations (CH₂F⁺, CHF⁺₂ and CF⁺₃) with the simple alkenes displayed a number of interesting reactions. In particular a "knock-on" elimination of :CF₂, and a concerted addition-elimination of fluoromethyl cation. They also gave important clues as to the actual mechanisms involved in these reactions and those of methyl cation with the simple alkenes.
The remaining investigations all involved the reactions of unsaturated species, mainly the simple alkenes and conjugated dienes. The design of the TQMS also allowed the cross reactions between the various species to be very easily studied. The spectra for the ethene and propene ion-molecule reactions confirmed the reaction sequences put forward in previous studies of these systems. The butenes on the other hand produced significant differences dependent on both collision gas structure and primary ion source structure, and a change in mechanism was observed as the collision gas pressure was increased, in both the cis but-2-ene and isobutene ion-molecule reactions. (At low pressure the major reaction was collision induced dissociation, which gave way to complex formation/breakdown at higher pressures.)
The fluorinated ethenes gave very interesting results when reacted with both themselves and ethene. In particular, we were able to show that reaction between the various fluorinated ethene radical cations and ethene proceeded via a loosely-bound cyclobutane transition state. Our investigations of the two C₄H₆ isomers (1,3-butadiene and but-2-yne) produced results which were at variance with the results obtained in previous studies. We showed that but-2-yne radical cation does not undergo isomerisation prior to fragmentation/reaction, whereas 1,3-butadiene radical cation does. The analogous C₅H₈ isomers (isoprene and pent-1-yne)were also investigated, and again differences were observed in the "low mass" area of the spectra, indicative of the different structures of the two primary ions. We suggest that like the 1,3-butadiene radical cation, the isoprene radical cation isomerises before reaction to the cyclopentene structure.
1988-01-01T00:00:00ZMitchell, Alan LyallA triple quadrupole mass spectrometer was used to study a number of different ion-molecule reactions. The TQMS is a relatively new device, and is ideally suited to the study of gaseous ion-molecule reactions. It avoids the major complication inherent in other techniques - namely, only one primary ion is ever present in the collision chamber. Consequently, the spectra which were obtained were much easier to interpret than before.
The initial experiments undertaken involved the use of two previously rarely used cationic species, CH⁺₃ and CH⁺₄ . These were reacted with n-, iso- and cyclo-alkanes, and the results showed that the two primary ionic species brought about ionisation of the collision molecules in different ways. Methane radical cation (CH⁺₄) effected ionisation by charge-transfer, whilst methyl cation (CH⁺₃) reacted via a hydride transfer, giving (M-1)+ ions. Thus ionised, we were then able to follow the breakdown of the collision molecules, producing fragmentation schemes for these species. Comparisons between the spectra for n-and iso- alkanes (using both primary ionic species), revealed that the (M-1)+ ions produced in the reactions with CH⁺₃ were in fact the same species. In other words, there is a structural rearrangement of the carbon skeleton before fragmentation. (No such rearrangement was observed for the M+ ions produced in CH⁺₄ ionisation).
The reaction of methyl and trideuteromethyl cations with ethyne produced an excess of the C₃H⁺₃ ion, which was shown to have the cyclopropenyl structure, rather than the propargyl structure.
The reactions of the fluoromethyl cations (CH₂F⁺, CHF⁺₂ and CF⁺₃) with the simple alkenes displayed a number of interesting reactions. In particular a "knock-on" elimination of :CF₂, and a concerted addition-elimination of fluoromethyl cation. They also gave important clues as to the actual mechanisms involved in these reactions and those of methyl cation with the simple alkenes.
The remaining investigations all involved the reactions of unsaturated species, mainly the simple alkenes and conjugated dienes. The design of the TQMS also allowed the cross reactions between the various species to be very easily studied. The spectra for the ethene and propene ion-molecule reactions confirmed the reaction sequences put forward in previous studies of these systems. The butenes on the other hand produced significant differences dependent on both collision gas structure and primary ion source structure, and a change in mechanism was observed as the collision gas pressure was increased, in both the cis but-2-ene and isobutene ion-molecule reactions. (At low pressure the major reaction was collision induced dissociation, which gave way to complex formation/breakdown at higher pressures.)
The fluorinated ethenes gave very interesting results when reacted with both themselves and ethene. In particular, we were able to show that reaction between the various fluorinated ethene radical cations and ethene proceeded via a loosely-bound cyclobutane transition state. Our investigations of the two C₄H₆ isomers (1,3-butadiene and but-2-yne) produced results which were at variance with the results obtained in previous studies. We showed that but-2-yne radical cation does not undergo isomerisation prior to fragmentation/reaction, whereas 1,3-butadiene radical cation does. The analogous C₅H₈ isomers (isoprene and pent-1-yne)were also investigated, and again differences were observed in the "low mass" area of the spectra, indicative of the different structures of the two primary ions. We suggest that like the 1,3-butadiene radical cation, the isoprene radical cation isomerises before reaction to the cyclopentene structure.Syntheses and properties of liquid crystalline macrocyclic complexesMcGregor, Alanhttps://hdl.handle.net/10023/218122021-10-21T13:31:30Z1997-01-01T00:00:00ZInvestigations are conducted into substituted tetraazaannulenes with the objective of forming novel liquid crystalline compounds. Various synthetic strategies are devised and the compounds tested by differential scanning calorimetry and heated-stage polarised optical microscopy. The electrochemistry and variable temperature solid state NMR properties of certain of these compounds were also investigated. A series of novel compounds was prepared utilising the active (3-methine site of the 7,16-dihydro-6,8,15,17-tetramethyldibenzo[b,i]-[ 1,4,8,1 l]tetraazacyclotetradecinato(2-) Ni(II)) complex starting material, commonly known as nickel tetramethyltetraazaannulene. Long aliphatic chains were joined to this macrocycle in an attempt to induce mesogenic properties in the crystals. Diazo functional groups were utilised as the link. However, the bulky nature of the benzene side groups on the macrocycle prevented liquid crystalline behaviour. The ability to replace the nickel centre in these macrocycles was demonstrated. The electrochemistry of the cobalt rod shaped complex was investigated on gold electrodes.
A further series of compounds based on a macrocycle with less bulky side groups was prepared. The dibenzo groups were replaced by ethylenediamine groups. Diazo linked compounds exhibited mesogenic behaviour for the longer chain length, the molecules displaying smectic A mesophases at high temperatures. Once liquid crystalline properties had been established by reducing the bulk of the molecules the effect of the linkage was examined. The diazo linkage was replaced with a dibenzoyl linkage while keeping all other factors constant. However, this small alteration was sufficient to destroy the mesogenic properties for the entire range of chain lengths. In V addition to the liquid crystal transitions several solid state crystalline transitions were observed for these compounds. The effect of making the inner core of the molecules more planar by removing the peripheral methyl groups was investigated. Results suggested that the methyl groups have opposing roles, i.e. they increase the steric bulk of the molecules, but at the same time prevent strong interactions between molecules. Unfortunately, the best synthetic route to such molecules also left the unsymmetrical mono substituted complex as an impurity which could not be easily removed. This impurity was likely to be liquid crystalline in its own right. Variable temperature solid state NMR studies of these compounds were begun by investigating the metal-free parent macrocycles and the intramolecular proton transfer which takes place between the four inner nitrogen atoms. Comparison with X-ray data and 15N isotope enriched studies revealed that the αC¹³C CP / MAS spectra was a valid probe for this tautomerism. This was then extended to TAA which had not been studied by solid state NMR. The results were consistent with an equal population of both tautomers, apparently in conflict with the evidence from the original crystal structure. Later crystallographic work by revealed that the packing in the crystal structure is dependent on the method of formation (recrystallisation or vacuum sublimation).
1997-01-01T00:00:00ZMcGregor, AlanInvestigations are conducted into substituted tetraazaannulenes with the objective of forming novel liquid crystalline compounds. Various synthetic strategies are devised and the compounds tested by differential scanning calorimetry and heated-stage polarised optical microscopy. The electrochemistry and variable temperature solid state NMR properties of certain of these compounds were also investigated. A series of novel compounds was prepared utilising the active (3-methine site of the 7,16-dihydro-6,8,15,17-tetramethyldibenzo[b,i]-[ 1,4,8,1 l]tetraazacyclotetradecinato(2-) Ni(II)) complex starting material, commonly known as nickel tetramethyltetraazaannulene. Long aliphatic chains were joined to this macrocycle in an attempt to induce mesogenic properties in the crystals. Diazo functional groups were utilised as the link. However, the bulky nature of the benzene side groups on the macrocycle prevented liquid crystalline behaviour. The ability to replace the nickel centre in these macrocycles was demonstrated. The electrochemistry of the cobalt rod shaped complex was investigated on gold electrodes.
A further series of compounds based on a macrocycle with less bulky side groups was prepared. The dibenzo groups were replaced by ethylenediamine groups. Diazo linked compounds exhibited mesogenic behaviour for the longer chain length, the molecules displaying smectic A mesophases at high temperatures. Once liquid crystalline properties had been established by reducing the bulk of the molecules the effect of the linkage was examined. The diazo linkage was replaced with a dibenzoyl linkage while keeping all other factors constant. However, this small alteration was sufficient to destroy the mesogenic properties for the entire range of chain lengths. In V addition to the liquid crystal transitions several solid state crystalline transitions were observed for these compounds. The effect of making the inner core of the molecules more planar by removing the peripheral methyl groups was investigated. Results suggested that the methyl groups have opposing roles, i.e. they increase the steric bulk of the molecules, but at the same time prevent strong interactions between molecules. Unfortunately, the best synthetic route to such molecules also left the unsymmetrical mono substituted complex as an impurity which could not be easily removed. This impurity was likely to be liquid crystalline in its own right. Variable temperature solid state NMR studies of these compounds were begun by investigating the metal-free parent macrocycles and the intramolecular proton transfer which takes place between the four inner nitrogen atoms. Comparison with X-ray data and 15N isotope enriched studies revealed that the αC¹³C CP / MAS spectra was a valid probe for this tautomerism. This was then extended to TAA which had not been studied by solid state NMR. The results were consistent with an equal population of both tautomers, apparently in conflict with the evidence from the original crystal structure. Later crystallographic work by revealed that the packing in the crystal structure is dependent on the method of formation (recrystallisation or vacuum sublimation).Some reactions of methyl 12-mesyloxyoleateSaid, Ahmed Ahbeilhttps://hdl.handle.net/10023/218062021-10-21T10:06:35Z1970-01-01T00:00:00ZMethylricinoleate contains a homoallylic hydroxy group and is therefore a potential source of homoallylic carbonium ions which can undergo an interesting rearrangement and furnish cyclopropane compounds. This thesis reports a study of the reaction of methyl 12-mesyloxyoleate, the mesyloxy group being a better leaving than a hydroxy group. Reactions carried out in methanol, acetic acid, and aqueous acetonitrile, in the presence of a suitable buffer to control the pH, gave interesting methoxy, acetoxy, and hydroxy cyclopropajse esters. In the absence of buffer the solution becomes acidic and the major product is the trans isomer of methyl 12-methoxy (acetoxy, hydroxy) octadecenoates. The substituted cyclopropane esters are very reactive and undergo rearrangement reactions. In other solvents (dimethylsulphoxide, acetonitrile, triglyme) sodium methoxide promotes an elimination reaction giving mixtures of conjugated and non-conjugated methyl octadecadienoates.
1970-01-01T00:00:00ZSaid, Ahmed AhbeilMethylricinoleate contains a homoallylic hydroxy group and is therefore a potential source of homoallylic carbonium ions which can undergo an interesting rearrangement and furnish cyclopropane compounds. This thesis reports a study of the reaction of methyl 12-mesyloxyoleate, the mesyloxy group being a better leaving than a hydroxy group. Reactions carried out in methanol, acetic acid, and aqueous acetonitrile, in the presence of a suitable buffer to control the pH, gave interesting methoxy, acetoxy, and hydroxy cyclopropajse esters. In the absence of buffer the solution becomes acidic and the major product is the trans isomer of methyl 12-methoxy (acetoxy, hydroxy) octadecenoates. The substituted cyclopropane esters are very reactive and undergo rearrangement reactions. In other solvents (dimethylsulphoxide, acetonitrile, triglyme) sodium methoxide promotes an elimination reaction giving mixtures of conjugated and non-conjugated methyl octadecadienoates.A study of reactions of the nitroprusside ion with some functional groups of clinical significanceHarrison, Adrianne Calsyhttps://hdl.handle.net/10023/218032021-10-22T02:07:55Z1988-01-01T00:00:00ZThe work described in this thesis represents an attempt to understand further the mode of action and metabolism of the hypotensive agent sodium nitroprusside (Na²[Feᴵᴵ(CN)₅NO]). The nitrosyl and cyanide ligands have been implicated in, respectively, the activity and toxicity of sodium nitroprusside and a brief review of the relevant literature is given in Chapter 1. Investigations of some in vitro reactions of the nitroprusside ion (NP), to better assess its in vivo reactions, are reported with particular interest in the integrity of the pentacyanoferrate moiety and reactions that result in nitrosation or release of NO. Most carbanions react with NP to form an oxime (Chapter 3), with the exceptions of the carbanions of pentane-2,4-dione and 3-methylpentane-2,4-dione for which an unusual mechanism involving metal to ligand charge transfer is proposed (Chapter 4). Consideration of the nmr spectra of some carbanions and oximes (Chapter 2) and the reactions of iron(II) with oximes (Chapter 3) contributes to the elucidation of this mechanism. A mechanism for the reactions of NP with a wide range of thiols, involving reduction of NP and slow release of NO, is proposed in Chapter 6. Although the primary product of NP reduction is [Fe(CN)₄NO]⁻ there has been no evidence of unbound cyanide, attributed to rapid ligand rearrangement yielding hexacyanoferrate(II). The same mechanism is consistent with the reactions of NP with the active site thiols of the enzymes papain and glyceraldehyde-3-phosphate dehydrogenase and the intracellular thiol glutathione of intact erythrocytes (Chapter 7). There is evidence (Chapter 8) of rapid reduction of NP and NO release upon reaction with the haem-containing enzymes catalase and lactoperoxidase, models for the enzyme guanylate cyclase through which NP and related agents are thought to effect hypotension.
1988-01-01T00:00:00ZHarrison, Adrianne CalsyThe work described in this thesis represents an attempt to understand further the mode of action and metabolism of the hypotensive agent sodium nitroprusside (Na²[Feᴵᴵ(CN)₅NO]). The nitrosyl and cyanide ligands have been implicated in, respectively, the activity and toxicity of sodium nitroprusside and a brief review of the relevant literature is given in Chapter 1. Investigations of some in vitro reactions of the nitroprusside ion (NP), to better assess its in vivo reactions, are reported with particular interest in the integrity of the pentacyanoferrate moiety and reactions that result in nitrosation or release of NO. Most carbanions react with NP to form an oxime (Chapter 3), with the exceptions of the carbanions of pentane-2,4-dione and 3-methylpentane-2,4-dione for which an unusual mechanism involving metal to ligand charge transfer is proposed (Chapter 4). Consideration of the nmr spectra of some carbanions and oximes (Chapter 2) and the reactions of iron(II) with oximes (Chapter 3) contributes to the elucidation of this mechanism. A mechanism for the reactions of NP with a wide range of thiols, involving reduction of NP and slow release of NO, is proposed in Chapter 6. Although the primary product of NP reduction is [Fe(CN)₄NO]⁻ there has been no evidence of unbound cyanide, attributed to rapid ligand rearrangement yielding hexacyanoferrate(II). The same mechanism is consistent with the reactions of NP with the active site thiols of the enzymes papain and glyceraldehyde-3-phosphate dehydrogenase and the intracellular thiol glutathione of intact erythrocytes (Chapter 7). There is evidence (Chapter 8) of rapid reduction of NP and NO release upon reaction with the haem-containing enzymes catalase and lactoperoxidase, models for the enzyme guanylate cyclase through which NP and related agents are thought to effect hypotension.Synthetic approaches to imidazo [4,5-b] and [4,5-c]pyridine-1 and/or 3-oxidesAndrews, Adrian Fergusonhttps://hdl.handle.net/10023/218012021-10-20T15:06:49Z1982-01-01T00:00:00ZIn Chapter 1, the syntheses of some known heterocyclic-N-oxides viz. purine-N-oxides, benzotriazole-N-oxides, benzimidazole-N-oxides and imidazopyridine-N-oxides, are discussed in varying degrees of depth. Some of the biological properties of these compounds are mentioned.
In Chapter 2, the reactions with bases of 3-amino-2-nitro and 2-amino-3-nitropyridine derivatives are studied.
2-p-Nitrophenyl-lH-imidazo[4,5-b]pyridine-3-oxide is obtained in high yield by the base-induced cyclisations of 2-nitro-3-N-p-nitrobenzylaminopyridine. The base reactions of the N-ethoxycarbonyl, N-methanesul phonyl and N-p-toluenesulphonyl derivatives of 2-nitro-3-N-p-nitrobenzylaminopyridine also yield the 3-oxide but in lower yield along with other products such as p-nitrobenzoic acid and/or 2-p-nitrophenylimidazo[4,5-b]- pyridine.
2-p-Nitrophenyl-3H-imidazo[4,5-b]pyridine-l-oxide is obtained by the corresponding reactions of bases with 3-nitro-2-N-p-nitrobenzylaminopyridine.
Cleavage is the main reaction when 3-N-methanesulphonyl-N-phenacylamino-2-nitropyridine is treated with bases. When the base used is aqueous ammonia, the major products of the reaction are 3-N-methanesulphonylamino-2-nitropyridine and 2-benzoyl-4(5)-phenylimidazole.
Various mechanisms to account for these results are discussed.
Also studied in this chapter is the reaction of pyridofuroxan with ethyl acetoacetate in the presence of various bases.
In Chapter 3, the reactions with sodium methoxide of the p-toluenesulphonyl derivative of 3-nitro-4-N-p-nitrobenzylaminopyridine and 3-nitro-4- N-phenacylaminopyridine are studied. The identified products of these reactions are cleavage products and the various mechanisms to account for these results are discussed. The attempted syntheses of some other 4-amino-3-nitropyridine derivatives are also discussed.
1982-01-01T00:00:00ZAndrews, Adrian FergusonIn Chapter 1, the syntheses of some known heterocyclic-N-oxides viz. purine-N-oxides, benzotriazole-N-oxides, benzimidazole-N-oxides and imidazopyridine-N-oxides, are discussed in varying degrees of depth. Some of the biological properties of these compounds are mentioned.
In Chapter 2, the reactions with bases of 3-amino-2-nitro and 2-amino-3-nitropyridine derivatives are studied.
2-p-Nitrophenyl-lH-imidazo[4,5-b]pyridine-3-oxide is obtained in high yield by the base-induced cyclisations of 2-nitro-3-N-p-nitrobenzylaminopyridine. The base reactions of the N-ethoxycarbonyl, N-methanesul phonyl and N-p-toluenesulphonyl derivatives of 2-nitro-3-N-p-nitrobenzylaminopyridine also yield the 3-oxide but in lower yield along with other products such as p-nitrobenzoic acid and/or 2-p-nitrophenylimidazo[4,5-b]- pyridine.
2-p-Nitrophenyl-3H-imidazo[4,5-b]pyridine-l-oxide is obtained by the corresponding reactions of bases with 3-nitro-2-N-p-nitrobenzylaminopyridine.
Cleavage is the main reaction when 3-N-methanesulphonyl-N-phenacylamino-2-nitropyridine is treated with bases. When the base used is aqueous ammonia, the major products of the reaction are 3-N-methanesulphonylamino-2-nitropyridine and 2-benzoyl-4(5)-phenylimidazole.
Various mechanisms to account for these results are discussed.
Also studied in this chapter is the reaction of pyridofuroxan with ethyl acetoacetate in the presence of various bases.
In Chapter 3, the reactions with sodium methoxide of the p-toluenesulphonyl derivative of 3-nitro-4-N-p-nitrobenzylaminopyridine and 3-nitro-4- N-phenacylaminopyridine are studied. The identified products of these reactions are cleavage products and the various mechanisms to account for these results are discussed. The attempted syntheses of some other 4-amino-3-nitropyridine derivatives are also discussed.Synthetic applications of flash vacuum pyrolysis over magnesiumOyewale, Adebayo Ojohttps://hdl.handle.net/10023/217982021-10-20T12:14:09Z1991-01-01T00:00:00ZThe thermal reaction over activated magnesium of some 120 organic
substrates has been investigated under flash vacuum pyrolysis(FVP)
conditions. The activation was achieved by freshly resublimed Grignard
grade magnesium onto glass wool at 700°C under vacuum. Magnesium
prepared in this form showed an effective dehalogenating activity on a
wide range of organic halides. FVP of simple aliphatic halides like
2-chloro-2,3-dimethylbutane and 2,3-dichloro-2,3-dimethylbutane,
resulted in dehydrohalogenation to give the corresponding monoenes and
dienes. The dehydrobromination of neopentyl bromide over magnesium
gave a mixture of 2-methyl-2-butene and 2-methyl-l-butene, a product
mixture that cannot be accounted for by either radical or carbene
chemistry. A similar process was observed with terminal dihalides to give
dienes, however with increased chain length a dehalogenation process
involving hydrogen transfer predominates to give monoenes. The
debromination of 1,3-dibromopropane over magnesium led to
cyclopropane. Dehydrohalogenation was similarly observed with cyclic
dihalides, haloalkenes and haloalkynes and for substrates of adequate
chain length, dehalogenation of the haloalkenes or haloalkynes was
followed by cyclisation on to the unsaturated end of the molecule to give
cyclic products. Germinal dihalides underwent dehalogenative
homocoupling to give symmetrical dienes except for 1,1-dichloropropane
and 2,2-dichloropropane where simple dehydrochlorination was observed
to give the chloroalkenes. FVP of benzylic- and benzylidene- halides over magnesium led to
dehalogenative homocoupling to give bibenzyls and stilbenes respectively. Various substituted
bibenzyls and stilbenes were prepared in moderate to
high yields. The amount of magnesium surface available for reaction and a comparative study of the thermal reaction of zinc, calcium and magnesium with benzyl chloride was carried out. On pyrolysis of
o-halobenzyl halides and o-halobenzylidene halides in the presence of
excess magnesium, the loss of both side chain and ring halogens led to
coupling and cyclisation to 9,10-dihydrophenanthrene and phenanthrene
respectively. The ease of ring dehalogenation decreases from iodine to
bromine and chlorine, with fluorine virtually unreactive. Attempts to
prepare symmetrical disubstituted phenanthrenes from substituted
o-halobenzylidene chlorides met with only limited success. Under the
pyrolytic conditions, benzotrichloride was converted to
α, α'-dichlorostilbene, α, α, α', α'-tetrachlorobibenzyl and diphenylacetylene,
the yield of the last two products being dependent on the reaction conditions.
The thermal dehalogenation of α, α'-dihalo-o-xylenes over
magnesium gave benzocyclobutene. The same process afforded fluorinated
benzocyclobutenes and benzodicyclobutene in good yields.
The debromination of α, α, α', α'-tetrabromo-m-xylene over magnesium led to pyrene.
For haloalkylbenzenes, the basic reaction on pyrolysis over
magnesium was dehydrohalogenation to arylalkenes, but this was
sometimes accompanied by bond isomerisation and rearrangement. In the
case of 1-chloro-4-phenylbutane, an additional process of cyclisation on to
the phenyl ring to give tetrahydronaphthalene was observed. The thermal
reaction of 3-chloropropiophenone and 2-bromoacetophenone over
magnesium led not only to dehalogenation products but also to
deoxygenated products. 2-Bromoethyl phenyl ether mainly underwent
dehalogenation and fragmentation to phenol. The
dehalogenation of chlorobenzene and 1,2-dihalobenzenes was also achieved on
pyrolysis over magnesium. Although the main product obtained from the latter was
triphenylene, the involvement of benzyne as an intermediate is in doubt.
The dehalogenation of long chain acid chloride over magnesium,
Was accompanied by fragmentation to give a mixture of alkenes and alkanes.
The magnesium-induced 1,6-dehalogenation of α, α'-halogenated
p -xylenes in the gas phase led to p-xylylenes, which
polymerised. α, α'-Dichloro-p-xylene gave poly(p-xylylene) and
poly(a-chloro-p-xylyene); while α, α, α', α'-tetrachloro-p-xylene and
α, α, α', α'-tetrabromo-p-xylene gave poly(α, α'-dichloro-p-xylylene) and
poly(α, α'-dibromo-p-xylyene) respectively. Also prepared were
poly(α, α,α',a'-tetrachloro-p-xylylene) and poly(α, α, α', α'-tetrafluoro-p-
xylylene) from the corresponding hexahalo-p-xylene. Thermal stability
measurements and the solid state 13C NMR, including molecular weight
estimation were carried out on the polymers.
Some of the processes observed with aryl compounds on pyrolysis
Over magnesium were extented to halogenated thiophene compounds,
especially for the preparation of 1,2-dithienylethenes and derivatives.
Attempts to prepare benzodithiophenes from halo-dichloromethyl-
thiophenes gave halogenated products and isomeric benzodithiophenes.
The isomeric benzodithiophenes obtained and the likely route to them was
investigated. Attempts to generated 2,3-thiophyne by dehalogenation of
mono- and di-halothiophe.nes were inconclusive. The thermal reaction of
a series of epoxides in the presence or absence of magnesium was
investigated. The main process in the absence of magnesium, was
rearrangement to carbonyl compounds, while in the presence of
magnesium, deoxygenation and dehydration reactions were observed in
addition to the thermal rearrangement.
1991-01-01T00:00:00ZOyewale, Adebayo OjoThe thermal reaction over activated magnesium of some 120 organic
substrates has been investigated under flash vacuum pyrolysis(FVP)
conditions. The activation was achieved by freshly resublimed Grignard
grade magnesium onto glass wool at 700°C under vacuum. Magnesium
prepared in this form showed an effective dehalogenating activity on a
wide range of organic halides. FVP of simple aliphatic halides like
2-chloro-2,3-dimethylbutane and 2,3-dichloro-2,3-dimethylbutane,
resulted in dehydrohalogenation to give the corresponding monoenes and
dienes. The dehydrobromination of neopentyl bromide over magnesium
gave a mixture of 2-methyl-2-butene and 2-methyl-l-butene, a product
mixture that cannot be accounted for by either radical or carbene
chemistry. A similar process was observed with terminal dihalides to give
dienes, however with increased chain length a dehalogenation process
involving hydrogen transfer predominates to give monoenes. The
debromination of 1,3-dibromopropane over magnesium led to
cyclopropane. Dehydrohalogenation was similarly observed with cyclic
dihalides, haloalkenes and haloalkynes and for substrates of adequate
chain length, dehalogenation of the haloalkenes or haloalkynes was
followed by cyclisation on to the unsaturated end of the molecule to give
cyclic products. Germinal dihalides underwent dehalogenative
homocoupling to give symmetrical dienes except for 1,1-dichloropropane
and 2,2-dichloropropane where simple dehydrochlorination was observed
to give the chloroalkenes. FVP of benzylic- and benzylidene- halides over magnesium led to
dehalogenative homocoupling to give bibenzyls and stilbenes respectively. Various substituted
bibenzyls and stilbenes were prepared in moderate to
high yields. The amount of magnesium surface available for reaction and a comparative study of the thermal reaction of zinc, calcium and magnesium with benzyl chloride was carried out. On pyrolysis of
o-halobenzyl halides and o-halobenzylidene halides in the presence of
excess magnesium, the loss of both side chain and ring halogens led to
coupling and cyclisation to 9,10-dihydrophenanthrene and phenanthrene
respectively. The ease of ring dehalogenation decreases from iodine to
bromine and chlorine, with fluorine virtually unreactive. Attempts to
prepare symmetrical disubstituted phenanthrenes from substituted
o-halobenzylidene chlorides met with only limited success. Under the
pyrolytic conditions, benzotrichloride was converted to
α, α'-dichlorostilbene, α, α, α', α'-tetrachlorobibenzyl and diphenylacetylene,
the yield of the last two products being dependent on the reaction conditions.
The thermal dehalogenation of α, α'-dihalo-o-xylenes over
magnesium gave benzocyclobutene. The same process afforded fluorinated
benzocyclobutenes and benzodicyclobutene in good yields.
The debromination of α, α, α', α'-tetrabromo-m-xylene over magnesium led to pyrene.
For haloalkylbenzenes, the basic reaction on pyrolysis over
magnesium was dehydrohalogenation to arylalkenes, but this was
sometimes accompanied by bond isomerisation and rearrangement. In the
case of 1-chloro-4-phenylbutane, an additional process of cyclisation on to
the phenyl ring to give tetrahydronaphthalene was observed. The thermal
reaction of 3-chloropropiophenone and 2-bromoacetophenone over
magnesium led not only to dehalogenation products but also to
deoxygenated products. 2-Bromoethyl phenyl ether mainly underwent
dehalogenation and fragmentation to phenol. The
dehalogenation of chlorobenzene and 1,2-dihalobenzenes was also achieved on
pyrolysis over magnesium. Although the main product obtained from the latter was
triphenylene, the involvement of benzyne as an intermediate is in doubt.
The dehalogenation of long chain acid chloride over magnesium,
Was accompanied by fragmentation to give a mixture of alkenes and alkanes.
The magnesium-induced 1,6-dehalogenation of α, α'-halogenated
p -xylenes in the gas phase led to p-xylylenes, which
polymerised. α, α'-Dichloro-p-xylene gave poly(p-xylylene) and
poly(a-chloro-p-xylyene); while α, α, α', α'-tetrachloro-p-xylene and
α, α, α', α'-tetrabromo-p-xylene gave poly(α, α'-dichloro-p-xylylene) and
poly(α, α'-dibromo-p-xylyene) respectively. Also prepared were
poly(α, α,α',a'-tetrachloro-p-xylylene) and poly(α, α, α', α'-tetrafluoro-p-
xylylene) from the corresponding hexahalo-p-xylene. Thermal stability
measurements and the solid state 13C NMR, including molecular weight
estimation were carried out on the polymers.
Some of the processes observed with aryl compounds on pyrolysis
Over magnesium were extented to halogenated thiophene compounds,
especially for the preparation of 1,2-dithienylethenes and derivatives.
Attempts to prepare benzodithiophenes from halo-dichloromethyl-
thiophenes gave halogenated products and isomeric benzodithiophenes.
The isomeric benzodithiophenes obtained and the likely route to them was
investigated. Attempts to generated 2,3-thiophyne by dehalogenation of
mono- and di-halothiophe.nes were inconclusive. The thermal reaction of
a series of epoxides in the presence or absence of magnesium was
investigated. The main process in the absence of magnesium, was
rearrangement to carbonyl compounds, while in the presence of
magnesium, deoxygenation and dehydration reactions were observed in
addition to the thermal rearrangement.Production of alkyl lactate esters by the alkoxycarbonylation of vinyl acetateRucklidge, Adam Jhttps://hdl.handle.net/10023/217972021-09-27T15:58:53Z2005-01-01T00:00:00ZThe methoxycarbonylation of vinyl acetate to methyl 2 and 3- (acetoxy)methylpropanoate has been studied using a variety of bidentate phosphine ligands in the presence of a palladium precursor and acid. In some cases (Bu ᵗ₂P(CH₂)ₙPBuᵗ₂ and 1,2-bis(di-tert-butyIphosphinomethyl)benzene (DTBPMB) the ligands were already known, but new syntheses were established for a variety of other ligands, mostly with xylene backbones. The compounds of general formula 1,2- (RR'PCH₂)C₆H₄ were synthesised either from the reaction of o-xylene with a mixture of KOᵗBu and n-BuLi, followed by R₂PCl (R = ᵗBu, R = ⁱPr, R = Ph, R = Et) or by the reaction of LiPRR'(BH₃) with l,2-bis(dichloromethyl)benzene (R = ᵗBu R' = ⁱPr). LiPRR'(BH₃) was in turn prepared from the reaction of PRR'Cl with NaBH₄ to form PRR'H, and the subsequent reaction with n-BuLi. Similar reactions were used to prepare l,2-bis(di-tert-butylphosphinomethyl)naphthalene (borane protected route) and 2,3-bis(di-tert-butylphosphinomethyl)naphthalene (dianion route). The synthesis of unsymmetrical ligands such as ᵗBuₙPr₂₋ₙPCH₂C₆H₄PCH₂ᵗBu₂ (n = 0 or 1) proved much more problematic. Eventually, they were successfully prepared from the sequential reaction of the cyclic sulphates with Li PRⁱPr(BH₃) (R = ⁱPr or ᵗBu) and Li PᵗBu₂ (BH₃). During the methoxycarbonylation of vinyl acetate, the competing transesterification with methanol to give methyl acetate and dimethoxyethane via ethanal, usually drastically reduces the yield. The addition of tertiary phosphines such as PEt₃, but not DTBPMB, catalyses the degradation reaction, as does methanesulphonic acid. However, provided that the ligand is present in excess over the acid, so that all the acid is present as the phosphonium salt, the degradation reaction does not occur even at 80 °C. The phosphonium salt is sufficiently acidic to allow protonation of the palladium catalyst and DTBPMB promotes good activity for the methoxycarbonylation of vinyl acetate even under very mild conditions (1 bar CO, 25 °C). Optimisation studies have allowed the branched:dinear (b:l) to be improved from 1.2 at 30 bar and 80 °C to 3.6:1 at 1 bar and 25 °C. l,2-bis(di-tert-butylphosphinomethyl)naphthalene and 2,3-bis(di-tert-butylphosphinomethyl)naphthalene both give very similar results, but the other ligands are all inferior. The relative importance of steric and electronic effects on the reaction selectivity are discussed.
2005-01-01T00:00:00ZRucklidge, Adam JThe methoxycarbonylation of vinyl acetate to methyl 2 and 3- (acetoxy)methylpropanoate has been studied using a variety of bidentate phosphine ligands in the presence of a palladium precursor and acid. In some cases (Bu ᵗ₂P(CH₂)ₙPBuᵗ₂ and 1,2-bis(di-tert-butyIphosphinomethyl)benzene (DTBPMB) the ligands were already known, but new syntheses were established for a variety of other ligands, mostly with xylene backbones. The compounds of general formula 1,2- (RR'PCH₂)C₆H₄ were synthesised either from the reaction of o-xylene with a mixture of KOᵗBu and n-BuLi, followed by R₂PCl (R = ᵗBu, R = ⁱPr, R = Ph, R = Et) or by the reaction of LiPRR'(BH₃) with l,2-bis(dichloromethyl)benzene (R = ᵗBu R' = ⁱPr). LiPRR'(BH₃) was in turn prepared from the reaction of PRR'Cl with NaBH₄ to form PRR'H, and the subsequent reaction with n-BuLi. Similar reactions were used to prepare l,2-bis(di-tert-butylphosphinomethyl)naphthalene (borane protected route) and 2,3-bis(di-tert-butylphosphinomethyl)naphthalene (dianion route). The synthesis of unsymmetrical ligands such as ᵗBuₙPr₂₋ₙPCH₂C₆H₄PCH₂ᵗBu₂ (n = 0 or 1) proved much more problematic. Eventually, they were successfully prepared from the sequential reaction of the cyclic sulphates with Li PRⁱPr(BH₃) (R = ⁱPr or ᵗBu) and Li PᵗBu₂ (BH₃). During the methoxycarbonylation of vinyl acetate, the competing transesterification with methanol to give methyl acetate and dimethoxyethane via ethanal, usually drastically reduces the yield. The addition of tertiary phosphines such as PEt₃, but not DTBPMB, catalyses the degradation reaction, as does methanesulphonic acid. However, provided that the ligand is present in excess over the acid, so that all the acid is present as the phosphonium salt, the degradation reaction does not occur even at 80 °C. The phosphonium salt is sufficiently acidic to allow protonation of the palladium catalyst and DTBPMB promotes good activity for the methoxycarbonylation of vinyl acetate even under very mild conditions (1 bar CO, 25 °C). Optimisation studies have allowed the branched:dinear (b:l) to be improved from 1.2 at 30 bar and 80 °C to 3.6:1 at 1 bar and 25 °C. l,2-bis(di-tert-butylphosphinomethyl)naphthalene and 2,3-bis(di-tert-butylphosphinomethyl)naphthalene both give very similar results, but the other ligands are all inferior. The relative importance of steric and electronic effects on the reaction selectivity are discussed.Synthesis, characterisation and catalytic applications of mesocaged solidsGarcia-Bennett, Alfonso Eduardohttps://hdl.handle.net/10023/217912021-09-28T02:05:30Z2003-01-01T00:00:00ZThe synthesis of mesoporous materials has been investigated using a variety of liquid crystal surfactant systems as structure directing agents. Syntheses have been conducted in acid and basic media and at a variety of temperatures ranging from -4°C to 100°C and using different surfactant concentrations in order to control the resulting mesophase and its morphology. The mesoporous materials made have been characterised extensively using High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy, X-ray diffraction, adsorption-desorption isotherms of various gases (nitrogen, w-hexane, cyclopentane, and mesitylene) and solid state Nuclear Magnetic Resonance (NMR). Hence, the morphology, structure and pore characteristics of known mesoporous materials SBA-1, SBA-2 and novel mesoporous materials, STA-10 (hexagonal, P6₃/mmc) and STA-11 (cubic, Ia3d), have been characterised. Results have yielded interesting information on the bimodal nature and dimensions of cages in SBA-1, the cage window size of SBA-2 and its cubic polytypic intergrowth STAC-1, their structural defects and their potential use as heterogeneous catalysts. The mesoporous phase STA-11, synthesised using triblock polymer PEO-PPO-PEO as a template displays one of the largest unit cells yet reported and has a cubic structure similar to that of MCM-48. This material has been extensively studied by HRTEM. In addition, we have explored the incorporation of heteroatoms (aluminium and titanium) into mesoporous molecular sieves, leading to the formation of tetrahedral catalytic active sites within the internal surface area of the mesopores via direct and post synthesis procedures. The active sites have been characterised using ²⁷A1 MAS NMR and Ti-EXAFS, respectively. These materials have been tested as catalysts for, among others, the epoxidation of cyclohexene and 1-octene (for those with titanium as the active site) and in the alkoxylation of a-pinene and limonene, and the skeletal isomerisation of butene (for those samples with aluminium as the active sites). Improvement of conversions and selectivity to the desired product has been achieved by post-synthetic treatment of the heteroatom-incorporated materials, for example treatment with ammonia for aluminium samples.
2003-01-01T00:00:00ZGarcia-Bennett, Alfonso EduardoThe synthesis of mesoporous materials has been investigated using a variety of liquid crystal surfactant systems as structure directing agents. Syntheses have been conducted in acid and basic media and at a variety of temperatures ranging from -4°C to 100°C and using different surfactant concentrations in order to control the resulting mesophase and its morphology. The mesoporous materials made have been characterised extensively using High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy, X-ray diffraction, adsorption-desorption isotherms of various gases (nitrogen, w-hexane, cyclopentane, and mesitylene) and solid state Nuclear Magnetic Resonance (NMR). Hence, the morphology, structure and pore characteristics of known mesoporous materials SBA-1, SBA-2 and novel mesoporous materials, STA-10 (hexagonal, P6₃/mmc) and STA-11 (cubic, Ia3d), have been characterised. Results have yielded interesting information on the bimodal nature and dimensions of cages in SBA-1, the cage window size of SBA-2 and its cubic polytypic intergrowth STAC-1, their structural defects and their potential use as heterogeneous catalysts. The mesoporous phase STA-11, synthesised using triblock polymer PEO-PPO-PEO as a template displays one of the largest unit cells yet reported and has a cubic structure similar to that of MCM-48. This material has been extensively studied by HRTEM. In addition, we have explored the incorporation of heteroatoms (aluminium and titanium) into mesoporous molecular sieves, leading to the formation of tetrahedral catalytic active sites within the internal surface area of the mesopores via direct and post synthesis procedures. The active sites have been characterised using ²⁷A1 MAS NMR and Ti-EXAFS, respectively. These materials have been tested as catalysts for, among others, the epoxidation of cyclohexene and 1-octene (for those with titanium as the active site) and in the alkoxylation of a-pinene and limonene, and the skeletal isomerisation of butene (for those samples with aluminium as the active sites). Improvement of conversions and selectivity to the desired product has been achieved by post-synthetic treatment of the heteroatom-incorporated materials, for example treatment with ammonia for aluminium samples.Optimisation of performance of tin oxide based anodes for high energy density lithium batteriesAttidekou, Pierrot S.https://hdl.handle.net/10023/217692021-04-06T02:01:30Z2005-06-22T00:00:00ZThe goal of this work was to synthesise and investigate a tin based oxide compound, SnP₂O₇ and its doped analogues, as a potential negative electrode for lithium battery. SnP₂O₇ has two polymorphs: the cubic and the layered forms. It has been proven that the cubic form has a better performance on cycling compared to the layered. This work has focused on the cubic form in order to understand the mechanisms occurring upon charge and discharge in order to improve the capacity and the cycling ability. The achievement of this task requires several steps.
SnP₂O₇ was synthesised and fully characterised structurally and electrochemically. The structural characterisation has elucidated the complexity of the material that crystallises in a 3x3x3 superstructure with the presence of nanodomains. Electrochemical characterisation has shown that on insertion of lithium into the material, finely dispersed tin nanoparticles are formed in an amorphous lithiated pyrophosphate matrix before the tin particles alloy with lithium providing the useful capacity of the battery. This material displays an irreversible capacity of 965mAh/g and a reversible capacity of 365 mAh/g. The overall reaction of lithium toward SnP₂O₇ was divided into 3 different zones and the kinetic and thermodynamic features evaluated. The thermodynamic study made on a cell with SnP₂O₇ electrode has provided a very high value of entropy upon the conversion of SnP₂O₇ to metallic tin plus lithiated pyrophosphate matrix. The lithiated phosphate matrix form is then reduced to another lithiated phosphate matrix, which is stable with an unusual oxidation state of phosphorus that we believe to be Pᴵⱽ. The lithium diffusion was estimated as 8x10⁻¹⁵cm²/s and matches those obtained for other lithium battery materials.
The addition of borate to the tin pyrophosphate system such as (SnO₂:B₂O₃)[sub](y/2)/(SnP₂O₇)[sub](1-y/2) was studied in order to lighten the matrix and increase the specific capacity and to evaluate the role of the matrix toward capacity retention. As it has been shown that amorphous materials often cycle better than the crystalline tin composite oxides, the addition of borate should be beneficial due to the decrease in crystallinity. This study has revealed upon substitution 3 different phase domains that were characterised to be crystalline up to y = 0.19, a mix of crystalline and amorphous (0.25 < y < 1.75) and a fully amorphous region for high borate content (y > 1.75). At all levels of substitution there was a decrease in both irreversible and reversible capacity. The best capacity of borate doped samples was found in the low borate crystalline region. Therefore borate appears not to be a suitable matrix for lithium batteries.
Titanium was added to SnP₂O₇ to see the effect of a smaller cation in the system. Titanium substitution has shown a co-existence of different chemistry types such as both alloying and non-alloying processes for Sn₁₋ₓTiₓP₂O₇ system. Pure titanium pyrophosphate has shown complex electrochemistry and seems to form a transition metal oxide in a phosphate matrix, with additional formation of SEI that was depicted by HRTEM. The electrochemistry has shown formation of several different linephases, biphasic regions and solid solution transformations. The best capacity found was for composition with y = 0.15, which has shown an increase of the reversible capacity of 10% over pure SnP₂O₇.
2005-06-22T00:00:00ZAttidekou, Pierrot S.The goal of this work was to synthesise and investigate a tin based oxide compound, SnP₂O₇ and its doped analogues, as a potential negative electrode for lithium battery. SnP₂O₇ has two polymorphs: the cubic and the layered forms. It has been proven that the cubic form has a better performance on cycling compared to the layered. This work has focused on the cubic form in order to understand the mechanisms occurring upon charge and discharge in order to improve the capacity and the cycling ability. The achievement of this task requires several steps.
SnP₂O₇ was synthesised and fully characterised structurally and electrochemically. The structural characterisation has elucidated the complexity of the material that crystallises in a 3x3x3 superstructure with the presence of nanodomains. Electrochemical characterisation has shown that on insertion of lithium into the material, finely dispersed tin nanoparticles are formed in an amorphous lithiated pyrophosphate matrix before the tin particles alloy with lithium providing the useful capacity of the battery. This material displays an irreversible capacity of 965mAh/g and a reversible capacity of 365 mAh/g. The overall reaction of lithium toward SnP₂O₇ was divided into 3 different zones and the kinetic and thermodynamic features evaluated. The thermodynamic study made on a cell with SnP₂O₇ electrode has provided a very high value of entropy upon the conversion of SnP₂O₇ to metallic tin plus lithiated pyrophosphate matrix. The lithiated phosphate matrix form is then reduced to another lithiated phosphate matrix, which is stable with an unusual oxidation state of phosphorus that we believe to be Pᴵⱽ. The lithium diffusion was estimated as 8x10⁻¹⁵cm²/s and matches those obtained for other lithium battery materials.
The addition of borate to the tin pyrophosphate system such as (SnO₂:B₂O₃)[sub](y/2)/(SnP₂O₇)[sub](1-y/2) was studied in order to lighten the matrix and increase the specific capacity and to evaluate the role of the matrix toward capacity retention. As it has been shown that amorphous materials often cycle better than the crystalline tin composite oxides, the addition of borate should be beneficial due to the decrease in crystallinity. This study has revealed upon substitution 3 different phase domains that were characterised to be crystalline up to y = 0.19, a mix of crystalline and amorphous (0.25 < y < 1.75) and a fully amorphous region for high borate content (y > 1.75). At all levels of substitution there was a decrease in both irreversible and reversible capacity. The best capacity of borate doped samples was found in the low borate crystalline region. Therefore borate appears not to be a suitable matrix for lithium batteries.
Titanium was added to SnP₂O₇ to see the effect of a smaller cation in the system. Titanium substitution has shown a co-existence of different chemistry types such as both alloying and non-alloying processes for Sn₁₋ₓTiₓP₂O₇ system. Pure titanium pyrophosphate has shown complex electrochemistry and seems to form a transition metal oxide in a phosphate matrix, with additional formation of SEI that was depicted by HRTEM. The electrochemistry has shown formation of several different linephases, biphasic regions and solid solution transformations. The best capacity found was for composition with y = 0.15, which has shown an increase of the reversible capacity of 10% over pure SnP₂O₇.Title redactedGao, Sisihttps://hdl.handle.net/10023/217622021-04-02T13:00:27Z2020-12-02T00:00:00Z2020-12-02T00:00:00ZGao, SisiInvestigations of methanol-to-hydrocarbons catalysis in zeolites by synchrotron infrared microspectroscopyMinova, Ivalina Blagovestovahttps://hdl.handle.net/10023/217562021-08-23T11:24:17Z2020-12-01T00:00:00ZThe catalytic conversion of methanol to hydrocarbons (MTH reaction) has been investigated by a synchrotron-based spectroscopic method that was developed at the Diamond Light Source. The operando synchrotron infrared microspectroscopy (OIMS) method presented here measures time-resolved spectra from large zeolite crystals with simultaneous on-line analysis of gas phase products by mass spectrometry. The results showed that OIMS can follow reactions on crystals down to 30 microns in size, with a time resolution of 2 s routinely, and down to 0.25 s. Heterogeneities in the acid site density of steamed samples can be visualised.
Large crystals of two commercially-relevant materials, HZSM-5 and HSAPO-34, were prepared to gain mechanistic insights into the MTH, methanol-to-olefins (MTO) and dimethyl ether-to-olefins (DMTO) reactions. Initial studies focused on the elementary steps of olefins formation in the early stages of the MTH reaction over HZSM-5 during pulses of methanol and continuous flow of dimethyl ether. Surface bound methoxy groups (SMS) were identified as the key reactive species for the direct formation of olefins. The studies of both HZSM-5 and HSAPO-34 suggest that SMS (produced from methanol or dimethyl ether) couple directly via a carbene-like transition state to make the first olefins. This was confirmed by studies with deuterium-labelled reactants. The reactivity of SMS was found to be dependent on zeolite topology and acid site strength with lower reactivity seen for HSAPO-34. Identification of methylated cyclopentenyl carbenium ions, oligomers and cracking reactions were compared for HZSM-5 and HSAPO-34 and for three different crystal sizes of HZSM-5. Varying the crystal size reduced the diffusion path lengths and shortened the induction period, and reduced induction periods were also seen at higher reaction temperatures in the 473–673 K range studied.
The last chapter explored the effect of steaming on the structure and catalytic properties of HSAPO-34. A steaming protocol was developed to investigate the effect of varying the severity of the treatment (up to 1023 K) on the structural and textural properties of the materials and their catalytic performance in the MTO reaction. Ex-situ characterisation, MTO catalytic performance and operando FTIR studies were analysed, suggesting a three-stage transformation is occurring during steaming of HSAPO-34. Under mild to moderate steaming there is redistribution of silica, followed by the development of an optically dark ‘core’ that contains meso- and macropores, but under harsh steaming conditions the samples rapidly recrystallise to a denser phase losing its micropore volume.
2020-12-01T00:00:00ZMinova, Ivalina BlagovestovaThe catalytic conversion of methanol to hydrocarbons (MTH reaction) has been investigated by a synchrotron-based spectroscopic method that was developed at the Diamond Light Source. The operando synchrotron infrared microspectroscopy (OIMS) method presented here measures time-resolved spectra from large zeolite crystals with simultaneous on-line analysis of gas phase products by mass spectrometry. The results showed that OIMS can follow reactions on crystals down to 30 microns in size, with a time resolution of 2 s routinely, and down to 0.25 s. Heterogeneities in the acid site density of steamed samples can be visualised.
Large crystals of two commercially-relevant materials, HZSM-5 and HSAPO-34, were prepared to gain mechanistic insights into the MTH, methanol-to-olefins (MTO) and dimethyl ether-to-olefins (DMTO) reactions. Initial studies focused on the elementary steps of olefins formation in the early stages of the MTH reaction over HZSM-5 during pulses of methanol and continuous flow of dimethyl ether. Surface bound methoxy groups (SMS) were identified as the key reactive species for the direct formation of olefins. The studies of both HZSM-5 and HSAPO-34 suggest that SMS (produced from methanol or dimethyl ether) couple directly via a carbene-like transition state to make the first olefins. This was confirmed by studies with deuterium-labelled reactants. The reactivity of SMS was found to be dependent on zeolite topology and acid site strength with lower reactivity seen for HSAPO-34. Identification of methylated cyclopentenyl carbenium ions, oligomers and cracking reactions were compared for HZSM-5 and HSAPO-34 and for three different crystal sizes of HZSM-5. Varying the crystal size reduced the diffusion path lengths and shortened the induction period, and reduced induction periods were also seen at higher reaction temperatures in the 473–673 K range studied.
The last chapter explored the effect of steaming on the structure and catalytic properties of HSAPO-34. A steaming protocol was developed to investigate the effect of varying the severity of the treatment (up to 1023 K) on the structural and textural properties of the materials and their catalytic performance in the MTO reaction. Ex-situ characterisation, MTO catalytic performance and operando FTIR studies were analysed, suggesting a three-stage transformation is occurring during steaming of HSAPO-34. Under mild to moderate steaming there is redistribution of silica, followed by the development of an optically dark ‘core’ that contains meso- and macropores, but under harsh steaming conditions the samples rapidly recrystallise to a denser phase losing its micropore volume.Nanometre distances, orientation and multimerisation equilibria from pulse dipolar EPR spectroscopyOranges, Mariahttps://hdl.handle.net/10023/215802022-08-08T13:26:22Z2020-12-01T00:00:00ZPulse Dipolar Electron Paramagnetic Resonance (PD-EPR) spectroscopy, has become a very powerful method for investigating the structures and conformational equilibria biological systems adapt during their function.
Pulse ELectron-electron DOuble Resonance (PELDOR) spectroscopy, can recover the weak magnetic dipole-dipole coupling interaction between paramagnetic centres. The latter ones are often endogenous to the system, like paramagnetic metal ions, protein bound radical cofactors, iron sulfur clusters, or amino acid radicals. Nevertheless, with the invention of the Site-Directed Spin-Labelling (SDSL), it has become possible to covalently bind a spin label to a cysteine residue engineered to a specific site of a protein. In combination with PD-EPR, this method has been extensively used for studying the structures of biomolecules, conformational changes, conformational states and multimerisation equilibria, by probing different sites of the molecules through spin labelling. Here, a method using PELDOR to study conformational changes within one monomeric unit of a multimeric system is proposed. This consists in identifying the intra-monomer distance among the inter-monomer distances when the monomers are doubly spin labelled. Moreover, a solution multimerisation study of a model protein found as dimer in its crystal structure is presented.
The Relaxation-Induced Dipolar Modulation Enhancement (RIDME) experiment, is another method to resolve weak dipole-dipole interactions between paramagnetic centres. It has become a very attractive alternative to PELDOR when the measurements involve paramagnetic metal ions, because the dipolar interaction is induced by the spontaneous longitudinal relaxation of the metal ion spins which often display broad spectra limiting PELDOR sensitivity.
An approach to retrieve angular constraints from RIDME distance measurements is shown. This is performed on a protein model system using a copper(II)-nitroxide spin pair.
Finally, a metal templated dimerisation model is demonstrated to simultaneously match PELDOR and RIDME data for monitoring and characterising the dimerisation of monomeric units of a protein on a template.
2020-12-01T00:00:00ZOranges, MariaPulse Dipolar Electron Paramagnetic Resonance (PD-EPR) spectroscopy, has become a very powerful method for investigating the structures and conformational equilibria biological systems adapt during their function.
Pulse ELectron-electron DOuble Resonance (PELDOR) spectroscopy, can recover the weak magnetic dipole-dipole coupling interaction between paramagnetic centres. The latter ones are often endogenous to the system, like paramagnetic metal ions, protein bound radical cofactors, iron sulfur clusters, or amino acid radicals. Nevertheless, with the invention of the Site-Directed Spin-Labelling (SDSL), it has become possible to covalently bind a spin label to a cysteine residue engineered to a specific site of a protein. In combination with PD-EPR, this method has been extensively used for studying the structures of biomolecules, conformational changes, conformational states and multimerisation equilibria, by probing different sites of the molecules through spin labelling. Here, a method using PELDOR to study conformational changes within one monomeric unit of a multimeric system is proposed. This consists in identifying the intra-monomer distance among the inter-monomer distances when the monomers are doubly spin labelled. Moreover, a solution multimerisation study of a model protein found as dimer in its crystal structure is presented.
The Relaxation-Induced Dipolar Modulation Enhancement (RIDME) experiment, is another method to resolve weak dipole-dipole interactions between paramagnetic centres. It has become a very attractive alternative to PELDOR when the measurements involve paramagnetic metal ions, because the dipolar interaction is induced by the spontaneous longitudinal relaxation of the metal ion spins which often display broad spectra limiting PELDOR sensitivity.
An approach to retrieve angular constraints from RIDME distance measurements is shown. This is performed on a protein model system using a copper(II)-nitroxide spin pair.
Finally, a metal templated dimerisation model is demonstrated to simultaneously match PELDOR and RIDME data for monitoring and characterising the dimerisation of monomeric units of a protein on a template.Electrochemical studies of solid solution electrodesSmith, Michael J.https://hdl.handle.net/10023/209762020-11-14T03:06:30Z1983-01-01T00:00:00ZUsing a method based on the analysis of the voltage transient recorded during the application of a galvanostatic pulse to a solid state, three electrode cell, diffusion coefficients of silver electro-active
species in AgₓTiS₁.₈ and AgₓNbS₂ were obtained. The activation energy of the diffusion process was found to be approximately 30 kJ mole⁻¹ for TiS₁.₈ and between 34 kJ mole⁻¹ and 24 kJ mole⁻¹, decreasing with increasing guest concentration, for NbS₂. Non-linearity at extended times in the
experimental timescale was ascribed to finite length effects, variation of the thermodynamic enhancement factor during the pulse, or a combination of these influences.
Temperature and composition variation of the cell emf, for AgₓTiS₁.₈ and AgₓNbS₂ systems, permitted thermodynamic parameters and the compositional variation of the enhancement factors to be obtained.
Investigation of the effect of the temperature of oven pre-treatment on compressed powder samples of a lithium ion conducting vitreous electrolyte on the bulk conductivity was carried out using a scanning electron microscope and ac conductivity measurements.
Electronic conductivity measurements, using Wagner's method were undertaken on samples of iodotungstate and iodoarsenate glass with a view to confirmation of the low levels necessary for the use of these electrolytes in galvanic cells.
1983-01-01T00:00:00ZSmith, Michael J.Using a method based on the analysis of the voltage transient recorded during the application of a galvanostatic pulse to a solid state, three electrode cell, diffusion coefficients of silver electro-active
species in AgₓTiS₁.₈ and AgₓNbS₂ were obtained. The activation energy of the diffusion process was found to be approximately 30 kJ mole⁻¹ for TiS₁.₈ and between 34 kJ mole⁻¹ and 24 kJ mole⁻¹, decreasing with increasing guest concentration, for NbS₂. Non-linearity at extended times in the
experimental timescale was ascribed to finite length effects, variation of the thermodynamic enhancement factor during the pulse, or a combination of these influences.
Temperature and composition variation of the cell emf, for AgₓTiS₁.₈ and AgₓNbS₂ systems, permitted thermodynamic parameters and the compositional variation of the enhancement factors to be obtained.
Investigation of the effect of the temperature of oven pre-treatment on compressed powder samples of a lithium ion conducting vitreous electrolyte on the bulk conductivity was carried out using a scanning electron microscope and ac conductivity measurements.
Electronic conductivity measurements, using Wagner's method were undertaken on samples of iodotungstate and iodoarsenate glass with a view to confirmation of the low levels necessary for the use of these electrolytes in galvanic cells.X-ray studies of novel metal-organic frameworksCarpenter-Warren, Cameron Lewishttps://hdl.handle.net/10023/209272021-08-14T10:55:15Z2020-12-01T00:00:00ZMOFs (Metal-organic frameworks) are a series of record-breaking materials that
have been developed rapidly, in terms of variety, functionality, popularity and understanding, over the past quarter of a century. MOFs are defined not only by their
inclusion of inorganic SBUs (Secondary building units) held together by organic
linkers, but also by their potential for containing void space within their structures.
MOFs quickly became the most porous materials in the world, surpassing the previous
record holders, zeolites. Interest in these materials began with their ability to
store and separate different gasses efficiently. It is however, their unique tunability
that makes these materials so exciting, and they have since been put to work solving
innumerable problems throughout the chemical and materials fields.
The majority of MOFs use anionic, polydentate linkers, such as carboxylates,
because they result in neutral MOFs with large SBUs, which retain their porosity
upon solvent removal. It was found early on that using just neutral, N-donor linkers
results in cationic frameworks which collapse upon guest removal. The work in this
thesis explores the use of both N- and O-donor linkers in the same system, with the
aim of synthesizing novel structures with unique topologies and physical properties.
The first two chapters of this work will briefly introduce the history and theory
behind crystallography and diffraction techniques, then MOFs and some of the
associated characterisation techniques and structural features.
The main chapter of this work will then detail the structural characterisation of
18 novel mixed N/O-donor MOFs synthesized by the author or by Reza Abazari's
group at Tarbiat Modares University, Iran. The materials produced spanned a range
of dimensionalities, and the geometrical and topological features of these new compounds
are discussed and compared with analogues in the literature. Unique SBUs
were achieved in some of these structures, resulting in three new MOF topologies.
The two chapters following this will describe some additional MOFs which, despite
failing to incorporate the N-donor linkers, are still new structures. The first of these
two chapters focuses mainly on transition metal structures, with some examples of
SBU modification by N-donor ligands to produce rare topologies. The second of
these chapters focuses solely on new lanthanoid MOFs.
The penultimate chapter contains the experimental procedures involved in synthesizing
and characterizing the MOFs in this work. The final chapter is an additional
structures section, depicting some of the other new structures run and solved by the
author. The Supplementary information can be found at the end of this volume and
contains a SC-XRD experimental table for each structure presented in this work.
2020-12-01T00:00:00ZCarpenter-Warren, Cameron LewisMOFs (Metal-organic frameworks) are a series of record-breaking materials that
have been developed rapidly, in terms of variety, functionality, popularity and understanding, over the past quarter of a century. MOFs are defined not only by their
inclusion of inorganic SBUs (Secondary building units) held together by organic
linkers, but also by their potential for containing void space within their structures.
MOFs quickly became the most porous materials in the world, surpassing the previous
record holders, zeolites. Interest in these materials began with their ability to
store and separate different gasses efficiently. It is however, their unique tunability
that makes these materials so exciting, and they have since been put to work solving
innumerable problems throughout the chemical and materials fields.
The majority of MOFs use anionic, polydentate linkers, such as carboxylates,
because they result in neutral MOFs with large SBUs, which retain their porosity
upon solvent removal. It was found early on that using just neutral, N-donor linkers
results in cationic frameworks which collapse upon guest removal. The work in this
thesis explores the use of both N- and O-donor linkers in the same system, with the
aim of synthesizing novel structures with unique topologies and physical properties.
The first two chapters of this work will briefly introduce the history and theory
behind crystallography and diffraction techniques, then MOFs and some of the
associated characterisation techniques and structural features.
The main chapter of this work will then detail the structural characterisation of
18 novel mixed N/O-donor MOFs synthesized by the author or by Reza Abazari's
group at Tarbiat Modares University, Iran. The materials produced spanned a range
of dimensionalities, and the geometrical and topological features of these new compounds
are discussed and compared with analogues in the literature. Unique SBUs
were achieved in some of these structures, resulting in three new MOF topologies.
The two chapters following this will describe some additional MOFs which, despite
failing to incorporate the N-donor linkers, are still new structures. The first of these
two chapters focuses mainly on transition metal structures, with some examples of
SBU modification by N-donor ligands to produce rare topologies. The second of
these chapters focuses solely on new lanthanoid MOFs.
The penultimate chapter contains the experimental procedures involved in synthesizing
and characterizing the MOFs in this work. The final chapter is an additional
structures section, depicting some of the other new structures run and solved by the
author. The Supplementary information can be found at the end of this volume and
contains a SC-XRD experimental table for each structure presented in this work.Li@C₆₀, the molecular maraca : exploring the properties of lithium endohedral fullerenes on transition metal surfaces for potential use in molecular electronicsChandler, Henry Jameshttps://hdl.handle.net/10023/209172023-04-26T02:05:48Z2020-12-01T00:00:00ZThe following thesis describes the exploration of lithium endohedral fullerenes (Li@C₆₀) on Au(111) and Cu(110)-(2×1)O utilising an ultra-high vacuum low temperature scanning tunnelling microscope (UHV LT-STM). In collaboration with researchers from the University of Edinburgh and the University of Liège, the effect of Li-encapsulation on the electronic structure of C₆₀ has been experimentally identified on single molecules for the first time, with particular attention to the superatom molecular orbitals (SAMOs). It was hypothesised these would stabilise due to the hybridisation of orbitals from the carbon cage and lithium. However, since the Li is known to stabilise in an off-centre position within the C₆₀, this asymmetry induces a non-degenerate stabilisation of the SAMOs. This stabilisation is analysed with scanning tunnelling spectroscopy (STS), and our conclusions are confirmed by photoelectron spectroscopy (PES) and time dependent density functional theory (TDDFT) data provided by our collaborators.
Once the electronic structure is understood, the experiments detailed herein turn towards studying the Li@C₆₀ for potential as a multi-state single molecular switch. Upon identifying a set of parameters which allow the repeated, and reversible, manipulation of Li@C₆₀, the process is studied methodically and reveals that Li@C₆₀ can be switched between 14 distinct states. This is the highest number of discrete, accessible states to be observed on a single molecule switch to date. A mixture of scanning tunnelling microscopy (STM) and spectroscopy (STS) is required to identify these states, and high manipulation biases and tunnelling currents are needed to activate the switch. Since these parameters are orders of magnitude higher than those typically used, a new mechanism is required to describe the process. The suggestion made here is that resonant tunnelling electrons couple with the p[sub](x,y)-SAMOs to bypass the carbon cage thus activating the encapsulated Li and avoiding vibrational excitation of the C₆₀. Upon exciting the Li, it rattles around the interior of the fullerene before randomly stabilising in one of the identified 14 states.
2020-12-01T00:00:00ZChandler, Henry JamesThe following thesis describes the exploration of lithium endohedral fullerenes (Li@C₆₀) on Au(111) and Cu(110)-(2×1)O utilising an ultra-high vacuum low temperature scanning tunnelling microscope (UHV LT-STM). In collaboration with researchers from the University of Edinburgh and the University of Liège, the effect of Li-encapsulation on the electronic structure of C₆₀ has been experimentally identified on single molecules for the first time, with particular attention to the superatom molecular orbitals (SAMOs). It was hypothesised these would stabilise due to the hybridisation of orbitals from the carbon cage and lithium. However, since the Li is known to stabilise in an off-centre position within the C₆₀, this asymmetry induces a non-degenerate stabilisation of the SAMOs. This stabilisation is analysed with scanning tunnelling spectroscopy (STS), and our conclusions are confirmed by photoelectron spectroscopy (PES) and time dependent density functional theory (TDDFT) data provided by our collaborators.
Once the electronic structure is understood, the experiments detailed herein turn towards studying the Li@C₆₀ for potential as a multi-state single molecular switch. Upon identifying a set of parameters which allow the repeated, and reversible, manipulation of Li@C₆₀, the process is studied methodically and reveals that Li@C₆₀ can be switched between 14 distinct states. This is the highest number of discrete, accessible states to be observed on a single molecule switch to date. A mixture of scanning tunnelling microscopy (STM) and spectroscopy (STS) is required to identify these states, and high manipulation biases and tunnelling currents are needed to activate the switch. Since these parameters are orders of magnitude higher than those typically used, a new mechanism is required to describe the process. The suggestion made here is that resonant tunnelling electrons couple with the p[sub](x,y)-SAMOs to bypass the carbon cage thus activating the encapsulated Li and avoiding vibrational excitation of the C₆₀. Upon exciting the Li, it rattles around the interior of the fullerene before randomly stabilising in one of the identified 14 states.Synthesis and characterisation of novel ion conductorsWilson, Stephyhttps://hdl.handle.net/10023/203892021-07-29T13:38:24Z2020-07-27T00:00:00ZAs hydrogen is a renewable energy source, the studies for materials exhibiting fast hydrogen transport can have great potential to be used as electrolytes for electrochemical devices and as strong reducing agents for electrochemical conversion reactions.
The alkaline earth metals, AeH₂, where Ae = Ca, Sr and Ba are of interest as they exhibit fast hydride ion conductivity which may enable them to be used as solid-state electrolytes in electrochemical devices. BaH₂ has a high hydride ion conductivity of 0.2 S cm⁻¹ at 630 °C, which is an order of magnitude higher than other oxide ion conductors at a similar temperature. The in-situ PDF and conductivity study of BaD₂ was performed to examine the local deviation from the average crystal structure. The technique using neutron total scattering helped to examine possible short-range correlations between atoms to understand the local structure of BaD₂.
BaH₂ was doped with the monovalent ions Na or Li and its structural and electrical properties, were investigated. LiₓBa₁₋ₓH₂₋ₓ (x = 0.05, 0.10, 0.15 and 0.20) were synthesised by the solid-state reaction in which Li₀.₁₀Ba₀.₉₀H₁.₉₀ has achieved highest conductivity of 0.38 S cm⁻¹ at 600 °C.
LiBaH₃ was synthesised by mechanochemical reaction at room temperature and solid-state reaction at high temperature, and their structural and electrical properties were analysed. LiBaH₃ has a conductivity of 0.01 S cm⁻¹ at 600 °C. NaₓLi₁₋ₓBaH₃ (x = 0.05, 0.15 and 0.20) were also synthesised by solid-state reaction and their structural and electrical properties were examined. Na₀.₁₅Li₀.₈₅BaH₃ has the highest conductivity of the Na-doped LiBaH₃ samples studied, exhibiting a conductivity of 0.03 S cm⁻¹ at 600 °C.
Nitridation in LiₓBa₁₋ₓH₂₋ₓ (x = 0.05, 0.10, 0.15 and 0.20), NaₓBa₁₋ₓH₂₋ₓ (x = 0.01, 0.05 and 0.10), LiBaH₃ and NaₓLi₁₋ₓBaH₃ (x = 0.05, 0.15 and 0.20) increases their conductivity by 0.02 S cm⁻¹ initially due to exothermic reaction, except the nitridation of BaH₂ at 600 °C, where their conductivity decreases by 0.04 S cm⁻¹ upon nitridation due to endothermic reaction.
2020-07-27T00:00:00ZWilson, StephyAs hydrogen is a renewable energy source, the studies for materials exhibiting fast hydrogen transport can have great potential to be used as electrolytes for electrochemical devices and as strong reducing agents for electrochemical conversion reactions.
The alkaline earth metals, AeH₂, where Ae = Ca, Sr and Ba are of interest as they exhibit fast hydride ion conductivity which may enable them to be used as solid-state electrolytes in electrochemical devices. BaH₂ has a high hydride ion conductivity of 0.2 S cm⁻¹ at 630 °C, which is an order of magnitude higher than other oxide ion conductors at a similar temperature. The in-situ PDF and conductivity study of BaD₂ was performed to examine the local deviation from the average crystal structure. The technique using neutron total scattering helped to examine possible short-range correlations between atoms to understand the local structure of BaD₂.
BaH₂ was doped with the monovalent ions Na or Li and its structural and electrical properties, were investigated. LiₓBa₁₋ₓH₂₋ₓ (x = 0.05, 0.10, 0.15 and 0.20) were synthesised by the solid-state reaction in which Li₀.₁₀Ba₀.₉₀H₁.₉₀ has achieved highest conductivity of 0.38 S cm⁻¹ at 600 °C.
LiBaH₃ was synthesised by mechanochemical reaction at room temperature and solid-state reaction at high temperature, and their structural and electrical properties were analysed. LiBaH₃ has a conductivity of 0.01 S cm⁻¹ at 600 °C. NaₓLi₁₋ₓBaH₃ (x = 0.05, 0.15 and 0.20) were also synthesised by solid-state reaction and their structural and electrical properties were examined. Na₀.₁₅Li₀.₈₅BaH₃ has the highest conductivity of the Na-doped LiBaH₃ samples studied, exhibiting a conductivity of 0.03 S cm⁻¹ at 600 °C.
Nitridation in LiₓBa₁₋ₓH₂₋ₓ (x = 0.05, 0.10, 0.15 and 0.20), NaₓBa₁₋ₓH₂₋ₓ (x = 0.01, 0.05 and 0.10), LiBaH₃ and NaₓLi₁₋ₓBaH₃ (x = 0.05, 0.15 and 0.20) increases their conductivity by 0.02 S cm⁻¹ initially due to exothermic reaction, except the nitridation of BaH₂ at 600 °C, where their conductivity decreases by 0.04 S cm⁻¹ upon nitridation due to endothermic reaction.Title redactedMalapati, Ajaya Kumarhttps://hdl.handle.net/10023/203412022-05-10T10:06:18Z2020-07-29T00:00:00Z2020-07-29T00:00:00ZMalapati, Ajaya KumarExploration of vanadium sulfates as positive electrodes for battery applicationsLinnell, Stephanie Franceshttps://hdl.handle.net/10023/203282022-07-06T02:09:31Z2020-07-29T00:00:00ZThe exploration and development of safer and less expensive positive electrode materials, for high energy density lithium ion batteries (LIBs), are essential for large scale applications, such as electric vehicles and grid energy storage. Of all the candidates, vanadium based compounds have attracted considerable interest. This is due to vanadium’s ability to adopt a range of oxidation states, with oxidation states of III, IV and V being particularly common in battery materials. This enables vanadium to undergo multi electron transfer processes, which allow reversible insertion/extraction of more than one Li⁺ ion per transition metal.
This thesis explores a range of vanadium based materials as candidate positive electrode materials for LIBs. The materials were separated into three groups (i) phases containing the mononuclear [VO] ³⁺ species, AVO(SO₄)₂ (A = NH₄⁺, K⁺), (ii) phases containing the mononuclear [VO₂]⁺ species, AVO₂SO₄ (A = NH₄⁺, K⁺), and (iii) V₂O₃(SO₄)₂ which contains the [V₂O₃]⁴⁺ species.
NH₄V⁽ⱽ⁾O(SO₄)₂ and KV⁽ⱽ⁾O(SO₄)₂ were studied initially. While these materials have previously been synthesised, their electrochemical properties have not been evaluated before. NH₄VO(SO₄)₂ and KVO(SO₄)₂ were prepared via solution based methods using low temperatures (≤200 °C) and were characterised using X-ray diffraction, infrared spectroscopy, scanning electron microscopy and optical microscopy. These compounds are isostructural and are made up of distorted VO₆ octahedra corner sharing with five SO₄ tetrahedra, forming layered structures. The thermal stability of these materials was examined by means of thermogravimetric analysis. Additionally, the intermediate phases identified from thermogravimetric analysis were characterised and this work led to the structural study of the layered material, 2VOSO₄·H₂SO₄, in order to determine the positions of the hydrogen atoms and evaluate the disorder associated with the H₂SO₄ layer. The electrochemical performance of NH₄VO(SO₄)₂ and KVO(SO₄)₂ as positive electrode materials for LIBs were tested for the first time. Both materials were found to operate at a high voltage of 4.05 V versus Li⁺/Li⁰ and presented similar discharge profiles and specific discharge capacities of <20 mA h g⁻¹.
Thereafter, the dioxovanadium phases, KV⁽ⱽ⁾O₂SO₄ and NH₄V⁽ⱽ⁾O₂SO₄ were explored. The synthesis of the KVO₂SO₄ phase has previously been reported in literature but its electrochemical properties were tested here for the first time. KVO₂SO₄ was synthesised by a solid state route at 300 – 400 °C, forming a three dimensional framework structure consisting of corner sharing VO₆ octahedra interconnected by corner sharing and edge sharing SO₄ tetrahedra. This material delivered a discharge capacity of 22 mA h g⁻¹ and its discharge profile showed multiple reduction processes at 3.05, 2.32 and 1.97 V versus Li⁺/Li⁰. Additionally, a new material, NH₄VO₂SO₄, was synthesised for the first time via a low temperature solution based route. The composition, structure, morphology, thermal stability and electrochemical properties of this new material were analysed using a range of techniques. Single crystal X-ray diffraction showed NH₄VO₂SO₄ crystallises in a large monoclinic unit cell, consisting of two chain types; (i) edge sharing VO₆ octahedra with bridging SO₄ tetrahedra and (ii) isolated VO₆ octahedra interconnected by bridging SO₄ tetrahedra. Despite the structural differences between NH₄VO₂SO₄ and NH₄VO(SO₄)₂, these materials exhibited similar thermal stabilities as well as comparable open circuit voltages (4.10 V versus Li⁺/Li⁰), discharge profiles and specific discharge capacities of <20 mA h g⁻¹.
Finally, a systematic investigation of the electrochemical and chemical insertion of Li⁺ into V⁽ⱽ⁾₂O₃(SO₄)₂ was performed. Although the synthesis of V₂O₃(SO₄)₂ has previously been reported, here it was prepared at a lower temperature of 140 °C and its electrochemical performance tested for the first time. This material contains the [V₂O₃]⁴⁺ species which consists of pairs of VO₆ octahedra linked together by an oxygen bridge. The corner sharing VO₆ octahedra are interconnected by bridging SO₄ tetrahedra, creating a three dimensional framework with open channels running down the c axis. A series of electrochemical tests were carried out to evaluate the lithiation and delithiation process for this material. V₂O₃(SO₄)₂ displayed an interesting electrochemical profile, with multiple reversible processes occurring between 1.95 and 4.20 V versus Li⁺/Li⁰. A discharge capacity of 160 mA h g⁻¹ was obtained, corresponding to the insertion of 2.0 mol of Li per mol of V₂O₃(SO₄)₂. Consequently, ex situ studies were carried out to determine the phase evolution and structural changes which occurred during of the lithiation and delithiation process. To further evaluate the Li⁺ insertion into this phase, V₂O₃(SO₄)₂ was chemically lithiated using n butyllithium. Inductively coupled plasma optical emission spectrometry, X-ray absorption spectroscopy, and infrared spectroscopy measurements showed that a composition of Li₄V₂O₃(SO₄)₂ can be attained by chemical lithiation. Interestingly, the structural studies evidenced by X-ray and neutron powder diffraction on the lithiated samples showed that a significant amount of Li⁺ can be inserted into V₂O₃(SO₄)₂, while it maintains its three dimensional framework structure.
2020-07-29T00:00:00ZLinnell, Stephanie FrancesThe exploration and development of safer and less expensive positive electrode materials, for high energy density lithium ion batteries (LIBs), are essential for large scale applications, such as electric vehicles and grid energy storage. Of all the candidates, vanadium based compounds have attracted considerable interest. This is due to vanadium’s ability to adopt a range of oxidation states, with oxidation states of III, IV and V being particularly common in battery materials. This enables vanadium to undergo multi electron transfer processes, which allow reversible insertion/extraction of more than one Li⁺ ion per transition metal.
This thesis explores a range of vanadium based materials as candidate positive electrode materials for LIBs. The materials were separated into three groups (i) phases containing the mononuclear [VO] ³⁺ species, AVO(SO₄)₂ (A = NH₄⁺, K⁺), (ii) phases containing the mononuclear [VO₂]⁺ species, AVO₂SO₄ (A = NH₄⁺, K⁺), and (iii) V₂O₃(SO₄)₂ which contains the [V₂O₃]⁴⁺ species.
NH₄V⁽ⱽ⁾O(SO₄)₂ and KV⁽ⱽ⁾O(SO₄)₂ were studied initially. While these materials have previously been synthesised, their electrochemical properties have not been evaluated before. NH₄VO(SO₄)₂ and KVO(SO₄)₂ were prepared via solution based methods using low temperatures (≤200 °C) and were characterised using X-ray diffraction, infrared spectroscopy, scanning electron microscopy and optical microscopy. These compounds are isostructural and are made up of distorted VO₆ octahedra corner sharing with five SO₄ tetrahedra, forming layered structures. The thermal stability of these materials was examined by means of thermogravimetric analysis. Additionally, the intermediate phases identified from thermogravimetric analysis were characterised and this work led to the structural study of the layered material, 2VOSO₄·H₂SO₄, in order to determine the positions of the hydrogen atoms and evaluate the disorder associated with the H₂SO₄ layer. The electrochemical performance of NH₄VO(SO₄)₂ and KVO(SO₄)₂ as positive electrode materials for LIBs were tested for the first time. Both materials were found to operate at a high voltage of 4.05 V versus Li⁺/Li⁰ and presented similar discharge profiles and specific discharge capacities of <20 mA h g⁻¹.
Thereafter, the dioxovanadium phases, KV⁽ⱽ⁾O₂SO₄ and NH₄V⁽ⱽ⁾O₂SO₄ were explored. The synthesis of the KVO₂SO₄ phase has previously been reported in literature but its electrochemical properties were tested here for the first time. KVO₂SO₄ was synthesised by a solid state route at 300 – 400 °C, forming a three dimensional framework structure consisting of corner sharing VO₆ octahedra interconnected by corner sharing and edge sharing SO₄ tetrahedra. This material delivered a discharge capacity of 22 mA h g⁻¹ and its discharge profile showed multiple reduction processes at 3.05, 2.32 and 1.97 V versus Li⁺/Li⁰. Additionally, a new material, NH₄VO₂SO₄, was synthesised for the first time via a low temperature solution based route. The composition, structure, morphology, thermal stability and electrochemical properties of this new material were analysed using a range of techniques. Single crystal X-ray diffraction showed NH₄VO₂SO₄ crystallises in a large monoclinic unit cell, consisting of two chain types; (i) edge sharing VO₆ octahedra with bridging SO₄ tetrahedra and (ii) isolated VO₆ octahedra interconnected by bridging SO₄ tetrahedra. Despite the structural differences between NH₄VO₂SO₄ and NH₄VO(SO₄)₂, these materials exhibited similar thermal stabilities as well as comparable open circuit voltages (4.10 V versus Li⁺/Li⁰), discharge profiles and specific discharge capacities of <20 mA h g⁻¹.
Finally, a systematic investigation of the electrochemical and chemical insertion of Li⁺ into V⁽ⱽ⁾₂O₃(SO₄)₂ was performed. Although the synthesis of V₂O₃(SO₄)₂ has previously been reported, here it was prepared at a lower temperature of 140 °C and its electrochemical performance tested for the first time. This material contains the [V₂O₃]⁴⁺ species which consists of pairs of VO₆ octahedra linked together by an oxygen bridge. The corner sharing VO₆ octahedra are interconnected by bridging SO₄ tetrahedra, creating a three dimensional framework with open channels running down the c axis. A series of electrochemical tests were carried out to evaluate the lithiation and delithiation process for this material. V₂O₃(SO₄)₂ displayed an interesting electrochemical profile, with multiple reversible processes occurring between 1.95 and 4.20 V versus Li⁺/Li⁰. A discharge capacity of 160 mA h g⁻¹ was obtained, corresponding to the insertion of 2.0 mol of Li per mol of V₂O₃(SO₄)₂. Consequently, ex situ studies were carried out to determine the phase evolution and structural changes which occurred during of the lithiation and delithiation process. To further evaluate the Li⁺ insertion into this phase, V₂O₃(SO₄)₂ was chemically lithiated using n butyllithium. Inductively coupled plasma optical emission spectrometry, X-ray absorption spectroscopy, and infrared spectroscopy measurements showed that a composition of Li₄V₂O₃(SO₄)₂ can be attained by chemical lithiation. Interestingly, the structural studies evidenced by X-ray and neutron powder diffraction on the lithiated samples showed that a significant amount of Li⁺ can be inserted into V₂O₃(SO₄)₂, while it maintains its three dimensional framework structure.Electrochemical generation of metal structures using surface based molecular self-assemblies as templatesYao, Zhenhttps://hdl.handle.net/10023/202892021-07-27T09:55:59Z2020-07-29T00:00:00ZExploring electrochemical processes controlled by surface-based molecular assemblies, this thesis studies a coordination-controlled electrodeposition (CCED) scheme, which relies on chemical functionality, i.e., metal coordination, provided by the tail group of a self-assembled monolayer (SAM). Based on the electrochemical reduction of coordinated ions, the scheme is extended by introducing metal ions into the bulk electrolyte. Using a SAM of 3-(4-pyridine-4-yl-phenyl)-propane-1-thiol (BP3N) on Au(111) electrode, the co-deposition of coordinating Pd and non-coordinating Cu has been investigated. Following Pd²⁺-pyridine complexation, the electrochemical deposition was performed in an acidic Cu²⁺-containing electrolyte. Both cyclic voltammetry (CV) and chronoamperometry revealed the promoting effect of coordinated Pd²⁺ on bulk Cu deposition. The process involves three phases, (i) the Pd cluster formation, (ii) the intermix of Pd and Cu, and (iii) the deposition of bulk Cu. Depending on conditions, deposits with morphologies ranging from isolated CuPd nanoparticles to ultrathin metal films were generated and characterised with scanning tunnelling microscopy (STM). The Pd-Cu core-shell nature of these nanoparticles was confirmed by transmission electron microscopy (TEM). To understand the metal nucleation mechanism, density functional theory (DFT) calculations were carried out to clarify the initial stage of Pd aggregation. Furthermore, inspired by the calculation results, the effect of metal-SAM interaction in metal nucleation was illustrated by the reduced particle size for CCED on binary SAMs with protruding phenyl groups.
The exploration of the CCED scheme towards nanostructure generation was investigated using either patterns of CuPd nanoparticles fabricated by selective particle removal based on scanning probe lithography (STM or atomic force microscopy) or patterned SAMs produced by electron beam lithography. Metal films with thickness below 3 nm and metal structures with lateral features down to sub-10 nm were fabricated. Additionally, with SAMs serving to control the adhesion, a cyclic scheme consisting of electrodeposition on a patterned substrate and lift-off was investigated, offering the prospect of replicative nanostructure fabrication.
2020-07-29T00:00:00ZYao, ZhenExploring electrochemical processes controlled by surface-based molecular assemblies, this thesis studies a coordination-controlled electrodeposition (CCED) scheme, which relies on chemical functionality, i.e., metal coordination, provided by the tail group of a self-assembled monolayer (SAM). Based on the electrochemical reduction of coordinated ions, the scheme is extended by introducing metal ions into the bulk electrolyte. Using a SAM of 3-(4-pyridine-4-yl-phenyl)-propane-1-thiol (BP3N) on Au(111) electrode, the co-deposition of coordinating Pd and non-coordinating Cu has been investigated. Following Pd²⁺-pyridine complexation, the electrochemical deposition was performed in an acidic Cu²⁺-containing electrolyte. Both cyclic voltammetry (CV) and chronoamperometry revealed the promoting effect of coordinated Pd²⁺ on bulk Cu deposition. The process involves three phases, (i) the Pd cluster formation, (ii) the intermix of Pd and Cu, and (iii) the deposition of bulk Cu. Depending on conditions, deposits with morphologies ranging from isolated CuPd nanoparticles to ultrathin metal films were generated and characterised with scanning tunnelling microscopy (STM). The Pd-Cu core-shell nature of these nanoparticles was confirmed by transmission electron microscopy (TEM). To understand the metal nucleation mechanism, density functional theory (DFT) calculations were carried out to clarify the initial stage of Pd aggregation. Furthermore, inspired by the calculation results, the effect of metal-SAM interaction in metal nucleation was illustrated by the reduced particle size for CCED on binary SAMs with protruding phenyl groups.
The exploration of the CCED scheme towards nanostructure generation was investigated using either patterns of CuPd nanoparticles fabricated by selective particle removal based on scanning probe lithography (STM or atomic force microscopy) or patterned SAMs produced by electron beam lithography. Metal films with thickness below 3 nm and metal structures with lateral features down to sub-10 nm were fabricated. Additionally, with SAMs serving to control the adhesion, a cyclic scheme consisting of electrodeposition on a patterned substrate and lift-off was investigated, offering the prospect of replicative nanostructure fabrication.Multivalent thermal batteries : concept, development and advancesDickson, Stewart Alan Mackenziehttps://hdl.handle.net/10023/202552021-07-27T09:27:16Z2020-07-29T00:00:00ZThermal batteries are single-use energy devices designed to deliver a one-time source of power. They can be adapted to fit the application, such as high currents and pulse loads, making them important in military and space applications where reliable power generation is required. This work has sought to understand and analyse the possibility of producing a thermal battery which does not rely upon traditional lithium chemistry, by finding suitable magnesium and calcium eutectic electrolytes and cell compositions to challenge the traditional thoughts surrounding thermal battery chemistries.
All-magnesium thermal batteries were firstly studied by selection of magnesium-containing halide eutectics, which were analysed in depth through a variety of techniques including PXRD, SEM, wetting and conductivity. Cells were constructed using the well-characterised FeS₂ cathode material to find the optimal chemistries, of which the cells containing eutectic in the anode and eutectic and carbon in the cathode exhibited the best performance with capacities exceeding 400 mA h g⁻¹. The discharge mechanism of the cells was deemed to be unclear, with multiple possibilities examined. An operando neutron powder diffraction experiment was carried out to elucidate a mechanism, and found that MgS, FeS and iron were formed, indicating dissolution and reaction in the eutectic melt as KCl crystallised out. Also, a change in the unit cell of FeS₂ was observed, indicating some solid solution formation.
Experience of the magnesium cell chemistry was transferred over to the calcium analogues. A similar approach was undertaken using the CaCl₂-NaCl eutectic salt, with a wide variety of experiments to explore the properties of the eutectic. The cells constructed for these tests were found to perform most optimally with a pure calcium anode and cathode of FeS₂ mixed with the eutectic with voltages in excess of 2 V and capacities of ~ 200 mA h g⁻¹. As the cells were not able to be optimised to reach their full discharge potential, a mechanism was derived from the PXRD analysis, which found that the conversion of the material proceeded to form CaS, but only reached around ¼ of the total theoretical discharge capacity of FeS₂, which is due to a number of factors. The operando neutron diffraction experiment proved to be less successful but did identify the presence of CaS and FeS during operation, suggesting a similar mechanism as the magnesium derivative.
Finally, several new cathode materials were tested against for these cell chemistries. CoS₂ is an alternative sulfide cathode material with greater temperature resistance, and obtained similar performances to the FeS₂ material, though the discharge mechanisms observed were also affected by the conversion of CoS₂ to CoCl₂ by dissolution in the electrolyte, in both the magnesium and calcium eutectics. ZrS₃ was also synthesised and analysed as a potential cathode material in both the optimised magnesium and calcium systems, which showed some appreciable performance. Cells were then analysed in a mixed-phase by using LiCl-KCl in the magnesium cathode material. The cells performed well and demonstrated a very long discharge plateau of over 300 mA h g⁻¹ capacity, but the discharge mechanism was different to what has been observed in literature. Instead, the formation of other phases was observed instead of the Li₂ZrS₄ spinel structure shown in literature, which is explained in greater detail.
Two phosphate-based materials were synthesised and characterised, Cu₃(PO₄)₂ (CP) and Na₃V₂(PO₄)₂F₃ (NVPF). Both materials were firstly studied against the lithium silicon alloy to understand their discharge mechanisms. The Cu₃(PO₄)₂ material exhibited a large sloping discharge plateau from 2.6 V, with a long discharge plateau at around 1.4 V. The discharge mechanism was deemed to follow literature procedure, converting into Li₃PO₄ and copper with a capacity of > 400 mA h g⁻¹. Substitution of copper for vanadium was found to increase the voltage of the material slightly but was not able to be substituted in significant levels due to the coordination of the copper sites in the material. At higher current densities, most of the capacity was retained and a higher initial voltage, closer to literature, was observed at the start of the discharges when the material was processed by ball milling. Multivalent cells were also explored and deemed to show some, but not ideal performance in terms of capacity and voltage.
Na₃V₂(PO₄)₂F₃ was also synthesised by two separate methods. Both powders showed a pure phase and then one tested against the lithium silicon alloy. The discharge plot identified a plateau at 1.6 V which corresponded to the insertion of 1 lithium into the material. The discharge mechanism of the material was not able to be identified, due to the amorphization of the material during discharge, but it was assumed from the electrochemical data that an insertion mechanism occurred to produce the reduced Na₃LiV₂(PO₄)₂F₃ material. The rate capability of the material was also analysed and was found to perform extremely well at high current densities. A magnesium-based cell showed an expected lower voltage with lower capacity, whilst the calcium cell exhibited similar voltage plateau to the lithium derivative, however with even lower capacity than the magnesium cell. This proved that the multivalent ions were unlikely to favourably react with the material.
2020-07-29T00:00:00ZDickson, Stewart Alan MackenzieThermal batteries are single-use energy devices designed to deliver a one-time source of power. They can be adapted to fit the application, such as high currents and pulse loads, making them important in military and space applications where reliable power generation is required. This work has sought to understand and analyse the possibility of producing a thermal battery which does not rely upon traditional lithium chemistry, by finding suitable magnesium and calcium eutectic electrolytes and cell compositions to challenge the traditional thoughts surrounding thermal battery chemistries.
All-magnesium thermal batteries were firstly studied by selection of magnesium-containing halide eutectics, which were analysed in depth through a variety of techniques including PXRD, SEM, wetting and conductivity. Cells were constructed using the well-characterised FeS₂ cathode material to find the optimal chemistries, of which the cells containing eutectic in the anode and eutectic and carbon in the cathode exhibited the best performance with capacities exceeding 400 mA h g⁻¹. The discharge mechanism of the cells was deemed to be unclear, with multiple possibilities examined. An operando neutron powder diffraction experiment was carried out to elucidate a mechanism, and found that MgS, FeS and iron were formed, indicating dissolution and reaction in the eutectic melt as KCl crystallised out. Also, a change in the unit cell of FeS₂ was observed, indicating some solid solution formation.
Experience of the magnesium cell chemistry was transferred over to the calcium analogues. A similar approach was undertaken using the CaCl₂-NaCl eutectic salt, with a wide variety of experiments to explore the properties of the eutectic. The cells constructed for these tests were found to perform most optimally with a pure calcium anode and cathode of FeS₂ mixed with the eutectic with voltages in excess of 2 V and capacities of ~ 200 mA h g⁻¹. As the cells were not able to be optimised to reach their full discharge potential, a mechanism was derived from the PXRD analysis, which found that the conversion of the material proceeded to form CaS, but only reached around ¼ of the total theoretical discharge capacity of FeS₂, which is due to a number of factors. The operando neutron diffraction experiment proved to be less successful but did identify the presence of CaS and FeS during operation, suggesting a similar mechanism as the magnesium derivative.
Finally, several new cathode materials were tested against for these cell chemistries. CoS₂ is an alternative sulfide cathode material with greater temperature resistance, and obtained similar performances to the FeS₂ material, though the discharge mechanisms observed were also affected by the conversion of CoS₂ to CoCl₂ by dissolution in the electrolyte, in both the magnesium and calcium eutectics. ZrS₃ was also synthesised and analysed as a potential cathode material in both the optimised magnesium and calcium systems, which showed some appreciable performance. Cells were then analysed in a mixed-phase by using LiCl-KCl in the magnesium cathode material. The cells performed well and demonstrated a very long discharge plateau of over 300 mA h g⁻¹ capacity, but the discharge mechanism was different to what has been observed in literature. Instead, the formation of other phases was observed instead of the Li₂ZrS₄ spinel structure shown in literature, which is explained in greater detail.
Two phosphate-based materials were synthesised and characterised, Cu₃(PO₄)₂ (CP) and Na₃V₂(PO₄)₂F₃ (NVPF). Both materials were firstly studied against the lithium silicon alloy to understand their discharge mechanisms. The Cu₃(PO₄)₂ material exhibited a large sloping discharge plateau from 2.6 V, with a long discharge plateau at around 1.4 V. The discharge mechanism was deemed to follow literature procedure, converting into Li₃PO₄ and copper with a capacity of > 400 mA h g⁻¹. Substitution of copper for vanadium was found to increase the voltage of the material slightly but was not able to be substituted in significant levels due to the coordination of the copper sites in the material. At higher current densities, most of the capacity was retained and a higher initial voltage, closer to literature, was observed at the start of the discharges when the material was processed by ball milling. Multivalent cells were also explored and deemed to show some, but not ideal performance in terms of capacity and voltage.
Na₃V₂(PO₄)₂F₃ was also synthesised by two separate methods. Both powders showed a pure phase and then one tested against the lithium silicon alloy. The discharge plot identified a plateau at 1.6 V which corresponded to the insertion of 1 lithium into the material. The discharge mechanism of the material was not able to be identified, due to the amorphization of the material during discharge, but it was assumed from the electrochemical data that an insertion mechanism occurred to produce the reduced Na₃LiV₂(PO₄)₂F₃ material. The rate capability of the material was also analysed and was found to perform extremely well at high current densities. A magnesium-based cell showed an expected lower voltage with lower capacity, whilst the calcium cell exhibited similar voltage plateau to the lithium derivative, however with even lower capacity than the magnesium cell. This proved that the multivalent ions were unlikely to favourably react with the material.Title redactedFinley, Kirsten Lhttps://hdl.handle.net/10023/202532021-02-08T10:14:02Z2020-07-29T00:00:00Z2020-07-29T00:00:00ZFinley, Kirsten LProbing the reactivity of α,β-unsaturated acyl ammonium intermediates in organocatalysisWu, Jiufenghttps://hdl.handle.net/10023/201812021-07-26T17:18:24Z2020-07-29T00:00:00ZThe research described in this thesis focuses on probing the reactivity of α,β-unsaturated acyl ammonium intermediates and the use of theses reactive intermediates in a new concept: aryloxide-facilitated catalyst turnover in α,β-unsaturated acyl ammonium catalysis.
Chapter 2: Initially, the concept of aryloxide-facilitated catalyst turnover was used in a novel isothiourea-catalysed transfer hydrogenation reaction of α,β-unsaturated p-nitrophenyl esters. An efficient synthetic procedure was successfully developed, which was demonstrated to be applicable to a range of α,β-unsaturated PNP esters (15 examples, 38−98% yield), typically with electron withdrawing β-substituents proving most reactive. Attempts to perform the reaction enantioselectively showed that in principle α,β-unsaturated acyl ammonium intermediates generated from α,β-unsaturated PNP esters and a chiral isothiourea catalyst can react enantioselectively.
Chapter 3: Following on the established new concept in α,β-unsaturated acyl ammonium catalysis, enantioselective Michael addition of nucleophiles to α,β-unsaturated PNP esters has been further explored using the aryloxide-facilitated catalyst turnover strategy. This new method was applicable for a range of malonates and malonate derivatives as pro-nucleophiles, resulting in generally good yields with excellent enantioselectivities (14 examples, up to 86% yield, > 99:1 er). This work demonstrated for the first time that simple nucleophiles could be applied in stoichiometric quantities in enantioselective a,b-unsaturated acyl ammonium catalysis.
Chapter 4: A detailed variable time normalisation kinetic analysis (VTNKA) was performed to investigate the kinetics of the enantioselective Michael addition of malonates to α,β-unsaturated PNP esters, using 19F{1H} NMR spectroscopic analysis. The order with respect to α,β-unsaturated ester, malonate and catalyst were found to be first order, but zero order with respect to base, indicating the turnover-limiting step is likely to be the Michael addition of malonate to the α,β-unsaturated acyl ammonium intermediate.
2020-07-29T00:00:00ZWu, JiufengThe research described in this thesis focuses on probing the reactivity of α,β-unsaturated acyl ammonium intermediates and the use of theses reactive intermediates in a new concept: aryloxide-facilitated catalyst turnover in α,β-unsaturated acyl ammonium catalysis.
Chapter 2: Initially, the concept of aryloxide-facilitated catalyst turnover was used in a novel isothiourea-catalysed transfer hydrogenation reaction of α,β-unsaturated p-nitrophenyl esters. An efficient synthetic procedure was successfully developed, which was demonstrated to be applicable to a range of α,β-unsaturated PNP esters (15 examples, 38−98% yield), typically with electron withdrawing β-substituents proving most reactive. Attempts to perform the reaction enantioselectively showed that in principle α,β-unsaturated acyl ammonium intermediates generated from α,β-unsaturated PNP esters and a chiral isothiourea catalyst can react enantioselectively.
Chapter 3: Following on the established new concept in α,β-unsaturated acyl ammonium catalysis, enantioselective Michael addition of nucleophiles to α,β-unsaturated PNP esters has been further explored using the aryloxide-facilitated catalyst turnover strategy. This new method was applicable for a range of malonates and malonate derivatives as pro-nucleophiles, resulting in generally good yields with excellent enantioselectivities (14 examples, up to 86% yield, > 99:1 er). This work demonstrated for the first time that simple nucleophiles could be applied in stoichiometric quantities in enantioselective a,b-unsaturated acyl ammonium catalysis.
Chapter 4: A detailed variable time normalisation kinetic analysis (VTNKA) was performed to investigate the kinetics of the enantioselective Michael addition of malonates to α,β-unsaturated PNP esters, using 19F{1H} NMR spectroscopic analysis. The order with respect to α,β-unsaturated ester, malonate and catalyst were found to be first order, but zero order with respect to base, indicating the turnover-limiting step is likely to be the Michael addition of malonate to the α,β-unsaturated acyl ammonium intermediate.Pyrrole acetic acid derivatives in Lewis base catalyzed enantioselective formal [4+2] cycloadditionsZhang, Shuyuehttps://hdl.handle.net/10023/200762021-07-26T17:58:11Z2020-07-29T00:00:00ZThis thesis describes the use of C(1) ammonium enolate chemistry with Lewis base isothiourea catalysis in Michael addition-lactonization/lactamization between 2-pyrrolyl acetic acid derivatives and various Michael acceptors.
Chapter 2 proved the principle that amino esters protected as benzophenone Schiff base could be α-functionalized using Lewis base catalysis.
Chapter 3 described the use of 2-pyrrolyl acetic acid in enantioselective Michael addition-lactonization with CCl3 enone. After in situ ring-opening, a range of 30 diesters and diamides in up to 98% yield, >95:5 dr and >99:1 er. Further demonstration of the synthetic utility of these ring-opening derivatives was achieved with an intramolecular Friedel-Crafts acylation utilizing the electron-rich nature of pyrrole to afforded dihydroindolizinone derivatives in up to 90% yield with no erosion in stereoselectivity.
Chapter 4 described the use of either α,β-unsaturated trifluoromethyl ketones or α-keto-β,γ-unsaturated esters with 2-pyrrolyl acetic acid to synthesize tetrahydroindolizine derivatives in one-pot, with up to 98% yield, >95:5 dr and >99:1 er.
Chapter 5 described the synthesis of dihydropyridinones from chalcone-derived N-Ts ketimine and unsaturated cyclic sulfonamide derived from saccharin in up to 97% yield, >95:5 dr and >99:1 er.
Chapter 6 described the synthesis of tetrasubstituted pyridines using a variety of unsaturated ketimines bearing esters with DHPB catalyst in up to 66% yield. Further derivatization was demonstrated via transforming 2-pivaloyloxy group into 2-OTs group in a two-step process, enabling the Pd-catalyzed cross coupling and reduction.
2020-07-29T00:00:00ZZhang, ShuyueThis thesis describes the use of C(1) ammonium enolate chemistry with Lewis base isothiourea catalysis in Michael addition-lactonization/lactamization between 2-pyrrolyl acetic acid derivatives and various Michael acceptors.
Chapter 2 proved the principle that amino esters protected as benzophenone Schiff base could be α-functionalized using Lewis base catalysis.
Chapter 3 described the use of 2-pyrrolyl acetic acid in enantioselective Michael addition-lactonization with CCl3 enone. After in situ ring-opening, a range of 30 diesters and diamides in up to 98% yield, >95:5 dr and >99:1 er. Further demonstration of the synthetic utility of these ring-opening derivatives was achieved with an intramolecular Friedel-Crafts acylation utilizing the electron-rich nature of pyrrole to afforded dihydroindolizinone derivatives in up to 90% yield with no erosion in stereoselectivity.
Chapter 4 described the use of either α,β-unsaturated trifluoromethyl ketones or α-keto-β,γ-unsaturated esters with 2-pyrrolyl acetic acid to synthesize tetrahydroindolizine derivatives in one-pot, with up to 98% yield, >95:5 dr and >99:1 er.
Chapter 5 described the synthesis of dihydropyridinones from chalcone-derived N-Ts ketimine and unsaturated cyclic sulfonamide derived from saccharin in up to 97% yield, >95:5 dr and >99:1 er.
Chapter 6 described the synthesis of tetrasubstituted pyridines using a variety of unsaturated ketimines bearing esters with DHPB catalyst in up to 66% yield. Further derivatization was demonstrated via transforming 2-pivaloyloxy group into 2-OTs group in a two-step process, enabling the Pd-catalyzed cross coupling and reduction.Studies on selectively fluorinated cycloalkanesFang, Zeguohttps://hdl.handle.net/10023/199992021-07-26T17:44:23Z2020-07-29T00:00:00ZThe thesis focuses on the synthesis of novel fluorinated cycloalkanes and their polar properties.
Chapter 2 describes the synthesis of all cis-1,2,3,4-tetrafluorocyclopentane and its deuterated isotopomer. They were prepared from the dicyclopentadiene. The structure of cis-1,2,3,4-tetrafluorocyclopentane was characterised by NMR and X-ray crystallography. This structure proved to have high polarity and a calculated dipole moment is 4.9 Debye. The deuterated isotopomer was also characterised by NMR and it indicated that this molecule has highly polarized faces similar to all cis-1,2,3,4-tetrafluorocyclopentane. The polarity of the isotopomers were compared by GC-MS analysis and this gave an indication that per-deuterated isotopomer is more polar than the all cis-1,2,3,4-tetrafluorocyclopentane.
Chapter 3 describes the synthesis of a series of fluorinated cyclopropanes, with a particular focus on the preparation of the all cis-1,2,3-trifluorocyclopropane motif. The synthesis started from the fluorinated styrene, followed by bromofluocarbene (:CFBr) addition and reductive debromination. This provided the first synthetic access to this motif. The lipophilicity (Log P) of a series of fluorinated cyclopropanes was investigated and the results demonstrated that the all cis-1,2,3-trifluorocyclopropane was the most polar compound among this series.
Chapter 4 describes unexpected results from the fluorination of benzo[a,e]cyclooctatetraene with NBS, HF·Py and AgF(I), which was anticipated to generate all-cis-5,6,11,12-tetrafluoro-5,6,11,12-tetrahydrodibenzo[a,e]cyclooctane. However, the reaction gave a mixture of products and the product outcomes strongly suggests that an extensive carbocation/phenonium rearrangements pathway occurred during the reaction. The origin of oxygen in the final ether products was shown by an 18O isotope labelling experiment with water and the result suggests a {Ag}O- species is the most likely oxygen provider.
Chapter 5 describes the synthesis of a series of novel liquid crystals with fluorinated cyclopropane motifs at their terminus. The synthesis proved straightforward such that these novel liquid crystal candidates can be prepared on scale. Their thermodynamic and physical properties, such as birefringence (Δn), dielectric anisotropy (Δε) and rotational viscosity (ϒ) were analysed by Merck & Co. Although none of the liquid crystal candidates met all the criteria for Liquid Crystal Display (LCD) development, the study gives an insight into the potential for fluorinated cyclopropane motifs in liquid crystals.
2020-07-29T00:00:00ZFang, ZeguoThe thesis focuses on the synthesis of novel fluorinated cycloalkanes and their polar properties.
Chapter 2 describes the synthesis of all cis-1,2,3,4-tetrafluorocyclopentane and its deuterated isotopomer. They were prepared from the dicyclopentadiene. The structure of cis-1,2,3,4-tetrafluorocyclopentane was characterised by NMR and X-ray crystallography. This structure proved to have high polarity and a calculated dipole moment is 4.9 Debye. The deuterated isotopomer was also characterised by NMR and it indicated that this molecule has highly polarized faces similar to all cis-1,2,3,4-tetrafluorocyclopentane. The polarity of the isotopomers were compared by GC-MS analysis and this gave an indication that per-deuterated isotopomer is more polar than the all cis-1,2,3,4-tetrafluorocyclopentane.
Chapter 3 describes the synthesis of a series of fluorinated cyclopropanes, with a particular focus on the preparation of the all cis-1,2,3-trifluorocyclopropane motif. The synthesis started from the fluorinated styrene, followed by bromofluocarbene (:CFBr) addition and reductive debromination. This provided the first synthetic access to this motif. The lipophilicity (Log P) of a series of fluorinated cyclopropanes was investigated and the results demonstrated that the all cis-1,2,3-trifluorocyclopropane was the most polar compound among this series.
Chapter 4 describes unexpected results from the fluorination of benzo[a,e]cyclooctatetraene with NBS, HF·Py and AgF(I), which was anticipated to generate all-cis-5,6,11,12-tetrafluoro-5,6,11,12-tetrahydrodibenzo[a,e]cyclooctane. However, the reaction gave a mixture of products and the product outcomes strongly suggests that an extensive carbocation/phenonium rearrangements pathway occurred during the reaction. The origin of oxygen in the final ether products was shown by an 18O isotope labelling experiment with water and the result suggests a {Ag}O- species is the most likely oxygen provider.
Chapter 5 describes the synthesis of a series of novel liquid crystals with fluorinated cyclopropane motifs at their terminus. The synthesis proved straightforward such that these novel liquid crystal candidates can be prepared on scale. Their thermodynamic and physical properties, such as birefringence (Δn), dielectric anisotropy (Δε) and rotational viscosity (ϒ) were analysed by Merck & Co. Although none of the liquid crystal candidates met all the criteria for Liquid Crystal Display (LCD) development, the study gives an insight into the potential for fluorinated cyclopropane motifs in liquid crystals.Genome sequencing, analysis, heterologous expression and genetic modification of antibiotic encoding biosynthetic gene clustersAbraham, Emilyhttps://hdl.handle.net/10023/199792023-10-16T11:27:35Z2020-06-01T00:00:00ZMicrobial natural products represent an unparalleled starting point for drug discovery. This
thesis therefore focuses on microbial natural products, and the biosynthetic gene clusters
(BGCs) that encode them. A series of investigations are reported including genome sequencing,
genome reading and the exploration of heterologous expression toward enabling the discovery
of novel natural products. The heterologous expression of large and highly repetitive BGCs
was investigated, in addition to the heterologous expression of individual cytochrome P450
enzymes to complement existing biosynthetic pathways, as an approach toward accessing new
to nature natural products.
Firstly, a series of novel BGCs were identified in silico from public databases and from novel
marine strains which were sequenced using MinION nanopore technology. The rationale being
that novel BGCs are likely to encode for new compounds. BGCs encoded for by Saccharothrix
espanaensis were heterologously expressed and molecular networking of mass spectrometry
data helped to identify masses uniquely produced by the heterologously expressed BGCs.
Next, the putative BGC encoding for Marinomycin A, a potent antibiotic and anticancer agent
produced by Marinispora CNQ-140, was also heterologously expressed using a direct-cloning
approach. Future work will involve both promoter refactoring and sequencing of the cloned
BGC to identify any sequence rearrangements, as Marinomycin A production could not be
detected in the heterologous host. Moreover, the construction of a Marinispora CNQ-140 BAC
library, a library containing an average insert size of 145 kb, represents an alternate way to
capture and heterologously express this 72 kb BGC, with its challengingly high level of
sequence repetition. Genome sequencing of Marinispora CNQ-140 also revealed additional
novel BGCs which can be targeted using this BAC library.
Lastly, work towards establishing a biocatalyst toolkit to enable the epoxidation of a series of
natural products was conducted. An introduced epoxide can act as a biorthogonal handle,
therefore facilitating downstream chemical modifications of the natural product. Success was
gained using a series of evolved P450 BM3 variants in vitro, which were able to convert
substrates such as Novobiocin and Pimaricin. Moreover, a series of cytochrome P450s from
uncharacterised BGCs with origins similar to a series of compounds that we wished to modify,
were also mined and tested.
2020-06-01T00:00:00ZAbraham, EmilyMicrobial natural products represent an unparalleled starting point for drug discovery. This
thesis therefore focuses on microbial natural products, and the biosynthetic gene clusters
(BGCs) that encode them. A series of investigations are reported including genome sequencing,
genome reading and the exploration of heterologous expression toward enabling the discovery
of novel natural products. The heterologous expression of large and highly repetitive BGCs
was investigated, in addition to the heterologous expression of individual cytochrome P450
enzymes to complement existing biosynthetic pathways, as an approach toward accessing new
to nature natural products.
Firstly, a series of novel BGCs were identified in silico from public databases and from novel
marine strains which were sequenced using MinION nanopore technology. The rationale being
that novel BGCs are likely to encode for new compounds. BGCs encoded for by Saccharothrix
espanaensis were heterologously expressed and molecular networking of mass spectrometry
data helped to identify masses uniquely produced by the heterologously expressed BGCs.
Next, the putative BGC encoding for Marinomycin A, a potent antibiotic and anticancer agent
produced by Marinispora CNQ-140, was also heterologously expressed using a direct-cloning
approach. Future work will involve both promoter refactoring and sequencing of the cloned
BGC to identify any sequence rearrangements, as Marinomycin A production could not be
detected in the heterologous host. Moreover, the construction of a Marinispora CNQ-140 BAC
library, a library containing an average insert size of 145 kb, represents an alternate way to
capture and heterologously express this 72 kb BGC, with its challengingly high level of
sequence repetition. Genome sequencing of Marinispora CNQ-140 also revealed additional
novel BGCs which can be targeted using this BAC library.
Lastly, work towards establishing a biocatalyst toolkit to enable the epoxidation of a series of
natural products was conducted. An introduced epoxide can act as a biorthogonal handle,
therefore facilitating downstream chemical modifications of the natural product. Success was
gained using a series of evolved P450 BM3 variants in vitro, which were able to convert
substrates such as Novobiocin and Pimaricin. Moreover, a series of cytochrome P450s from
uncharacterised BGCs with origins similar to a series of compounds that we wished to modify,
were also mined and tested.Developing genetic and chemical tools for the GenoChemetic generation of natural product analoguesBailey, Christopher Samuelhttps://hdl.handle.net/10023/199692021-07-26T17:27:14Z2020-06-01T00:00:00ZNatural products provide one of the corner stones of both modern and historical medicine, contributing towards over 65 % of new FDA approved drugs that entered clinical trials between 1981 and 2014. It is partly down to the historic success of natural products in medicine that many people are once again looking to nature for a solution to the rise in antibiotic resistant bacterial infections. However, developing natural products towards clinical use poses a number of challenges. Notable examples of these challenges include the need to generate analogues of these compounds, which are oftentimes structurally complex, and the instability of many natural products. Within this work several approaches are set out to address these challenges, exploring novel genetic and complementary synthetic technologies, as well as looking towards natural solutions for sequestering and stabilising molecules.
Chapters 2 – 5 explore tools towards the GenoChemetic generation of natural product analogues. Firstly the utilisation of alkyne tags in a GenoChemetic approach is explored. Chapter 2 first looks towards exploring the flexibility of a series of biosynthetic gene clusters to the uptake of alkyne containing starter units. Chapter 3 then generates genetic cassettes for the in situ biosynthesis of such starter units, for subsequent potential incorporation into natural products.
A well utilised bioorthogonal handle within the group are aryl halides. Chapter 4 looks towards the genetic installation of such a handle onto natural products. Chapter 5 than goes on to explore work towards the development of a fluorogenic screening platform that could be used to screen for halogenase enzyme activity.
Finally, in Chapter 6, a novel approach towards the photoprotection of polyene natural products is explored. Medicinally promising compounds that have poor photostability are often discounted from development. Here, Sporopollenin Exine Capsules (SpECs) are used to encapsulate the potent polyene antibiotic, marinomycin A, with a subsequent increase in its half-life under intense light from 95 s to over 7 hrs. This cheap, simple, and sustainable technology has the potential to provide a powerful new approach to drug stabilisation and delivery, as well as an exciting new tool for natural product extraction and purification.
2020-06-01T00:00:00ZBailey, Christopher SamuelNatural products provide one of the corner stones of both modern and historical medicine, contributing towards over 65 % of new FDA approved drugs that entered clinical trials between 1981 and 2014. It is partly down to the historic success of natural products in medicine that many people are once again looking to nature for a solution to the rise in antibiotic resistant bacterial infections. However, developing natural products towards clinical use poses a number of challenges. Notable examples of these challenges include the need to generate analogues of these compounds, which are oftentimes structurally complex, and the instability of many natural products. Within this work several approaches are set out to address these challenges, exploring novel genetic and complementary synthetic technologies, as well as looking towards natural solutions for sequestering and stabilising molecules.
Chapters 2 – 5 explore tools towards the GenoChemetic generation of natural product analogues. Firstly the utilisation of alkyne tags in a GenoChemetic approach is explored. Chapter 2 first looks towards exploring the flexibility of a series of biosynthetic gene clusters to the uptake of alkyne containing starter units. Chapter 3 then generates genetic cassettes for the in situ biosynthesis of such starter units, for subsequent potential incorporation into natural products.
A well utilised bioorthogonal handle within the group are aryl halides. Chapter 4 looks towards the genetic installation of such a handle onto natural products. Chapter 5 than goes on to explore work towards the development of a fluorogenic screening platform that could be used to screen for halogenase enzyme activity.
Finally, in Chapter 6, a novel approach towards the photoprotection of polyene natural products is explored. Medicinally promising compounds that have poor photostability are often discounted from development. Here, Sporopollenin Exine Capsules (SpECs) are used to encapsulate the potent polyene antibiotic, marinomycin A, with a subsequent increase in its half-life under intense light from 95 s to over 7 hrs. This cheap, simple, and sustainable technology has the potential to provide a powerful new approach to drug stabilisation and delivery, as well as an exciting new tool for natural product extraction and purification.Catalytic enantioselective acyl transfer for the synthesis of atropisomersMunday, Elizabeth Sarahhttps://hdl.handle.net/10023/196392021-07-26T16:40:23Z2020-06-24T00:00:00ZThis thesis details the development of enantioselective, isothiourea-catalysed, acyl-transfer
methodology for the synthesis of atropisomers.
Chapter 1 aims to introduce organocatalysis in the context of the current state-of-the art in Lewis
base catalysis and its application in enantioselective acyl transfer. Following this, the importance
of axial chirality and the current art in the synthesis of biaryl and non-biaryl atropisomers is
introduced. The potential for isothiourea catalysis to provide a new platform in this area is then
outlined.
Chapter 2 outlines development of methodology for the acylative desymmetrisation of biaryl
phenols. After optimisation of the desymmetrisation of a model system, computational and
experimental techniques were used to probe the selectivity and mechanism of the process. The
methodology was then extended to a scope of 14 biaryl substrates, providing highly
enantioenriched products (up to 98:2 er, 54% isolated yield). Discussion of the mechanism of
their formation, and the enantioselectivity of the process is also provided.
Chapter 3 outlines attempts to extend the methodology developed in chapter 2 to the synthesis
of molecules with a C–N stereogenic axis. The synthesis of several target biaryl heterocycle
substrates was attempted and tentative attempts to adapt current acyl transfer methodology to
these species is described. Additionally, the synthesis of atropisomeric anilides via N-acylation of
secondary anilines is detailed.
Chapter 4 contains a summary of the work that has been carried out for this thesis and the
potential extensions to future work within the field of Lewis base organocatalysis.
Chapter 5 provides the experimental details for the synthesis of the compounds which are
contained in this thesis, as well as the associated analytical data for their characterisation.
2020-06-24T00:00:00ZMunday, Elizabeth SarahThis thesis details the development of enantioselective, isothiourea-catalysed, acyl-transfer
methodology for the synthesis of atropisomers.
Chapter 1 aims to introduce organocatalysis in the context of the current state-of-the art in Lewis
base catalysis and its application in enantioselective acyl transfer. Following this, the importance
of axial chirality and the current art in the synthesis of biaryl and non-biaryl atropisomers is
introduced. The potential for isothiourea catalysis to provide a new platform in this area is then
outlined.
Chapter 2 outlines development of methodology for the acylative desymmetrisation of biaryl
phenols. After optimisation of the desymmetrisation of a model system, computational and
experimental techniques were used to probe the selectivity and mechanism of the process. The
methodology was then extended to a scope of 14 biaryl substrates, providing highly
enantioenriched products (up to 98:2 er, 54% isolated yield). Discussion of the mechanism of
their formation, and the enantioselectivity of the process is also provided.
Chapter 3 outlines attempts to extend the methodology developed in chapter 2 to the synthesis
of molecules with a C–N stereogenic axis. The synthesis of several target biaryl heterocycle
substrates was attempted and tentative attempts to adapt current acyl transfer methodology to
these species is described. Additionally, the synthesis of atropisomeric anilides via N-acylation of
secondary anilines is detailed.
Chapter 4 contains a summary of the work that has been carried out for this thesis and the
potential extensions to future work within the field of Lewis base organocatalysis.
Chapter 5 provides the experimental details for the synthesis of the compounds which are
contained in this thesis, as well as the associated analytical data for their characterisation.Insights into the structure and reactivity of the biopolymer lignin using diffusion ordered spectroscopy and synthetic model studiesMontgomery, Jameshttps://hdl.handle.net/10023/195852024-03-20T15:48:48Z2020-06-24T00:00:00Z2020-06-24T00:00:00ZMontgomery, JamesExploiting peri-substitution to promote coupling reactionsLawson, Bethany Jane Mollyhttps://hdl.handle.net/10023/195812023-09-26T13:24:33Z2020-06-24T00:00:00Z2020-06-24T00:00:00ZLawson, Bethany Jane MollyRhodium catalysed asymmetric synthesis of tertiary aminesGilbert, Sophie Hannahhttps://hdl.handle.net/10023/195282023-04-25T02:01:50Z2020-06-24T00:00:00ZThe asymmetric synthesis of tertiary amines is a highly desirable goal, but far fewer efficient
synthetic methods exist for their synthesis, relative to primary and secondary amines. A
possible atom-efficient method of tertiary amine formation is catalytic hydrogenation.
Despite the demand, there are only a few reported examples of asymmetric enamine
hydrogenation, and none of these conditions are efficient enough to be viable for industrial
processes. Until 2019, there were no reported examples of tertiary amine formation by using
direct asymmetric reductive amination using H₂ as the reductant.
This thesis describes the development of both enantioselective and diastereoselective
reductive aminations, using hydrogen gas and homogeneous rhodium catalysts. The
enantioselective reductive amination uses an electron deficient phanephos ligand and
reduces bicyclic aryl ketones at low catalyst loadings but moderate selectivity. The
diastereoselective reductive amination uses electron deficient monophosphines as ligands
and includes many chiral 3-substituted cyclic ketones in the substrate scope, mainly 3-
arylcyclohexanones.
These 3-arylcyclohexanones substrates were synthesised by rhodium catalysed conjugate
addition. This enantioselective conjugate addition was combined with our diastereoselective
reductive amination, to form a highly stereoselective one-pot process. The rhodium used in
the conjugate addition was recycled for the reductive amination step using an ‘assisted
tandem catalysis’ strategy. The rhodium catalyst was modified in situ by the sequential
addition of a monophosphine ligand, allowing it to catalyse the second step. This process
formed a chiral tertiary amine with high selectivity and conversion.
While developing this one-pot process, BOBPHOS, a phospholane-phosphite ligand, was
identified as a highly active ligand in rhodium catalysed conjugate additions. The potential
of BOBPHOS-Rh catalysed conjugate additions of challenging substrates like piperidones,
coumarins and heteroarylboronic acids was examined, leading to improved protocols.
2020-06-24T00:00:00ZGilbert, Sophie HannahThe asymmetric synthesis of tertiary amines is a highly desirable goal, but far fewer efficient
synthetic methods exist for their synthesis, relative to primary and secondary amines. A
possible atom-efficient method of tertiary amine formation is catalytic hydrogenation.
Despite the demand, there are only a few reported examples of asymmetric enamine
hydrogenation, and none of these conditions are efficient enough to be viable for industrial
processes. Until 2019, there were no reported examples of tertiary amine formation by using
direct asymmetric reductive amination using H₂ as the reductant.
This thesis describes the development of both enantioselective and diastereoselective
reductive aminations, using hydrogen gas and homogeneous rhodium catalysts. The
enantioselective reductive amination uses an electron deficient phanephos ligand and
reduces bicyclic aryl ketones at low catalyst loadings but moderate selectivity. The
diastereoselective reductive amination uses electron deficient monophosphines as ligands
and includes many chiral 3-substituted cyclic ketones in the substrate scope, mainly 3-
arylcyclohexanones.
These 3-arylcyclohexanones substrates were synthesised by rhodium catalysed conjugate
addition. This enantioselective conjugate addition was combined with our diastereoselective
reductive amination, to form a highly stereoselective one-pot process. The rhodium used in
the conjugate addition was recycled for the reductive amination step using an ‘assisted
tandem catalysis’ strategy. The rhodium catalyst was modified in situ by the sequential
addition of a monophosphine ligand, allowing it to catalyse the second step. This process
formed a chiral tertiary amine with high selectivity and conversion.
While developing this one-pot process, BOBPHOS, a phospholane-phosphite ligand, was
identified as a highly active ligand in rhodium catalysed conjugate additions. The potential
of BOBPHOS-Rh catalysed conjugate additions of challenging substrates like piperidones,
coumarins and heteroarylboronic acids was examined, leading to improved protocols.Studies towards the total synthesis of Leiodolide AStell, Matthewhttps://hdl.handle.net/10023/195122021-07-23T10:22:56Z2020-06-24T00:00:00ZIn 2006, Leiodolide A (12) was isolated from the marine sponge Leiodermatium sp., which was collected near Uchelbeluu Reef in Palau. Leiodolide A represents a novel class of macrocyclic secondary metabolites, containing a conjugated oxazole moiety within a 19-membered macrolide ring. The purified natural product was tested against the National Cancer Institute’s 60-cell line assay and displayed low micromolar potency against three unrelated cell lines. During characterisation, by employing coupling constant and NOE analysis in conjunction with chemical derivatisation, the absolute stereochemistry of the C15, C16, C17 and C24 positions was confidently determined. Similar analysis of the C4 and C5 stereogenic centres yielded ‘tenuous’ assignments and the remote nature of the C13 stereogenic centre prevented its assignment.
This work describes the use of the DP4 structure probability methodology to predict the most likely correct diastereomer from a possible eight. The 4S5S13R diastereomer 128, disparate from the original ‘tenuous’ assignment, was assigned the highest probability and is the principal target of all synthetic work. Initial attempts towards the installation of the C4 and C5 stereogenic centres were unsuccessful but this was resolved with an efficacious application of the Evans anti-aldol methodology. Following the completion of the northern (C10 – C20) and southern (C1 – C9) fragments, the deprotection of the southern fragment could not be realised without degradation. Attempts to remedy this, by exploration of other fragment coupling methodologies, were unsuccessful. However, following the selection of appropriate protection and deprotection protocols, coupling of the key fragments was achieved and elaboration to the corresponding secoacid, required for the study of the crucial Mitsunobu macrolactonisation, represents the most advanced intermediate in a total synthesis of Leiodolide A reported to date.
2020-06-24T00:00:00ZStell, MatthewIn 2006, Leiodolide A (12) was isolated from the marine sponge Leiodermatium sp., which was collected near Uchelbeluu Reef in Palau. Leiodolide A represents a novel class of macrocyclic secondary metabolites, containing a conjugated oxazole moiety within a 19-membered macrolide ring. The purified natural product was tested against the National Cancer Institute’s 60-cell line assay and displayed low micromolar potency against three unrelated cell lines. During characterisation, by employing coupling constant and NOE analysis in conjunction with chemical derivatisation, the absolute stereochemistry of the C15, C16, C17 and C24 positions was confidently determined. Similar analysis of the C4 and C5 stereogenic centres yielded ‘tenuous’ assignments and the remote nature of the C13 stereogenic centre prevented its assignment.
This work describes the use of the DP4 structure probability methodology to predict the most likely correct diastereomer from a possible eight. The 4S5S13R diastereomer 128, disparate from the original ‘tenuous’ assignment, was assigned the highest probability and is the principal target of all synthetic work. Initial attempts towards the installation of the C4 and C5 stereogenic centres were unsuccessful but this was resolved with an efficacious application of the Evans anti-aldol methodology. Following the completion of the northern (C10 – C20) and southern (C1 – C9) fragments, the deprotection of the southern fragment could not be realised without degradation. Attempts to remedy this, by exploration of other fragment coupling methodologies, were unsuccessful. However, following the selection of appropriate protection and deprotection protocols, coupling of the key fragments was achieved and elaboration to the corresponding secoacid, required for the study of the crucial Mitsunobu macrolactonisation, represents the most advanced intermediate in a total synthesis of Leiodolide A reported to date.Artificial metalloenzymes : modified proteins as tuneable transition metal catalysts and their application in oxidative lignin degradationDoble, Megan V.https://hdl.handle.net/10023/192422021-04-08T16:23:34Z2019-12-03T00:00:00ZThe selective oxidation of organic molecules is fundamentally important to life and immensely
useful in industry.
Metalloenzyme catalysed oxidations often display exquisite substrate
specificity as well as regio and/or stereoselectivity. Huge strides have occurred in the field of
biocatalysis in recent years. Work has developed by taking inspiration from nature’s enzymes,
to use directed evolution and engineering methods to create tailor made catalysts. Artificial
Metalloenzymes (ArMs) provide the possibility to expand this repertoire further by combining
the advantageous features of enzymes with the versatile reaction scope of transition metals.
The initial chapter in this thesis takes a look into recent literature about artificial
metalloenzymes and their application in oxidation catalysis.
Chapter two describes the design rationale and synthesis of protein templates and synthetic
cofactors for the development of artificial metalloenzymes. Successful modification was
achieved for a wide library of nitrogen donor ligands, creating an array of artificial
metalloenzymes that can be tested in catalytic reactions. In the absence of a crystal
structure of the modified protein, UV and CD analysis were carried out to gather
characteristic information about the artificial metalloenzymes and their metal binding
properties. An investigation was also carried out to determine the most accurate method to
calculate protein concentration once it has been modified with a cofactor.
The third chapter describes the application of protein engineering to increase the
thermostability of the target protein. Variants of an artificial metalloenzyme were created by
rational design using structural and bioinformatic information. The variants were tested to
identify mutations that enhanced the stability of the protein scaffold. Significant increases in
melting temperature were observed in a number of the modified metalloenzymes. Their
ability to withstand higher reaction temperatures resulted in increased activity in the
hydroformylation of 1-octene, with >5-fold improvements in turnover numbers (TON).
The fourth chapter reports the use of artificial metalloenzymes in oxidation catalysis. In
particular their application to the degradation of lignin is investigated. Using a model
compound that mimics the most abundant linkage within lignin as a substrate, a wide array
of artificial metalloenzymes were tested to study if any oxidation or cleavage occurs.
Investigations were carried out to find the optimum conditions varying catalyst loading and
buffer/solvent composition. Complete selective conversion to ketone product is observed
using SCP-2L A100C modified with a tris(2-pyridylmethyl) amine based cofactor, coordinated
to Fe(OTf)₂.2MeCN. Engineering the protein scaffold to incorporate glutamic acid was found
to improve the ArM activity, showing that rational design of the protein environment using
metal binding amino acids can be a method to improve the overall activity of an artificial
metalloenzyme.
2019-12-03T00:00:00ZDoble, Megan V.The selective oxidation of organic molecules is fundamentally important to life and immensely
useful in industry.
Metalloenzyme catalysed oxidations often display exquisite substrate
specificity as well as regio and/or stereoselectivity. Huge strides have occurred in the field of
biocatalysis in recent years. Work has developed by taking inspiration from nature’s enzymes,
to use directed evolution and engineering methods to create tailor made catalysts. Artificial
Metalloenzymes (ArMs) provide the possibility to expand this repertoire further by combining
the advantageous features of enzymes with the versatile reaction scope of transition metals.
The initial chapter in this thesis takes a look into recent literature about artificial
metalloenzymes and their application in oxidation catalysis.
Chapter two describes the design rationale and synthesis of protein templates and synthetic
cofactors for the development of artificial metalloenzymes. Successful modification was
achieved for a wide library of nitrogen donor ligands, creating an array of artificial
metalloenzymes that can be tested in catalytic reactions. In the absence of a crystal
structure of the modified protein, UV and CD analysis were carried out to gather
characteristic information about the artificial metalloenzymes and their metal binding
properties. An investigation was also carried out to determine the most accurate method to
calculate protein concentration once it has been modified with a cofactor.
The third chapter describes the application of protein engineering to increase the
thermostability of the target protein. Variants of an artificial metalloenzyme were created by
rational design using structural and bioinformatic information. The variants were tested to
identify mutations that enhanced the stability of the protein scaffold. Significant increases in
melting temperature were observed in a number of the modified metalloenzymes. Their
ability to withstand higher reaction temperatures resulted in increased activity in the
hydroformylation of 1-octene, with >5-fold improvements in turnover numbers (TON).
The fourth chapter reports the use of artificial metalloenzymes in oxidation catalysis. In
particular their application to the degradation of lignin is investigated. Using a model
compound that mimics the most abundant linkage within lignin as a substrate, a wide array
of artificial metalloenzymes were tested to study if any oxidation or cleavage occurs.
Investigations were carried out to find the optimum conditions varying catalyst loading and
buffer/solvent composition. Complete selective conversion to ketone product is observed
using SCP-2L A100C modified with a tris(2-pyridylmethyl) amine based cofactor, coordinated
to Fe(OTf)₂.2MeCN. Engineering the protein scaffold to incorporate glutamic acid was found
to improve the ArM activity, showing that rational design of the protein environment using
metal binding amino acids can be a method to improve the overall activity of an artificial
metalloenzyme.Electron microscopy of some inorganic crystals with novel morphologiesChen, Jialuhttps://hdl.handle.net/10023/191562023-04-19T02:06:39Z2019-12-03T00:00:00ZThis project concerns crystal growth of some inorganic crystals which have novel
morphologies. In order to study their crystal growth routes and further reveal their crystal
growth mechanism, intermediate samples were collected and analysed, including samples
produced after reduced reaction time, with different concentration of reactant or at reduced
reaction temperature. The analysis was mainly completed by scanning electron microscopy
and high resolution transmission electron microscopy. Other complementary techniques are
powder X-ray diffraction, energy dispersive X-ray spectroscopy, selected area electron
diffraction, mass spectrometry, inductively coupled plasma - optical emission spectrometry
and photoelectrochemical measurement.
Investigated inorganic crystals include hematite nanotubes and nanorings, silver dendrites
and copper dendrites, and graphene-based metal oxides. Hematite nanotubes and nanorings
can be fabricated through hydrolysis of ferric chloride in different concentrations of
phosphate via hydrothermal reaction. Intermediate samples at a range of different times were
collected and characterised. It was revealed that hematite nanocrystallites form from
decomposition of β-FeOOH nanorods, and that the final morphology depends on the
competition between aggregation of β-FeOOH nanorods and decomposition into hematite
nanocrystallites. Silver dendrites and copper dendrites can be produced via replacement
reaction at room temperature. When synthetic conditions were changed, dendrites of different
morphologies can be synthesised. The crystal growth direction and growth mechanism were
investigated. Metal oxides such as manganese oxide nanoparticles and nickel oxide hollow
particles can form on electrochemically exfoliated graphene via hydrolysis and
polymerisation process. It was found that polymerisation is a vital process in the formation of
metal oxides on graphene since polymers have multiple interaction sites with the surface of
graphene. The intermediate samples and growth process were studied in detail.
2019-12-03T00:00:00ZChen, JialuThis project concerns crystal growth of some inorganic crystals which have novel
morphologies. In order to study their crystal growth routes and further reveal their crystal
growth mechanism, intermediate samples were collected and analysed, including samples
produced after reduced reaction time, with different concentration of reactant or at reduced
reaction temperature. The analysis was mainly completed by scanning electron microscopy
and high resolution transmission electron microscopy. Other complementary techniques are
powder X-ray diffraction, energy dispersive X-ray spectroscopy, selected area electron
diffraction, mass spectrometry, inductively coupled plasma - optical emission spectrometry
and photoelectrochemical measurement.
Investigated inorganic crystals include hematite nanotubes and nanorings, silver dendrites
and copper dendrites, and graphene-based metal oxides. Hematite nanotubes and nanorings
can be fabricated through hydrolysis of ferric chloride in different concentrations of
phosphate via hydrothermal reaction. Intermediate samples at a range of different times were
collected and characterised. It was revealed that hematite nanocrystallites form from
decomposition of β-FeOOH nanorods, and that the final morphology depends on the
competition between aggregation of β-FeOOH nanorods and decomposition into hematite
nanocrystallites. Silver dendrites and copper dendrites can be produced via replacement
reaction at room temperature. When synthetic conditions were changed, dendrites of different
morphologies can be synthesised. The crystal growth direction and growth mechanism were
investigated. Metal oxides such as manganese oxide nanoparticles and nickel oxide hollow
particles can form on electrochemically exfoliated graphene via hydrolysis and
polymerisation process. It was found that polymerisation is a vital process in the formation of
metal oxides on graphene since polymers have multiple interaction sites with the surface of
graphene. The intermediate samples and growth process were studied in detail.Defect chemistry in perovskite titanate : from materials to interfacesHui, Jianinghttps://hdl.handle.net/10023/191012021-05-11T06:49:20Z2019-06-26T00:00:00ZThe increasing demand for energy consumption and environmental protection
accelerates renewable energy applications. Due to the intermittence supply of
renewables such as wind and wave, the development of energy conversion and
storage techniques is in urgent need. H₂, with high energy density, huge
reserves and zero emissions, becomes one of the most promising energy
carriers in the future. High temperature steam electrolysis and photoelectrolysis
are two promising methods for H₂ production that can use
renewable energies like wind and solar. However, the catalysts degradation is
still the main drawback for their wide application.
This thesis explores a promising candidate perovskite titanate that can be used
as catalyst substrates. The influences of A-site cation deficiency on materials
microstructure, electronic structure and redox stability are the main issues
studied in this project.
This work illustrates the metal-oxide interactions enhancements when cation
deficiency exists in perovskite titanate oxides. Promoted cation migration
results in metal-oxide interface reconstruction, which in turn increases contact
area and adhesion force between catalyst and substrate. Electron microscopy
and thermogravimetry analysis showed enhanced particle stability on A-site
deficient perovskite at 700 °C in redox atmosphere.
The influence of cation deficiency on perovskites electronic structure was also
discussed based on La and Cr co-doped SrTiO₃. Although A-site deficiency
doesn’t contribute to band structure, it introduces electrons and increases
carrier mobility. Thus, a dramatical enhancement in H₂ production rate was
achieved in materials containing a small amount of cation deficiency. The
highest H₂ production rate is 7.5 μM·h⁻¹ under visible light (>420 nm, 250 W).
The reduction of perovskite in strong reducing atmosphere not only creates
oxygen vacancies, but also pushes B-site cations out the lattice when A-site
cation deficiency exists. Here, a series of materials doped with Fe, Co, Ni and
Cu were prepared and analysed to compare the different exsolution ability.
Cation size, oxygen vacancies and doping level all affect the exsolution process
of transition metals. N-type conductivity due to Ti reduction suggests the
possibility usage for anode material in SOFC. The initial trial with such material
achieved 0.7 W·cm⁻² for single fuel cell with wet H₂ (3%H₂O) at 900 °C. Also, it
can produce H₂ efficiently when working in SOEC mode.
The fundamental properties of A-site deficient perovskite titanate explored in
this thesis gives insight for further material design related to various
functionality.
2019-06-26T00:00:00ZHui, JianingThe increasing demand for energy consumption and environmental protection
accelerates renewable energy applications. Due to the intermittence supply of
renewables such as wind and wave, the development of energy conversion and
storage techniques is in urgent need. H₂, with high energy density, huge
reserves and zero emissions, becomes one of the most promising energy
carriers in the future. High temperature steam electrolysis and photoelectrolysis
are two promising methods for H₂ production that can use
renewable energies like wind and solar. However, the catalysts degradation is
still the main drawback for their wide application.
This thesis explores a promising candidate perovskite titanate that can be used
as catalyst substrates. The influences of A-site cation deficiency on materials
microstructure, electronic structure and redox stability are the main issues
studied in this project.
This work illustrates the metal-oxide interactions enhancements when cation
deficiency exists in perovskite titanate oxides. Promoted cation migration
results in metal-oxide interface reconstruction, which in turn increases contact
area and adhesion force between catalyst and substrate. Electron microscopy
and thermogravimetry analysis showed enhanced particle stability on A-site
deficient perovskite at 700 °C in redox atmosphere.
The influence of cation deficiency on perovskites electronic structure was also
discussed based on La and Cr co-doped SrTiO₃. Although A-site deficiency
doesn’t contribute to band structure, it introduces electrons and increases
carrier mobility. Thus, a dramatical enhancement in H₂ production rate was
achieved in materials containing a small amount of cation deficiency. The
highest H₂ production rate is 7.5 μM·h⁻¹ under visible light (>420 nm, 250 W).
The reduction of perovskite in strong reducing atmosphere not only creates
oxygen vacancies, but also pushes B-site cations out the lattice when A-site
cation deficiency exists. Here, a series of materials doped with Fe, Co, Ni and
Cu were prepared and analysed to compare the different exsolution ability.
Cation size, oxygen vacancies and doping level all affect the exsolution process
of transition metals. N-type conductivity due to Ti reduction suggests the
possibility usage for anode material in SOFC. The initial trial with such material
achieved 0.7 W·cm⁻² for single fuel cell with wet H₂ (3%H₂O) at 900 °C. Also, it
can produce H₂ efficiently when working in SOEC mode.
The fundamental properties of A-site deficient perovskite titanate explored in
this thesis gives insight for further material design related to various
functionality.Towards mitochondrial targeting for the treatment of Alzheimer's DiseaseAbdul Razzak, Ranahttps://hdl.handle.net/10023/188692021-03-03T12:42:59Z2019-06-26T00:00:00ZNanoparticles (NPs) have emerged as a promising approach to overcoming biological
barriers imposed by the human body. Polymeric NPs offer a superior synthetic
flexibility and advances in polymerization chemistries have made polymeric
architectures with precisely tuned properties accessible. Ring opening metathesis
polymerization (ROMP) has become a popular polymerization technique due to its mild
conditions a tolerance to an array of functional groups. We successfully synthesized
two generations of ROMP monomers that feature polymerizable group and a
mitochondrial targeting ligand linked together via a hydrophilic spacer. This monomer
can be co-polymerized with another ROMP monomer bearing a fluorescent molecule
to enable the visualization of the polymeric NPs in the cell. The second-generation
monomers differ from the first-generation analogues by their three-fold longer
hydrophilic linkers. Co-polymers prepared from second-generation monomers show
cellular up-take but no mitochondrial localization.
2019-06-26T00:00:00ZAbdul Razzak, RanaNanoparticles (NPs) have emerged as a promising approach to overcoming biological
barriers imposed by the human body. Polymeric NPs offer a superior synthetic
flexibility and advances in polymerization chemistries have made polymeric
architectures with precisely tuned properties accessible. Ring opening metathesis
polymerization (ROMP) has become a popular polymerization technique due to its mild
conditions a tolerance to an array of functional groups. We successfully synthesized
two generations of ROMP monomers that feature polymerizable group and a
mitochondrial targeting ligand linked together via a hydrophilic spacer. This monomer
can be co-polymerized with another ROMP monomer bearing a fluorescent molecule
to enable the visualization of the polymeric NPs in the cell. The second-generation
monomers differ from the first-generation analogues by their three-fold longer
hydrophilic linkers. Co-polymers prepared from second-generation monomers show
cellular up-take but no mitochondrial localization.Preparation, characterisation and application of ordered mesoporous materialsSakina, Farzeenhttps://hdl.handle.net/10023/188622021-02-24T17:55:17Z2019-06-26T00:00:00ZThe history of ordered mesoporous materials starts with the discovery of MCM-41(Mobil
Composition of Matter-41) in 1992 using an organic template as structure directing agent.
Mesoporous materials have not only proved to be ideal candidates in various fields like,
for example, catalysis but could also be potentially used as a hard template for
synthesising other useful mesoporous materials. The aim of this research was to develop
industrially feasible and environmentally friendly methods for the preparation of ordered
mesoporous materials, to characterise these and to study their applications. The main
techniques used for the characterisation of these mesoporous materials were N₂
physisorption, XRD and TEM. In the first part of the study, metal- and halogen-free
ordered mesoporous polymer and carbon materials having 2D hexagonal (P6mm) and
body centered cubic (Im3̅m) mesostructures were made using a modified two phase
method employing alternative polymerisation and condensation catalysts. These
materials had high surface area and pore volume and had narrow pore size distributions.
Their physical evolution with increasing calcination temperature was examined as were
the effects of varying synthesis parameters on the nature of the final mesostructure. The
second part of the study was focused on the synthesis of ordered mesoporous ceria using
metal- and halogen-free ordered mesoporous carbon materials - made in the first part of
the study - as the hard template. The mesoporous ceria having 2D hexagonal arrangement
of pores were successfully synthesised using a solid-liquid method which is a solvent
free, easy to use and environmentally friendly method. The carbon template calcined at
400 °C was found to be the best template in terms of giving high loading of precursor and
giving high quality product. The synthesis of body centered cubic ceria was less
successful than hoped due to the small pore openings in this template material. The third
part of study involved the preparation of mesoporous carbon supported Pd catalysts and
their use in the hydrodechlorination of trichloromethane (TCM). The results were very
promising, and 100 % conversions were obtained at 175 °C with high selectivity to
alkanes and low selectivity to intermediate chlorinated products.
2019-06-26T00:00:00ZSakina, FarzeenThe history of ordered mesoporous materials starts with the discovery of MCM-41(Mobil
Composition of Matter-41) in 1992 using an organic template as structure directing agent.
Mesoporous materials have not only proved to be ideal candidates in various fields like,
for example, catalysis but could also be potentially used as a hard template for
synthesising other useful mesoporous materials. The aim of this research was to develop
industrially feasible and environmentally friendly methods for the preparation of ordered
mesoporous materials, to characterise these and to study their applications. The main
techniques used for the characterisation of these mesoporous materials were N₂
physisorption, XRD and TEM. In the first part of the study, metal- and halogen-free
ordered mesoporous polymer and carbon materials having 2D hexagonal (P6mm) and
body centered cubic (Im3̅m) mesostructures were made using a modified two phase
method employing alternative polymerisation and condensation catalysts. These
materials had high surface area and pore volume and had narrow pore size distributions.
Their physical evolution with increasing calcination temperature was examined as were
the effects of varying synthesis parameters on the nature of the final mesostructure. The
second part of the study was focused on the synthesis of ordered mesoporous ceria using
metal- and halogen-free ordered mesoporous carbon materials - made in the first part of
the study - as the hard template. The mesoporous ceria having 2D hexagonal arrangement
of pores were successfully synthesised using a solid-liquid method which is a solvent
free, easy to use and environmentally friendly method. The carbon template calcined at
400 °C was found to be the best template in terms of giving high loading of precursor and
giving high quality product. The synthesis of body centered cubic ceria was less
successful than hoped due to the small pore openings in this template material. The third
part of study involved the preparation of mesoporous carbon supported Pd catalysts and
their use in the hydrodechlorination of trichloromethane (TCM). The results were very
promising, and 100 % conversions were obtained at 175 °C with high selectivity to
alkanes and low selectivity to intermediate chlorinated products.Complementary hydrazone-based dynamic covalent nanoparticlesMarro, Nicolashttps://hdl.handle.net/10023/188572021-02-25T17:42:46Z2019-06-26T00:00:00ZThe extraordinary and unique properties exhibited by monolayer-stabilised metal
nanoparticles suggest exciting potential applications. Surface-bound molecules stabilize the
material in colloidal form, but also define a whole host of physicochemical properties and
provide a means to link nanoparticles with any number of other components. Post-synthetic
strategies for functionalizing nanoparticle-bound monolayers are therefore critical for
virtually all applications. However, established methods each have limitations. The
emerging concept of dynamic covalent nanoparticle building blocks provides a
transformative strategy for achieving responsive and adaptive surface-engineering of
nanomaterials.
Previously, dynamic covalent hydrazone exchange has been employed to reversibly alter
gold nanoparticle-bound monolayers using electrophilic molecular modifiers (aldehydes),
establishing the possibility of using dynamic covalent reactions to manipulate
nanoparticle-bond functionality. This thesis takes several steps towards developing this
approach into a general strategy for divergent modification of nanoparticle surface
functionality.
Exploiting the directional nature of the hydrazone bond, a complementary family of
dynamic covalent nanoparticles having the electrophilic species tethered to the
nanoparticle surface, was created. The scope of the dynamic covalent nanoparticle
strategy is thus significantly expanded, allowing reversible post-synthetic
functionalization using nucleophilic exchange units. Using solution-state NMR
spectroscopy, hydrazone exchange kinetics for these two sets of complementary
nanoparticles were investigated, revealing how the surface-confined reactivity
compares to bulk solution and also significant differences in reactivity between the
complementary pair of nanoparticles.
The reversible nature of dynamic covalent reactions allows each member of the
complementary family of nanoparticle building block to be assembled in a predictable
and controlled way, governed by simple abiotic molecular systems. Furthermore, the
complementary reactivity of these two systems provides access to binary nanoparticle
assemblies without requiring any molecular linkers. Finally, a detailed understanding about surface-confined chemical reactivities offers the opportunity to explore self-sorting behaviour of complementary nanoparticles.
Dynamic covalent exchange can be used to not only switch nanoparticle solvent compatibility between widely differing solvents (from hexane to water), but also to progressively tune solubility across the entire continuum between these extremes. Indeed,
molecular-level control over surface-confined reactions, allows to produce a self-consistent
family of kinetically stable nanoparticles with different mixed-ligands monolayer compositions, providing a unique platform to study structure–property relationships on the nanoscale.
2019-06-26T00:00:00ZMarro, NicolasThe extraordinary and unique properties exhibited by monolayer-stabilised metal
nanoparticles suggest exciting potential applications. Surface-bound molecules stabilize the
material in colloidal form, but also define a whole host of physicochemical properties and
provide a means to link nanoparticles with any number of other components. Post-synthetic
strategies for functionalizing nanoparticle-bound monolayers are therefore critical for
virtually all applications. However, established methods each have limitations. The
emerging concept of dynamic covalent nanoparticle building blocks provides a
transformative strategy for achieving responsive and adaptive surface-engineering of
nanomaterials.
Previously, dynamic covalent hydrazone exchange has been employed to reversibly alter
gold nanoparticle-bound monolayers using electrophilic molecular modifiers (aldehydes),
establishing the possibility of using dynamic covalent reactions to manipulate
nanoparticle-bond functionality. This thesis takes several steps towards developing this
approach into a general strategy for divergent modification of nanoparticle surface
functionality.
Exploiting the directional nature of the hydrazone bond, a complementary family of
dynamic covalent nanoparticles having the electrophilic species tethered to the
nanoparticle surface, was created. The scope of the dynamic covalent nanoparticle
strategy is thus significantly expanded, allowing reversible post-synthetic
functionalization using nucleophilic exchange units. Using solution-state NMR
spectroscopy, hydrazone exchange kinetics for these two sets of complementary
nanoparticles were investigated, revealing how the surface-confined reactivity
compares to bulk solution and also significant differences in reactivity between the
complementary pair of nanoparticles.
The reversible nature of dynamic covalent reactions allows each member of the
complementary family of nanoparticle building block to be assembled in a predictable
and controlled way, governed by simple abiotic molecular systems. Furthermore, the
complementary reactivity of these two systems provides access to binary nanoparticle
assemblies without requiring any molecular linkers. Finally, a detailed understanding about surface-confined chemical reactivities offers the opportunity to explore self-sorting behaviour of complementary nanoparticles.
Dynamic covalent exchange can be used to not only switch nanoparticle solvent compatibility between widely differing solvents (from hexane to water), but also to progressively tune solubility across the entire continuum between these extremes. Indeed,
molecular-level control over surface-confined reactions, allows to produce a self-consistent
family of kinetically stable nanoparticles with different mixed-ligands monolayer compositions, providing a unique platform to study structure–property relationships on the nanoscale.The design of acyl modified co-enzyme-A ester analogues as enzyme inhibitorsRubanu, Maria Graziahttps://hdl.handle.net/10023/188502021-04-15T11:02:42Z2019-12-03T00:00:00ZThis thesis is focused on the design and synthesis of analogues of thioesters of Co-enzyme A which are involved in many important biosynthetic pathways.
Acetyl-CoA is converted into citrate by citrate synthase in the first step of the Krebs cycle that is central for the cellular respiration.
Chapter 2 is focused on the successful synthesis of five analogues of acetyl-CoA and their investigation as inhibitors of citrate synthase. This project is based on the finding that Fluorovinyl thioether-CoA (FV-CoA) is a micromolar inhibitor of citrate synthase (Kᵢᵃᵖᵖ = 4.4 µM). Sulfoxide-CoA, with a sulfonyl and a methylene group replacing the carbonyl group and the sulfur atom of acetyl-CoA, was found to be a modest micromolar inhibitor of citrate synthase (11.1 µM), indicating its potential as hydrogen bonding acceptor. The remaining compounds showed poor or too low binding affinity for the enzyme. Although these compounds showed poor inhibitory capacity towards citrate synthase, they could be potential inhibitors of other acetyl-CoA utilizing enzymes, such as malate synthase that catalyzes the conversion of acetyl-CoA into malate. Its activity is correlated to different pathogens pathway (Mycobacterium tubercolosis) and its regulation could potentially prevent the bacterial growth.
Chapter 3 describes the attempted synthesis of a fluorovinyl thioacrylate derivative as malonyl-CoA analogue and potential covalent inhibitor of acetyl-CoA carboxylase (ACC). ACC catalyzes the irreversible conversion of acetyl-CoA into malonyl-CoA in the first step of fatty acid synthesis. The regulation of ACC is associated to many cardiovascular diseases such as diabetes, obesity and its inhibition can lead to the development of novel antibiotics for their treatment. Due to the challenging synthesis of the precursor thioester, this malonyl-CoA analogue could not be prepared.
Chapter 4 reports the synthesis of α,α,β-trifluoro cyclopropane-CoA and was found to be a poor inhibitor of citrate synthase (Kᵢ = 65.2 µM ). However, this compound has potential to be a covalent inhibitor of citrate synthase and other enzymes such as malate synthase, thus future investigations will be carried out to this purpose.
Furthermore, chapter 4 reports the attempted synthesis of an α,α-difluoroethyl thioether-CoA as an acetyl-CoA analogue. This compound bears two electronegative fluorine atoms, thus it could interact electrostatically with the active site residues of citrate synthase through hydrogen bonds, leading to its inhibition. Unfortunately, due to the instability of the difluoro moiety under the enzymatic reaction conditions, this was not converted to the corresponding acetyl-CoA analogue.
Electronic version excludes material for which permission has not been granted by the rights holder
2019-12-03T00:00:00ZRubanu, Maria GraziaThis thesis is focused on the design and synthesis of analogues of thioesters of Co-enzyme A which are involved in many important biosynthetic pathways.
Acetyl-CoA is converted into citrate by citrate synthase in the first step of the Krebs cycle that is central for the cellular respiration.
Chapter 2 is focused on the successful synthesis of five analogues of acetyl-CoA and their investigation as inhibitors of citrate synthase. This project is based on the finding that Fluorovinyl thioether-CoA (FV-CoA) is a micromolar inhibitor of citrate synthase (Kᵢᵃᵖᵖ = 4.4 µM). Sulfoxide-CoA, with a sulfonyl and a methylene group replacing the carbonyl group and the sulfur atom of acetyl-CoA, was found to be a modest micromolar inhibitor of citrate synthase (11.1 µM), indicating its potential as hydrogen bonding acceptor. The remaining compounds showed poor or too low binding affinity for the enzyme. Although these compounds showed poor inhibitory capacity towards citrate synthase, they could be potential inhibitors of other acetyl-CoA utilizing enzymes, such as malate synthase that catalyzes the conversion of acetyl-CoA into malate. Its activity is correlated to different pathogens pathway (Mycobacterium tubercolosis) and its regulation could potentially prevent the bacterial growth.
Chapter 3 describes the attempted synthesis of a fluorovinyl thioacrylate derivative as malonyl-CoA analogue and potential covalent inhibitor of acetyl-CoA carboxylase (ACC). ACC catalyzes the irreversible conversion of acetyl-CoA into malonyl-CoA in the first step of fatty acid synthesis. The regulation of ACC is associated to many cardiovascular diseases such as diabetes, obesity and its inhibition can lead to the development of novel antibiotics for their treatment. Due to the challenging synthesis of the precursor thioester, this malonyl-CoA analogue could not be prepared.
Chapter 4 reports the synthesis of α,α,β-trifluoro cyclopropane-CoA and was found to be a poor inhibitor of citrate synthase (Kᵢ = 65.2 µM ). However, this compound has potential to be a covalent inhibitor of citrate synthase and other enzymes such as malate synthase, thus future investigations will be carried out to this purpose.
Furthermore, chapter 4 reports the attempted synthesis of an α,α-difluoroethyl thioether-CoA as an acetyl-CoA analogue. This compound bears two electronegative fluorine atoms, thus it could interact electrostatically with the active site residues of citrate synthase through hydrogen bonds, leading to its inhibition. Unfortunately, due to the instability of the difluoro moiety under the enzymatic reaction conditions, this was not converted to the corresponding acetyl-CoA analogue.Toxic gas adsorption and water stability in metal-organic frameworksMcHugh, Lauren Nicolehttps://hdl.handle.net/10023/188482021-11-18T03:02:53Z2019-12-03T00:00:00ZThis thesis largely focuses on the development of water stable metal-organic frameworks (MOFs) for the removal of toxic industrial chemicals (TICs) from airstreams. The aim of the research is to investigate the water stability and adsorptive properties of a series of copper MOFs for potential use inside a filter in future air purification systems.
Chapter 4 introduces a member of the STAM series of MOFs: STAM-17-OEt, which has formed the main focus of the project. STAM-17-OEt displays exceptional hydrolytic stability and ammonia adsorption properties that are in part explained by the new crumple zone mechanism shown by the material.
The other members of the STAM series of MOFs are presented in chapter 5, where the long-term water stability first seen in STAM-17-OEt is shown to be present for other members of the series. Ammonia adsorption testing provides promising results, with a clear linear adsorption trend visible across the series, and though the materials remove hydrogen cyanide from an airstream, testing does not show a clear trend.
Chapter 6 describes the synthesis of MOF-activated carbon composite materials, where selected STAM MOFs are grown inside BPL activated carbon at a series of loadings. The composites allow a typically powdered MOF sample to be manufactured into a form that may potentially be used inside a filter and by altering the loading of MOF within the composites, the materials may be tailored to remove a broader range of contaminants than the individual components alone.
Chapter 7 discusses the synthesis and characterisation of two new copper frameworks, where STAM-NMe2 is a member of the STAM series with a nitrogen-containing side chain and copper-1,3-bis(4-carboxyphenyl)-5-ethoxybenzene forms as a ‘layered coordination framework’ and is not related to the STAM series.
2019-12-03T00:00:00ZMcHugh, Lauren NicoleThis thesis largely focuses on the development of water stable metal-organic frameworks (MOFs) for the removal of toxic industrial chemicals (TICs) from airstreams. The aim of the research is to investigate the water stability and adsorptive properties of a series of copper MOFs for potential use inside a filter in future air purification systems.
Chapter 4 introduces a member of the STAM series of MOFs: STAM-17-OEt, which has formed the main focus of the project. STAM-17-OEt displays exceptional hydrolytic stability and ammonia adsorption properties that are in part explained by the new crumple zone mechanism shown by the material.
The other members of the STAM series of MOFs are presented in chapter 5, where the long-term water stability first seen in STAM-17-OEt is shown to be present for other members of the series. Ammonia adsorption testing provides promising results, with a clear linear adsorption trend visible across the series, and though the materials remove hydrogen cyanide from an airstream, testing does not show a clear trend.
Chapter 6 describes the synthesis of MOF-activated carbon composite materials, where selected STAM MOFs are grown inside BPL activated carbon at a series of loadings. The composites allow a typically powdered MOF sample to be manufactured into a form that may potentially be used inside a filter and by altering the loading of MOF within the composites, the materials may be tailored to remove a broader range of contaminants than the individual components alone.
Chapter 7 discusses the synthesis and characterisation of two new copper frameworks, where STAM-NMe2 is a member of the STAM series with a nitrogen-containing side chain and copper-1,3-bis(4-carboxyphenyl)-5-ethoxybenzene forms as a ‘layered coordination framework’ and is not related to the STAM series.Self-assembled monolayers of oligophenylene carboxylic acids on the underpotentially deposited silver(111) surfaceOrtiz De La Morena, Rodrigo M.https://hdl.handle.net/10023/187582021-03-10T12:31:37Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZOrtiz De La Morena, Rodrigo M.Title redactedChavez Cardenas, Hirepanhttps://hdl.handle.net/10023/187472021-03-05T16:42:22Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZChavez Cardenas, HirepanIndependent and combined Lewis acid-Lewis base catalysis with N-heterocyclic carbenes and rare-earth ionsKerr, Ryan William Frederickhttps://hdl.handle.net/10023/187412021-02-26T16:27:06Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZKerr, Ryan William FrederickStructural and chemical investigation of three biosynthetic enzymesGe, Yinghttps://hdl.handle.net/10023/187232021-02-19T16:58:23Z2019-06-26T00:00:00ZRibosomally synthesized and post-translationally modified peptides (RiPPs) are a
burgeoning family of natural products with desirable bioactivities. The cyanobactin
class of RiPPs have demonstrated anticancer, anti-microbial activities and more, and
have therefore attracted research attentions. Cyanobactins are synthesised as a precursor
peptide (PatE homologues) containing recognition sequences and core peptides (sequences
that become the final products), the latter of which undergo various modifications
including heterocyclization, prenylation, oxidation and macrocyclization. The posttranslational
modification enzymes (PTMEs) utilised to modify the cyanobactin precursor
have demonstrated magnificent versatilities that are potentially exploitable for the creation
of libraries of natural and unnatural compounds. The structure and function of each
of these enzymes are reviewed in Chapter 1, along with the current application of the
cyanobactin biosynthetic pathway.
Chapter 2 describes my work on creating and characterising modified heterocyclases.
The leader peptide was appended to heterocyclases that produce both thiazolines and
(methyl)oxazolines. The modified catalysts are not only capable of utilising leaderless
peptides, but also have higher yields than the native enzyme.
The next chapter investigates the reaction order of heterocyclase enzymes. The leader
peptide was found to be partially responsible for the reaction order. In Chapter 4 the same
investigation was applied to the oxidase, which aromatises and stabilises the heterocycles.
The oxidase reaction was determined to be independent of the leader.
Chapter 5 delves into the phosphate chemistry of the heterocyclase, which uses
ATP/Mg²⁺ via a kinase mechanism, but subsequently catalyses additional reactions that
yield AMP and PPᵢ.
Finally, Chapter 6 describes the structural characterisation of Psychrobacter arcticus
ATP phosphoribosyltransferase (ATPPRT), which is the first dedicated enzyme in
histidine biosynthesis, and provides a key regulatory point for this pathway.
2019-06-26T00:00:00ZGe, YingRibosomally synthesized and post-translationally modified peptides (RiPPs) are a
burgeoning family of natural products with desirable bioactivities. The cyanobactin
class of RiPPs have demonstrated anticancer, anti-microbial activities and more, and
have therefore attracted research attentions. Cyanobactins are synthesised as a precursor
peptide (PatE homologues) containing recognition sequences and core peptides (sequences
that become the final products), the latter of which undergo various modifications
including heterocyclization, prenylation, oxidation and macrocyclization. The posttranslational
modification enzymes (PTMEs) utilised to modify the cyanobactin precursor
have demonstrated magnificent versatilities that are potentially exploitable for the creation
of libraries of natural and unnatural compounds. The structure and function of each
of these enzymes are reviewed in Chapter 1, along with the current application of the
cyanobactin biosynthetic pathway.
Chapter 2 describes my work on creating and characterising modified heterocyclases.
The leader peptide was appended to heterocyclases that produce both thiazolines and
(methyl)oxazolines. The modified catalysts are not only capable of utilising leaderless
peptides, but also have higher yields than the native enzyme.
The next chapter investigates the reaction order of heterocyclase enzymes. The leader
peptide was found to be partially responsible for the reaction order. In Chapter 4 the same
investigation was applied to the oxidase, which aromatises and stabilises the heterocycles.
The oxidase reaction was determined to be independent of the leader.
Chapter 5 delves into the phosphate chemistry of the heterocyclase, which uses
ATP/Mg²⁺ via a kinase mechanism, but subsequently catalyses additional reactions that
yield AMP and PPᵢ.
Finally, Chapter 6 describes the structural characterisation of Psychrobacter arcticus
ATP phosphoribosyltransferase (ATPPRT), which is the first dedicated enzyme in
histidine biosynthesis, and provides a key regulatory point for this pathway.Application of isothioureas in enantioselective organocatalysis : heterocycle synthesis and kinetic resolutions in flowNeyya Ppadath, Rifahath Monhttps://hdl.handle.net/10023/187212021-02-19T16:43:39Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZNeyya Ppadath, Rifahath MonApplication of aryloxide-promoted catalyst turnover in enantioselective isothiourea catalysisArokianathar, Jude Nithelanhttps://hdl.handle.net/10023/187192021-04-06T15:18:26Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZArokianathar, Jude NithelanManganese catalysed hydrogenation of carbonyl compoundsWidegren, Magnus Benkthttps://hdl.handle.net/10023/187052022-09-13T11:25:56Z2019-12-03T00:00:00ZThe use of manganese catalysts represents a new area of research in the field of catalytic homogenous hydrogenation. This thesis covers the work on the synthesis and evaluation of manganese complexes in the hydrogenation of carbonyl groups.
A N^P^N type ligand was synthesised and coordinated to ruthenium (II) and manganese (I) sources and evaluated in carbonyl reduction using hydrogen gas. The catalysts were found to be less active when compared to state-of-the-art catalysts derived from ruthenium and manganese and tridentate ligands. Both catalysts were found to work well using wet ethanol.
Chapters 3-5 describe the development of new ligands derived from the PPFAPy (N-(2-methylpyridine)diphenylphosphinoferroceneamine) precursor and coordination of those ligands with manganese (I) and the evaluation of these catalysts in the hydrogenation of carbonyl compounds. The first catalyst was able to asymmetrically reduce ketones being the first reported manganese catalyst to do so using hydrogen as the reductant.
The discovery of using mild bases such as potassium carbonate in hydrogenation using these catalysts was used to successfully reduce enantiomerically pure esters with minimal loss of purity.
Kinetic experiments revealed the substrate to be 0th order and the catalyst 1st order in ketone hydrogenation indicating the hydrogen activation being the rate-determining step. In ester hydrogenation both the substrate and catalyst were found to be 1st order indicating that the rate-determining step was the ester reduction.
By variation of the substituents on the ligand phosphine the activity of the catalyst can be altered with electron-rich phosphines increasing and electron-poor phosphines decreasing the catalytic activity. An electron-donating group in the 4-position of the pyridine gave a further increase in the activity, whilst an electron-withdrawing group in the same position led to a lowering in activity. The best combination was found to be an electron-rich phosphine paired with an electron-rich pyridine. The active manganese catalyst was able to reduce acetophenone at a catalyst loading of 0.01 mol%. Minimal impact on enantioselectivity was found with the substitution on either the phosphine or pyridine. The solubility of the catalysts was significantly improved by the increased substitution of the ligands.
2019-12-03T00:00:00ZWidegren, Magnus BenktThe use of manganese catalysts represents a new area of research in the field of catalytic homogenous hydrogenation. This thesis covers the work on the synthesis and evaluation of manganese complexes in the hydrogenation of carbonyl groups.
A N^P^N type ligand was synthesised and coordinated to ruthenium (II) and manganese (I) sources and evaluated in carbonyl reduction using hydrogen gas. The catalysts were found to be less active when compared to state-of-the-art catalysts derived from ruthenium and manganese and tridentate ligands. Both catalysts were found to work well using wet ethanol.
Chapters 3-5 describe the development of new ligands derived from the PPFAPy (N-(2-methylpyridine)diphenylphosphinoferroceneamine) precursor and coordination of those ligands with manganese (I) and the evaluation of these catalysts in the hydrogenation of carbonyl compounds. The first catalyst was able to asymmetrically reduce ketones being the first reported manganese catalyst to do so using hydrogen as the reductant.
The discovery of using mild bases such as potassium carbonate in hydrogenation using these catalysts was used to successfully reduce enantiomerically pure esters with minimal loss of purity.
Kinetic experiments revealed the substrate to be 0th order and the catalyst 1st order in ketone hydrogenation indicating the hydrogen activation being the rate-determining step. In ester hydrogenation both the substrate and catalyst were found to be 1st order indicating that the rate-determining step was the ester reduction.
By variation of the substituents on the ligand phosphine the activity of the catalyst can be altered with electron-rich phosphines increasing and electron-poor phosphines decreasing the catalytic activity. An electron-donating group in the 4-position of the pyridine gave a further increase in the activity, whilst an electron-withdrawing group in the same position led to a lowering in activity. The best combination was found to be an electron-rich phosphine paired with an electron-rich pyridine. The active manganese catalyst was able to reduce acetophenone at a catalyst loading of 0.01 mol%. Minimal impact on enantioselectivity was found with the substitution on either the phosphine or pyridine. The solubility of the catalysts was significantly improved by the increased substitution of the ligands.Synthesis and testing of a natural product derived library against trypanosomatid parasitesCockram, Peterhttps://hdl.handle.net/10023/186732021-04-09T16:14:02Z2019-12-03T00:00:00ZNeglected tropical diseases caused by trypanosomatid parasites are a continuing and escalating problem, which devastate the less economically developed cultures in which they are endemic by impairing both human and animal health. Current drugs for these diseases are regarded as out-of-date, expensive, with unacceptable side-effects and mounting parasite resistance, meaning there is an urgent need for new therapeutics. In this work, we capitalise on the longstanding reputation of natural products as a resource of potent and structurally diverse bioactive molecules. We have explored four new, easily accessible drug scaffolds inspired by prevalent motifs from reported trypanocidal natural products, developing their chemical synthesis and investigating structure-activity relationships. All four scaffolds have produced promising lead compound structures through potency-based optimisation, which will benefit the development of new trypanocidal agents against T. brucei, T. cruzi and L. major. Many of the compounds give promising evidence for trypanosome-specific biological activity, and surpass external guidelines for the identification of novel lead structures. This work provides a solid platform for further development of the potency and selectivity of these trypanocidal core structures, as well as for the identification of their cellular targets. We have already begun work to identify the targets of a few select lead scaffolds, facilitated by biochemical assays, as well as metabolomic and proteomic analyses.
2019-12-03T00:00:00ZCockram, PeterNeglected tropical diseases caused by trypanosomatid parasites are a continuing and escalating problem, which devastate the less economically developed cultures in which they are endemic by impairing both human and animal health. Current drugs for these diseases are regarded as out-of-date, expensive, with unacceptable side-effects and mounting parasite resistance, meaning there is an urgent need for new therapeutics. In this work, we capitalise on the longstanding reputation of natural products as a resource of potent and structurally diverse bioactive molecules. We have explored four new, easily accessible drug scaffolds inspired by prevalent motifs from reported trypanocidal natural products, developing their chemical synthesis and investigating structure-activity relationships. All four scaffolds have produced promising lead compound structures through potency-based optimisation, which will benefit the development of new trypanocidal agents against T. brucei, T. cruzi and L. major. Many of the compounds give promising evidence for trypanosome-specific biological activity, and surpass external guidelines for the identification of novel lead structures. This work provides a solid platform for further development of the potency and selectivity of these trypanocidal core structures, as well as for the identification of their cellular targets. We have already begun work to identify the targets of a few select lead scaffolds, facilitated by biochemical assays, as well as metabolomic and proteomic analyses.Title redactedCartmell, Christopherhttps://hdl.handle.net/10023/186722021-04-09T16:44:44Z2019-12-03T00:00:00Z2019-12-03T00:00:00ZCartmell, Christopherα,β-Unsaturated acyl ammonium intermediates in
enantioselective organocatalysisMatviitsuk, Anastassiahttps://hdl.handle.net/10023/186672023-05-08T10:21:40Z2019-06-26T00:00:00ZThe research outlined in this thesis focuses on the study of the reactivity of α,β-unsaturated acyl
ammonium intermediates and their utility in the development of new enantioselective processes
exploiting isothiourea organocatalysts.
Chapter 2: A novel isothiourea-catalysed domino process has been developed demonstrating the
synthetic power of α,β-unsaturated acyl ammonium intermediates to generate a library of
complex heterocyclic compounds.
The use of these intermediates, generated in situ from trichlorophenol-activated ester and
HyperBTM, proved successful in the development of an asymmetric Michael-Michaellactonisation
reaction with 1,3-dicarbonyls. This method gives a quick and simple approach to a
wide range of highly functionalised lactones (20 examples) bearing three contiguous stereocentres
in moderate to good yields (46-79%). Excellent diastereo- and enantioselectivities (up to >95:5
dr, up to >99:1 er) were obtained due to the catalyst controlled nucleophilic addition. Resulting
indane derivatives represent potential biologically and pharmaceutically relevant molecules.
Chapter 3: The scope of the new domino reaction was extended employing benzazoles as an
alternative pro-nucleophile class. Utilising acyl benzothiazoles selective N-cyclisation was
observed through the operation of a domino Michael-lactamisation-Michael reaction, whilst the
use of acyl benzimidazoles gave an alternative domino reaction pathway and selective access to
quaternary stereocentres. The stereodivergence of these domino processes was studied by varying
the electronic properties of the benzothiazole nucleophiles. A broad scope of complex fused
polycycles (26 examples) was synthesised using this methodology with good to excellent yields
(up to 94%) and high levels of stereocontrol (up to >95:5 dr; up to 97:3 er).
Chapter 4: A new general concept for α-unsaturated acyl ammonium catalysis has been
developed which exploits 4-nitrophenoxide release from an α,β-unsaturated 4-nitrophenyl ester
substrate to facilitate catalyst turnover. This method was used for the enantioselective isothioureacatalysed
Michael addition of nitroalkanes to α,β-unsaturated 4-nitrophenyl esters (27 examples,
up to 79% yield, 99:1 er). The synthetic utility of this methodology was demonstrated through a
simple synthesis of highly enantioenriched pyrrolidinones. Mechanistic investigations including
kinetic analysis, catalyst labelling and crossover studies have delivered a fundamental
understanding of this process, with the application of a recently reported variable time
normalisation graphical analysis method used to allow the complex reaction kinetics to be probed. Chapter 5: Alternative catalyst turnover within α,β-unsaturated acyl ammonium catalysis was
further explored. A novel approach to highly enantioenriched y-nitro esters was developed, which
exploits the use of silyl nitronates to both undergo enantioselective Michael addition and facilitate
catalyst turnover, through a silyl migration/[3,3]-rearrangement pathway, unprecedented in
enantioselective catalysis. Application of silyl nitronates, as more active surrogates than their
parent nucleophiles nitroalkanes, allows their use as stoichiometric reagents with a wide range of
resulting y-nitro-substituted silyl esters (25 examples) obtained with good to excellent diastereoand
enantioselectivity (up to >95:5 dr, up to >99:1 er).
2019-06-26T00:00:00ZMatviitsuk, AnastassiaThe research outlined in this thesis focuses on the study of the reactivity of α,β-unsaturated acyl
ammonium intermediates and their utility in the development of new enantioselective processes
exploiting isothiourea organocatalysts.
Chapter 2: A novel isothiourea-catalysed domino process has been developed demonstrating the
synthetic power of α,β-unsaturated acyl ammonium intermediates to generate a library of
complex heterocyclic compounds.
The use of these intermediates, generated in situ from trichlorophenol-activated ester and
HyperBTM, proved successful in the development of an asymmetric Michael-Michaellactonisation
reaction with 1,3-dicarbonyls. This method gives a quick and simple approach to a
wide range of highly functionalised lactones (20 examples) bearing three contiguous stereocentres
in moderate to good yields (46-79%). Excellent diastereo- and enantioselectivities (up to >95:5
dr, up to >99:1 er) were obtained due to the catalyst controlled nucleophilic addition. Resulting
indane derivatives represent potential biologically and pharmaceutically relevant molecules.
Chapter 3: The scope of the new domino reaction was extended employing benzazoles as an
alternative pro-nucleophile class. Utilising acyl benzothiazoles selective N-cyclisation was
observed through the operation of a domino Michael-lactamisation-Michael reaction, whilst the
use of acyl benzimidazoles gave an alternative domino reaction pathway and selective access to
quaternary stereocentres. The stereodivergence of these domino processes was studied by varying
the electronic properties of the benzothiazole nucleophiles. A broad scope of complex fused
polycycles (26 examples) was synthesised using this methodology with good to excellent yields
(up to 94%) and high levels of stereocontrol (up to >95:5 dr; up to 97:3 er).
Chapter 4: A new general concept for α-unsaturated acyl ammonium catalysis has been
developed which exploits 4-nitrophenoxide release from an α,β-unsaturated 4-nitrophenyl ester
substrate to facilitate catalyst turnover. This method was used for the enantioselective isothioureacatalysed
Michael addition of nitroalkanes to α,β-unsaturated 4-nitrophenyl esters (27 examples,
up to 79% yield, 99:1 er). The synthetic utility of this methodology was demonstrated through a
simple synthesis of highly enantioenriched pyrrolidinones. Mechanistic investigations including
kinetic analysis, catalyst labelling and crossover studies have delivered a fundamental
understanding of this process, with the application of a recently reported variable time
normalisation graphical analysis method used to allow the complex reaction kinetics to be probed. Chapter 5: Alternative catalyst turnover within α,β-unsaturated acyl ammonium catalysis was
further explored. A novel approach to highly enantioenriched y-nitro esters was developed, which
exploits the use of silyl nitronates to both undergo enantioselective Michael addition and facilitate
catalyst turnover, through a silyl migration/[3,3]-rearrangement pathway, unprecedented in
enantioselective catalysis. Application of silyl nitronates, as more active surrogates than their
parent nucleophiles nitroalkanes, allows their use as stoichiometric reagents with a wide range of
resulting y-nitro-substituted silyl esters (25 examples) obtained with good to excellent diastereoand
enantioselectivity (up to >95:5 dr, up to >99:1 er).Title redactedLahive, Ciaran Williamhttps://hdl.handle.net/10023/186602019-10-14T16:19:43Z2018-06-27T00:00:00Z2018-06-27T00:00:00ZLahive, Ciaran WilliamTetra- and penta-vicinally fluorinated cyclohexane ring motifsBykova, Tetianahttps://hdl.handle.net/10023/186102019-11-27T15:11:38Z2019-06-26T00:00:00ZOrganofluorine compounds have had an important influence on the advances in the
healthcare and agricultural industries. Selective substitution with fluorine can produce a
significant impact on the pharmacokinetic properties of bioactive compounds; generally this
is through stereoelectronic effects that the fluorine atom can confer. As such, there is a
continuous interest in the development of novel organofluorine compounds and the
incorporation of fluorine into bioactive compounds and natural products.
The all-cis-1,2,4,5-tetrafluorocyclohexane motifs were the first examples of facially polarised
cyclohexane rings which possess a dipolar nature arising from two 1,3-diaxial C-F bonds. The
fluorine face, which possesses a negative electrostatic profile, along with the positively
polarized methylene hydrogens on the opposite face give a unique facial polarity to this
motif.
These highly polarized fluorinated ring systems present as novel building blocks for use in
drug development and agricultural programs; hence the aim of this study was the
development of functionalised derivatives of these all-cis tetrafluoro-cyclohexanes.
Transformations of previously reported phenyl all-cis-2, 3, 5, 6-tetrafluoro-cyclohexane were
explored in a variety of directions and new pathways towards partially fluorinated
cyclohexanes were investigated. The range of all-cis-tetrafluorocyclohexane motifs
produced, with functional groups attached directly to the fluorinated cyclohexane ring,
varied from methyl substituted all-cis-tetrafluorocyclohexane alcohols, aldehydes, nitriles
and amines to all-cis-tetrafluorocyclohexane amino acid, pentafluoro carboxylic acid and
alcohol derivatives.
These novel derivatives were then used in liquid-phase peptide synthesis, incorporated into
peptidomimetic systems through Ugi multi-component reactions and utilised in the
formation of bis-systems, in order to demonstrate their reactivity and to gain an insight into
their possible intramolecular conformational preferences and supramolecular
arrangements.
2019-06-26T00:00:00ZBykova, TetianaOrganofluorine compounds have had an important influence on the advances in the
healthcare and agricultural industries. Selective substitution with fluorine can produce a
significant impact on the pharmacokinetic properties of bioactive compounds; generally this
is through stereoelectronic effects that the fluorine atom can confer. As such, there is a
continuous interest in the development of novel organofluorine compounds and the
incorporation of fluorine into bioactive compounds and natural products.
The all-cis-1,2,4,5-tetrafluorocyclohexane motifs were the first examples of facially polarised
cyclohexane rings which possess a dipolar nature arising from two 1,3-diaxial C-F bonds. The
fluorine face, which possesses a negative electrostatic profile, along with the positively
polarized methylene hydrogens on the opposite face give a unique facial polarity to this
motif.
These highly polarized fluorinated ring systems present as novel building blocks for use in
drug development and agricultural programs; hence the aim of this study was the
development of functionalised derivatives of these all-cis tetrafluoro-cyclohexanes.
Transformations of previously reported phenyl all-cis-2, 3, 5, 6-tetrafluoro-cyclohexane were
explored in a variety of directions and new pathways towards partially fluorinated
cyclohexanes were investigated. The range of all-cis-tetrafluorocyclohexane motifs
produced, with functional groups attached directly to the fluorinated cyclohexane ring,
varied from methyl substituted all-cis-tetrafluorocyclohexane alcohols, aldehydes, nitriles
and amines to all-cis-tetrafluorocyclohexane amino acid, pentafluoro carboxylic acid and
alcohol derivatives.
These novel derivatives were then used in liquid-phase peptide synthesis, incorporated into
peptidomimetic systems through Ugi multi-component reactions and utilised in the
formation of bis-systems, in order to demonstrate their reactivity and to gain an insight into
their possible intramolecular conformational preferences and supramolecular
arrangements.Synthesis, structure and properties of carboxylate coordination polymersClulow, Rebeccahttps://hdl.handle.net/10023/185912021-08-07T02:07:52Z2019-12-03T00:00:00ZThe work in this thesis focuses on several coordination polymers, their crystal structures
and their potential applications as functional materials, in particular, their ferroelectric
and magnetic properties.
The mechanism of the known ferroelectric phase transition of (C₃NO₂H₇)₃CaCl₂ (TSCC)
was studied in detail using both X-ray and neutron diffraction data. The key structural
changes occurring in the vicinity of TC were identified in the Ca-O-C bond angles, which
change by up to 12˚. The structure of the compound was determined between 300 and
20 K to investigate potential phase transitions as suggested in the literature. The
diffraction data did not suggest an additional phase transition within this temperature
range. However, the detailed crystallographic studies did uncover new evidence of
ferrielectricity, which is consistent with electrical hysteresis data.
The origins of the ferroelectricity of TSCC were also probed through the synthesis and
characterisation of a range TSCC-related compounds which incorporated a range of
alternative halides and metal 2+ cations. Each compound formed coordination polymers
which were linked by sarcosine molecules, although the connectivity and structures
formed were dependent upon the composition. Whilst none of the TSCC derivatives had
ferroelectric properties, diffraction experiments were limited to a low temperature of
90 K and there could be additional phase transitions below this point.
A family of oxalate-based coordination polymers ALi₃M(C₂O₄)₃ with a perovskite-like
structures were also synthesised. The structural flexibility of these systems was
investigated through the incorporation of different A site cations and their magnetic
properties were investigated. Polyhedral distortions increase significantly upon the
inclusion of rubidium or caesium. Both KLi₃Co(C₂O₄)₃ and KLi₃Ni(C₂O₄)₃ have weak
antiferromagnetic exchange and μ[sub](eff) of 4.82 μ[sub]B and 3.62 μ[sub]B, respectively. The syntheses and structures of four new oxalate containing compounds, namely Rb₂Co(C₂O₄)₂.4H₂O,
Rb₂CoCl₂(C₂O₄), K₂Li₂Cu(C₂O₄)₃ and Li₄Co(C₂O₄)₃, which could have interesting magnetic
and electrochemical properties, are also reported.
2019-12-03T00:00:00ZClulow, RebeccaThe work in this thesis focuses on several coordination polymers, their crystal structures
and their potential applications as functional materials, in particular, their ferroelectric
and magnetic properties.
The mechanism of the known ferroelectric phase transition of (C₃NO₂H₇)₃CaCl₂ (TSCC)
was studied in detail using both X-ray and neutron diffraction data. The key structural
changes occurring in the vicinity of TC were identified in the Ca-O-C bond angles, which
change by up to 12˚. The structure of the compound was determined between 300 and
20 K to investigate potential phase transitions as suggested in the literature. The
diffraction data did not suggest an additional phase transition within this temperature
range. However, the detailed crystallographic studies did uncover new evidence of
ferrielectricity, which is consistent with electrical hysteresis data.
The origins of the ferroelectricity of TSCC were also probed through the synthesis and
characterisation of a range TSCC-related compounds which incorporated a range of
alternative halides and metal 2+ cations. Each compound formed coordination polymers
which were linked by sarcosine molecules, although the connectivity and structures
formed were dependent upon the composition. Whilst none of the TSCC derivatives had
ferroelectric properties, diffraction experiments were limited to a low temperature of
90 K and there could be additional phase transitions below this point.
A family of oxalate-based coordination polymers ALi₃M(C₂O₄)₃ with a perovskite-like
structures were also synthesised. The structural flexibility of these systems was
investigated through the incorporation of different A site cations and their magnetic
properties were investigated. Polyhedral distortions increase significantly upon the
inclusion of rubidium or caesium. Both KLi₃Co(C₂O₄)₃ and KLi₃Ni(C₂O₄)₃ have weak
antiferromagnetic exchange and μ[sub](eff) of 4.82 μ[sub]B and 3.62 μ[sub]B, respectively. The syntheses and structures of four new oxalate containing compounds, namely Rb₂Co(C₂O₄)₂.4H₂O,
Rb₂CoCl₂(C₂O₄), K₂Li₂Cu(C₂O₄)₃ and Li₄Co(C₂O₄)₃, which could have interesting magnetic
and electrochemical properties, are also reported.Biosynthesis and metabolism of selected organofluorine compoundsRodil García, Andreahttps://hdl.handle.net/10023/184852021-04-06T15:43:08Z2019-12-03T00:00:00ZThe St Andrews group has recently developed a range of novel fluorinated motifs, which include all-cis fluorocyclohexanes, difluoro oxy- and thio- ethers and α,β,β-trifluorocyclopropanes. Fluorinated motifs are often sought after in medicinal chemistry, and it became one of the aims of this thesis to explore these new motifs in order to assess their validity for drug discovery programmes.
The metabolic stability of each motif was probed in incubations with Cunninghamella elegans. This fungus is well known for its ability to biotransform xenobiotics mimicking the mammalian P₄₅₀ profile, and thus, providing a useful model for metabolic vulnerability. This showed that the all-cis cyclohexyl derivatives were increasingly stable to the action of P₄₅₀’s with increasing fluorine substitution. The α,α-difluoro thioethers showed oxidation to sulfoxides and sulfones, and the difluorooxy analogue showed a rapid biodegradation into the corresponding acetate ester. The studied α,β,β-trifluorocyclopropanes proved challenging to isolate and identify, but it could be established that the fluorinated motif remained intact after the incubations. The enantioselectivity with which C. elegans transforms the products was explored by chiral HPLC, which allowed an estimation of the enantiomeric resolution of racemates, and also the enantioselectivity of sulfoxide formation. In both cases selectivities were relatively low. Additionally, the lipophilicity of the fluorinated motifs was calculated by reverse-phase HPLC. A general trend was that increasing fluorination led to increased polarity.
A second aim was to explore the fluorometabolite biosynthesis in Streptomyces sp. MA37, isolated in Ghana (2014), which contains an active fluorinase. The metabolic pathway in Streptomyces sp. MA37 branches at 5-fluororibose phosphate (5-FDRP), allowing the formation of 5-fluoro-2,3,4-trihydroxypentanoic acid (5-FHPA) and other unknown metabolites. Each of the steps leading to 5-FHPA was studied, and the biotransformation was reconstituted in vitro.
The production of fluorometabolites by Streptomyces sp. MA37 was investigated by carrying out cell-free and whole cell feeding experiments with [5’,5’-²H₂]-5’-FDA. Incorporation into the fluorometabolites from [5’,5’-²H₂]-5’-FDA was successful.
2019-12-03T00:00:00ZRodil García, AndreaThe St Andrews group has recently developed a range of novel fluorinated motifs, which include all-cis fluorocyclohexanes, difluoro oxy- and thio- ethers and α,β,β-trifluorocyclopropanes. Fluorinated motifs are often sought after in medicinal chemistry, and it became one of the aims of this thesis to explore these new motifs in order to assess their validity for drug discovery programmes.
The metabolic stability of each motif was probed in incubations with Cunninghamella elegans. This fungus is well known for its ability to biotransform xenobiotics mimicking the mammalian P₄₅₀ profile, and thus, providing a useful model for metabolic vulnerability. This showed that the all-cis cyclohexyl derivatives were increasingly stable to the action of P₄₅₀’s with increasing fluorine substitution. The α,α-difluoro thioethers showed oxidation to sulfoxides and sulfones, and the difluorooxy analogue showed a rapid biodegradation into the corresponding acetate ester. The studied α,β,β-trifluorocyclopropanes proved challenging to isolate and identify, but it could be established that the fluorinated motif remained intact after the incubations. The enantioselectivity with which C. elegans transforms the products was explored by chiral HPLC, which allowed an estimation of the enantiomeric resolution of racemates, and also the enantioselectivity of sulfoxide formation. In both cases selectivities were relatively low. Additionally, the lipophilicity of the fluorinated motifs was calculated by reverse-phase HPLC. A general trend was that increasing fluorination led to increased polarity.
A second aim was to explore the fluorometabolite biosynthesis in Streptomyces sp. MA37, isolated in Ghana (2014), which contains an active fluorinase. The metabolic pathway in Streptomyces sp. MA37 branches at 5-fluororibose phosphate (5-FDRP), allowing the formation of 5-fluoro-2,3,4-trihydroxypentanoic acid (5-FHPA) and other unknown metabolites. Each of the steps leading to 5-FHPA was studied, and the biotransformation was reconstituted in vitro.
The production of fluorometabolites by Streptomyces sp. MA37 was investigated by carrying out cell-free and whole cell feeding experiments with [5’,5’-²H₂]-5’-FDA. Incorporation into the fluorometabolites from [5’,5’-²H₂]-5’-FDA was successful.Investigating the use of first-principles calculations for NMR studies of disorder in the solid stateMoran, Roberthttps://hdl.handle.net/10023/183742021-03-26T17:07:25Z2019-01-01T00:00:00ZIn this thesis, the use of first-principles calculations to assist solid-state
NMR spectroscopic studies of disordered inorganic materials has been
investigated, with emphasis placed on understanding the most relevant and
efficient methods for computationally modelling a system. The first class of
materials studied are oxide ceramics, more specifically Y₂SnₓTi₂₋ₓO₇,
La₂SnₓZr₂₋ₓO₇, Y₂Zr₂O₇ and Y₂Hf₂O₇; the first two of which are pyrochlore
solid solutions, while the latter adopt the disordered defect fluorite phase.
Both pyrochlore systems exhibit configurational disorder in the form of B-site
cation
mixing,
which
leads
to
the
overlapping
and
complex
experimental
solid-state
NMR
spectra
being
challenging
to
assign.
By
considering
several
methods to generate structural models computationally, the site occupancy
disorder (SOD) method was found to be particularly well suited to
producing a set of structural models capable of representing the
configurational disorder in these materials with the predicted
⁸⁹Y, ¹¹⁹Sn and ¹⁷O NMR parameters able to assist the assignment of the experimental NMR
spectra and provide significant structural insight. Investigation into Y₂Zr₂O₇
and Y₂Hf₂O₇ defect fluorites proved considerably more challenging, with the
high level of structural disorder preventing easy implementation of SOD-based approaches, and necessitating a less sophisticated and more manual
modelling approach being employed. Although some understanding of the
origin of the signals seen in the NMR spectra was able to be obtained in this
way, the limited scope of this computational investigation prevents a more
detailed and quantitative analysis.
The second class of materials investigated in this thesis are hydrous silicate
minerals found in the inner-Earth, specifically, hydrous Fe-free wadsleyite
(β-Mg₂SiO₄), a system that is challenging to study experimentally due to the
positional disorder of the incorporated protons (and of the charge-balancing
associated cation vacancies). In combination with experimental solid-state
NMR spectra and the first-principles calculation of NMR parameters, the ab
initio random structure searching (AIRSS) approach was used to probe the
structure of hydrous wadsleyite, by identifying many possible protonation arrangements for semi- and fully-hydrous wadsleyite. Through this
investigation, enthalpically stable protonation arrangements were identified
for both semi- and fully-hydrous wadsleyite, with predicted NMR
parameters for the AIRSS-generated structures used to assist assignment of
the solid-state NMR spectra of a sample of wadsleyite containing ~3 wt%
H₂O. By using the experimental NMR spectra to validate the accuracy and
relevance of AIRSS-generated structural models, a new structural picture of
the disorder in fully-hydrous wadsleyite was proposed, highlighting the
success with which first-principles calculations can be used to assist the
assignment of the solid-state NMR spectra of disordered inorganic materials.
2019-01-01T00:00:00ZMoran, RobertIn this thesis, the use of first-principles calculations to assist solid-state
NMR spectroscopic studies of disordered inorganic materials has been
investigated, with emphasis placed on understanding the most relevant and
efficient methods for computationally modelling a system. The first class of
materials studied are oxide ceramics, more specifically Y₂SnₓTi₂₋ₓO₇,
La₂SnₓZr₂₋ₓO₇, Y₂Zr₂O₇ and Y₂Hf₂O₇; the first two of which are pyrochlore
solid solutions, while the latter adopt the disordered defect fluorite phase.
Both pyrochlore systems exhibit configurational disorder in the form of B-site
cation
mixing,
which
leads
to
the
overlapping
and
complex
experimental
solid-state
NMR
spectra
being
challenging
to
assign.
By
considering
several
methods to generate structural models computationally, the site occupancy
disorder (SOD) method was found to be particularly well suited to
producing a set of structural models capable of representing the
configurational disorder in these materials with the predicted
⁸⁹Y, ¹¹⁹Sn and ¹⁷O NMR parameters able to assist the assignment of the experimental NMR
spectra and provide significant structural insight. Investigation into Y₂Zr₂O₇
and Y₂Hf₂O₇ defect fluorites proved considerably more challenging, with the
high level of structural disorder preventing easy implementation of SOD-based approaches, and necessitating a less sophisticated and more manual
modelling approach being employed. Although some understanding of the
origin of the signals seen in the NMR spectra was able to be obtained in this
way, the limited scope of this computational investigation prevents a more
detailed and quantitative analysis.
The second class of materials investigated in this thesis are hydrous silicate
minerals found in the inner-Earth, specifically, hydrous Fe-free wadsleyite
(β-Mg₂SiO₄), a system that is challenging to study experimentally due to the
positional disorder of the incorporated protons (and of the charge-balancing
associated cation vacancies). In combination with experimental solid-state
NMR spectra and the first-principles calculation of NMR parameters, the ab
initio random structure searching (AIRSS) approach was used to probe the
structure of hydrous wadsleyite, by identifying many possible protonation arrangements for semi- and fully-hydrous wadsleyite. Through this
investigation, enthalpically stable protonation arrangements were identified
for both semi- and fully-hydrous wadsleyite, with predicted NMR
parameters for the AIRSS-generated structures used to assist assignment of
the solid-state NMR spectra of a sample of wadsleyite containing ~3 wt%
H₂O. By using the experimental NMR spectra to validate the accuracy and
relevance of AIRSS-generated structural models, a new structural picture of
the disorder in fully-hydrous wadsleyite was proposed, highlighting the
success with which first-principles calculations can be used to assist the
assignment of the solid-state NMR spectra of disordered inorganic materials.Applications of EPR methodology towards understanding Cr/PNP based ethylene tetramerisationChabbra, Soniahttps://hdl.handle.net/10023/182702021-03-30T09:36:00Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZChabbra, SoniaTandem allylic amination and [2,3]-rearrangement for the synthesis of enantioenriched α-amino acid derivativesSpoehrle, Stéphanie S. M.https://hdl.handle.net/10023/179912019-08-16T09:14:16Z2018-07-01T00:00:00ZThis thesis details the development of tandem allylic amination and [2,3]-rearrangement methodologies for the synthesis of enantioenriched α-amino ester derivatives.
Chapter 1 aims to introduce [2,3]-sigmatropic rearrangements and give an overview of the relevant literature precedents in terms of catalytic stereoselective [2,3]-rearrangements of allylic ammonium ylides. The different types of tandem catalytic processes and some key examples are then discussed. Finally, the aims of this thesis are presented.
Chapter 2 details the development of a tandem palladium and isothiourea relay catalysis for the enantioselective [2,3]-rearrangement of allylic ammonium ylides. In this one-pot methodology, the intermediate ammonium salt is generated in situ via a palladium catalysed allylic amination. The subsequent enantioselective [2,3]-rearrangement is promoted by a chiral isothiourea catalyst to generate syn-α-amino ester derivatives in moderate to high yield (32-91%) and excellent stereocontrol (up to >95:5 dr and >99:1 er). The synthetic utility of the products is then demonstrated with a range of derivatisation reactions. Moreover, mechanistic experiments give insight into the mechanism of this palladium/isothiourea relay catalysis.
Chapter 3 focuses on the synthesis of enantioenriched pyrrolidines via a tandem palladium-catalysed allylic amination/[2,3]-rearrangement methodology. Starting from enantiopure proline-derivatives, pyrrolidines were obtained in good to excellent yield (61-94%) and diastereoselectivity (up to 91:9 dr) with moderate enantioenrichment (up to 80:20 er). This process relies on transfer of chirality from the starting material to the product.
Chapter 4 summarises the work described in this thesis and discusses potential future work within the area.
2018-07-01T00:00:00ZSpoehrle, Stéphanie S. M.This thesis details the development of tandem allylic amination and [2,3]-rearrangement methodologies for the synthesis of enantioenriched α-amino ester derivatives.
Chapter 1 aims to introduce [2,3]-sigmatropic rearrangements and give an overview of the relevant literature precedents in terms of catalytic stereoselective [2,3]-rearrangements of allylic ammonium ylides. The different types of tandem catalytic processes and some key examples are then discussed. Finally, the aims of this thesis are presented.
Chapter 2 details the development of a tandem palladium and isothiourea relay catalysis for the enantioselective [2,3]-rearrangement of allylic ammonium ylides. In this one-pot methodology, the intermediate ammonium salt is generated in situ via a palladium catalysed allylic amination. The subsequent enantioselective [2,3]-rearrangement is promoted by a chiral isothiourea catalyst to generate syn-α-amino ester derivatives in moderate to high yield (32-91%) and excellent stereocontrol (up to >95:5 dr and >99:1 er). The synthetic utility of the products is then demonstrated with a range of derivatisation reactions. Moreover, mechanistic experiments give insight into the mechanism of this palladium/isothiourea relay catalysis.
Chapter 3 focuses on the synthesis of enantioenriched pyrrolidines via a tandem palladium-catalysed allylic amination/[2,3]-rearrangement methodology. Starting from enantiopure proline-derivatives, pyrrolidines were obtained in good to excellent yield (61-94%) and diastereoselectivity (up to 91:9 dr) with moderate enantioenrichment (up to 80:20 er). This process relies on transfer of chirality from the starting material to the product.
Chapter 4 summarises the work described in this thesis and discusses potential future work within the area.Solid-phase synthesis of recyclable phosphorus donor ligands for the development of immobilized transition-metal catalyst librariesKonrath, Roberthttps://hdl.handle.net/10023/179662021-10-23T02:05:42Z2019-06-01T00:00:00ZPhosphorus-based ligands play a key role in a plethora of transition-metal catalyzed transformations. To date, only a few privileged ligand motifs have been developed for high performance application in a wide range of reactions. Despite the advances in rational design of highly selective phosphorus-based ligands in (asymmetric) homogeneous catalysis, synthetic approaches through trial-and-error remain the most common methodologies for the discovery of new powerful catalysts. High throughput experimentation has been embraced by both academia and industry to accelerate catalyst optimization requiring accesses to large and diverse ligand libraries. There is, however, still a lack of efficient combinatorial techniques enabling the synthesis and screening of vast phosphorus-based ligand libraries.
Solid-phase synthesis (SPS) offers an useful tool towards the parallel synthesis of large multidentate ligand libraries. While being covalently bound to an insoluble polymeric support, a stepwise preparation of modular ligands can be realized via systematic variation of various building blocks. Moreover, purification procedures can be greatly simplified when employing this SPS approach, often requiring only easy filtration steps. Another advantage offered by immobilization of homogeneous catalysts on insoluble supports is the facilitated catalyst recovery and recycling as catalyst separation remains one of the major problems in applied homogenous catalysis. Consequently, resin-bound catalysts represent promising candidates for application in continuously operated processes.
This thesis presents the efficient preparation of multidentate phosphorus ligand libraries using as solid-phase synthesis approach. Chapter 2 describes the modular access to a large and highly diverse supported phosphine-phosphite ligand library for application in asymmetric hydrogenation of enamides. The synthesis of a supported PNP pincer ligand library for application in ester reduction underlines the versatility of this SPS approach (chapter 3). Furthermore, the combinatorial ligand synthesis on a solid support has been successfully transferred to chiral PNP-type ligands (chapter 4). In chapter 5, a series of supported tripodal phosphorus ligand-based ruthenium complexes has been employed in nitrile hydrogenation providing tunable product selectivity by a simple change in the catalyst structure. Ultimately, the recovery and reusability of these heterogenized homogeneous catalysts has been investigated under batch and continuous flow conditions.
2019-06-01T00:00:00ZKonrath, RobertPhosphorus-based ligands play a key role in a plethora of transition-metal catalyzed transformations. To date, only a few privileged ligand motifs have been developed for high performance application in a wide range of reactions. Despite the advances in rational design of highly selective phosphorus-based ligands in (asymmetric) homogeneous catalysis, synthetic approaches through trial-and-error remain the most common methodologies for the discovery of new powerful catalysts. High throughput experimentation has been embraced by both academia and industry to accelerate catalyst optimization requiring accesses to large and diverse ligand libraries. There is, however, still a lack of efficient combinatorial techniques enabling the synthesis and screening of vast phosphorus-based ligand libraries.
Solid-phase synthesis (SPS) offers an useful tool towards the parallel synthesis of large multidentate ligand libraries. While being covalently bound to an insoluble polymeric support, a stepwise preparation of modular ligands can be realized via systematic variation of various building blocks. Moreover, purification procedures can be greatly simplified when employing this SPS approach, often requiring only easy filtration steps. Another advantage offered by immobilization of homogeneous catalysts on insoluble supports is the facilitated catalyst recovery and recycling as catalyst separation remains one of the major problems in applied homogenous catalysis. Consequently, resin-bound catalysts represent promising candidates for application in continuously operated processes.
This thesis presents the efficient preparation of multidentate phosphorus ligand libraries using as solid-phase synthesis approach. Chapter 2 describes the modular access to a large and highly diverse supported phosphine-phosphite ligand library for application in asymmetric hydrogenation of enamides. The synthesis of a supported PNP pincer ligand library for application in ester reduction underlines the versatility of this SPS approach (chapter 3). Furthermore, the combinatorial ligand synthesis on a solid support has been successfully transferred to chiral PNP-type ligands (chapter 4). In chapter 5, a series of supported tripodal phosphorus ligand-based ruthenium complexes has been employed in nitrile hydrogenation providing tunable product selectivity by a simple change in the catalyst structure. Ultimately, the recovery and reusability of these heterogenized homogeneous catalysts has been investigated under batch and continuous flow conditions.X-ray crystallographic analysis of ADORable zeolites and metal-organic frameworksHenkelis, Susan Elizabethhttps://hdl.handle.net/10023/179232021-03-02T09:51:29Z2019-06-26T00:00:00ZThis thesis largely focuses on the mechanistic analysis of the Assembly-Disassembly-
Organisation-Reassembly (ADOR) process through a range of crystallographic techniques
including powder X-ray diffraction and Pair Distribution Function (PDF) analysis and
subsequent analysis using solid-state kinetics.
Chapter 4 describes the development of a new standard protocol to using the ADOR
process. The protocol describes the development of a procedure used for identifying the
optimum conditions (time of reaction, temperature, acidity, etc.) for the ADOR process. In
developing the protocol, Ge-containing UTL zeolites were subjected to hydrolysis
conditions using both water and hydrochloric acid as media, which provides an
understanding of the effects of temperature and pH on the Disassembly (D) and
Organisation (O) steps of the process that define the potential products. Samples were
analysed by powder X-ray diffraction to yield a time course for the reaction at each set of
conditions.
Chapter 5 continues work on the ADOR process and presents the first kinetic study on the
two most prominent steps in the process; Disassembly and Organisation. By using solid-
state kinetic models, Avrami-Erofeev and its linear equivalent Sharp-Hancock, the
dependence on temperature and presence of liquid water was investigated and the activation
energy of the rearrangement process quantified. Work on the rearrangement step aimed to
understand where the silica species intercalates from and which material formed as the
kinetic and thermodynamic product from the reaction.
Chapter 6 describes a study into the Disassembly and Organisation steps of the ADOR
process through in situ Pair Distribution Function (PDF) analysis. This hopes to shed light
on the selectivity of the ADOR process in different media and the mechanism by which the
double-four-ring (d4r) breakdown.
On a different note, Chapter 7 describes the refinement of synthesis conditions used to
prepare poly-crystalline CPO-27-M (MOF-74) with lower concentrations of base and at low
temperature. Refinement of the synthesis of single crystal CPO-27-Mg, -Zn and UTSA-74
was undertaken and the necessary components to forming large single crystals understood.
2019-06-26T00:00:00ZHenkelis, Susan ElizabethThis thesis largely focuses on the mechanistic analysis of the Assembly-Disassembly-
Organisation-Reassembly (ADOR) process through a range of crystallographic techniques
including powder X-ray diffraction and Pair Distribution Function (PDF) analysis and
subsequent analysis using solid-state kinetics.
Chapter 4 describes the development of a new standard protocol to using the ADOR
process. The protocol describes the development of a procedure used for identifying the
optimum conditions (time of reaction, temperature, acidity, etc.) for the ADOR process. In
developing the protocol, Ge-containing UTL zeolites were subjected to hydrolysis
conditions using both water and hydrochloric acid as media, which provides an
understanding of the effects of temperature and pH on the Disassembly (D) and
Organisation (O) steps of the process that define the potential products. Samples were
analysed by powder X-ray diffraction to yield a time course for the reaction at each set of
conditions.
Chapter 5 continues work on the ADOR process and presents the first kinetic study on the
two most prominent steps in the process; Disassembly and Organisation. By using solid-
state kinetic models, Avrami-Erofeev and its linear equivalent Sharp-Hancock, the
dependence on temperature and presence of liquid water was investigated and the activation
energy of the rearrangement process quantified. Work on the rearrangement step aimed to
understand where the silica species intercalates from and which material formed as the
kinetic and thermodynamic product from the reaction.
Chapter 6 describes a study into the Disassembly and Organisation steps of the ADOR
process through in situ Pair Distribution Function (PDF) analysis. This hopes to shed light
on the selectivity of the ADOR process in different media and the mechanism by which the
double-four-ring (d4r) breakdown.
On a different note, Chapter 7 describes the refinement of synthesis conditions used to
prepare poly-crystalline CPO-27-M (MOF-74) with lower concentrations of base and at low
temperature. Refinement of the synthesis of single crystal CPO-27-Mg, -Zn and UTSA-74
was undertaken and the necessary components to forming large single crystals understood.Zeolite catalysts for nitric oxide productionRussell, Samanthahttps://hdl.handle.net/10023/179182021-02-17T15:51:22Z2019-06-26T00:00:00ZThis thesis considers the nitric oxide production from a range of zeolite catalysts with
either acid or copper active sites. The aim of the research was to find potential candidates
for stent coatings that could help to prevent stent thrombosis.
Acid site mordenite, ferrierite, SSZ-13 and ZSM-5 are studied in chapter 4 for the catalytic
conversion of sodium nitrite to nitric oxide. All zeolites successfully produced nitric oxide,
with ranging levels of conversion from 14 – 24 %. Recycled samples revealed the
consumption of the acid site, rendering the acid site zeolites non-catalytic.
Copper site zeolites were considered in chapters 5 and 6, with copper mordenite,
ferrierite, SSZ-13, ZSM-5 and UZM-4 being studied. All zeolites successfully converted
sodium nitrite to nitric oxide, with SSZ-13, ZSM-5 and UZM-4 producing around 100 %
conversion. The use of cysteine as a sacrificial reductant to activate the copper sites
allowed catalytic nitric oxide production. The promising catalytic tests led to further
studies of the materials, including copper leaching and toxicology.
Chapter 6 looked further into the catalytic copper zeolites with nitric oxide flow studies
and polymer incorporation. Flow studies showed sustained levels of nitric oxide
production. Incorporation of the zeolite powders into the polymer of intrinsic
microporosity, EATB(Me), showed good nitric oxide production from the initial studies.
Recycled samples, however, showed a drop in production.
Lastly, chapter 7 explored the use of the ADOR (Assembly-Disassembly-Organisation-
Reassembly) process to generate a series of zeolites for catalysis. Aluminium was
incorporated into zeolites IPC-2, 4 and 6 through the organisation step to create
aluminated zeolites. The aforementioned zeolites, as well as Al-UTL, were assessed for
nitric oxide production with acid active sites. The results showed an interesting relation
between ring size and nitric oxide production, with the largest rings of Al-UTL having the
highest production and the smallest rings of Al-IPC-4 having the lowest.
2019-06-26T00:00:00ZRussell, SamanthaThis thesis considers the nitric oxide production from a range of zeolite catalysts with
either acid or copper active sites. The aim of the research was to find potential candidates
for stent coatings that could help to prevent stent thrombosis.
Acid site mordenite, ferrierite, SSZ-13 and ZSM-5 are studied in chapter 4 for the catalytic
conversion of sodium nitrite to nitric oxide. All zeolites successfully produced nitric oxide,
with ranging levels of conversion from 14 – 24 %. Recycled samples revealed the
consumption of the acid site, rendering the acid site zeolites non-catalytic.
Copper site zeolites were considered in chapters 5 and 6, with copper mordenite,
ferrierite, SSZ-13, ZSM-5 and UZM-4 being studied. All zeolites successfully converted
sodium nitrite to nitric oxide, with SSZ-13, ZSM-5 and UZM-4 producing around 100 %
conversion. The use of cysteine as a sacrificial reductant to activate the copper sites
allowed catalytic nitric oxide production. The promising catalytic tests led to further
studies of the materials, including copper leaching and toxicology.
Chapter 6 looked further into the catalytic copper zeolites with nitric oxide flow studies
and polymer incorporation. Flow studies showed sustained levels of nitric oxide
production. Incorporation of the zeolite powders into the polymer of intrinsic
microporosity, EATB(Me), showed good nitric oxide production from the initial studies.
Recycled samples, however, showed a drop in production.
Lastly, chapter 7 explored the use of the ADOR (Assembly-Disassembly-Organisation-
Reassembly) process to generate a series of zeolites for catalysis. Aluminium was
incorporated into zeolites IPC-2, 4 and 6 through the organisation step to create
aluminated zeolites. The aforementioned zeolites, as well as Al-UTL, were assessed for
nitric oxide production with acid active sites. The results showed an interesting relation
between ring size and nitric oxide production, with the largest rings of Al-UTL having the
highest production and the smallest rings of Al-IPC-4 having the lowest.Design and synthesis of novel natural product inspired trypanosomatid inhibitorsZacharova, Marija Ksenijahttps://hdl.handle.net/10023/178962022-08-22T11:29:07Z2019-06-26T00:00:00ZChamuvarinin is a natural product known to have low micromolar activity against Trypanosoma
brucei, causative agent of Human African Trypanosomiasis (HAT). Having completed the total
synthesis of chamuvarinin in 2010, the Florence group started a phenotypic screening-based drug
discovery campaign to identify simplified analogues of chamuvarinin with trypanocidal activity. The
ideal lead compounds sought after need to have retained or improved activity in Trypanosoma
brucei compared to chamuvarinin, as well as being >10 times more potent in parasitic cells than in
mammalian cells. An additional desirable property is broad range activity across a panel of
trypanosomes - Trypanosoma brucei, Trypanosoma cruzi and Leishmania major.
The work described in this thesis is a contribution towards this campaign, looking to expand the
chemical space occupied by the inhibitors synthesised in the group. Two series of inhibitors were
designed and synthesised, one based on THP-furan-THP scaffold and another on the previously
established biphenyl motif-containing lead. The design of inhibitors was partially informed by in
silico studies of the target protein identified in the group using proteomics experiments. This thesis
details the synthesis of the inhibitors and discusses their biological profiles and how the findings can
inform future directions the drug discovery campaign can undertake.
2019-06-26T00:00:00ZZacharova, Marija KsenijaChamuvarinin is a natural product known to have low micromolar activity against Trypanosoma
brucei, causative agent of Human African Trypanosomiasis (HAT). Having completed the total
synthesis of chamuvarinin in 2010, the Florence group started a phenotypic screening-based drug
discovery campaign to identify simplified analogues of chamuvarinin with trypanocidal activity. The
ideal lead compounds sought after need to have retained or improved activity in Trypanosoma
brucei compared to chamuvarinin, as well as being >10 times more potent in parasitic cells than in
mammalian cells. An additional desirable property is broad range activity across a panel of
trypanosomes - Trypanosoma brucei, Trypanosoma cruzi and Leishmania major.
The work described in this thesis is a contribution towards this campaign, looking to expand the
chemical space occupied by the inhibitors synthesised in the group. Two series of inhibitors were
designed and synthesised, one based on THP-furan-THP scaffold and another on the previously
established biphenyl motif-containing lead. The design of inhibitors was partially informed by in
silico studies of the target protein identified in the group using proteomics experiments. This thesis
details the synthesis of the inhibitors and discusses their biological profiles and how the findings can
inform future directions the drug discovery campaign can undertake.Thionylimide and related systemsMcGeachie, Liam John Roberthttps://hdl.handle.net/10023/178722021-02-24T17:33:25Z2019-06-26T00:00:00ZWhile the synthesis of organic thionylimino (NSO) compounds has been known for over 140 years the
synthesis of inorganic species was much less known and only really begun in the 1970s. The previous
syntheses for these inorganic species were often complicated and involved highly reactive species.
The goal of this work was to simplify the synthesis of transition metal complexes and main group
compounds containing the thionylimide anion.
An existing literature synthesis was improved and developed in to a new method using a solution of
thionyl chloride in tetrahydrofuran and liquid ammonia. This led to significant yield increases over
previous syntheses and in a much more efficient “one-pot” reaction. The scope of the reaction was
investigated and complexes and compounds containing titanium, zirconium, hafnium, platinum,
copper, zinc and antimony were synthesised. The first examples of antimony(V) and copper
thionylimino compounds and complexes were prepared. The series of group IV metal complexes
Cp₂Ti(NSO)₂, Cp*₂M(NSO)₂ (M = Ti, Zr and Hf) was synthesised. Cp*₂M(NSO)₂ (M = Ti and Hf) are novel
complexes. These complexes along with the other thionylimino compounds and complexes formed
the basis of an examination of the bonding properties of the thionylimino group in inorganic
compounds.
The reactivity of these species was examined and led to the isolation of a transition metal complex of
the [N(SO₃)₂]³⁻ anion in the complex (2,2’- bipyridyl)₃Cu₂Cl(N(SO₃)₂). This was the first transition metal
complex of this anion to be examined by single crystal X-ray crystallography.
The reactivity of Cp₂Ti(NSO)₂ under various conditions was examined. It was discovered that
Cp₂Ti(NSO)₂ could act as a metalloligand which contains bridging thionylimino groups. These species
were shown to bridge via the nitrogen atom of the thionylimino groups. A series of metal complexes
containing; copper, molybdenum, cobalt, mercury, and silver were synthesised. The electrochemistry
of Cp₂Ti(NSO)₂, the neutral copper complexes and the molybdenum complex was examined in detail.
The synthesis of various five-membered sulfur-nitrogen rings containing phosphorus, antimony,
titanium and selenium was attempted. The synthesis of the five-membered selenium nitrogen species
nBu₂SnSe₂N₂ was also attempted and gave promising preliminary results.
2019-06-26T00:00:00ZMcGeachie, Liam John RobertWhile the synthesis of organic thionylimino (NSO) compounds has been known for over 140 years the
synthesis of inorganic species was much less known and only really begun in the 1970s. The previous
syntheses for these inorganic species were often complicated and involved highly reactive species.
The goal of this work was to simplify the synthesis of transition metal complexes and main group
compounds containing the thionylimide anion.
An existing literature synthesis was improved and developed in to a new method using a solution of
thionyl chloride in tetrahydrofuran and liquid ammonia. This led to significant yield increases over
previous syntheses and in a much more efficient “one-pot” reaction. The scope of the reaction was
investigated and complexes and compounds containing titanium, zirconium, hafnium, platinum,
copper, zinc and antimony were synthesised. The first examples of antimony(V) and copper
thionylimino compounds and complexes were prepared. The series of group IV metal complexes
Cp₂Ti(NSO)₂, Cp*₂M(NSO)₂ (M = Ti, Zr and Hf) was synthesised. Cp*₂M(NSO)₂ (M = Ti and Hf) are novel
complexes. These complexes along with the other thionylimino compounds and complexes formed
the basis of an examination of the bonding properties of the thionylimino group in inorganic
compounds.
The reactivity of these species was examined and led to the isolation of a transition metal complex of
the [N(SO₃)₂]³⁻ anion in the complex (2,2’- bipyridyl)₃Cu₂Cl(N(SO₃)₂). This was the first transition metal
complex of this anion to be examined by single crystal X-ray crystallography.
The reactivity of Cp₂Ti(NSO)₂ under various conditions was examined. It was discovered that
Cp₂Ti(NSO)₂ could act as a metalloligand which contains bridging thionylimino groups. These species
were shown to bridge via the nitrogen atom of the thionylimino groups. A series of metal complexes
containing; copper, molybdenum, cobalt, mercury, and silver were synthesised. The electrochemistry
of Cp₂Ti(NSO)₂, the neutral copper complexes and the molybdenum complex was examined in detail.
The synthesis of various five-membered sulfur-nitrogen rings containing phosphorus, antimony,
titanium and selenium was attempted. The synthesis of the five-membered selenium nitrogen species
nBu₂SnSe₂N₂ was also attempted and gave promising preliminary results.Title redactedR R, Ram Prasadhttps://hdl.handle.net/10023/178702021-03-11T11:04:18Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZR R, Ram PrasadInvestigation of fluorite and perovskite materials for energy applicationsAbdoun, Amanehttps://hdl.handle.net/10023/178572021-03-24T12:50:09Z2019-06-26T00:00:00ZReducing the carbon footprint of the actual energy supply system is of vital importance so as to address the issue of climate change. Thus, the development of energy conversion & storage technologies, tackling the electricity’s intermittency of the renewables source technologies, is of great interest. Solid oxide fuel cells (SOFCs) possess valuable advantages compared to the other energy storage & conversion devices, such as its long-term durability, high values of conductivities or its utilization with various types of gases. However, issues still exist on the hydrogen electrode. Therefore, the development of alternative hydrogen electrodes represents a challenge as it needs to meet several requirements, such as good ionic and electronic conductivities, redox stability or being single-phase.
Copper doped ceria (CCO) is considered as a promising candidate. This work focused on solving some issues inherent to this material. The challenge of synthesizing a single-phase solid-solution of CCO has been resolved and synthesis’ parameters influences were investigated. Cu solubility has been determined and equals to 10%[sub]mol for the solid-solutions. The absence of consensus concerning the oxidation states of the cations has also been inquired. In both surface and bulk, Cu +2 is declared as the main oxidation state of Cu. However, the presence of Cu +1 is assured. This confirms the significant concentration of Ce +3 detected in CCO, counter-balancing the charge imbalance due to the creation of oxygen vacancies. In addition to the obtaining of the phase diagram of copper doped ceria, preliminary results on the application of exsolution of nanoparticles on CCO fluorites were obtained and Cu enriched nanoparticles were generated on the surface.
Ru-doped strontium yttrium titanate (SYTRu) was also investigated as alternative anode material. In this work, the main issue of this material refers to the incorporation of Ru into the perovskite lattice. Evidences concerning the real substitution of Ti by Ru were obtained by X-ray absorption spectroscopy (XAS). Furthermore, reduced samples showed Ru nanoparticles on their surface.
2019-06-26T00:00:00ZAbdoun, AmaneReducing the carbon footprint of the actual energy supply system is of vital importance so as to address the issue of climate change. Thus, the development of energy conversion & storage technologies, tackling the electricity’s intermittency of the renewables source technologies, is of great interest. Solid oxide fuel cells (SOFCs) possess valuable advantages compared to the other energy storage & conversion devices, such as its long-term durability, high values of conductivities or its utilization with various types of gases. However, issues still exist on the hydrogen electrode. Therefore, the development of alternative hydrogen electrodes represents a challenge as it needs to meet several requirements, such as good ionic and electronic conductivities, redox stability or being single-phase.
Copper doped ceria (CCO) is considered as a promising candidate. This work focused on solving some issues inherent to this material. The challenge of synthesizing a single-phase solid-solution of CCO has been resolved and synthesis’ parameters influences were investigated. Cu solubility has been determined and equals to 10%[sub]mol for the solid-solutions. The absence of consensus concerning the oxidation states of the cations has also been inquired. In both surface and bulk, Cu +2 is declared as the main oxidation state of Cu. However, the presence of Cu +1 is assured. This confirms the significant concentration of Ce +3 detected in CCO, counter-balancing the charge imbalance due to the creation of oxygen vacancies. In addition to the obtaining of the phase diagram of copper doped ceria, preliminary results on the application of exsolution of nanoparticles on CCO fluorites were obtained and Cu enriched nanoparticles were generated on the surface.
Ru-doped strontium yttrium titanate (SYTRu) was also investigated as alternative anode material. In this work, the main issue of this material refers to the incorporation of Ru into the perovskite lattice. Evidences concerning the real substitution of Ti by Ru were obtained by X-ray absorption spectroscopy (XAS). Furthermore, reduced samples showed Ru nanoparticles on their surface.Nucleophilic heterocyclic carbene catalysis : generation of azolium enolates for novel enantioselective inter- and intramolecular formal [4+2] cycloadditionsAttaba, Nassiliahttps://hdl.handle.net/10023/177802023-04-05T02:05:40Z2019-06-26T00:00:00ZN-Heterocyclic carbene (NHC)-catalysed processes that utilise azolium enolates
intermediates have been used for a broad range of transformations such as enantioselective
cycloaddition, protonation, halogenation, Mannich reactions and desymmetrisation
processes. One efficient way to quickly build molecular complexity is through
cycloadditions such as formal [4+2] cycloadditions. In this context, ketenes, aldehydes,
esters, enals and α-halo aldehydes have been used in numerous reactions for the construction
of 6-membered rings. Nevertheless, the current limitations include lack of stability from the
precursors and unwanted side-reactions. To broaden the synthetic utility of azolium enolates,
alternative precursors are necessary This has been addressed in this thesis in novel inter- and
intramolecular formal [4+2] cycloadditions using α-aroyloxyaldehydes and enone-acids as
bench-stable azolium enolate precursors.
An intermolecular NHC-catalysed [4+2]-hetero-Diels-Alder process using
α-aroyloxyaldehydes as azolium enolate precursors and trichloromethyl ketone Michael
acceptors was first explored. This methodology led to the formation of syndihydropyranones
in up to 95% yield, >95:5 dr and >99:1 er. A sequential [4+2]
cycloaddition/nucleophilic ring-opening with amines or alcohols led to the selective
synthesis of either highly functionalised diamides or γ-ester amide derivatives in up to 90%
with excellent diastereo- and enantioselectivity. This highlighted the ability of
trichloromethyl ketones to act as amide surrogates.
An investigation of using carboxylic acids bearing a pendant enone, referred as enone-acid,
led to the first NHC-catalysed formal [4+2] cycloaddition protocol. A range of
dihydrobenzofurans were accessed in moderate to high yield, and high to excellent diastereoand
enantioselectivity. This novel methodology could be extended to the synthesis of syndihydropyranone
and syn-dihydrochromenone derivatives in moderate to high yield and
excellent diastereo- and enantioselectivity.
2019-06-26T00:00:00ZAttaba, NassiliaN-Heterocyclic carbene (NHC)-catalysed processes that utilise azolium enolates
intermediates have been used for a broad range of transformations such as enantioselective
cycloaddition, protonation, halogenation, Mannich reactions and desymmetrisation
processes. One efficient way to quickly build molecular complexity is through
cycloadditions such as formal [4+2] cycloadditions. In this context, ketenes, aldehydes,
esters, enals and α-halo aldehydes have been used in numerous reactions for the construction
of 6-membered rings. Nevertheless, the current limitations include lack of stability from the
precursors and unwanted side-reactions. To broaden the synthetic utility of azolium enolates,
alternative precursors are necessary This has been addressed in this thesis in novel inter- and
intramolecular formal [4+2] cycloadditions using α-aroyloxyaldehydes and enone-acids as
bench-stable azolium enolate precursors.
An intermolecular NHC-catalysed [4+2]-hetero-Diels-Alder process using
α-aroyloxyaldehydes as azolium enolate precursors and trichloromethyl ketone Michael
acceptors was first explored. This methodology led to the formation of syndihydropyranones
in up to 95% yield, >95:5 dr and >99:1 er. A sequential [4+2]
cycloaddition/nucleophilic ring-opening with amines or alcohols led to the selective
synthesis of either highly functionalised diamides or γ-ester amide derivatives in up to 90%
with excellent diastereo- and enantioselectivity. This highlighted the ability of
trichloromethyl ketones to act as amide surrogates.
An investigation of using carboxylic acids bearing a pendant enone, referred as enone-acid,
led to the first NHC-catalysed formal [4+2] cycloaddition protocol. A range of
dihydrobenzofurans were accessed in moderate to high yield, and high to excellent diastereoand
enantioselectivity. This novel methodology could be extended to the synthesis of syndihydropyranone
and syn-dihydrochromenone derivatives in moderate to high yield and
excellent diastereo- and enantioselectivity.The effect of changing crystal structures on the magnetic and superconducting properties of the iron based superconductors and their parent compoundsTrainer, Christopher William Jameshttps://hdl.handle.net/10023/177552019-07-17T13:19:18Z2018-09-01T00:00:00ZSuperconductivity in high temperature superconducting materials arises due to the constituent electrons becoming strongly correlated. In particular, in the Iron based family of superconductors, antiferromagnetic fluctuations of the electron spins and charge fluctuations of the Iron d-orbitals are thought to be important. The strong correlations of the electrons in an Iron based superconductor lead to the electronic ground state adopting a lower symmetry than the crystal lattice. Transport studies of these systems under the application of uniaxial strain show a strongly anisotropic response of the materials to straining along different lattice directions, suggesting that the electronic correlations are in fact coupled to the lattice. In this thesis I present a study of the response of the magnetic and superconducting states of these Iron based materials to changes of their crystal structure induced by applying uniaxial strain or through doping. I first examine the response of the magnetism in Fe₁₊ₓTe, the parent compound of the Iron chalcogenides, to the change that occurs in the crystal structure as the system is doped with Iron. I present a spin polarized STM study of the magnetism throughout the phase diagram of Fe₁₊ₓTe using in-situ prepared magnetic tips to measure the spin structure. By using the STM tip to remove excess Iron atoms from the surface I show that it is possible to decouple the effects of the excess Iron atoms from the change of crystal structure. Therefore showing the effect of the structural change on the magnetism. Next I present an STM study of how the superconductivity in the tetragonal LiFeAs system responds to the application of uniaxial strain deforming the crystal structure. I describe the construction of a modifed STM sample holder that allows for the in-situ application of a variable Strain to the LiFeAs sample. I present the resulting impact of this straining process to the superconductivity of LiFeAs on an atomic scale and report the formation of a strain induced charge density wave state that coexists with the superconductivity. In the final chapter I report a quasiparticle interference study of the superconducting state of Sulphur doped FeSe and discuss the results in comparison of those from the literature for the undoped FeSe system.
2018-09-01T00:00:00ZTrainer, Christopher William JamesSuperconductivity in high temperature superconducting materials arises due to the constituent electrons becoming strongly correlated. In particular, in the Iron based family of superconductors, antiferromagnetic fluctuations of the electron spins and charge fluctuations of the Iron d-orbitals are thought to be important. The strong correlations of the electrons in an Iron based superconductor lead to the electronic ground state adopting a lower symmetry than the crystal lattice. Transport studies of these systems under the application of uniaxial strain show a strongly anisotropic response of the materials to straining along different lattice directions, suggesting that the electronic correlations are in fact coupled to the lattice. In this thesis I present a study of the response of the magnetic and superconducting states of these Iron based materials to changes of their crystal structure induced by applying uniaxial strain or through doping. I first examine the response of the magnetism in Fe₁₊ₓTe, the parent compound of the Iron chalcogenides, to the change that occurs in the crystal structure as the system is doped with Iron. I present a spin polarized STM study of the magnetism throughout the phase diagram of Fe₁₊ₓTe using in-situ prepared magnetic tips to measure the spin structure. By using the STM tip to remove excess Iron atoms from the surface I show that it is possible to decouple the effects of the excess Iron atoms from the change of crystal structure. Therefore showing the effect of the structural change on the magnetism. Next I present an STM study of how the superconductivity in the tetragonal LiFeAs system responds to the application of uniaxial strain deforming the crystal structure. I describe the construction of a modifed STM sample holder that allows for the in-situ application of a variable Strain to the LiFeAs sample. I present the resulting impact of this straining process to the superconductivity of LiFeAs on an atomic scale and report the formation of a strain induced charge density wave state that coexists with the superconductivity. In the final chapter I report a quasiparticle interference study of the superconducting state of Sulphur doped FeSe and discuss the results in comparison of those from the literature for the undoped FeSe system.Design and synthesis of novel zeotypesWatts, Abigail Elisehttps://hdl.handle.net/10023/176312021-03-04T16:36:11Z2019-04-01T00:00:00Z2019-04-01T00:00:00ZWatts, Abigail EliseTitle redactedBoubalouta, Youcefhttps://hdl.handle.net/10023/175142019-04-12T13:26:20Z2016-06-22T00:00:00Z2016-06-22T00:00:00ZBoubalouta, YoucefOptimization of spray pyrolysis for cathode-supported solid oxide fuel cellsTsimekas, Georgioshttps://hdl.handle.net/10023/173852022-04-09T02:07:24Z2019-06-26T00:00:00ZCathode-supported solid oxide fuel cells (SOFCs) have been the most reliable devices for direct conversion of fuels in electrical power. However, processing at high temperatures to obtain a gas-tight electrolyte is prohibited due to formation of interfacial secondary phases between the electrolyte and the cathode support. Various deposition techniques such as electrochemical vapor deposition have been successfully employed to deposit thin electrolytes, but with a high cost. Therefore, a fabrication method that can meet the requirements of an industrial application at lower cost is the key for commercialization of this type of SOFCs.
The aim of this study was to optimize air-pressurized spray pyrolysis technique for preparation of ultra-thin and dense electrolytes at low temperatures, for cathode-supported SOFCs. This process is cost-effective and easy scalable, suitable for deposition of thin films over large areas.
Cathode-supported SOFCs were developed with thin 3.5-5.5μm yttria-stabilized zirconia (YSZ) electrolytes of columnar structure, at deposition temperatures as low as 170°C and deposition rates ≥10 μm h⁻¹. The surface of the composite LSM-YSZ cathode support was modified by spraying a LSM interlayer to reduce the roughness of the substrate and thus, secure a uniform thickness of the post-deposited electrolyte layer. To complete the cell with an anode electrode, cobalt ceria Co-CeO₂ with mixed ionic-electronic conductivity (MIEC) was also deposited by spray pyrolysis. Optimization of spray pyrolysis process parameters revealed the precursor concentration in conjunction with deposition time as the most important parameters to shift the morphology of the film from dense to porous depended on the target film structure. Sintering, from 750°C up to 950°C, proved to suppress the formation of zirconate phases at the interface of the YSZ/LSM that would severely degrade the performance of the cell.
The cathode-supported SOFCs were electrochemically tested using 5%H₂/Ar as fuel and air as oxidant within a temperature range of 700-850°C. The measured open circuit voltage values were close to the theoretical ones with a maximum of 1.002 V at 850°C, indicating a gas-tight electrolyte. A power density of 127 mW/cm² at 850°C for a cathode-supported SOFC with a 3.5 μm thick YSZ electrolyte, was achieved. The activation energy of the whole cell was 0.15 eV corroborating the actual ohmic resistance values correspond to the cathode support which is the limiting factor of the cell's performance. Long-term stability test of five days showed a performance degradation to 83 mW/cm² at 850°C due to particle agglomeration of the cobalt metal in the anode electrode and reduction of the catalytic active area. The above indicate spray pyrolysis is an established technique for preparation of thin films for use in cathode-supported SOFCs.
2019-06-26T00:00:00ZTsimekas, GeorgiosCathode-supported solid oxide fuel cells (SOFCs) have been the most reliable devices for direct conversion of fuels in electrical power. However, processing at high temperatures to obtain a gas-tight electrolyte is prohibited due to formation of interfacial secondary phases between the electrolyte and the cathode support. Various deposition techniques such as electrochemical vapor deposition have been successfully employed to deposit thin electrolytes, but with a high cost. Therefore, a fabrication method that can meet the requirements of an industrial application at lower cost is the key for commercialization of this type of SOFCs.
The aim of this study was to optimize air-pressurized spray pyrolysis technique for preparation of ultra-thin and dense electrolytes at low temperatures, for cathode-supported SOFCs. This process is cost-effective and easy scalable, suitable for deposition of thin films over large areas.
Cathode-supported SOFCs were developed with thin 3.5-5.5μm yttria-stabilized zirconia (YSZ) electrolytes of columnar structure, at deposition temperatures as low as 170°C and deposition rates ≥10 μm h⁻¹. The surface of the composite LSM-YSZ cathode support was modified by spraying a LSM interlayer to reduce the roughness of the substrate and thus, secure a uniform thickness of the post-deposited electrolyte layer. To complete the cell with an anode electrode, cobalt ceria Co-CeO₂ with mixed ionic-electronic conductivity (MIEC) was also deposited by spray pyrolysis. Optimization of spray pyrolysis process parameters revealed the precursor concentration in conjunction with deposition time as the most important parameters to shift the morphology of the film from dense to porous depended on the target film structure. Sintering, from 750°C up to 950°C, proved to suppress the formation of zirconate phases at the interface of the YSZ/LSM that would severely degrade the performance of the cell.
The cathode-supported SOFCs were electrochemically tested using 5%H₂/Ar as fuel and air as oxidant within a temperature range of 700-850°C. The measured open circuit voltage values were close to the theoretical ones with a maximum of 1.002 V at 850°C, indicating a gas-tight electrolyte. A power density of 127 mW/cm² at 850°C for a cathode-supported SOFC with a 3.5 μm thick YSZ electrolyte, was achieved. The activation energy of the whole cell was 0.15 eV corroborating the actual ohmic resistance values correspond to the cathode support which is the limiting factor of the cell's performance. Long-term stability test of five days showed a performance degradation to 83 mW/cm² at 850°C due to particle agglomeration of the cobalt metal in the anode electrode and reduction of the catalytic active area. The above indicate spray pyrolysis is an established technique for preparation of thin films for use in cathode-supported SOFCs.Studies towards the total synthesis of the pyrronazolsMcLennan, Ross Sinclairhttps://hdl.handle.net/10023/173682024-02-23T11:58:30Z2019-06-26T00:00:00ZIn 2014, the pyrronazols, a family of closely related natural products were isolated from a soil dwelling myxobacteria, Nannocystis pusilla strain Ari7. The family represent a novel structural class of secondary metabolites, containing a conjugated chlorinated pyrrole-oxazole unit. The total synthesis of pyrronazols A and A2, 20 and 21, has still to be accomplished and is of specific interest, not only for its unusual and interesting structure, but also to expand on the very limited biological profile. This could be probed further through the synthesis of structural analogues, thus requiring a synthetic strategy that tolerates rapid modifications to probe SAR.
A synthetic strategy for the pyrronazol family must be flexible to allow for the synthesis of both isomers from a single privileged intermediate. Through our attempts towards the synthesis of the pyrronazol family this work details a highly syn-selective, substrate controlled vinylogous Mukaiyama aldol reaction (vMAR) which has been developed and optimised to install the required stereocentres on the pyranone ring. The (4S,5S) C₁-C₇ pyranone fragment has been utilised in the synthesis of two advanced intermediates, both a single reduction step away from pyrronazol A2, that have proved resistant to reduction. The alkene geometry, directing the synthesis towards pyrronazol A2, was set by an unprecedently selective Knoevenagel condensation between 5-chloro-2-formylpyrrole and amidoester partners. Our C₁-C₇ fragment has also been used in a convergent, modular synthesis of pyrronazol B, which afforded the natural product alongside an isomeric product.
2019-06-26T00:00:00ZMcLennan, Ross SinclairIn 2014, the pyrronazols, a family of closely related natural products were isolated from a soil dwelling myxobacteria, Nannocystis pusilla strain Ari7. The family represent a novel structural class of secondary metabolites, containing a conjugated chlorinated pyrrole-oxazole unit. The total synthesis of pyrronazols A and A2, 20 and 21, has still to be accomplished and is of specific interest, not only for its unusual and interesting structure, but also to expand on the very limited biological profile. This could be probed further through the synthesis of structural analogues, thus requiring a synthetic strategy that tolerates rapid modifications to probe SAR.
A synthetic strategy for the pyrronazol family must be flexible to allow for the synthesis of both isomers from a single privileged intermediate. Through our attempts towards the synthesis of the pyrronazol family this work details a highly syn-selective, substrate controlled vinylogous Mukaiyama aldol reaction (vMAR) which has been developed and optimised to install the required stereocentres on the pyranone ring. The (4S,5S) C₁-C₇ pyranone fragment has been utilised in the synthesis of two advanced intermediates, both a single reduction step away from pyrronazol A2, that have proved resistant to reduction. The alkene geometry, directing the synthesis towards pyrronazol A2, was set by an unprecedently selective Knoevenagel condensation between 5-chloro-2-formylpyrrole and amidoester partners. Our C₁-C₇ fragment has also been used in a convergent, modular synthesis of pyrronazol B, which afforded the natural product alongside an isomeric product.Targeted chemical modification of butanosolv lignin using catalytic methodsPanovic, Isabellahttps://hdl.handle.net/10023/173642021-02-17T15:17:05Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZPanovic, IsabellaStructure-property relationships in ferroelectric tungsten bronze oxidesMcNulty, Jason Allanhttps://hdl.handle.net/10023/173522021-02-19T14:46:38Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZMcNulty, Jason AllanAsymmetric synthesis using branched selective hydroformylationPittaway, Rachaelhttps://hdl.handle.net/10023/171432019-08-05T13:26:29Z2018-01-01T00:00:00Z2018-01-01T00:00:00ZPittaway, RachaelExploiting ¹⁷O NMR and first-principles calculations for the study of disorder in ceramic oxidesFernandes, Arantxahttps://hdl.handle.net/10023/171382021-02-17T11:23:06Z2019-01-28T00:00:00ZCeramic oxides of the type A₂B₂O₇ (A = La, Y and B = Sn, Ti, Zr and Hf) were investigated in this thesis. Initial work was concerned with the ¹¹⁹Sn NMR study of phase transitions and cation distribution in La₂(Sn,Ti)₂O₇ ceramics, supported by DFT calculations. This study suggested a random distribution of Ti cations in the pyrochlore phase, while a preferential substitution of Sn on to the two bulk perovskite-like sites was observed for La₂Ti₂O₇. However, for most starting compositions a two phase mixture was obtained. ¹¹⁹Sn was also employed to study cation disorder in La₂(Sn,Zr)₂O₇ and La₂(Sn,Hf)₂O₇ pyrochlores. Although well-resolved resonances were obtained these proved difficult to assign and interpret owing to the overlap of signals from different local environments, suggesting an alternative approach is required.
¹⁷O NMR spectroscopy offers an alternative or additional approach for the study structure and disorder, and would be of particular use in systems that lack appropriate spin I = ½ nuclei, such as e.g., La₂Ti₂O₇, La₂Zr₂O₇ and La₂Hf₂O₇. Owing to the low natural abundance of ¹⁷O (~0.037%), samples in this work were enriched post-synthetically with 70% ¹⁷O₂(g). A systematic study of the conditions required to obtain uniform enrichment was performed for a series of end member compositions, before ¹⁷O NMR was applied to more complex materials (e.g., Y₂Hf₂₋ₓSnₓO₇, La₂Sn₂₋ₓTiₓO₇). This work explains in detail how quantitative spectral acquisition can be achieved for ¹⁷O, with emphasis on differences in nutation rates of different O species, differences in longitudinal relaxation (T1) and additional contributions from quadrupolar satellite transitions to the central transition signal. The O sites in the pyrochlore materials showed uniform enrichment with heating at 900 °C for 12 h, while defect fluorite and layered perovskite-like materials enriched uniformly at a relatively lower temperature (i.e., 600 °C for 12h). However, the absolute levels of enrichment in all materials were found to be better at the highest enrichment temperatures.
This study proves that ¹⁷O quantitative enrichment can be achieved in a cost-effective manner and ¹⁷O NMR is an informative probe for investigating local structure and disorder in oxides. Although complex spectra can be obtained in some cases, e.g., multi-phase systems, ¹⁷O NMR can provide important information, which would have been difficult to obtain using other approaches and offers great potential for the future.
2019-01-28T00:00:00ZFernandes, ArantxaCeramic oxides of the type A₂B₂O₇ (A = La, Y and B = Sn, Ti, Zr and Hf) were investigated in this thesis. Initial work was concerned with the ¹¹⁹Sn NMR study of phase transitions and cation distribution in La₂(Sn,Ti)₂O₇ ceramics, supported by DFT calculations. This study suggested a random distribution of Ti cations in the pyrochlore phase, while a preferential substitution of Sn on to the two bulk perovskite-like sites was observed for La₂Ti₂O₇. However, for most starting compositions a two phase mixture was obtained. ¹¹⁹Sn was also employed to study cation disorder in La₂(Sn,Zr)₂O₇ and La₂(Sn,Hf)₂O₇ pyrochlores. Although well-resolved resonances were obtained these proved difficult to assign and interpret owing to the overlap of signals from different local environments, suggesting an alternative approach is required.
¹⁷O NMR spectroscopy offers an alternative or additional approach for the study structure and disorder, and would be of particular use in systems that lack appropriate spin I = ½ nuclei, such as e.g., La₂Ti₂O₇, La₂Zr₂O₇ and La₂Hf₂O₇. Owing to the low natural abundance of ¹⁷O (~0.037%), samples in this work were enriched post-synthetically with 70% ¹⁷O₂(g). A systematic study of the conditions required to obtain uniform enrichment was performed for a series of end member compositions, before ¹⁷O NMR was applied to more complex materials (e.g., Y₂Hf₂₋ₓSnₓO₇, La₂Sn₂₋ₓTiₓO₇). This work explains in detail how quantitative spectral acquisition can be achieved for ¹⁷O, with emphasis on differences in nutation rates of different O species, differences in longitudinal relaxation (T1) and additional contributions from quadrupolar satellite transitions to the central transition signal. The O sites in the pyrochlore materials showed uniform enrichment with heating at 900 °C for 12 h, while defect fluorite and layered perovskite-like materials enriched uniformly at a relatively lower temperature (i.e., 600 °C for 12h). However, the absolute levels of enrichment in all materials were found to be better at the highest enrichment temperatures.
This study proves that ¹⁷O quantitative enrichment can be achieved in a cost-effective manner and ¹⁷O NMR is an informative probe for investigating local structure and disorder in oxides. Although complex spectra can be obtained in some cases, e.g., multi-phase systems, ¹⁷O NMR can provide important information, which would have been difficult to obtain using other approaches and offers great potential for the future.New catalysts for branched selective hydroformylation of alkenesIu, Leohttps://hdl.handle.net/10023/170682023-12-21T15:35:01Z2019-06-26T00:00:00ZBoth products, n-butyraldehyde and iso-butyraldehyde from propene hydroformylation are
key building blocks for the synthesis of many chemical intermediates, and although high linear
selectivity has been achieved, any form of branched selectivity remains very difficult to attain.
This project aims to deliver a catalyst that can selectively produce branched iso-butyraldehyde
as the major product from propene hydroformylation.
One approach discussed is to study terphenyl phosphines as ligands. The synthesis of
substituted terphenyls through Suzuki-Miyaura coupling reactions between aryl boronic acids
and 2,6-dichloroanisole was studied. Novel phosphine-phosphanamine ligands with bulky
terphenyl substituents were synthesised and tested in propene hydroformylation, and also
asymmetric hydroformylation of other alkenes. The synthesis of several ferrocene-based
phosphine-phosphoramidite ligands is also discussed. These ligands were then tested in
rhodium-catalysed propene hydroformylation and their reactivities and selectivities are
reported. These ligands/Rh catalysts showed a moderate reactivity for propene
hydroformylation and up to 56% branched selectivity, which is close to the best selectivity
known under industrially relevant conditions. The introduction of bulky substituents on the
phosphoramidite part of the ligand did not deliver any huge increases in regioselectivity, but
a large improvement in catalyst thermal stability was observed in experiments conducted using
in situ high pressure infrared spectroscopy.
The reaction conditions for rhodium-catalysed propene hydroformylation using the
BOBPHOS ligand were investigated, with unprecedented branched selectivity of up to 82%
achieved. A variety of aspects was examined, including the solvent, reaction temperature,
reaction pressure with varying partial pressure of CO and H₂, and rhodium to ligand ratio.
BOBPHOS derivatives which are more synthetically accessible and economically attractive
were synthesised and tested in rhodium-catalysed propene hydroformylation. Comparable
results with their parent ligand/Rh catalyst were obtained and improved thermal stabilities
were observed in selected catalysts.
Different directions for potential future works are suggested, which hopefully, along with the
findings in this thesis, can be a major contribution to the development of an efficient, branched
selective catalytic system for industrial propene hydroformylation.
2019-06-26T00:00:00ZIu, LeoBoth products, n-butyraldehyde and iso-butyraldehyde from propene hydroformylation are
key building blocks for the synthesis of many chemical intermediates, and although high linear
selectivity has been achieved, any form of branched selectivity remains very difficult to attain.
This project aims to deliver a catalyst that can selectively produce branched iso-butyraldehyde
as the major product from propene hydroformylation.
One approach discussed is to study terphenyl phosphines as ligands. The synthesis of
substituted terphenyls through Suzuki-Miyaura coupling reactions between aryl boronic acids
and 2,6-dichloroanisole was studied. Novel phosphine-phosphanamine ligands with bulky
terphenyl substituents were synthesised and tested in propene hydroformylation, and also
asymmetric hydroformylation of other alkenes. The synthesis of several ferrocene-based
phosphine-phosphoramidite ligands is also discussed. These ligands were then tested in
rhodium-catalysed propene hydroformylation and their reactivities and selectivities are
reported. These ligands/Rh catalysts showed a moderate reactivity for propene
hydroformylation and up to 56% branched selectivity, which is close to the best selectivity
known under industrially relevant conditions. The introduction of bulky substituents on the
phosphoramidite part of the ligand did not deliver any huge increases in regioselectivity, but
a large improvement in catalyst thermal stability was observed in experiments conducted using
in situ high pressure infrared spectroscopy.
The reaction conditions for rhodium-catalysed propene hydroformylation using the
BOBPHOS ligand were investigated, with unprecedented branched selectivity of up to 82%
achieved. A variety of aspects was examined, including the solvent, reaction temperature,
reaction pressure with varying partial pressure of CO and H₂, and rhodium to ligand ratio.
BOBPHOS derivatives which are more synthetically accessible and economically attractive
were synthesised and tested in rhodium-catalysed propene hydroformylation. Comparable
results with their parent ligand/Rh catalyst were obtained and improved thermal stabilities
were observed in selected catalysts.
Different directions for potential future works are suggested, which hopefully, along with the
findings in this thesis, can be a major contribution to the development of an efficient, branched
selective catalytic system for industrial propene hydroformylation.Palladium and gold N-heterocyclic carbene complexes : synthesis and catalytic applicationsZinser, Caroline Magdalenehttps://hdl.handle.net/10023/170662019-02-14T12:15:39Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZZinser, Caroline MagdaleneTitle redactedGkotsi, Danai Stellahttps://hdl.handle.net/10023/170602019-10-15T09:28:35Z2018-02-23T00:00:00Z2018-02-23T00:00:00ZGkotsi, Danai StellaOrganocatalytic kinetic and dynamic kinetic resolutions of alcoholsMusolino, Stefania Francescahttps://hdl.handle.net/10023/170582019-08-16T07:44:59Z2019-06-26T00:00:00Z2019-06-26T00:00:00ZMusolino, Stefania FrancescaExploiting site-selective reactivity in the processing of ligninMiles-Barrett, Danielhttps://hdl.handle.net/10023/170562023-01-11T13:51:48Z2019-01-08T00:00:00Z2019-01-08T00:00:00ZMiles-Barrett, DanielTitle redactedCarins, George Michaelhttps://hdl.handle.net/10023/170442019-02-12T16:35:01Z2016-06-22T00:00:00Z2016-06-22T00:00:00ZCarins, George MichaelApplication of modified xantphos ligands
in homogeneous catalysis and
photochemistryForero Cortés, Paola Andreahttps://hdl.handle.net/10023/170422021-01-08T03:07:04Z2019-11-29T00:00:00Z2019-11-29T00:00:00ZForero Cortés, Paola AndreaIsothiourea-mediated synthesis of functionalised heterocyclesStark, Daniel G.https://hdl.handle.net/10023/170082019-07-02T02:00:52Z2016-09-26T00:00:00ZThe research outlined in this thesis describes methodologies for the synthesis of
functionalised heterocycles through the use of C1-ammonium enolate catalysis utilising
isothiourea organocatalysts.
Chapter 2: Initial work demonstrated a DHPB-mediated Michael addition-lactamisation/PhSH elimination/N- to O-sulfonyl transfer one-pot cascade for the synthesis of
2,4,6-substituted pyridine sulfonates. Applying (phenylthio)acetic acid and a range of a,ß-unsaturated ketimines, pyridine sulfonates were obtained in moderate to good yield (40-69%)
with the functionalisation of the incorporated sulfonate group examined through various
derivatisations.
Chapter 3: The established isothiourea-mediated pyridine methodology was expanded
into the synthesis of 2,3- and 2,3,5-substituted pyridine 6-tosylates through a three-stage
Michael addition-lactamisation, S-oxidation-sulfoxide elimination and N- to O-sulfonyl transfer
protocol. Using (phenylthio)acetic acids and 2-N-tosyliminoacrylates a range of pyridine
products were provided in moderate to good yield over the three-stage process (44-72%).
Derivatisation of the installed sulfonate group allowed access into 2,3-, 2,3,5-, 2,3,6 and 2,3,5,6-substituted pyridines.
Chapter 4: Subsequent studies expanded the scope of dihydropyranone and
dihydropyridinone products accessible through isothiourea-catalysis using 2-aroyl acrylates or
2-N-tosyliminoacrylates in an enantioselective Michael addition-cyclisation process. It was
discovered that the use of homoanhydride enolate precursors was necessary when applying 2-aroyl acrylates to ensure high enantioselectivity (up to 99%) and reproducibility of the
dihydropyranone products, while carboxylic acids can be used with 2-N-tosyliminoacrylates,
providing dihydropyridinones in high enantioselectivity (typically >90% ee).
Chapter 5: Enantioselective Michael addition-lactonisation of 2-aryl and 2-alkenylacetic acids and a,ß-unsaturated trichloromethyl ketones, catalysed by (2S,3R)-HyperBTM was shown to give dihydropyranones with subsequent ring opening and substitution
of the CCl₃ group providing a range of diesters and diamides in high diastereo- and
enantioselectivity (up to 95:5 and up to >99% ee).
Chapter 6: The pyrrolizine core is present in many biologically relevant molecules. It
was demonstrated that an isothiourea-catalysed enantioselective Michael addition-lactonisation/ring opening process gives access to these important molecules with exquisite
diastereo- and enantioselectivity (typically >95:5 dr and >99% ee). A novel synthetic route into
the synthesis of the pyrrole enone-acid substrates was established, hence making the overall
methodology more efficient and reproducible. Computational studies are provided to compliment the synthetic studies with investigations into the origin of the high stereocontrol
observed in this process.
Chapter 7: Saccharin-derived Michael acceptors have been shown as useful substrates
in isothiourea-catalysis. (2R,3S)-HyperBTM catalyses the Michael addition-lactamisation of
carboxylic acids and saccharin-derived Michael acceptors to give 8,9-dihydro-7H
benzo[4,5]isothiazolo[2,3-a]pyridin-7-one 5,5-dioxides in good to excellent stereocontrol
(80:20->95:5 dr and 71->99% ee). Furthermore, these Michael acceptors can be utilised with 1-(1H-imidazol-1-yl)-2-(phenylthio)ethan-1-one in a Michael addition-lactamisation/PhSH
elimination process giving access to the corresponding 1,2-benzoisothiazolopyridone 1,1-dioxide heterocycle in a chromatography-free procedure.
2016-09-26T00:00:00ZStark, Daniel G.The research outlined in this thesis describes methodologies for the synthesis of
functionalised heterocycles through the use of C1-ammonium enolate catalysis utilising
isothiourea organocatalysts.
Chapter 2: Initial work demonstrated a DHPB-mediated Michael addition-lactamisation/PhSH elimination/N- to O-sulfonyl transfer one-pot cascade for the synthesis of
2,4,6-substituted pyridine sulfonates. Applying (phenylthio)acetic acid and a range of a,ß-unsaturated ketimines, pyridine sulfonates were obtained in moderate to good yield (40-69%)
with the functionalisation of the incorporated sulfonate group examined through various
derivatisations.
Chapter 3: The established isothiourea-mediated pyridine methodology was expanded
into the synthesis of 2,3- and 2,3,5-substituted pyridine 6-tosylates through a three-stage
Michael addition-lactamisation, S-oxidation-sulfoxide elimination and N- to O-sulfonyl transfer
protocol. Using (phenylthio)acetic acids and 2-N-tosyliminoacrylates a range of pyridine
products were provided in moderate to good yield over the three-stage process (44-72%).
Derivatisation of the installed sulfonate group allowed access into 2,3-, 2,3,5-, 2,3,6 and 2,3,5,6-substituted pyridines.
Chapter 4: Subsequent studies expanded the scope of dihydropyranone and
dihydropyridinone products accessible through isothiourea-catalysis using 2-aroyl acrylates or
2-N-tosyliminoacrylates in an enantioselective Michael addition-cyclisation process. It was
discovered that the use of homoanhydride enolate precursors was necessary when applying 2-aroyl acrylates to ensure high enantioselectivity (up to 99%) and reproducibility of the
dihydropyranone products, while carboxylic acids can be used with 2-N-tosyliminoacrylates,
providing dihydropyridinones in high enantioselectivity (typically >90% ee).
Chapter 5: Enantioselective Michael addition-lactonisation of 2-aryl and 2-alkenylacetic acids and a,ß-unsaturated trichloromethyl ketones, catalysed by (2S,3R)-HyperBTM was shown to give dihydropyranones with subsequent ring opening and substitution
of the CCl₃ group providing a range of diesters and diamides in high diastereo- and
enantioselectivity (up to 95:5 and up to >99% ee).
Chapter 6: The pyrrolizine core is present in many biologically relevant molecules. It
was demonstrated that an isothiourea-catalysed enantioselective Michael addition-lactonisation/ring opening process gives access to these important molecules with exquisite
diastereo- and enantioselectivity (typically >95:5 dr and >99% ee). A novel synthetic route into
the synthesis of the pyrrole enone-acid substrates was established, hence making the overall
methodology more efficient and reproducible. Computational studies are provided to compliment the synthetic studies with investigations into the origin of the high stereocontrol
observed in this process.
Chapter 7: Saccharin-derived Michael acceptors have been shown as useful substrates
in isothiourea-catalysis. (2R,3S)-HyperBTM catalyses the Michael addition-lactamisation of
carboxylic acids and saccharin-derived Michael acceptors to give 8,9-dihydro-7H
benzo[4,5]isothiazolo[2,3-a]pyridin-7-one 5,5-dioxides in good to excellent stereocontrol
(80:20->95:5 dr and 71->99% ee). Furthermore, these Michael acceptors can be utilised with 1-(1H-imidazol-1-yl)-2-(phenylthio)ethan-1-one in a Michael addition-lactamisation/PhSH
elimination process giving access to the corresponding 1,2-benzoisothiazolopyridone 1,1-dioxide heterocycle in a chromatography-free procedure.Synthesis of the zeolites mordenite and ferrierite for applications in catalysisPrice, David J.https://hdl.handle.net/10023/169852019-02-01T16:48:30Z2017-06-21T00:00:00Z2017-06-21T00:00:00ZPrice, David J.Lipidomic investigations into the phospholipid content and metabolism of various kinetoplastidsRoberts, Matthew D.https://hdl.handle.net/10023/169832019-07-01T10:15:15Z2017-06-21T00:00:00ZThis work expands the knowledge on phospholipid metabolism in the kinetoplastid
parasites: T. brucei, T. cruzi, Leishmania spp. that cause neglected tropical diseases
and the related non-human pathogenic Crithidia fasiculata.
As a close relative of parasitic kinetoplasts, specifically Leishmania, it is hypothesised
that Crithidia fasiculata possesses a similar lipid biosynthetic capability and therefore
represent an attractive model organism. Database mining the Crithidia genome
revealed the ability to biosynthesise all of the main phospholipid species. Utilising
various lipidomic techniques, a high level of an ω-6 18:3 fatty acid was observed,
alongside an uncommon Δ19:0 fatty acid that was later identified to be exclusive
attributed to PE species. Sphingolipid metabolism was shown to resemble that of
Leishmania and T. cruzi, given the exclusive production of inositol-phosphoceramide
species and no sphingomyelin species being observed. Using labelled precursors,
Crithidia were seen to uptake and incorporate extracellular inositol into both
phosphatidylinositol and inositol-phosphoceramide species. Crithidia were also
shown to utilise both the Kennedy pathway and methylation of
phosphatidylethanolamine to form phosphatidylcholine.
The phospholipidome of T. cruzi revealed several phosphatidylserine species for the
first time, suggesting a functional phosphatidylserine synthase. Current knowledge
of T.cruzi sphingolipid biosynthesis was also confirmed as only inositol
xxxi
phosphoceramide species were observed. The identification and subsequent
characterisation of novel phosphonolipid species are reported for the first time.
Utilising lipidomic methodologies and labelled precursors, the relative contribution
of the intracellular inositol pools within bloodstream and procyclic T. brucei towards
PI biosynthesis was examined. This highlighted that the synthesis/turnover rates for
specific phosphatidylinositol and inositol-phosphoceramide species are unequal.
Efforts to optimise media conditions highlighted that under reduced levels of
serum/glucose/inositol, bloodstream T. brucei unexpectedly adjusts its inositol
metabolism. The procyclic parasite exemplifies this fact, as under inositol/glucose
deficient media conditions they appear to have adapted to utilising glucogenesis and
inositol de-novo synthesis.
This work highlights that these parasites are rapidly dividing, their unique features of
lipid metabolism may be exploitable for drug discovery purposes.
2017-06-21T00:00:00ZRoberts, Matthew D.This work expands the knowledge on phospholipid metabolism in the kinetoplastid
parasites: T. brucei, T. cruzi, Leishmania spp. that cause neglected tropical diseases
and the related non-human pathogenic Crithidia fasiculata.
As a close relative of parasitic kinetoplasts, specifically Leishmania, it is hypothesised
that Crithidia fasiculata possesses a similar lipid biosynthetic capability and therefore
represent an attractive model organism. Database mining the Crithidia genome
revealed the ability to biosynthesise all of the main phospholipid species. Utilising
various lipidomic techniques, a high level of an ω-6 18:3 fatty acid was observed,
alongside an uncommon Δ19:0 fatty acid that was later identified to be exclusive
attributed to PE species. Sphingolipid metabolism was shown to resemble that of
Leishmania and T. cruzi, given the exclusive production of inositol-phosphoceramide
species and no sphingomyelin species being observed. Using labelled precursors,
Crithidia were seen to uptake and incorporate extracellular inositol into both
phosphatidylinositol and inositol-phosphoceramide species. Crithidia were also
shown to utilise both the Kennedy pathway and methylation of
phosphatidylethanolamine to form phosphatidylcholine.
The phospholipidome of T. cruzi revealed several phosphatidylserine species for the
first time, suggesting a functional phosphatidylserine synthase. Current knowledge
of T.cruzi sphingolipid biosynthesis was also confirmed as only inositol
xxxi
phosphoceramide species were observed. The identification and subsequent
characterisation of novel phosphonolipid species are reported for the first time.
Utilising lipidomic methodologies and labelled precursors, the relative contribution
of the intracellular inositol pools within bloodstream and procyclic T. brucei towards
PI biosynthesis was examined. This highlighted that the synthesis/turnover rates for
specific phosphatidylinositol and inositol-phosphoceramide species are unequal.
Efforts to optimise media conditions highlighted that under reduced levels of
serum/glucose/inositol, bloodstream T. brucei unexpectedly adjusts its inositol
metabolism. The procyclic parasite exemplifies this fact, as under inositol/glucose
deficient media conditions they appear to have adapted to utilising glucogenesis and
inositol de-novo synthesis.
This work highlights that these parasites are rapidly dividing, their unique features of
lipid metabolism may be exploitable for drug discovery purposes.PELDOR in multi-spin systems : from model systems synthesis to biological applicationsValera, Silviahttps://hdl.handle.net/10023/169602019-03-29T11:24:26Z2016-11-30T00:00:00ZPulsed electron-electron double resonance (PELDOR) is an emerging technique for nanometre distance measurements in nano-sized assemblies and between specific sites of molecules. Most commonly nitroxide radicals are used as probes for EPR distance measurements because they are easy to introduce in biological systems such as soluble and membrane proteins or nucleic acids.
PELDOR distance measurements currently rely on data processing software which has been proven to accurately extract inter-spin distances from the dipolar coupling between two paramagnetic centres. However, when the dipolar coupling is affected by contributions from other close-by unpaired electrons inaccuracies as broadening effects and artefacts are introduced in the distance distributions derived. This challenge, commonly referred as multi-spin effects, has been affecting the extraction of accurate distance information from PELDOR measurements in chemical and biological systems with multiple spin labels.
The aim of this project is to approach, identify and suppress inaccuracies introduced in PELDOR-based distance distributions by multi-spin effects. This is achieved through the synthesis of multiply labelled model systems which would allow for assessment of the impact of multi-spin effects on distance measurements of simple geometries whose behaviour can be easily predicted and modelled. In this work existing methods for suppression of multi-spin effects are tested, together with their efficiency and limitations. The results are used to devise better sets of parameters including alternative settings for extraction of accurate distances from multi-spin systems and to explore their efficiency and limitations. Additional effects influencing distance measurements by pulsed EPR are also examined; in particular the effects of orientation selection and their interplay with multi-spin effects is studied in depth.
Studies on rigid symmetric and asymmetric chemical model systems together with heptameric channel membrane proteins allow for outlining of recommendations for PELDOR distance measurements settings on systems presenting similar structural features, including symmetries and inter-spin distances.
2016-11-30T00:00:00ZValera, SilviaPulsed electron-electron double resonance (PELDOR) is an emerging technique for nanometre distance measurements in nano-sized assemblies and between specific sites of molecules. Most commonly nitroxide radicals are used as probes for EPR distance measurements because they are easy to introduce in biological systems such as soluble and membrane proteins or nucleic acids.
PELDOR distance measurements currently rely on data processing software which has been proven to accurately extract inter-spin distances from the dipolar coupling between two paramagnetic centres. However, when the dipolar coupling is affected by contributions from other close-by unpaired electrons inaccuracies as broadening effects and artefacts are introduced in the distance distributions derived. This challenge, commonly referred as multi-spin effects, has been affecting the extraction of accurate distance information from PELDOR measurements in chemical and biological systems with multiple spin labels.
The aim of this project is to approach, identify and suppress inaccuracies introduced in PELDOR-based distance distributions by multi-spin effects. This is achieved through the synthesis of multiply labelled model systems which would allow for assessment of the impact of multi-spin effects on distance measurements of simple geometries whose behaviour can be easily predicted and modelled. In this work existing methods for suppression of multi-spin effects are tested, together with their efficiency and limitations. The results are used to devise better sets of parameters including alternative settings for extraction of accurate distances from multi-spin systems and to explore their efficiency and limitations. Additional effects influencing distance measurements by pulsed EPR are also examined; in particular the effects of orientation selection and their interplay with multi-spin effects is studied in depth.
Studies on rigid symmetric and asymmetric chemical model systems together with heptameric channel membrane proteins allow for outlining of recommendations for PELDOR distance measurements settings on systems presenting similar structural features, including symmetries and inter-spin distances.Applications of isothioureas in surface chemistry : modification of self-assembled monolayers and immobilisation on polymer supportsChisholm, Rosshttps://hdl.handle.net/10023/169252019-06-29T02:06:13Z2017-05-11T00:00:00ZThe research outlined in this thesis describes the development of organocatalytic methodology
for the modification of self-assembled monolayers on silicon dioxide surfaces and its extension
towards an asymmetric protocol and immobilisation of isothiourea organocatalysts to polystyrene
supports.
Chapter 1 aims to describe the fundamental aspects of self-assembled monolayers and their place
within the wider area of surface chemistry. A recent overview of catalytic surface
functionalisation is discussed as well as the historical context of this project, with respect to
research within the Smith group, is also presented. A statement of the initial aims and objectives
of the research is presented.
Chapter 2 describes the proof-of-concept study undertaken to develop methodology towards the
functionalisation of silicon oxide surfaces using an isothiourea-catalysed organocatalytic Michael
addition-lactonisation process. Subsequent characterisation of the resulting surfaces and a
reaction scope is also carried out in this system.
Chapter 3 describes an extension of the methodology carried out in the previous chapter to allow
for an asymmetric protocol. The sense of enantioenduction of the resulting surfaces was then
examined using chemical force microscopy using a novel AFM probe with the results show that
chiral discrimination can be achieved using this methodology. Control experiments were also
undertaken by depositing enantiopure starting materials on a surface and measuring the adhesion
forces confirming the presence of a chiral surface.
Chapter 4 describes the immobilisation (R)-BTM and (2R,3S)-HyperBTM analogues onto
polystyrene supports and their evaluation in several different reaction classes previously
investigated within the Smith group. Results show that the polymer-supported catalyst (2R,3S)-
HyperBTM can be recycled up to 8 times without any major loss in yield or selectivity.
Chapter 5 offers a brief summary of the work undertaken in this PhD and some of the conclusions
that can be drawn from it as well as an insight into the potential future developments of this
research and areas where it could possibly expand and develop.
2017-05-11T00:00:00ZChisholm, RossThe research outlined in this thesis describes the development of organocatalytic methodology
for the modification of self-assembled monolayers on silicon dioxide surfaces and its extension
towards an asymmetric protocol and immobilisation of isothiourea organocatalysts to polystyrene
supports.
Chapter 1 aims to describe the fundamental aspects of self-assembled monolayers and their place
within the wider area of surface chemistry. A recent overview of catalytic surface
functionalisation is discussed as well as the historical context of this project, with respect to
research within the Smith group, is also presented. A statement of the initial aims and objectives
of the research is presented.
Chapter 2 describes the proof-of-concept study undertaken to develop methodology towards the
functionalisation of silicon oxide surfaces using an isothiourea-catalysed organocatalytic Michael
addition-lactonisation process. Subsequent characterisation of the resulting surfaces and a
reaction scope is also carried out in this system.
Chapter 3 describes an extension of the methodology carried out in the previous chapter to allow
for an asymmetric protocol. The sense of enantioenduction of the resulting surfaces was then
examined using chemical force microscopy using a novel AFM probe with the results show that
chiral discrimination can be achieved using this methodology. Control experiments were also
undertaken by depositing enantiopure starting materials on a surface and measuring the adhesion
forces confirming the presence of a chiral surface.
Chapter 4 describes the immobilisation (R)-BTM and (2R,3S)-HyperBTM analogues onto
polystyrene supports and their evaluation in several different reaction classes previously
investigated within the Smith group. Results show that the polymer-supported catalyst (2R,3S)-
HyperBTM can be recycled up to 8 times without any major loss in yield or selectivity.
Chapter 5 offers a brief summary of the work undertaken in this PhD and some of the conclusions
that can be drawn from it as well as an insight into the potential future developments of this
research and areas where it could possibly expand and develop.Title redactedHernández Reta, Juan Carloshttps://hdl.handle.net/10023/168982019-01-30T10:55:43Z2016-10-24T00:00:00Z2016-10-24T00:00:00ZHernández Reta, Juan CarlosTitle redactedVasseur, Mariehttps://hdl.handle.net/10023/168792019-10-15T09:27:20Z2017-10-10T00:00:00Z2017-10-10T00:00:00ZVasseur, MarieSynthesis and reactivity of copper(I) and aluminium(III) complexes of N-heterocyclic carbenesTrose, Michaelhttps://hdl.handle.net/10023/168742023-12-01T14:59:45Z2017-12-07T00:00:00ZN-heterocyclic carbene (NHC) ligands are nowadays an irreplaceable tool for the stabilisation of both transition metal (TM) and main group (MG) elements. NHC-TM complexes have been widely studied and successfully applied in catalysis, whereas NHCs have enabled the isolation and characterisation of elusive MG species, as for example with the MG element in a low oxidation state. In this thesis, investigation of both classes is covered, utilising copper(I) as TM and aluminium(III) as MG element.
Regarding NHC-copper(I) species, the first investigation was their application as catalysts for the synthesis of 2-substituted oxazolines and 2-substituted thiazoline from nitriles and aminoalcohols or aminothiols respectively (Chapter 2).The second focus lies in the functionalisation of the copper centre by changing the anionic ligand to obtain new NHC-copper(I) complexes. Two different classes were synthesised, the first bears azole ligands (Chapter 3) and the second azide (Chapter 4). The former were applied in the hydrosilylation of ketones and mechanistic investigations were performed in order to ascertain the effect of both the NHC and azole ligand on catalytic activity. The latter was reacted with different organic molecules and with cationic NHC-copper(I) species to explore the reactivity of the azide moiety.
Concerning NHC-aluminium(III) complexes, the main focus was the functionalisation of [AlH3(NHC)] species to obtain new compounds and study of their reactivity (Chapter 5). Different transformations, ranging from halogenation to the reaction with bis(pinacolato)diboron, are covered. Moreover, attempts to reduce Al(III) complexes to low valent aluminium species are presented.
2017-12-07T00:00:00ZTrose, MichaelN-heterocyclic carbene (NHC) ligands are nowadays an irreplaceable tool for the stabilisation of both transition metal (TM) and main group (MG) elements. NHC-TM complexes have been widely studied and successfully applied in catalysis, whereas NHCs have enabled the isolation and characterisation of elusive MG species, as for example with the MG element in a low oxidation state. In this thesis, investigation of both classes is covered, utilising copper(I) as TM and aluminium(III) as MG element.
Regarding NHC-copper(I) species, the first investigation was their application as catalysts for the synthesis of 2-substituted oxazolines and 2-substituted thiazoline from nitriles and aminoalcohols or aminothiols respectively (Chapter 2).The second focus lies in the functionalisation of the copper centre by changing the anionic ligand to obtain new NHC-copper(I) complexes. Two different classes were synthesised, the first bears azole ligands (Chapter 3) and the second azide (Chapter 4). The former were applied in the hydrosilylation of ketones and mechanistic investigations were performed in order to ascertain the effect of both the NHC and azole ligand on catalytic activity. The latter was reacted with different organic molecules and with cationic NHC-copper(I) species to explore the reactivity of the azide moiety.
Concerning NHC-aluminium(III) complexes, the main focus was the functionalisation of [AlH3(NHC)] species to obtain new compounds and study of their reactivity (Chapter 5). Different transformations, ranging from halogenation to the reaction with bis(pinacolato)diboron, are covered. Moreover, attempts to reduce Al(III) complexes to low valent aluminium species are presented.Title redactedSmith, Duncan Robert Millerhttps://hdl.handle.net/10023/168152019-10-15T09:27:47Z2017-12-07T00:00:00Z2017-12-07T00:00:00ZSmith, Duncan Robert MillerDevelopment and testing of mixed-phase oxygen transport membranesDehaney-Steven, Zachary Alexanderhttps://hdl.handle.net/10023/168072019-06-20T10:44:06Z2017-11-09T00:00:00ZPerhaps mankind’s most urgent challenge at present is anthropogenic climate change, with the associated sea-level rise and desertification set to produce major losses of arable land and living space, as well as loss of life. The key to preventing the worst effects of AGW lies in limiting humanity’s emissions of the greenhouse gas carbon dioxide, of which the vast majority comes from the burning of fossil fuels such as coal, oil and natural gas. However, fossil fuels are embedded in all of the world’s economies, responsible for almost all of the provision of electrical power and transport, making the sizable reductions required in the timescale necessary somewhat impractical. One solution lies in Carbon Capture and Storage (CCS), which involves, in one incarnation, the combustion of fossil fuels in pure oxygen, simplifying the processing and storage of the carbon dioxide produced. There is potential for very high process efficiencies if oxygen is provided by Oxygen Transport Membranes (OTM).
This thesis is concerned with the development of membranes and test procedures for mixed-phase OTM, which typically consist of a dense, gastight layer of perovskite and fluorite phases. An inactive support layer may also be present. The surface area, and therefore surface exchange of either side is improved by the addition of exchange layers to either side. Oxide ion migration is accomplished by applying a pO₂ differential to the membrane at high temperature.
Causes and mechanisms for degradation are not fully understood, and there is potential to improve oxygen flux. One way to achieve this is by the use of very thin, supported membranes, and this thesis demonstrates that such membranes can be fabricated with well-understood manufacturing processes.
Another method of improving oxygen flux is by the use of catalysts on the exchange layers of the membrane. The most popular method of introducing 6 catalysts to an exchange layer or electrode involves impregnation of a metal salt into a ceramic backbone, followed by reduction to yield a catalytically active phase. However, this process is wasteful of catalyst, labour-intensive and control of the distribution of catalyst is difficult or impossible. An alternative exists, where metals doped into a perovskite migrate to the surface and form nanoparticles on exposure to a sufficiently high temperature and reducing atmosphere, and this thesis demonstrates the benefits of using such an approach. Improvements in oxygen flux of up to a factor of 7 over an undoped perovskite exchange layer have been demonstrated.
The conductivity and crystal structures of (La₀.₈Sr₀.₂)₀.₉₅Cr₀.₅Fe₀.₅O[sub](3-δ) and (Sc₂O₃)₀.₁₉(CrO₂)₀.₀₁(ZrO₂)₀.₇₈₉O₁.₉₄ under oxidising and reducing atmospheres at high temperatures have been evaluated using neutron powder diffraction and a novel in-situ rig, demonstrating that the OTM composition is a p-type conductor, and quantifying the effect of oxygen stoichiometry on conductivity and unit cell parameters.
2017-11-09T00:00:00ZDehaney-Steven, Zachary AlexanderPerhaps mankind’s most urgent challenge at present is anthropogenic climate change, with the associated sea-level rise and desertification set to produce major losses of arable land and living space, as well as loss of life. The key to preventing the worst effects of AGW lies in limiting humanity’s emissions of the greenhouse gas carbon dioxide, of which the vast majority comes from the burning of fossil fuels such as coal, oil and natural gas. However, fossil fuels are embedded in all of the world’s economies, responsible for almost all of the provision of electrical power and transport, making the sizable reductions required in the timescale necessary somewhat impractical. One solution lies in Carbon Capture and Storage (CCS), which involves, in one incarnation, the combustion of fossil fuels in pure oxygen, simplifying the processing and storage of the carbon dioxide produced. There is potential for very high process efficiencies if oxygen is provided by Oxygen Transport Membranes (OTM).
This thesis is concerned with the development of membranes and test procedures for mixed-phase OTM, which typically consist of a dense, gastight layer of perovskite and fluorite phases. An inactive support layer may also be present. The surface area, and therefore surface exchange of either side is improved by the addition of exchange layers to either side. Oxide ion migration is accomplished by applying a pO₂ differential to the membrane at high temperature.
Causes and mechanisms for degradation are not fully understood, and there is potential to improve oxygen flux. One way to achieve this is by the use of very thin, supported membranes, and this thesis demonstrates that such membranes can be fabricated with well-understood manufacturing processes.
Another method of improving oxygen flux is by the use of catalysts on the exchange layers of the membrane. The most popular method of introducing 6 catalysts to an exchange layer or electrode involves impregnation of a metal salt into a ceramic backbone, followed by reduction to yield a catalytically active phase. However, this process is wasteful of catalyst, labour-intensive and control of the distribution of catalyst is difficult or impossible. An alternative exists, where metals doped into a perovskite migrate to the surface and form nanoparticles on exposure to a sufficiently high temperature and reducing atmosphere, and this thesis demonstrates the benefits of using such an approach. Improvements in oxygen flux of up to a factor of 7 over an undoped perovskite exchange layer have been demonstrated.
The conductivity and crystal structures of (La₀.₈Sr₀.₂)₀.₉₅Cr₀.₅Fe₀.₅O[sub](3-δ) and (Sc₂O₃)₀.₁₉(CrO₂)₀.₀₁(ZrO₂)₀.₇₈₉O₁.₉₄ under oxidising and reducing atmospheres at high temperatures have been evaluated using neutron powder diffraction and a novel in-situ rig, demonstrating that the OTM composition is a p-type conductor, and quantifying the effect of oxygen stoichiometry on conductivity and unit cell parameters.Reversed crystal growthZhou, Wuzonghttps://hdl.handle.net/10023/167842023-04-18T23:55:30Z2018-12-22T00:00:00ZIn the last decade, reversed growth route has been found in many crystal growth processes. In these systems, a single crystal does not develop from a single nucleus. The precursor molecules/ions or nanocrystallites aggregate into some large amorphous or polycrystalline particles. Multiple-nucleation on surface of the amorphous particles or surface re-crystallization of the polycrystalline particles then takes place, forming a single crystal shell with a regular morphology. Finally, the crystallization extends from the surface to the core to form single crystals. This non-classical crystal growth route often results in some special morphologies, such as core-shell structures, hollow single crystals, sandwich structures, etc. This article gives a brief review of the research in the reversed crystal growth and demonstrates that investigation of detailed mechanisms of crystal growth enables us to better understand the formation of many novel morphologies of the crystals. Some unsolved problems are also discussed.
2018-12-22T00:00:00ZZhou, WuzongIn the last decade, reversed growth route has been found in many crystal growth processes. In these systems, a single crystal does not develop from a single nucleus. The precursor molecules/ions or nanocrystallites aggregate into some large amorphous or polycrystalline particles. Multiple-nucleation on surface of the amorphous particles or surface re-crystallization of the polycrystalline particles then takes place, forming a single crystal shell with a regular morphology. Finally, the crystallization extends from the surface to the core to form single crystals. This non-classical crystal growth route often results in some special morphologies, such as core-shell structures, hollow single crystals, sandwich structures, etc. This article gives a brief review of the research in the reversed crystal growth and demonstrates that investigation of detailed mechanisms of crystal growth enables us to better understand the formation of many novel morphologies of the crystals. Some unsolved problems are also discussed.Title redactedYoung, Claire M.https://hdl.handle.net/10023/167542019-10-18T15:47:08Z2017-11-09T00:00:00Z2017-11-09T00:00:00ZYoung, Claire M.Investigation of surface modification of perovskite with different catalystsMao, Donglaihttps://hdl.handle.net/10023/167392019-04-22T08:46:38Z2016-11-30T00:00:00ZThe increasing energy requirements of mankind have stimulated the need to search for
renewable clean energy in order to protect the environment. Proton Exchange
Membrane Fuel Cells (PEMFC) are one of the most promising types of fuel cell among
the entire range of power generation devices. However, the high quantity of noble metal
catalysts used in PEMFCs hinders their commercialization due to the associated high
cost. Decreasing the amount of noble metal catalysts without sacrificing the
performance of the fuel cell is therefore desirable.
This thesis explores the possibility of modifying the perovskites with small quantities of
the most commonly used catalysts (Ni, Ru and Pd) on its surface, with the intention to
create a potentially cost-effective electrode material for PEMFC. The perovskites
employed in this thesis include two of the most commonly studied perovskite materials,
A-site deficient titanate based perovskites and LaCrO₃ based perovskites. The concept
of the modification method is to combine two of the most promising state of the art
methods, impregnation and exsolution, to improve the properties of the perovskite.
Instead of incorporating the catalyst in the whole lattice of the perovskite, the
impregnation method was used to dope the catalyst into the surface of the perovskite
only. The exsolution of the doped catalysts from the perovskite was then attempted. This
would theoretically produce nanoparticles with certain parts of its body anchored inside
the perovskite, thus avoiding the catalyst agglomeration problem which has been
reported for the normal impregnation method.
The A-site deficient titanate perovskite used to investigate surface doping modifications
is La₀.₄Sr₀.₄GaₓTi₁₋ₓO[sub](3-x/2) (LSGT). At first, a Ni catalyst was used to explore the
possibility and optimal experimental conditions for catalyst doping of the perovskite
from the surface and subsequent exsolution. The microstructure of the LSGT scaffold
was optimized for later experiments. The results from the Ni doping study were then
applied to the surface doping of Pd and Ru catalysts. This work demonstrates the
possibility of incorporating Ni, Ru and Pd catalysts into the surface of A-site deficient
titanate LSGT perovskite, using a pre-reduction treatment. The doped Ni and Pd
catalysts managed to exsolve to the surface of the perovskite as nanoparticles after reduction treatment. However, the Ru catalyst did not exsolve under the same
experimental conditions. It has been found that different catalysts require different
conditions to be able to dissolve into the perovskite for example, the heating atmosphere.
In addition, the mechanism of incorporating Pd into the A-site deficient titanate has
been studied, showing that the Pd is doped into the A-site deficient titanate in the form
of Pd²⁺ with square planar 4-fold coordination on the B-site.
The LaCrO₃ based perovskite employed for studying the incorporation of a catalyst into
the surface of the perovskite was La₀.₇₅Sr₀.₂₅Cr₀.₅Mn₀.₅O₃ (LSCM). The possibility of
doping ruthenium into the surface of LSCM perovskite with the aid of a ball milling
process has been explored by VT-XRD. It has been demonstrated that the Ru catalysts
are able to dissolve into the lattice of LSCM perovskite on oxidation and exsolve as
nanoparticles upon reduction. In addition, the addition of a Ru catalyst into the LSCM
has been shown to improve the reducibility of the perovskite. Then the possibility of
incorporating a Pd catalyst into the surface of LSCM perovskite was investigated. It was
found that the Pd was unable to be doped into the LSCM perovskite due to the fact that
the structure of LSCM was not rigid enough to accommodate the deficiencies
introduced by Pd.
Catalytic tests of RWGS reactions were carried out with a few selected samples to
preliminarily investigate the influence of the catalyst coating on the performance of the
perovskite. It has been demonstrated that the catalyst coating technique was helpful in
improving the catalytic activity of the perovskites.
The possibility of incorporating the catalyst into the perovskite from the surface and
exsolving it afterwards depends on the properties of the host lattice and the catalyst
itself, such as the sizes of the host lattice and the catalyst cations, the stability of the
host lattice, etc. Through careful matching of the catalyst and the host lattice of the
perovskite, the incorporation of the catalyst into the perovskite surface can be a
promising method for decreasing the amount of catalyst required and therefore
developing cost-efficient electrode materials for PEMFC.
2016-11-30T00:00:00ZMao, DonglaiThe increasing energy requirements of mankind have stimulated the need to search for
renewable clean energy in order to protect the environment. Proton Exchange
Membrane Fuel Cells (PEMFC) are one of the most promising types of fuel cell among
the entire range of power generation devices. However, the high quantity of noble metal
catalysts used in PEMFCs hinders their commercialization due to the associated high
cost. Decreasing the amount of noble metal catalysts without sacrificing the
performance of the fuel cell is therefore desirable.
This thesis explores the possibility of modifying the perovskites with small quantities of
the most commonly used catalysts (Ni, Ru and Pd) on its surface, with the intention to
create a potentially cost-effective electrode material for PEMFC. The perovskites
employed in this thesis include two of the most commonly studied perovskite materials,
A-site deficient titanate based perovskites and LaCrO₃ based perovskites. The concept
of the modification method is to combine two of the most promising state of the art
methods, impregnation and exsolution, to improve the properties of the perovskite.
Instead of incorporating the catalyst in the whole lattice of the perovskite, the
impregnation method was used to dope the catalyst into the surface of the perovskite
only. The exsolution of the doped catalysts from the perovskite was then attempted. This
would theoretically produce nanoparticles with certain parts of its body anchored inside
the perovskite, thus avoiding the catalyst agglomeration problem which has been
reported for the normal impregnation method.
The A-site deficient titanate perovskite used to investigate surface doping modifications
is La₀.₄Sr₀.₄GaₓTi₁₋ₓO[sub](3-x/2) (LSGT). At first, a Ni catalyst was used to explore the
possibility and optimal experimental conditions for catalyst doping of the perovskite
from the surface and subsequent exsolution. The microstructure of the LSGT scaffold
was optimized for later experiments. The results from the Ni doping study were then
applied to the surface doping of Pd and Ru catalysts. This work demonstrates the
possibility of incorporating Ni, Ru and Pd catalysts into the surface of A-site deficient
titanate LSGT perovskite, using a pre-reduction treatment. The doped Ni and Pd
catalysts managed to exsolve to the surface of the perovskite as nanoparticles after reduction treatment. However, the Ru catalyst did not exsolve under the same
experimental conditions. It has been found that different catalysts require different
conditions to be able to dissolve into the perovskite for example, the heating atmosphere.
In addition, the mechanism of incorporating Pd into the A-site deficient titanate has
been studied, showing that the Pd is doped into the A-site deficient titanate in the form
of Pd²⁺ with square planar 4-fold coordination on the B-site.
The LaCrO₃ based perovskite employed for studying the incorporation of a catalyst into
the surface of the perovskite was La₀.₇₅Sr₀.₂₅Cr₀.₅Mn₀.₅O₃ (LSCM). The possibility of
doping ruthenium into the surface of LSCM perovskite with the aid of a ball milling
process has been explored by VT-XRD. It has been demonstrated that the Ru catalysts
are able to dissolve into the lattice of LSCM perovskite on oxidation and exsolve as
nanoparticles upon reduction. In addition, the addition of a Ru catalyst into the LSCM
has been shown to improve the reducibility of the perovskite. Then the possibility of
incorporating a Pd catalyst into the surface of LSCM perovskite was investigated. It was
found that the Pd was unable to be doped into the LSCM perovskite due to the fact that
the structure of LSCM was not rigid enough to accommodate the deficiencies
introduced by Pd.
Catalytic tests of RWGS reactions were carried out with a few selected samples to
preliminarily investigate the influence of the catalyst coating on the performance of the
perovskite. It has been demonstrated that the catalyst coating technique was helpful in
improving the catalytic activity of the perovskites.
The possibility of incorporating the catalyst into the perovskite from the surface and
exsolving it afterwards depends on the properties of the host lattice and the catalyst
itself, such as the sizes of the host lattice and the catalyst cations, the stability of the
host lattice, etc. Through careful matching of the catalyst and the host lattice of the
perovskite, the incorporation of the catalyst into the perovskite surface can be a
promising method for decreasing the amount of catalyst required and therefore
developing cost-efficient electrode materials for PEMFC.Title redactedMottram, Andrewhttps://hdl.handle.net/10023/167372019-05-02T13:14:01Z2016-11-30T00:00:00Z2016-11-30T00:00:00ZMottram, AndrewA study on GE₅O(PO₄)₆ : an oxide ion conductorTham, Markhttps://hdl.handle.net/10023/167312019-10-08T02:00:21Z2016-06-22T00:00:00ZThe work in this thesis concerns the synthesis, structural, and electrical analysis of the oxide ion
conductor Ge₅O(PO₄)₆ and related materials. The syntheses of the materials were performed using the traditional solid state method.
Variable temperature NPD was performed on Ge₅O(PO₄)₆ and the isostructural material, Si₅O(PO₄)₆.
For Ge₅O(PO₄)₆ this gave an insight into the oxygen conduction mechanism that occurs within the
material. NPD provided experimental evidence of the origin of the mobile oxide ion within the
‘excess’ oxygen structure and the local lattice distortions that mobilise and stabilise migrating oxide
ions. Fourier difference calculations were also performed to determine the location of interstitial oxide ions between the temperature range of 300-1073 K. In addition to this, the data was compared and contrasted to the Si₅O(PO₄)₆ NPD data to determine structural nuances between the two materials. A comparison of bond lengths and angles also showed there were local differences in the isostructural materials. The structural studies suggest that there was the formation of highly distorted SiO₆ when compared to the more ideal octahedral geometry of the GeO₆ subunit within Ge₅O(PO₄)₆.
Related materials are synthesised by the doping of cations such as Si, Sn, Ga, Al and Ti onto the Ge
site. A solid solution was established between the Ge and Si end members. This was evaluated by the changes in unit cell parameters with varying Si:Ge ratios. Sn-doped materials were also evaluated. An increase in unit cell size for the Sn-doped materials suggested that tin was successfully entering the structure. Electrical measurements were also performed. It showed that Ge₅O(PO₄)₆ has a low activation energy for oxide ion conduction. Whilst the dopants of the Ga, Al and Ti doped
compositions did not significantly improve oxide ion conducting properties, they gave an insight into
the structural changes that effect oxide ion conductivity.
2016-06-22T00:00:00ZTham, MarkThe work in this thesis concerns the synthesis, structural, and electrical analysis of the oxide ion
conductor Ge₅O(PO₄)₆ and related materials. The syntheses of the materials were performed using the traditional solid state method.
Variable temperature NPD was performed on Ge₅O(PO₄)₆ and the isostructural material, Si₅O(PO₄)₆.
For Ge₅O(PO₄)₆ this gave an insight into the oxygen conduction mechanism that occurs within the
material. NPD provided experimental evidence of the origin of the mobile oxide ion within the
‘excess’ oxygen structure and the local lattice distortions that mobilise and stabilise migrating oxide
ions. Fourier difference calculations were also performed to determine the location of interstitial oxide ions between the temperature range of 300-1073 K. In addition to this, the data was compared and contrasted to the Si₅O(PO₄)₆ NPD data to determine structural nuances between the two materials. A comparison of bond lengths and angles also showed there were local differences in the isostructural materials. The structural studies suggest that there was the formation of highly distorted SiO₆ when compared to the more ideal octahedral geometry of the GeO₆ subunit within Ge₅O(PO₄)₆.
Related materials are synthesised by the doping of cations such as Si, Sn, Ga, Al and Ti onto the Ge
site. A solid solution was established between the Ge and Si end members. This was evaluated by the changes in unit cell parameters with varying Si:Ge ratios. Sn-doped materials were also evaluated. An increase in unit cell size for the Sn-doped materials suggested that tin was successfully entering the structure. Electrical measurements were also performed. It showed that Ge₅O(PO₄)₆ has a low activation energy for oxide ion conduction. Whilst the dopants of the Ga, Al and Ti doped
compositions did not significantly improve oxide ion conducting properties, they gave an insight into
the structural changes that effect oxide ion conductivity.Investigation and development of cuprous delafossites for solid oxide fuel cell cathodesRoss, Iona Catherinehttps://hdl.handle.net/10023/167262022-10-26T02:09:27Z2017-06-21T00:00:00ZThe research into materials for use as cathode materials for solid oxide fuel cells (SOFC)
is ongoing, with many different avenues being investigated. Copper based delafossites
were studied for cathode side applications in SOFCs, as a novel and comparatively cheap
material. The aim was to identify suitable materials with appropriate electrical
conductivity, thermal, chemical and mechanical stability in air. Furthermore,
understanding the behaviour of the delafossites during the thermal oxidation to spinel
and copper oxide would be beneficial to further development of the materials.
The structure and properties of the copper based delafossites CuFeO₂, CuAlO₂ and CuCrO₂
were studied, alongside several doped compositions for each parent composition. The
electronic conductivity of the CuFeO₂ family was improved by doping fluorine into the
structure, with 1 atomic % doping producing ~3.8 S cm⁻¹ at 800 °C. However, as reported in literature the structure is vulnerable to oxidation at higher temperatures. In contrast,
CuAlO₂ was stable over the SOFC temperature range, and therefore had appropriate
thermal expansion coefficients (TEC) of ~11 x 10⁻⁶ K⁻¹, but relatively low electronic conductivity. CuCrO₂ compositions had good overall TECs, but aliovalent doping of Mg²⁺ improved the conductivity to ~17.1 S cm⁻¹ at 800°C for 2.5 atomic % doped CuCrO₂.
Neutron diffraction was utilised to study members of the solid solution CuFe₁₋ₓCrₓO₂ (x =
0, 0.25 and 0.5) during in-situ oxidation at high temperature. Points of positive scattering
density were identified within the CuFeO₂ structure, which were attributed to the location
of the intercalated oxygen ions before the transformation proceeded. Additionally, the
cation distribution between the tetrahedral and octahedral sites within the developing
spinel were characterised for x = 0, and partially for the x = 0.25 and 0.5 compositions
using complimentary XRD patterns.
Finally, magnesium doped CuCrO₂ delafossites were used in several different preliminary
symmetrical cells for study using electrochemical impedance spectroscopy (EIS). Pure
delafossite inks gave relatively large area specific resistance (ASR) values,
1.29 – 2.69 Ω cm² at 800 °C. It was attempted to improve upon these values through infiltration
of CeO₂ and through change in microstructure using composite type inks, without much success. Inks using CuCr₀.₈Fe₀.₂O₂ were also tested as both a single phase electrode and as a
composite type electrode. The pure delafossite electrode still had a large ASR value,
(~33.4 Ω cm² at 800 °C) while composite electrodes obtained much more respectable ASR
values ~0.75 Ω cm² at 800 °C.
2017-06-21T00:00:00ZRoss, Iona CatherineThe research into materials for use as cathode materials for solid oxide fuel cells (SOFC)
is ongoing, with many different avenues being investigated. Copper based delafossites
were studied for cathode side applications in SOFCs, as a novel and comparatively cheap
material. The aim was to identify suitable materials with appropriate electrical
conductivity, thermal, chemical and mechanical stability in air. Furthermore,
understanding the behaviour of the delafossites during the thermal oxidation to spinel
and copper oxide would be beneficial to further development of the materials.
The structure and properties of the copper based delafossites CuFeO₂, CuAlO₂ and CuCrO₂
were studied, alongside several doped compositions for each parent composition. The
electronic conductivity of the CuFeO₂ family was improved by doping fluorine into the
structure, with 1 atomic % doping producing ~3.8 S cm⁻¹ at 800 °C. However, as reported in literature the structure is vulnerable to oxidation at higher temperatures. In contrast,
CuAlO₂ was stable over the SOFC temperature range, and therefore had appropriate
thermal expansion coefficients (TEC) of ~11 x 10⁻⁶ K⁻¹, but relatively low electronic conductivity. CuCrO₂ compositions had good overall TECs, but aliovalent doping of Mg²⁺ improved the conductivity to ~17.1 S cm⁻¹ at 800°C for 2.5 atomic % doped CuCrO₂.
Neutron diffraction was utilised to study members of the solid solution CuFe₁₋ₓCrₓO₂ (x =
0, 0.25 and 0.5) during in-situ oxidation at high temperature. Points of positive scattering
density were identified within the CuFeO₂ structure, which were attributed to the location
of the intercalated oxygen ions before the transformation proceeded. Additionally, the
cation distribution between the tetrahedral and octahedral sites within the developing
spinel were characterised for x = 0, and partially for the x = 0.25 and 0.5 compositions
using complimentary XRD patterns.
Finally, magnesium doped CuCrO₂ delafossites were used in several different preliminary
symmetrical cells for study using electrochemical impedance spectroscopy (EIS). Pure
delafossite inks gave relatively large area specific resistance (ASR) values,
1.29 – 2.69 Ω cm² at 800 °C. It was attempted to improve upon these values through infiltration
of CeO₂ and through change in microstructure using composite type inks, without much success. Inks using CuCr₀.₈Fe₀.₂O₂ were also tested as both a single phase electrode and as a
composite type electrode. The pure delafossite electrode still had a large ASR value,
(~33.4 Ω cm² at 800 °C) while composite electrodes obtained much more respectable ASR
values ~0.75 Ω cm² at 800 °C.Isothiourea-catalysed enantioselective [2,3]-sigmatropic rearrangements of allylic ammonium ylides : synthetic and mechanistic studiesWest, Thomas H.https://hdl.handle.net/10023/166752019-03-29T11:23:29Z2017-06-21T00:00:00ZThe research in this thesis describes the development of an isothiourea-catalysed enantioselective [2,3]-rearrangement of allylic ammonium ylides, subsequent mechanistic and collaborative computational
studies and the its application to the enantioselective synthesis of free α-amino esters.
Chapter 1 aims to place this work in the context of the previous literature, highlighting a range of
stereoselective [2,3]-rearrangements of allylic ammonium ylides. Examples of catalytic stereoselective
[2,3]-rearrangement of allylic ammonium ylides as well as state-of-the-art examples of organocatalytic
enantioselective variants of the related [2,3]-Wittig rearrangement are discussed. The aims of this
research project are also set out.
Chapter 2 describes the discovery and optimisation of the isothiourea-catalysed [2,3]-rearrangement of
4-nitrophenyl ester quaternary ammonium salts (either isolated or generated in situ) to give a range of
syn-α-amino acid derivatives in excellent yields (33-89%) and stereocontrol (up to >95:5 dr and >99%
ee). This represents the first catalytic enantioselective variant of a [2,3]-rearrangement of allylic
ammonium ylides.
Chapter 3 describes mechanistic studies. Reaction kinetic analysis by ¹⁹F NMR has allowed reaction
profiles to be built up, orders of each component to be determined and catalyst resting state to be probed.
A catalytic intermediate has been observed; its constitution was proved unambiguously by
¹³C and ¹⁵N isotopic labelling. Isotopic entrainment has proved the observed intermediate to be on-cycle and
productive towards catalysis. Competition kinetic isotope effects have provided detailed insight into the
[2,3]-rearrangement step of the process. The effect of HOBt upon stereocontrol and the resting state of
the catalyst have been probed through in situ
¹⁹F NMR. Crossover experiments have given detailed
insight into the reversibility of each of the proposed catalytic steps. Collaborative computational work
has elucidated the origins of stereocontrol and has supported the experimentally proposed mechanism.
Chapter 4 describes the application of this methodology to the enantioselective synthesis of free α-amino esters via [2,3]-rearrangement of N,N-diallyl allylic ammonium ylides. Enantio- and
chemoselective [2,3]-rearrangement gave a range of N,N-diallyl α-amino esters, which could be readily
selectively mono- or bis-N-allyl deprotected. Bis-N-allyl deprotection gave a range of enantioenriched
free α-amino esters. Selective mono-N-allyl deprotection was employed in the synthesis of a
functionalised piperidine motif.
Chapter 5 summarises the work outlined in this thesis and draws conclusions, as well as giving insight
into potential future projects within the area.
2017-06-21T00:00:00ZWest, Thomas H.The research in this thesis describes the development of an isothiourea-catalysed enantioselective [2,3]-rearrangement of allylic ammonium ylides, subsequent mechanistic and collaborative computational
studies and the its application to the enantioselective synthesis of free α-amino esters.
Chapter 1 aims to place this work in the context of the previous literature, highlighting a range of
stereoselective [2,3]-rearrangements of allylic ammonium ylides. Examples of catalytic stereoselective
[2,3]-rearrangement of allylic ammonium ylides as well as state-of-the-art examples of organocatalytic
enantioselective variants of the related [2,3]-Wittig rearrangement are discussed. The aims of this
research project are also set out.
Chapter 2 describes the discovery and optimisation of the isothiourea-catalysed [2,3]-rearrangement of
4-nitrophenyl ester quaternary ammonium salts (either isolated or generated in situ) to give a range of
syn-α-amino acid derivatives in excellent yields (33-89%) and stereocontrol (up to >95:5 dr and >99%
ee). This represents the first catalytic enantioselective variant of a [2,3]-rearrangement of allylic
ammonium ylides.
Chapter 3 describes mechanistic studies. Reaction kinetic analysis by ¹⁹F NMR has allowed reaction
profiles to be built up, orders of each component to be determined and catalyst resting state to be probed.
A catalytic intermediate has been observed; its constitution was proved unambiguously by
¹³C and ¹⁵N isotopic labelling. Isotopic entrainment has proved the observed intermediate to be on-cycle and
productive towards catalysis. Competition kinetic isotope effects have provided detailed insight into the
[2,3]-rearrangement step of the process. The effect of HOBt upon stereocontrol and the resting state of
the catalyst have been probed through in situ
¹⁹F NMR. Crossover experiments have given detailed
insight into the reversibility of each of the proposed catalytic steps. Collaborative computational work
has elucidated the origins of stereocontrol and has supported the experimentally proposed mechanism.
Chapter 4 describes the application of this methodology to the enantioselective synthesis of free α-amino esters via [2,3]-rearrangement of N,N-diallyl allylic ammonium ylides. Enantio- and
chemoselective [2,3]-rearrangement gave a range of N,N-diallyl α-amino esters, which could be readily
selectively mono- or bis-N-allyl deprotected. Bis-N-allyl deprotection gave a range of enantioenriched
free α-amino esters. Selective mono-N-allyl deprotection was employed in the synthesis of a
functionalised piperidine motif.
Chapter 5 summarises the work outlined in this thesis and draws conclusions, as well as giving insight
into potential future projects within the area.Studies of enzymes relevant to the biotransformation of fluorinated natural productsBandaranayaka, Nouchalihttps://hdl.handle.net/10023/166192021-07-27T02:00:52Z2018-06-27T00:00:00ZThis thesis is focused on enzymes related to the biosynthetic pathway of fluorometabolite
synthesis in S.cattleya. The first native fluorinating enzyme, fluorinase was isolated from a
soil bacterium, Streptomyces cattleya in 2002. Fluorinase catalyses the reaction between
S-adenosyl-L-methionine and inorganic fluoride to produce 5′-fluoro-5-deoxyadenosine (5′FDA) and L-methionine as the first step of the fluorometabolite biosynthetic pathway.
Fluorinase has been an attractive tool for incorporating ¹⁸F into a limited number of
substrates for applications in positron emission tomography (PET). This thesis describes
a preparation of the fluorinase for PET, and then the production of [¹⁸F]-5-fluoro-5-deoxy-
D-ribose ([¹⁸F]-FDR) via fluorinase mediated enzymatic synthesis. S. cattleya fluorinase
has been the only fluorinase identified until recently when four more fluorinases have been
identified by gene mining. These new fluorinase isolations are presented in the thesis. In
addition this thesis describes the crystallisation of 5-deoxy-5-fluoro-D-ribose 1-phosphate
isomerase (FDRPi), an aldose-ketose isomerase involved in the biosynthetic pathway of
fluorometabolite biosynthesis in S.cattleya.
Chapter 1 presents the background of this research focusing on the enzymes involved in
the biosynthesis of the two fluorometabolites; fluoroacetate and 4-fluoro-L-threonine,
produced by S.cattleya.
Chapter 2 describes the development of a practical, ‘off the shelf’ method of producing
[¹⁸F]-FDR in remote radiochemistry labs. Enzymes, fluorinase and nucleoside hydrolase,
isolated from Trypanosoma vivax (TvNH) were freeze-dried in their buffers to produce a
shelf stable, potentially portable kit, where rehydration on site, would then provide catalysts
on demand for radiochemical synthesis of [¹⁸F]-FDR. This kit was practical enough to
conduct a successful tumour imaging using a mouse model at Vrije University in
Amsterdam.
Chapter 3 presents the over-expression and purification of fluorinase gene product (FLA1)
from a newly isolated soil bacterium Streptomyces sp. MA37. The gene was identified by
sequence mining of the Streptomyces sp. MA37 genome. This fluorinase shared high
homology to S.cattleya fluorinase and the flA1 was cloned into E.coli, over-expressed,
purified, assayed and shown to be a fluorinase. The FlA1 was also crystallized and the
structure solved.
Chapter 4 describes the successful crystallisation of FDRPi, an enzyme involved in the
fluorometabolite synthesis of S. cattleya. The FDRPi was over expressed, purified,
crystallised and the structure was solved.
2018-06-27T00:00:00ZBandaranayaka, NouchaliThis thesis is focused on enzymes related to the biosynthetic pathway of fluorometabolite
synthesis in S.cattleya. The first native fluorinating enzyme, fluorinase was isolated from a
soil bacterium, Streptomyces cattleya in 2002. Fluorinase catalyses the reaction between
S-adenosyl-L-methionine and inorganic fluoride to produce 5′-fluoro-5-deoxyadenosine (5′FDA) and L-methionine as the first step of the fluorometabolite biosynthetic pathway.
Fluorinase has been an attractive tool for incorporating ¹⁸F into a limited number of
substrates for applications in positron emission tomography (PET). This thesis describes
a preparation of the fluorinase for PET, and then the production of [¹⁸F]-5-fluoro-5-deoxy-
D-ribose ([¹⁸F]-FDR) via fluorinase mediated enzymatic synthesis. S. cattleya fluorinase
has been the only fluorinase identified until recently when four more fluorinases have been
identified by gene mining. These new fluorinase isolations are presented in the thesis. In
addition this thesis describes the crystallisation of 5-deoxy-5-fluoro-D-ribose 1-phosphate
isomerase (FDRPi), an aldose-ketose isomerase involved in the biosynthetic pathway of
fluorometabolite biosynthesis in S.cattleya.
Chapter 1 presents the background of this research focusing on the enzymes involved in
the biosynthesis of the two fluorometabolites; fluoroacetate and 4-fluoro-L-threonine,
produced by S.cattleya.
Chapter 2 describes the development of a practical, ‘off the shelf’ method of producing
[¹⁸F]-FDR in remote radiochemistry labs. Enzymes, fluorinase and nucleoside hydrolase,
isolated from Trypanosoma vivax (TvNH) were freeze-dried in their buffers to produce a
shelf stable, potentially portable kit, where rehydration on site, would then provide catalysts
on demand for radiochemical synthesis of [¹⁸F]-FDR. This kit was practical enough to
conduct a successful tumour imaging using a mouse model at Vrije University in
Amsterdam.
Chapter 3 presents the over-expression and purification of fluorinase gene product (FLA1)
from a newly isolated soil bacterium Streptomyces sp. MA37. The gene was identified by
sequence mining of the Streptomyces sp. MA37 genome. This fluorinase shared high
homology to S.cattleya fluorinase and the flA1 was cloned into E.coli, over-expressed,
purified, assayed and shown to be a fluorinase. The FlA1 was also crystallized and the
structure solved.
Chapter 4 describes the successful crystallisation of FDRPi, an enzyme involved in the
fluorometabolite synthesis of S. cattleya. The FDRPi was over expressed, purified,
crystallised and the structure was solved.A computational investigation of oxygen storage and migration in energy materialsMcInnes, Gregor Davidhttps://hdl.handle.net/10023/165782023-04-20T11:17:11Z2018-06-27T00:00:00ZThis thesis describes a computational investigation into the oxygen storage material copper doped ceria and electrolyte material Ge₅O(PO₄)₆ for use in Solid Oxide Fuel Cells.
In Chapter 1, a background on fuel cells is given along with explanations and examples of different oxygen migration mechanisms. After this, a background on the materials Ge₅O(PO₄)₆ and copper doped ceria is given,.
Chapter 2 presents background on the computational techniques used. This includes discussion of first principles techniques and an explanation of the CALPHAD method.
Chapter 3 presents the detailed results of the investigation into copper doped ceria. This investigation concentrated on the stability of copper ceria as well as on the ionic makeup of the material. The main findings of this investigation are that Cu¹⁺ and Cu²⁺ ions can be doped into ceria with the maximum doping reaching 0.09 mole fraction Cu.
In Chapter 4 the details of the computation investigation into Ge₅O(PO₄)₆ are given. This investigation looked at the possible oxygen migration pathways. From the findings of this investigation we were able to rule out several different possible pathways through the structure.
Chapter 5 gives a brief overview of the findings of each of the projects and provides recommendations on future work that may be carried out on each of the systems.
Appendix A provides supplementary data on the copper doped ceria project, specifically the coding of the thermodynamic database created during the project.
2018-06-27T00:00:00ZMcInnes, Gregor DavidThis thesis describes a computational investigation into the oxygen storage material copper doped ceria and electrolyte material Ge₅O(PO₄)₆ for use in Solid Oxide Fuel Cells.
In Chapter 1, a background on fuel cells is given along with explanations and examples of different oxygen migration mechanisms. After this, a background on the materials Ge₅O(PO₄)₆ and copper doped ceria is given,.
Chapter 2 presents background on the computational techniques used. This includes discussion of first principles techniques and an explanation of the CALPHAD method.
Chapter 3 presents the detailed results of the investigation into copper doped ceria. This investigation concentrated on the stability of copper ceria as well as on the ionic makeup of the material. The main findings of this investigation are that Cu¹⁺ and Cu²⁺ ions can be doped into ceria with the maximum doping reaching 0.09 mole fraction Cu.
In Chapter 4 the details of the computation investigation into Ge₅O(PO₄)₆ are given. This investigation looked at the possible oxygen migration pathways. From the findings of this investigation we were able to rule out several different possible pathways through the structure.
Chapter 5 gives a brief overview of the findings of each of the projects and provides recommendations on future work that may be carried out on each of the systems.
Appendix A provides supplementary data on the copper doped ceria project, specifically the coding of the thermodynamic database created during the project.Crystal structure and phase transitions in various functional perovskitesDixon, Charlotte A. L.https://hdl.handle.net/10023/165722020-04-01T02:02:23Z2018-06-27T00:00:00ZThere has been specific interest over the past decade in the discovery and
development of new piezoelectric and ferroelectric materials for the use in
functional devices, specifically with the aim of replacing the widespread use of
PbZrₓTi₁₋ₓO₃.
The work detailed in this thesis focuses on the structural characterisation and
thermal behaviour of several perovskites possessing interesting physical
characteristics, such as ferroelectricity or magnetism. Structural evolution and
phase behaviour is characterised using Rietveld refinement techniques on high
resolution powder neutron diffraction data. Additional analytical techniques such
as symmetry mode analysis, permittivity measurements and second harmonic
generation measurements are also often exploited.
The work on the LiₓNa₁₋ₓNbO₃ system demonstrated a susceptibility to softening
of the T₄ octahedral tilt mode up to a composition of at least x = 0.12, indicating
that the LNN-X solid solution could yield a number of unique perovskite structures.
A rationale for how this T₄ mode varies across the composition range is offered.
The higher doped composition at a value of x = 0.20, displays even more intriguing
structural behaviour with the adoption of not one but two variants of the very rare
a⁺a⁺c⁻ Glazer tilt system.
A detailed bond length/bond angle analysis as a function of temperature is used
to rationalise the nature of the octahedral distortion that drives the c > a crossover
in the rare earth orthoferrite LaFeO₃. Symmetry mode analysis is exploited to
assist in the structural comparison to the related compound Bi₀.₅La₀.₅FeO₃,
highlighting the anomalous behaviour it exhibits as a result of magnetoelectric
coupling effects.
The nature of the paraelectric – ferroelectric transition in the layered perovskitelike
Dion Jacobson phase, CsBi₀.₆La₀.₄Nb₂O₇ is identified as a direct “avalanche”
type transition, making it an example of a hybrid improper ferroelectric.
Ferroelectricity in this case does not occur as a result of traditional second-order
Jahn-Teller distortions, but is achieved via a mechanism known as trilinear
coupling. Experimental analysis is important in understanding the intricacies of
this trilinear coupling mechanism. Symmetry mode analysis of CsBi₀.₆La₀.₄Nb₂O₇ shows that two zone boundary primary order parameters (M₂⁺ and M₅⁻) associated
with octahedral tilting condense simultaneously, and couple to a zone centre
ferroelectric distortion mode (Γ₄⁻). The similar temperature dependency for the
two octahedral tilt modes excludes the presence of an intermediary phase,
suggesting that the trilinear coupling in this layered phase is strong.
Detailed structural characterisations such as those highlighted in this thesis are of
fundamental importance as they can identify new design-led approaches to
functional materials.
2018-06-27T00:00:00ZDixon, Charlotte A. L.There has been specific interest over the past decade in the discovery and
development of new piezoelectric and ferroelectric materials for the use in
functional devices, specifically with the aim of replacing the widespread use of
PbZrₓTi₁₋ₓO₃.
The work detailed in this thesis focuses on the structural characterisation and
thermal behaviour of several perovskites possessing interesting physical
characteristics, such as ferroelectricity or magnetism. Structural evolution and
phase behaviour is characterised using Rietveld refinement techniques on high
resolution powder neutron diffraction data. Additional analytical techniques such
as symmetry mode analysis, permittivity measurements and second harmonic
generation measurements are also often exploited.
The work on the LiₓNa₁₋ₓNbO₃ system demonstrated a susceptibility to softening
of the T₄ octahedral tilt mode up to a composition of at least x = 0.12, indicating
that the LNN-X solid solution could yield a number of unique perovskite structures.
A rationale for how this T₄ mode varies across the composition range is offered.
The higher doped composition at a value of x = 0.20, displays even more intriguing
structural behaviour with the adoption of not one but two variants of the very rare
a⁺a⁺c⁻ Glazer tilt system.
A detailed bond length/bond angle analysis as a function of temperature is used
to rationalise the nature of the octahedral distortion that drives the c > a crossover
in the rare earth orthoferrite LaFeO₃. Symmetry mode analysis is exploited to
assist in the structural comparison to the related compound Bi₀.₅La₀.₅FeO₃,
highlighting the anomalous behaviour it exhibits as a result of magnetoelectric
coupling effects.
The nature of the paraelectric – ferroelectric transition in the layered perovskitelike
Dion Jacobson phase, CsBi₀.₆La₀.₄Nb₂O₇ is identified as a direct “avalanche”
type transition, making it an example of a hybrid improper ferroelectric.
Ferroelectricity in this case does not occur as a result of traditional second-order
Jahn-Teller distortions, but is achieved via a mechanism known as trilinear
coupling. Experimental analysis is important in understanding the intricacies of
this trilinear coupling mechanism. Symmetry mode analysis of CsBi₀.₆La₀.₄Nb₂O₇ shows that two zone boundary primary order parameters (M₂⁺ and M₅⁻) associated
with octahedral tilting condense simultaneously, and couple to a zone centre
ferroelectric distortion mode (Γ₄⁻). The similar temperature dependency for the
two octahedral tilt modes excludes the presence of an intermediary phase,
suggesting that the trilinear coupling in this layered phase is strong.
Detailed structural characterisations such as those highlighted in this thesis are of
fundamental importance as they can identify new design-led approaches to
functional materials.Title redactedOrsi, Angelica Fortunatahttps://hdl.handle.net/10023/165652023-11-13T13:35:32Z2018-06-27T00:00:00Z2018-06-27T00:00:00ZOrsi, Angelica FortunataVaried studies on bioactive natural products, their synthesis, biosynthesis and activityBown, Rhea Tamarhttps://hdl.handle.net/10023/165602019-08-15T09:32:04Z2018-06-27T00:00:00Z2018-06-27T00:00:00ZBown, Rhea TamarControl of water and toxic gas adsorption in metal-organic frameworksMcPherson, Matthew Josephhttps://hdl.handle.net/10023/164892023-04-27T10:55:45Z2016-06-22T00:00:00ZThe research presented in this thesis aims to determine the effectiveness of the uptake of toxic gases by several MOFs for future use in gas-mask cartridges, and to attempt to compensate for any deficiencies they show in “real-world” conditions. The main findings of this thesis confirm that MOFs are suitable candidates for the use in respirator cartridge materials and provide high capacity for adsorption of toxic gases like ammonia and STAM-1 in particular showed an impressive improvement in humid conditions, which normally decrease the performance of MOFs made from the same materials, such as HKUST-1. STAM-1’s improved performance in humid conditions is attributed to the structural shift it displays upon dehydration and rehydration and this was shown to be the case in a structural analogue, CuEtOip, which was synthesised in the author’s research group. This analogue was analysed using a combination of single crystal XRD and solid state MAS-NMR, both of which showed the structural change occurring and displays similar gas sorption behaviours, suggesting that this mechanism is the source of STAM-1’s improved performance in humid conditions. This thesis also examines the “Armoured MOF” process and investigates the transferability of the process of deposition of mesoporous silica onto MOFs with vastly different properties and synthetic methods compared to those published in the original publication. Alongside this, attempts to protect MOFs using mesoporous silicates were investigated for their viability.
2016-06-22T00:00:00ZMcPherson, Matthew JosephThe research presented in this thesis aims to determine the effectiveness of the uptake of toxic gases by several MOFs for future use in gas-mask cartridges, and to attempt to compensate for any deficiencies they show in “real-world” conditions. The main findings of this thesis confirm that MOFs are suitable candidates for the use in respirator cartridge materials and provide high capacity for adsorption of toxic gases like ammonia and STAM-1 in particular showed an impressive improvement in humid conditions, which normally decrease the performance of MOFs made from the same materials, such as HKUST-1. STAM-1’s improved performance in humid conditions is attributed to the structural shift it displays upon dehydration and rehydration and this was shown to be the case in a structural analogue, CuEtOip, which was synthesised in the author’s research group. This analogue was analysed using a combination of single crystal XRD and solid state MAS-NMR, both of which showed the structural change occurring and displays similar gas sorption behaviours, suggesting that this mechanism is the source of STAM-1’s improved performance in humid conditions. This thesis also examines the “Armoured MOF” process and investigates the transferability of the process of deposition of mesoporous silica onto MOFs with vastly different properties and synthetic methods compared to those published in the original publication. Alongside this, attempts to protect MOFs using mesoporous silicates were investigated for their viability.Isothiourea-mediated acylative kinetic resolution of heterocyclic and acyclic tertiary alcoholsSmith, Samuel M.https://hdl.handle.net/10023/164702023-06-13T02:02:25Z2018-09-27T00:00:00ZThis thesis describes the isothiourea-catalyzed acylative kinetic resolution (KR) of heterocyclic and acyclic tertiary alcohols. The protocols developed for the resolution of these challenging substrates provide access to biologically-relevant small molecules in highly enantioenriched form.
Chapter 2 describes the acylative KR of a range of 3-hydroxy-3-substituted oxindole substrates, bearing up to three potential recognition motifs at the stereogenic tertiary carbinol centre. Experimental and computational studies have identified a C=O•••isothiouronium interaction as the key stabilizing interaction for efficient enantiodiscrimination. This interaction was exploited in reactions using the isothiourea catalyst, (2S,3R)-HyperBTM, generally at low catalyst loadings (1 mol %) and isobutyric or acetic anhydride as acylating agent, enabling s values of up to > 200 (30 examples).
Chapter 3 focuses on extending the KR protocol to 3-hydroxypyrrolidinone substrates, which do not possess the benzannulation present in the core structure of the substrates resolved in Chapter 2. Re-optimization of the previous KR conditions found (2S,3R)-HyperBTM (2 mol %) as catalyst, acetic anhydride (0.7 equiv.) as acylating agent, in toluene at 0 °C as optimal, enabling s values of up to > 200 to be obtained (27 examples). Variation of the substitution patterns and electronic nature of the pyrrolidinone substrates were investigated, including extension of the protocol for the KR of α-hydroxy-β- and δ-lactam derivatives.
Chapter 4 investigates the complete removal of the cyclic structure of the substrate through the KR of a range of acyclic tertiary alcohols. No acylation was observed for acyclic α-hydroxy amides, and poor reactivity and selectivity was observed for α-hydroxy ketones and α-hydroxy phosphonates. However, acylation is readily achieved when using α-hydroxy esters, and this chapter focuses on the KR of these substrates. Optimization studies found (2S,3R)-HyperBTM (5 mol %) as catalyst, isobutyric anhydride (2.0 equiv.) as acylating agent in diethyl ether at rt as optimal, enabling s values of up to 140 (21 examples). The protocol is currently limited to the KR of α-hydroxy esters bearing an aromatic substituent and a methyl group at the carbinol stereocentre, with alkyl substituents larger than methyl leading to either low conversion or selectivity.
2018-09-27T00:00:00ZSmith, Samuel M.This thesis describes the isothiourea-catalyzed acylative kinetic resolution (KR) of heterocyclic and acyclic tertiary alcohols. The protocols developed for the resolution of these challenging substrates provide access to biologically-relevant small molecules in highly enantioenriched form.
Chapter 2 describes the acylative KR of a range of 3-hydroxy-3-substituted oxindole substrates, bearing up to three potential recognition motifs at the stereogenic tertiary carbinol centre. Experimental and computational studies have identified a C=O•••isothiouronium interaction as the key stabilizing interaction for efficient enantiodiscrimination. This interaction was exploited in reactions using the isothiourea catalyst, (2S,3R)-HyperBTM, generally at low catalyst loadings (1 mol %) and isobutyric or acetic anhydride as acylating agent, enabling s values of up to > 200 (30 examples).
Chapter 3 focuses on extending the KR protocol to 3-hydroxypyrrolidinone substrates, which do not possess the benzannulation present in the core structure of the substrates resolved in Chapter 2. Re-optimization of the previous KR conditions found (2S,3R)-HyperBTM (2 mol %) as catalyst, acetic anhydride (0.7 equiv.) as acylating agent, in toluene at 0 °C as optimal, enabling s values of up to > 200 to be obtained (27 examples). Variation of the substitution patterns and electronic nature of the pyrrolidinone substrates were investigated, including extension of the protocol for the KR of α-hydroxy-β- and δ-lactam derivatives.
Chapter 4 investigates the complete removal of the cyclic structure of the substrate through the KR of a range of acyclic tertiary alcohols. No acylation was observed for acyclic α-hydroxy amides, and poor reactivity and selectivity was observed for α-hydroxy ketones and α-hydroxy phosphonates. However, acylation is readily achieved when using α-hydroxy esters, and this chapter focuses on the KR of these substrates. Optimization studies found (2S,3R)-HyperBTM (5 mol %) as catalyst, isobutyric anhydride (2.0 equiv.) as acylating agent in diethyl ether at rt as optimal, enabling s values of up to 140 (21 examples). The protocol is currently limited to the KR of α-hydroxy esters bearing an aromatic substituent and a methyl group at the carbinol stereocentre, with alkyl substituents larger than methyl leading to either low conversion or selectivity.Conversion of renewable feedstocks into polymer precursors and pharmaceutical drugsShi, Yipinghttps://hdl.handle.net/10023/164612019-07-16T14:55:55Z2018-12-06T00:00:00ZFossils fuels are highly demanded in everyday life domestically or industrially. Fossil fuels are finite resources and they are rapidly depleting, as such alternative renewable feedstocks are sought to replace fossil fuels. Tall oil from paper processing and cashew nut shell liquid from the cashew nut industry are the two major renewable sources we studied, they are both waste byproducts, and have the potential to be converted into value-added materials.
Tall oil from the paper industry mainly contained tall oil fatty acid, and under isomerising methoxycarbonylation with palladium catalyst, dimethyl 1,19-dimethyl nonadecanedioate can be obtained. This difunctional ester, dimethyl 1,19-dimethyl nonadecanedioate, is converted to diols, secondary and primary diamines by a hydrogenation reaction with ruthenium complexes of 1,1,1-tris(diphenylphosphinometyl)ethane (triphos) as catalysts in the presence of water, amine or aqueous ammonia respectively. In the case of aqueous ammonia it is necessary to use a two step reaction via diol to obtain 1,19-diaminononadecane. Diesters, diols and diamines are useful precursors for the synthesis of polyesters and polyamides. Difunctional substrates with 8-19 carbon chains are all tolerated under the reaction conditions and are successfully converted to the corresponding diols and diamines in high yields.
Under similar hydrogenation conditions with the same ruthenium catalyst, cyclic products were predominantly produced with decreased chain length. N-heterocycles, which are important building blocks for the synthesis of drug molecules, were formed from the hydrogenation of diesters with 4-7 carbon chains in the presence of an amine. Another polymer precursor, ε-caprolactam, which is the precursor for Nylon 6, is obtained in a reasonable yield from both adipic acid and adipate esters together with aqueous ammonia in the presence of ruthenium catalyst.
Cashew nut shell liquid was also converted into useful medical drugs, such as norfenefrine, rac-phenylephrine, etilefrine and fenoprofene in reasonable yields. Most of these drug molecules have been formed from 3-vinylphenol by catalytic hydroxyamination followed by methylation or ethylation. 3-Vinylphenol was synthesised from cardanol by ethenolysis to 3-non-8-enylphenol followed by isomerising ethenolysis, whilst the N-alkylation reactions used methyl or ethyl triflate to avoid dialkylation. Fenoprofene was formed by firstly O-phenylating cardanol then ethenolysis followed by isomerising ethenolysis to form 1-phenoxy-3-vinylbenzene. Methoxycarbonyation followed by hydrolysis formed the final product in good yield.
Our methods start from renewable waste materials and avoid unpleasant reagents in the original stoichiometric synthesis of those drugs, for example, cyanide is no longer essential for the synthesis of fenoprofene.
2018-12-06T00:00:00ZShi, YipingFossils fuels are highly demanded in everyday life domestically or industrially. Fossil fuels are finite resources and they are rapidly depleting, as such alternative renewable feedstocks are sought to replace fossil fuels. Tall oil from paper processing and cashew nut shell liquid from the cashew nut industry are the two major renewable sources we studied, they are both waste byproducts, and have the potential to be converted into value-added materials.
Tall oil from the paper industry mainly contained tall oil fatty acid, and under isomerising methoxycarbonylation with palladium catalyst, dimethyl 1,19-dimethyl nonadecanedioate can be obtained. This difunctional ester, dimethyl 1,19-dimethyl nonadecanedioate, is converted to diols, secondary and primary diamines by a hydrogenation reaction with ruthenium complexes of 1,1,1-tris(diphenylphosphinometyl)ethane (triphos) as catalysts in the presence of water, amine or aqueous ammonia respectively. In the case of aqueous ammonia it is necessary to use a two step reaction via diol to obtain 1,19-diaminononadecane. Diesters, diols and diamines are useful precursors for the synthesis of polyesters and polyamides. Difunctional substrates with 8-19 carbon chains are all tolerated under the reaction conditions and are successfully converted to the corresponding diols and diamines in high yields.
Under similar hydrogenation conditions with the same ruthenium catalyst, cyclic products were predominantly produced with decreased chain length. N-heterocycles, which are important building blocks for the synthesis of drug molecules, were formed from the hydrogenation of diesters with 4-7 carbon chains in the presence of an amine. Another polymer precursor, ε-caprolactam, which is the precursor for Nylon 6, is obtained in a reasonable yield from both adipic acid and adipate esters together with aqueous ammonia in the presence of ruthenium catalyst.
Cashew nut shell liquid was also converted into useful medical drugs, such as norfenefrine, rac-phenylephrine, etilefrine and fenoprofene in reasonable yields. Most of these drug molecules have been formed from 3-vinylphenol by catalytic hydroxyamination followed by methylation or ethylation. 3-Vinylphenol was synthesised from cardanol by ethenolysis to 3-non-8-enylphenol followed by isomerising ethenolysis, whilst the N-alkylation reactions used methyl or ethyl triflate to avoid dialkylation. Fenoprofene was formed by firstly O-phenylating cardanol then ethenolysis followed by isomerising ethenolysis to form 1-phenoxy-3-vinylbenzene. Methoxycarbonyation followed by hydrolysis formed the final product in good yield.
Our methods start from renewable waste materials and avoid unpleasant reagents in the original stoichiometric synthesis of those drugs, for example, cyanide is no longer essential for the synthesis of fenoprofene.Title redactedBlack, Nicholashttps://hdl.handle.net/10023/163382019-06-11T13:42:05Z2018-03-16T00:00:00Z2018-03-16T00:00:00ZBlack, NicholasUse of the Claisen rearrangement in natural product synthesisNeal, Andrewhttps://hdl.handle.net/10023/161292024-01-22T11:11:55Z2018-01-01T00:00:00Z2018-01-01T00:00:00ZNeal, AndrewSynthesis, characterisation and optoelectronic properties of phosphorescent iridium complexes : from five to six-membered ring chelatesHierlinger, Claushttps://hdl.handle.net/10023/161262019-10-15T02:04:35Z2018-12-06T00:00:00ZHere, the design, synthesis and characterisation and the optoelectronic properties of Ir(III) complexes for application in nonlinear optical and electroluminescent devices are described. The type of complexes varies from those of the form [Ir(C^N)₂(N^N)]+ with conjugated and nonconjugated ligands (where C^N = cyclometalating ligand and N^N = neutral ligand) to those of the form [Ir(C^N^C)(N^N)Cl] (where C^N^C = tridentate tripod ligand).
Chapter 1 gives an introduction into photophysics occurring in transition metal complexes and possible applications in visual displays. The background of nonlinear optical (NLO) properties and the use of transition metal complexes as NLO chromophores is described.
In Chapter 2, the impact of the use of sterically congested cyclometalating ligands on the photoluminescence properties of cationic iridium(III) complexes and their performance in light-emitting electrochemical cells is investigated.
Chapter 3 explores the use of electron donors on the cyclometalating ligand towards modulating the NLO properties of the complexes. Combining strongly electron-donating substituents on the C^N ligand and electron-accepting substituents on the N^N ligand results in strong NLO activity.
Chapter 4 summarises a new series of cationic iridium(III) complexes bearing benzylpyridinato as cyclometalating ligands. The methylene spacer in the C^N ligands provides flexibility, resulting in two conformers. NMR studies combined with density functional theory (DFT) studies show how the fluxional behaviour is influenced by the choice of the ancillary ligand.
In Chapter 5, Ir(III) complexes bearing an unusual nonconjugated bis(six-membered) tridentate tripod ligand of the form [Ir(C^N^C)(N^N)Cl] are introduced. Depending on the substitutions of the C^N^C ligand phosphorescence ranging from yellow to red was obtained. Substitution of the N^N results in a panchromatic NIR dye, suitable for DSSC applications.
In Chapter 6, the concept of a nonconjugated ligand was expanded to the N^N ligand. Blue-green and sky-blue emission was obtained, demonstrating a strategy to successfully tune the emission to the blue.
2018-12-06T00:00:00ZHierlinger, ClausHere, the design, synthesis and characterisation and the optoelectronic properties of Ir(III) complexes for application in nonlinear optical and electroluminescent devices are described. The type of complexes varies from those of the form [Ir(C^N)₂(N^N)]+ with conjugated and nonconjugated ligands (where C^N = cyclometalating ligand and N^N = neutral ligand) to those of the form [Ir(C^N^C)(N^N)Cl] (where C^N^C = tridentate tripod ligand).
Chapter 1 gives an introduction into photophysics occurring in transition metal complexes and possible applications in visual displays. The background of nonlinear optical (NLO) properties and the use of transition metal complexes as NLO chromophores is described.
In Chapter 2, the impact of the use of sterically congested cyclometalating ligands on the photoluminescence properties of cationic iridium(III) complexes and their performance in light-emitting electrochemical cells is investigated.
Chapter 3 explores the use of electron donors on the cyclometalating ligand towards modulating the NLO properties of the complexes. Combining strongly electron-donating substituents on the C^N ligand and electron-accepting substituents on the N^N ligand results in strong NLO activity.
Chapter 4 summarises a new series of cationic iridium(III) complexes bearing benzylpyridinato as cyclometalating ligands. The methylene spacer in the C^N ligands provides flexibility, resulting in two conformers. NMR studies combined with density functional theory (DFT) studies show how the fluxional behaviour is influenced by the choice of the ancillary ligand.
In Chapter 5, Ir(III) complexes bearing an unusual nonconjugated bis(six-membered) tridentate tripod ligand of the form [Ir(C^N^C)(N^N)Cl] are introduced. Depending on the substitutions of the C^N^C ligand phosphorescence ranging from yellow to red was obtained. Substitution of the N^N results in a panchromatic NIR dye, suitable for DSSC applications.
In Chapter 6, the concept of a nonconjugated ligand was expanded to the N^N ligand. Blue-green and sky-blue emission was obtained, demonstrating a strategy to successfully tune the emission to the blue.The preparation of n-methyl-menthylamines etc. by means of a new method of n-alkylationHendry, James Allanhttps://hdl.handle.net/10023/160892019-03-29T11:24:21Z1940-01-01T00:00:00Z1940-01-01T00:00:00ZHendry, James AllanThermally activated chemical pathways of polyaromatic hydrocarbons on a reactive surface : the assembly of intermediates towards grapheneTreanor, Michael-Johnhttps://hdl.handle.net/10023/160882019-04-01T11:52:28Z2017-01-01T00:00:00Z2017-01-01T00:00:00ZTreanor, Michael-JohnMetal/metal oxide co-impregnated lanthanum strontium calcium titanate anodes for solid oxide fuel cellsPrice, Roberthttps://hdl.handle.net/10023/160182018-09-12T11:44:03Z2018-11-06T00:00:00ZSolid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (µ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material.
This research explores the ‘powder to power’ development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La₀.₂₀Sr₀.₂₅Ca₀.₄₅TiO₃ (LSCT[sub](A-)) anode ‘backbone’ microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions.
A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective’ electrical conductivity of 17.5 S cm⁻¹ at 850 °C.
Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce₀.₈₀Gd₀.₂₀O₁.₉₀ (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm⁻², using thick (160 µm) 6ScSZ electrolytes.
Durability testing of SOFC with Ni/CGO, Ni/CeO₂, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO₂ component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of <1.9% kh⁻¹ which, to the author’s knowledge, has not previously been reported for an alternative, SrTiO₃-based anode material.
Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.
2018-11-06T00:00:00ZPrice, RobertSolid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (µ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material.
This research explores the ‘powder to power’ development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La₀.₂₀Sr₀.₂₅Ca₀.₄₅TiO₃ (LSCT[sub](A-)) anode ‘backbone’ microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions.
A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective’ electrical conductivity of 17.5 S cm⁻¹ at 850 °C.
Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce₀.₈₀Gd₀.₂₀O₁.₉₀ (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm⁻², using thick (160 µm) 6ScSZ electrolytes.
Durability testing of SOFC with Ni/CGO, Ni/CeO₂, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO₂ component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of <1.9% kh⁻¹ which, to the author’s knowledge, has not previously been reported for an alternative, SrTiO₃-based anode material.
Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.Non-classical crystal growth of metal organic frameworks MIL-68(In) and ZIF-67McRoberts, Kirstyhttps://hdl.handle.net/10023/160142018-09-12T10:44:00Z2018-11-01T00:00:00ZThis project investigated the non-classical crystal growth of two different metal-organic frameworks. The growth of crystal was studied by carrying out solvothermal or room temperature growth methods across a range of reaction times, with the samples produced at each time analysed using scanning electron microscopy. Supporting evidence for their growth was provided by transmission electron microscopy, powder X-ray diffraction and thermogravimetric analysis.
MIL-68(In) under solvothermal conditions revealed a non-classical crystal growth mechanism, with the metal-organic framework growth proceeding via a route of nanocrystallite – aggregation – surface recrystallisation – extension of recrystallisation from the surface to the core of the particle, resulting in single-crystal hexagonal microrods. Terephthalic acid molecules which are adsorbed onto the surface of nanocrystallites are believed to strengthen the inter-particle interaction, leading to a non-classical growth mechanism. Initially crystal growth may be inhibited by blocking agents such as pyridine, but if the reaction is allowed to reach equilibria under thermodynamic control, this effect will be minimised, and growth will proceed as would otherwise be expected.
ZIF-67 was synthesised by two routes, one solvothermal, and one room temperature. Unlike the MIL-68(In) studied in this project, for ZIF-67 the solvothermal route revealed a classical crystal growth mechanism. However, the room temperature method appears to follow a non-classical crystal growth mechanism.
2018-11-01T00:00:00ZMcRoberts, KirstyThis project investigated the non-classical crystal growth of two different metal-organic frameworks. The growth of crystal was studied by carrying out solvothermal or room temperature growth methods across a range of reaction times, with the samples produced at each time analysed using scanning electron microscopy. Supporting evidence for their growth was provided by transmission electron microscopy, powder X-ray diffraction and thermogravimetric analysis.
MIL-68(In) under solvothermal conditions revealed a non-classical crystal growth mechanism, with the metal-organic framework growth proceeding via a route of nanocrystallite – aggregation – surface recrystallisation – extension of recrystallisation from the surface to the core of the particle, resulting in single-crystal hexagonal microrods. Terephthalic acid molecules which are adsorbed onto the surface of nanocrystallites are believed to strengthen the inter-particle interaction, leading to a non-classical growth mechanism. Initially crystal growth may be inhibited by blocking agents such as pyridine, but if the reaction is allowed to reach equilibria under thermodynamic control, this effect will be minimised, and growth will proceed as would otherwise be expected.
ZIF-67 was synthesised by two routes, one solvothermal, and one room temperature. Unlike the MIL-68(In) studied in this project, for ZIF-67 the solvothermal route revealed a classical crystal growth mechanism. However, the room temperature method appears to follow a non-classical crystal growth mechanism.Title redactedIzquierdo, Frédéric P.https://hdl.handle.net/10023/159122018-08-30T16:16:19Z2017-12-07T00:00:00Z2017-12-07T00:00:00ZIzquierdo, Frédéric P.Metal-loaded graphitic carbon nitride for photocatalytic hydrogen production and the development of an innovative photo-thermal reactorCaux, Marinehttps://hdl.handle.net/10023/158732018-08-24T10:20:53Z2018-12-06T00:00:00ZThe path towards mitigation of anthropogenic greenhouse gas emissions lies in the transition from conventional to sustainable energy resources. The Hydrogen Economy, a cyclic economy based on hydrogen as a fuel, is suggested as a tool in the necessary energy transition. Photocatalysis makes use of sunlight to promote thermodynamically non-favoured reactions such as water splitting, allowing for sustainable hydrogen production. Harvesting thermal energy along with photonic energy is an interesting concept to decrease the activation energy of water splitting (i.e. ΔG = + 237.2 kJ∙mol⁻¹). This work aims to confront this hypothesis in a gas phase photo-thermal reactor designed specifically for this study.
The photocatalyst chosen is graphitic carbon nitride (g-C₃N₄), an organic semiconductor possessing a narrow band gap (i.e. 2.7 eV) as well as a band structure which theoretically permits water splitting. The photocatalytic performance of Pt/g-C₃N₄ for hydrogen evolution was tuned by altering its synthetic temperature. Electron paramagnetic resonance was used to gain insight on the evolution of the photocatalyst activity with synthesis temperature.
Then, gold nanoparticles were deposited on g-C₃N₄ surface. Localized surface plasmon resonance properties of gold nanoparticles are reported in the literature to be influenced by temperature. Therefore Au/g-C₃N₄ appeared as a promising candidate for photo-thermal water splitting. X-ray spectroscopy unveiled interesting observations on the gold oxidation state. Moreover, under specific reduction conditions, gold nanoparticles with a wide variety of shapes characterized by sharp edges were formed.
Finally, the development of the photo-thermal reactor is presented. The design process and the implementation of this innovative reactor are discussed. The reactor was successfully utilized to probe photoreactions. Then, the highly energy-demanding photocatalytic water splitting was proven not to be activated by temperature in the photo-thermal apparatus.
2018-12-06T00:00:00ZCaux, MarineThe path towards mitigation of anthropogenic greenhouse gas emissions lies in the transition from conventional to sustainable energy resources. The Hydrogen Economy, a cyclic economy based on hydrogen as a fuel, is suggested as a tool in the necessary energy transition. Photocatalysis makes use of sunlight to promote thermodynamically non-favoured reactions such as water splitting, allowing for sustainable hydrogen production. Harvesting thermal energy along with photonic energy is an interesting concept to decrease the activation energy of water splitting (i.e. ΔG = + 237.2 kJ∙mol⁻¹). This work aims to confront this hypothesis in a gas phase photo-thermal reactor designed specifically for this study.
The photocatalyst chosen is graphitic carbon nitride (g-C₃N₄), an organic semiconductor possessing a narrow band gap (i.e. 2.7 eV) as well as a band structure which theoretically permits water splitting. The photocatalytic performance of Pt/g-C₃N₄ for hydrogen evolution was tuned by altering its synthetic temperature. Electron paramagnetic resonance was used to gain insight on the evolution of the photocatalyst activity with synthesis temperature.
Then, gold nanoparticles were deposited on g-C₃N₄ surface. Localized surface plasmon resonance properties of gold nanoparticles are reported in the literature to be influenced by temperature. Therefore Au/g-C₃N₄ appeared as a promising candidate for photo-thermal water splitting. X-ray spectroscopy unveiled interesting observations on the gold oxidation state. Moreover, under specific reduction conditions, gold nanoparticles with a wide variety of shapes characterized by sharp edges were formed.
Finally, the development of the photo-thermal reactor is presented. The design process and the implementation of this innovative reactor are discussed. The reactor was successfully utilized to probe photoreactions. Then, the highly energy-demanding photocatalytic water splitting was proven not to be activated by temperature in the photo-thermal apparatus.Synthetic, spectroscopic and structural studies of chalcogen peri-substituted heterocycles : a solid-state NMR perspectiveSanz Camacho, Paulahttps://hdl.handle.net/10023/158542019-03-29T11:21:44Z2016-06-27T00:00:00ZChalcogen-containing materials are an area of increasing interest for
spintronic applications. The synthesis, structures and reactivity of these
novel compounds are normally studied by solution-state nuclear magnetic
resonance (NMR) spectroscopy, density functional theory (DFT)
calculations and single-crystal X-ray diffraction. In this thesis, a range of
chalcogen-containing heterocycles has been explored, focussing on the
solid-state nature and exploring the bulk samples. Therefore, all materials
were studied by powder X-ray diffraction and solid-state NMR, in
addition to conventional solution-state NMR and single-crystal X-ray
diffraction. DFT calculations were also used to interpret the solid-state
NMR spectra and to gain insight into the NMR parameters. In the first
chapter of results, a series of mixed Te, Se acenaphthenes is investigated.
⁷⁷Se and ¹²⁵Te NMR parameters are explored to determine whether
changes in the Te aryl-group have an impact on the local environments of
both nuclei. Dynamics and the requirement to consider relativistic effects
for calculations of NMR parameters of heavy atoms is discussed. In the
second results chapter, a series of novel P-S and P-Se six-membered
heterocycles are described in terms of their synthesis, reactivity, and ³¹P
and ⁷⁷Se local environments. We observed and measured some unusual
“through-space” couplings that occur between molecules and which
mechanism and pathways are supported by DFT calculations. In the third
results chapter, these heterocycles are oxidised with O, S and Se and the
NMR parameters are discussed in terms of the structure. Polymorphism,
phase transitions and weak interactions are some of the phenomena
present in these novel compounds. This thesis demonstrated that solid-state
NMR is a very good probe to study Se- and Te-containing materials.
2016-06-27T00:00:00ZSanz Camacho, PaulaChalcogen-containing materials are an area of increasing interest for
spintronic applications. The synthesis, structures and reactivity of these
novel compounds are normally studied by solution-state nuclear magnetic
resonance (NMR) spectroscopy, density functional theory (DFT)
calculations and single-crystal X-ray diffraction. In this thesis, a range of
chalcogen-containing heterocycles has been explored, focussing on the
solid-state nature and exploring the bulk samples. Therefore, all materials
were studied by powder X-ray diffraction and solid-state NMR, in
addition to conventional solution-state NMR and single-crystal X-ray
diffraction. DFT calculations were also used to interpret the solid-state
NMR spectra and to gain insight into the NMR parameters. In the first
chapter of results, a series of mixed Te, Se acenaphthenes is investigated.
⁷⁷Se and ¹²⁵Te NMR parameters are explored to determine whether
changes in the Te aryl-group have an impact on the local environments of
both nuclei. Dynamics and the requirement to consider relativistic effects
for calculations of NMR parameters of heavy atoms is discussed. In the
second results chapter, a series of novel P-S and P-Se six-membered
heterocycles are described in terms of their synthesis, reactivity, and ³¹P
and ⁷⁷Se local environments. We observed and measured some unusual
“through-space” couplings that occur between molecules and which
mechanism and pathways are supported by DFT calculations. In the third
results chapter, these heterocycles are oxidised with O, S and Se and the
NMR parameters are discussed in terms of the structure. Polymorphism,
phase transitions and weak interactions are some of the phenomena
present in these novel compounds. This thesis demonstrated that solid-state
NMR is a very good probe to study Se- and Te-containing materials.Title redactedDavies, Alyn T.https://hdl.handle.net/10023/156972019-09-30T13:12:59Z2016-01-01T00:00:00Z2016-01-01T00:00:00ZDavies, Alyn T.Synthesis and battery application of nanomaterials and the mechanism of O₂ reduction in aprotic Li-O₂ batteriesLiu, Zhenghttps://hdl.handle.net/10023/156942019-03-29T11:19:28Z2016-03-01T00:00:00ZHunting for improved energy storage devices based on rechargeable Li-ion batteries and
other advanced rechargeable batteries is one of the hottest topics in today’s society. Both Li-
ion batteries and Li-O₂ batteries have been studied within the thesis. The research work of
this thesis contains two different parts. Part 1. The controlled synthesis of the extreme small
sized nanoparticles and their application for Li-ion batteries; Part 2. The study of the O₂
reduction mechanism in Li-O₂ batteries with aprotic electrolytes.
In the first part, two different types of extremely small-sized TiO₂ nanoparticles with at lease
on dimension less than 3 nm was synthesised via solvothermal/hydrothermal reaction, i.e.,
anatase nanosheets and TiO₂(B). These nanoparticles were obtained without any
contamination of long chain organic surfactants. A series of systematic characterisation
methods were employed to analyse the size, phase purity, and surface condition. These
extremely small-sized nanoparticles exhibit improved capacity, rate performance as anode
materials for Li-ion batteries. The shapes of load curves of charge and discharge are
significantly modified due to the reduced size of TiO₂ nanoparticles.
In chapter 3, we will see the variation of the capacity and the load curve shape of the anatase
nanosheets according to their thickness and surface conditions. The origin of the excessive
capacity is analysed based on the electrochemical data. It has been identified that both
pseudocapacitive (interfacial) Li+ storage and the excessive Li+ -storage from the bulk
contribute to the increased capacity.
In chapter 4, the shape and size of the sub-3 nm TiO₂(B) nanoparticles are studied, a method
based the PXRD data is established. These nanoparticles demonstrate a reversible capacity of
221 mAh/g at a rate of 600 mA/g and remain 135 mAh/g at 18000 mA/g without significant
capacity fading during cycling.
In the last part, a systematic study of O₂ reduction mechanism for aprotic Li-O₂ batteries
based on the combination of a series of electrochemical and spectroscopic data is presented.
The novel mechanism unifies two previous models for the growth of Li₂O₂ during discharge,
i.e., Li₂O₂ particle formation in the solution phase and Li₂O₂ film formation on the electrode
surface. The new mechanism provides fundamental conceptions for the improvement of
Li₂O₂ batteries and shed light on the future research of Li₂O₂ batteries.
2016-03-01T00:00:00ZLiu, ZhengHunting for improved energy storage devices based on rechargeable Li-ion batteries and
other advanced rechargeable batteries is one of the hottest topics in today’s society. Both Li-
ion batteries and Li-O₂ batteries have been studied within the thesis. The research work of
this thesis contains two different parts. Part 1. The controlled synthesis of the extreme small
sized nanoparticles and their application for Li-ion batteries; Part 2. The study of the O₂
reduction mechanism in Li-O₂ batteries with aprotic electrolytes.
In the first part, two different types of extremely small-sized TiO₂ nanoparticles with at lease
on dimension less than 3 nm was synthesised via solvothermal/hydrothermal reaction, i.e.,
anatase nanosheets and TiO₂(B). These nanoparticles were obtained without any
contamination of long chain organic surfactants. A series of systematic characterisation
methods were employed to analyse the size, phase purity, and surface condition. These
extremely small-sized nanoparticles exhibit improved capacity, rate performance as anode
materials for Li-ion batteries. The shapes of load curves of charge and discharge are
significantly modified due to the reduced size of TiO₂ nanoparticles.
In chapter 3, we will see the variation of the capacity and the load curve shape of the anatase
nanosheets according to their thickness and surface conditions. The origin of the excessive
capacity is analysed based on the electrochemical data. It has been identified that both
pseudocapacitive (interfacial) Li+ storage and the excessive Li+ -storage from the bulk
contribute to the increased capacity.
In chapter 4, the shape and size of the sub-3 nm TiO₂(B) nanoparticles are studied, a method
based the PXRD data is established. These nanoparticles demonstrate a reversible capacity of
221 mAh/g at a rate of 600 mA/g and remain 135 mAh/g at 18000 mA/g without significant
capacity fading during cycling.
In the last part, a systematic study of O₂ reduction mechanism for aprotic Li-O₂ batteries
based on the combination of a series of electrochemical and spectroscopic data is presented.
The novel mechanism unifies two previous models for the growth of Li₂O₂ during discharge,
i.e., Li₂O₂ particle formation in the solution phase and Li₂O₂ film formation on the electrode
surface. The new mechanism provides fundamental conceptions for the improvement of
Li₂O₂ batteries and shed light on the future research of Li₂O₂ batteries.Title redactedHeutz, Frank J. L.https://hdl.handle.net/10023/156782018-11-20T10:03:18Z2016-01-01T00:00:00Z2016-01-01T00:00:00ZHeutz, Frank J. L.Metal organic frameworks : from anticancer multifunctional drug delivery systems to novel vaccine adjuvantsMorley, Katarzyna Annahttps://hdl.handle.net/10023/156702019-06-21T02:02:39Z2016-01-01T00:00:00ZThe research presented in this thesis aims to assess the capacity of metal organic frameworks
for potential applications as drug delivery systems and novel vaccine adjuvants.
The opening chapter (Chapter 1) provides a reader with a background to the field, metal
organic frameworks synthesis routes and their potential applications in medicine and insight
into the basics of immunology and biological assays as well as the anti-cancer drugs
mechanisms and how it can be used to target the tumour cells.
Chapter 3 describes the experimental techniques used in this research combining biological
with chemical testing.
Investigation of Zr-MOFs (UiO66 and UiO66-NH₂) and CPO – 27 (CPO Mg and CPO Ni) for
their potential application as drug delivery systems for cisplatin is presented and compared in
Chapter 4, as well as two different drug incorporation techniques (conjugation and physical
encapsulation) in the case of UiO66-NH₂. The route proved to be more efficient when
compared with encapsulation for the same MOF, and overall the most promising candidate for
a drug delivery system for cisplatin, due to its large pores, was UiO66.
Chapter 5 focuses on the potential application of Zr-MOFs and CPO-27 (Mg and Ni) as a
drug delivery system for 5-Fluorouracil, a drug which because of its sparse solubility in water
is challenging when it comes to its administration in the human body. Chapter 7 investigates
the possibility to design multiple drug delivery systems utilising MOFs that contain cisplatin
and fluorouracil in their framework, loading them with nitric oxide to increase the anti-cancer
action and also to prevent thrombosis that may pose a danger to patients who undergo anti-cancer therapies. Chapter 6 describes the new concept of investigating MOFs (Zr-MOFs and
Al-MOFs) as potential candidates as vaccine adjuvants. The research concluded that the
performance of Al-MOFs, was better when compared to commercially available adjuvants.
2016-01-01T00:00:00ZMorley, Katarzyna AnnaThe research presented in this thesis aims to assess the capacity of metal organic frameworks
for potential applications as drug delivery systems and novel vaccine adjuvants.
The opening chapter (Chapter 1) provides a reader with a background to the field, metal
organic frameworks synthesis routes and their potential applications in medicine and insight
into the basics of immunology and biological assays as well as the anti-cancer drugs
mechanisms and how it can be used to target the tumour cells.
Chapter 3 describes the experimental techniques used in this research combining biological
with chemical testing.
Investigation of Zr-MOFs (UiO66 and UiO66-NH₂) and CPO – 27 (CPO Mg and CPO Ni) for
their potential application as drug delivery systems for cisplatin is presented and compared in
Chapter 4, as well as two different drug incorporation techniques (conjugation and physical
encapsulation) in the case of UiO66-NH₂. The route proved to be more efficient when
compared with encapsulation for the same MOF, and overall the most promising candidate for
a drug delivery system for cisplatin, due to its large pores, was UiO66.
Chapter 5 focuses on the potential application of Zr-MOFs and CPO-27 (Mg and Ni) as a
drug delivery system for 5-Fluorouracil, a drug which because of its sparse solubility in water
is challenging when it comes to its administration in the human body. Chapter 7 investigates
the possibility to design multiple drug delivery systems utilising MOFs that contain cisplatin
and fluorouracil in their framework, loading them with nitric oxide to increase the anti-cancer
action and also to prevent thrombosis that may pose a danger to patients who undergo anti-cancer therapies. Chapter 6 describes the new concept of investigating MOFs (Zr-MOFs and
Al-MOFs) as potential candidates as vaccine adjuvants. The research concluded that the
performance of Al-MOFs, was better when compared to commercially available adjuvants.Structural and mechanistic studies on the biosynthesis of the 3'-deoxy nucleoside of the pacidamycinsMichailidou, Freiderikihttps://hdl.handle.net/10023/156682019-10-15T09:26:05Z2018-03-01T00:00:00ZNucleic acids are ubiquitous in nature and modified nucleosides are present in a wide range of anti-viral, anti-cancer drugs and antibiotics. Although a variety of naturally occurring nucleoside analogues exist, few include modifications to the ribose or deoxyribose ring. Intriguingly, the uridyl peptide antibiotics (UPAs), such as pacidamycin, contain a biosynthetically unique 3'-deoxyuridine which resembles synthetic anti-retrovirals. Elucidation of the biosynthesis of this structuraly unique nucleoside motif suggests a degree of substrate flexibility, making it a highly attractive prospect for biosynthetic approaches to nucleoside modification. In order to fully exploit the biotransformative potential, a detailed mechanistic understanding of the individual enzymes involved in the biosynthesis of the nucleoside moiety, and especially the enzyme employed at the installation of the 3'-deoxy modification, is required.
Chapter 1, the introduction the thesis, discusses the importance of nucleosides for Chemistry and Biology. The section describes the biosynthesis of the nucleoside antibiotics and reviews the recent advances relating to the synthesis and biosynthesis of 3'-deoxy-nucleosides. The Chapter proceeds to describes the biosynthesis of deoxy-sugars, deoxy-nucleosides and nucleotides, reviewing the most common dehydratase mechanisms in addition to examining unusual dehydratases involved in carbohydrate metabolism. Chapter 2, the study of Pac13, the uridine-5'-aldehyde dehydratase of the pacidamyicin nucleoside cluster, is reported. Through detailed functional, structural and kinetic analysis of the wild-type enzyme as well a series of mutants, Chapter 2 provides insight into the mechanism emplyed by this unusual enzyme. Chapter 3 describes the structural and functional analysis of Pac11, the flavin-dependent oxidoreductase of the nucleoside biosynthetic cluster, while Chapter 4 revolves around Pac5, the PLP-dependent aminotransferase. In Chapter 5, the chemical synthesis of fluorinated nucleosides, as probes for exploring the enzymes' mechanism is investigated. Chapter 7 reports the experimental procedures for the research described in this document. The work described in this thesis broadens the understanding of the biosynthesis of deoxy-nucleosides and constitutes the first structural and mechanistic study of the biosynthesis of the biosynthesis of the valuable yet, synthetically challenging 3'-deoxy nucleosides.
2018-03-01T00:00:00ZMichailidou, FreiderikiNucleic acids are ubiquitous in nature and modified nucleosides are present in a wide range of anti-viral, anti-cancer drugs and antibiotics. Although a variety of naturally occurring nucleoside analogues exist, few include modifications to the ribose or deoxyribose ring. Intriguingly, the uridyl peptide antibiotics (UPAs), such as pacidamycin, contain a biosynthetically unique 3'-deoxyuridine which resembles synthetic anti-retrovirals. Elucidation of the biosynthesis of this structuraly unique nucleoside motif suggests a degree of substrate flexibility, making it a highly attractive prospect for biosynthetic approaches to nucleoside modification. In order to fully exploit the biotransformative potential, a detailed mechanistic understanding of the individual enzymes involved in the biosynthesis of the nucleoside moiety, and especially the enzyme employed at the installation of the 3'-deoxy modification, is required.
Chapter 1, the introduction the thesis, discusses the importance of nucleosides for Chemistry and Biology. The section describes the biosynthesis of the nucleoside antibiotics and reviews the recent advances relating to the synthesis and biosynthesis of 3'-deoxy-nucleosides. The Chapter proceeds to describes the biosynthesis of deoxy-sugars, deoxy-nucleosides and nucleotides, reviewing the most common dehydratase mechanisms in addition to examining unusual dehydratases involved in carbohydrate metabolism. Chapter 2, the study of Pac13, the uridine-5'-aldehyde dehydratase of the pacidamyicin nucleoside cluster, is reported. Through detailed functional, structural and kinetic analysis of the wild-type enzyme as well a series of mutants, Chapter 2 provides insight into the mechanism emplyed by this unusual enzyme. Chapter 3 describes the structural and functional analysis of Pac11, the flavin-dependent oxidoreductase of the nucleoside biosynthetic cluster, while Chapter 4 revolves around Pac5, the PLP-dependent aminotransferase. In Chapter 5, the chemical synthesis of fluorinated nucleosides, as probes for exploring the enzymes' mechanism is investigated. Chapter 7 reports the experimental procedures for the research described in this document. The work described in this thesis broadens the understanding of the biosynthesis of deoxy-nucleosides and constitutes the first structural and mechanistic study of the biosynthesis of the biosynthesis of the valuable yet, synthetically challenging 3'-deoxy nucleosides.α functionalization of carbonyl compounds via Brønsted and Lewis base organocatalysisBarrios Antúnez, Diego-Javierhttps://hdl.handle.net/10023/156672023-03-15T03:01:34Z2018-05-01T00:00:00ZThis thesis describes the development of new methodologies promoted by bifunctional Brønsted basic H-bonding catalysis and Lewis basic organocatalysts. Chapter 2 describes the synthesis of novel chiral guanidines and their application as Brønsted and Lewis base catalysts in a variety of processes. Chapter 3 screens an array of Brønsted basic organocatalysts for the synthesis of trans-dihydrobenzofurans. A tertiary amine-thiourea bifunctional catalyst is used for an intramolecular Michael addition using keto-enones. The desired dihydrozofurans were obtained in excellent yield and with excellent diastereo- and good enantiocontrol. Chapter 4 describes the use of an isothiourea catalyst, HyperBTM, for the formal [2+2] cycloaddition between homohydrides and perfluorinated ketones to furnish β-lactones. The products were obtained in excellent yield and with excellent diastereo- and enantioselectivity. A large scope of 36 examples is reported. The derivatizion of the obtained β-lactones via ring-opening with a range of nucleophiles gave access to an array of β-hydroxycarbonyl compounds. Oxetanes could be accessed by a two step protocol, consisting of β-lactone reduction to give a diol, followed by cyclization. Chapter 5 describes a mechanic investigation on the isothiourea-catalysed formal [2+2] cycloaddition. A variable time normalisation graphical analysis method was used to determine the partial orders for anhydride, ketone and catalyst. The catalyst resting state was determined to be free catalysts by use of a fluorine-labelled catalysts.
2018-05-01T00:00:00ZBarrios Antúnez, Diego-JavierThis thesis describes the development of new methodologies promoted by bifunctional Brønsted basic H-bonding catalysis and Lewis basic organocatalysts. Chapter 2 describes the synthesis of novel chiral guanidines and their application as Brønsted and Lewis base catalysts in a variety of processes. Chapter 3 screens an array of Brønsted basic organocatalysts for the synthesis of trans-dihydrobenzofurans. A tertiary amine-thiourea bifunctional catalyst is used for an intramolecular Michael addition using keto-enones. The desired dihydrozofurans were obtained in excellent yield and with excellent diastereo- and good enantiocontrol. Chapter 4 describes the use of an isothiourea catalyst, HyperBTM, for the formal [2+2] cycloaddition between homohydrides and perfluorinated ketones to furnish β-lactones. The products were obtained in excellent yield and with excellent diastereo- and enantioselectivity. A large scope of 36 examples is reported. The derivatizion of the obtained β-lactones via ring-opening with a range of nucleophiles gave access to an array of β-hydroxycarbonyl compounds. Oxetanes could be accessed by a two step protocol, consisting of β-lactone reduction to give a diol, followed by cyclization. Chapter 5 describes a mechanic investigation on the isothiourea-catalysed formal [2+2] cycloaddition. A variable time normalisation graphical analysis method was used to determine the partial orders for anhydride, ketone and catalyst. The catalyst resting state was determined to be free catalysts by use of a fluorine-labelled catalysts.Target elucidation of novel trypanosomatid inhibitorsFraser, Andrew Loganhttps://hdl.handle.net/10023/156662019-09-27T12:32:04Z2018-03-01T00:00:00ZIn 2010 the Florence group completed the total synthesis of the natural product chamuvarinin which, in collaboration with the Smith group, was found to be a potent inhibitor of the pathogenic parasite T. brucei. Several simplified analogues were found to maintain this inhibitory activity alongside activity against the related species T. cruzi and L. major. The mechanism of action and structural features of these compounds responsible for the observed biological activity remained elusive despite a large synthetic effort by the Florence group. With the aim of identifying protein targets in trypanosomatids to understand the mechanism of action, several photo-affinity labeling analogs have been successfully synthesised and utilised to identify a primary protein target. This protein target was fully validated and molecule docking to this protein was evaluated in-silico. This computational data was used to evaluate the mode of action and aided in the design of simplified compounds which were found to maintain the previously observed anti-parasitic activity but with decreased toxicity to mammalian cells alongside decreased synthetic complexity. The total synthesis of the natural product ascr#18 is also described alongside the synthesis of photo-affinity labeling analogs. This natural product is implicated in the modulation of pathogen resistance in plants and has potential application in crop production.
2018-03-01T00:00:00ZFraser, Andrew LoganIn 2010 the Florence group completed the total synthesis of the natural product chamuvarinin which, in collaboration with the Smith group, was found to be a potent inhibitor of the pathogenic parasite T. brucei. Several simplified analogues were found to maintain this inhibitory activity alongside activity against the related species T. cruzi and L. major. The mechanism of action and structural features of these compounds responsible for the observed biological activity remained elusive despite a large synthetic effort by the Florence group. With the aim of identifying protein targets in trypanosomatids to understand the mechanism of action, several photo-affinity labeling analogs have been successfully synthesised and utilised to identify a primary protein target. This protein target was fully validated and molecule docking to this protein was evaluated in-silico. This computational data was used to evaluate the mode of action and aided in the design of simplified compounds which were found to maintain the previously observed anti-parasitic activity but with decreased toxicity to mammalian cells alongside decreased synthetic complexity. The total synthesis of the natural product ascr#18 is also described alongside the synthesis of photo-affinity labeling analogs. This natural product is implicated in the modulation of pathogen resistance in plants and has potential application in crop production.A manifold destiny : advancing the frontiers of the ADOR processFirth, Daniel Seanhttps://hdl.handle.net/10023/156642019-03-29T11:20:40Z2017-01-01T00:00:00ZThis thesis deals with the various attempts to expand the ADOR (Assembly, Disassembly,
Organisation and Reassembly) process. This includes the use of the ADOR process to
incorporate new elements into a zeolite framework, the expansion of the ADOR process
to other germanosilicate frameworks, and the first ever synthesis of a new ADORable
germanosilicate and its subsequent daughters.
Chapter 4 deals with the expansion of the ADOR process to the already known ADORable
zeolite UTL, using the organisation and reassembly steps to incorporate Al and P,
resulting in the formation of a zeolite-AlPO hybrid with distinct silicate layers connected
by AlPO based s4r linkages. The material was shown to contain Al and P species and was
unstable to acidic medium, atypical of the wholly silica zeolite frameworks produced by
the ADOR process. MAS NMR studies showed the presence of both tetrahedral P and Al
species in the material and that the presence of Si-OH groups was limited. Indicating that
the layers had been reconnected with Al and P now present, forming a zeolite-AlPO
hybrid. 29
Si-enriched materials were synthesised to confirm the presence of P-O-Si bonds,
through 2D MAS NMR correlation experiments; however, results were limited due to the
lack of signal strength.
Chapter 5 deals with attempts to expand the ADOR process by applying the ADOR process
to other already known germanosilicates. It was found that the non-ideal ADORable
candidates NUD-1 and ITQ-33 were unable to undergo a controlled disassembly process,
primarily due to their high Ge content and distribution of d4r/d3r. The zeolites ITQ-38
and IM-20 showed more promise. Both could undergo disassembly to form a layered
material, which could then be organised and reassembled to form new materials.
However, these materials were shown to not form perfect daughter zeolites and had a high
degree of disorder. This was associated with the complexity of the ADOR process and the
many factors that play a role in each step.
Chapter 6 deals with the use of a family of SDAs (with the same biphenyl backbone) to
synthesise new ADORable zeolites. The synthesis of the SDAs and their use in various
zeolite syntheses was discussed. The potential of these SDAs for the synthesis of new
zeolites was then evaluated. The investigations were relatively successful with the
successful formation of an ADORable zeolite, which was already known, UTL. However,
the suitability of such SDAs also put into question, due to their instability under
hydrothermal conditions.
Chapter 7 discussed the first successful a priori synthesis of a parent germanosilicate and
its daughter zeolites by the ADOR process. The successful synthesis of an ADORable
zeolite (SAZ-1) was conducted with the use of an imidazolium-naphthalene based SDA.
Investigations were first conducted into changing the synthesis condition, exploring the
impact of these changes on the resulting products, and optimising the synthesis
conditions to favour the formation of the new zeolite SAZ-1. These investigations led to
the new zeolite framework SAZ-1, which showed similarities to the zeolites NUD-2 and
CIT-13, which were developed simultaneously by other institutions. The properties of the
SAZ-1 framework were discussed and were found to be highly suitable for the ADOR
process. SAZ-1 was then successfully disassembled, organised, and reassembled to form
two new daughter zeolites SAZ-2 and SAZ-3. The alumination of SAZ-1P to form
aluminated SAZ-2 and SAZ-3 was also attempted. Both zeolites showed an increase in
catalytic activity, compared to the typical pure-silica daughter zeolites. The layers of SAZ-
1P were also able to undergo the same shifting process as seen for the ‘unfeasible’ zeolites
IPC-9 and IPC-10, but the resultant products were not as ordered as these previous
examples. This in addition to the previous work highlighted some of the non-ideal
properties of SAZ-1 compared to other ADORable zeolites, like UTL.
2017-01-01T00:00:00ZFirth, Daniel SeanThis thesis deals with the various attempts to expand the ADOR (Assembly, Disassembly,
Organisation and Reassembly) process. This includes the use of the ADOR process to
incorporate new elements into a zeolite framework, the expansion of the ADOR process
to other germanosilicate frameworks, and the first ever synthesis of a new ADORable
germanosilicate and its subsequent daughters.
Chapter 4 deals with the expansion of the ADOR process to the already known ADORable
zeolite UTL, using the organisation and reassembly steps to incorporate Al and P,
resulting in the formation of a zeolite-AlPO hybrid with distinct silicate layers connected
by AlPO based s4r linkages. The material was shown to contain Al and P species and was
unstable to acidic medium, atypical of the wholly silica zeolite frameworks produced by
the ADOR process. MAS NMR studies showed the presence of both tetrahedral P and Al
species in the material and that the presence of Si-OH groups was limited. Indicating that
the layers had been reconnected with Al and P now present, forming a zeolite-AlPO
hybrid. 29
Si-enriched materials were synthesised to confirm the presence of P-O-Si bonds,
through 2D MAS NMR correlation experiments; however, results were limited due to the
lack of signal strength.
Chapter 5 deals with attempts to expand the ADOR process by applying the ADOR process
to other already known germanosilicates. It was found that the non-ideal ADORable
candidates NUD-1 and ITQ-33 were unable to undergo a controlled disassembly process,
primarily due to their high Ge content and distribution of d4r/d3r. The zeolites ITQ-38
and IM-20 showed more promise. Both could undergo disassembly to form a layered
material, which could then be organised and reassembled to form new materials.
However, these materials were shown to not form perfect daughter zeolites and had a high
degree of disorder. This was associated with the complexity of the ADOR process and the
many factors that play a role in each step.
Chapter 6 deals with the use of a family of SDAs (with the same biphenyl backbone) to
synthesise new ADORable zeolites. The synthesis of the SDAs and their use in various
zeolite syntheses was discussed. The potential of these SDAs for the synthesis of new
zeolites was then evaluated. The investigations were relatively successful with the
successful formation of an ADORable zeolite, which was already known, UTL. However,
the suitability of such SDAs also put into question, due to their instability under
hydrothermal conditions.
Chapter 7 discussed the first successful a priori synthesis of a parent germanosilicate and
its daughter zeolites by the ADOR process. The successful synthesis of an ADORable
zeolite (SAZ-1) was conducted with the use of an imidazolium-naphthalene based SDA.
Investigations were first conducted into changing the synthesis condition, exploring the
impact of these changes on the resulting products, and optimising the synthesis
conditions to favour the formation of the new zeolite SAZ-1. These investigations led to
the new zeolite framework SAZ-1, which showed similarities to the zeolites NUD-2 and
CIT-13, which were developed simultaneously by other institutions. The properties of the
SAZ-1 framework were discussed and were found to be highly suitable for the ADOR
process. SAZ-1 was then successfully disassembled, organised, and reassembled to form
two new daughter zeolites SAZ-2 and SAZ-3. The alumination of SAZ-1P to form
aluminated SAZ-2 and SAZ-3 was also attempted. Both zeolites showed an increase in
catalytic activity, compared to the typical pure-silica daughter zeolites. The layers of SAZ-
1P were also able to undergo the same shifting process as seen for the ‘unfeasible’ zeolites
IPC-9 and IPC-10, but the resultant products were not as ordered as these previous
examples. This in addition to the previous work highlighted some of the non-ideal
properties of SAZ-1 compared to other ADORable zeolites, like UTL.A novel approach towards the stereoselective synthesis of inositols and its application in the synthesis of biologically important moleculesSayer, Lloydhttps://hdl.handle.net/10023/156582019-03-29T11:22:36Z2016-06-22T00:00:00ZMyo-inositol is ubiquitous in nature and is found at the structural core of a diverse range of biologically important derivatives, including phosphatidylinositols, inositol phosphates and mycothiol. The synthesis of myo-inositol derivatives is notoriously difficult due to the need to control both regio- and enantioselectivity. As a result, synthetic routes to derivatives of this type are often lengthy and low yielding. The first biosynthetic step in the production of all myo-inositol metabolites is the isomerisation of D-glucose 6- phosphate to L-myo-inositol 1-phosphate as mediated by L-myo-inositol 1-phosphate synthase (INO1). For the protozoan parasite Trypanosoma brucei, INO1 is essential for survival and its version of the enzyme (TbINO1) has a high turnover. This makes TbINO1 an attractive candidate for the biocatalytic production of L-myo-inositol 1- phosphate, and a potential starting point for drastically shortened syntheses of important myo-inositol derivatives.
The production of L-myo-inositol 1-phosphate by TbINO1 has been optimised to achieve complete conversion in reaction conditions that facilitate product isolation. Due to problems with an in-batch process, the TbINO1 enzyme was immobilised and the process was transferred to a flow system. This has allowed for production of significant quantities of L-myo-inositol 1-phosphate with a high level of purity. L-myo-inositol 1- phosphate obtained from the flow system has been used to prepare mycothiol glycosylation acceptor, 1,2,4,5,6-penta-O-acetyl-D-myo-inositol, in a concise synthesis with a greatly improved yield over the literature.
2016-06-22T00:00:00ZSayer, LloydMyo-inositol is ubiquitous in nature and is found at the structural core of a diverse range of biologically important derivatives, including phosphatidylinositols, inositol phosphates and mycothiol. The synthesis of myo-inositol derivatives is notoriously difficult due to the need to control both regio- and enantioselectivity. As a result, synthetic routes to derivatives of this type are often lengthy and low yielding. The first biosynthetic step in the production of all myo-inositol metabolites is the isomerisation of D-glucose 6- phosphate to L-myo-inositol 1-phosphate as mediated by L-myo-inositol 1-phosphate synthase (INO1). For the protozoan parasite Trypanosoma brucei, INO1 is essential for survival and its version of the enzyme (TbINO1) has a high turnover. This makes TbINO1 an attractive candidate for the biocatalytic production of L-myo-inositol 1- phosphate, and a potential starting point for drastically shortened syntheses of important myo-inositol derivatives.
The production of L-myo-inositol 1-phosphate by TbINO1 has been optimised to achieve complete conversion in reaction conditions that facilitate product isolation. Due to problems with an in-batch process, the TbINO1 enzyme was immobilised and the process was transferred to a flow system. This has allowed for production of significant quantities of L-myo-inositol 1-phosphate with a high level of purity. L-myo-inositol 1- phosphate obtained from the flow system has been used to prepare mycothiol glycosylation acceptor, 1,2,4,5,6-penta-O-acetyl-D-myo-inositol, in a concise synthesis with a greatly improved yield over the literature.A new reversible 1,3-dipolar cycloaddition and its application in dynamic covalent chemistryVan Brussel, Davidhttps://hdl.handle.net/10023/156532019-03-29T11:24:02Z2016-05-01T00:00:00ZIn the past decades, chemists have designed and investigated artificial self-replicating molecules. A self-replicating molecule is one that can assemble its
building blocks through molecular recognition, the building blocks are brought in
close proximity and can react to form another copy of the self-replicator. Self-replicators are important to consider in the context of the origin of life, as it is
hypothesised that molecular self-replicating entities are at the basis of the emergence
of life on earth. Previously, self-replicating molecules have been reported based on
cycloaddition reactions, and in particular the Philp Laboratory worked on a self-replicating system based on the cycloaddition reaction between a maleimide and a
nitrone. The thesis presented here, however, focuses on the implementation of
another dipolarophile in a recognition-mediated reaction with a nitrone. 2-Arylidene-1,3-indandiones can react with nitrones in a 1,3-dipolar cycloaddition and these
compounds can be functionalised with a recognition site.
Initially, the reactivity of the indandiones in a 1,3-dipolar cycloaddition with a nitrone
is studied in the absence of recognition-mediated reaction pathways. The
investigation is carried out experimentally and computationally with semi-empirical
methods and Density Functional Theory. Secondly, we investigated the effect of
molecular recognition on the rate and conversion of the cycloaddition reaction.
Depending on the location of the recognition site relative to the reactive site on the
nitrone, the rate can be accelerated up to almost seven times.
Synthetic chemists, traditionally, investigate chemical reactions in isolation and one
product is purified after the chemical reaction. In biochemical systems, however, a
mixture of many compounds is present. In the final part of this thesis, the recognition-mediated reaction is described between the indandione and a mixture of nitrones and
any difference in behaviour between the reaction in isolation and the reaction in a
mixture of starting materials is investigated.
2016-05-01T00:00:00ZVan Brussel, DavidIn the past decades, chemists have designed and investigated artificial self-replicating molecules. A self-replicating molecule is one that can assemble its
building blocks through molecular recognition, the building blocks are brought in
close proximity and can react to form another copy of the self-replicator. Self-replicators are important to consider in the context of the origin of life, as it is
hypothesised that molecular self-replicating entities are at the basis of the emergence
of life on earth. Previously, self-replicating molecules have been reported based on
cycloaddition reactions, and in particular the Philp Laboratory worked on a self-replicating system based on the cycloaddition reaction between a maleimide and a
nitrone. The thesis presented here, however, focuses on the implementation of
another dipolarophile in a recognition-mediated reaction with a nitrone. 2-Arylidene-1,3-indandiones can react with nitrones in a 1,3-dipolar cycloaddition and these
compounds can be functionalised with a recognition site.
Initially, the reactivity of the indandiones in a 1,3-dipolar cycloaddition with a nitrone
is studied in the absence of recognition-mediated reaction pathways. The
investigation is carried out experimentally and computationally with semi-empirical
methods and Density Functional Theory. Secondly, we investigated the effect of
molecular recognition on the rate and conversion of the cycloaddition reaction.
Depending on the location of the recognition site relative to the reactive site on the
nitrone, the rate can be accelerated up to almost seven times.
Synthetic chemists, traditionally, investigate chemical reactions in isolation and one
product is purified after the chemical reaction. In biochemical systems, however, a
mixture of many compounds is present. In the final part of this thesis, the recognition-mediated reaction is described between the indandione and a mixture of nitrones and
any difference in behaviour between the reaction in isolation and the reaction in a
mixture of starting materials is investigated.Structural and functional studies of porins from pathogenic bacteriaFerrara, Luanahttps://hdl.handle.net/10023/156392021-04-02T11:41:30Z2018-01-01T00:00:00ZMulti-drug resistant bacteria have become a real threat to public health worldwide. Gram-negative bacteria, in particular, have shown high level of antibiotic resistance due to the presence of an additional membrane, known as outer-membrane (OM), that acts as an extra barrier. Most antibiotics enter the cells via a particular class of outer-membrane proteins (OMPs) known as porins. Porins are β-barrel channels that allow the passive diffusion of hydrophobic compounds. The porins are known to select against molecules on the basis of size and charge. When exposed to antibiotics, bacteria can modify the OM permeability by altering their porins profile. Mutations affecting the size and conductivity of the pore channel, and modification of the level of porins expression are just a few examples of how the bacteria can decrease the influx of antibiotics.
In order to better understand their interaction with antibiotics, this thesis presents structural and functional studies on porins from pathogenic bacteria. The structure of the natively expressed major outer-membrane protein (MOMP) from Campylobacter jejuni was determines, revelling the presence of a calcium-binding site inside the channel. Electro-physiology and in silico modelling analysis have shown to be important for the stability and the function of the protein. Omp50 from C. jejuni was expressed in E. Coli and its tyrosine kinase activity was analysed in vitro. Finally the structures of the two major porins from Enterobacter aerogens were determined and compared to their orthologs within the Enterobacteriaceae family. Further, a liposome-swelling assay (LSA) was used to deter-mine the rate of permeation of clinically relevant antibiotics through a series of porins. Combining these data allow a more detailed molecular understanding of translocation.
2018-01-01T00:00:00ZFerrara, LuanaMulti-drug resistant bacteria have become a real threat to public health worldwide. Gram-negative bacteria, in particular, have shown high level of antibiotic resistance due to the presence of an additional membrane, known as outer-membrane (OM), that acts as an extra barrier. Most antibiotics enter the cells via a particular class of outer-membrane proteins (OMPs) known as porins. Porins are β-barrel channels that allow the passive diffusion of hydrophobic compounds. The porins are known to select against molecules on the basis of size and charge. When exposed to antibiotics, bacteria can modify the OM permeability by altering their porins profile. Mutations affecting the size and conductivity of the pore channel, and modification of the level of porins expression are just a few examples of how the bacteria can decrease the influx of antibiotics.
In order to better understand their interaction with antibiotics, this thesis presents structural and functional studies on porins from pathogenic bacteria. The structure of the natively expressed major outer-membrane protein (MOMP) from Campylobacter jejuni was determines, revelling the presence of a calcium-binding site inside the channel. Electro-physiology and in silico modelling analysis have shown to be important for the stability and the function of the protein. Omp50 from C. jejuni was expressed in E. Coli and its tyrosine kinase activity was analysed in vitro. Finally the structures of the two major porins from Enterobacter aerogens were determined and compared to their orthologs within the Enterobacteriaceae family. Further, a liposome-swelling assay (LSA) was used to deter-mine the rate of permeation of clinically relevant antibiotics through a series of porins. Combining these data allow a more detailed molecular understanding of translocation.Density functional theory investigations of molecules on surfaces : from nano-electronics to catalysisGarrido Torres, José A.https://hdl.handle.net/10023/156182021-07-23T14:55:11Z2017-01-01T00:00:00ZIn this thesis, a wide breadth of topics related to the field of surface science are addressed using density functional theory (DFT). Specifically, five studies with relevance to molecular electronics and heterogeneous catalysis are presented, with a particular focus on interadsorbate interactions, reactivity and characterisation of molecules on transition metal surfaces.
The first part of this work focuses on giving strong theoretical underpinning to the atomic-scale observations provided by scanning tunnelling microscopy (STM) experiments conducted by my group colleagues. The theoretical calculations presented here provide support to the experimental evidences but also serve to unravel information that is inaccessible from the experiments. On the one hand, the variety of results obtained in this thesis using standard DFT methods serve to highlight the capabilities of the computationally low-demanding methods for modelling processes occurring on metal surfaces. On the other hand, we notice that these workhorse methods in DFT have inherent limitations for providing an accurate description of some properties, in particular binding energies. This, further improvements in the level of theory are necessary for advancing the computational accuracy of standard DFT methods in materials science.
The second part of this thesis is devoted to highlight the high level of accuracy obtained by the new theoretical approaches in the field of materials science. Due to the recent implementation of new algorithms combined with the increasing computer power that is available to the scientific community, these sophisticated methods are becoming more accessible for modelling solid-state systems. Here, the recent implementation of the random-phase approximation (RPA) for solids is employed to perform to benchmark study on the adsorption of benzene on different close-packed transition metal surfaces.
The development of new theoretical tools is also essential to improve our predictive capabilities in surface science. A novel approach to correct vibrational intensities by including anharmonicities using density functional perturbation theory (DFPT) is proposed. The new method is tested for the adsorption of different organic molecules on various transition metal surfaces. The results obtained by this implementation demonstrate excellent improvements for predicting accurate spectra of molecules on surfaces.
2017-01-01T00:00:00ZGarrido Torres, José A.In this thesis, a wide breadth of topics related to the field of surface science are addressed using density functional theory (DFT). Specifically, five studies with relevance to molecular electronics and heterogeneous catalysis are presented, with a particular focus on interadsorbate interactions, reactivity and characterisation of molecules on transition metal surfaces.
The first part of this work focuses on giving strong theoretical underpinning to the atomic-scale observations provided by scanning tunnelling microscopy (STM) experiments conducted by my group colleagues. The theoretical calculations presented here provide support to the experimental evidences but also serve to unravel information that is inaccessible from the experiments. On the one hand, the variety of results obtained in this thesis using standard DFT methods serve to highlight the capabilities of the computationally low-demanding methods for modelling processes occurring on metal surfaces. On the other hand, we notice that these workhorse methods in DFT have inherent limitations for providing an accurate description of some properties, in particular binding energies. This, further improvements in the level of theory are necessary for advancing the computational accuracy of standard DFT methods in materials science.
The second part of this thesis is devoted to highlight the high level of accuracy obtained by the new theoretical approaches in the field of materials science. Due to the recent implementation of new algorithms combined with the increasing computer power that is available to the scientific community, these sophisticated methods are becoming more accessible for modelling solid-state systems. Here, the recent implementation of the random-phase approximation (RPA) for solids is employed to perform to benchmark study on the adsorption of benzene on different close-packed transition metal surfaces.
The development of new theoretical tools is also essential to improve our predictive capabilities in surface science. A novel approach to correct vibrational intensities by including anharmonicities using density functional perturbation theory (DFPT) is proposed. The new method is tested for the adsorption of different organic molecules on various transition metal surfaces. The results obtained by this implementation demonstrate excellent improvements for predicting accurate spectra of molecules on surfaces.Nickel- and palladium-catalysed deprotonative cross-couplingsMarelli, Enricohttps://hdl.handle.net/10023/156032019-03-29T11:21:02Z2017-01-01T00:00:00ZTransition metal-catalysed cross coupling chemistry is a valuable tool for synthetic
organic chemistry, enabling the preparation of compounds of great interest. The
catalytic metal of choice is usually palladium, which generally offer better
performances in term of catalytic activity and easy handling. On the other hand, the
use of nickel in this class of reactions is gaining attention, as it would provide more
economically and environmentally sustainable processes.
Deprotonative cross couplings are a subgroup of these reactions, in which the
nucleophile is generated in situ by direct deprotonation of a (relatively) acidic C–H
bond, for example those of an enolizable ketone or an imine. The reaction products
often represent intermediates towards more complex molecular architectures, by virtue
of the well-known carbonyl chemistry.
The development of a Pd-catalysed methodology for the prototypical deprotonative
coupling, the a-arylation of ketones, is reported in this thesis. It requires significantly
lower catalyst loadings compared to previous reports, and displays good tolerance
towards functionalised substrates. A related protocol for the intramolecular a-arylation
of imines towards indoles was subsequently disclosed: as it requires low catalyst
loadings and displays good scalability and simple setup, this methodology is a
promising hit for industrial applications.
The parallel development of nickel-catalysed protocols afforded an efficient method for
the a-arylation of ketones, using chloroarenes as electrophile for the first time in the
literature. The method was further optimised for the synthesis of an intermediate
towards a commercial medicinally active compound. Building up on these findings,
the first nickel-catalysed protocol for the deprotonative arylation of benzylaminederived
imines was also developed.
Last, the first aqueous palladium-catalysed protocol for the a-arylation of ketones was
investigated. The method proved flexible, showing excellent functional group
tolerance: compounds containing base-sensitive functional groups, halogenated small-molecule
drugs, and Boc-protected amino acids were all suitable substrates.
2017-01-01T00:00:00ZMarelli, EnricoTransition metal-catalysed cross coupling chemistry is a valuable tool for synthetic
organic chemistry, enabling the preparation of compounds of great interest. The
catalytic metal of choice is usually palladium, which generally offer better
performances in term of catalytic activity and easy handling. On the other hand, the
use of nickel in this class of reactions is gaining attention, as it would provide more
economically and environmentally sustainable processes.
Deprotonative cross couplings are a subgroup of these reactions, in which the
nucleophile is generated in situ by direct deprotonation of a (relatively) acidic C–H
bond, for example those of an enolizable ketone or an imine. The reaction products
often represent intermediates towards more complex molecular architectures, by virtue
of the well-known carbonyl chemistry.
The development of a Pd-catalysed methodology for the prototypical deprotonative
coupling, the a-arylation of ketones, is reported in this thesis. It requires significantly
lower catalyst loadings compared to previous reports, and displays good tolerance
towards functionalised substrates. A related protocol for the intramolecular a-arylation
of imines towards indoles was subsequently disclosed: as it requires low catalyst
loadings and displays good scalability and simple setup, this methodology is a
promising hit for industrial applications.
The parallel development of nickel-catalysed protocols afforded an efficient method for
the a-arylation of ketones, using chloroarenes as electrophile for the first time in the
literature. The method was further optimised for the synthesis of an intermediate
towards a commercial medicinally active compound. Building up on these findings,
the first nickel-catalysed protocol for the deprotonative arylation of benzylaminederived
imines was also developed.
Last, the first aqueous palladium-catalysed protocol for the a-arylation of ketones was
investigated. The method proved flexible, showing excellent functional group
tolerance: compounds containing base-sensitive functional groups, halogenated small-molecule
drugs, and Boc-protected amino acids were all suitable substrates.New advanced electrode materials for lithium-ion batteryLi, Dahttps://hdl.handle.net/10023/156012018-12-20T12:40:46Z2018-01-01T00:00:00ZThis thesis includes five main studies/ first, in order to enhance the conductivity of LiTi₂0₄, a new doping strategy is used and LiTi₂0₄₋ₓCₓ ramsdellite is successfully fabricated. It is found that unit cell parameters a and b decline while c increases with more carbon inserted. The conductivity of LiTi₂0₄₋ₓCₓ increases with more carbon insertion. Material with more carbon shows better reversibility and lower electrochemical polarization observed from potentiostatic curve. The material has better retention rate and rate ability with more carbon substitute doped. LiTi₂0₃.₉₂₅C₀.₀₃₇₅ has 151 mAh∙g⁻¹ capacity under current density of 100 mAh∙g⁻¹ and capacity decreased by 5.57% after 100 cycles.
Second, in order to improve the capacity of LiTi₂0₄₋ₓCₓ, Ti₂0₄₋ₓCₓ is successfully fabricated through topotactic oxidation. It is found that the lattice parameters b and c decline while a keeps stable. With more carbon inserted, the retention ability increases. Ti0₁.₉₆₂₅C₀.₀₃₇₅ has the capacity 320 mAh∙g⁻¹ under 200 mAh∙g⁻¹ and capacity retention loss by 9.1% per 100 cycles due to the balance of high conductivity and disordered channel resistance.
Third, in order to study the process of lithium insertion, the structures and the atom sites of LiTi₂0₄₋ₓCₓ ( R ) are obtained through refinement of the neutron diffraction patterns. The unit cell parameters a and b increase while c keeps stable for more lithium, atoms insertion. The channels for lithium insertion become wider and more round with lithium arranged in a line when x rises in the range of 0<x<0.5. When the x increases to 1, the channels turn into ordered parallelogram.
Fourth, the lithium-contained spinelloid (a potential cathode material) is explored, but it is not found in this work. But spinels LI₁₋₀.₅ₓFe₂.₅ₓM₁₋ₓP₁₋ₓO₄ (M=Fe, Co, Ni, Mn) are found and phosphorous insertion makes the structure stable during cycling.
At last, to enhance the energy density, the 3D electrode is fabricated in in-situ growth by infiltration method. By powder infiltration, the load of activity material reaches over 60% of electrode mass. The morphology is porous and the particle size of the activity material is 20nm. The energy density based on LiCoO2 (250 WH∙g⁻¹) is much higher than that of the traditional (200 WH∙g⁻¹) 2D electrode reported.
2018-01-01T00:00:00ZLi, DaThis thesis includes five main studies/ first, in order to enhance the conductivity of LiTi₂0₄, a new doping strategy is used and LiTi₂0₄₋ₓCₓ ramsdellite is successfully fabricated. It is found that unit cell parameters a and b decline while c increases with more carbon inserted. The conductivity of LiTi₂0₄₋ₓCₓ increases with more carbon insertion. Material with more carbon shows better reversibility and lower electrochemical polarization observed from potentiostatic curve. The material has better retention rate and rate ability with more carbon substitute doped. LiTi₂0₃.₉₂₅C₀.₀₃₇₅ has 151 mAh∙g⁻¹ capacity under current density of 100 mAh∙g⁻¹ and capacity decreased by 5.57% after 100 cycles.
Second, in order to improve the capacity of LiTi₂0₄₋ₓCₓ, Ti₂0₄₋ₓCₓ is successfully fabricated through topotactic oxidation. It is found that the lattice parameters b and c decline while a keeps stable. With more carbon inserted, the retention ability increases. Ti0₁.₉₆₂₅C₀.₀₃₇₅ has the capacity 320 mAh∙g⁻¹ under 200 mAh∙g⁻¹ and capacity retention loss by 9.1% per 100 cycles due to the balance of high conductivity and disordered channel resistance.
Third, in order to study the process of lithium insertion, the structures and the atom sites of LiTi₂0₄₋ₓCₓ ( R ) are obtained through refinement of the neutron diffraction patterns. The unit cell parameters a and b increase while c keeps stable for more lithium, atoms insertion. The channels for lithium insertion become wider and more round with lithium arranged in a line when x rises in the range of 0<x<0.5. When the x increases to 1, the channels turn into ordered parallelogram.
Fourth, the lithium-contained spinelloid (a potential cathode material) is explored, but it is not found in this work. But spinels LI₁₋₀.₅ₓFe₂.₅ₓM₁₋ₓP₁₋ₓO₄ (M=Fe, Co, Ni, Mn) are found and phosphorous insertion makes the structure stable during cycling.
At last, to enhance the energy density, the 3D electrode is fabricated in in-situ growth by infiltration method. By powder infiltration, the load of activity material reaches over 60% of electrode mass. The morphology is porous and the particle size of the activity material is 20nm. The energy density based on LiCoO2 (250 WH∙g⁻¹) is much higher than that of the traditional (200 WH∙g⁻¹) 2D electrode reported.Identification and metabolism studies of fluorometabolites from different StreptomycesBartholomé, Axelhttps://hdl.handle.net/10023/155922019-04-05T15:47:58Z2017-01-01T00:00:00ZTo date, only five fluorinated natural products have been identified. These were isolated from
both plants and bacteria. The bacterium Streptomyces cattleya has the ability to biosynthesise
fluoroacetate and 4-fluoro-L-threonine. The first enzyme discovered to be capable of
catalysing a C-F bond from fluoride ion, the fluorinase, was identified from S. cattleya in 2002
and is involved in the first step in the biosynthesis of fluorometabolites. The complete
metabolic pathway of fluoroacetate and 4-fluoro-L-threonine in S. cattleya was elucidated
utilising a variety of different techniques.
Recently, genome studies revealed the presence of four new fluorinase enzymes from
different bacterial species. Cultures of one of these species, named Streptomyces sp. MA37,
showed the production of new unidentified fluorometabolites. Over-expression of the FdrC
gene from Streptomyces sp. MA37 was performed, and enzymatic assays of the FdrC enzyme
allowed the conversion of 5-fluoro-5-deoxy-ribose to (2R,3S,4S)-5-fluoro-2,3,4-
trihydroxypentanoic acid. Identification of (2R,3S,4S)-5-fluoro-2,3,4-trihydroxypentanoic acid
as a new fluorometabolite was then confirmed by synthetic synthesis.
Nucleocidin, an antibiotic containing fluorine, was isolated in 1957 from the soil bacterium,
Streptomyces calvus. Since its isolation, attempts at re-establishing nucleocidin producing
cultures have proven unsuccessful. The biosynthesis of nucleocidin involves a C-F bond-
forming enzyme unique to Streptomyces calvus. Production of a commercial strain from Pfizer
was established and isotopic labelling studies with different labelled glycerols were completed.
Pulse feeding experiments with (2R)-[1- ²H₂]-glycerol, (2S)-[1- ²H₂]-glycerol, glycerol-1,1,2,3,3-d₅ and [2-¹³ C]-glycerol proved to be successful. Concomitantly, synthesis of highly pure putative substrates for the fluorinating enzyme was carried out. Unfortunately, cell-free extract experiments were achieved, but results from these were not conclusive.
2017-01-01T00:00:00ZBartholomé, AxelTo date, only five fluorinated natural products have been identified. These were isolated from
both plants and bacteria. The bacterium Streptomyces cattleya has the ability to biosynthesise
fluoroacetate and 4-fluoro-L-threonine. The first enzyme discovered to be capable of
catalysing a C-F bond from fluoride ion, the fluorinase, was identified from S. cattleya in 2002
and is involved in the first step in the biosynthesis of fluorometabolites. The complete
metabolic pathway of fluoroacetate and 4-fluoro-L-threonine in S. cattleya was elucidated
utilising a variety of different techniques.
Recently, genome studies revealed the presence of four new fluorinase enzymes from
different bacterial species. Cultures of one of these species, named Streptomyces sp. MA37,
showed the production of new unidentified fluorometabolites. Over-expression of the FdrC
gene from Streptomyces sp. MA37 was performed, and enzymatic assays of the FdrC enzyme
allowed the conversion of 5-fluoro-5-deoxy-ribose to (2R,3S,4S)-5-fluoro-2,3,4-
trihydroxypentanoic acid. Identification of (2R,3S,4S)-5-fluoro-2,3,4-trihydroxypentanoic acid
as a new fluorometabolite was then confirmed by synthetic synthesis.
Nucleocidin, an antibiotic containing fluorine, was isolated in 1957 from the soil bacterium,
Streptomyces calvus. Since its isolation, attempts at re-establishing nucleocidin producing
cultures have proven unsuccessful. The biosynthesis of nucleocidin involves a C-F bond-
forming enzyme unique to Streptomyces calvus. Production of a commercial strain from Pfizer
was established and isotopic labelling studies with different labelled glycerols were completed.
Pulse feeding experiments with (2R)-[1- ²H₂]-glycerol, (2S)-[1- ²H₂]-glycerol, glycerol-1,1,2,3,3-d₅ and [2-¹³ C]-glycerol proved to be successful. Concomitantly, synthesis of highly pure putative substrates for the fluorinating enzyme was carried out. Unfortunately, cell-free extract experiments were achieved, but results from these were not conclusive.Petrological, geochemical, and diagenetic studies of the Euphrates Limestone Formation (Lower Miocene) of the Jambur area, Northeast IraqRashid, Ibrahim Abdul Karimhttps://hdl.handle.net/10023/155812019-03-29T11:22:09Z1989-01-01T00:00:00ZThe Euphrates Limestone Formation in north Iraq is encountered at depth in Jambur Field and eight cores were studied in this work. The formation is overlain by Dhiban Anhydrite Formation and underlain by the basinal Serikagni Formation. The formation was deposited in a shallow lagoonal environment. Three types of dolomites have been observed in the Euphrates Limestone Formation. The first type is class A which is very fine (4-10 microns) and associated with anhydrite and gypsum. Its origin is presumed to be of contemporaneous primary dolomite formed in a supratidal environment. The second type is class B (10-30 microns in grain size) formed as a replacement of pre-existing carbonate sediments. Reflux of hypersaline brines is presumed to have been the source of magnesium for this type of dolomite. The third type of dolomite is formed of larger crystals 50-100 microns. This type is formed of euhedral and inclusion-free rhombs filling pores and vugs, and sometimes disseminated between other types of dolomite. This dolomite probably formed by mixing of meteoric water with sea water. The dolomite in the Euphrates Limestone Formation is mainly stoichiometric and well-ordered in the southern part of the studied area. Eight types of dolomitization fabrics are observed in the formation. These types range between partial to complete dolomitization with complete obliteration of the original textures. The degree of dolomitization is very extensive in the southeast part of the studied area, and decreases in the northwest direction. Dolomitization also decreases with depth. Therefore three different areas are recognized during the present work, these areas are; the southeastern (A), the central (B), and the northwestern (C). Euphrates Limestone Formation dolomite has O¹⁸O values ranging between 0.23 to 3.37 %o, which is heavier than most normal marine waters today and very close to modern sabkha dolomites. These heavy values of oxygen isotopes indicates a hypersaline environment as a source for most of the dolomite in the formation Strontium contents in the dolomite are relatively high (500-700 ppm) compared with most ancient dolomites, and similar to the concentration in Holocene dolomite. Different types of diagenetic processes which were responsible for cementation, compaction, dissolution, precipitation of anhydrite, and dolomitization are recognized in the formation. Different types of cements have been identified in the formation, namely isopachous crusts, micritic envelopes, ferroan and non-ferroan calcite. Very high moldic porosity in the oolitic fossilifeous grainstone facies are detected. The overall porosity of the formation in the dolomitized part is high and very low in undolomitized parts.
1989-01-01T00:00:00ZRashid, Ibrahim Abdul KarimThe Euphrates Limestone Formation in north Iraq is encountered at depth in Jambur Field and eight cores were studied in this work. The formation is overlain by Dhiban Anhydrite Formation and underlain by the basinal Serikagni Formation. The formation was deposited in a shallow lagoonal environment. Three types of dolomites have been observed in the Euphrates Limestone Formation. The first type is class A which is very fine (4-10 microns) and associated with anhydrite and gypsum. Its origin is presumed to be of contemporaneous primary dolomite formed in a supratidal environment. The second type is class B (10-30 microns in grain size) formed as a replacement of pre-existing carbonate sediments. Reflux of hypersaline brines is presumed to have been the source of magnesium for this type of dolomite. The third type of dolomite is formed of larger crystals 50-100 microns. This type is formed of euhedral and inclusion-free rhombs filling pores and vugs, and sometimes disseminated between other types of dolomite. This dolomite probably formed by mixing of meteoric water with sea water. The dolomite in the Euphrates Limestone Formation is mainly stoichiometric and well-ordered in the southern part of the studied area. Eight types of dolomitization fabrics are observed in the formation. These types range between partial to complete dolomitization with complete obliteration of the original textures. The degree of dolomitization is very extensive in the southeast part of the studied area, and decreases in the northwest direction. Dolomitization also decreases with depth. Therefore three different areas are recognized during the present work, these areas are; the southeastern (A), the central (B), and the northwestern (C). Euphrates Limestone Formation dolomite has O¹⁸O values ranging between 0.23 to 3.37 %o, which is heavier than most normal marine waters today and very close to modern sabkha dolomites. These heavy values of oxygen isotopes indicates a hypersaline environment as a source for most of the dolomite in the formation Strontium contents in the dolomite are relatively high (500-700 ppm) compared with most ancient dolomites, and similar to the concentration in Holocene dolomite. Different types of diagenetic processes which were responsible for cementation, compaction, dissolution, precipitation of anhydrite, and dolomitization are recognized in the formation. Different types of cements have been identified in the formation, namely isopachous crusts, micritic envelopes, ferroan and non-ferroan calcite. Very high moldic porosity in the oolitic fossilifeous grainstone facies are detected. The overall porosity of the formation in the dolomitized part is high and very low in undolomitized parts.Mining subsidence: its effects on the South-East Fife coastline, ScotlandSaiu, Elisabethhttps://hdl.handle.net/10023/155532019-03-29T11:23:57Z1999-01-01T00:00:00ZThis thesis is concerned with the impact of coal mining activities upon the coastal zone of southeast Fife. Coastal changes over a 100 year period from 1894 to 1996 have been evaluated by determining the plan variation of the High Water and Low Water datum recorded on different editions of large scale Ordnance Survey (O.S.) Plans of the area. Deposition and erosion implied by the movement of the tidal datum are related to the longshore dispersal of spoil deposition from the coastal bings (1) and to mining subsidence. Mining subsidence is evaluated using the Surface Deformation Prediction System (SDPS), previously used at sites in the United States, and now applied for the first time to a United Kingdom coalfield. A new technique is developed that enables the subsidence values to be generated along O.S. co-ordinates at 10m intervals. Subsidence values are recorded with an accuracy of ±20% along the tidal marks of 1894, 1914, 1960, 1994 and 1996. Between Buckhaven and Dysart the coastline is found to have subsided with only small pockets having been left unaffected. Indeed, in the West Sands Bay area a subsidence trough with a maximum of 5.7+l.lm is calculated. The extent of recent coastal erosion along the shore can be seen to correlate with predicted subsidence over different mining panels and thus confirms the importance of this factor upon the coastal process in south-east Fife. These results are reinforced by comparing bench-mark heights against subsidence values producing a correlation coefficient of 0.9. The state of the pre-mining coastline is evaluated using historic documents and photographs. This provides a starting point for evaluating the changes wrought on the coastline by the large scale mining activities which commenced about 1898 and terminated with the closure of the Frances colliery in 1984. Following this, the extent of coastal change from the analysis of O.S Plans is presented. Subsequent chapters evaluate the possible factors which may have caused the observed coastal changes including long term changes, land uplift or subsidence following the last glaciation, mining activities and possible sea level changes due to global warming. To ensure the greatest possible accuracy in the determination of coastal changes against subsidence data a rigorous GIS is employed to analyse both map and mining data allowing for registrations to be obtained between the different surveys. This involves the manipulation of both vector and raster data from the O.S. plans and the SDPS software requiring the laborious and lime consuming transfer of data between different computer platforms. Despite this caveat this novel method is demonstrated, in the thesis, to be a flexible and precise method which can be applied to any given site for the accurate prediction of mining subsidence. 1: Bing is the Scottish phrase for slag heap.
1999-01-01T00:00:00ZSaiu, ElisabethThis thesis is concerned with the impact of coal mining activities upon the coastal zone of southeast Fife. Coastal changes over a 100 year period from 1894 to 1996 have been evaluated by determining the plan variation of the High Water and Low Water datum recorded on different editions of large scale Ordnance Survey (O.S.) Plans of the area. Deposition and erosion implied by the movement of the tidal datum are related to the longshore dispersal of spoil deposition from the coastal bings (1) and to mining subsidence. Mining subsidence is evaluated using the Surface Deformation Prediction System (SDPS), previously used at sites in the United States, and now applied for the first time to a United Kingdom coalfield. A new technique is developed that enables the subsidence values to be generated along O.S. co-ordinates at 10m intervals. Subsidence values are recorded with an accuracy of ±20% along the tidal marks of 1894, 1914, 1960, 1994 and 1996. Between Buckhaven and Dysart the coastline is found to have subsided with only small pockets having been left unaffected. Indeed, in the West Sands Bay area a subsidence trough with a maximum of 5.7+l.lm is calculated. The extent of recent coastal erosion along the shore can be seen to correlate with predicted subsidence over different mining panels and thus confirms the importance of this factor upon the coastal process in south-east Fife. These results are reinforced by comparing bench-mark heights against subsidence values producing a correlation coefficient of 0.9. The state of the pre-mining coastline is evaluated using historic documents and photographs. This provides a starting point for evaluating the changes wrought on the coastline by the large scale mining activities which commenced about 1898 and terminated with the closure of the Frances colliery in 1984. Following this, the extent of coastal change from the analysis of O.S Plans is presented. Subsequent chapters evaluate the possible factors which may have caused the observed coastal changes including long term changes, land uplift or subsidence following the last glaciation, mining activities and possible sea level changes due to global warming. To ensure the greatest possible accuracy in the determination of coastal changes against subsidence data a rigorous GIS is employed to analyse both map and mining data allowing for registrations to be obtained between the different surveys. This involves the manipulation of both vector and raster data from the O.S. plans and the SDPS software requiring the laborious and lime consuming transfer of data between different computer platforms. Despite this caveat this novel method is demonstrated, in the thesis, to be a flexible and precise method which can be applied to any given site for the accurate prediction of mining subsidence. 1: Bing is the Scottish phrase for slag heap.NMR investigations of dynamic phenomena in crystalline organic solidsCameron, Kenneth Stuarthttps://hdl.handle.net/10023/155402019-03-29T11:21:29Z1997-01-01T00:00:00ZThe study of the following compounds is based on the premise that high symmetry in molecules should lead to low barriers to molecular motion even in the solid state i.e. the principle of least distress. The study of 3,3-diethylpentane is a very nice example of a phase change which results in no chemical shift changes but, produces a sharp discontinuity in the rate of ethyl group rotation. A large discontinuity in rate of molecular motion is also observed in 4,4-dipropylheptane which is also due to a phase change. The following study of tetraalkyl ammonium halides revealed both alkyl group rotation and cation tumbling to be occurring. This is most significant in the tetramethyl ammonium halides where the effects of methyl rotation and cation tumbling are shown to overlap considerably. The activation energies for the cation tumbling in the tetramethyl ammonium halides are Ea= 30 - 36 kJ mol⁻¹ and for ethyl group rotation in tetraethyl ammonium chloride are, △H†; = 57.8 kJ mol⁻¹ and △S†; = 45.9 J K⁻¹ mol⁻¹. The chemical shift differences in each chain due to different chain lengths is seen in tetrabutyl ammonium iodate which also shows a sudden coalescence and introduction of rapid molecular motion after two small phase changes. This compound has a large phase change which also affects the rate of molecular motion. The tetraalkyl phosphonium halides have a greater degree of molecular motion than the ammoniums in the temperature range studied and also offer the chance to use Tip measurements. The tetramethyl phosphonium halides show a distinct cation tumbling as opposed to the ammoniums. The process in the chloride and bromide which have hexagonal structures gives △H†; ~ 30 kJ mol⁻¹ and negative △S†; values and the lower symmetry iodide has △H†; = 45.2 kJ mol⁻¹ and a positive value of △S†;. The tetraethyl phosphonium halides show ethyl group rotations measurable to varying degrees by 13CT1p. The tetrabutyl phosphonium halides also have the different chain lengths as seen for the ammonium compounds. They also show bond rotations which are quite difficult to measure by 13CT1p values. The study of bis-(hydroxymethyl)cyclopentane (BHMCP) in an attempt to study ring puckering/pseudorotation in cyclopentane derivatives in the solid state reveals a hydrogen bond exchange process (△Gc†;~ 60 kJ mol⁻¹). The bicyclic derivatives of BHMCP showed no such molecular motions but did reveal some interesting solid- solid phase transitions and chemical shift changes. The study of trans-cyclopentanediol yields △H†; = 77.0 and △S&†; = 184 J K⁻¹ mol⁻¹ for the processes involved. The study of 4,4-dimethyl-trans⁻¹,2-cyclopentanediol reveals two processes. One results in the coalescence of resonances and appears to be a hydrogen bonding exchange process. The other is a much lower energy process (Ea ~ 26 kJ mol⁻¹) which could be a ring puckering process. The study of sulpholane also shows significant molecular motion with △H&†; = 50.6 kJ mol⁻¹ and △S&†; = 77.9 J K⁻¹ mol⁻¹.
1997-01-01T00:00:00ZCameron, Kenneth StuartThe study of the following compounds is based on the premise that high symmetry in molecules should lead to low barriers to molecular motion even in the solid state i.e. the principle of least distress. The study of 3,3-diethylpentane is a very nice example of a phase change which results in no chemical shift changes but, produces a sharp discontinuity in the rate of ethyl group rotation. A large discontinuity in rate of molecular motion is also observed in 4,4-dipropylheptane which is also due to a phase change. The following study of tetraalkyl ammonium halides revealed both alkyl group rotation and cation tumbling to be occurring. This is most significant in the tetramethyl ammonium halides where the effects of methyl rotation and cation tumbling are shown to overlap considerably. The activation energies for the cation tumbling in the tetramethyl ammonium halides are Ea= 30 - 36 kJ mol⁻¹ and for ethyl group rotation in tetraethyl ammonium chloride are, △H†; = 57.8 kJ mol⁻¹ and △S†; = 45.9 J K⁻¹ mol⁻¹. The chemical shift differences in each chain due to different chain lengths is seen in tetrabutyl ammonium iodate which also shows a sudden coalescence and introduction of rapid molecular motion after two small phase changes. This compound has a large phase change which also affects the rate of molecular motion. The tetraalkyl phosphonium halides have a greater degree of molecular motion than the ammoniums in the temperature range studied and also offer the chance to use Tip measurements. The tetramethyl phosphonium halides show a distinct cation tumbling as opposed to the ammoniums. The process in the chloride and bromide which have hexagonal structures gives △H†; ~ 30 kJ mol⁻¹ and negative △S†; values and the lower symmetry iodide has △H†; = 45.2 kJ mol⁻¹ and a positive value of △S†;. The tetraethyl phosphonium halides show ethyl group rotations measurable to varying degrees by 13CT1p. The tetrabutyl phosphonium halides also have the different chain lengths as seen for the ammonium compounds. They also show bond rotations which are quite difficult to measure by 13CT1p values. The study of bis-(hydroxymethyl)cyclopentane (BHMCP) in an attempt to study ring puckering/pseudorotation in cyclopentane derivatives in the solid state reveals a hydrogen bond exchange process (△Gc†;~ 60 kJ mol⁻¹). The bicyclic derivatives of BHMCP showed no such molecular motions but did reveal some interesting solid- solid phase transitions and chemical shift changes. The study of trans-cyclopentanediol yields △H†; = 77.0 and △S&†; = 184 J K⁻¹ mol⁻¹ for the processes involved. The study of 4,4-dimethyl-trans⁻¹,2-cyclopentanediol reveals two processes. One results in the coalescence of resonances and appears to be a hydrogen bonding exchange process. The other is a much lower energy process (Ea ~ 26 kJ mol⁻¹) which could be a ring puckering process. The study of sulpholane also shows significant molecular motion with △H&†; = 50.6 kJ mol⁻¹ and △S&†; = 77.9 J K⁻¹ mol⁻¹.Structural studies of some heterocyclic and organometallic compoundsHolden, Hazel Dianehttps://hdl.handle.net/10023/155382019-03-29T11:22:54Z1981-01-01T00:00:00ZSingle crystal X-ray work was carried out for four heterocyclic compounds: prior to this, definitive structures could not be written for any of these. The heterocyclic compounds reported are: 5,6-dihydro-1-thiobenzoylmethylene-1H-thiazolo[2,3-c][1,2,4] thiadiazole, (I); 4-N-(4'-bromophenylamino)-3-butylfuroxan, (II); 4,4'-methylenebis(1,3,5-trimethyl-4-imidazolin-2-one), (III), and 4-phenyl-3-phenylamino-1,2,4-thiadiazoline-5-one, (IV). These are then discussed, along with work which has been carried out for similar compounds. Trithiapentalenes and analogues having linear multisulphur systems are mentioned as criteria for deciding whether the NSS skeleton in (I) is best considered as N-S...S or N-S-S. Following this, the X-ray structure determinations of bis(4-methylpyridine)hydrogen(I) tetraphenylborate, (V), and bis(triphenylarsineoxide)hydrogen(I) tetrafluoroborate, (VI), arereported. Both (V) and (VI) are bis-cations which have strong hydrogen bonding. Other compounds with short 0...H...0 and N...H...N distances are mentioned, stabilities of such bis-cations compared to those of the monocations, and (amine-halogen-amine)⁺ complexes discussed. The final two X-ray structure determinations are for the compounds 1,1,1,3,3,3-hexaphenyldisilazane and µ-nitrido-bis (triphenylphosphorus)((I) thiocyanate. MNDO was used to calculate force constants for bending of linear molecular pseudohalides. The aim of such work was to rationalise 'unusual' geometries in some silicon-containing compounds via Second Order Jahn-Teller distortions, postulating that such compounds are easily distorted along a "soft' normal vibration coordinate.
1981-01-01T00:00:00ZHolden, Hazel DianeSingle crystal X-ray work was carried out for four heterocyclic compounds: prior to this, definitive structures could not be written for any of these. The heterocyclic compounds reported are: 5,6-dihydro-1-thiobenzoylmethylene-1H-thiazolo[2,3-c][1,2,4] thiadiazole, (I); 4-N-(4'-bromophenylamino)-3-butylfuroxan, (II); 4,4'-methylenebis(1,3,5-trimethyl-4-imidazolin-2-one), (III), and 4-phenyl-3-phenylamino-1,2,4-thiadiazoline-5-one, (IV). These are then discussed, along with work which has been carried out for similar compounds. Trithiapentalenes and analogues having linear multisulphur systems are mentioned as criteria for deciding whether the NSS skeleton in (I) is best considered as N-S...S or N-S-S. Following this, the X-ray structure determinations of bis(4-methylpyridine)hydrogen(I) tetraphenylborate, (V), and bis(triphenylarsineoxide)hydrogen(I) tetrafluoroborate, (VI), arereported. Both (V) and (VI) are bis-cations which have strong hydrogen bonding. Other compounds with short 0...H...0 and N...H...N distances are mentioned, stabilities of such bis-cations compared to those of the monocations, and (amine-halogen-amine)⁺ complexes discussed. The final two X-ray structure determinations are for the compounds 1,1,1,3,3,3-hexaphenyldisilazane and µ-nitrido-bis (triphenylphosphorus)((I) thiocyanate. MNDO was used to calculate force constants for bending of linear molecular pseudohalides. The aim of such work was to rationalise 'unusual' geometries in some silicon-containing compounds via Second Order Jahn-Teller distortions, postulating that such compounds are easily distorted along a "soft' normal vibration coordinate.Optical investigation of the energy levels of manganese in zinc selenide, zinc sulphide and zinc seleno-sulphideLeslie, Thomas Couttshttps://hdl.handle.net/10023/155372019-03-29T11:21:46Z1980-01-01T00:00:00ZThis thesis describes the results of a course of experimental research into the optical properties of manganese impurities in the II-VI host lattices ZnSe, ZnS, and ZnSe[sub]xS₁₋[sub]x.
These materials are of some commercial importance, since they exhibit electroluminescence when appropriately prepared. For this reason it is desirable to ascertain which inherent properties of the materials would determine device performance, and to try to distinguish these from apparently limiting criteria which are in fact cause by unknown and unwanted defects. Removal of such undesirable impurities may substantially benefit device performance.
These materials are also of interest in that they exhibit some of the more complex properties of solids which can only be studied by the selection of a material which manifests the effects in question. That is, although the effects are studied in these compounds, it is to be expected that they will also occur more generally, although not perhaps as obviously.
In order to fully appreciate some of the more complex effects which are studied, it is necessary to provide a substantial theoretical background. This is the function of chapters two, three, and four in this work. Chapter two is an introduction to the fundamental problem of transition metal impurities in solids, together with an indication of the approaches which have been made, and the approximation invoked. In chapter three the general problem of electron lattice interactions is discussed, with the aim being to offer an insight into the Jahn-Teller and Ham effects. Chapter four deals more specifically with the zero- phonon lines, including a mechanism which had hitherto received scant attention in this context.
The details of the experimental apparatus and techniques are given in chapter 5, together with computational methods. Also included in this chapter is a method of determining mixed crystal composition, applicable to the ZnSe[sub]xS₁-[sub]x system which is much simpler than other techniques which have been employed.
Chapter six reports the results of investigations into the zero-phonon lines in ZnSe:Mn. These results are interpreted in terms of the Jahn-Teller and Ham effects, and from the type of broadening mechanism invoked to explain the temperature dependence of the lines, a more accurate assignation of the energies of states split by the spin-orbit and Jahn-Teller interactions is made. The broadening mechanism invoked is of some importance, since it appears to have been largely ignored in studies on zero-phonon lines, although it is well known in those on spin-lattice relaxation.
In chapter 7, the problem of non-radiative transitions in all three materials is studied, with the emphasis being on the limitations which they inflict on possible devices. Radiationless processes are considered first of all by investigating thermal dependence of emission intensity, and secondly by examining the effects of temperature on the lifetime of the excited state involved in the transition. It is demonstrated that the thermal quenching of luminescence is not an inherent property of the materials used, which had previously been suggested, but is dependent on the existence of some unidentified defect.
Those chapters (i.e. six and seven) are essentially complete in themselves, including conclusions. In chapter eight, a brief, general summing-up is given, together with suggestions for some further work.
1980-01-01T00:00:00ZLeslie, Thomas CouttsThis thesis describes the results of a course of experimental research into the optical properties of manganese impurities in the II-VI host lattices ZnSe, ZnS, and ZnSe[sub]xS₁₋[sub]x.
These materials are of some commercial importance, since they exhibit electroluminescence when appropriately prepared. For this reason it is desirable to ascertain which inherent properties of the materials would determine device performance, and to try to distinguish these from apparently limiting criteria which are in fact cause by unknown and unwanted defects. Removal of such undesirable impurities may substantially benefit device performance.
These materials are also of interest in that they exhibit some of the more complex properties of solids which can only be studied by the selection of a material which manifests the effects in question. That is, although the effects are studied in these compounds, it is to be expected that they will also occur more generally, although not perhaps as obviously.
In order to fully appreciate some of the more complex effects which are studied, it is necessary to provide a substantial theoretical background. This is the function of chapters two, three, and four in this work. Chapter two is an introduction to the fundamental problem of transition metal impurities in solids, together with an indication of the approaches which have been made, and the approximation invoked. In chapter three the general problem of electron lattice interactions is discussed, with the aim being to offer an insight into the Jahn-Teller and Ham effects. Chapter four deals more specifically with the zero- phonon lines, including a mechanism which had hitherto received scant attention in this context.
The details of the experimental apparatus and techniques are given in chapter 5, together with computational methods. Also included in this chapter is a method of determining mixed crystal composition, applicable to the ZnSe[sub]xS₁-[sub]x system which is much simpler than other techniques which have been employed.
Chapter six reports the results of investigations into the zero-phonon lines in ZnSe:Mn. These results are interpreted in terms of the Jahn-Teller and Ham effects, and from the type of broadening mechanism invoked to explain the temperature dependence of the lines, a more accurate assignation of the energies of states split by the spin-orbit and Jahn-Teller interactions is made. The broadening mechanism invoked is of some importance, since it appears to have been largely ignored in studies on zero-phonon lines, although it is well known in those on spin-lattice relaxation.
In chapter 7, the problem of non-radiative transitions in all three materials is studied, with the emphasis being on the limitations which they inflict on possible devices. Radiationless processes are considered first of all by investigating thermal dependence of emission intensity, and secondly by examining the effects of temperature on the lifetime of the excited state involved in the transition. It is demonstrated that the thermal quenching of luminescence is not an inherent property of the materials used, which had previously been suggested, but is dependent on the existence of some unidentified defect.
Those chapters (i.e. six and seven) are essentially complete in themselves, including conclusions. In chapter eight, a brief, general summing-up is given, together with suggestions for some further work.Studies on the photocatalytic activity of titanium dioxideFraser, Ian Muirhttps://hdl.handle.net/10023/155302019-03-29T11:20:57Z1986-01-01T00:00:00ZA novel technique for determining the photoactivity of anatase and rutile forms of TiO₂ has been developed. This involves measurement of the rate of oxygen-uptake in the propan-2-ol/propanone dehydrogenation system, which is photocatalysed by TiO₂ particles maintained in suspension. The system has been studied under several experimental conditions, including the variation of incident light intensity and sample temperature. The effect of varying the alcohol concentration on the oxygen-uptake rate has been studied and, found to be related to the self-association properties of the alcohol, as determined from a series of NMR studies. In addition, strong organic bases have been shown to be effective in reducing the oxygen-uptake rate and a mechanism involving the blocking of surface sites on TiO₂ is proposed. The generation and participation H₂O₂ of in the alcohol to ketone conversion has been studied and, in particular, a technique has been developed to enable the luminescence, which has been observed to emanate from the vortex of the irradiated suspension, to be studied under various experimental conditions. This technique revealed the rapid nature of the interaction of H₂O₂ at the TiO₂ surface. The overall mechanism of the photocatalysed dehydrogenation is discussed in terms of two interdependent pathways: one involving oxygen, the other H₂O₂. Photoluminescence from dry, powdered samples of anatase and rutile has been observed at low temperatures upon excitation with a pulsed nitrogen laser. The decay kinetics of the photoluminesoence have been modelled via computer fitting techniques and the participation of two sets of trapping sites is postulated for anatase and rutile. The photophysical behaviour of benzophenone in poly(methylmethacrylate) films has been studied and a dual pathway for triplet deactivation, involving delayed fluorescence and triplet-triplet annihilation put forward.
1986-01-01T00:00:00ZFraser, Ian MuirA novel technique for determining the photoactivity of anatase and rutile forms of TiO₂ has been developed. This involves measurement of the rate of oxygen-uptake in the propan-2-ol/propanone dehydrogenation system, which is photocatalysed by TiO₂ particles maintained in suspension. The system has been studied under several experimental conditions, including the variation of incident light intensity and sample temperature. The effect of varying the alcohol concentration on the oxygen-uptake rate has been studied and, found to be related to the self-association properties of the alcohol, as determined from a series of NMR studies. In addition, strong organic bases have been shown to be effective in reducing the oxygen-uptake rate and a mechanism involving the blocking of surface sites on TiO₂ is proposed. The generation and participation H₂O₂ of in the alcohol to ketone conversion has been studied and, in particular, a technique has been developed to enable the luminescence, which has been observed to emanate from the vortex of the irradiated suspension, to be studied under various experimental conditions. This technique revealed the rapid nature of the interaction of H₂O₂ at the TiO₂ surface. The overall mechanism of the photocatalysed dehydrogenation is discussed in terms of two interdependent pathways: one involving oxygen, the other H₂O₂. Photoluminescence from dry, powdered samples of anatase and rutile has been observed at low temperatures upon excitation with a pulsed nitrogen laser. The decay kinetics of the photoluminesoence have been modelled via computer fitting techniques and the participation of two sets of trapping sites is postulated for anatase and rutile. The photophysical behaviour of benzophenone in poly(methylmethacrylate) films has been studied and a dual pathway for triplet deactivation, involving delayed fluorescence and triplet-triplet annihilation put forward.An examination of some aromatic molecules by the method of electron impactHamer, Allan Normanhttps://hdl.handle.net/10023/155292019-03-29T11:22:26Z1957-01-01T00:00:00ZThe thesis begins with an account of the behaviour of molecules on electron impact and explains how bond dissociation energies may be deduced from a study of ionization processes. The experimental work was carried out with a mass spectrometer designed and built for the purpose, and a full description of this instrument is provided, together with an account of the problems which arose during its construction and development, and the performance of which it was ultimately capable. After the reliability of the instrument had been tested by investigating some simple ionization processes, it was used to study the formation of benzyl ions from a number of related aromatic compounds. When the appearance potentials obtained in this way are combined with the ionization potential of the benzyl radical (which is the subject of a separate and direct determination) it is possible to make provisional estimates of the benzyl-x bond energy in dibenzyl, benzyl chloride, and benzyl iodide. The derived value of D (PhCH₂ -CH₂Ph) is used to verify Swarc's value of 77.5 kcal for D (PhCH₂ -H). From this quantity, the following bond energies may be deduced thermochemically: D (PhCH₂ -CH₂Ph) - 45±3 kcal;/ D (PhCH₂ -CH₃) - 63±3 kcal; D(PhCH₂-Ph) - 74.4±3 kcal, D (PhCH₂ -I) - 36.6±4 kcal; D (PhCH₂ -C1) - 62±4 kcal. The last two values are confirmed by the direct electron impact data. Lastly, an indirect estimate of I(Ph) - 9.7 eV is based on a measurement of the appearance potential of this radical from benzene, and a thermochemical value for D (Ph-H). The thesis ends with a description of how the instrument was modified by the inclusion of a reactor furnace in order to study the mechanisms of thermal decomposition reactions. Results are included of a brief experiment involving the pyrolysis of benzyl iodide out by this means.
1957-01-01T00:00:00ZHamer, Allan NormanThe thesis begins with an account of the behaviour of molecules on electron impact and explains how bond dissociation energies may be deduced from a study of ionization processes. The experimental work was carried out with a mass spectrometer designed and built for the purpose, and a full description of this instrument is provided, together with an account of the problems which arose during its construction and development, and the performance of which it was ultimately capable. After the reliability of the instrument had been tested by investigating some simple ionization processes, it was used to study the formation of benzyl ions from a number of related aromatic compounds. When the appearance potentials obtained in this way are combined with the ionization potential of the benzyl radical (which is the subject of a separate and direct determination) it is possible to make provisional estimates of the benzyl-x bond energy in dibenzyl, benzyl chloride, and benzyl iodide. The derived value of D (PhCH₂ -CH₂Ph) is used to verify Swarc's value of 77.5 kcal for D (PhCH₂ -H). From this quantity, the following bond energies may be deduced thermochemically: D (PhCH₂ -CH₂Ph) - 45±3 kcal;/ D (PhCH₂ -CH₃) - 63±3 kcal; D(PhCH₂-Ph) - 74.4±3 kcal, D (PhCH₂ -I) - 36.6±4 kcal; D (PhCH₂ -C1) - 62±4 kcal. The last two values are confirmed by the direct electron impact data. Lastly, an indirect estimate of I(Ph) - 9.7 eV is based on a measurement of the appearance potential of this radical from benzene, and a thermochemical value for D (Ph-H). The thesis ends with a description of how the instrument was modified by the inclusion of a reactor furnace in order to study the mechanisms of thermal decomposition reactions. Results are included of a brief experiment involving the pyrolysis of benzyl iodide out by this means.The Fe3+/2+ redox couple in liquid and solid solventsChristie, Lynnhttps://hdl.handle.net/10023/155282019-03-29T11:23:35Z1996-01-01T00:00:00ZThe Fe³⁺/²⁺ redox couple, in the form of Fe (II) and Fe (III) trifluoromethane sulphonate, has been investigated in several non-aqueous solvents; propylene carbonate (PC), acetonitrile (ACN), tetrahydrofuran (THF), dimethyl sulphoxide (DMSO) and dimethyl formamide (DMF), as well as in tetraethyleneglycol dimethylether, a low molecular weight liquid polyether, and poly(ethylene oxide), a high molecular weight solid polyether. It has been shown that the Fe³⁺/²⁺ couple exhibits a simple one electron transfer reaction in all cases. The influence of the solvent on the electrode kinetics of the Fe³⁺/²⁺ redox couple has been investigated with a view to identifying the factors controlling the rate of the simple electron transfer process for this redox couple. The standard apparent rate constant (ksh) in each system was determined via ac impedance spectroscopy. For studies in the solid polyether solvent a new technique has been developed involving ac impedance spectroscopy at an ultramicroelectrode. This new technique proved to be a very powerful tool in the identification of interfacial processes occurring in highly resistive media. Using the Marcus and the Levich, Dogonadze & Kuznetsov theories for activation of electron transfer, kinetic data were interpreted in terms of inner and outer sphere contributions from the solvent. For the liquid solvents a correlation between ksh and the donor number of the solvent was found, indicating inner sphere activation of electron transfer via vibration of the coordinate bond. However, for the solid solvent activation of electron transfer was found to be influenced by outer sphere solvent dynamics as solvent reorganisation in the polymer is slower than in the liquid solvents.
1996-01-01T00:00:00ZChristie, LynnThe Fe³⁺/²⁺ redox couple, in the form of Fe (II) and Fe (III) trifluoromethane sulphonate, has been investigated in several non-aqueous solvents; propylene carbonate (PC), acetonitrile (ACN), tetrahydrofuran (THF), dimethyl sulphoxide (DMSO) and dimethyl formamide (DMF), as well as in tetraethyleneglycol dimethylether, a low molecular weight liquid polyether, and poly(ethylene oxide), a high molecular weight solid polyether. It has been shown that the Fe³⁺/²⁺ couple exhibits a simple one electron transfer reaction in all cases. The influence of the solvent on the electrode kinetics of the Fe³⁺/²⁺ redox couple has been investigated with a view to identifying the factors controlling the rate of the simple electron transfer process for this redox couple. The standard apparent rate constant (ksh) in each system was determined via ac impedance spectroscopy. For studies in the solid polyether solvent a new technique has been developed involving ac impedance spectroscopy at an ultramicroelectrode. This new technique proved to be a very powerful tool in the identification of interfacial processes occurring in highly resistive media. Using the Marcus and the Levich, Dogonadze & Kuznetsov theories for activation of electron transfer, kinetic data were interpreted in terms of inner and outer sphere contributions from the solvent. For the liquid solvents a correlation between ksh and the donor number of the solvent was found, indicating inner sphere activation of electron transfer via vibration of the coordinate bond. However, for the solid solvent activation of electron transfer was found to be influenced by outer sphere solvent dynamics as solvent reorganisation in the polymer is slower than in the liquid solvents.Alkali metal beams from solid state electrochemical sourcesRoy, Stephen Campbellhttps://hdl.handle.net/10023/155262019-03-29T11:19:52Z1995-01-01T00:00:00ZAll solid state electrochemical cells capable of producing beams of lithium, sodium and potassium in ultrahigh vacuum have been developed and investigated. The evolution of alkali metal vapour has been demonstrated by deposition of the metal on a substrate during polarisation of the cell followed by ex-situ analysis of the metal using laser ionisation mass analysis (LIMA). The electrochemistry of alkali metal evolution from these unusual solid state cells has been investigated using cyclic voltammetry, chronoamperometry and AC impedance measurements at pressures of 10⁻³ mbar and 10⁻⁸ mbar (UHV). It has been found for all three sources that the mechanism at relatively high pressure involves the nucleation and growth of liquid alkali metals or compounds containing alkali metals on the working electrode prior to their evaporation. In UHV the mechanism for potassium and sodium emission appears to involve the transfer of atoms directly into the gas phase whereas lithium exhibits nucleation and growth. In order to obtain a more complete characterization of the electrochemical mechanisms a spectro-electrochemical technique involving the simultaneous mass spectrometric analysis of the evolved vapour under UHV conditions along with cyclic voltammetry was developed. The formation of p-type ZnSe is essential to the fabrication of blue light emitting diodes and semiconductor lasers but has long represented a major problem in optoelectronics. This work shows that the potassium source can be used to p-dope ZnSe during growth of the material by molecular beam epitaxy (MBE). Efforts directed to the preparation of n-type diamond using a lithium source in microwave enhanced chemical vapour deposition (MWECVD) apparatus have demonstrated that the source can introduce lithium to diamond, although full semiconductor characterization of this material has yet to be made.
1995-01-01T00:00:00ZRoy, Stephen CampbellAll solid state electrochemical cells capable of producing beams of lithium, sodium and potassium in ultrahigh vacuum have been developed and investigated. The evolution of alkali metal vapour has been demonstrated by deposition of the metal on a substrate during polarisation of the cell followed by ex-situ analysis of the metal using laser ionisation mass analysis (LIMA). The electrochemistry of alkali metal evolution from these unusual solid state cells has been investigated using cyclic voltammetry, chronoamperometry and AC impedance measurements at pressures of 10⁻³ mbar and 10⁻⁸ mbar (UHV). It has been found for all three sources that the mechanism at relatively high pressure involves the nucleation and growth of liquid alkali metals or compounds containing alkali metals on the working electrode prior to their evaporation. In UHV the mechanism for potassium and sodium emission appears to involve the transfer of atoms directly into the gas phase whereas lithium exhibits nucleation and growth. In order to obtain a more complete characterization of the electrochemical mechanisms a spectro-electrochemical technique involving the simultaneous mass spectrometric analysis of the evolved vapour under UHV conditions along with cyclic voltammetry was developed. The formation of p-type ZnSe is essential to the fabrication of blue light emitting diodes and semiconductor lasers but has long represented a major problem in optoelectronics. This work shows that the potassium source can be used to p-dope ZnSe during growth of the material by molecular beam epitaxy (MBE). Efforts directed to the preparation of n-type diamond using a lithium source in microwave enhanced chemical vapour deposition (MWECVD) apparatus have demonstrated that the source can introduce lithium to diamond, although full semiconductor characterization of this material has yet to be made.Structural studies of new inorganic oxides and polymer electrolytesThomson, James Burgesshttps://hdl.handle.net/10023/155232019-03-29T11:25:11Z1997-01-01T00:00:00ZA knowledge of structure is crucial to the understanding of inorganic solids and polymers. Neutron and X-ray powder diffraction are two powerful complementary techniques which can be used in the structural characterisation of a variety of crystalline materials. Chemical and electrochemical oxygen intercalation techniques involving both aqueous and non-aqueous systems, have been investigated for a number of crystalline inorganic oxides. The pyrochlore structure has been discovered to be a new class of host for the chemical intercalation of oxygett and the interstitial solid solution of Ce₂Zr₂O₇₊x based on this structure-type has been investigated. Intercalation in this system is found to involve an unusual mechanism of oxygen displacement. The structures of other complex metal oxides have also been elucidated using a combination of X-ray and neutron powder diffraction, including those of Li₂9Zr9Nb₃O₄0 and Li₂9Zr9.₆Ta₂.₄O₄0. The doping behaviour of magnesium into the technologically important material lithium niobate has also been studied using these techniques. Polymer electrolytes are a class of ionically conducting solid phases formed by the dissolution of salts in ion co-ordinating macromolecules. The relationship between the crystalline and amorphous phase of the polymer-salt complex PEO₃.LiCF₃SO₃ has been examined by variable-temperature powder X-ray diffraction. This has shed new light on the relationship between the crystalline and amorphous structures of polymer electrolytes. Finally, the crystal structure of the polymer-salt complex PEO₄:RbSCN has been determined.
1997-01-01T00:00:00ZThomson, James BurgessA knowledge of structure is crucial to the understanding of inorganic solids and polymers. Neutron and X-ray powder diffraction are two powerful complementary techniques which can be used in the structural characterisation of a variety of crystalline materials. Chemical and electrochemical oxygen intercalation techniques involving both aqueous and non-aqueous systems, have been investigated for a number of crystalline inorganic oxides. The pyrochlore structure has been discovered to be a new class of host for the chemical intercalation of oxygett and the interstitial solid solution of Ce₂Zr₂O₇₊x based on this structure-type has been investigated. Intercalation in this system is found to involve an unusual mechanism of oxygen displacement. The structures of other complex metal oxides have also been elucidated using a combination of X-ray and neutron powder diffraction, including those of Li₂9Zr9Nb₃O₄0 and Li₂9Zr9.₆Ta₂.₄O₄0. The doping behaviour of magnesium into the technologically important material lithium niobate has also been studied using these techniques. Polymer electrolytes are a class of ionically conducting solid phases formed by the dissolution of salts in ion co-ordinating macromolecules. The relationship between the crystalline and amorphous phase of the polymer-salt complex PEO₃.LiCF₃SO₃ has been examined by variable-temperature powder X-ray diffraction. This has shed new light on the relationship between the crystalline and amorphous structures of polymer electrolytes. Finally, the crystal structure of the polymer-salt complex PEO₄:RbSCN has been determined.Ion transport in polymer electrolytesShi, Jiehttps://hdl.handle.net/10023/155222020-11-13T17:11:35Z1993-01-01T00:00:00ZThe ion-polymer and ion-ion interactions in polymer electrolytes based on high molecular weight, amorphous methoxy-linked PEO (PMEO) and lithium salts have been investigated by conductivity measurement, magic-angle spinning NMR (mas NMR) and pulsed field gradient NMR (pfgNMR) techniques. In the very dilute salt concentration region, ion pairing effects are dominant in these polymer electrolytes. Ion association is found to increase with temperature and salt concentration. Ion transport for these electrolytes is controlled both by segmental motion of the polymer and activation process, in which the former is important for the dilute concentration samples while the latter is important for the concentrated samples. The mass transport process in polymer electrolytes based on a zinc salt has been investigated by steady state dc polarisation and Hittorf techniques. Zinc ion constituents in these electrolytes are mobile with a limiting current fraction of about 0.2 at 80°C, and the transference number measured by the Hittorf method is less than 0.1. The main species in these electrolytes are proposed to be neutral mobile triples. The electrode-electrolyte interfaces in polymer electrolytes based on calcium and magnesium salts have been studied. Dc polarisation experiments for these polymer electrolytes were carried out using two electrode cells with the metal anode and mercury film amalgam cathode. The results of dc polarisation experiments suggest that calcium species are mobile in high molecular weight electrolytes, while magnesium species are immobile. The influence of the molecular weight of the polymer on the dynamics of cation constituents has been studied based on the experimental results of dc polarisation and pfg NMR, and on the theoretical analyses of the reptation theory and the Rouse model. It is found that the transport of the gravity centre of the polymer will influence the ion transport in polymer electrolytes based on PEO in a manner described by the Rouse model when the molecular weight of PEO is less than 3200.
1993-01-01T00:00:00ZShi, JieThe ion-polymer and ion-ion interactions in polymer electrolytes based on high molecular weight, amorphous methoxy-linked PEO (PMEO) and lithium salts have been investigated by conductivity measurement, magic-angle spinning NMR (mas NMR) and pulsed field gradient NMR (pfgNMR) techniques. In the very dilute salt concentration region, ion pairing effects are dominant in these polymer electrolytes. Ion association is found to increase with temperature and salt concentration. Ion transport for these electrolytes is controlled both by segmental motion of the polymer and activation process, in which the former is important for the dilute concentration samples while the latter is important for the concentrated samples. The mass transport process in polymer electrolytes based on a zinc salt has been investigated by steady state dc polarisation and Hittorf techniques. Zinc ion constituents in these electrolytes are mobile with a limiting current fraction of about 0.2 at 80°C, and the transference number measured by the Hittorf method is less than 0.1. The main species in these electrolytes are proposed to be neutral mobile triples. The electrode-electrolyte interfaces in polymer electrolytes based on calcium and magnesium salts have been studied. Dc polarisation experiments for these polymer electrolytes were carried out using two electrode cells with the metal anode and mercury film amalgam cathode. The results of dc polarisation experiments suggest that calcium species are mobile in high molecular weight electrolytes, while magnesium species are immobile. The influence of the molecular weight of the polymer on the dynamics of cation constituents has been studied based on the experimental results of dc polarisation and pfg NMR, and on the theoretical analyses of the reptation theory and the Rouse model. It is found that the transport of the gravity centre of the polymer will influence the ion transport in polymer electrolytes based on PEO in a manner described by the Rouse model when the molecular weight of PEO is less than 3200.Conductivity and nuclear magnetic resonance studies on polymer electrolytes based on poly(ethylene oxide)Tomlin, Anthony Stephenhttps://hdl.handle.net/10023/155202019-03-29T11:22:55Z1988-01-01T00:00:00ZThe thesis details studies relating to polymer electrolytes; the solid ionic conductors farmed by the dissolution of salts in suitable high molecular weight polymers. An outline of polymer electrolyte study is presented with respect to current understanding of the phase behaviour, morphology and conductance behaviour of the electrolyte materials. (In particular, those based upon the linear homopolymer poly(ethylene oxide), PEO.) An electrochemical study has been undertaken (₂98 K) involving a low molecular weight PEO analogue, PEO(₄00)e = CH₃C0₂(CH₂CH₂0) CO CH₃ (n = 8 - 9 ), containing LiCF₃SO₃ or LiClO₄. The study has shown that at low to medium salt concentrations in polyether media ion - ion interactions are important and are realized as ion association. The conductance vs. concentration behaviour has been modelled according to an equilibrium between single, ion pair and triple ion species where the concentration of simple (single) ions are small and decreasing, and above a total salt concentration of about 0.01 mol kg⁻¹, the majority of the current is carried by triple ion species of the form Li₂X- LiX₂ (X = CF₃SO₃ , CIO₄). Equilibrium constant data were obtained for single and triple ion formation (from neutral ion pairs). Determination of triple ion formation constants vs. temperature has shown that the triple ion formation process for LiCF₃SO₃ in PEO(₄00)e is an exothermic process, negative, whereas for LiClO₄ AH = 0 kJinal⁻¹. Using nuclear magnetic resonance (nmr), diffusion coefficients have been obtained for the oligomer chain in PEO(₄00)e and PEO(₄00)e.LiCF₃SO₃ solutions. The chain diffusion coefficients have been shown to give good agreement with those for salt diffusion, determined from conductance measurements via the Nernst - Einstein relation. An in - depth nmr investigation of the PEO.LICF₃SO₃ system (high molecular weight PEO) has shown that there is partition of lithium environments, probably within the salt rich crystalline phase (EQ/Li - ₃.5/1). Significant numbers of lithium nuclei are not observed with the nmr technique because they occupy environments of law symmetry. This was reinforced by other nmr measurements which suggested cation - anion proximity in the crystalline phase. A mixed salt system has been studied, PEO. LiCF₃SO₃. Nal, and it has been shown that the mixing of salts gave materials with superior conductivities to the relevant single salt systems (PEO. LiCF₃SO₃ and PEO.Nal) of the same overall salt content. Nmr has shown that the mixed salt effect was due to a larger amorphous (conducting) polymer phase and more potential charge carriers for the mixed salt in comparison to the single salt materials. A marked effect upon lithium motion was observed for PEO.LiCF₃SO₃ Nal system in comparison to PEO.LiCF₃SO₃ and it has been proposed that this was due to the observed lithium species becoming mobile at notably lower temperatures for the mixed salt system.
1988-01-01T00:00:00ZTomlin, Anthony StephenThe thesis details studies relating to polymer electrolytes; the solid ionic conductors farmed by the dissolution of salts in suitable high molecular weight polymers. An outline of polymer electrolyte study is presented with respect to current understanding of the phase behaviour, morphology and conductance behaviour of the electrolyte materials. (In particular, those based upon the linear homopolymer poly(ethylene oxide), PEO.) An electrochemical study has been undertaken (₂98 K) involving a low molecular weight PEO analogue, PEO(₄00)e = CH₃C0₂(CH₂CH₂0) CO CH₃ (n = 8 - 9 ), containing LiCF₃SO₃ or LiClO₄. The study has shown that at low to medium salt concentrations in polyether media ion - ion interactions are important and are realized as ion association. The conductance vs. concentration behaviour has been modelled according to an equilibrium between single, ion pair and triple ion species where the concentration of simple (single) ions are small and decreasing, and above a total salt concentration of about 0.01 mol kg⁻¹, the majority of the current is carried by triple ion species of the form Li₂X- LiX₂ (X = CF₃SO₃ , CIO₄). Equilibrium constant data were obtained for single and triple ion formation (from neutral ion pairs). Determination of triple ion formation constants vs. temperature has shown that the triple ion formation process for LiCF₃SO₃ in PEO(₄00)e is an exothermic process, negative, whereas for LiClO₄ AH = 0 kJinal⁻¹. Using nuclear magnetic resonance (nmr), diffusion coefficients have been obtained for the oligomer chain in PEO(₄00)e and PEO(₄00)e.LiCF₃SO₃ solutions. The chain diffusion coefficients have been shown to give good agreement with those for salt diffusion, determined from conductance measurements via the Nernst - Einstein relation. An in - depth nmr investigation of the PEO.LICF₃SO₃ system (high molecular weight PEO) has shown that there is partition of lithium environments, probably within the salt rich crystalline phase (EQ/Li - ₃.5/1). Significant numbers of lithium nuclei are not observed with the nmr technique because they occupy environments of law symmetry. This was reinforced by other nmr measurements which suggested cation - anion proximity in the crystalline phase. A mixed salt system has been studied, PEO. LiCF₃SO₃. Nal, and it has been shown that the mixing of salts gave materials with superior conductivities to the relevant single salt systems (PEO. LiCF₃SO₃ and PEO.Nal) of the same overall salt content. Nmr has shown that the mixed salt effect was due to a larger amorphous (conducting) polymer phase and more potential charge carriers for the mixed salt in comparison to the single salt materials. A marked effect upon lithium motion was observed for PEO.LiCF₃SO₃ Nal system in comparison to PEO.LiCF₃SO₃ and it has been proposed that this was due to the observed lithium species becoming mobile at notably lower temperatures for the mixed salt system.Studies of mass transport in some poly(ethyleneoxide)-based polymer electrolytesHardgrave, Martin Thomashttps://hdl.handle.net/10023/155182020-11-13T17:07:46Z1991-01-01T00:00:00ZThe work in this thesis relates to the transport of salt species in polymer electrolytes, which are solid ionic conductors in which mass transport is similar to that in liquids, rather than in ion-conducting glasses. A brief examination of some of the experimental techniques which have been used to study polymer electrolytes is given before examining in more detail the processes involved when these materials are polarised between non-blocking electrodes. A theoretical treatment is given for various models of polymer electrolytes, in particular polymer electrolytes containing free ions and polymer electrolytes containing free ions and ion-pairs. Non-ideality has been considered for the free ion model. Computer simulations of the free ion and ion-pair model predict that the steady-state current that these materials pass may be proportional to the applied potential difference for many tens of volts, in contrast with the free ion model, where the potential difference limit is of the order of millivolts. The use of the terms "transference number" and "transport number" is discouraged, because of the effect of the motion of uncharged species in practical systems. A new parameter, the current fraction, is defined for steady-state polarisation experiments. An experimental study of amorphous polymer electrolytes is described, in which electrolytes were polarised to steady-state using non-blocking electrodes. The application of the Hittorf technique to these materials has been demonstrated, with true transference numbers determined for some electrolytes. Conductivity and neutron scattering experiments suggest that the reported unusual conductivity behaviour of lithium triflate-based electrolytes does not exist or is not generally displayed.
1991-01-01T00:00:00ZHardgrave, Martin ThomasThe work in this thesis relates to the transport of salt species in polymer electrolytes, which are solid ionic conductors in which mass transport is similar to that in liquids, rather than in ion-conducting glasses. A brief examination of some of the experimental techniques which have been used to study polymer electrolytes is given before examining in more detail the processes involved when these materials are polarised between non-blocking electrodes. A theoretical treatment is given for various models of polymer electrolytes, in particular polymer electrolytes containing free ions and polymer electrolytes containing free ions and ion-pairs. Non-ideality has been considered for the free ion model. Computer simulations of the free ion and ion-pair model predict that the steady-state current that these materials pass may be proportional to the applied potential difference for many tens of volts, in contrast with the free ion model, where the potential difference limit is of the order of millivolts. The use of the terms "transference number" and "transport number" is discouraged, because of the effect of the motion of uncharged species in practical systems. A new parameter, the current fraction, is defined for steady-state polarisation experiments. An experimental study of amorphous polymer electrolytes is described, in which electrolytes were polarised to steady-state using non-blocking electrodes. The application of the Hittorf technique to these materials has been demonstrated, with true transference numbers determined for some electrolytes. Conductivity and neutron scattering experiments suggest that the reported unusual conductivity behaviour of lithium triflate-based electrolytes does not exist or is not generally displayed.Multivalent ions in polymer electrolytesMehta, Mary Annehttps://hdl.handle.net/10023/155172019-03-29T11:21:53Z1993-01-01T00:00:00ZThe electrochemical, thermal and structural properties of polyethylene oxide (PEO) based polymer electrolytes containing multivalent ions were investigated. The phase diagram for the PEO:Ca(CF₃SO₃)₂ system was determined by x-ray diffraction and differential scanning calorimetry techniques. Precipitation of the salt from the system at high temperatures was directly observed by variable temperature x- ray diffraction. This was ascribed to a negative entropy of dissolution of the salt in the polymer. A new crystalline complex PEO₆Ca(CF₃SO₃)₂, which exhibits a phase transition between two polymorphic forms was observed. The temperature dependence of ionic conductivity was related to the phase diagram. Redox behaviour of the PEO:Nil₂ system was probed. Motion of the Ni(II) species through the system was extremely slow as evidenced by the low effective diffusion coefficient (1.82 x 10 ¹¹ cm ²s⁻¹) and cationic current fraction (F₊ < 0.1). Deposition of nickel from the polymer was characterised by instantaneous nucleation followed by three dimensional diffusion controlled growth. Investigation of the redox behaviour of the PE0:Eu(CF₃SO₃)₃ system indicated that reduction of Eu³⁺ followed an ec mechanism. Evidence was obtained for extremely slow diffusion of Eu3+ containing species (D[sub]eff ~ 3.66 x 10 ⁻¹⁶cm²s⁻¹) through the system and slow kinetics of electron transfer. Thermal studies of the PEO:Co(SCN)₂ system indicated that the glass transition temperature (Tg) was grossly elevated by the presence of Co(SCN)₂ in the polymer. The absence of a crystalline PEO:Co(SCN)₂ complex was ascribed to the high Tg which leads to slow crystallisation kinetics. UV-visible spectra indicated that the Co²⁺ ion was tetrahedrally coordinated in the system at low salt concentrations. The structure of the PEO₃NaClO₄ crystalline complex was reported as a subsidiary study.
1993-01-01T00:00:00ZMehta, Mary AnneThe electrochemical, thermal and structural properties of polyethylene oxide (PEO) based polymer electrolytes containing multivalent ions were investigated. The phase diagram for the PEO:Ca(CF₃SO₃)₂ system was determined by x-ray diffraction and differential scanning calorimetry techniques. Precipitation of the salt from the system at high temperatures was directly observed by variable temperature x- ray diffraction. This was ascribed to a negative entropy of dissolution of the salt in the polymer. A new crystalline complex PEO₆Ca(CF₃SO₃)₂, which exhibits a phase transition between two polymorphic forms was observed. The temperature dependence of ionic conductivity was related to the phase diagram. Redox behaviour of the PEO:Nil₂ system was probed. Motion of the Ni(II) species through the system was extremely slow as evidenced by the low effective diffusion coefficient (1.82 x 10 ¹¹ cm ²s⁻¹) and cationic current fraction (F₊ < 0.1). Deposition of nickel from the polymer was characterised by instantaneous nucleation followed by three dimensional diffusion controlled growth. Investigation of the redox behaviour of the PE0:Eu(CF₃SO₃)₃ system indicated that reduction of Eu³⁺ followed an ec mechanism. Evidence was obtained for extremely slow diffusion of Eu3+ containing species (D[sub]eff ~ 3.66 x 10 ⁻¹⁶cm²s⁻¹) through the system and slow kinetics of electron transfer. Thermal studies of the PEO:Co(SCN)₂ system indicated that the glass transition temperature (Tg) was grossly elevated by the presence of Co(SCN)₂ in the polymer. The absence of a crystalline PEO:Co(SCN)₂ complex was ascribed to the high Tg which leads to slow crystallisation kinetics. UV-visible spectra indicated that the Co²⁺ ion was tetrahedrally coordinated in the system at low salt concentrations. The structure of the PEO₃NaClO₄ crystalline complex was reported as a subsidiary study.Investigations of some energy transfer processes associated with acetylacetonate complexes of the lanthanoid and groups I and II metal ionsNeilson, John Duncanhttps://hdl.handle.net/10023/155152019-03-29T11:19:49Z1979-01-01T00:00:00ZIntermolecular energy transfer occurs between Tb(aa)₃.3H₂0 and Ln(aa)₃.3H₂O complexes (Ln = Pr, Nd, Sm, Eu, Dy, Ho or Er; aa = acetylacetonate) in n-butanol solution at 293K. Measurement of the decay time of the Tb³⁺ ⁵D₄level indicates that transfer occurs from this level to excited levels of the Ln³⁺ ions with bimolecular rate constants within the range 0.5 - 4.9 x 10⁵ dm³ mol s ⁻¹. Data from similar measurements on a mixed crystal EuxTb(1-x)(aa)₃.3H₂O and other considerations indicate that this is a very short range electron-exchange transfer. Similar measurements of the Tb³⁺ ion phosphorescence yield indicate the presence of a further intermolecular transfer process between a higher excited state of the Tb³⁺ complex and the added Ln³⁺ complexes. The Stern-Volmer Quenching constants vary from 11 dm³ mol⁻¹ for Ho and Sm to 110 dm³ mol⁻¹ for Pr. It is concluded that this transfer is unlikely to occur from either the ligand singlet or triplet levels and it is proposed that a higher Tb³⁺ level such as the ⁵D₃ may be involved in both inter- and intramolecular energy transfer. Intermolecular energy transfer between excited state Tb³⁺ ions in Tb(aa)₃.3H₂O and Ln³⁺ ions in Ln(aa)₃.3H₂O, where Ln = Eu and Sm, is shown to be markedly solvent dependent. It is proposed that the Tb³⁺ → Ln³⁺ energy transfer occurs in mixed metal dimers where the Tb-Ln distance is likely to be ca. 0.4 nm. The solvent dependent behaviour is related to the relative concentrations of monomeric and dimeric species in the various solvents. The rate controlling step in the intermolecular energy transfer is probably that, of monomer-dimer reaction which at 273K is of the order of 10⁵ dm³ mol⁻¹ s⁻¹. The activation energy of this reaction between Tb, Eu and Sm acetylacetonates is estimated to be ca. 23 kJ mol⁻¹. ¹H NMR spectra of Lu(aa)3.2H2O in several solvents are reported. The spectral profiles are temperature dependent in benzene and toluene solutions and the multiplicity of ligand methyl resonances is attributed to slow exchange between non-equivalent methyl groups in a dimeric structure. The temperature dependence in acetone solution is consistent with the presence of a monomer-dimer equilibrium with △H° = -28.2 ± 1.5 kJ mol⁻¹ and △S° = -74.5 ± 4.5 J K ⁻¹ mol⁻¹. The single ligand-methyland 3-H resonances in the' strongly coordinating solvents dimethyl sulphoxide and pyridine indicate the sole presence of solvated monomers. Previous proposals about the anomalous spectrum of Mg(aa)₂ in CDCl₃ are also discussed. The extremely low efficiency of the intermolecular enrgy transfer process in europium acetylacetonate compared with the corresponding terbium acetylacetonate is attributed to the presence of a charge-transfer excited state lying below the ligand singlet states. This is supported by the anomalous absorption spectrum of the Eu³⁺complex and the effects of added anions in other ligand systems. The phosphorescence spectra of the Group I and Group II metal acetylacetonates (Metal = Li, Na, K, Rb, Gs, Mg, Ca, Sr and Ba) have all been measured in solid Ethanol glass solutions at 77K and found to have profiles similar to that of Al(aa)₃. The phosphorescence decays are non-exponential and this behaviour is attributed to the presence of both coordinated and free acetylacetonate anion. Time resolved spectroscopy and other considerations indicate that the energies of the lowest excited ligand singlet and triplet states of the aa⁻ ion are, unlike the triplet state lifetime, little affected by coordination. Solvolysis is reported in ethanol solution which invalidates some previously-reported spectral parameters.
1979-01-01T00:00:00ZNeilson, John DuncanIntermolecular energy transfer occurs between Tb(aa)₃.3H₂0 and Ln(aa)₃.3H₂O complexes (Ln = Pr, Nd, Sm, Eu, Dy, Ho or Er; aa = acetylacetonate) in n-butanol solution at 293K. Measurement of the decay time of the Tb³⁺ ⁵D₄level indicates that transfer occurs from this level to excited levels of the Ln³⁺ ions with bimolecular rate constants within the range 0.5 - 4.9 x 10⁵ dm³ mol s ⁻¹. Data from similar measurements on a mixed crystal EuxTb(1-x)(aa)₃.3H₂O and other considerations indicate that this is a very short range electron-exchange transfer. Similar measurements of the Tb³⁺ ion phosphorescence yield indicate the presence of a further intermolecular transfer process between a higher excited state of the Tb³⁺ complex and the added Ln³⁺ complexes. The Stern-Volmer Quenching constants vary from 11 dm³ mol⁻¹ for Ho and Sm to 110 dm³ mol⁻¹ for Pr. It is concluded that this transfer is unlikely to occur from either the ligand singlet or triplet levels and it is proposed that a higher Tb³⁺ level such as the ⁵D₃ may be involved in both inter- and intramolecular energy transfer. Intermolecular energy transfer between excited state Tb³⁺ ions in Tb(aa)₃.3H₂O and Ln³⁺ ions in Ln(aa)₃.3H₂O, where Ln = Eu and Sm, is shown to be markedly solvent dependent. It is proposed that the Tb³⁺ → Ln³⁺ energy transfer occurs in mixed metal dimers where the Tb-Ln distance is likely to be ca. 0.4 nm. The solvent dependent behaviour is related to the relative concentrations of monomeric and dimeric species in the various solvents. The rate controlling step in the intermolecular energy transfer is probably that, of monomer-dimer reaction which at 273K is of the order of 10⁵ dm³ mol⁻¹ s⁻¹. The activation energy of this reaction between Tb, Eu and Sm acetylacetonates is estimated to be ca. 23 kJ mol⁻¹. ¹H NMR spectra of Lu(aa)3.2H2O in several solvents are reported. The spectral profiles are temperature dependent in benzene and toluene solutions and the multiplicity of ligand methyl resonances is attributed to slow exchange between non-equivalent methyl groups in a dimeric structure. The temperature dependence in acetone solution is consistent with the presence of a monomer-dimer equilibrium with △H° = -28.2 ± 1.5 kJ mol⁻¹ and △S° = -74.5 ± 4.5 J K ⁻¹ mol⁻¹. The single ligand-methyland 3-H resonances in the' strongly coordinating solvents dimethyl sulphoxide and pyridine indicate the sole presence of solvated monomers. Previous proposals about the anomalous spectrum of Mg(aa)₂ in CDCl₃ are also discussed. The extremely low efficiency of the intermolecular enrgy transfer process in europium acetylacetonate compared with the corresponding terbium acetylacetonate is attributed to the presence of a charge-transfer excited state lying below the ligand singlet states. This is supported by the anomalous absorption spectrum of the Eu³⁺complex and the effects of added anions in other ligand systems. The phosphorescence spectra of the Group I and Group II metal acetylacetonates (Metal = Li, Na, K, Rb, Gs, Mg, Ca, Sr and Ba) have all been measured in solid Ethanol glass solutions at 77K and found to have profiles similar to that of Al(aa)₃. The phosphorescence decays are non-exponential and this behaviour is attributed to the presence of both coordinated and free acetylacetonate anion. Time resolved spectroscopy and other considerations indicate that the energies of the lowest excited ligand singlet and triplet states of the aa⁻ ion are, unlike the triplet state lifetime, little affected by coordination. Solvolysis is reported in ethanol solution which invalidates some previously-reported spectral parameters.Pyrolysis of diphenylmethane and fluoreneMcCrae, James Osbornehttps://hdl.handle.net/10023/155092019-03-29T11:24:28Z1953-01-01T00:00:00ZThis thesis is divided into four main sections. In the 'Introduction' an attempt has been made to give, by a historical approach, a brief account of some of the advances which have been made towards a solution of the general problem of evaluating the energy associated with chemical bonds in the undisturbed molecule and also that required to disrupt the molecule into two fragments. A detailed review of the many experimental methods available for the determination of bond dissociation energies has not been given since there are now good accounts available in the literature, but attention has been focused on those techniques which are of interest in connection with the present investigation. The 'Present Investigation' deals with all the experimental work which has been carried out in the examination of diphenyl-methane, fluorene, diphenyl ethyl bromide, tetraphenylethane and toluene. Discussion in this section has been confined mainly to experimental points. In the third section, the 'Discussion', the results are dealt with, not in the chronological order in which they were obtained, but in a sequence which permits a more satisfactory treatment. AS the Information obtained from the studios on fluorine is required in the discussion of the diphenylmetgane results it is considered first. Then an examination is made of data from other investigations in order to assess what products might have been expected from the pyrolysis of diphenyl methane, and this is followed by a consideration of the results of the present work carried out on this compound. Board dissolution energies have been derived for the methylenic C-H bond in fluorene and in disphenylmethane, also for the central C-C bond in tetraphenylethane. A mechanics is proposed for the decomposition of diphenylmethyl bromide but the limited experimental date does not permit a definite conclusion to be reached. An account of the method of analysis of the ultra-violet absorption curves of the toluene pyrolysis products precedes a brief resume of the limitations of the method of analysis by ultra-violet spectrophotometric examination of the mixtures resulting from hydrocarbon pyrolysis. The section is concluded with a short account concerning the existence of unsaturated diner analogues in the thermal decomposition products of hydrocarbons. In the 'Appendix' details are given of thermochemical and kinetic calculations, the results of which are used in the 'Discussion' section.
1953-01-01T00:00:00ZMcCrae, James OsborneThis thesis is divided into four main sections. In the 'Introduction' an attempt has been made to give, by a historical approach, a brief account of some of the advances which have been made towards a solution of the general problem of evaluating the energy associated with chemical bonds in the undisturbed molecule and also that required to disrupt the molecule into two fragments. A detailed review of the many experimental methods available for the determination of bond dissociation energies has not been given since there are now good accounts available in the literature, but attention has been focused on those techniques which are of interest in connection with the present investigation. The 'Present Investigation' deals with all the experimental work which has been carried out in the examination of diphenyl-methane, fluorene, diphenyl ethyl bromide, tetraphenylethane and toluene. Discussion in this section has been confined mainly to experimental points. In the third section, the 'Discussion', the results are dealt with, not in the chronological order in which they were obtained, but in a sequence which permits a more satisfactory treatment. AS the Information obtained from the studios on fluorine is required in the discussion of the diphenylmetgane results it is considered first. Then an examination is made of data from other investigations in order to assess what products might have been expected from the pyrolysis of diphenyl methane, and this is followed by a consideration of the results of the present work carried out on this compound. Board dissolution energies have been derived for the methylenic C-H bond in fluorene and in disphenylmethane, also for the central C-C bond in tetraphenylethane. A mechanics is proposed for the decomposition of diphenylmethyl bromide but the limited experimental date does not permit a definite conclusion to be reached. An account of the method of analysis of the ultra-violet absorption curves of the toluene pyrolysis products precedes a brief resume of the limitations of the method of analysis by ultra-violet spectrophotometric examination of the mixtures resulting from hydrocarbon pyrolysis. The section is concluded with a short account concerning the existence of unsaturated diner analogues in the thermal decomposition products of hydrocarbons. In the 'Appendix' details are given of thermochemical and kinetic calculations, the results of which are used in the 'Discussion' section.Excited state properties of 1-naphthol and its sulphonatesHenson, Robert M. C.https://hdl.handle.net/10023/155072019-03-29T11:25:20Z1973-01-01T00:00:00ZThe transient absorption spectrum of 1-naphthol was first sought by flash photolysis at higher acidities than had been previously investigated. While no transient absorption was observed for l-naphthol itself, strong transient absorptions were observed for l-naphthol-2 and -4-sulphonates even in aqueous solution. This enabled pK(T₁) for the protonation of the naphtholate ions to be measured directly from the strength of triplet-triplet absorptions and this value was compared with the pK(T₁) obtained from Forster Cycle calculations on phosphorescence maxima,. Values of pK(S₁) and pK(S₀) were also obtained and the order of the pK values was found to be pK(S₀) > pK(T₁) >> pK(S₁), It is likely that this order is the same for l-naphthol and therefore disagrees with the results of some recent quantum mechanical calculations, A strong fluorescence was also observed for l-naphthol-2- sulphonate in aqueous acidic solutions, in contrast with the weak fluorescence observed for 1-naphthol and l-naphthol-4-sulphonate. This is explained in terms of intramolecular hydrogen bonding in l-naphthol-2-sulphonate which prevents quenching of the first excited singlet state by hydrogen bonding with solvent water molecules. The fluorescence intensity of 1-naphthol, l-naphthol-2-sulphonate, and l~naphthol-4-sulphonate in aqueous acidic solutions is also found to increase as the water concentration is effectively reduced by the addition of certain solutes in large quantities, A corresponding increase in the triplet yield is also found for l-naphthol-2-sulphonate in acidic solutions. These increases are also explained in terms of reducing the hydrogen bonding to solvent water molecules and hence reducing the deactivation of the state, l-Naphthol sulphonates and protonates in concentrated sulphuric acid and it is deduced that protonation occurs at a carbon atom in the naphthalene ring, A value of pK(S₀ ) was determined for this protonation.
1973-01-01T00:00:00ZHenson, Robert M. C.The transient absorption spectrum of 1-naphthol was first sought by flash photolysis at higher acidities than had been previously investigated. While no transient absorption was observed for l-naphthol itself, strong transient absorptions were observed for l-naphthol-2 and -4-sulphonates even in aqueous solution. This enabled pK(T₁) for the protonation of the naphtholate ions to be measured directly from the strength of triplet-triplet absorptions and this value was compared with the pK(T₁) obtained from Forster Cycle calculations on phosphorescence maxima,. Values of pK(S₁) and pK(S₀) were also obtained and the order of the pK values was found to be pK(S₀) > pK(T₁) >> pK(S₁), It is likely that this order is the same for l-naphthol and therefore disagrees with the results of some recent quantum mechanical calculations, A strong fluorescence was also observed for l-naphthol-2- sulphonate in aqueous acidic solutions, in contrast with the weak fluorescence observed for 1-naphthol and l-naphthol-4-sulphonate. This is explained in terms of intramolecular hydrogen bonding in l-naphthol-2-sulphonate which prevents quenching of the first excited singlet state by hydrogen bonding with solvent water molecules. The fluorescence intensity of 1-naphthol, l-naphthol-2-sulphonate, and l~naphthol-4-sulphonate in aqueous acidic solutions is also found to increase as the water concentration is effectively reduced by the addition of certain solutes in large quantities, A corresponding increase in the triplet yield is also found for l-naphthol-2-sulphonate in acidic solutions. These increases are also explained in terms of reducing the hydrogen bonding to solvent water molecules and hence reducing the deactivation of the state, l-Naphthol sulphonates and protonates in concentrated sulphuric acid and it is deduced that protonation occurs at a carbon atom in the naphthalene ring, A value of pK(S₀ ) was determined for this protonation.The development of a quinquaquadrupole mass spectrometer - the study of ion-molecule reactions in the gas phase using multiple quadrupole instruments.Hall, Robin Gibsonhttps://hdl.handle.net/10023/155062019-03-29T11:21:14Z1991-01-01T00:00:00ZThe field of quadrupole mass spectrometry has grown enormously since the early 1980's. The invention of the triple quadrupole mass spectrometer led to the development of tandem quadrupole mass spectrometers of many different configurations. A large number of tandem quadrupole mass spectrometers have also been developed by linking one or more quadrupole mass filters to a traditional magnetic or electric filter. The versatility of multiple quadrupole mass spectrometers along with their potential to rapidly produce a huge amount of data on a particular ion makes them ideal instruments for routine analytical analysis as well as for fundamental research The quinquaquadrupole mass spectrometer has been developed as an extension to the available multiple quadrupole systems. It offers the possibility to obtain even more data on the fragmentation of ions as well as enabling the study of novel ions to be carried out. The development of the quinquaquadrupole mass spectrometer forms the main part of this thesis. Also discussed are the reactions studied to evaluate the instrumental performance. The the ion molecule reactions of some halogen containing cations with saturated and unsaturated hydrocarbons performed on the triple quadrupole mass spectrometer are also discussed.
1991-01-01T00:00:00ZHall, Robin GibsonThe field of quadrupole mass spectrometry has grown enormously since the early 1980's. The invention of the triple quadrupole mass spectrometer led to the development of tandem quadrupole mass spectrometers of many different configurations. A large number of tandem quadrupole mass spectrometers have also been developed by linking one or more quadrupole mass filters to a traditional magnetic or electric filter. The versatility of multiple quadrupole mass spectrometers along with their potential to rapidly produce a huge amount of data on a particular ion makes them ideal instruments for routine analytical analysis as well as for fundamental research The quinquaquadrupole mass spectrometer has been developed as an extension to the available multiple quadrupole systems. It offers the possibility to obtain even more data on the fragmentation of ions as well as enabling the study of novel ions to be carried out. The development of the quinquaquadrupole mass spectrometer forms the main part of this thesis. Also discussed are the reactions studied to evaluate the instrumental performance. The the ion molecule reactions of some halogen containing cations with saturated and unsaturated hydrocarbons performed on the triple quadrupole mass spectrometer are also discussed.Studies of ylidesMillar, Ross Woodhttps://hdl.handle.net/10023/155032019-03-29T11:21:37Z1975-01-01T00:00:00ZThe preparation and attempted preparation of diaminomethylene-sulphuranes (thiouronium ylides) by various routes is described. The principal route chosen was by proton abstraction from the conjugate acid (thiouronium salt) using a suitable non-hydroxylic base, usually phenyl lithium or triethylamine. In the range of compounds examined where the carbanionic substituents contained electron withdrawing groups such as carbonyl, sulphonyl, nitrile and nitro groups, considerable difficulty was encountered in the preparation of the precursor salts. Of the few salts in this category that were obtainable, only one (disulphonyl substituted) gave rise to a stable ylide. On the other hand, many salts containing the cyclopentadiene ring gave rise to ylides. Some of these, notably the fluorenylides, could be isolated and characterised, while the properties of others could only be observed in solution and they decomposed or rearranged on attempted isolation. A second preparative route was briefly investigated, namely the thermal decomposition of 9-diazofluorene in the presence of arylthioureas, but in several cases this led to unexpected products. Comparative studies of the reactivities of the fluorenylides towards carbonyl compounds and hydrolysis have been made, and some other reactions of these ylides are also described. The 2,3,4-triphenylcyclopentadienylides have been found to undergo novel cyclisation reactions with aldehydes and nitrosobenzene. A product from the former reaction was dehydrogenated to give a stable heterocycle with a 14Π electron periphery. An attempt to prepare a selenium analogue of one of the thiouronium fluorenylides is described. The attempted preparation of guanidinium fluorenylides by various methods is described, principally the 'salt' and 'diazo' methods. The former method was more suitable for alkyl substituted guanidines, whereas the latter method was of benefit with aryl substituents. Proton abstraction from ono of the alkylguanidinium salts gave rise to a product which showed some evidence for ylide character. On the other hand, the aryl substituted products appeared to show no ylide-like properties, A further point of interest arose in the diazo reaction, whore the fluorene nucleus was shown to have substituted on the more sterically hindered position, which was verified later by synthesis.
1975-01-01T00:00:00ZMillar, Ross WoodThe preparation and attempted preparation of diaminomethylene-sulphuranes (thiouronium ylides) by various routes is described. The principal route chosen was by proton abstraction from the conjugate acid (thiouronium salt) using a suitable non-hydroxylic base, usually phenyl lithium or triethylamine. In the range of compounds examined where the carbanionic substituents contained electron withdrawing groups such as carbonyl, sulphonyl, nitrile and nitro groups, considerable difficulty was encountered in the preparation of the precursor salts. Of the few salts in this category that were obtainable, only one (disulphonyl substituted) gave rise to a stable ylide. On the other hand, many salts containing the cyclopentadiene ring gave rise to ylides. Some of these, notably the fluorenylides, could be isolated and characterised, while the properties of others could only be observed in solution and they decomposed or rearranged on attempted isolation. A second preparative route was briefly investigated, namely the thermal decomposition of 9-diazofluorene in the presence of arylthioureas, but in several cases this led to unexpected products. Comparative studies of the reactivities of the fluorenylides towards carbonyl compounds and hydrolysis have been made, and some other reactions of these ylides are also described. The 2,3,4-triphenylcyclopentadienylides have been found to undergo novel cyclisation reactions with aldehydes and nitrosobenzene. A product from the former reaction was dehydrogenated to give a stable heterocycle with a 14Π electron periphery. An attempt to prepare a selenium analogue of one of the thiouronium fluorenylides is described. The attempted preparation of guanidinium fluorenylides by various methods is described, principally the 'salt' and 'diazo' methods. The former method was more suitable for alkyl substituted guanidines, whereas the latter method was of benefit with aryl substituents. Proton abstraction from ono of the alkylguanidinium salts gave rise to a product which showed some evidence for ylide character. On the other hand, the aryl substituted products appeared to show no ylide-like properties, A further point of interest arose in the diazo reaction, whore the fluorene nucleus was shown to have substituted on the more sterically hindered position, which was verified later by synthesis.Vapour pressures of some inorganic sulphates at high temperaturesJagannathan, Gomatam V.https://hdl.handle.net/10023/155002019-03-29T11:24:55Z1977-01-01T00:00:00ZThe vapour pressures of some inorganic sulphates at high temperatures were determined by the combined use of the Knudsen effusion, transpiration, and matrix isolation methods. After a detailed comparison with the results of other investigators, it is concluded that the principal vapour species in the case of K₂SO₄, Rb₂SO₄, and Cs₂SO₄ are the undecomposed sulphate molecules themselves, and in the case of Li₂SO₄ the decomposition products, Li, SO₂, and O₂. The sodium salt also decomposes to some extent into Na, SO₂, and O₂, but it is deduced that the vapour concentration of the species Na₂O₄ is probably greater than was formerly supposed. The decomposition of alkaline earth sulphates is also discussed, especially in the light of the dependence of the Knudsen effusion results upon the size of the orifice used. On the basis of the vapour constitutions deduced, thermodynamic functions for the important species present are tabulated up to 1400 K or above. Reference is also made to the function of sodium sulphate in the glass-making industry and to the possible mechanism of its corrosive action on furnace walls.
1977-01-01T00:00:00ZJagannathan, Gomatam V.The vapour pressures of some inorganic sulphates at high temperatures were determined by the combined use of the Knudsen effusion, transpiration, and matrix isolation methods. After a detailed comparison with the results of other investigators, it is concluded that the principal vapour species in the case of K₂SO₄, Rb₂SO₄, and Cs₂SO₄ are the undecomposed sulphate molecules themselves, and in the case of Li₂SO₄ the decomposition products, Li, SO₂, and O₂. The sodium salt also decomposes to some extent into Na, SO₂, and O₂, but it is deduced that the vapour concentration of the species Na₂O₄ is probably greater than was formerly supposed. The decomposition of alkaline earth sulphates is also discussed, especially in the light of the dependence of the Knudsen effusion results upon the size of the orifice used. On the basis of the vapour constitutions deduced, thermodynamic functions for the important species present are tabulated up to 1400 K or above. Reference is also made to the function of sodium sulphate in the glass-making industry and to the possible mechanism of its corrosive action on furnace walls.A study of solute-solvent interactions in some associated liquidsMartinus, Nicholashttps://hdl.handle.net/10023/154982020-11-13T17:12:01Z1977-01-01T00:00:00ZThe variation of the viscosity of aqueous and non-aqueous electrolyte solutions with salt concentration has been studied and the results interpreted in terms of a number of mathematical models. The effects of ion-association on the viscosity of electrolyte solutions has been investigated by measuring the viscosity of aqueous solutions of some thallous salts. The viscosities of alkali halide salts in formamide have been determined over a range of temperatures and new methods for the division of viscosity B-coefficients into ionic contributions have been proposed. The results of these studies have been interpreted in terms of the ion-solvent interactions. The intermolecular interactions present in binary liquid mixtures of formamide with methanol, ethanol propan-l-ol and butan-l-ol have been studied by viscosity measurements over the complete concentration range. Finally the usefulness of time domain dielectric spectroscopy in solute-solvent interaction studies has been briefly investigated.
1977-01-01T00:00:00ZMartinus, NicholasThe variation of the viscosity of aqueous and non-aqueous electrolyte solutions with salt concentration has been studied and the results interpreted in terms of a number of mathematical models. The effects of ion-association on the viscosity of electrolyte solutions has been investigated by measuring the viscosity of aqueous solutions of some thallous salts. The viscosities of alkali halide salts in formamide have been determined over a range of temperatures and new methods for the division of viscosity B-coefficients into ionic contributions have been proposed. The results of these studies have been interpreted in terms of the ion-solvent interactions. The intermolecular interactions present in binary liquid mixtures of formamide with methanol, ethanol propan-l-ol and butan-l-ol have been studied by viscosity measurements over the complete concentration range. Finally the usefulness of time domain dielectric spectroscopy in solute-solvent interaction studies has been briefly investigated.Viscosity studies of solution interactions in formamideMcDowall, Joseph McCartneyhttps://hdl.handle.net/10023/154952020-11-13T17:12:33Z1973-01-01T00:00:00ZThe effect of some simple salts on the viscosity of formamide has been studied at a number of temperatures and interpreted in terms of ion-solvent interactions using the equation suggested by Jones and Dole. Further evidence to support the various conclusions drawn has been provided by application of Eyring's reaction rate theory to the viscosity processes in solution. The viscosities of binary mixtures of formamide and water, methanol or dimethylformamide have been investigated over the whole composition range and the ability of three semi-empirical models to describe these systems has been discussed. A new three parameter equation has been proposed. Finally the effect of sodium chloride on the binary mixture formamide/water has been considered. It has been shown that, in general, for viscosity measurements to be a useful tool for investigating ion-solvent and solvent-solvent interactions, it is important that the measurements be made at more than one temperature.
1973-01-01T00:00:00ZMcDowall, Joseph McCartneyThe effect of some simple salts on the viscosity of formamide has been studied at a number of temperatures and interpreted in terms of ion-solvent interactions using the equation suggested by Jones and Dole. Further evidence to support the various conclusions drawn has been provided by application of Eyring's reaction rate theory to the viscosity processes in solution. The viscosities of binary mixtures of formamide and water, methanol or dimethylformamide have been investigated over the whole composition range and the ability of three semi-empirical models to describe these systems has been discussed. A new three parameter equation has been proposed. Finally the effect of sodium chloride on the binary mixture formamide/water has been considered. It has been shown that, in general, for viscosity measurements to be a useful tool for investigating ion-solvent and solvent-solvent interactions, it is important that the measurements be made at more than one temperature.Diffusion and thermodynamic studies in amide solutionsSichali, Atusaye Kayanahttps://hdl.handle.net/10023/154942020-11-13T17:11:14Z1973-01-01T00:00:00Z(A) Diffusion Studies A study has been made on the effects of some selected halide salts on the structure of formamide by measuring molecular diffusion coefficients, A neutral molecule, ferrocene v/as allowed to diffuse in pure formamide and in halide salts solutions of formamide and its diffusion coefficients were determined, A test molecule was chosen rather than a test ion in order to avoid electrostatic effects due to ion--ion and ion-dipole interactions. Graphs of diffusion coefficient versus concentration of salts were drawn and the shapes of these curves have been discussed in terms of the "microscopic" and "macroscopic" effects of these salts on formamide structure. Use of two diffusion techniques was made - (i) an electrochemical diffusion method based on the Cottrell equation and (ii) a diaphragm-cell method based on steady-state diffusion. Only the latter was successful. A number of experimental methods were investigated in order to find a suitable analytical method for determining ferrocene (necessary for the diaphragm-cell measurements). A method for preparing radioactive ferrocene and a successful radiometric analytical technique were developed. (B) Thermodynamics Studies In this section the vapour pressures of binary mixtures of water-formamide, water-N-methylformamide and water-dimethylformamide were measured using a Zimmerli manometric gauge over several temperatures. The graphs of partial pressures of water (determined by a transpiration technique) vorsus mole fractions of water are given and explained in terms of the nature of interactions of water and the amides. Bj' means of the Clausius-Clapeyron equation the enthalpies of vaporization of water were calculated and the results versus water mole fractions are shown in graphs. In the case of water-formamide, the enthalpies of vaporization and the enthalpies of viscous flow are compared.
1973-01-01T00:00:00ZSichali, Atusaye Kayana(A) Diffusion Studies A study has been made on the effects of some selected halide salts on the structure of formamide by measuring molecular diffusion coefficients, A neutral molecule, ferrocene v/as allowed to diffuse in pure formamide and in halide salts solutions of formamide and its diffusion coefficients were determined, A test molecule was chosen rather than a test ion in order to avoid electrostatic effects due to ion--ion and ion-dipole interactions. Graphs of diffusion coefficient versus concentration of salts were drawn and the shapes of these curves have been discussed in terms of the "microscopic" and "macroscopic" effects of these salts on formamide structure. Use of two diffusion techniques was made - (i) an electrochemical diffusion method based on the Cottrell equation and (ii) a diaphragm-cell method based on steady-state diffusion. Only the latter was successful. A number of experimental methods were investigated in order to find a suitable analytical method for determining ferrocene (necessary for the diaphragm-cell measurements). A method for preparing radioactive ferrocene and a successful radiometric analytical technique were developed. (B) Thermodynamics Studies In this section the vapour pressures of binary mixtures of water-formamide, water-N-methylformamide and water-dimethylformamide were measured using a Zimmerli manometric gauge over several temperatures. The graphs of partial pressures of water (determined by a transpiration technique) vorsus mole fractions of water are given and explained in terms of the nature of interactions of water and the amides. Bj' means of the Clausius-Clapeyron equation the enthalpies of vaporization of water were calculated and the results versus water mole fractions are shown in graphs. In the case of water-formamide, the enthalpies of vaporization and the enthalpies of viscous flow are compared.Studies of meneidic systemsMcNab, Hamishhttps://hdl.handle.net/10023/154922019-03-29T11:22:38Z1974-01-01T00:00:00ZThe nmr spectra of 2,3-dihydro-1,4-diazepinium salts are discussed. From the magnitude of the coupling constants around the conjugated part of the molecules, a planar partial structure with complete electron delocalisation is indicated. The molecule as a whole adopts a half-chair configuration which rapidly inverts at room temperature. The effect of ring substitution on this exchange process is correlated with the size of the substituents. The mass spectra of a variety of 2,3-dihydro-1,4-diazepinium salts are reported. The molecular ion of the cation is only rarely observable due to thermal dissociation of the salt. The 1 2 major breakdown process involves the loss of the (N¹-C²) fragment but other pathways are also considered. The factors governing some anomalous fragmentation patterns are discussed. The rates of bromination in methanol of a number of 2,3-dihydro-1,4-diazepinium salts were measured under first-order conditions, normally by stopped flow methods. Differences in rate of factors of up to 10000 between dihydrodiazepines with only alkyl or aryl substituents, are correlated with steric effects in the region of the reaction site, 5,6,7-Unsubstituted 2,3-dihydro-1,4-diazepinium salts are tedious to make by standard methods, Their facile preparation from l,5-diaryl-1,5-diazapentadienium salts under high dilution conditions, is discussed, and the scope of the synthesis was explored. The mechanism of the reaction was investigated using mono-amine model compounds. Attempts to prepare 5,7-dimethyl-dihydrodiazepinium salts by this method generally resulted in the formation of 2-methylimidazolines. The parent 2,3-dihydro-1,4-diazepinium perchlorate was obtainable by this high dilution synthesis in sufficient quantities for a study of its properties to be made. it is active towards electrophiles, giving 6-substitution products, and reacts with-nucleophiles at the 5(7) position. In contrast to 5,7" substituted dihydrodiazepines, the 6-halogeno derivatives are inert towards nucleophiles at the 6-positiono A series of 1,2-dihydropyrimidines was prepared, and the chemical and spectroscopic properties of these heterocycles are compared with those of the isoelectronic 2,3-dihydro-1,4-diazepines. Dihydropyrimidines show meneidic reactions with electrophiles at the 5-position, taut only 6-unsubstituted derivatives react with nucleophiles at the 6-position. A convenient synthetic route from 4-methyldihydropyrimidines to 5-methyldihydrodiazepinium salts is described. The effect of electronic perturbation on the 1,5-diazapentadienium system was investigated using series of 1,3-dimethyl-1,2-dihydro-2-oxo- and 2-thiopyrimidinium salts. Substitution reactions of 4,6-unsutastituted derivatives with electrophiles have been shown to proceed by alternative mechanisms; those pyrimidines with 4(6)-methyl substituents also show substitution reactions in the methyl groups. Stable adducts are formed by reaction of the 4,6-unsubstituted compounds with bases. The structure and chemical properties of these pseudobases are discussed. The electronic structure of 2,3-dihydro-1,4-diazepinium perchlorates and the other 1,5-diazapentadienium salts considered in this thesis, was investigated by ¹³C nmr spectroscopy.
1974-01-01T00:00:00ZMcNab, HamishThe nmr spectra of 2,3-dihydro-1,4-diazepinium salts are discussed. From the magnitude of the coupling constants around the conjugated part of the molecules, a planar partial structure with complete electron delocalisation is indicated. The molecule as a whole adopts a half-chair configuration which rapidly inverts at room temperature. The effect of ring substitution on this exchange process is correlated with the size of the substituents. The mass spectra of a variety of 2,3-dihydro-1,4-diazepinium salts are reported. The molecular ion of the cation is only rarely observable due to thermal dissociation of the salt. The 1 2 major breakdown process involves the loss of the (N¹-C²) fragment but other pathways are also considered. The factors governing some anomalous fragmentation patterns are discussed. The rates of bromination in methanol of a number of 2,3-dihydro-1,4-diazepinium salts were measured under first-order conditions, normally by stopped flow methods. Differences in rate of factors of up to 10000 between dihydrodiazepines with only alkyl or aryl substituents, are correlated with steric effects in the region of the reaction site, 5,6,7-Unsubstituted 2,3-dihydro-1,4-diazepinium salts are tedious to make by standard methods, Their facile preparation from l,5-diaryl-1,5-diazapentadienium salts under high dilution conditions, is discussed, and the scope of the synthesis was explored. The mechanism of the reaction was investigated using mono-amine model compounds. Attempts to prepare 5,7-dimethyl-dihydrodiazepinium salts by this method generally resulted in the formation of 2-methylimidazolines. The parent 2,3-dihydro-1,4-diazepinium perchlorate was obtainable by this high dilution synthesis in sufficient quantities for a study of its properties to be made. it is active towards electrophiles, giving 6-substitution products, and reacts with-nucleophiles at the 5(7) position. In contrast to 5,7" substituted dihydrodiazepines, the 6-halogeno derivatives are inert towards nucleophiles at the 6-positiono A series of 1,2-dihydropyrimidines was prepared, and the chemical and spectroscopic properties of these heterocycles are compared with those of the isoelectronic 2,3-dihydro-1,4-diazepines. Dihydropyrimidines show meneidic reactions with electrophiles at the 5-position, taut only 6-unsubstituted derivatives react with nucleophiles at the 6-position. A convenient synthetic route from 4-methyldihydropyrimidines to 5-methyldihydrodiazepinium salts is described. The effect of electronic perturbation on the 1,5-diazapentadienium system was investigated using series of 1,3-dimethyl-1,2-dihydro-2-oxo- and 2-thiopyrimidinium salts. Substitution reactions of 4,6-unsutastituted derivatives with electrophiles have been shown to proceed by alternative mechanisms; those pyrimidines with 4(6)-methyl substituents also show substitution reactions in the methyl groups. Stable adducts are formed by reaction of the 4,6-unsubstituted compounds with bases. The structure and chemical properties of these pseudobases are discussed. The electronic structure of 2,3-dihydro-1,4-diazepinium perchlorates and the other 1,5-diazapentadienium salts considered in this thesis, was investigated by ¹³C nmr spectroscopy.Phase studies of inorganic sulphates at high temperaturesCampbell, David Alexanderhttps://hdl.handle.net/10023/154902019-03-29T11:21:25Z1985-01-01T00:00:00ZThe theme of this thesis is the high-temperature phase studies of inorganic metal sulphates and the aspects specifically dealt with are phase diagrams and drop calorimetry. Chapters 1,2, and 3 are concerned with the first of these. Chapter 1 briefly describes the features encountered in one and two-component systems and provides the thermodynamic background which allows such systems to be calculated. Chapter 2 describes a selection of experimental techniques used to determine phase diagrams. Apparatus to perform Differential Thermal Analysis (DTA) was constructed as part of the work of this thesis and so this technique is fully described, including details of the apparatus, and a section on interpretation of DTA results relating to phase studies. Pointers are included as to further applications of this technique and improvements or modifications that might be made to the present apparatus. Chapter 3 presents the phase diagram of the previously undetermined system Ag₂SO₄-LA₂(SO₄)₃ and also includes some observations on the kinetics of some phase changes and a description of the optical furnace which was built to study them. Also presented is a re-investigation of the system Ag₂SO₄-CdSO₄, which contains many features not evident in an earlier study. Chapter 4 is concerned with the thermodynamics of substances at high-temperatures and describes in detail the design, construction and experimental procedure for a drop calorimeter. This apparatus allows the equilibrium temperature of high-temperature polymorphic phase transitions and their enthalpies of transition to be determined. A preliminary study on CdSO₄ was performed, which ties in with the study in Chapter 3, and an attempt was made to resolve the long standing controversy on the temperatures of the CdSO₄ phase transitions. Drop Calorimetry can provide some of the data necessary for the calculation of phase diagrams as described in Chapter 1, and so a brief introduction to the thermodynamics of non-reacting systems and the treatment of results is presented.
1985-01-01T00:00:00ZCampbell, David AlexanderThe theme of this thesis is the high-temperature phase studies of inorganic metal sulphates and the aspects specifically dealt with are phase diagrams and drop calorimetry. Chapters 1,2, and 3 are concerned with the first of these. Chapter 1 briefly describes the features encountered in one and two-component systems and provides the thermodynamic background which allows such systems to be calculated. Chapter 2 describes a selection of experimental techniques used to determine phase diagrams. Apparatus to perform Differential Thermal Analysis (DTA) was constructed as part of the work of this thesis and so this technique is fully described, including details of the apparatus, and a section on interpretation of DTA results relating to phase studies. Pointers are included as to further applications of this technique and improvements or modifications that might be made to the present apparatus. Chapter 3 presents the phase diagram of the previously undetermined system Ag₂SO₄-LA₂(SO₄)₃ and also includes some observations on the kinetics of some phase changes and a description of the optical furnace which was built to study them. Also presented is a re-investigation of the system Ag₂SO₄-CdSO₄, which contains many features not evident in an earlier study. Chapter 4 is concerned with the thermodynamics of substances at high-temperatures and describes in detail the design, construction and experimental procedure for a drop calorimeter. This apparatus allows the equilibrium temperature of high-temperature polymorphic phase transitions and their enthalpies of transition to be determined. A preliminary study on CdSO₄ was performed, which ties in with the study in Chapter 3, and an attempt was made to resolve the long standing controversy on the temperatures of the CdSO₄ phase transitions. Drop Calorimetry can provide some of the data necessary for the calculation of phase diagrams as described in Chapter 1, and so a brief introduction to the thermodynamics of non-reacting systems and the treatment of results is presented.Some experiments on the pyrolysis of tolueneSmith, Francis Geraldinehttps://hdl.handle.net/10023/154872019-03-29T11:22:35Z1959-01-01T00:00:00ZA critical survey of aspects of our knowledge of the heat of formation of the benzyl radical is given in view of its relevance to the heat change in the dissociation process:- C₆H₅CH₃ + C₆H₅CH₂- + H-
(2) Previous work on the pyrolysis of toluene by flow techniques in summarized and apparatus devised to study the reaction under more defined conditions with independent variation of reaction time and partial pressure. Analytical investigations were extended to continuous observation of hydrogen production, and mass spectrometry was applied to identification of gases, liquids and solids.
(3) The existence of the postulated reaction:- H- + C₆H₅CH₃ = C₆H₆ + CH₃- has been checked by decomposing toluene and fluorine together in the flow system. The latter substances provides excess hydrogen atoms, and an increase in decomposition was observed.
(4) Decompositions of toluene in the presence of deuterium have shown that products and unchanged reactant all show appreciable deuteration, and it seems that extensive exchange reactions, probably initiated by hydrogen and deuterium atoms, occur at a rate faster than the decomposition process as judged by (hydrogen + methane) formation.
(5) The products of the reaction not condensable in liquid air averaged 76.7% hydrogen and 23.3% methane. In addition to methane, ethane and ethylene have been shown to be present in appreciable amounts. The liquid products contained benzene, but not in amount equivalent to the methane and C2-hydrocarbons found to be present. The solid products have been shown, by the application of mass spectrometry to a few milligrams of product, to include the following substances in the molar proportions indicated:- 50-60 mole percent dibenzyl, 1-2 mole percent diphenyl, and the remainder dimethyldiphenyls and monomethyldiphenyls in the ratio 4:1.
(6) The kinetic data on the reaction have been obtained within the following range of conditions:- 772-880°c; reaction times 0.565 - 2.076 seconds; toluene partial pressures 0.56 - 2.34 mm.; total gas pressure 3.33- 10.73 mm. The carrier gases have included nitrogen, helium and deuterium. A small number of experiments in a static system extended the temperature range to 750°c.
(7) It has been shown that, judged by the (hydrogen + methane) production, the reaction was first order over the range of flow system variables indicated in (6). In order to get consistent data 'seasoning' of the reaction vessel was essential, and this process was followed by application of a thermal conductivity gauge method.
(8) The temperature dependence of the first order rate constants was given by log.10k(sec⁻¹) =-84700/2.303RT +15.1.
(9) The results of this work have been compared at relevant points with previous data. It is concluded that Szwarc's views on the simple nature of the processes occurring cannot be maintained. Steacie's criticisms of Szwarc's findings are substantiated even within the latter’s temperature range of investigation. It is not felt possible to assert that the experimental activation energy quoted in (8) is the bond dissociation energy for the side chain C-H bond in toluene. It may be the case since it is in agreement with recent independent determinations of the heat of formation of the benzyl radical, but the complexities of the products weaken the case.
1959-01-01T00:00:00ZSmith, Francis GeraldineA critical survey of aspects of our knowledge of the heat of formation of the benzyl radical is given in view of its relevance to the heat change in the dissociation process:- C₆H₅CH₃ + C₆H₅CH₂- + H-
(2) Previous work on the pyrolysis of toluene by flow techniques in summarized and apparatus devised to study the reaction under more defined conditions with independent variation of reaction time and partial pressure. Analytical investigations were extended to continuous observation of hydrogen production, and mass spectrometry was applied to identification of gases, liquids and solids.
(3) The existence of the postulated reaction:- H- + C₆H₅CH₃ = C₆H₆ + CH₃- has been checked by decomposing toluene and fluorine together in the flow system. The latter substances provides excess hydrogen atoms, and an increase in decomposition was observed.
(4) Decompositions of toluene in the presence of deuterium have shown that products and unchanged reactant all show appreciable deuteration, and it seems that extensive exchange reactions, probably initiated by hydrogen and deuterium atoms, occur at a rate faster than the decomposition process as judged by (hydrogen + methane) formation.
(5) The products of the reaction not condensable in liquid air averaged 76.7% hydrogen and 23.3% methane. In addition to methane, ethane and ethylene have been shown to be present in appreciable amounts. The liquid products contained benzene, but not in amount equivalent to the methane and C2-hydrocarbons found to be present. The solid products have been shown, by the application of mass spectrometry to a few milligrams of product, to include the following substances in the molar proportions indicated:- 50-60 mole percent dibenzyl, 1-2 mole percent diphenyl, and the remainder dimethyldiphenyls and monomethyldiphenyls in the ratio 4:1.
(6) The kinetic data on the reaction have been obtained within the following range of conditions:- 772-880°c; reaction times 0.565 - 2.076 seconds; toluene partial pressures 0.56 - 2.34 mm.; total gas pressure 3.33- 10.73 mm. The carrier gases have included nitrogen, helium and deuterium. A small number of experiments in a static system extended the temperature range to 750°c.
(7) It has been shown that, judged by the (hydrogen + methane) production, the reaction was first order over the range of flow system variables indicated in (6). In order to get consistent data 'seasoning' of the reaction vessel was essential, and this process was followed by application of a thermal conductivity gauge method.
(8) The temperature dependence of the first order rate constants was given by log.10k(sec⁻¹) =-84700/2.303RT +15.1.
(9) The results of this work have been compared at relevant points with previous data. It is concluded that Szwarc's views on the simple nature of the processes occurring cannot be maintained. Steacie's criticisms of Szwarc's findings are substantiated even within the latter’s temperature range of investigation. It is not felt possible to assert that the experimental activation energy quoted in (8) is the bond dissociation energy for the side chain C-H bond in toluene. It may be the case since it is in agreement with recent independent determinations of the heat of formation of the benzyl radical, but the complexities of the products weaken the case.The thermal decomposition of dibenzylPittilo, Robert Neilsonhttps://hdl.handle.net/10023/154812019-03-29T11:20:32Z1959-01-01T00:00:00ZThe opening pages of this section are devoted to a review of the evidence revealed by the various experiment al techniques which have been applied to the problem. The relationships between the several products and their variations with temperature and pressure have been illustrated graphically and the significance of thane change discussed. The lack of stoichiometric balance is also considered and some possible explanations proposed. This is followed by an outline of the various mechanisms which are available for the production of the resultants in the observed quantities, and the relative merits of these are discussed. On the basis of this discussion a value is proposed for the dissociation energy of the central c-c bond. The final section is concerned with the conclusions which can be drawn from this value regarding the energies involved in other steps of the reaction and their significance in the general scheme of bond energies.
1959-01-01T00:00:00ZPittilo, Robert NeilsonThe opening pages of this section are devoted to a review of the evidence revealed by the various experiment al techniques which have been applied to the problem. The relationships between the several products and their variations with temperature and pressure have been illustrated graphically and the significance of thane change discussed. The lack of stoichiometric balance is also considered and some possible explanations proposed. This is followed by an outline of the various mechanisms which are available for the production of the resultants in the observed quantities, and the relative merits of these are discussed. On the basis of this discussion a value is proposed for the dissociation energy of the central c-c bond. The final section is concerned with the conclusions which can be drawn from this value regarding the energies involved in other steps of the reaction and their significance in the general scheme of bond energies.The thermal decomposition of trifluoromethyl iodideDowns, Gordon Wyliehttps://hdl.handle.net/10023/154802019-03-29T11:21:32Z1959-01-01T00:00:00ZThe pyrolysis of trifluoromethyl lodide has been investigated under two entirely different sets of conditions (i) in a low pressure flow system (ii) in sealed tubes at higher pressure in the flow system, nickel and pyrox reaction vessels were used. The nickel vessel was used when no material was added to react with OF5 radicals which it was feared would attack pyrex glass. During the course of the Investigations, it was deoided to add toluene, hydrogen iodine as additional reagents. The conditions in the flow system were varied within the following Limits:- Temperature 698°K to 797°K Contact Time. 526 to 2.52 secs. CF3I Pressure 0.016 mms to 0.58 mms. Toluene Pressure 0 to 3.76 mms. Hydrogen Iodide Pressure 0 to 4.08 mms. N2 carrier gas Pressure 1.50 to 14.5 mms. A carrier gas Pressure 1.59 to 12.4 mms. C6H5OF5 Pressure 0 to 2.65 mms. Pressure of added iodine (as atoms) 0 to. 0176 mms. Surface to Volume Retio 1.95 to 6.15 cms⁻¹ only pyrex reaction vessels were used in the sealed tube reactions. OF5 I was never heated alone but always in the presence of HI. In these reactions, conditions were varied within the Limits:- Temperature 440°K to 522°K Reaction Time 10,800 secs. To 259,200 secs. CF5I Pressure 4.0 mms to 57 mms. Hydrogen Iodide Pressure 5.7 mms to 565 mms. Pressure of added iodine (as molecules) 0 to 5.0 mms. An attempt was made to find the stoichiometry of the reaction under all conditions. In order to do this, titration, Low temperature distillation, U.V. and I.R. absorption spectrophotometry and mass spectrometry were used. A reaction scheme has been proposed which agrees with the major experimental findings.
1959-01-01T00:00:00ZDowns, Gordon WylieThe pyrolysis of trifluoromethyl lodide has been investigated under two entirely different sets of conditions (i) in a low pressure flow system (ii) in sealed tubes at higher pressure in the flow system, nickel and pyrox reaction vessels were used. The nickel vessel was used when no material was added to react with OF5 radicals which it was feared would attack pyrex glass. During the course of the Investigations, it was deoided to add toluene, hydrogen iodine as additional reagents. The conditions in the flow system were varied within the following Limits:- Temperature 698°K to 797°K Contact Time. 526 to 2.52 secs. CF3I Pressure 0.016 mms to 0.58 mms. Toluene Pressure 0 to 3.76 mms. Hydrogen Iodide Pressure 0 to 4.08 mms. N2 carrier gas Pressure 1.50 to 14.5 mms. A carrier gas Pressure 1.59 to 12.4 mms. C6H5OF5 Pressure 0 to 2.65 mms. Pressure of added iodine (as atoms) 0 to. 0176 mms. Surface to Volume Retio 1.95 to 6.15 cms⁻¹ only pyrex reaction vessels were used in the sealed tube reactions. OF5 I was never heated alone but always in the presence of HI. In these reactions, conditions were varied within the Limits:- Temperature 440°K to 522°K Reaction Time 10,800 secs. To 259,200 secs. CF5I Pressure 4.0 mms to 57 mms. Hydrogen Iodide Pressure 5.7 mms to 565 mms. Pressure of added iodine (as molecules) 0 to 5.0 mms. An attempt was made to find the stoichiometry of the reaction under all conditions. In order to do this, titration, Low temperature distillation, U.V. and I.R. absorption spectrophotometry and mass spectrometry were used. A reaction scheme has been proposed which agrees with the major experimental findings.The rate of thermal dissociation of direnzylDavidson, Iain Munro Thomsonhttps://hdl.handle.net/10023/154792019-03-29T11:23:22Z1958-01-01T00:00:00Z1) The most recent work on the pyrolysis of dibenzyl suggested that a thermal equilibrium:- PhCH₂CH₂Ph == 2 PhCH₂- was set up as a preliminary to decomposition. The aim of this research was to test this idea by heating mixtures of PhCH₂CH₂Ph (M.W. 182) and PhCD₂CD₂Ph (M.W. 186) and following mass spectrometrically the growth of PhCH₂CH₂Ph (M.W. 184) formed by radical recombination. 2) A four stage synthesis of deuterated dibenzyl was developed and used to prepare dibenzyl of 95% isotopic purity with the composition:- PhCD₂CD₂Ph, 81%; PhCD₂CDHPh, 18 %; PhCDHCDHPh, 1%. PhCH₂CD₂Ph was synthesized by the same sequence of reactions. 3) In order to provide the necessary experimental equipment, the following items have been developed and constructed and descriptions of them are given in this Thesis:- a) a 2 litre reaction vessel with an electronically controlled furnace was arranged with a gas circulating system feeding the inlet of a mass spectrometer; b) an existing mass spectrometer was extensively modified in order to give resolution of 1 in 200:- i) the spectrometer tube was stiffened and accurately re-aligned; ii) the ion collector unit was made detachable and its construction improved; iii) a new ion source was designed and built to the required high accuracy; iv) a new scanning unit was built for variation of the magnetic field. 4) The rate of formation of PhCH₂CD₂Ph was followed in mixtures of PhCH₂CD₂Ph and PhCD₂CD₂Ph at pressures of 0.08 to 0.66 mm. in the reaction vessel, and at pressure up to 142 mm. in sealed tubes, using temperatures between 400° and 500°C. Data were also obtained on the rate of decomposition of PhCH₂CH₂Ph alone in similar systems. 5) The rate of radical exchange was found to be first order, independent of surface and of pressure of added A, N₂, D₂, and O₂. The decomposition reaction was shown to be 1.5 order at low pressures, and tended to first order at high pressures. At lower pressures it was much slower than the radical exchange. 6) A rate equation for radical exchange in terms of the rate of dissociation of dibenzyl, making due allowance for the simultaneous decomposition of dibenzyl has been developed and applied in the lower pressure region where exchange was of major importance. It gives:- kf sec⁻¹ = 10 ¹⁴.⁰³ exp -6000/RT 7) The energy of activation in 6) has been identified with D(PhCH₂-CD₂Ph) in dibenzyl. This value has been discussed in relation to current data on the heat of formation of the benzyl radical and bond dissociation energies in benzyl compounds, notably D(PhCH₂-H) in toluene. 8) The energy of activation for the decomposition was found to be 47 kcal and the nature and proportions of the reaction products were established and compared with previous work. The proportions of side-chain deuterated toluenes formed were consistent with a deuterium isotope effect of 2 or less, and with toluene being made by the abstraction of hydrogen from the central carbon atoms of dibenzyl by benzyl radicals. Benzyl radicals were also shown to react with deuterium to form toluene.
1958-01-01T00:00:00ZDavidson, Iain Munro Thomson1) The most recent work on the pyrolysis of dibenzyl suggested that a thermal equilibrium:- PhCH₂CH₂Ph == 2 PhCH₂- was set up as a preliminary to decomposition. The aim of this research was to test this idea by heating mixtures of PhCH₂CH₂Ph (M.W. 182) and PhCD₂CD₂Ph (M.W. 186) and following mass spectrometrically the growth of PhCH₂CH₂Ph (M.W. 184) formed by radical recombination. 2) A four stage synthesis of deuterated dibenzyl was developed and used to prepare dibenzyl of 95% isotopic purity with the composition:- PhCD₂CD₂Ph, 81%; PhCD₂CDHPh, 18 %; PhCDHCDHPh, 1%. PhCH₂CD₂Ph was synthesized by the same sequence of reactions. 3) In order to provide the necessary experimental equipment, the following items have been developed and constructed and descriptions of them are given in this Thesis:- a) a 2 litre reaction vessel with an electronically controlled furnace was arranged with a gas circulating system feeding the inlet of a mass spectrometer; b) an existing mass spectrometer was extensively modified in order to give resolution of 1 in 200:- i) the spectrometer tube was stiffened and accurately re-aligned; ii) the ion collector unit was made detachable and its construction improved; iii) a new ion source was designed and built to the required high accuracy; iv) a new scanning unit was built for variation of the magnetic field. 4) The rate of formation of PhCH₂CD₂Ph was followed in mixtures of PhCH₂CD₂Ph and PhCD₂CD₂Ph at pressures of 0.08 to 0.66 mm. in the reaction vessel, and at pressure up to 142 mm. in sealed tubes, using temperatures between 400° and 500°C. Data were also obtained on the rate of decomposition of PhCH₂CH₂Ph alone in similar systems. 5) The rate of radical exchange was found to be first order, independent of surface and of pressure of added A, N₂, D₂, and O₂. The decomposition reaction was shown to be 1.5 order at low pressures, and tended to first order at high pressures. At lower pressures it was much slower than the radical exchange. 6) A rate equation for radical exchange in terms of the rate of dissociation of dibenzyl, making due allowance for the simultaneous decomposition of dibenzyl has been developed and applied in the lower pressure region where exchange was of major importance. It gives:- kf sec⁻¹ = 10 ¹⁴.⁰³ exp -6000/RT 7) The energy of activation in 6) has been identified with D(PhCH₂-CD₂Ph) in dibenzyl. This value has been discussed in relation to current data on the heat of formation of the benzyl radical and bond dissociation energies in benzyl compounds, notably D(PhCH₂-H) in toluene. 8) The energy of activation for the decomposition was found to be 47 kcal and the nature and proportions of the reaction products were established and compared with previous work. The proportions of side-chain deuterated toluenes formed were consistent with a deuterium isotope effect of 2 or less, and with toluene being made by the abstraction of hydrogen from the central carbon atoms of dibenzyl by benzyl radicals. Benzyl radicals were also shown to react with deuterium to form toluene.Studies in the pyrolysis of methyl iodide with particular reference to the transition from first to second order kinetic behaviourCundall, Robert Bowserhttps://hdl.handle.net/10023/154782019-03-29T11:21:27Z1953-01-01T00:00:00Z(1) The previous work of Lapage on the decomposition of methyl iodide has been extended and confirmed in all essential detail. In particular attention has been paid to the transition from first order to second order kineties as the total pressure of the reacting system is lowered and the activating efficiencies of different inert gases have been evaluated. (2) It is concluded that the reaction mechanism shows the following features:- (a) the primary step under all conditions is the dissociation into methyl radicals and iodine atoms. High Pressure Experiments. (b) It has been shown that increasing additions of toluene can result in the complete capture of the methyl radicals provided that its pressure is about 8 mm. and the inert gas pressure is about 600 mm. thereby impeding diffusion to the walls where destruction can otherwise occur by 4CH₃ 3CH₄ + C. (The toluene pressures used by Lapage tended to be rather low for the purpose). (c) The reaction conducted in the above conditions with added toluene is faster than in its absence. This shows no chain reaction is involved but a recombination process of methyl radicals and iodine is occurring. (d) The recombination reaction has been proved by the effect of increasing additions of iodine to the system, causing a decrease in rate. This point was not proved in previous work. (e) During the investigations with added toluene it has been noted and proved by separate experiments that iodine and toluene react with the production of hydrogen iodide. It is suggested that this is due to C₆H₅CH₃ + I. Experiments on this aspect of the work involved mass spectrometric analysis of products. (f) In the presence of sufficient toluene and with about 600 mm. of nitrogen the first order constant has a temperature dependence given by log k₁ = 13.7 - 54,700/2.303RT in agreement with Lapege. (g) A study has been made of the effect of nitrogen pressure on the rate of reaction in the range 100 - 600 mm. nitrogen. No effect was observed. Taken in conjunction with the conclusions detailed below, it is considered that this shows that the high pressure limiting rate of decomposition was stained in this region. Low Pressure Experiments. (a) The products of the reaction were shown to be carbon, methane and iodine, in agreement with the equation 4CH₃I 3CH₄ + C2I₂. Analyses were made by the mass spectrometer for ethane and it was shown to account for only 1% approximately of the products. (b) Reproducibility of the experiments was enhanced by using a carbon coated vessel. (c) At the low pressures used (4 mm. nitrogen and 0.1 mm. methyl iodide) with decompositions usually no greater than 3 % iodine did not spear to inhibit the reaction. This was proved by direct additions. (d) Extensive verification has been made of the fact that a decline in rate of reaction occurs as the pressures of nitrogen and methyl iodide are lowered below 10 mm. and 0.5 mm. respectively. This has been shown to occur over a wide range of temperatures and the first order behaviour changes to second order at lower pressures. (e) The effect of the following gases has been investigated in order to confirm the theory of second order to first order transition for this reaction. All the data are in agreement with this view. (f) Using a treatment analogous that given by johnston102 the following efficiencies as activators have been deduced. CH₃I 1, N₂ 0.13, CH₄ 0.083, CO 0.038, NO 0.80, He 0.043, Ne 0.049, A 0.053, Kr 0.041. (g) The bimolecular constant for the reaction has been found at various temperatures and shown to be described by log k₂ = 14.5 - E/RT. 2.303 (1.mol.⁻¹ sec.⁻¹). E = 54.4 k.cal./mole. This value of E is in agreement with that derived from the high pressure first order constants. (h) A discussion of the efficiencies of the inert gases has been given.
1953-01-01T00:00:00ZCundall, Robert Bowser(1) The previous work of Lapage on the decomposition of methyl iodide has been extended and confirmed in all essential detail. In particular attention has been paid to the transition from first order to second order kineties as the total pressure of the reacting system is lowered and the activating efficiencies of different inert gases have been evaluated. (2) It is concluded that the reaction mechanism shows the following features:- (a) the primary step under all conditions is the dissociation into methyl radicals and iodine atoms. High Pressure Experiments. (b) It has been shown that increasing additions of toluene can result in the complete capture of the methyl radicals provided that its pressure is about 8 mm. and the inert gas pressure is about 600 mm. thereby impeding diffusion to the walls where destruction can otherwise occur by 4CH₃ 3CH₄ + C. (The toluene pressures used by Lapage tended to be rather low for the purpose). (c) The reaction conducted in the above conditions with added toluene is faster than in its absence. This shows no chain reaction is involved but a recombination process of methyl radicals and iodine is occurring. (d) The recombination reaction has been proved by the effect of increasing additions of iodine to the system, causing a decrease in rate. This point was not proved in previous work. (e) During the investigations with added toluene it has been noted and proved by separate experiments that iodine and toluene react with the production of hydrogen iodide. It is suggested that this is due to C₆H₅CH₃ + I. Experiments on this aspect of the work involved mass spectrometric analysis of products. (f) In the presence of sufficient toluene and with about 600 mm. of nitrogen the first order constant has a temperature dependence given by log k₁ = 13.7 - 54,700/2.303RT in agreement with Lapege. (g) A study has been made of the effect of nitrogen pressure on the rate of reaction in the range 100 - 600 mm. nitrogen. No effect was observed. Taken in conjunction with the conclusions detailed below, it is considered that this shows that the high pressure limiting rate of decomposition was stained in this region. Low Pressure Experiments. (a) The products of the reaction were shown to be carbon, methane and iodine, in agreement with the equation 4CH₃I 3CH₄ + C2I₂. Analyses were made by the mass spectrometer for ethane and it was shown to account for only 1% approximately of the products. (b) Reproducibility of the experiments was enhanced by using a carbon coated vessel. (c) At the low pressures used (4 mm. nitrogen and 0.1 mm. methyl iodide) with decompositions usually no greater than 3 % iodine did not spear to inhibit the reaction. This was proved by direct additions. (d) Extensive verification has been made of the fact that a decline in rate of reaction occurs as the pressures of nitrogen and methyl iodide are lowered below 10 mm. and 0.5 mm. respectively. This has been shown to occur over a wide range of temperatures and the first order behaviour changes to second order at lower pressures. (e) The effect of the following gases has been investigated in order to confirm the theory of second order to first order transition for this reaction. All the data are in agreement with this view. (f) Using a treatment analogous that given by johnston102 the following efficiencies as activators have been deduced. CH₃I 1, N₂ 0.13, CH₄ 0.083, CO 0.038, NO 0.80, He 0.043, Ne 0.049, A 0.053, Kr 0.041. (g) The bimolecular constant for the reaction has been found at various temperatures and shown to be described by log k₂ = 14.5 - E/RT. 2.303 (1.mol.⁻¹ sec.⁻¹). E = 54.4 k.cal./mole. This value of E is in agreement with that derived from the high pressure first order constants. (h) A discussion of the efficiencies of the inert gases has been given.The pyrolysis of benzil and desoxybenzoinBarraclough, Ralph Neilhttps://hdl.handle.net/10023/154772019-03-29T11:20:22Z1959-01-01T00:00:00Z1959-01-01T00:00:00ZBarraclough, Ralph NeilThe thermal decomposition of benzyl iodideGow, John Stobiehttps://hdl.handle.net/10023/154652019-03-29T11:19:35Z1961-01-01T00:00:00ZThe results of the work, described in this thesis, may be summarized as follows:- 1) The gas phase pyrolysis of benzyl iodide, either alone or in the presence of added free iodine, proceeds via the following mechanism
BzI ⟷Ke Bz + I
I + I ⟷ I ₂
Bz + Bz ⟶ k2 Bz-Bz
An analysis of the data has been carried out where reactions (a) and (b) are presumed to reach equilibrium and reaction (c) is rate determining. Over a temperature range of 516°K, carried out using both static (516-557°K) and flow (611-702°K) systems with benzyl iodide partial pressures from. 03 mm. to 9.0 mm., the logarithm of 2 k₂Ke² plotted against 1/(T°K) gave a straight line. The slope of this Line on the above mechanism is equal to (2 △h+E)/2.3R (where △ = change in heat content associated with the equilibrium BzI ⟷Bz + I and E = the activation energy of the reaction Bz + Bz ⟶ Bz-Bz) and (2 △H + E) was found to be 84 K cal./mol. On the assumption that E = O, this is equivalent to a benzyl iodide bond strength of 42 K cal./mol. This experimentally derived bond strength must be reduced by 1 K cal./mol. for every 2 K cal./mol. Of energy of activation required by the recombination of tow benzyl radicals. A review of the literature, on free radical recombination energies, suggests that for benzyl radicals it is not likely to exceed 4-5 L cal./mol. And therefore the present investigation leads to a value of 40-42 K cal./mol. for the strength of the carbon-iodine bond in benzyl iodide.
2) It has been shown that, in the presence of excess hydrogen iodide as a radical acceptor, benzyl iodide decomposes according to the following mechanism –
(a) BzI ⟶ Bz + I
(b) I + I ⟷I₂
(d) Bz + HI ⟶ Bz-H + I
(e) I + BzI ⟶ Bz + I₂
In this scheme, the rate determining process is the dissociation process in (a) since, with sufficient HI present, reaction (d) prevents an equilibrium concentration of benzyl radicals being built up. It has been shown to be possible to obtain conditions where the rate of iodine formation is independent of HI concentrations. Using such conditions, reaction epsilon was shown to be a very significant contributor to the total rate. Moreover, the elimination of the back reaction in (a) produced a large increase in decomposition rate, so much so that the range of temperature used in this section of the work was over 100oC below that for the previous section. The energy of activation of the reaction (e); has been determined as 4.1 K cal./mol. (This value was calculated from results covering the temperature range 505 to 585°K). Using Perlman and Rollefson's(78) data on the dissociation of molecular iodine, this activation energy of 4.1 K cal./mol. is equivalent to a benzyl iodide bond strength of 40.6 K cal./mol. This value is in good agreement with that obtained from the pyrolysis work in the absence of a radical acceptor. The initial dissociation reaction (Bzl ⟶ Bz + I) has been found to be between first and second order at the partial pressures of benzyl iodide used (0.02 mm. - 0.13 mm.) and this is attributed to the normal Hinshelwood-Lindemann effect for unimolecular reactions. An approximate value of 0.35 sec.⁻¹ for the high pressure limiting rate constant at 585°K has been deduced. This corresponds to an Arrhenius factor for the decomposition of 1014.6 sec.⁻¹, if the benzyl iodide bond strength is assumed to be 40.6 K cal./mol. 3) At the very lowest partial pressures used (~0.02 mm.), the initial dissociation reaction approaches second order behaviour and the temperature dependence of assumed second order rate constants leads to an activation energy of 40 K cal./mol. for the decomposition. The corresponding pre-exponential factor is 10 ²⁰.⁴, which is of the order of magnitude to be expected for a reaction of this type. The data, in this low pressure region, are, however, insufficient to establish that the reaction in accurately second order at these pressure. 4) If the bond strength of benzyl iodide is taken as 41 K cal./mol., as determined in this present investigation, a value may be calculated for the heat of formation of the benzyl radical. Using 27.2 K cal./mol. for the heat of benzyl iodide, as suggested by skinner(63), a value of 43 K cal./mol. is obtained for △Hf (benzyl). This is in close agreement with the values of 45.3 K cal./mol. and 44.8 cal./mol., obtained in this department by Alexander(58) and Davidson(59) respectively - their values were derived their determinations of the bond strength of the central carbon-carbon bond in dibenzyl. The present value of 43 L cal./mol. is also in accord with the 44.9 K cal./mol., deduced from Benson and buss(47) determination of the toluene bond strength as 84 K cal./mol. The more commonly quoted toluene bond strength of 77.5 K cal./mol., obtained by Szwarc(48) leads to a △Hf (Benzyl) of only 37.4 K cal./mol. and would, therefore, seem to be too low.
1961-01-01T00:00:00ZGow, John StobieThe results of the work, described in this thesis, may be summarized as follows:- 1) The gas phase pyrolysis of benzyl iodide, either alone or in the presence of added free iodine, proceeds via the following mechanism
BzI ⟷Ke Bz + I
I + I ⟷ I ₂
Bz + Bz ⟶ k2 Bz-Bz
An analysis of the data has been carried out where reactions (a) and (b) are presumed to reach equilibrium and reaction (c) is rate determining. Over a temperature range of 516°K, carried out using both static (516-557°K) and flow (611-702°K) systems with benzyl iodide partial pressures from. 03 mm. to 9.0 mm., the logarithm of 2 k₂Ke² plotted against 1/(T°K) gave a straight line. The slope of this Line on the above mechanism is equal to (2 △h+E)/2.3R (where △ = change in heat content associated with the equilibrium BzI ⟷Bz + I and E = the activation energy of the reaction Bz + Bz ⟶ Bz-Bz) and (2 △H + E) was found to be 84 K cal./mol. On the assumption that E = O, this is equivalent to a benzyl iodide bond strength of 42 K cal./mol. This experimentally derived bond strength must be reduced by 1 K cal./mol. for every 2 K cal./mol. Of energy of activation required by the recombination of tow benzyl radicals. A review of the literature, on free radical recombination energies, suggests that for benzyl radicals it is not likely to exceed 4-5 L cal./mol. And therefore the present investigation leads to a value of 40-42 K cal./mol. for the strength of the carbon-iodine bond in benzyl iodide.
2) It has been shown that, in the presence of excess hydrogen iodide as a radical acceptor, benzyl iodide decomposes according to the following mechanism –
(a) BzI ⟶ Bz + I
(b) I + I ⟷I₂
(d) Bz + HI ⟶ Bz-H + I
(e) I + BzI ⟶ Bz + I₂
In this scheme, the rate determining process is the dissociation process in (a) since, with sufficient HI present, reaction (d) prevents an equilibrium concentration of benzyl radicals being built up. It has been shown to be possible to obtain conditions where the rate of iodine formation is independent of HI concentrations. Using such conditions, reaction epsilon was shown to be a very significant contributor to the total rate. Moreover, the elimination of the back reaction in (a) produced a large increase in decomposition rate, so much so that the range of temperature used in this section of the work was over 100oC below that for the previous section. The energy of activation of the reaction (e); has been determined as 4.1 K cal./mol. (This value was calculated from results covering the temperature range 505 to 585°K). Using Perlman and Rollefson's(78) data on the dissociation of molecular iodine, this activation energy of 4.1 K cal./mol. is equivalent to a benzyl iodide bond strength of 40.6 K cal./mol. This value is in good agreement with that obtained from the pyrolysis work in the absence of a radical acceptor. The initial dissociation reaction (Bzl ⟶ Bz + I) has been found to be between first and second order at the partial pressures of benzyl iodide used (0.02 mm. - 0.13 mm.) and this is attributed to the normal Hinshelwood-Lindemann effect for unimolecular reactions. An approximate value of 0.35 sec.⁻¹ for the high pressure limiting rate constant at 585°K has been deduced. This corresponds to an Arrhenius factor for the decomposition of 1014.6 sec.⁻¹, if the benzyl iodide bond strength is assumed to be 40.6 K cal./mol. 3) At the very lowest partial pressures used (~0.02 mm.), the initial dissociation reaction approaches second order behaviour and the temperature dependence of assumed second order rate constants leads to an activation energy of 40 K cal./mol. for the decomposition. The corresponding pre-exponential factor is 10 ²⁰.⁴, which is of the order of magnitude to be expected for a reaction of this type. The data, in this low pressure region, are, however, insufficient to establish that the reaction in accurately second order at these pressure. 4) If the bond strength of benzyl iodide is taken as 41 K cal./mol., as determined in this present investigation, a value may be calculated for the heat of formation of the benzyl radical. Using 27.2 K cal./mol. for the heat of benzyl iodide, as suggested by skinner(63), a value of 43 K cal./mol. is obtained for △Hf (benzyl). This is in close agreement with the values of 45.3 K cal./mol. and 44.8 cal./mol., obtained in this department by Alexander(58) and Davidson(59) respectively - their values were derived their determinations of the bond strength of the central carbon-carbon bond in dibenzyl. The present value of 43 L cal./mol. is also in accord with the 44.9 K cal./mol., deduced from Benson and buss(47) determination of the toluene bond strength as 84 K cal./mol. The more commonly quoted toluene bond strength of 77.5 K cal./mol., obtained by Szwarc(48) leads to a △Hf (Benzyl) of only 37.4 K cal./mol. and would, therefore, seem to be too low.A study of some free radicals by electron spin resonanceRorke, Davidhttps://hdl.handle.net/10023/154622019-03-29T11:19:23Z1965-01-01T00:00:00Z1965-01-01T00:00:00ZRorke, DavidSynthesis and anti-tumour activity of some new derivatives of flavone-8-acetic acidWilson, David William Josephhttps://hdl.handle.net/10023/154612019-03-29T11:19:37Z1995-01-01T00:00:00ZA robust six-step synthesis of substituted flavone-8-acetic acid sodium salts has been developed and optimised to allow preparation of a wide variety of products for testing as anti-tumour agents. The condensation and cyclisation steps have been combined in an efficient one-pot procedure and efficient procedures for subsequent oxidative cleavage of an allyl group and salt formation have been developed. Using this method a total of 18 derivatives bearing substituents on the 2-phenyl ring have been prepared. Based on encouraging activity from methoxy substituted compounds, attention has been concentrated on these and various mono-, di-, tri- and tetramethoxy compounds have been prepared, most for the first time. Activity of these against MAC15A, both in vitro and in vivo has been determined by collaborators at Bradford and several compounds have comparable or greater activity than the unsubstituted prototype. The presence of a 2'-methoxyl substituent appears to be particularly favourable to activity. Five different heterocyclic analogues with furyl, thienyl and benzothienyl groups at the 2-position have been obtained and these also show good activity with the 3-methyl-2-thienyl compound showing the highest in vivo activity of any compound examined. Attempts to prepare pyridyl and quinolyl derivatives were unsuccessful. The 2-benzyl and 2-diphenylmethyl compounds have also been prepared and while the former shows good activity in vitro, it is inactive in vivo probably due to metabolic breakdown. The latter compound is completely inactive probably due to a requirement for planarity in the 2- substituent. An extended derivative has been obtained by an unexpected mode of reaction encountered in an attempt to prepare the 2-phenylethynyl compound. Both this and a dimeric ether analogue show significant activity, thereby adding to our understanding of the structural requirements for activity. Variation in the 8-acetic acid substituted has been examined by synthesis of three compounds with CH₂C(O)CH₂OH at this position and, by a separate multi-stage synthesis, the compound with tetrazolylmethyl. The former compounds are too insoluble for activity to be measured, while the latter is inactive. A comparison of electron density, as reflected by ¹H and ¹³C NMR shifts, against activity in vitro has been made for all the compounds prepared, and while some trends may be discerned, the correlation is generally poor. A suitable single crystal of flavone acetic acid was prepared and its X-ray structure was obtained by the SERC Crystallography Unit, Cardiff. The structure, which proved to be of the monohydrate showed the preferred orientation of the 2- and 8-substituents and provided accurate dimensions for future theoretical work.
1995-01-01T00:00:00ZWilson, David William JosephA robust six-step synthesis of substituted flavone-8-acetic acid sodium salts has been developed and optimised to allow preparation of a wide variety of products for testing as anti-tumour agents. The condensation and cyclisation steps have been combined in an efficient one-pot procedure and efficient procedures for subsequent oxidative cleavage of an allyl group and salt formation have been developed. Using this method a total of 18 derivatives bearing substituents on the 2-phenyl ring have been prepared. Based on encouraging activity from methoxy substituted compounds, attention has been concentrated on these and various mono-, di-, tri- and tetramethoxy compounds have been prepared, most for the first time. Activity of these against MAC15A, both in vitro and in vivo has been determined by collaborators at Bradford and several compounds have comparable or greater activity than the unsubstituted prototype. The presence of a 2'-methoxyl substituent appears to be particularly favourable to activity. Five different heterocyclic analogues with furyl, thienyl and benzothienyl groups at the 2-position have been obtained and these also show good activity with the 3-methyl-2-thienyl compound showing the highest in vivo activity of any compound examined. Attempts to prepare pyridyl and quinolyl derivatives were unsuccessful. The 2-benzyl and 2-diphenylmethyl compounds have also been prepared and while the former shows good activity in vitro, it is inactive in vivo probably due to metabolic breakdown. The latter compound is completely inactive probably due to a requirement for planarity in the 2- substituent. An extended derivative has been obtained by an unexpected mode of reaction encountered in an attempt to prepare the 2-phenylethynyl compound. Both this and a dimeric ether analogue show significant activity, thereby adding to our understanding of the structural requirements for activity. Variation in the 8-acetic acid substituted has been examined by synthesis of three compounds with CH₂C(O)CH₂OH at this position and, by a separate multi-stage synthesis, the compound with tetrazolylmethyl. The former compounds are too insoluble for activity to be measured, while the latter is inactive. A comparison of electron density, as reflected by ¹H and ¹³C NMR shifts, against activity in vitro has been made for all the compounds prepared, and while some trends may be discerned, the correlation is generally poor. A suitable single crystal of flavone acetic acid was prepared and its X-ray structure was obtained by the SERC Crystallography Unit, Cardiff. The structure, which proved to be of the monohydrate showed the preferred orientation of the 2- and 8-substituents and provided accurate dimensions for future theoretical work.Structural and chemical properties of solid organic inclusion compoundsShannon, Ian Jameshttps://hdl.handle.net/10023/154592019-03-29T11:22:57Z1995-01-01T00:00:00ZUrea and thiourea form inclusion compounds in which organic and organometallic guest molecules are confined within non-intersecting, unidirectional tunnels within a solid urea or thiourea host structure. In this thesis, studies have been undertaken using a variety of techniques to examine the properties of urea and thiourea inclusion compounds, with a view to improving the understanding of the forces controlling the ordering of these systems on a molecular scale. From single crystal X-ray diffraction studies of urea inclusion compounds carried out at room temperature, different modes of ordering between guest molecules in adjacent tunnels, dependent on the guest species present, have been observed. Extension of these studies to low temperature, in conjunction with powder X-ray diffraction, has revealed information on phase transitions in both the host and guest substructures of urea inclusion compounds. Computer modelling, using a mathematical model developed for application to one-dimensional inclusion compounds, has been applied to model properties of n-alkane/urea and dimethylketone/urea inclusion compounds. The model has also been applied to the chlorocyclohexane/thiourea inclusion compound. EXAFS spectroscopy has been carried out on α,w-dibromoalkane/urea inclusion compounds to examine the local structural properties of the guest molecules. Halogenocyclohexane/thiourea and halogenocyclohexanes included within the pores of several zeolite-type hosts have also been investigated to determine the conformation of the guest molecules when constrained to occupy a confined environment. Additional studies have examined the potential for the polymerisation of monomeric guest molecules within the tunnels of the organic host structure of perhydrotriphenylene, and a solid state NMR investigation on the effect of magic angle spinning on the observed NMR spectrum for metallocenes.
1995-01-01T00:00:00ZShannon, Ian JamesUrea and thiourea form inclusion compounds in which organic and organometallic guest molecules are confined within non-intersecting, unidirectional tunnels within a solid urea or thiourea host structure. In this thesis, studies have been undertaken using a variety of techniques to examine the properties of urea and thiourea inclusion compounds, with a view to improving the understanding of the forces controlling the ordering of these systems on a molecular scale. From single crystal X-ray diffraction studies of urea inclusion compounds carried out at room temperature, different modes of ordering between guest molecules in adjacent tunnels, dependent on the guest species present, have been observed. Extension of these studies to low temperature, in conjunction with powder X-ray diffraction, has revealed information on phase transitions in both the host and guest substructures of urea inclusion compounds. Computer modelling, using a mathematical model developed for application to one-dimensional inclusion compounds, has been applied to model properties of n-alkane/urea and dimethylketone/urea inclusion compounds. The model has also been applied to the chlorocyclohexane/thiourea inclusion compound. EXAFS spectroscopy has been carried out on α,w-dibromoalkane/urea inclusion compounds to examine the local structural properties of the guest molecules. Halogenocyclohexane/thiourea and halogenocyclohexanes included within the pores of several zeolite-type hosts have also been investigated to determine the conformation of the guest molecules when constrained to occupy a confined environment. Additional studies have examined the potential for the polymerisation of monomeric guest molecules within the tunnels of the organic host structure of perhydrotriphenylene, and a solid state NMR investigation on the effect of magic angle spinning on the observed NMR spectrum for metallocenes.The vacuum thermal degradation of poly(methyl acrylate) and poly(benzyl acrylate)Kane, David Rosshttps://hdl.handle.net/10023/154572019-03-29T11:23:41Z1966-01-01T00:00:00Z1966-01-01T00:00:00ZKane, David RossTheoretical investigations on some biological systemsScano, Paolahttps://hdl.handle.net/10023/154552019-03-29T11:24:27Z1997-01-01T00:00:00ZIn this thesis molecular properties of different biological systems are studied by means of Quantum Mechanical methods. After a brief introduction, the basic theory of the methods here used is presented in Chapter 1. In Chapter 2 the heats of formation and the ionization potentials of some carcinogenic compounds such as Polycyclic Aromatic Hydrocarbons are studied and compared with experimental data. The methods used are the semiempirical methods with the AM1 and PM3 Hamiltonians. The results show that the experimental heats of formation are better reproduced by PM3, while as far as the ionization potentials are concerned AM1 is slightly better than PM3. In Chapter 3, the Lipid Peroxidation mechanism has been studied at the molecular level. The energetic details of the pathway proposed by Porter have been studied using the semiempirical AM1 and PM3 Hamiltonians. Six model compounds, which retain the same functional characteristics as the physiological fatty acid, have been used. The results are in good agreement with the experimental observations. Characteristics and metabolism of the anticancer drug NMF (N-Methylformide) have been studied in detail in Chapter 4. Accurate ab initio calculations have been carried out and the effect of the solvent has been taken into account. The results represent a good example of the high quality of information that the application of ab initio methods can give when properties of molecules and energetic details of pathways are examined.
1997-01-01T00:00:00ZScano, PaolaIn this thesis molecular properties of different biological systems are studied by means of Quantum Mechanical methods. After a brief introduction, the basic theory of the methods here used is presented in Chapter 1. In Chapter 2 the heats of formation and the ionization potentials of some carcinogenic compounds such as Polycyclic Aromatic Hydrocarbons are studied and compared with experimental data. The methods used are the semiempirical methods with the AM1 and PM3 Hamiltonians. The results show that the experimental heats of formation are better reproduced by PM3, while as far as the ionization potentials are concerned AM1 is slightly better than PM3. In Chapter 3, the Lipid Peroxidation mechanism has been studied at the molecular level. The energetic details of the pathway proposed by Porter have been studied using the semiempirical AM1 and PM3 Hamiltonians. Six model compounds, which retain the same functional characteristics as the physiological fatty acid, have been used. The results are in good agreement with the experimental observations. Characteristics and metabolism of the anticancer drug NMF (N-Methylformide) have been studied in detail in Chapter 4. Accurate ab initio calculations have been carried out and the effect of the solvent has been taken into account. The results represent a good example of the high quality of information that the application of ab initio methods can give when properties of molecules and energetic details of pathways are examined.Studies in the electronic structure of something triatomic radicalsBrotchie, Douglas Alexanderhttps://hdl.handle.net/10023/154462019-03-29T11:24:37Z1973-01-01T00:00:00ZRestricted Hartree-Fock calculations, with explicit non-empirical calculation of all integrals, are presented for the ground states and some low-lying excited states of eight triatomic radicals (BF₂, NH₂, HBF, HCO, HNF, FCO, NF₂, FO₂). Geometries are calculated for these species, and the results related to experiment where possible. The nature of the bonding in each species is discussed. The effect of varying the size of the Gaussian basis sets employed was examined intensively, with particular attention being paid to changes in the total calculated energy, the optimal geometry, bonding and spin density distribution. It was concluded that for reliable geometry predictions a basis of 9 s and 5 P Gaussian functions was required on each first row atom, preferably augmented by polarisation functions possessing higher orbital angular momentum quantum number. This is particularly necessary to obtain the correct bond angles for hydrides. To predict spin densities accurately a basis set of essentially Hartree-Fock quality, possessing at least 11 s functions, is required. For this latter application considerations of balancing the size of the representation on the various atoms in the molecule is particularly crucial.
1973-01-01T00:00:00ZBrotchie, Douglas AlexanderRestricted Hartree-Fock calculations, with explicit non-empirical calculation of all integrals, are presented for the ground states and some low-lying excited states of eight triatomic radicals (BF₂, NH₂, HBF, HCO, HNF, FCO, NF₂, FO₂). Geometries are calculated for these species, and the results related to experiment where possible. The nature of the bonding in each species is discussed. The effect of varying the size of the Gaussian basis sets employed was examined intensively, with particular attention being paid to changes in the total calculated energy, the optimal geometry, bonding and spin density distribution. It was concluded that for reliable geometry predictions a basis of 9 s and 5 P Gaussian functions was required on each first row atom, preferably augmented by polarisation functions possessing higher orbital angular momentum quantum number. This is particularly necessary to obtain the correct bond angles for hydrides. To predict spin densities accurately a basis set of essentially Hartree-Fock quality, possessing at least 11 s functions, is required. For this latter application considerations of balancing the size of the representation on the various atoms in the molecule is particularly crucial.A theoretical investigation of the electronic structure and properties of glutathione, ascorbic acid and related moleculesLaurence, Patricia R.https://hdl.handle.net/10023/154442019-03-29T11:20:31Z1982-01-01T00:00:00ZThe methods of molecular quantum mechanics have been used to study the important biological molecules glutathione, ascorbic acid and related compounds. The preferred conformations of glutathione, its constituent amino acids and their residues have been investigated using the semi-empirical PCILO procedure. Comparisons with ab initio calculations are given for the smaller molecules. The electronic structure and properties of ascorbic acid and its metabolites have been studied using ab initio procedures. The calculations include geometry optimizations, electrostatic molecular potential maps, spin density calculations on the radical species and investigations of charge transfer interactions and of metal complexing.
1982-01-01T00:00:00ZLaurence, Patricia R.The methods of molecular quantum mechanics have been used to study the important biological molecules glutathione, ascorbic acid and related compounds. The preferred conformations of glutathione, its constituent amino acids and their residues have been investigated using the semi-empirical PCILO procedure. Comparisons with ab initio calculations are given for the smaller molecules. The electronic structure and properties of ascorbic acid and its metabolites have been studied using ab initio procedures. The calculations include geometry optimizations, electrostatic molecular potential maps, spin density calculations on the radical species and investigations of charge transfer interactions and of metal complexing.Homolytic ring fission in small, strange bicyclic moleculesRoberts, Charleshttps://hdl.handle.net/10023/154422019-03-29T11:24:07Z1984-01-01T00:00:00ZThe homolytic ring fission of strained bicycloalkyl radicals was investigated by E.S.R. spectroscopy. These bicycloalkyl radicals provided examples of cycloalkyl-, cyclopropylmethyl-, and cyclobutylmethyl-type radicals in which the preferred mode, and rate of β-scission could be studied. Three types of compounds were investigated; i.e. (i) bicyclo[n.1.0]alkanes, where n = 3-6; (ii) spiro[2.n]alkanes, where n = 3,4; and (iii) spiro[3.3]heptanes. Observations on the corresponding radicals enabled the influence of; (a) ring size (and consequent ring strain), and (b) the orientation of the SOMO on the rearrangement to be assessed. The series of bicyclo[n.1.0]alk-2-yl radicals, where n = 3-6, were found to undergo β-scission of the outer cyclopropane bond to give the corresponding cycloalkenylmethyl radical. Ring fission was very rapid, and only the rearranged radicals could be detected in the accessible temperature range. In contrast, the first two members of the series (n = 1,2) rearranged by fission of the internal cyclopropane bond to give cycloalkenyl radicals. The conformations of the rearranged cycloalkenylmethyl radicals were determined from the temperature dependance of the β-hydrogen h.f.s., and were interpreted in terms of steric effects. The geometries of the radical species, their enthalpies of activation, and the enthalpies of reaction were calculated by semi-empirical MNDO computations. Photobromination of the n = 3 and n = 4 bicycloalkanes was carried out. The major products were identified and analysed. The main process in each case was homolytic displacement by bromine atoms with consequent fission of the outer cyclopropane bond. This SH2 reaction showed a clear parallel to the β-scission in the series of radicals. However, the change in the mode of fission from internal to outer cyclopropane bond with increasing ring size was less clear cut. Hydrogen abstraction from the spiro[2.n]alkanes gave SFd.ro[2.n]alk-4-yl radicals which ring open in one mode only to give cycloalkenylethyl radicals. The rate of β-scission increased greatly from the n = 2 to the n = 3 to the n = 4 member of the series. With spiro[2.3]hex-4-yl radicals both unrearranged and rearranged radicals were detectable. The Arrhenius parameters for the rearrangement were determined from measurements on the concentrations of the two species. The conformations of the ring opened cycloalkenylethyl radicals were deduced from the temperature dependance of the β-hydrogen h.f.s. The photobromination of spiro[2.3]hexane gave mainly 1-bromo-1-(2-bromoethyl)cyclobutane and 1,1-bis(bromomethyl)-cyclobutane from the SH2 attack of bromine atoms at the cyclopropane n carbon atom. Semi-empirical MNDO calculations were carried out to predict the enthalpies of activation, and the enthalpies of reaction for the rearrangements. Bromine abstraction from 2-bromomethylspiro[3.3]heptane gave rise to a cyclobutylmethyl like radical, namely the spiro-[3.3]heptane-2-methyl, radical. This radical rearranged via β-scission to a 1-(prop-2-enyl)cyclobutylmethyl radical. Both unrearranged and rearranged radicals were detectable. As with spiro[2.3]hex-4-yl radicals the Arrhenius parameters for the rearrangement were determined. The enthalpy of activation, and the enthalpy of reaction were also calculated by semi-empirical MNDO ccmputations. The conformation of the unrearranged radical was determined from the temperature dependance of the β-hydrogen h.f.s. Attempts to generate spiro[3.3]hept-1-yl radicals from spiro[3.3]heptane were unsuccessful due to the failure to prepare spiro[3.3]heptane. The spiro[3.3]hept-2-yl radical was however observed. This radical did not undergo β-scission. With the cyclobutylmethyl-, and cyclopropylmethyl like radicals β-scission was observed to occur in a stereoelectronically allowed manner. Overall this study has confirmed that the major influence in the ring fission of cycloalkylmethyl radicals is the stereoelectronic effect. Thus orbital interaction, through maximised overlap, is a prerequisite to β-scission of both cyclopropylmethyl- and cyclobutylmethyl-like radicals. The study of spiro[2.n]alkanes revealed that ring size may affect the rate of ring fission by way of a conformational effect.
1984-01-01T00:00:00ZRoberts, CharlesThe homolytic ring fission of strained bicycloalkyl radicals was investigated by E.S.R. spectroscopy. These bicycloalkyl radicals provided examples of cycloalkyl-, cyclopropylmethyl-, and cyclobutylmethyl-type radicals in which the preferred mode, and rate of β-scission could be studied. Three types of compounds were investigated; i.e. (i) bicyclo[n.1.0]alkanes, where n = 3-6; (ii) spiro[2.n]alkanes, where n = 3,4; and (iii) spiro[3.3]heptanes. Observations on the corresponding radicals enabled the influence of; (a) ring size (and consequent ring strain), and (b) the orientation of the SOMO on the rearrangement to be assessed. The series of bicyclo[n.1.0]alk-2-yl radicals, where n = 3-6, were found to undergo β-scission of the outer cyclopropane bond to give the corresponding cycloalkenylmethyl radical. Ring fission was very rapid, and only the rearranged radicals could be detected in the accessible temperature range. In contrast, the first two members of the series (n = 1,2) rearranged by fission of the internal cyclopropane bond to give cycloalkenyl radicals. The conformations of the rearranged cycloalkenylmethyl radicals were determined from the temperature dependance of the β-hydrogen h.f.s., and were interpreted in terms of steric effects. The geometries of the radical species, their enthalpies of activation, and the enthalpies of reaction were calculated by semi-empirical MNDO computations. Photobromination of the n = 3 and n = 4 bicycloalkanes was carried out. The major products were identified and analysed. The main process in each case was homolytic displacement by bromine atoms with consequent fission of the outer cyclopropane bond. This SH2 reaction showed a clear parallel to the β-scission in the series of radicals. However, the change in the mode of fission from internal to outer cyclopropane bond with increasing ring size was less clear cut. Hydrogen abstraction from the spiro[2.n]alkanes gave SFd.ro[2.n]alk-4-yl radicals which ring open in one mode only to give cycloalkenylethyl radicals. The rate of β-scission increased greatly from the n = 2 to the n = 3 to the n = 4 member of the series. With spiro[2.3]hex-4-yl radicals both unrearranged and rearranged radicals were detectable. The Arrhenius parameters for the rearrangement were determined from measurements on the concentrations of the two species. The conformations of the ring opened cycloalkenylethyl radicals were deduced from the temperature dependance of the β-hydrogen h.f.s. The photobromination of spiro[2.3]hexane gave mainly 1-bromo-1-(2-bromoethyl)cyclobutane and 1,1-bis(bromomethyl)-cyclobutane from the SH2 attack of bromine atoms at the cyclopropane n carbon atom. Semi-empirical MNDO calculations were carried out to predict the enthalpies of activation, and the enthalpies of reaction for the rearrangements. Bromine abstraction from 2-bromomethylspiro[3.3]heptane gave rise to a cyclobutylmethyl like radical, namely the spiro-[3.3]heptane-2-methyl, radical. This radical rearranged via β-scission to a 1-(prop-2-enyl)cyclobutylmethyl radical. Both unrearranged and rearranged radicals were detectable. As with spiro[2.3]hex-4-yl radicals the Arrhenius parameters for the rearrangement were determined. The enthalpy of activation, and the enthalpy of reaction were also calculated by semi-empirical MNDO ccmputations. The conformation of the unrearranged radical was determined from the temperature dependance of the β-hydrogen h.f.s. Attempts to generate spiro[3.3]hept-1-yl radicals from spiro[3.3]heptane were unsuccessful due to the failure to prepare spiro[3.3]heptane. The spiro[3.3]hept-2-yl radical was however observed. This radical did not undergo β-scission. With the cyclobutylmethyl-, and cyclopropylmethyl like radicals β-scission was observed to occur in a stereoelectronically allowed manner. Overall this study has confirmed that the major influence in the ring fission of cycloalkylmethyl radicals is the stereoelectronic effect. Thus orbital interaction, through maximised overlap, is a prerequisite to β-scission of both cyclopropylmethyl- and cyclobutylmethyl-like radicals. The study of spiro[2.n]alkanes revealed that ring size may affect the rate of ring fission by way of a conformational effect.A theoretical method for electronic structure calculations on systems of biological importance - the group function approachPaci, Donatellahttps://hdl.handle.net/10023/154392019-03-29T11:22:59Z1994-01-01T00:00:00ZTheoretical methods for studying molecules of biological importance are reviewed, both ab initio and semi-empirical. The Group Function Approach is developed in detail in its strong orthogonal form and corrections to the energy are added for taking into account non-orthogonality effects, depending on the overlaps of the group functions. Approximations are introduced and tested so that this method can be applied to large molecules. In particular, a system (or a relevant fragment of it) is built up from localized two-electron groups, each one described by a two-electron group function (geminal). Each group function is optimized by using an SCF method with an effective hamiltonian consisting of the two-electron hamiltonian of the group together with the effective potential due to the presence of the other electron groups (and to the external environment, eventually). The wavefunction for the whole molecule is an antisymmetrized product of geminals. The energy is computed as a sum of group contributions. Corrections, depending on up to the second power of the overlaps of two groups at a time, are particularly important in conformational studies. The approximations introduced are based on the consideration that distant groups consisting of two positive and two negative charges see each other as neutral entities and thus do not contribute appreciably in the definition of the effective hamiltonian: the computing effort is greatly reduced in this way, the error introduced is small and can be estimated easily. The theoretical method presented in this thesis offers a powerful tool for making qualitative predictions of the changes resulting from localized effects, such as twisting around a bond, and it can be usefully applied to conformational studies and geometry optimizations. The other properties which can be calculated axe for the most part directly related to the electron density; this determines, for example, the electrostatic potential outside a molecule and hence the position of attack by approaching ions or polar species. Chemical reactions, which involve breaking or re-arrangement of bonds, provide another vast field of application. Such processes usually involve only localized regions in a molecule and the admission of intragroup CI ensures that the study of bond breaking remains valid throughout the whole process. All necessary computer programmes have been developed and numerical applications have been made to a range of molecules, including hydrocarbons, small molecules containing double bonds and lone pairs, and the amino acid glycine.
1994-01-01T00:00:00ZPaci, DonatellaTheoretical methods for studying molecules of biological importance are reviewed, both ab initio and semi-empirical. The Group Function Approach is developed in detail in its strong orthogonal form and corrections to the energy are added for taking into account non-orthogonality effects, depending on the overlaps of the group functions. Approximations are introduced and tested so that this method can be applied to large molecules. In particular, a system (or a relevant fragment of it) is built up from localized two-electron groups, each one described by a two-electron group function (geminal). Each group function is optimized by using an SCF method with an effective hamiltonian consisting of the two-electron hamiltonian of the group together with the effective potential due to the presence of the other electron groups (and to the external environment, eventually). The wavefunction for the whole molecule is an antisymmetrized product of geminals. The energy is computed as a sum of group contributions. Corrections, depending on up to the second power of the overlaps of two groups at a time, are particularly important in conformational studies. The approximations introduced are based on the consideration that distant groups consisting of two positive and two negative charges see each other as neutral entities and thus do not contribute appreciably in the definition of the effective hamiltonian: the computing effort is greatly reduced in this way, the error introduced is small and can be estimated easily. The theoretical method presented in this thesis offers a powerful tool for making qualitative predictions of the changes resulting from localized effects, such as twisting around a bond, and it can be usefully applied to conformational studies and geometry optimizations. The other properties which can be calculated axe for the most part directly related to the electron density; this determines, for example, the electrostatic potential outside a molecule and hence the position of attack by approaching ions or polar species. Chemical reactions, which involve breaking or re-arrangement of bonds, provide another vast field of application. Such processes usually involve only localized regions in a molecule and the admission of intragroup CI ensures that the study of bond breaking remains valid throughout the whole process. All necessary computer programmes have been developed and numerical applications have been made to a range of molecules, including hydrocarbons, small molecules containing double bonds and lone pairs, and the amino acid glycine.Synthetic and structural studies of foot-and-mouth disease virus polyprotein processingLenman, Morag Mayhttps://hdl.handle.net/10023/154362019-03-29T11:22:49Z1996-01-01T00:00:00ZThe 2A region of the foot-and-mouth disease virus (FMDV) polyprotein is only 16 amino acids in length. During synthesis of the FMDV polyprotein, a primary proteolytic processing event occurs between the 2A and 2B regions of the polyprotein at a Gly-Pro junction. Since the 2A region is too small to be an enzyme, and there is evidence to rule out host protease involvement, it is proposed that the 2A segment represents a self-cleaving system. Synthetic oligopeptides containing the 2A sequence have been prepared using solid phase peptide synthesis and their three-dimensional structures in different solvents have been investigated, using NMR and CD techniques. Computer modelling studies of the 2A region have been carried out and have indicated the presence of a cis prolyl bond. Short peptide fragments containing the sequence of the 2A region around the scissile bond have also been prepared by solution phase peptide synthesis and their conformations examined, using NMR spectroscopy. In particular, the NPGP tetrapeptide, which is alleged to possess cleavage activity was prepared and its reactivity investigated. The influence of prolyl cis/trans isomerism on the structure of polypeptides is poorly understood and a synthetic approach has been used to prepare cis X-Pro peptides. The strategy involved the formation of bicyclic compounds containing a hydrazide linkage with a view to breaking the N-N bond under mild conditions to give the natural cis X-Pro peptide. The design, synthesis and reactivity of various novel, bicyclic cis X-Pro dipeptides is described. These compounds represent a new class of type VI beta-turn mimetics and as it has been shown that they can be easily extended at the amino and carboxy termini for incorporation into larger peptides. X-ray crystal structures for some of the compounds and intermediates are presented. Investigations into the reductive cleavage of these compounds were carried out and some were found to display unusual reactivity with the chosen reduction method. In particular, a novel intramolecular transamidation reaction is reported and its mechanism has been investigated by the use of various substituted derivatives.
1996-01-01T00:00:00ZLenman, Morag MayThe 2A region of the foot-and-mouth disease virus (FMDV) polyprotein is only 16 amino acids in length. During synthesis of the FMDV polyprotein, a primary proteolytic processing event occurs between the 2A and 2B regions of the polyprotein at a Gly-Pro junction. Since the 2A region is too small to be an enzyme, and there is evidence to rule out host protease involvement, it is proposed that the 2A segment represents a self-cleaving system. Synthetic oligopeptides containing the 2A sequence have been prepared using solid phase peptide synthesis and their three-dimensional structures in different solvents have been investigated, using NMR and CD techniques. Computer modelling studies of the 2A region have been carried out and have indicated the presence of a cis prolyl bond. Short peptide fragments containing the sequence of the 2A region around the scissile bond have also been prepared by solution phase peptide synthesis and their conformations examined, using NMR spectroscopy. In particular, the NPGP tetrapeptide, which is alleged to possess cleavage activity was prepared and its reactivity investigated. The influence of prolyl cis/trans isomerism on the structure of polypeptides is poorly understood and a synthetic approach has been used to prepare cis X-Pro peptides. The strategy involved the formation of bicyclic compounds containing a hydrazide linkage with a view to breaking the N-N bond under mild conditions to give the natural cis X-Pro peptide. The design, synthesis and reactivity of various novel, bicyclic cis X-Pro dipeptides is described. These compounds represent a new class of type VI beta-turn mimetics and as it has been shown that they can be easily extended at the amino and carboxy termini for incorporation into larger peptides. X-ray crystal structures for some of the compounds and intermediates are presented. Investigations into the reductive cleavage of these compounds were carried out and some were found to display unusual reactivity with the chosen reduction method. In particular, a novel intramolecular transamidation reaction is reported and its mechanism has been investigated by the use of various substituted derivatives.Peptide secondary structure mimetics: The alpha-helix and beta-turnArwel, Lewishttps://hdl.handle.net/10023/154332019-03-29T11:22:05Z1998-01-01T00:00:00ZThis thesis describes research undertaken in peptidomimetic chemistry, concerned with stabilisation of peptide secondary structure. The first section describes the successful synthesis of two triazepinediones for potential application as cis prolyl mimetics and/or β-turn mimetics. The first triazepinedione 64, carrying an N-phenyl substituent, was subjected to reductive conditions in an unsuccessful attempt to generate a cis prolyl peptide. The second triazepinedione 72 was designed as a Gly-cw Pro-Phe peptidomimetic. Its synthesis proceeded in 8 steps, via a chiral a-hydrazino acid. Triazepinedione 72 was extended from both the N and C termini, demonstrating that it could be incorporated into a peptide. The second section describes the design and attempted synthesis of an N-terminal template for stabilisation of a-helical structure in an attached peptide. Preliminary efforts to produce a Pro-Pro-Ala macrocycle 91 and a Pro-Pro-Pro ether macrocycle 98 were unsuccessful. Attempts to synthesise a Pro-Pro-Pro thioether macrocycle 112 resulted in formation of a cyclic dimer 122. The formation of this dimer was proposed to be due to excessive steric hindrance in the transition state to cyclisation. Attempts to stabilise the desired folded transition state by α-methylation of proline residues or hydrogen bonding did not allow synthesis of any of the desired monomeric cyclic material. A monomeric cyclic compound was finally obtained by increasing the flexibility of the linear precursor, affording a Pro-(2R)-Ala-Pro thioether macrocycle 151. X-Ray crystallography and 2D NMR studies established that this macrocycle lacked the required arrangement of carbonyl groups conducive to initiation of an α-helix. Further NMR studies of macrocycle-peptide conjugates suggested that the macrocycle exerted a conformational influence only over the first residue of the attached peptide. The carbonyl groups of the macrocycle were found to adopt a significant degree of α-helical geometry upon attachment of a C-terminal cationic trialkylammonium group.
1998-01-01T00:00:00ZArwel, LewisThis thesis describes research undertaken in peptidomimetic chemistry, concerned with stabilisation of peptide secondary structure. The first section describes the successful synthesis of two triazepinediones for potential application as cis prolyl mimetics and/or β-turn mimetics. The first triazepinedione 64, carrying an N-phenyl substituent, was subjected to reductive conditions in an unsuccessful attempt to generate a cis prolyl peptide. The second triazepinedione 72 was designed as a Gly-cw Pro-Phe peptidomimetic. Its synthesis proceeded in 8 steps, via a chiral a-hydrazino acid. Triazepinedione 72 was extended from both the N and C termini, demonstrating that it could be incorporated into a peptide. The second section describes the design and attempted synthesis of an N-terminal template for stabilisation of a-helical structure in an attached peptide. Preliminary efforts to produce a Pro-Pro-Ala macrocycle 91 and a Pro-Pro-Pro ether macrocycle 98 were unsuccessful. Attempts to synthesise a Pro-Pro-Pro thioether macrocycle 112 resulted in formation of a cyclic dimer 122. The formation of this dimer was proposed to be due to excessive steric hindrance in the transition state to cyclisation. Attempts to stabilise the desired folded transition state by α-methylation of proline residues or hydrogen bonding did not allow synthesis of any of the desired monomeric cyclic material. A monomeric cyclic compound was finally obtained by increasing the flexibility of the linear precursor, affording a Pro-(2R)-Ala-Pro thioether macrocycle 151. X-Ray crystallography and 2D NMR studies established that this macrocycle lacked the required arrangement of carbonyl groups conducive to initiation of an α-helix. Further NMR studies of macrocycle-peptide conjugates suggested that the macrocycle exerted a conformational influence only over the first residue of the attached peptide. The carbonyl groups of the macrocycle were found to adopt a significant degree of α-helical geometry upon attachment of a C-terminal cationic trialkylammonium group.Mechanistic studies in porphobilinogen biosynthesisGeorge, Sharon Deenahttps://hdl.handle.net/10023/154312019-03-29T11:25:04Z1993-01-01T00:00:00Z[4-¹⁵c]ALA.HC1 (50% enriched) and [¹⁵N]ALA.HC1 (50% enriched) have been synthesised and utilised in mechanistic studies. The synthesis of the former was achieved via a modified literature procedure, employing [2-¹³C] glycine (99.8% enriched) as the starting material. The NMR spectral data of the labelled materials have been fully characterised. ¹³C NMR studies of [4-¹³C]ALA.HCl (50% enriched) have demonstrated the forms of ALA and its autocondensation products under physiological conditions, ¹⁷O and ¹H NMR studies have confirmed the existence of the alternative forms of ALA and its condensation products at neutral pH. The non-enzymatic cyclic dimerisation of ALA leads to the formation of 2,5-bis(2- carboxyethyl)pyrazine and under some circumstances, pseudo-PBG. The condensation products of ALA under a variety of conditions have been identified from their NMR spectra and mechanisms for their formation are proposed. The condensation of ALA and its 5-methyl analogue with a variety of carbonyl compounds have been investigated and the products (novel substituted pyrroles in some cases) characterised by their melting points, elementary analyses, mass spectra and NMR spectra. A hydrogen bonded enaminoketone in a chelated ring has been identified as the intermediate in the reaction between ALA and 1,l,l-trlfluoropentane-2,4-dione, by 1H and 15N NMR spectroscopy. 13C NMR kinetics of the reaction between ALA and pentane- 2,4-dione has revealed that the reaction proceeds via an enaminoketone intermediate. The nature of the intermediate species in the above reaction was confirmed by 15N NMR spectroscopy. On the basis of the kinetic evidence obtained for the reaction between ALA and 1,1, l-trifluoropentane-2,4-dione, a mechanism has been proposed for the Knorr and Fischer-Fink P3nrrole syntheses. Studies with the bovine liver enzyme, ALA dehydratase, has revealed that it is very specific in the reaction that it catalyses: the Knorr-type dimerisation of two molecules of ALA to form PBG. The substrate analogues, levulinic acid and the methyl ester of ALA were found to be a non-competitive inhibitor and a very poor substrate of the enzyme respectively. The substrate analogues, N,N-dimethyl- ALA and 5-methyl-ALA do not bind to the enzyme and therefore do not affect the rate of production of PBG. A mechanism has been postulated for PBG biosynthesis, similar to the one proposed for the Knorr pyrrole synthesis. Stopped-flow kinetics of the reaction between p-nitrophenyl- diazonium tetrafluoroborate and bilirubin ditaurate disodium salt has revealed that diazonium ions are solely responsible for the cleavage of the central methylene bridge of the bilirubin conjugate molecule. On the basis of the above evidence, a mechanism has been proposed for the diazo coupling reaction.
1993-01-01T00:00:00ZGeorge, Sharon Deena[4-¹⁵c]ALA.HC1 (50% enriched) and [¹⁵N]ALA.HC1 (50% enriched) have been synthesised and utilised in mechanistic studies. The synthesis of the former was achieved via a modified literature procedure, employing [2-¹³C] glycine (99.8% enriched) as the starting material. The NMR spectral data of the labelled materials have been fully characterised. ¹³C NMR studies of [4-¹³C]ALA.HCl (50% enriched) have demonstrated the forms of ALA and its autocondensation products under physiological conditions, ¹⁷O and ¹H NMR studies have confirmed the existence of the alternative forms of ALA and its condensation products at neutral pH. The non-enzymatic cyclic dimerisation of ALA leads to the formation of 2,5-bis(2- carboxyethyl)pyrazine and under some circumstances, pseudo-PBG. The condensation products of ALA under a variety of conditions have been identified from their NMR spectra and mechanisms for their formation are proposed. The condensation of ALA and its 5-methyl analogue with a variety of carbonyl compounds have been investigated and the products (novel substituted pyrroles in some cases) characterised by their melting points, elementary analyses, mass spectra and NMR spectra. A hydrogen bonded enaminoketone in a chelated ring has been identified as the intermediate in the reaction between ALA and 1,l,l-trlfluoropentane-2,4-dione, by 1H and 15N NMR spectroscopy. 13C NMR kinetics of the reaction between ALA and pentane- 2,4-dione has revealed that the reaction proceeds via an enaminoketone intermediate. The nature of the intermediate species in the above reaction was confirmed by 15N NMR spectroscopy. On the basis of the kinetic evidence obtained for the reaction between ALA and 1,1, l-trifluoropentane-2,4-dione, a mechanism has been proposed for the Knorr and Fischer-Fink P3nrrole syntheses. Studies with the bovine liver enzyme, ALA dehydratase, has revealed that it is very specific in the reaction that it catalyses: the Knorr-type dimerisation of two molecules of ALA to form PBG. The substrate analogues, levulinic acid and the methyl ester of ALA were found to be a non-competitive inhibitor and a very poor substrate of the enzyme respectively. The substrate analogues, N,N-dimethyl- ALA and 5-methyl-ALA do not bind to the enzyme and therefore do not affect the rate of production of PBG. A mechanism has been postulated for PBG biosynthesis, similar to the one proposed for the Knorr pyrrole synthesis. Stopped-flow kinetics of the reaction between p-nitrophenyl- diazonium tetrafluoroborate and bilirubin ditaurate disodium salt has revealed that diazonium ions are solely responsible for the cleavage of the central methylene bridge of the bilirubin conjugate molecule. On the basis of the above evidence, a mechanism has been proposed for the diazo coupling reaction.Asymmetric synthesis of amino acid derivatives as molecular probes for the mechanism of 3-methylaspsartate ammonia-lyaseLasry, Philippehttps://hdl.handle.net/10023/154302019-03-29T11:21:16Z1998-01-01T00:00:00Z3-Methylaspartate ammonia-lyase is a bacterial enzyme that catalyses the reversible elimination of ammonia, in the presence of monovalent and divalent metal ions, from (2S,3S)-3-methylaspartic acid to yield mesaconic acid. The catalytic mechanism of the wild type enzyme obtained from Clostridium tetanomorphum involves a concerted elimination of ammonia and is thought to operate via the intermediacy of a dehydroalanine residue at the active site. No direct evidence has been established so far concerning the existence of this dehydroalanine residue, except that 3-methylaspartate ammonia-lyase was found to be irreversibly inactivated by phenylhydrazine. Inactivation of the enzyme with labelled ¹⁵Nβ-phenylhydrazine and subsequent ¹⁵N-edited NMR spectra of the digested enzyme resulted in a proposal for the inhibition mechanism by phenylhydrazine. This mechanism involved the conjugate addition of phenylhydrazine onto the dehydroalanine moiety and the subsequent cyclisation to give a cyclic adduct. A synthetic model containing a ¹⁵N atom of this adduct was synthesised and the NMR data obtained were compared with the spectra obtained earlier from the enzyme experiment. In order to carry out mapping studies of the active site it was highly desirable to prepare molecules capable of reacting specifically and irreversibly at the active site. To this end, the synthesis of aminofumaric acid and (2S,3S)-3-methyl N-amino aziridine dicarboxylic acid were attempted. (2S,3R) and (2R,3R)-3-Methylsuccinic acids were prepared in 5 steps from (2S,3S)-3-methyl aspartic acid. These compounds were found to behave as noncompetitive inhibitors of β-methylaspartase. (2S)-3,3-Dimethylaspartic acid was also synthesised and found to be a competitive inhibitor having the same binding affinity as the natural substrate. In order to prepare a β-electrophilic amino acid analogue of the physiological substrate, an asymmetric synthesis was designed that involved the stereoselective alkylation and acylation of suitably protected (2S,3S)-3-methylaspartic acid. The stereochemistry of the reaction was established via the X-ray structure of the camphanic derivative resulting from the alkylation of protected (2S,3S)-3-methylaspartic acid with chloroiodomethane. The X-ray structure of an acylated adduct was also determined. This method allowed diastereoselective synthesis of a highly functionalised amino acid, (2S,3S)-3-formyl-3-methylaspartic acid, in 7 steps which was found to be a powerful competitive inhibitor (Ki = 0.57 µM). The inhibitory properties could be explained via the interaction of the cyclic furanyl form of the aldehyde. In addition, this synthesis also proved to be useful in the synthesis of a stable protected trans-(2S,3S)-3-methylazetidine 1,2-dicarboxylate diester for which a X-ray structure was determined.
1998-01-01T00:00:00ZLasry, Philippe3-Methylaspartate ammonia-lyase is a bacterial enzyme that catalyses the reversible elimination of ammonia, in the presence of monovalent and divalent metal ions, from (2S,3S)-3-methylaspartic acid to yield mesaconic acid. The catalytic mechanism of the wild type enzyme obtained from Clostridium tetanomorphum involves a concerted elimination of ammonia and is thought to operate via the intermediacy of a dehydroalanine residue at the active site. No direct evidence has been established so far concerning the existence of this dehydroalanine residue, except that 3-methylaspartate ammonia-lyase was found to be irreversibly inactivated by phenylhydrazine. Inactivation of the enzyme with labelled ¹⁵Nβ-phenylhydrazine and subsequent ¹⁵N-edited NMR spectra of the digested enzyme resulted in a proposal for the inhibition mechanism by phenylhydrazine. This mechanism involved the conjugate addition of phenylhydrazine onto the dehydroalanine moiety and the subsequent cyclisation to give a cyclic adduct. A synthetic model containing a ¹⁵N atom of this adduct was synthesised and the NMR data obtained were compared with the spectra obtained earlier from the enzyme experiment. In order to carry out mapping studies of the active site it was highly desirable to prepare molecules capable of reacting specifically and irreversibly at the active site. To this end, the synthesis of aminofumaric acid and (2S,3S)-3-methyl N-amino aziridine dicarboxylic acid were attempted. (2S,3R) and (2R,3R)-3-Methylsuccinic acids were prepared in 5 steps from (2S,3S)-3-methyl aspartic acid. These compounds were found to behave as noncompetitive inhibitors of β-methylaspartase. (2S)-3,3-Dimethylaspartic acid was also synthesised and found to be a competitive inhibitor having the same binding affinity as the natural substrate. In order to prepare a β-electrophilic amino acid analogue of the physiological substrate, an asymmetric synthesis was designed that involved the stereoselective alkylation and acylation of suitably protected (2S,3S)-3-methylaspartic acid. The stereochemistry of the reaction was established via the X-ray structure of the camphanic derivative resulting from the alkylation of protected (2S,3S)-3-methylaspartic acid with chloroiodomethane. The X-ray structure of an acylated adduct was also determined. This method allowed diastereoselective synthesis of a highly functionalised amino acid, (2S,3S)-3-formyl-3-methylaspartic acid, in 7 steps which was found to be a powerful competitive inhibitor (Ki = 0.57 µM). The inhibitory properties could be explained via the interaction of the cyclic furanyl form of the aldehyde. In addition, this synthesis also proved to be useful in the synthesis of a stable protected trans-(2S,3S)-3-methylazetidine 1,2-dicarboxylate diester for which a X-ray structure was determined.Synthesis of ganglioside analogues as biological probes for enzymes that modify sialic acidsTurnbull, W. Brucehttps://hdl.handle.net/10023/154282019-03-29T11:21:47Z1998-01-01T00:00:00ZGanglioside GM3, a glycosphingolipid found in the outer membrane of all mammalian cells, is expressed at much higher concentrations than normal in cancer cells. It has been reported that GM3 can inhibit signal transduction via the EGF receptor kinase, ultimately down regulating cell growth. In contrast to this, de-N-acetyl GM3, another ganglioside that has been found in a number of cancer cell lines, is reported to be a potent promoter of cell growth. Evidence suggests that GM3 and de-N-acetyl GM3 are inter-converted by enzymes that remove and replace the N-acetyl group on sialic acid. In this thesis, the syntheses of a number of simplified analogues of gangliosides are described, including some in which an inter-glycosidic oxygen atom is replaced by sulfur. Synthesis of O-linked ganglioside analogues was achieved by both a totally chemical route and also by a chemo-enzymatic route, involving the use of a recombinant construct of trypanosoma cruzi trans-sialidase for glycosylation with sialic acid. A novel strategy for the synthesis of ganglioside analogues that contain a sialic acid α(2-->3) galactose thioglycosidic linkage, is also described. These compounds were evaluated as substrates and inhibitors for Clostridium perfringens neuraminidase and Trypanosoma cruzi trans-sialidase. Some of the ganglioside analogues described herein were used to develop biochemical assays for detecting the putatative de-N-acetylase and N-acetyltransferase activities that would be required for the inter-conversion of gangliosides GM3 and de-N-acetyl GM3.
1998-01-01T00:00:00ZTurnbull, W. BruceGanglioside GM3, a glycosphingolipid found in the outer membrane of all mammalian cells, is expressed at much higher concentrations than normal in cancer cells. It has been reported that GM3 can inhibit signal transduction via the EGF receptor kinase, ultimately down regulating cell growth. In contrast to this, de-N-acetyl GM3, another ganglioside that has been found in a number of cancer cell lines, is reported to be a potent promoter of cell growth. Evidence suggests that GM3 and de-N-acetyl GM3 are inter-converted by enzymes that remove and replace the N-acetyl group on sialic acid. In this thesis, the syntheses of a number of simplified analogues of gangliosides are described, including some in which an inter-glycosidic oxygen atom is replaced by sulfur. Synthesis of O-linked ganglioside analogues was achieved by both a totally chemical route and also by a chemo-enzymatic route, involving the use of a recombinant construct of trypanosoma cruzi trans-sialidase for glycosylation with sialic acid. A novel strategy for the synthesis of ganglioside analogues that contain a sialic acid α(2-->3) galactose thioglycosidic linkage, is also described. These compounds were evaluated as substrates and inhibitors for Clostridium perfringens neuraminidase and Trypanosoma cruzi trans-sialidase. Some of the ganglioside analogues described herein were used to develop biochemical assays for detecting the putatative de-N-acetylase and N-acetyltransferase activities that would be required for the inter-conversion of gangliosides GM3 and de-N-acetyl GM3.Studies on threonine synthaseNeal, Tracyhttps://hdl.handle.net/10023/154272019-03-29T11:20:25Z1998-01-01T00:00:00ZThreonine synthase (TS, EC 4.2.99.2), catalyses a β,γ-replacement reaction to convert (2S)-0-phosphohomoserine (32) into (2S,3S)-threonine (33). Although threonine as an essential amino acid is vital to all lifeforms, the enzyme is not expressed in mammals. This makes it an ideal target enzyme for herbicides, fungicides and bactericides, and several inhibitors of the enzyme have been produced with this in mind. In particular, the enzyme from Escherichia coli has previously been the subject of inhibition studies, and the reaction mechanism of this particular TS has also been partially elucidated. However, no product inhibition studies have been carried out on TS from E. coli. In order to carry out such studies, a [U-¹⁴C]-labelled version of the substrate (32b) was synthesised in this work, starting from [U-¹⁴C]-(2S)-aspartate (28b), via a route previously developed for producing the unlabelled substrate. Various analogues of the substrate have been synthesised and these were also to be tested with the enzyme, either as potential inhibitors, or to elucidate further the reaction mechanism and active-site structure of TS. The mutant E. coli strain K-12 Tir8, which had been used previously as a source of TS, appeared to have reverted to wild-type, no longer over-expressing the enzymes of the thr operon. Therefore, the thrC gene from E. coli, coding for TS, was cloned into a pET-expression system. In a host cell containing such a construct TS could amount to 50% of total cell protein. ThrC was amplified via PCR and inserted into a cloning vector, pGEM-T, and then subcloned into pET-3a, pET-3b and pET-16b. pET-16b constructs produce a His-tagged version of the recombinant protein. Sequencing of the recombinant gene in two pGEM-T constructs revealed one deletion and two mutations in the thrC sequence, which probably occurred during the PCR-amplification of the gene. These alterations were confirmed in sequences obtained for the pET-contructs. N,N-diisopropyldichlorophosphamidite (78), a precursor to a reagent used originally for the phosphorylation of ?-isopropyl-N-trifluoroacetyl-(2S)-homoserine (75), proved difficult to synthesise. Instead, dipentafluorophenyl phosphorochloridate (81) was used for the phosphorylation reaction, as it was easier to synthesise and gave a good yield of the phosphate ester. Deprotection of dipentafluorophenyl phosphates has, however, only been achieved previously on the solid-phase. The solid-phase synthesis of the substrate was therefore attempted using Wang, p-hydroxymethyl polystyrene and Merrifield resins. A new linker was attached to Merrifield, to produce the novel resin, polystyrene-4-oxymethyl-2-phenylethanol (97). Although selective opening of the N-trifIuoroacetyl-(25)-aspartic anhydride (73) was successfully accomplished to attach the α-carboxyl group to these resins, subsequent reduction of the β-acid has not been achieved. α-p-Benzyloxybenzylpolystyrene-N-trifluoroacetyl-(25)-aspartate (87) proved unstable towards reducing agents and bases. It is hoped that compounds attached to 97 will prove more stable towards reducing agents.
1998-01-01T00:00:00ZNeal, TracyThreonine synthase (TS, EC 4.2.99.2), catalyses a β,γ-replacement reaction to convert (2S)-0-phosphohomoserine (32) into (2S,3S)-threonine (33). Although threonine as an essential amino acid is vital to all lifeforms, the enzyme is not expressed in mammals. This makes it an ideal target enzyme for herbicides, fungicides and bactericides, and several inhibitors of the enzyme have been produced with this in mind. In particular, the enzyme from Escherichia coli has previously been the subject of inhibition studies, and the reaction mechanism of this particular TS has also been partially elucidated. However, no product inhibition studies have been carried out on TS from E. coli. In order to carry out such studies, a [U-¹⁴C]-labelled version of the substrate (32b) was synthesised in this work, starting from [U-¹⁴C]-(2S)-aspartate (28b), via a route previously developed for producing the unlabelled substrate. Various analogues of the substrate have been synthesised and these were also to be tested with the enzyme, either as potential inhibitors, or to elucidate further the reaction mechanism and active-site structure of TS. The mutant E. coli strain K-12 Tir8, which had been used previously as a source of TS, appeared to have reverted to wild-type, no longer over-expressing the enzymes of the thr operon. Therefore, the thrC gene from E. coli, coding for TS, was cloned into a pET-expression system. In a host cell containing such a construct TS could amount to 50% of total cell protein. ThrC was amplified via PCR and inserted into a cloning vector, pGEM-T, and then subcloned into pET-3a, pET-3b and pET-16b. pET-16b constructs produce a His-tagged version of the recombinant protein. Sequencing of the recombinant gene in two pGEM-T constructs revealed one deletion and two mutations in the thrC sequence, which probably occurred during the PCR-amplification of the gene. These alterations were confirmed in sequences obtained for the pET-contructs. N,N-diisopropyldichlorophosphamidite (78), a precursor to a reagent used originally for the phosphorylation of ?-isopropyl-N-trifluoroacetyl-(2S)-homoserine (75), proved difficult to synthesise. Instead, dipentafluorophenyl phosphorochloridate (81) was used for the phosphorylation reaction, as it was easier to synthesise and gave a good yield of the phosphate ester. Deprotection of dipentafluorophenyl phosphates has, however, only been achieved previously on the solid-phase. The solid-phase synthesis of the substrate was therefore attempted using Wang, p-hydroxymethyl polystyrene and Merrifield resins. A new linker was attached to Merrifield, to produce the novel resin, polystyrene-4-oxymethyl-2-phenylethanol (97). Although selective opening of the N-trifIuoroacetyl-(25)-aspartic anhydride (73) was successfully accomplished to attach the α-carboxyl group to these resins, subsequent reduction of the β-acid has not been achieved. α-p-Benzyloxybenzylpolystyrene-N-trifluoroacetyl-(25)-aspartate (87) proved unstable towards reducing agents and bases. It is hoped that compounds attached to 97 will prove more stable towards reducing agents.Mechanistic studies on threonine synthaseBarclay, Fionahttps://hdl.handle.net/10023/154262019-03-29T11:23:01Z1995-01-01T00:00:00ZThreonine synthase catalyses the conversion of (2S)-0-phosphohomoserine to (2S,3R)-threonine with the elimination of phosphate. A novel and efficient synthesis of (2S)-0-phosphohomoserine has been developed starting from (2S)- aspartic acid. Using this methodology the singly labelled isotopomers (2S,3S)- [3-²H1]-, (2S,3R)-[3-²H1]-, and (2S)-[2-²H1]-0-phosphohomoserine have also been synthesised from labelled (2S)-aspartic acid and used to probe the mechanism of the enzyme. Measurement of the kinetic deuterium isotope effects for the labelled substrates showed that both the Cα-H and Cβ-H proton removal steps in E. coli threonine synthase display primary deuterium isotope effects, and that cleavage of the C-3-(pro-S)-H bond is at least partially rate limiting. This confirms data already available for the yeast enzyme, which indicated that the 3-pro-S proton is removed in the course of the reaction. The kinetic isotope effect for the removal of the 3-pro-S proton indicates a high forward commitment for the elimination of phosphate. Threonine synthase from E. coli was also shown to be activated in the presence of S-adenosyl methionine. This activation has been documented for the plant enzyme, but this is the first time such an activation has been seen for the bacterial enzyme. Threonine synthase for the study was partially purified from E. coli K12 Tir8, using novel methodology.
1995-01-01T00:00:00ZBarclay, FionaThreonine synthase catalyses the conversion of (2S)-0-phosphohomoserine to (2S,3R)-threonine with the elimination of phosphate. A novel and efficient synthesis of (2S)-0-phosphohomoserine has been developed starting from (2S)- aspartic acid. Using this methodology the singly labelled isotopomers (2S,3S)- [3-²H1]-, (2S,3R)-[3-²H1]-, and (2S)-[2-²H1]-0-phosphohomoserine have also been synthesised from labelled (2S)-aspartic acid and used to probe the mechanism of the enzyme. Measurement of the kinetic deuterium isotope effects for the labelled substrates showed that both the Cα-H and Cβ-H proton removal steps in E. coli threonine synthase display primary deuterium isotope effects, and that cleavage of the C-3-(pro-S)-H bond is at least partially rate limiting. This confirms data already available for the yeast enzyme, which indicated that the 3-pro-S proton is removed in the course of the reaction. The kinetic isotope effect for the removal of the 3-pro-S proton indicates a high forward commitment for the elimination of phosphate. Threonine synthase from E. coli was also shown to be activated in the presence of S-adenosyl methionine. This activation has been documented for the plant enzyme, but this is the first time such an activation has been seen for the bacterial enzyme. Threonine synthase for the study was partially purified from E. coli K12 Tir8, using novel methodology.The minor alkaloids of ipecacuanhaDavidson, George Cameronhttps://hdl.handle.net/10023/154252019-03-29T11:21:26Z1964-01-01T00:00:00ZIpecacuanha had been used for many years in medical practice before Rogers (1), in 1912, showed that emetine, one of the constituent alkaloids, was a specific agent against dysentery. This discovery, in relation to the toll which the diseases takes in tropical countries, intensified the efforts of chemists to deduce the structure of the alkaloid in the hope of synthesising it. This hope was not finally achieved until 1950.
The final stages in selecting the correct structure for emetine were aided by a consideration fo the possible biogenetic route to the alkaloid in the light of current theories of the biogenesis of alkaloids. In consequences of this, a detailed examination of the alkaloidal material present in the root was undertaken in the hope of isolating some compound which might be a biogenetic intermediate. The results of that investigation are described in this thesis. At the same time the opportunity was taken to study the chemistry of the minor alkaloids.
The work on the structural formula of emetine had shown the marked specificity of the alkaloid in the treatment of amoebic dysentery. There are four centres of asymmetry in the molecule and inversion of the configuration at the asymmetric centres had to be ascertained. In the latter part of the thesis the initial experiments in the elucidation of the stereochemistry of emetine are described.
These results and the subsequent elucidation of the stereochemistry and the stereospecific synthesis of emetine and emetamine have been reported by Dr. Battersby and his associates in a series of papers in the Journal of the Society of Chemistry and Industrial and the Journal of the Chemical Society (80)(56)(57).
1964-01-01T00:00:00ZDavidson, George CameronIpecacuanha had been used for many years in medical practice before Rogers (1), in 1912, showed that emetine, one of the constituent alkaloids, was a specific agent against dysentery. This discovery, in relation to the toll which the diseases takes in tropical countries, intensified the efforts of chemists to deduce the structure of the alkaloid in the hope of synthesising it. This hope was not finally achieved until 1950.
The final stages in selecting the correct structure for emetine were aided by a consideration fo the possible biogenetic route to the alkaloid in the light of current theories of the biogenesis of alkaloids. In consequences of this, a detailed examination of the alkaloidal material present in the root was undertaken in the hope of isolating some compound which might be a biogenetic intermediate. The results of that investigation are described in this thesis. At the same time the opportunity was taken to study the chemistry of the minor alkaloids.
The work on the structural formula of emetine had shown the marked specificity of the alkaloid in the treatment of amoebic dysentery. There are four centres of asymmetry in the molecule and inversion of the configuration at the asymmetric centres had to be ascertained. In the latter part of the thesis the initial experiments in the elucidation of the stereochemistry of emetine are described.
These results and the subsequent elucidation of the stereochemistry and the stereospecific synthesis of emetine and emetamine have been reported by Dr. Battersby and his associates in a series of papers in the Journal of the Society of Chemistry and Industrial and the Journal of the Chemical Society (80)(56)(57).Studies of the interactions of resin acids with Pigment Yellow 13Spark, Roger A.https://hdl.handle.net/10023/154242019-03-29T11:22:57Z1996-01-01T00:00:00ZThe surface interaction between Pigment Yellow 13, a classical diarylide pigment, and abietic acid type resin acids, used commercially to coat pigment products, was investigated by the joint techniques of solid-state ¹³CP/MAS NMR and powder X-ray diffraction. The initial objective of the study was to synthesise ¹³C labelled resin acid analogues to provide a handle for the NMR study. Attempts were made to label the carboxylic acid carbon of abietic acid, via a Barton reaction and subsequent Grignard reaction and carboxylation. Esterification of various resin acid substrates with ¹³C labelled diazomethane was also attempted. These routes proved difficult, due to the sterically hindered nature of the acid substrates. Labelled adducts were formed from ¹³C-malcic anhydride and isomerised abietic acid, but were found to be lost from the pigment during resination. Attempts to form a more stable adduct with N-methylmaleimide were unsuccessful. A series of experiments was carried out to coat Pigment Yellow 13 with incremental amounts of abietic acid, maleopimaric acid and dihydroabietic acid. The maleopimaric acid was lost during processing. The pigment samples resinated with abietic acid and dihydroabietic acid were analysed by the techniques mentioned previously. The presence of resin acids during pigment processing was found to enhance the crystallinity of the pigment particles, as opposed to the heat treatment during processing which promotes particle size. The resin acids were found to be more amorphous than the starting resin when reprecipitated on the pigment particles, ¹³C CP/MAS NMR shows that there is no chemical interaction between the pigment molecule and the carboxylic acid of the resin.
1996-01-01T00:00:00ZSpark, Roger A.The surface interaction between Pigment Yellow 13, a classical diarylide pigment, and abietic acid type resin acids, used commercially to coat pigment products, was investigated by the joint techniques of solid-state ¹³CP/MAS NMR and powder X-ray diffraction. The initial objective of the study was to synthesise ¹³C labelled resin acid analogues to provide a handle for the NMR study. Attempts were made to label the carboxylic acid carbon of abietic acid, via a Barton reaction and subsequent Grignard reaction and carboxylation. Esterification of various resin acid substrates with ¹³C labelled diazomethane was also attempted. These routes proved difficult, due to the sterically hindered nature of the acid substrates. Labelled adducts were formed from ¹³C-malcic anhydride and isomerised abietic acid, but were found to be lost from the pigment during resination. Attempts to form a more stable adduct with N-methylmaleimide were unsuccessful. A series of experiments was carried out to coat Pigment Yellow 13 with incremental amounts of abietic acid, maleopimaric acid and dihydroabietic acid. The maleopimaric acid was lost during processing. The pigment samples resinated with abietic acid and dihydroabietic acid were analysed by the techniques mentioned previously. The presence of resin acids during pigment processing was found to enhance the crystallinity of the pigment particles, as opposed to the heat treatment during processing which promotes particle size. The resin acids were found to be more amorphous than the starting resin when reprecipitated on the pigment particles, ¹³C CP/MAS NMR shows that there is no chemical interaction between the pigment molecule and the carboxylic acid of the resin.The chemistry of seed oils: With particular reference to oils containing hydroxy and/or epoxy acidsBharucha, Kurshed Erachshahttps://hdl.handle.net/10023/154222019-03-29T11:24:19Z1956-01-01T00:00:00ZPart I. Study of Fatty Oils Containing Epoxy and/or Hydroxy Acids An analytical procedure has been devised for the analysis of oils containing epoxy and/or hydroxy acids, and this has been applied to the examination of Vernonia anthelmintica. Cenhalocroton cordofanus and Strophanthua hispidus seed oils, and to Ergot oil. The unusual acid present in C, cordofanus seed oil hat been shown to be cis-12: 13-eponroctaclec-cis-9-enoic acid, identical With the acid in V. anthelmintica seed oil, and not ricinoleic acid as previously reported. The hydroxy acid, present in Irgot oil has been shown to be, identical with natural ricinoleic acid, Attempts have been made to improve the method of determination of α-dihydroxy acids in oils and fats by periodate oxidation. Part II. The Preparation of Eight 9:10:12:13-Tetrahydroxysteario, Acids. The availability of cis-12: 13-epoxyoctadeo-cis-8-enolc acid has opened a new Way for the preparation of 9:10:12:13- tetrahydroxysteario acids, hitherto prepared from linoleic acid. The epoxyoleic acid has been converted to threo- and erythro- 12:13-dihydroxyoctadec-cis-9-enoic acids and these on oxidation with either dilute alkaline potassium permanganate or with performic acid affords 9:10:12:13-teirahydroxysteario acids, Eight tetrahydroxysteario acids have thus been prepared, and these, like the stating materials are optically active.
1956-01-01T00:00:00ZBharucha, Kurshed ErachshaPart I. Study of Fatty Oils Containing Epoxy and/or Hydroxy Acids An analytical procedure has been devised for the analysis of oils containing epoxy and/or hydroxy acids, and this has been applied to the examination of Vernonia anthelmintica. Cenhalocroton cordofanus and Strophanthua hispidus seed oils, and to Ergot oil. The unusual acid present in C, cordofanus seed oil hat been shown to be cis-12: 13-eponroctaclec-cis-9-enoic acid, identical With the acid in V. anthelmintica seed oil, and not ricinoleic acid as previously reported. The hydroxy acid, present in Irgot oil has been shown to be, identical with natural ricinoleic acid, Attempts have been made to improve the method of determination of α-dihydroxy acids in oils and fats by periodate oxidation. Part II. The Preparation of Eight 9:10:12:13-Tetrahydroxysteario, Acids. The availability of cis-12: 13-epoxyoctadeo-cis-8-enolc acid has opened a new Way for the preparation of 9:10:12:13- tetrahydroxysteario acids, hitherto prepared from linoleic acid. The epoxyoleic acid has been converted to threo- and erythro- 12:13-dihydroxyoctadec-cis-9-enoic acids and these on oxidation with either dilute alkaline potassium permanganate or with performic acid affords 9:10:12:13-teirahydroxysteario acids, Eight tetrahydroxysteario acids have thus been prepared, and these, like the stating materials are optically active.Quantitative examination of seed oils by chromatographic proceduresBadami, Rajashekhar Chanabasappahttps://hdl.handle.net/10023/154202019-03-29T11:20:53Z1962-01-01T00:00:00Z1962-01-01T00:00:00ZBadami, Rajashekhar ChanabasappaSearch for practical alternatives to organotin hydridesBaguley, Paul A.https://hdl.handle.net/10023/154192019-03-29T11:20:44Z1998-01-01T00:00:00ZA summary of the tin hydride method of generating radicals in organic synthesis is presented, followed by illustrative examples of other methods available for mediating radical reactions, with a particular emphasis on recent developments. This is followed by four chapters describing our efforts to introduce alternative methods for generating radicals. A range of l-alkylcyclohexa-2,5-diene-l-carboxylic acids have been prepared by Birch reduction-alkylation methodology and shown to generate the corresponding alkyl radical by thermal initiation with dibenzoyl peroxide. The 1-benzyl, cyclopentyl and t-butyl precursors (17,15, and 16 respectively), acted as sources of radicals which were trapped with cyclohexenone to give the corresponding 3-alkylcyclohexanone adducts in yields of 52%, 30% and 25% respectively. Addition products were also observed when acrylonitrile and vinyl benzoate were employed as the radical traps. 1-[2-(Cylohex-2-enyloxy)ethyl]cyclohexa-2,5-diene-l-carboxylic acid 32 and l-[2-(6,6- dimethylbicyclo[3.1. l]hept-2-en-2-ylmethoxy)ethyl]cyclohexa-2,5-diene- 1-carboxyhc acid 33 are new compounds which were prepared in four straightforward steps from cyclohexene and β-pinene respectively. The route leading to acid 32 involved the preparation of four new compounds and three new compounds were prepared during the synthesis of acid 33. When refluxed in benzene in the presence of dibenzoyl peroxide, carboxylic acid 32 generated a primary alkyl radical which cyclised to yield 7- oxabicyclo[4.3.0]-nonane in 55% yield. The tin-mediated cyclisation of 3-(2'- iodoethoxy)cyclohexene 36 yielded the same compound in 60% yield, in addition to 3- ethoxycyclohexene (12%). Similarly, carboxylic acid 33 generated a primary alkyl radical which cyclised to yield the new compound oxacyclopentane-3-spiro-2-6,6- dimethylbicyclo[3.1.1]heptane in 10% yield. The tin-mediated cyclisation of 6,6-dimethyl- 2-(2-iodoethoxymethyl)bicyclo[3.1.1]hept-2-ene 37 yielded the same spiro compound in 31% yield. EPR spectroscopic studies provided direct evidence for the formation of the cyclohexadienyl radicals from all of the carboxylic acids investigated. Carboxylic acids 15- 17 and l-[2-(ethenyloxy)benzyl]cyclohexa-2,5-diene-l-carboxylic acid 34 also generated alkyl radicals which were clearly observed by EPR spectroscopy. The carboxylic acid radical precursors would have yielded products in higher yields if the competitive loss of a hydroxyformyl radical did not occur. An account of our work directed towards the synthesis of l-phenylcyclohexa-2,5-diene-l- carboxylic acid 8 is given. Thus, 1,4-dihydrobiphenyl was deprotonated with BuLi, added to CO2 and the isomeric acid, 3-carboxylic acid-3,4-dihydrobiphenyl was removed by reacting with maleic anhydride to give the Diels-Alder adduct. 2-(Cyclohex-2-enyloxy)ethyl l-phenylcyclohexa-2,5-diene-l-carboxylate 24 was treated with dibenzoyl peroxide to afford 7-oxabicyclo[4.3.0]nonane in yields of 32-36%. A variety of N-carboalkoxy-l,2-dihydropyridines have been prepared from the reaction of pyridine and the appropriate chloroforniate in the presence of NaBH₄. EPR studies have shown that these esters produce aza-cyclohexadienyl radicals on photolysis in the presence of di-t-butyl peroxide, but no decarboxylation was observed. These compounds do not generate alkyl radicals efficiently when reacted with dibenzoyl peroxide. In each case the major product identified was the corresponding benzoate ester, which resulted from the combination of an alkoxycarbonyl radical and a phenyl radical.
1998-01-01T00:00:00ZBaguley, Paul A.A summary of the tin hydride method of generating radicals in organic synthesis is presented, followed by illustrative examples of other methods available for mediating radical reactions, with a particular emphasis on recent developments. This is followed by four chapters describing our efforts to introduce alternative methods for generating radicals. A range of l-alkylcyclohexa-2,5-diene-l-carboxylic acids have been prepared by Birch reduction-alkylation methodology and shown to generate the corresponding alkyl radical by thermal initiation with dibenzoyl peroxide. The 1-benzyl, cyclopentyl and t-butyl precursors (17,15, and 16 respectively), acted as sources of radicals which were trapped with cyclohexenone to give the corresponding 3-alkylcyclohexanone adducts in yields of 52%, 30% and 25% respectively. Addition products were also observed when acrylonitrile and vinyl benzoate were employed as the radical traps. 1-[2-(Cylohex-2-enyloxy)ethyl]cyclohexa-2,5-diene-l-carboxylic acid 32 and l-[2-(6,6- dimethylbicyclo[3.1. l]hept-2-en-2-ylmethoxy)ethyl]cyclohexa-2,5-diene- 1-carboxyhc acid 33 are new compounds which were prepared in four straightforward steps from cyclohexene and β-pinene respectively. The route leading to acid 32 involved the preparation of four new compounds and three new compounds were prepared during the synthesis of acid 33. When refluxed in benzene in the presence of dibenzoyl peroxide, carboxylic acid 32 generated a primary alkyl radical which cyclised to yield 7- oxabicyclo[4.3.0]-nonane in 55% yield. The tin-mediated cyclisation of 3-(2'- iodoethoxy)cyclohexene 36 yielded the same compound in 60% yield, in addition to 3- ethoxycyclohexene (12%). Similarly, carboxylic acid 33 generated a primary alkyl radical which cyclised to yield the new compound oxacyclopentane-3-spiro-2-6,6- dimethylbicyclo[3.1.1]heptane in 10% yield. The tin-mediated cyclisation of 6,6-dimethyl- 2-(2-iodoethoxymethyl)bicyclo[3.1.1]hept-2-ene 37 yielded the same spiro compound in 31% yield. EPR spectroscopic studies provided direct evidence for the formation of the cyclohexadienyl radicals from all of the carboxylic acids investigated. Carboxylic acids 15- 17 and l-[2-(ethenyloxy)benzyl]cyclohexa-2,5-diene-l-carboxylic acid 34 also generated alkyl radicals which were clearly observed by EPR spectroscopy. The carboxylic acid radical precursors would have yielded products in higher yields if the competitive loss of a hydroxyformyl radical did not occur. An account of our work directed towards the synthesis of l-phenylcyclohexa-2,5-diene-l- carboxylic acid 8 is given. Thus, 1,4-dihydrobiphenyl was deprotonated with BuLi, added to CO2 and the isomeric acid, 3-carboxylic acid-3,4-dihydrobiphenyl was removed by reacting with maleic anhydride to give the Diels-Alder adduct. 2-(Cyclohex-2-enyloxy)ethyl l-phenylcyclohexa-2,5-diene-l-carboxylate 24 was treated with dibenzoyl peroxide to afford 7-oxabicyclo[4.3.0]nonane in yields of 32-36%. A variety of N-carboalkoxy-l,2-dihydropyridines have been prepared from the reaction of pyridine and the appropriate chloroforniate in the presence of NaBH₄. EPR studies have shown that these esters produce aza-cyclohexadienyl radicals on photolysis in the presence of di-t-butyl peroxide, but no decarboxylation was observed. These compounds do not generate alkyl radicals efficiently when reacted with dibenzoyl peroxide. In each case the major product identified was the corresponding benzoate ester, which resulted from the combination of an alkoxycarbonyl radical and a phenyl radical.New reagents and syntheses in heterocyclic organoselenium chemistrySpeirs, Richard Allanhttps://hdl.handle.net/10023/154172019-03-29T11:21:24Z1986-01-01T00:00:00ZThe main aim of this project was to develop new reagents capable of exchanging selenium for oxygen under mild conditions, to obtain new carboselenaldehyde (1) and selone (2) compounds. Phenylphosphonoselenoic dichloride (3) was prepared as a solution in xylene. It was reacted with (1,2-dithiol-3-ylidene)carbaldehydes and indolizine-3-carbaldehydes to afford 1,6aλ⁴-dithia-6-selena-pentalenes (5) and indolizine-3-carboselenaldehydes (6), respectively. The indolizine-3-carbaldehydes had previously been prepared from the corresponding indolizines, in turn prepared from the appropriate pyridinium bromide salts. CHSe(5)(6)Phenylphosphonoselenoic dichloride (3) was also reacted with several other carbonyl compounds. Reactions with N,N.-dimethyl- fonnamide, 5-phenyl-3H-1,2-dithiol-3-one, 2,6-dimethyl-4H.-pyran-4-one, 4-hydroxypyridine, 1-methylpyrrolidin-2-one, hexeihydro-2H-azepin-2-one, and 2,4,6-cycloheptatrien-1-one met with varied success, and only N,N-dimethylselenoformamide (7), 5-phenyl-3H-1,2-dithiole-3-selone (8), and 2,6-dimethy1-4H-pyraxi-4-selone (9) were obtained.(8)(9)The presence of a stabilising substituent was therefore required, and was introduced as a tungsten pentacarboiyl species. Pentacarbon-yl(indolizine-3-carboselenaldehyde-Se) tungsten(0) (10) and penta-carbonyl(2,4,6-cycloheptatriene-1-selone-Se)tungsten(0) (11) were obtained from the reaction of the corresponding oarboryl compounds with phenylphosphonoselenoic dichloride (3) in the presence of tetra- ethylanunonium iodopentacarbonyltungstate(0).The reagent (4) was prepared from the reaction of chlorodlphenyl- phosphine and tetramethylammonium selenocyanate, and was reacted in situ with indolizine-3-carbaldehydes to produce not only indolizine-3-carboselenaldehydes (6), but also compounds which were proposed on the strength of spectral and analytical evidence as being members of the novel 3-(indolizin-3-yl)-2,5-dihydro-2-selenoformyl-1,2,4-selena- diazole-5-selone (12) system.
See full text of thesis for diagrams (1) to (12), pp. xvii - xix
1986-01-01T00:00:00ZSpeirs, Richard AllanThe main aim of this project was to develop new reagents capable of exchanging selenium for oxygen under mild conditions, to obtain new carboselenaldehyde (1) and selone (2) compounds. Phenylphosphonoselenoic dichloride (3) was prepared as a solution in xylene. It was reacted with (1,2-dithiol-3-ylidene)carbaldehydes and indolizine-3-carbaldehydes to afford 1,6aλ⁴-dithia-6-selena-pentalenes (5) and indolizine-3-carboselenaldehydes (6), respectively. The indolizine-3-carbaldehydes had previously been prepared from the corresponding indolizines, in turn prepared from the appropriate pyridinium bromide salts. CHSe(5)(6)Phenylphosphonoselenoic dichloride (3) was also reacted with several other carbonyl compounds. Reactions with N,N.-dimethyl- fonnamide, 5-phenyl-3H-1,2-dithiol-3-one, 2,6-dimethyl-4H.-pyran-4-one, 4-hydroxypyridine, 1-methylpyrrolidin-2-one, hexeihydro-2H-azepin-2-one, and 2,4,6-cycloheptatrien-1-one met with varied success, and only N,N-dimethylselenoformamide (7), 5-phenyl-3H-1,2-dithiole-3-selone (8), and 2,6-dimethy1-4H-pyraxi-4-selone (9) were obtained.(8)(9)The presence of a stabilising substituent was therefore required, and was introduced as a tungsten pentacarboiyl species. Pentacarbon-yl(indolizine-3-carboselenaldehyde-Se) tungsten(0) (10) and penta-carbonyl(2,4,6-cycloheptatriene-1-selone-Se)tungsten(0) (11) were obtained from the reaction of the corresponding oarboryl compounds with phenylphosphonoselenoic dichloride (3) in the presence of tetra- ethylanunonium iodopentacarbonyltungstate(0).The reagent (4) was prepared from the reaction of chlorodlphenyl- phosphine and tetramethylammonium selenocyanate, and was reacted in situ with indolizine-3-carbaldehydes to produce not only indolizine-3-carboselenaldehydes (6), but also compounds which were proposed on the strength of spectral and analytical evidence as being members of the novel 3-(indolizin-3-yl)-2,5-dihydro-2-selenoformyl-1,2,4-selena- diazole-5-selone (12) system.
See full text of thesis for diagrams (1) to (12), pp. xvii - xixStudies of 6a-thiathiophthenes, 1,6,6a-triselenapentalenes, and related systemsJackson, Michael Georgehttps://hdl.handle.net/10023/153322019-03-29T11:24:33Z1973-01-01T00:00:00ZReaction of hydrogen selenide with l-methyl (ene)-1,3-diones in ethanolic hydrogen chloride containing iron(III) chloride affords either bis(3-methyl(ene)-1,2-diselenolium)tetrachloroferrates (II) or tris(1-niethyl(ene)-1,3-diselenato)iron(II) complexes, and 2,4,6,8-tetraselenaadamantanes, Bis(3-methyl (ene)-1,2-diselenelium) tetrachloroferrates (II) are readily converted into the corresponding perchlorates. Dimethylthipformamide condenses with both 3 methyl(ene)-1,2-diselenolium perchlorates and tris(l-methyl (ene)-l,-3-diselenato) iron (III) complexes to give 3-(2-dimethylaminovinyl)-1,2-diseleolium (Vilsmeier) salts, These salts react with sodium hydroxide to form 3-acylmethylne-3H-l,2-dise1enoles, with sodium hydrogen sulphide to give 1-thia-6,6a-dise1napentalene, and with sodium hydrogen selenide, to form 1,6, 6a-diselenapentalenes, and with sodium hydrogen selenide to fom 1, 6, 6a-triselenapentalenes. In addition, treatment of 3-(2-dimethylamino-1-methylvinyl)-4-methy1-1, 2-dislenolium percholorate with sodium hydroxide, sodium hydrogen sulphide, and sodium hydrogen selenide affords 3, 5-dimethyl-4H-pyran-4-selenoketpne, 3, 5-dimethyl- 4H-thopyran-4-seleoacetone, and 3, 5-Dimthyl-4H-slenopyran-4-selenoketone respectively. 3, 5Dimethyl-4H-selenopyran-4-selotone is hydrolysed to 3,5-dimethyl-4H-selenopyrap-4-on in wet chloroform solutton. As a dry crystalline solid, 3,5-dimethyl-4Hr-selemopyrao-4-selenoketone is a tmospherically oxidised to 3, 5-dimethyl-4H-selenopyran-4-one, 3-(l- formylethylidene)-4-methyl-3H-l,2-diselenole, and 3,4-dmethyl-1,6-dioxa-6a-selenapnta1ene, 3,4-Dimthyl-l,6,6a-triselenapentalene and 4,5-dihydro-3H-bnzo[cd)]. 1,6,6a-trisolonapenalene are formed by treatment of 3-(l-formylethy1idene)-4-methyl-3H,1-2-diselenole and 3-formyl-5,6-dihydro-411-bonzo[c]1,2-diselenole respectively with phosphoryl chloride in dpiethylformamide and subsequent addition f aqueous potassium selenosulphate or potassium selenotrithionate. Compounds containing oxygen and selenium atoms in the 1- and 6, positons of the 6a-selenapentalene ring, when treated with phosphorus pentasulpc.1e, form 1,6-dithta-6a-selenapentalnes provided the 2- and 5-positions are unsubstituted. The structures of 3-acylmethylene-3H-l,2-diselenoles and 1-thia-6,6a-diselenapontalenes are discussed in relation to spectroscopic data and compared with those of 3-acymetbylene-3H-l,2dithioes and 6a-thiathiophthepo respectively, The crystal structures of 6a-thiathiophthene, 1,6.dftia-6a-selenapentalene, and 1 ,6,6a-triselnapentalene are compared and the structures of l,6-dithia-6a-selepapeptalenes and 1,6,6a-triselenapentlenes are discussed in relation to spectroscopic data, A bicyclic structure containing an oygen-selenium-oxygen bonding sequence is proposed for 3,4-dimethyl-1,6dipxa6a-selenapentaleqe on the basis of its N.M.R and I.R, spectra. The mechanism of the rearrangement of 6a-thiathiopbthenes by aqueous sodium sulphide to 4H-thiopyran-4-thiones has been studied with sodium sulphide-S-35. The initial step in the rearrangement is a reductive cleavage of sulphur-sulphur bond forming an anion which is then susceptible to nucleophilic attack by sulphide ion at the 2- (and/or 5-) position(s).
1973-01-01T00:00:00ZJackson, Michael GeorgeReaction of hydrogen selenide with l-methyl (ene)-1,3-diones in ethanolic hydrogen chloride containing iron(III) chloride affords either bis(3-methyl(ene)-1,2-diselenolium)tetrachloroferrates (II) or tris(1-niethyl(ene)-1,3-diselenato)iron(II) complexes, and 2,4,6,8-tetraselenaadamantanes, Bis(3-methyl (ene)-1,2-diselenelium) tetrachloroferrates (II) are readily converted into the corresponding perchlorates. Dimethylthipformamide condenses with both 3 methyl(ene)-1,2-diselenolium perchlorates and tris(l-methyl (ene)-l,-3-diselenato) iron (III) complexes to give 3-(2-dimethylaminovinyl)-1,2-diseleolium (Vilsmeier) salts, These salts react with sodium hydroxide to form 3-acylmethylne-3H-l,2-dise1enoles, with sodium hydrogen sulphide to give 1-thia-6,6a-dise1napentalene, and with sodium hydrogen selenide, to form 1,6, 6a-diselenapentalenes, and with sodium hydrogen selenide to fom 1, 6, 6a-triselenapentalenes. In addition, treatment of 3-(2-dimethylamino-1-methylvinyl)-4-methy1-1, 2-dislenolium percholorate with sodium hydroxide, sodium hydrogen sulphide, and sodium hydrogen selenide affords 3, 5-dimethyl-4H-pyran-4-selenoketpne, 3, 5-dimethyl- 4H-thopyran-4-seleoacetone, and 3, 5-Dimthyl-4H-slenopyran-4-selenoketone respectively. 3, 5Dimethyl-4H-selenopyran-4-selotone is hydrolysed to 3,5-dimethyl-4H-selenopyrap-4-on in wet chloroform solutton. As a dry crystalline solid, 3,5-dimethyl-4Hr-selemopyrao-4-selenoketone is a tmospherically oxidised to 3, 5-dimethyl-4H-selenopyran-4-one, 3-(l- formylethylidene)-4-methyl-3H-l,2-diselenole, and 3,4-dmethyl-1,6-dioxa-6a-selenapnta1ene, 3,4-Dimthyl-l,6,6a-triselenapentalene and 4,5-dihydro-3H-bnzo[cd)]. 1,6,6a-trisolonapenalene are formed by treatment of 3-(l-formylethy1idene)-4-methyl-3H,1-2-diselenole and 3-formyl-5,6-dihydro-411-bonzo[c]1,2-diselenole respectively with phosphoryl chloride in dpiethylformamide and subsequent addition f aqueous potassium selenosulphate or potassium selenotrithionate. Compounds containing oxygen and selenium atoms in the 1- and 6, positons of the 6a-selenapentalene ring, when treated with phosphorus pentasulpc.1e, form 1,6-dithta-6a-selenapentalnes provided the 2- and 5-positions are unsubstituted. The structures of 3-acylmethylene-3H-l,2-diselenoles and 1-thia-6,6a-diselenapontalenes are discussed in relation to spectroscopic data and compared with those of 3-acymetbylene-3H-l,2dithioes and 6a-thiathiophthepo respectively, The crystal structures of 6a-thiathiophthene, 1,6.dftia-6a-selenapentalene, and 1 ,6,6a-triselnapentalene are compared and the structures of l,6-dithia-6a-selepapeptalenes and 1,6,6a-triselenapentlenes are discussed in relation to spectroscopic data, A bicyclic structure containing an oygen-selenium-oxygen bonding sequence is proposed for 3,4-dimethyl-1,6dipxa6a-selenapentaleqe on the basis of its N.M.R and I.R, spectra. The mechanism of the rearrangement of 6a-thiathiopbthenes by aqueous sodium sulphide to 4H-thiopyran-4-thiones has been studied with sodium sulphide-S-35. The initial step in the rearrangement is a reductive cleavage of sulphur-sulphur bond forming an anion which is then susceptible to nucleophilic attack by sulphide ion at the 2- (and/or 5-) position(s).A potentiometric study of some solution equilibria involving biological ligands and transition metal ionsMakar, George Kamel Rizkallahttps://hdl.handle.net/10023/153292019-03-29T11:23:03Z1976-01-01T00:00:00ZThe formation constants for several metal ion-ligand complexes have been measured by glass electrode potentiometry in aqueous solution at 37°C using an ionic background of 150mM sodium perchlorate. The three topics comprising this thesis are (i) a study of the reaction of several metal ions, namely Co(II), Ni(II), Cu(II) and Zn(II), with ligands such as adeninate, cyclohexylamine and cyclopentylamine. These were studied in order to gain experience in the techniques of potentiometry and computation. (ii) The second topic, which comprises the major portion of the thesis, involved the in vitro study of zinc complexes with a series of ligands which can be divided into two groups; those containing only oxygen donor groups (acetate, galacturonate, hydroxybutyrate, malate, malonate, oxalate, salicylate and tartarate) and those which contain oxygen and nitrogen donor groups (glycinate, glycylglycinate and glycylglycylglycinate); the purpose of this investigation being to suggest the best zinc supplementing drug for treating zinc deficiency conditions. Hydroxybutyrate and galacturonate are suggested to be the most promising ligands for zinc absorption. (iii) Finally, computer simulation models of equilibria involving zinc and ligands in intestinal solution were used to correlate the rate of growth of turkey poults with the type of metal-ligand complexing occurring in intestinal fluid.
1976-01-01T00:00:00ZMakar, George Kamel RizkallaThe formation constants for several metal ion-ligand complexes have been measured by glass electrode potentiometry in aqueous solution at 37°C using an ionic background of 150mM sodium perchlorate. The three topics comprising this thesis are (i) a study of the reaction of several metal ions, namely Co(II), Ni(II), Cu(II) and Zn(II), with ligands such as adeninate, cyclohexylamine and cyclopentylamine. These were studied in order to gain experience in the techniques of potentiometry and computation. (ii) The second topic, which comprises the major portion of the thesis, involved the in vitro study of zinc complexes with a series of ligands which can be divided into two groups; those containing only oxygen donor groups (acetate, galacturonate, hydroxybutyrate, malate, malonate, oxalate, salicylate and tartarate) and those which contain oxygen and nitrogen donor groups (glycinate, glycylglycinate and glycylglycylglycinate); the purpose of this investigation being to suggest the best zinc supplementing drug for treating zinc deficiency conditions. Hydroxybutyrate and galacturonate are suggested to be the most promising ligands for zinc absorption. (iii) Finally, computer simulation models of equilibria involving zinc and ligands in intestinal solution were used to correlate the rate of growth of turkey poults with the type of metal-ligand complexing occurring in intestinal fluid.Conformational studies of heterocyclic compoundsMagennis, Isabel Maryhttps://hdl.handle.net/10023/153252019-03-29T11:23:03Z1970-01-01T00:00:00ZTwelve heterocyclic ring compounds have been prepared and a high resolution Nuclear Magnetic Resonance study of each carried out. In particular, solvent effects and coupling constants have been studied. Some axial and equatorial shifts of methylene protons were found to be reversed compared to the predicted situation, Observed coupling constants have been found to be slightly solvent dependent. Some interesting values of coupling constants prompted a full X-ray crystal analysis of two of the compounds. This has been done, yielding bond lengths, bond angles, configuration around the phosphorus atom and conformation of the heterocyclic ring, all in the solid state. Dihedral angles for P-O-C-H systems have been calculated and an attempt has been made to correlate observed coupling constants with dihedral angles and electronegativity of substituents.
1970-01-01T00:00:00ZMagennis, Isabel MaryTwelve heterocyclic ring compounds have been prepared and a high resolution Nuclear Magnetic Resonance study of each carried out. In particular, solvent effects and coupling constants have been studied. Some axial and equatorial shifts of methylene protons were found to be reversed compared to the predicted situation, Observed coupling constants have been found to be slightly solvent dependent. Some interesting values of coupling constants prompted a full X-ray crystal analysis of two of the compounds. This has been done, yielding bond lengths, bond angles, configuration around the phosphorus atom and conformation of the heterocyclic ring, all in the solid state. Dihedral angles for P-O-C-H systems have been calculated and an attempt has been made to correlate observed coupling constants with dihedral angles and electronegativity of substituents.Natural and synthetic long-chained furanoid acidsWijesundera, Rajendranath Chakrapanihttps://hdl.handle.net/10023/153202019-03-29T11:24:58Z1978-01-01T00:00:00ZFatty acids containing a furan ring system were recently discovered by North American Scientists in the liver and testicular lipids of northern pike. We developed an analytical procedure based on urea crystallization and argentation thin layer chromatography for the isolation of small quantities of these novel acids. Using this method a large number of fish lipids taken from both freshwater and marine habitats wore examined. Our results show the wide occurrence of furanoid acids in fish at a low level (up to 5%), These unusual acids tend to concentrate in the cholesterol esters and appear to be absent from the phospholipids. Contrary to claims by the North American researchers we do not find a significant relation between the occurrence of these acids and the sex of the species or on whether the lipid is derived from a freshwater or marine source. We consider rather that the nutritional status of the animal is more significant. Cod liver oil usually contains furanoid acids at about 1% level but in two starved cod the proportion of these acids rose dramatically to 34 and 48% respectively. We also examined four commercial fish meals but furanoid acids were not present in any of them. Furanoid fatty acids were found to accumulate in the adipose tissue of rats given cod liver oil. No furanoid acids were demonstrable in comparable samples from rats given synthetic 10,13-furan acid. A furanoid fatty acid has been isolated from Exocarpus cupressiformis seed oil. In two samples of this seed available to us we did not detect any furanoid acids but found 8-hydroxyoctadoc-trans-11-en-9-noic acid (5%).The methodology used in the isolation of furanoid acids also allowed the study of methyl-branched acids. Whilst confirming the wide distribution of three phytol-based acids in fish lipids we have also detected three other compounds which we believe are diunsaturated derivatives of 7,9-dimethylhexadecanoic, 7,9- and 9,11-dimethyloctadecanoic acids respectively. The opportunity was also taken to study the more common acids of some fish species not previously examined. Besides confirming the well-known differences between the lipids of freshwater and marine origin, we find a significant difference between the fatty acids of male and female fish of freshwater origin, with the female containing more n-3 polyene acids and less monoene acids than does the male. The n-3/n-6 ratio is the most significant feature distinguishing freshwater from marine fish lipids. The 10,13-, 9,12-, and 8,11-isomers of the C₁₈ furanoid acids were prepared by one or more of the following methods. (i) Pd(II)-catalysed cyclodehydrogenation of oxygen-containing unsaturated acids, (ii) dehydration of diepoxides and dehydrogenation of epoxy alkenes with propyl iodide-sodium iodide-dimethylsulphoxide, and (iii) dehydration of endoperoxides. Synthesis of heterocyclic compounds by Pd(II)-promoted cyclization reactions is a fairly new development. The reactivity of various long-chain oxygenated esters with this unique reagent is discussed. The endoperoxide route is also novel and leads to speculation about the biosynthesis of natural furanoid acids. Recognition and identification of long-chain furanoid acids by their chromatographic and spectroscopic behaviour is discussed. Mass spectrometry is a powerful method of structure determination of these substances. Some chemical reactions of long-chain furanoid acids are also described.
1978-01-01T00:00:00ZWijesundera, Rajendranath ChakrapaniFatty acids containing a furan ring system were recently discovered by North American Scientists in the liver and testicular lipids of northern pike. We developed an analytical procedure based on urea crystallization and argentation thin layer chromatography for the isolation of small quantities of these novel acids. Using this method a large number of fish lipids taken from both freshwater and marine habitats wore examined. Our results show the wide occurrence of furanoid acids in fish at a low level (up to 5%), These unusual acids tend to concentrate in the cholesterol esters and appear to be absent from the phospholipids. Contrary to claims by the North American researchers we do not find a significant relation between the occurrence of these acids and the sex of the species or on whether the lipid is derived from a freshwater or marine source. We consider rather that the nutritional status of the animal is more significant. Cod liver oil usually contains furanoid acids at about 1% level but in two starved cod the proportion of these acids rose dramatically to 34 and 48% respectively. We also examined four commercial fish meals but furanoid acids were not present in any of them. Furanoid fatty acids were found to accumulate in the adipose tissue of rats given cod liver oil. No furanoid acids were demonstrable in comparable samples from rats given synthetic 10,13-furan acid. A furanoid fatty acid has been isolated from Exocarpus cupressiformis seed oil. In two samples of this seed available to us we did not detect any furanoid acids but found 8-hydroxyoctadoc-trans-11-en-9-noic acid (5%).The methodology used in the isolation of furanoid acids also allowed the study of methyl-branched acids. Whilst confirming the wide distribution of three phytol-based acids in fish lipids we have also detected three other compounds which we believe are diunsaturated derivatives of 7,9-dimethylhexadecanoic, 7,9- and 9,11-dimethyloctadecanoic acids respectively. The opportunity was also taken to study the more common acids of some fish species not previously examined. Besides confirming the well-known differences between the lipids of freshwater and marine origin, we find a significant difference between the fatty acids of male and female fish of freshwater origin, with the female containing more n-3 polyene acids and less monoene acids than does the male. The n-3/n-6 ratio is the most significant feature distinguishing freshwater from marine fish lipids. The 10,13-, 9,12-, and 8,11-isomers of the C₁₈ furanoid acids were prepared by one or more of the following methods. (i) Pd(II)-catalysed cyclodehydrogenation of oxygen-containing unsaturated acids, (ii) dehydration of diepoxides and dehydrogenation of epoxy alkenes with propyl iodide-sodium iodide-dimethylsulphoxide, and (iii) dehydration of endoperoxides. Synthesis of heterocyclic compounds by Pd(II)-promoted cyclization reactions is a fairly new development. The reactivity of various long-chain oxygenated esters with this unique reagent is discussed. The endoperoxide route is also novel and leads to speculation about the biosynthesis of natural furanoid acids. Recognition and identification of long-chain furanoid acids by their chromatographic and spectroscopic behaviour is discussed. Mass spectrometry is a powerful method of structure determination of these substances. Some chemical reactions of long-chain furanoid acids are also described.Some substituent interactions of substituted o-nitroanilinesMachin, Johnhttps://hdl.handle.net/10023/153182019-03-29T11:20:59Z1977-01-01T00:00:00ZAn introduction to the methods of preparation and some general properties of benzimidezele-N-oxidec are discussed in Chapter 1. In Chapter 2, the reaction of N-P-nitrobenzyl-N-P-tolylsulphonyl-o-nitroaniline with sodium methoxide in methanol to give 2-p-nitrophenylbenzimidazole-3-oxide is discussed. With the aid of reaction kinetics a mechanism which involves cyclisation prior to detosylation is established. The corresponding reactions of N-methylsulphonyl, N-acetyl and N-benzoyl-N-P-nitrobenzyl-o-nitroaniline with sodium methoxide similarly involve cyclisation prior to deacylation, For the corresponding cyclisations of N-acetyl and N-benzoyl-N-banzylo-nitroaniline to 2-phenylbenzimidazole-3-oxide, a mechanism involving deacylation prior to cyclisation is proposed, The reaction of N-p-nitrobenzyl-N-p-tolylsulphonyl-2 ,4-di- nitroanilina and K"benzyl-N-p-tolylsulphonyl-2 , 4-dinitroaniline with sodium methoxide does not give expected cyclised product, but gives instead N-p-tolylsulphonyl-2,4-dinitroaniline. Various mechanisms to account for these results are discussed The reaction of ethyl N-o-nitrophenylcarbamate with base and p-nitrobenzy 1bromide gives along with the expected product N-ethoxycarbony1-N-p-nitrobenzyl-o-nitroaniline, l-p-nit robenzyloxy-2-p-nitrophenylbenzimidazole. In Chapter 3, the reaction of N-phenacyl-N-p-tolylsulphony1-o-nitroaniline and various substituted analogues with a selection of bases is discussed. The major product of these reactions in which the base is methoxide, ethoxide, and n-propoxide is the corresponding a-2-alkoxybensimidazole-3-oxide. A mechanism for this reaction is proposed and the steps taken to verify it discussed. The scope and limitations of this type of reaction are considered. Chapter 4 deals with the attempted synthesis of a reaction intermediate, namely l-p-tolylsulphonylbenzimidazole-3-oxcide, postulated in the reaction scheme used to explain the formation of the 2-alkoxybenzimidazole-3-oxides.
1977-01-01T00:00:00ZMachin, JohnAn introduction to the methods of preparation and some general properties of benzimidezele-N-oxidec are discussed in Chapter 1. In Chapter 2, the reaction of N-P-nitrobenzyl-N-P-tolylsulphonyl-o-nitroaniline with sodium methoxide in methanol to give 2-p-nitrophenylbenzimidazole-3-oxide is discussed. With the aid of reaction kinetics a mechanism which involves cyclisation prior to detosylation is established. The corresponding reactions of N-methylsulphonyl, N-acetyl and N-benzoyl-N-P-nitrobenzyl-o-nitroaniline with sodium methoxide similarly involve cyclisation prior to deacylation, For the corresponding cyclisations of N-acetyl and N-benzoyl-N-banzylo-nitroaniline to 2-phenylbenzimidazole-3-oxide, a mechanism involving deacylation prior to cyclisation is proposed, The reaction of N-p-nitrobenzyl-N-p-tolylsulphonyl-2 ,4-di- nitroanilina and K"benzyl-N-p-tolylsulphonyl-2 , 4-dinitroaniline with sodium methoxide does not give expected cyclised product, but gives instead N-p-tolylsulphonyl-2,4-dinitroaniline. Various mechanisms to account for these results are discussed The reaction of ethyl N-o-nitrophenylcarbamate with base and p-nitrobenzy 1bromide gives along with the expected product N-ethoxycarbony1-N-p-nitrobenzyl-o-nitroaniline, l-p-nit robenzyloxy-2-p-nitrophenylbenzimidazole. In Chapter 3, the reaction of N-phenacyl-N-p-tolylsulphony1-o-nitroaniline and various substituted analogues with a selection of bases is discussed. The major product of these reactions in which the base is methoxide, ethoxide, and n-propoxide is the corresponding a-2-alkoxybensimidazole-3-oxide. A mechanism for this reaction is proposed and the steps taken to verify it discussed. The scope and limitations of this type of reaction are considered. Chapter 4 deals with the attempted synthesis of a reaction intermediate, namely l-p-tolylsulphonylbenzimidazole-3-oxcide, postulated in the reaction scheme used to explain the formation of the 2-alkoxybenzimidazole-3-oxides.Preparation and reactions of 2-alkyltetrahydrofurans from fatty alcoholsDawes, Margarethttps://hdl.handle.net/10023/153152019-03-29T11:19:30Z1996-01-01T00:00:00Z2-Alkyltetrahydroftirans have been prepared from C₁₀-C₁₈ primary alcohols. Complete characterisation of these compounds by mass spectral and NMR studies has been achieved. Ring-opening reactions of the 2-alkyltetrahydrofurans have been studied and have provided an insight into the chemistry of these compounds, highlighting differences in reactivities and reaction products compared with the parent molecule, tetrahydrofuran. The C₁₀-C₁₈ 2-alkyltetrahydrofurans have been subjected to a variety of ring cleavage reactions involving reaction with Lewis acids and/or acyl halides to produce compounds of the type;
RCH(X)CH₂CH₂CH₂-Y and RCH(Y)CH₂CH₂CH₂-X
R = C₆H₂₉ - C₁₄H₂₉, X = halogen atom, Y = acyl group
This work has demonstrated the ease with which these compounds may be ring opened. In some cases the reaction with the 2-alkyltetrahydrofiirans was observed to be more rapid and vigorous than with tetrahydrofuran itself. This was not always the case: The acid catalysed reaction of tetrahydrofiaran with dodecanol resulted in formation of the diether shown below, and a diester was similarly formed by the acid catalysed reaction of tetrahydrofliran with lauric acid.
R0(CH₂)₄OR diether (R = C12H25) RCOO(CH₂)₄OCOR diester (R= C₁H₂₃)
The analogous reactions with substituted tetrahydrofurans were slow and diether/diester yield was extremely low. Introduction of the alkyl group at position two of the tetrahydrofuran ring severely impeded the reaction. Instead the hydroxy ethers shown below were the major cyclic ether derived products.
C₁₂H₂₅-O-CH(R)(CH₂)₃-OH and C₁₂H₂₅-O-(CH₂)₃CH(R)-0H.
(R = C₆H₁₃)
Oxidation of the 2-alkyltetrahydrofurans was readily achieved by treatment with ruthenium tetroxide and resulted in formation of the corresponding alpha-alkyl-gamma-lactones and gamma-keto acids in almost quantitative yields and
RCO(CH₂)₂COOH
(R=C₆H₁₃-C₁₄H₂₉)
1996-01-01T00:00:00ZDawes, Margaret2-Alkyltetrahydroftirans have been prepared from C₁₀-C₁₈ primary alcohols. Complete characterisation of these compounds by mass spectral and NMR studies has been achieved. Ring-opening reactions of the 2-alkyltetrahydrofurans have been studied and have provided an insight into the chemistry of these compounds, highlighting differences in reactivities and reaction products compared with the parent molecule, tetrahydrofuran. The C₁₀-C₁₈ 2-alkyltetrahydrofurans have been subjected to a variety of ring cleavage reactions involving reaction with Lewis acids and/or acyl halides to produce compounds of the type;
RCH(X)CH₂CH₂CH₂-Y and RCH(Y)CH₂CH₂CH₂-X
R = C₆H₂₉ - C₁₄H₂₉, X = halogen atom, Y = acyl group
This work has demonstrated the ease with which these compounds may be ring opened. In some cases the reaction with the 2-alkyltetrahydrofiirans was observed to be more rapid and vigorous than with tetrahydrofuran itself. This was not always the case: The acid catalysed reaction of tetrahydrofiaran with dodecanol resulted in formation of the diether shown below, and a diester was similarly formed by the acid catalysed reaction of tetrahydrofliran with lauric acid.
R0(CH₂)₄OR diether (R = C12H25) RCOO(CH₂)₄OCOR diester (R= C₁H₂₃)
The analogous reactions with substituted tetrahydrofurans were slow and diether/diester yield was extremely low. Introduction of the alkyl group at position two of the tetrahydrofuran ring severely impeded the reaction. Instead the hydroxy ethers shown below were the major cyclic ether derived products.
C₁₂H₂₅-O-CH(R)(CH₂)₃-OH and C₁₂H₂₅-O-(CH₂)₃CH(R)-0H.
(R = C₆H₁₃)
Oxidation of the 2-alkyltetrahydrofurans was readily achieved by treatment with ruthenium tetroxide and resulted in formation of the corresponding alpha-alkyl-gamma-lactones and gamma-keto acids in almost quantitative yields and
RCO(CH₂)₂COOH
(R=C₆H₁₃-C₁₄H₂₉)ChitoseGrant, Archibald Bradshawhttps://hdl.handle.net/10023/153102019-03-29T11:19:07Z1951-01-01T00:00:00Z1951-01-01T00:00:00ZGrant, Archibald BradshawReactions of long chain esters leading to oxygen-containing heterocyclic compoundsAbbot, Graham Georgehttps://hdl.handle.net/10023/153052019-03-29T11:23:06Z1970-01-01T00:00:00ZWith the intention of preparing long chain esters containing a carbocyclic system, methyl linoleate and related esters were subjected to strongly acidic reaction conditions. The major product of the reaction, however, was shown to be a mixture of isomeric 1,4-epoxidea (tetrahydrofurans) and for comparison, a mixture of the cis and trans 9,12-epoxidos was prepared by an unambiguous synthesis. The discovery of those hotorocyclic fatty esters prompted further investigations into their methods of preparation. The cyclodehydration of some trihydroxyacids containing a 1,4-diol system was examined and the mechanism of the reaction elucidated. Those studies led to the formulation of the absolute configurations of the 9,12,13-tri-hydroxystearic acids. Methyl ricinoleate and methyl 9-hydroxyoctadec-cis-12- enoate were found to give different types of product when epexidised, The former yielded the expected 1,2-epoxide, whilst the latter furnished a mixture of hydroxytetrahydrofurans (90%). Since it was evident that the second reaction involved participation by the hydroxyl function, other epoxidation Reactions of various hydroxy, oxo and acetylenic ostors were investigated. The results indicated that oxo and hydroxy functions can interact with a proformed epoxide to yield cyclic products. Finally, various unsubstiuted 1,4-opoxidos were prepared by free radical oxidations of some hydroxyostors. Both load totraacotate and metal oxido-halogon mixtures were used as oxidising agents.
1970-01-01T00:00:00ZAbbot, Graham GeorgeWith the intention of preparing long chain esters containing a carbocyclic system, methyl linoleate and related esters were subjected to strongly acidic reaction conditions. The major product of the reaction, however, was shown to be a mixture of isomeric 1,4-epoxidea (tetrahydrofurans) and for comparison, a mixture of the cis and trans 9,12-epoxidos was prepared by an unambiguous synthesis. The discovery of those hotorocyclic fatty esters prompted further investigations into their methods of preparation. The cyclodehydration of some trihydroxyacids containing a 1,4-diol system was examined and the mechanism of the reaction elucidated. Those studies led to the formulation of the absolute configurations of the 9,12,13-tri-hydroxystearic acids. Methyl ricinoleate and methyl 9-hydroxyoctadec-cis-12- enoate were found to give different types of product when epexidised, The former yielded the expected 1,2-epoxide, whilst the latter furnished a mixture of hydroxytetrahydrofurans (90%). Since it was evident that the second reaction involved participation by the hydroxyl function, other epoxidation Reactions of various hydroxy, oxo and acetylenic ostors were investigated. The results indicated that oxo and hydroxy functions can interact with a proformed epoxide to yield cyclic products. Finally, various unsubstiuted 1,4-opoxidos were prepared by free radical oxidations of some hydroxyostors. Both load totraacotate and metal oxido-halogon mixtures were used as oxidising agents.CyclopentadienylidesSneezum, John Stuarthttps://hdl.handle.net/10023/153042019-03-29T11:20:51Z1959-01-01T00:00:00ZCyclopontadienylides (e.g, (III)) were prepared from dibromocyclopentene (l) b the action of cyclic organic bases followed by treatment with caustic alkali. The intermediate was shown to be the dibromide of the diquaternary salt (e.g. (II)), and the reaction scheme may be represented, in the case of pyridine, by the equations: (See full file abstract for equation) These ylides are brown-red crystalline solids, which impart strong colours to their solutions. The colour varied with polarity of the solvent, e.g. from orange-red in alcohol to a slightly purplish-red in benzene. The reactions of various organic bases with dibromocyclopentene were investigated but satisfactory products were obtained only from pyridine and substituted pyridines. However, rod materials of uncertain composition were obtained from aniline and ammonia. Also a compound from dimethyl sulphide was obtained, probably having the structure (IV) although satisfactory analysis results were not obtained in this case. (See full file Abstract for equation) The structure of the ylide from pyridine was established by catalytic hydrogenation to N-cyclopontylpiperidine and comparison of derivatives obtained therefrom with those from an authentic sample. Tetraphenylcyclopentaoienylides were prepared from 1-brom-2:3:5-tetraphenylcyclopentadiene by allowing this bromo compound to stand with the bases at room temperature, and removing the elements of hydrogen bromide with sodium hydroxide. Ylides formed in this way were blue to blueish- purple crystalline solids, showing a corresponding range of colour in organic solvents. The unphenylated ylides decomposed fairly rapidly on exposure to the air in the solid state, but more slowly in solution. The phenylated derivatives were quite stable as solids, but the colour of their solution faded quickly, Stability was enhanced in each case by storing the samples under nitrogen or in vacuo. Derivatives were generally difficult to isolate, but compounds were obtained with picric acid (from phenylated ylides) and benzene diazonium chloride (from unphenylated ylides, including that from dimethyl sulphide), a preliminary investigation was also made into the possibility of preparing many membered carbon rings by pinacone reduction of a-w-diketones. a-w-heptadecane dicarboxyclic acid was prepared as an intermediate.
1959-01-01T00:00:00ZSneezum, John StuartCyclopontadienylides (e.g, (III)) were prepared from dibromocyclopentene (l) b the action of cyclic organic bases followed by treatment with caustic alkali. The intermediate was shown to be the dibromide of the diquaternary salt (e.g. (II)), and the reaction scheme may be represented, in the case of pyridine, by the equations: (See full file abstract for equation) These ylides are brown-red crystalline solids, which impart strong colours to their solutions. The colour varied with polarity of the solvent, e.g. from orange-red in alcohol to a slightly purplish-red in benzene. The reactions of various organic bases with dibromocyclopentene were investigated but satisfactory products were obtained only from pyridine and substituted pyridines. However, rod materials of uncertain composition were obtained from aniline and ammonia. Also a compound from dimethyl sulphide was obtained, probably having the structure (IV) although satisfactory analysis results were not obtained in this case. (See full file Abstract for equation) The structure of the ylide from pyridine was established by catalytic hydrogenation to N-cyclopontylpiperidine and comparison of derivatives obtained therefrom with those from an authentic sample. Tetraphenylcyclopentaoienylides were prepared from 1-brom-2:3:5-tetraphenylcyclopentadiene by allowing this bromo compound to stand with the bases at room temperature, and removing the elements of hydrogen bromide with sodium hydroxide. Ylides formed in this way were blue to blueish- purple crystalline solids, showing a corresponding range of colour in organic solvents. The unphenylated ylides decomposed fairly rapidly on exposure to the air in the solid state, but more slowly in solution. The phenylated derivatives were quite stable as solids, but the colour of their solution faded quickly, Stability was enhanced in each case by storing the samples under nitrogen or in vacuo. Derivatives were generally difficult to isolate, but compounds were obtained with picric acid (from phenylated ylides) and benzene diazonium chloride (from unphenylated ylides, including that from dimethyl sulphide), a preliminary investigation was also made into the possibility of preparing many membered carbon rings by pinacone reduction of a-w-diketones. a-w-heptadecane dicarboxyclic acid was prepared as an intermediate.Researches into the synthesis of some degradation products of emetineUre, George Reidhttps://hdl.handle.net/10023/153022019-03-29T11:21:17Z1954-01-01T00:00:00ZThe root bark of several species of the ipecacuanha plant, notably Cephaelis ipecacuanha and Psychotria acuminate, contains at least five alkaloids, of which the principal one is emetine. The minor alkaloids are closely related to emetine, and the elucidation of their structures follows directly from the structure of emetine. The chief interest in emetine lies in its peculiar therapeutic powers as a treatment for amoebic dysentery. The drug has other medicinal properties as an emetic and diaphoretic, but these have largely been superseded, and in any case do not compare with its importance as a specific against entamoeba histolytica, the organism responsible for the occurrence of amoebic dysentery. Its local irritant effects, however, render it unsuitable in some cases, and although various simple derivatives have been used in its place, none of them appear to be a significant improvement on emetine itself. The main hope of producing a more suitable therapeutic agent lies in a more radical alteration of the molecule, and before this can be attempted, the structure and properties of emetine must be known beyond all doubt. Natural and synthetic substitutes for emetine produced with this knowledge, have so far proved ineffective. The structure of emetine, however, is now known with virtual certainty, apart from a complete synthesis of the molecule itself, and progress in this field should be more rapid. The investigations recorded herein are part of a continuation of the series (1, 2, 3, 4) which has finally shown the structure of emetine clearly, and with it the structures of the minor alkaloids and the rubremetine salts (2). The present work is mainly concerned with synthetic investigations of the more immediate degradation products from emetine, with the aim of further confirming the molecular structure. A parallel aim has been the provision of suitable intermediates for analogous syntheses.
1954-01-01T00:00:00ZUre, George ReidThe root bark of several species of the ipecacuanha plant, notably Cephaelis ipecacuanha and Psychotria acuminate, contains at least five alkaloids, of which the principal one is emetine. The minor alkaloids are closely related to emetine, and the elucidation of their structures follows directly from the structure of emetine. The chief interest in emetine lies in its peculiar therapeutic powers as a treatment for amoebic dysentery. The drug has other medicinal properties as an emetic and diaphoretic, but these have largely been superseded, and in any case do not compare with its importance as a specific against entamoeba histolytica, the organism responsible for the occurrence of amoebic dysentery. Its local irritant effects, however, render it unsuitable in some cases, and although various simple derivatives have been used in its place, none of them appear to be a significant improvement on emetine itself. The main hope of producing a more suitable therapeutic agent lies in a more radical alteration of the molecule, and before this can be attempted, the structure and properties of emetine must be known beyond all doubt. Natural and synthetic substitutes for emetine produced with this knowledge, have so far proved ineffective. The structure of emetine, however, is now known with virtual certainty, apart from a complete synthesis of the molecule itself, and progress in this field should be more rapid. The investigations recorded herein are part of a continuation of the series (1, 2, 3, 4) which has finally shown the structure of emetine clearly, and with it the structures of the minor alkaloids and the rubremetine salts (2). The present work is mainly concerned with synthetic investigations of the more immediate degradation products from emetine, with the aim of further confirming the molecular structure. A parallel aim has been the provision of suitable intermediates for analogous syntheses.Synthesis of novel heterocyclic polymersEmans, Johnhttps://hdl.handle.net/10023/152992019-03-29T11:23:38Z1987-01-01T00:00:00ZThis work details the synthesis, characterisation and fabrication of a range of copolyesters, containing various angular disrupters, especially disubstituted 2,5-diphenyl- -1,3,4-oxadiazoles. These disrupters were incorporated into the polymers, to reduce the temperature at which the polymers may be processed, to enable their fabrication into fibres. The majority of the polymers prepared were found to be liquid crystalline. However, if the angular disrupter content of the polymer was high, it was found that the resultant polymers were non-liquid crystalline. The polymers were prepared by a melt acidolysis process carried out under a nitrogen flow and subsequently under vacuum, as described in Chapter 3. Eighteen of the polymers were characterised in some detail, though a measure of the relative molecular weights was thought to be of little importance in this work, since all polymers were of a different composition. Differential scanning calorimetry and hot-stage microscopy revealed that several of the polymers had rather unusual melting behaviour. The eighteen polymers that were closely characterised were spun into fibres, using a small melt-spinning apparatus that was designed and produced by Bradford University Research Ltd, The resultant fibres were characterised by differential scanning calorimetry, X-ray diffraction end tensile testing. The general conclusion of the work is that although a reduction in the processing temperature of the polymer is achieved by the incorporation of angular disruptors, which is advantageous, the tensile strength and thermal stability of the fibres produced from such polymers are reduced.
1987-01-01T00:00:00ZEmans, JohnThis work details the synthesis, characterisation and fabrication of a range of copolyesters, containing various angular disrupters, especially disubstituted 2,5-diphenyl- -1,3,4-oxadiazoles. These disrupters were incorporated into the polymers, to reduce the temperature at which the polymers may be processed, to enable their fabrication into fibres. The majority of the polymers prepared were found to be liquid crystalline. However, if the angular disrupter content of the polymer was high, it was found that the resultant polymers were non-liquid crystalline. The polymers were prepared by a melt acidolysis process carried out under a nitrogen flow and subsequently under vacuum, as described in Chapter 3. Eighteen of the polymers were characterised in some detail, though a measure of the relative molecular weights was thought to be of little importance in this work, since all polymers were of a different composition. Differential scanning calorimetry and hot-stage microscopy revealed that several of the polymers had rather unusual melting behaviour. The eighteen polymers that were closely characterised were spun into fibres, using a small melt-spinning apparatus that was designed and produced by Bradford University Research Ltd, The resultant fibres were characterised by differential scanning calorimetry, X-ray diffraction end tensile testing. The general conclusion of the work is that although a reduction in the processing temperature of the polymer is achieved by the incorporation of angular disruptors, which is advantageous, the tensile strength and thermal stability of the fibres produced from such polymers are reduced.Reactions of some secondary and tertiary o-nitroaniline derivatives with basesCollins, Pamela Annhttps://hdl.handle.net/10023/152962019-03-29T11:20:47Z1957-01-01T00:00:00ZIn chapter 1, a brief account of the chemical and physical properties of benzimidazole A-oxides is given. The scope and limitations of a method recently developed for the synthesis of the N-oxides from substituted o-nitroaniline derivatives are discussed. Chapter 2 discusses the reactions in the literature which are relevant to those being investigated. Chapter 3 describes the efforts made to investigate the involvement of the activatuig' groups of the o-nitroaniline derivatives in the reaction pathway. In chapter 4 the reactions of N-(4 and/or 6-substituted o-nitrophenyl) glycine and sarcosine esters with bases are described. All of the 4-substituted glycine esters and those with fluorine, acetamido and methyl on C-6 cyclized 'normally' to the corresponding NH-benzimidazole N'-oxides whereas those with chlorine, trifluoromethyl, and nitro on C-6 reacted 'abnormally' to give, in addition, such products as 1-hydroxy-quinoxaline-2,3-diones and diaminoazoxybenzenes. All of the sarcosine esters reacted 'abnormally' producing none of the N-methylbenzimidazole N'-oxides. Surprisingly they did form products indicating loss of the W-methyl group, e.g. quinoxalin-2-ones. The aldol-type condensation mechanism that has been previously applied to the syntheses of benzimidazole N-oxides does not explain these new results; they suggest that the presence of an amino-hydrogen in the starting material is necessary for N-oxide formation. An alternative mechanism is proposed which takes this possibility and the types of products formed into account. It involves the formation of an oxadiazine intermediate which can then react in a number of different ways to give the observed products. The reasons for some neighbouring substituents affecting the reaction pathway appears to be largely steric though there may also be an electronic factor. Chapter 5 contains a discussion of how the alternative mechanism could be applied to a number of other cyclizations of carbocyclic and heterocyclic compounds which involve interaction of a nitro group with a potentially nucleophilic ortho-substituent.
1957-01-01T00:00:00ZCollins, Pamela AnnIn chapter 1, a brief account of the chemical and physical properties of benzimidazole A-oxides is given. The scope and limitations of a method recently developed for the synthesis of the N-oxides from substituted o-nitroaniline derivatives are discussed. Chapter 2 discusses the reactions in the literature which are relevant to those being investigated. Chapter 3 describes the efforts made to investigate the involvement of the activatuig' groups of the o-nitroaniline derivatives in the reaction pathway. In chapter 4 the reactions of N-(4 and/or 6-substituted o-nitrophenyl) glycine and sarcosine esters with bases are described. All of the 4-substituted glycine esters and those with fluorine, acetamido and methyl on C-6 cyclized 'normally' to the corresponding NH-benzimidazole N'-oxides whereas those with chlorine, trifluoromethyl, and nitro on C-6 reacted 'abnormally' to give, in addition, such products as 1-hydroxy-quinoxaline-2,3-diones and diaminoazoxybenzenes. All of the sarcosine esters reacted 'abnormally' producing none of the N-methylbenzimidazole N'-oxides. Surprisingly they did form products indicating loss of the W-methyl group, e.g. quinoxalin-2-ones. The aldol-type condensation mechanism that has been previously applied to the syntheses of benzimidazole N-oxides does not explain these new results; they suggest that the presence of an amino-hydrogen in the starting material is necessary for N-oxide formation. An alternative mechanism is proposed which takes this possibility and the types of products formed into account. It involves the formation of an oxadiazine intermediate which can then react in a number of different ways to give the observed products. The reasons for some neighbouring substituents affecting the reaction pathway appears to be largely steric though there may also be an electronic factor. Chapter 5 contains a discussion of how the alternative mechanism could be applied to a number of other cyclizations of carbocyclic and heterocyclic compounds which involve interaction of a nitro group with a potentially nucleophilic ortho-substituent.Kinetic and NMR studies of some nitrogen heterocyclesAnderson, Lesley Marionhttps://hdl.handle.net/10023/152952019-03-29T11:22:30Z1990-01-01T00:00:00ZThe work carried out in this thesis involves the investigation of some reactions of heterocyclic compounds by a wide range of spectroscopic and kinetic techniques. Chapter 1 describes several methods, including stopped-flow spectrophotometry, high pressure kinetics and MNDO calculations, which are used to analyse the mechanism of the reaction of imidazole with diazonium ions. Chapter 2 describes the use of the temperature-jump technique to follow the extremely fast protonation of pyrroles. Diazonium ions are further investigated in Chapter 3 which examines the structure of p-nitrobenzenediazonium tetrafluoroborate by X-ray crystallography. The nature of other benzenediazonium ions and some of their complexes is also investigated by solid state ¹⁵N nmr spectroscopy. Chapter 4 switches the emphasis to nmr spectroscopy. The reactive intermediates of reactions of benzil with nitrogen heterocycles are investigated using ¹³c nmr spectroscopy in a kinetic application. Chapters 5 and 6 continue the use of nmr spectroscopy in the structural assignment of bilirubin and the determination of the nature of bilirubin inclusion complexes. Chapter 6 also examines by spectrophotometry the reaction used in the clinical analysis of bilirubin and the effect on this reaction of binding agents such as albumin and α-cyclodextrin.
1990-01-01T00:00:00ZAnderson, Lesley MarionThe work carried out in this thesis involves the investigation of some reactions of heterocyclic compounds by a wide range of spectroscopic and kinetic techniques. Chapter 1 describes several methods, including stopped-flow spectrophotometry, high pressure kinetics and MNDO calculations, which are used to analyse the mechanism of the reaction of imidazole with diazonium ions. Chapter 2 describes the use of the temperature-jump technique to follow the extremely fast protonation of pyrroles. Diazonium ions are further investigated in Chapter 3 which examines the structure of p-nitrobenzenediazonium tetrafluoroborate by X-ray crystallography. The nature of other benzenediazonium ions and some of their complexes is also investigated by solid state ¹⁵N nmr spectroscopy. Chapter 4 switches the emphasis to nmr spectroscopy. The reactive intermediates of reactions of benzil with nitrogen heterocycles are investigated using ¹³c nmr spectroscopy in a kinetic application. Chapters 5 and 6 continue the use of nmr spectroscopy in the structural assignment of bilirubin and the determination of the nature of bilirubin inclusion complexes. Chapter 6 also examines by spectrophotometry the reaction used in the clinical analysis of bilirubin and the effect on this reaction of binding agents such as albumin and α-cyclodextrin.Some new heterocyclic thermosetsNicolson, Neil Jameshttps://hdl.handle.net/10023/152932019-03-29T11:19:17Z1996-01-01T00:00:00ZThe original aim of this project was to investigate the possibility of synthesising a novel polymer system combining the best features of cyanate ester resins and epoxy resins. Chapter 1 presents the historical background for both types of resin. The remaining three chapters describe attempts to achieve this aim by a) finding a cyanate ester that cures at a lower temperature than those in current commercial use (Chapter 2); b) using mixed epoxy and cyanate ester resins (Chapter 3); and c) designing chemically completely novel polymers from knowledge of the existing ones (Chapter 4). In Chapter 2 it was revealed that different cyanate esters cure at different temperatures, but that no obvious correlation exists between curing temperature and either steric or electronic effects of the ring substituents. The mixing of two dicyanate esters, one of which cures at a lower temperature than the other, leads to some reduction in the overall curing temperature required, but not sufficient to warrant further study at this stage. In Chapter 3 the usefulness of a previously proposed co-reaction between cyanate esters and epoxides was examined. Previous work in this area is full of inconsistencies that put many of the proposed conclusions in doubt. Further examination of the alleged co-reaction reveals that any such co-reaction is unpredictable, can vary significantly with reaction conditions and is in any case a minor reaction pathway by comparison with the self-reactions of the two individual reactants. It was therefore decided that further pursuit of this strategy was also likely to prove unrewarding in the short term. In Chapter 4 a study was made into the effects of including novel monomers in a standard epoxy resin system. These novel monomers had a cyanurate backbone with epoxide functionality, and can be cured at the lower temperatures of epoxy resins. Tests on the properties (mechanical, dielectric, water absorption, fracture toughness etc.) of these polymers were of a preliminary "scouting" nature, but are sufficiently promising to encourage further study.
1996-01-01T00:00:00ZNicolson, Neil JamesThe original aim of this project was to investigate the possibility of synthesising a novel polymer system combining the best features of cyanate ester resins and epoxy resins. Chapter 1 presents the historical background for both types of resin. The remaining three chapters describe attempts to achieve this aim by a) finding a cyanate ester that cures at a lower temperature than those in current commercial use (Chapter 2); b) using mixed epoxy and cyanate ester resins (Chapter 3); and c) designing chemically completely novel polymers from knowledge of the existing ones (Chapter 4). In Chapter 2 it was revealed that different cyanate esters cure at different temperatures, but that no obvious correlation exists between curing temperature and either steric or electronic effects of the ring substituents. The mixing of two dicyanate esters, one of which cures at a lower temperature than the other, leads to some reduction in the overall curing temperature required, but not sufficient to warrant further study at this stage. In Chapter 3 the usefulness of a previously proposed co-reaction between cyanate esters and epoxides was examined. Previous work in this area is full of inconsistencies that put many of the proposed conclusions in doubt. Further examination of the alleged co-reaction reveals that any such co-reaction is unpredictable, can vary significantly with reaction conditions and is in any case a minor reaction pathway by comparison with the self-reactions of the two individual reactants. It was therefore decided that further pursuit of this strategy was also likely to prove unrewarding in the short term. In Chapter 4 a study was made into the effects of including novel monomers in a standard epoxy resin system. These novel monomers had a cyanurate backbone with epoxide functionality, and can be cured at the lower temperatures of epoxy resins. Tests on the properties (mechanical, dielectric, water absorption, fracture toughness etc.) of these polymers were of a preliminary "scouting" nature, but are sufficiently promising to encourage further study.Novel derivatives of DPP and related heterocyclesMorton, Colin J. H.https://hdl.handle.net/10023/152912019-03-29T11:19:42Z1999-01-01T00:00:00ZThis thesis discusses the synthesis of new organic, heterocyclic materials for potential application as pigments. Chapter 1 comprises an introduction to the field of pigment and dye chemistry, discussing the rudimentary elements of colour theory, before advancing to a review of the pertinent literature regarding high performance organic pigments. In particular, the development of 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) pigments is described and the central objective of synthesising alkenyl-DPPs is outlined. Chapters 2 and 3 describe synthetic efforts towards alkenyl-DPPs, employing retro Diels-Alder methodology. The reactions involving the furan-acrylonitrile adduct as the nitrile component in the standard DPP synthesis led mainly to aromatisation of the bicyclic system and the cyclopentadiene-acrylonitrile adduct failed to react altogether. The explanation for this failure has been investigated. In the course of this these studies, several DPPs incorporating a secondary alkyl substituent were prepared, not least a novel cyclohexenyl-DPP. Chapter 4 describes the use of α β-unsaturated nitriles in the standard DPP synthesis. These behaved as Michael acceptors and in the case of cinnamonitriles led to a new family of coloured materials, namely substituted 4-hydroxy-2/7- cyclopenta[c]pyrrol-1-one-5-carbonitriles. Chapter 5 describes the corresponding reaction of cinnamate esters, but in these cases bicyclic systems were not formed. The reactions are analogous to Claisen acylations and the stereochemistry of the products varied according to the substituents. Chapter 6 contains the detailed experimental work for these investigations and concludes with a portfolio of X-ray structural data.
1999-01-01T00:00:00ZMorton, Colin J. H.This thesis discusses the synthesis of new organic, heterocyclic materials for potential application as pigments. Chapter 1 comprises an introduction to the field of pigment and dye chemistry, discussing the rudimentary elements of colour theory, before advancing to a review of the pertinent literature regarding high performance organic pigments. In particular, the development of 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) pigments is described and the central objective of synthesising alkenyl-DPPs is outlined. Chapters 2 and 3 describe synthetic efforts towards alkenyl-DPPs, employing retro Diels-Alder methodology. The reactions involving the furan-acrylonitrile adduct as the nitrile component in the standard DPP synthesis led mainly to aromatisation of the bicyclic system and the cyclopentadiene-acrylonitrile adduct failed to react altogether. The explanation for this failure has been investigated. In the course of this these studies, several DPPs incorporating a secondary alkyl substituent were prepared, not least a novel cyclohexenyl-DPP. Chapter 4 describes the use of α β-unsaturated nitriles in the standard DPP synthesis. These behaved as Michael acceptors and in the case of cinnamonitriles led to a new family of coloured materials, namely substituted 4-hydroxy-2/7- cyclopenta[c]pyrrol-1-one-5-carbonitriles. Chapter 5 describes the corresponding reaction of cinnamate esters, but in these cases bicyclic systems were not formed. The reactions are analogous to Claisen acylations and the stereochemistry of the products varied according to the substituents. Chapter 6 contains the detailed experimental work for these investigations and concludes with a portfolio of X-ray structural data.Some aspects of the molecular structure of heterocyclic and organometallic compoundsCutherbertson, Alastair Fraserhttps://hdl.handle.net/10023/152892019-03-29T11:19:32Z1983-01-01T00:00:00ZVarious rules which have been used to rationalise molecular geometries are discussed. After this the results from MNDO calculations on simple carbenes, ethers and amines are presented, and these were designed to test the hypothesis that in the presence of ligands of low electronegativity lone pairs would not fulfil their stereochemical role assigned to them in the VSEPR model. Following on are MNDO calculations on cyclic molecules: the cyclopentadiene ring is planar in silylcyclopentadiene and non-planar in trimethylsilylcyclopentadiene. The calculations attempt to resolve this and in addition the nature of the fluxional exchange. The intermediates which are formed by diazepinium salts when they are protodebrominated are then discussed in the light of MNDO calculations. Single crystal x-ray work was carried out for four heterocyclic molecules. The compounds reported are: 4-phenyl-3-phenylamino-1,2,4-thiadiazolin-5-one; 5-(N-methylthiocarbamoylimino)-4-phenyl-3-phenylamino-4H-l,2,4-thiadiazoline; N,N-bis[2-(5-t-butyl-3H-1,2-dithiol-3-ylidene)ethylidene]hydrazine and N,N-dimethyl-N-[2-(5-t-butyl-3H-1,2-dithiol-3-ylidene)ethylidene]hydrazine. Details of MNDO calculations which were undertaken on molecules related to the x-ray work are then presented, and in the final chapter a discussion of the heterocyclic crystal structures appears. The first appendix reports the structure of a macrocyclic ligand, the second provides a list of publications and the third appendix is a list of the structure factors, least-squares planes and anisotropic temperature parameters for the crystal structure determinations.
1983-01-01T00:00:00ZCutherbertson, Alastair FraserVarious rules which have been used to rationalise molecular geometries are discussed. After this the results from MNDO calculations on simple carbenes, ethers and amines are presented, and these were designed to test the hypothesis that in the presence of ligands of low electronegativity lone pairs would not fulfil their stereochemical role assigned to them in the VSEPR model. Following on are MNDO calculations on cyclic molecules: the cyclopentadiene ring is planar in silylcyclopentadiene and non-planar in trimethylsilylcyclopentadiene. The calculations attempt to resolve this and in addition the nature of the fluxional exchange. The intermediates which are formed by diazepinium salts when they are protodebrominated are then discussed in the light of MNDO calculations. Single crystal x-ray work was carried out for four heterocyclic molecules. The compounds reported are: 4-phenyl-3-phenylamino-1,2,4-thiadiazolin-5-one; 5-(N-methylthiocarbamoylimino)-4-phenyl-3-phenylamino-4H-l,2,4-thiadiazoline; N,N-bis[2-(5-t-butyl-3H-1,2-dithiol-3-ylidene)ethylidene]hydrazine and N,N-dimethyl-N-[2-(5-t-butyl-3H-1,2-dithiol-3-ylidene)ethylidene]hydrazine. Details of MNDO calculations which were undertaken on molecules related to the x-ray work are then presented, and in the final chapter a discussion of the heterocyclic crystal structures appears. The first appendix reports the structure of a macrocyclic ligand, the second provides a list of publications and the third appendix is a list of the structure factors, least-squares planes and anisotropic temperature parameters for the crystal structure determinations.CyclopentadienylidesFreeman, Brian Hardinghttps://hdl.handle.net/10023/152862019-03-29T11:24:10Z1971-01-01T00:00:00ZThe thermal decomposition of 2,3,4,5-tetraphenyldiazocyclopentadiene in the presence of carbene acceptors having Group V and VI elements to give 2,3,4,5-tetraphenylcyclopentadienylides has been extended and the first example of a telluronium ylide has been prepared by this method. The procedure has also been extended to other substituted diazo-cyclopentadienes and various new phosphonium, arsonium and sulphonium ylides have been prepared. The reaction of diazocyclopentadienes with triphenylphosphine to give either phosphazines or phosphonium ylides has been studied and the reasons for the difference in reactivity of these diazo-compounds has been clarified to some extent. It has been shown that for phosphazine formation both lack of steric hindrance and the absence of an electron- donating group on the cyclopentadiene ring are required. The thermal reaction of diazocyclopentadienes is assumed to proceed via a carbene-type intermediate which is then attacked by the reagent present to give an ylide. This reaction can be catalysed by the presence of copper-bronze and, in this case, can be effected either under melt conditions or in solution. The stability of the carbenoid intermediate is demonstrated by its preferential reaction with triphenylarsine rather than with benzene, which is present as the solvent. The reaction of 2,5-diphenyldiazocyclopentadiene with triphenylarsine gives a rearranged 2,4-disubstituted product. The carbene-type intermediate in this case is presumed to rearrange before reaction with the triphenylarsine. Some cyclopentadienylidene triphenylphosphazines have been shown to decompose thermally in the presence of triphenylphosphine to give the related triphenylphosphonium ylides. Diazocyclopentadienes have been found to react with either hydrochloric or hydrobromic acid to give the monochloro or monobromo cyclopentadienes. The parent, unsubstituted triphenylarsonium cyclopentadienylide has been prepared by the reaction of triphenylarsine with dibromocyclopentene and basification of the bis-arsonium salt so formed. Its properties and reactions have been studied and are found to be similar to the analogous triphenylphosphonium ylide. The salt method for the preparation of cyclopentadienylides has also been investigated. Triphenylarsine has been shown to react with 5-bromo-1,2,3-triphenylcyclopentadiene in solution at room temperature to give the hydrobromide salt of the ylide. Various sulphides also reacted with the bromo-compound to give, in most cases, unexpected products. The reactions of the cyclopentadienylides prepared with aldehydes have been investigated and the results are in line with previous findings. The cyclopentadienylides also readily undergo electrophilic substitution on the five-membered ring. The reaction proceeds preferentially at the 2(5)-position.
1971-01-01T00:00:00ZFreeman, Brian HardingThe thermal decomposition of 2,3,4,5-tetraphenyldiazocyclopentadiene in the presence of carbene acceptors having Group V and VI elements to give 2,3,4,5-tetraphenylcyclopentadienylides has been extended and the first example of a telluronium ylide has been prepared by this method. The procedure has also been extended to other substituted diazo-cyclopentadienes and various new phosphonium, arsonium and sulphonium ylides have been prepared. The reaction of diazocyclopentadienes with triphenylphosphine to give either phosphazines or phosphonium ylides has been studied and the reasons for the difference in reactivity of these diazo-compounds has been clarified to some extent. It has been shown that for phosphazine formation both lack of steric hindrance and the absence of an electron- donating group on the cyclopentadiene ring are required. The thermal reaction of diazocyclopentadienes is assumed to proceed via a carbene-type intermediate which is then attacked by the reagent present to give an ylide. This reaction can be catalysed by the presence of copper-bronze and, in this case, can be effected either under melt conditions or in solution. The stability of the carbenoid intermediate is demonstrated by its preferential reaction with triphenylarsine rather than with benzene, which is present as the solvent. The reaction of 2,5-diphenyldiazocyclopentadiene with triphenylarsine gives a rearranged 2,4-disubstituted product. The carbene-type intermediate in this case is presumed to rearrange before reaction with the triphenylarsine. Some cyclopentadienylidene triphenylphosphazines have been shown to decompose thermally in the presence of triphenylphosphine to give the related triphenylphosphonium ylides. Diazocyclopentadienes have been found to react with either hydrochloric or hydrobromic acid to give the monochloro or monobromo cyclopentadienes. The parent, unsubstituted triphenylarsonium cyclopentadienylide has been prepared by the reaction of triphenylarsine with dibromocyclopentene and basification of the bis-arsonium salt so formed. Its properties and reactions have been studied and are found to be similar to the analogous triphenylphosphonium ylide. The salt method for the preparation of cyclopentadienylides has also been investigated. Triphenylarsine has been shown to react with 5-bromo-1,2,3-triphenylcyclopentadiene in solution at room temperature to give the hydrobromide salt of the ylide. Various sulphides also reacted with the bromo-compound to give, in most cases, unexpected products. The reactions of the cyclopentadienylides prepared with aldehydes have been investigated and the results are in line with previous findings. The cyclopentadienylides also readily undergo electrophilic substitution on the five-membered ring. The reaction proceeds preferentially at the 2(5)-position.Studies in the perinaphthene seriesSutherland, Ronald Georgehttps://hdl.handle.net/10023/152842019-03-29T11:22:25Z1962-01-01T00:00:00ZThe thesis comprises three parts, A, B and C. Each part is divided into a number of principle sections which are prefixed by Roman numerals. Most sections are divided into subsections prefixed by Roman numerals. Part A commences with a brief survey of aromaticity and aromatic reactivity in non-benzenoid aromatic compounds. This is followed by a detailed review of the chemistry of perinaphthene and its derivatives. Part B is a discussion of the results achieved in the course of investigations on the perinaphthane nucleus. Part C is the complement to part B, being a description of experimental details.
1962-01-01T00:00:00ZSutherland, Ronald GeorgeThe thesis comprises three parts, A, B and C. Each part is divided into a number of principle sections which are prefixed by Roman numerals. Most sections are divided into subsections prefixed by Roman numerals. Part A commences with a brief survey of aromaticity and aromatic reactivity in non-benzenoid aromatic compounds. This is followed by a detailed review of the chemistry of perinaphthene and its derivatives. Part B is a discussion of the results achieved in the course of investigations on the perinaphthane nucleus. Part C is the complement to part B, being a description of experimental details.The synthesis and chemical properties of some compounds containing the perinaphthene nucleusBonthrone, Williamhttps://hdl.handle.net/10023/152702019-03-29T11:19:13Z1958-01-01T00:00:00ZThis thesis comprises three parts, Parts A, B and C. Part A commences with a very brief survey based on the chemical literature of the concept of aromaticity. A number of excellent reviews covering both the historical and theoretical aspects of this subject have appeared recently and, in view of this, a more detailed consideration of aromaticity was deemed unnecessary. This is followed by a discussion of the chemistry of the mulenes with particular emphasis on the theoretical aspects of the subject. The chemistry of perinaphthene and its derivatives is then reviewed in detail and this leads logically to a reasoned description of the aims of the experimental investigation.
Part B is a discussion of the results achieved in the course of investigations centred on the perinaghtene nucleus. Part C is devoted entirely to a description of experimental details, and is the complement to part B.
1958-01-01T00:00:00ZBonthrone, WilliamThis thesis comprises three parts, Parts A, B and C. Part A commences with a very brief survey based on the chemical literature of the concept of aromaticity. A number of excellent reviews covering both the historical and theoretical aspects of this subject have appeared recently and, in view of this, a more detailed consideration of aromaticity was deemed unnecessary. This is followed by a discussion of the chemistry of the mulenes with particular emphasis on the theoretical aspects of the subject. The chemistry of perinaphthene and its derivatives is then reviewed in detail and this leads logically to a reasoned description of the aims of the experimental investigation.
Part B is a discussion of the results achieved in the course of investigations centred on the perinaghtene nucleus. Part C is devoted entirely to a description of experimental details, and is the complement to part B.Aromatic systems containing the perinaphthene nucleusAitken, I. M.https://hdl.handle.net/10023/152622019-03-29T11:25:09Z1958-01-01T00:00:00ZThis thesis compirses three parts, Parts A, B and C. Each part is divided into a number of principal sections prefixed by Roman numerals, and these sections are further divided into sub-sections prefixed by Arabic numerals. Each sub-section is uniquely indicated by a combination consisting of a capital letter, a Roman and Arabic numeral, e.g., (A, IV, 1) – Perinaphthene System: Nomenclature.
Part A commences with a brief analytical survey based on the chemical literature of the various aromatic carbocyclic systems and this is developed logically into a consideration of the perinaphthene system. A detailed review of the latter and its simple derivatives follow, with particular emphasis on the theoretical aspects of this system.
Part B is an account of the results achieved by the author in the course of investigations centred on aromatic compounds containing the perinaphthene nucleus. The synthesis and properties of indene [2,1-a] perinaphthene are described, in addition to preliminary experiments with a view to preparing cyclopenta[a]-perinaphthene. The outcome of the investigation is fully examined from the theoretical standpoint.
Part C is entirely devoted to experimental details, and is the complement to Part B. Ten plates, mainly of absorption spectra are to be found at the end of the thesis.
1958-01-01T00:00:00ZAitken, I. M.This thesis compirses three parts, Parts A, B and C. Each part is divided into a number of principal sections prefixed by Roman numerals, and these sections are further divided into sub-sections prefixed by Arabic numerals. Each sub-section is uniquely indicated by a combination consisting of a capital letter, a Roman and Arabic numeral, e.g., (A, IV, 1) – Perinaphthene System: Nomenclature.
Part A commences with a brief analytical survey based on the chemical literature of the various aromatic carbocyclic systems and this is developed logically into a consideration of the perinaphthene system. A detailed review of the latter and its simple derivatives follow, with particular emphasis on the theoretical aspects of this system.
Part B is an account of the results achieved by the author in the course of investigations centred on aromatic compounds containing the perinaphthene nucleus. The synthesis and properties of indene [2,1-a] perinaphthene are described, in addition to preliminary experiments with a view to preparing cyclopenta[a]-perinaphthene. The outcome of the investigation is fully examined from the theoretical standpoint.
Part C is entirely devoted to experimental details, and is the complement to Part B. Ten plates, mainly of absorption spectra are to be found at the end of the thesis.Polycarboxylic acids via catalytic hydrocarboxylation of polybutadienesPondicherry, Narayananhttps://hdl.handle.net/10023/152592019-03-29T11:20:11Z1992-01-01T00:00:00ZPolybutadiene having varying degrees of 1,4 and 1,2 units (0 - 100% cis, 14 - 60 % trans, 20-88 % pendant carbon-carbon double bonds) have been reacted with carbon monoxide in the presence of water and palladium based catalysts to give new polymers in which the double bonds are hydrocarboxylated. When using [PdCl₂(PPh₃)₂]/SnCl₂ as catalysts, very high regiospecificities can be obtained with only the double bonds pendant from the chain being hydrocarboxylated. When using PdCl₂ as catalyst, in the presence of CuCl₂ and O₂, hydrocarboxylation takes place both at the pendant carbon-carbon double bonds and back bone carbon-carbon double bonds. Complete hydrocarboxylation of all the carbon-carbon double bonds in polybutadiene can be carried out by sequential catalytic reaction i.e., catalysis by [PdCl₂(PPh₃)₂]/SnCl₂ followed by (recatalysis) [PdCl₂(PPh₃) ₂]/PPh₃. A new method based on ¹H and ¹³C n.m.r. has been developed to characterise polybutadienes and their hydrocarboxylated products. The hydrocarboxylation reaction catalysed by [PdCl₂(PPh₃) ₂]/SnCl₂ is truly homogeneous although catalytic decomposition is a problem because there exists a small temperature window between the onset of catalysis and the onset of catalytic decomposition. Unlike the starting materials the products, which are solids with melting points well above the room temperature are soluble in organic solvents or dilute base and have been shown to have corrosion inhibition and wood preservation properties.
1992-01-01T00:00:00ZPondicherry, NarayananPolybutadiene having varying degrees of 1,4 and 1,2 units (0 - 100% cis, 14 - 60 % trans, 20-88 % pendant carbon-carbon double bonds) have been reacted with carbon monoxide in the presence of water and palladium based catalysts to give new polymers in which the double bonds are hydrocarboxylated. When using [PdCl₂(PPh₃)₂]/SnCl₂ as catalysts, very high regiospecificities can be obtained with only the double bonds pendant from the chain being hydrocarboxylated. When using PdCl₂ as catalyst, in the presence of CuCl₂ and O₂, hydrocarboxylation takes place both at the pendant carbon-carbon double bonds and back bone carbon-carbon double bonds. Complete hydrocarboxylation of all the carbon-carbon double bonds in polybutadiene can be carried out by sequential catalytic reaction i.e., catalysis by [PdCl₂(PPh₃)₂]/SnCl₂ followed by (recatalysis) [PdCl₂(PPh₃) ₂]/PPh₃. A new method based on ¹H and ¹³C n.m.r. has been developed to characterise polybutadienes and their hydrocarboxylated products. The hydrocarboxylation reaction catalysed by [PdCl₂(PPh₃) ₂]/SnCl₂ is truly homogeneous although catalytic decomposition is a problem because there exists a small temperature window between the onset of catalysis and the onset of catalytic decomposition. Unlike the starting materials the products, which are solids with melting points well above the room temperature are soluble in organic solvents or dilute base and have been shown to have corrosion inhibition and wood preservation properties.Studies of quenching of excited states of aromatic molecules in polymer matricesJassim, Alwan Nsayiffhttps://hdl.handle.net/10023/152542019-03-29T11:24:56Z1980-01-01T00:00:00ZThe phosphorescence behaviour of a series of polycyclic aromatic compounds has been studied in different polymer matrices. Measurements have been carried out at 77K and from room temperature up to 350K. Studies at 77K have shown that the polymer matrix takes part in some quenching reaction, the rate constant depending on the additive being studied. At higher temperatures non-exponential decays were observed, for polystyrene this phenomenon is very marked. It is proposed that the cause of non-exponential decay is T-T annihilation resulting from mobile triplet exciton migration within the polymer matrix. It is proposed that the triplet levels are 285.9 and 297.4 kJ mole⁻¹ for polystyrene and poly(methylmethacrylate) respectively. The quenching of fluorescence for the polycyclic aromatic additives by oxygen has been examined and unusual plots obtained. At low pressures of oxygen enhanced singlet emission was observed but as the pressure was increased normal Stem-Volmer plots were obtained. Simultaneously as pressure of O₂ increased the triplet emission was very efficiently quenched and the increase in fluorescence was observed. When the phosphorescence ceased the intensity of singlet emission decreased with increasing pressure of O₂. The mechanism proposed to account for this very unusual behaviour involves paramagnetic quenching of the singlet state by the mobile triplet exciton. The increase in fluorescence resulting from removal of the triplet exciton by oxygen is greater than the direct singlet quenching by O₂.
1980-01-01T00:00:00ZJassim, Alwan NsayiffThe phosphorescence behaviour of a series of polycyclic aromatic compounds has been studied in different polymer matrices. Measurements have been carried out at 77K and from room temperature up to 350K. Studies at 77K have shown that the polymer matrix takes part in some quenching reaction, the rate constant depending on the additive being studied. At higher temperatures non-exponential decays were observed, for polystyrene this phenomenon is very marked. It is proposed that the cause of non-exponential decay is T-T annihilation resulting from mobile triplet exciton migration within the polymer matrix. It is proposed that the triplet levels are 285.9 and 297.4 kJ mole⁻¹ for polystyrene and poly(methylmethacrylate) respectively. The quenching of fluorescence for the polycyclic aromatic additives by oxygen has been examined and unusual plots obtained. At low pressures of oxygen enhanced singlet emission was observed but as the pressure was increased normal Stem-Volmer plots were obtained. Simultaneously as pressure of O₂ increased the triplet emission was very efficiently quenched and the increase in fluorescence was observed. When the phosphorescence ceased the intensity of singlet emission decreased with increasing pressure of O₂. The mechanism proposed to account for this very unusual behaviour involves paramagnetic quenching of the singlet state by the mobile triplet exciton. The increase in fluorescence resulting from removal of the triplet exciton by oxygen is greater than the direct singlet quenching by O₂.Some studies of the chemical reactivity of β-lactam antibioticsRobinson, Derek Ihttps://hdl.handle.net/10023/152462019-03-29T11:20:39Z1981-01-01T00:00:00ZRate coefficients for the inactivation of several penicillin in acids and alkalis at 30°C have been determined by means of ultraviolet spectroscopy. The case of benzylpenicillin, though well investigated in the past, has been studied again and, in the light of new experiments, a scheme detailing the proportions of the various degradation products has been proposed. A number of substituted phenylpenicillins have been synthesised, and their reactions with acid have been investigated. Product analysis was carried out by means of TLG and NMR studies, the degradation products (penicilloic, penilloic, penillic and penicillenic acids) having been previously prepared and characterised. From the manner in which the phenyl substituent on the penicillin affects the rate coefficient, it is deduced that the mechanism of inactivation by acids involves a rate-determining intramolecular attack by the side-chain carbonyl group on the protonated β-lactam function. An intermediate oxazolone-thiazolidine structure is formed, which then reacts further by three different pathways. The proportions of the products obtained from the phenylpenicillins are different from those obtained from benazylpenicillin, principally because the phenylpenicillenic acids are easier to form and are less reactive towards acid than is benzylpenicillenic acid. The imidazole-catalysed isomerisation of benzylpenicillin into penicillenic acid has been studied. This reaction was investigated using a number of substituted imidazoles and, from the rate equations which were obtained, a unified reaction mechanism has been proposed. This involves a rate-determining proton-transfer to an intermediate penicilloylimidazole complex, which is followed by fast ring opening and expulsion of imidazole. Some studies on the novel mono-cyclic β-lactam antibiotic nocardicin A have been carried out; its reaction in dilute and moderately-concentrated acid has been studied. It is proposed that the mechanism of hydrolysis involves a fast β-lactam cleavage followed by slower hydrolysis of the oxime function. Unlike most oximes, that of nocardicin A was found to hydrolyse faster as the acidity was increased. It is suggested that this unusual behaviour arises from the proximity of an amide group to the oxime. Similar behaviour has been observed for benzoyl formamide oxime.
1981-01-01T00:00:00ZRobinson, Derek IRate coefficients for the inactivation of several penicillin in acids and alkalis at 30°C have been determined by means of ultraviolet spectroscopy. The case of benzylpenicillin, though well investigated in the past, has been studied again and, in the light of new experiments, a scheme detailing the proportions of the various degradation products has been proposed. A number of substituted phenylpenicillins have been synthesised, and their reactions with acid have been investigated. Product analysis was carried out by means of TLG and NMR studies, the degradation products (penicilloic, penilloic, penillic and penicillenic acids) having been previously prepared and characterised. From the manner in which the phenyl substituent on the penicillin affects the rate coefficient, it is deduced that the mechanism of inactivation by acids involves a rate-determining intramolecular attack by the side-chain carbonyl group on the protonated β-lactam function. An intermediate oxazolone-thiazolidine structure is formed, which then reacts further by three different pathways. The proportions of the products obtained from the phenylpenicillins are different from those obtained from benazylpenicillin, principally because the phenylpenicillenic acids are easier to form and are less reactive towards acid than is benzylpenicillenic acid. The imidazole-catalysed isomerisation of benzylpenicillin into penicillenic acid has been studied. This reaction was investigated using a number of substituted imidazoles and, from the rate equations which were obtained, a unified reaction mechanism has been proposed. This involves a rate-determining proton-transfer to an intermediate penicilloylimidazole complex, which is followed by fast ring opening and expulsion of imidazole. Some studies on the novel mono-cyclic β-lactam antibiotic nocardicin A have been carried out; its reaction in dilute and moderately-concentrated acid has been studied. It is proposed that the mechanism of hydrolysis involves a fast β-lactam cleavage followed by slower hydrolysis of the oxime function. Unlike most oximes, that of nocardicin A was found to hydrolyse faster as the acidity was increased. It is suggested that this unusual behaviour arises from the proximity of an amide group to the oxime. Similar behaviour has been observed for benzoyl formamide oxime.Studies of some condensed polyazaheteroaromatic compoundsShepherd, Tomhttps://hdl.handle.net/10023/152422019-03-29T11:24:46Z1984-01-01T00:00:00ZThe cyanide induced cyclisation of a number of substituted 2-acetamido-N-(o-nitrobenzylidene)anilines was investigated, resulting in the formation of the appropriate unambiguously substituted quinoxalino[2,3-o]cinnolines. During the course of this study, it was found that by-products were formed during the reaction. These were investigated briefly, and found to be the 5-oxide of the parent quinoxalino[2,3-o]cinnoline, and a 2-amino-3-(o-nitrophenyl)-quinoxaline, thought to be formed by aerial oxidation of intermediates in the cyclisation process. The reaction of a number of substituted quinoxalinocinnolines with gaseous hydrogen halides was investigated. It was found that those quinoxalinocinnolines with no substituent at position 10 underwent chlorination at this site, by apparent replacement of a hydrogen atom with a chlorine atom. When compounds with substituents at position 10 were reacted, chlorination occurred at position 9 in a few cases, failed in a few others, and often gave product mixtures. With the aid of theoretical studies carried out on the chlorination process, a mechanism for chlorination is proposed, that attempts to explain the distribution of products. An investigation was carried out on quinoxalinocinnolines with halogeno-substituents, in order to determine whether the substituents are labile to methoxide ion. It was found that chlorine at position 10 was easily replaced in mono and dichloro-derivatives, while chlorine at position 9 was either resistant to replacement by methoxide, or was much less reactive than the chlorine at position 10. Bromine at position 10 was found to be relatively unreactive, while bromine at position 9 appeared totally inert. The ¹H n.m.r. and mass spectra of the quinoxalino-[2,3-o]cinnolines are discussed in detail.
1984-01-01T00:00:00ZShepherd, TomThe cyanide induced cyclisation of a number of substituted 2-acetamido-N-(o-nitrobenzylidene)anilines was investigated, resulting in the formation of the appropriate unambiguously substituted quinoxalino[2,3-o]cinnolines. During the course of this study, it was found that by-products were formed during the reaction. These were investigated briefly, and found to be the 5-oxide of the parent quinoxalino[2,3-o]cinnoline, and a 2-amino-3-(o-nitrophenyl)-quinoxaline, thought to be formed by aerial oxidation of intermediates in the cyclisation process. The reaction of a number of substituted quinoxalinocinnolines with gaseous hydrogen halides was investigated. It was found that those quinoxalinocinnolines with no substituent at position 10 underwent chlorination at this site, by apparent replacement of a hydrogen atom with a chlorine atom. When compounds with substituents at position 10 were reacted, chlorination occurred at position 9 in a few cases, failed in a few others, and often gave product mixtures. With the aid of theoretical studies carried out on the chlorination process, a mechanism for chlorination is proposed, that attempts to explain the distribution of products. An investigation was carried out on quinoxalinocinnolines with halogeno-substituents, in order to determine whether the substituents are labile to methoxide ion. It was found that chlorine at position 10 was easily replaced in mono and dichloro-derivatives, while chlorine at position 9 was either resistant to replacement by methoxide, or was much less reactive than the chlorine at position 10. Bromine at position 10 was found to be relatively unreactive, while bromine at position 9 appeared totally inert. The ¹H n.m.r. and mass spectra of the quinoxalino-[2,3-o]cinnolines are discussed in detail.Some studies in hydride transferPayne, Henry Arthur Sheldonhttps://hdl.handle.net/10023/152392019-03-29T11:22:19Z1966-01-01T00:00:00ZThe term “hydride-transfer” is used to describe the acquisition in a single step of a hydrogen nucleus together with a pair of electrons by one electrophilic centre at the expense of another, either in the same or in another module. This process is distinguished from proton-transfer by the absence of isotopic exchange with the labile protons of the medium and by the nature of the polarity at the point of reaction. This thesis is divided into three parts. Part A commences with a brief survey of the hydride-transfer reaction in its widest sense, followed by a discussion of the reagents which may act as hydride donors or acceptors. In conclusion some reactions involving quinones and amines are dealt with. Part B is a discussion of the result of a series of experiments involving carbonium ions and high potential quinones as hydride acceptors and also of some related experiments. Part C, complementary to Part B, is devoted to the description of experimental details.
1966-01-01T00:00:00ZPayne, Henry Arthur SheldonThe term “hydride-transfer” is used to describe the acquisition in a single step of a hydrogen nucleus together with a pair of electrons by one electrophilic centre at the expense of another, either in the same or in another module. This process is distinguished from proton-transfer by the absence of isotopic exchange with the labile protons of the medium and by the nature of the polarity at the point of reaction. This thesis is divided into three parts. Part A commences with a brief survey of the hydride-transfer reaction in its widest sense, followed by a discussion of the reagents which may act as hydride donors or acceptors. In conclusion some reactions involving quinones and amines are dealt with. Part B is a discussion of the result of a series of experiments involving carbonium ions and high potential quinones as hydride acceptors and also of some related experiments. Part C, complementary to Part B, is devoted to the description of experimental details.Some electrophilic reactions of pyrrole and related compoundsAlexander, Robert Scotthttps://hdl.handle.net/10023/152352019-03-29T11:23:11Z1977-01-01T00:00:00ZChapter One describes the mechanism of acid-catalysed hydrogen-exchange in methylpyrroles. Using buffer solutions it was found that this reaction is subject to general acid catalysis, confirming an A-S[sub]E2 mechanism. It was also found that the rate of hydrogen-exchange at the β-position of pyrrole was similar to that at the alpha-position. This seems to conflict with the known preference for alpha-substituted products obtained under 'synthetic' experimental conditions. However, both these findings have been rationalised in terms of the electron densities and the localisation energies prevalent in the pyrrole ring. The mechanism of the reaction between 4-dimethylamino-benzaldehyde (DMAB) and pyrroles in acid solution (Ehrlich's Reaction) is described in Chapter Two. This consists of a rate-determining electrophilic attack of O-protonated DMAB on unprotonated pyrrole followed by a rapid loss of a water molecule to give the highly-coloured conjugated product. The activating effect of methyl groups at various positions on the pyrrole ring on this reaction was also determined. Acid-catalysed hydrogen-exchange in methylthiophens is the subject of Chapter Three. In contrast to the situation found in pyrroles, the rate of exchange at the β-position of thiophen is much slower than at the alpha-position. An explanation for this is found in the difference in electron densities found in the two ring systems. The activating effect of methyl groups at various positions on the thiophen ring on the exchange reaction was also studied. It was found that these effects were not additive. The activating parameters for the exchange reactions at the alpha- and β-positions were also calculated and discussed. In Chapter Four the practical difficulties encountered in the quantitative determination of the clinically important pyrroles porphobilinogen and cryptopyrrole are discussed. A series of reagents were used in an attempt to improve on the present colourimetric test employing DMAB. It was found that the measurement of cryptopyrrole under acidic conditions is straightforward using DMAB, 2,4,6-trimethoxybenzaldehyde (TMB) or 2,4-bis(dimethylamino)benzaldehyde (BDMAB). In contrast to this situation, however, none of the reagents tested gave a completely stable coloured solution when reacted with aqueous porphobilinogen solutions. A test was devised, however, using the BDMAB reagent in acid solution which gave a colour, stable for up to 40 minutes, when reacted with test porphobilinogen solutions.
1977-01-01T00:00:00ZAlexander, Robert ScottChapter One describes the mechanism of acid-catalysed hydrogen-exchange in methylpyrroles. Using buffer solutions it was found that this reaction is subject to general acid catalysis, confirming an A-S[sub]E2 mechanism. It was also found that the rate of hydrogen-exchange at the β-position of pyrrole was similar to that at the alpha-position. This seems to conflict with the known preference for alpha-substituted products obtained under 'synthetic' experimental conditions. However, both these findings have been rationalised in terms of the electron densities and the localisation energies prevalent in the pyrrole ring. The mechanism of the reaction between 4-dimethylamino-benzaldehyde (DMAB) and pyrroles in acid solution (Ehrlich's Reaction) is described in Chapter Two. This consists of a rate-determining electrophilic attack of O-protonated DMAB on unprotonated pyrrole followed by a rapid loss of a water molecule to give the highly-coloured conjugated product. The activating effect of methyl groups at various positions on the pyrrole ring on this reaction was also determined. Acid-catalysed hydrogen-exchange in methylthiophens is the subject of Chapter Three. In contrast to the situation found in pyrroles, the rate of exchange at the β-position of thiophen is much slower than at the alpha-position. An explanation for this is found in the difference in electron densities found in the two ring systems. The activating effect of methyl groups at various positions on the thiophen ring on the exchange reaction was also studied. It was found that these effects were not additive. The activating parameters for the exchange reactions at the alpha- and β-positions were also calculated and discussed. In Chapter Four the practical difficulties encountered in the quantitative determination of the clinically important pyrroles porphobilinogen and cryptopyrrole are discussed. A series of reagents were used in an attempt to improve on the present colourimetric test employing DMAB. It was found that the measurement of cryptopyrrole under acidic conditions is straightforward using DMAB, 2,4,6-trimethoxybenzaldehyde (TMB) or 2,4-bis(dimethylamino)benzaldehyde (BDMAB). In contrast to this situation, however, none of the reagents tested gave a completely stable coloured solution when reacted with aqueous porphobilinogen solutions. A test was devised, however, using the BDMAB reagent in acid solution which gave a colour, stable for up to 40 minutes, when reacted with test porphobilinogen solutions.Preparation and pyrolysis of some sulphinyl-stabilised phosphorus ylidesRyan, Bruce Martinhttps://hdl.handle.net/10023/152332022-05-10T10:04:44Z1996-01-01T00:00:00ZThe results of further investigation into the pyrolytic behaviour of alkane- and arenesulphinyl alkoxycarbonyltriphenylphosphoranes are reported. Flash vacuum pyrolysis (FVP) of these ylides at 600°C gives vinyl sulphides, sulphides and aldehydes. The vinyl sulphides and aldehydes are explained by assuming extrusion of Ph₃P=O, followed by C-H insertion in the resulting carbene to give a β-lactone. This can either lose CO₂ to give the vinyl sulphides or fragment in the opposite sense to give the aldehydes together with unknown products. The sulphides are explained by assuming extrusion of Ph3P, followed by successive loss of CO and CO₂. A variable temperature study of Ph₃P=C(CO₂Et)SOEt has revealed a complex pattern of interdependent restricted rotation of both ester and sulphinyl groups. FVP of the alkanesulphinylbenzylidenetriphenylphosphoranes at 500°C gives the alkyl thiolobenzoates by oxygen transfer in the carbene formed by extrusion of Ph3P. The first three examples of arenesulphinyl benzylidenetriphenylphosphoranes have been prepared. FVP of these at 500°C gives a mixture containing aryl thiolobenzoates formed as above together with ketones, sulphides, thiols, disulphides and stilbene. Mechanisms are suggested for the formation of these products. Four new alkyl sulphonyldiazoacetates have been prepared. FVP of these at 600°C gives vinyl sulphones, while at lower temperatures, products resulting from transfer of oxygen in the carbenes formed by extrusion of N₂ predominate.
1996-01-01T00:00:00ZRyan, Bruce MartinThe results of further investigation into the pyrolytic behaviour of alkane- and arenesulphinyl alkoxycarbonyltriphenylphosphoranes are reported. Flash vacuum pyrolysis (FVP) of these ylides at 600°C gives vinyl sulphides, sulphides and aldehydes. The vinyl sulphides and aldehydes are explained by assuming extrusion of Ph₃P=O, followed by C-H insertion in the resulting carbene to give a β-lactone. This can either lose CO₂ to give the vinyl sulphides or fragment in the opposite sense to give the aldehydes together with unknown products. The sulphides are explained by assuming extrusion of Ph3P, followed by successive loss of CO and CO₂. A variable temperature study of Ph₃P=C(CO₂Et)SOEt has revealed a complex pattern of interdependent restricted rotation of both ester and sulphinyl groups. FVP of the alkanesulphinylbenzylidenetriphenylphosphoranes at 500°C gives the alkyl thiolobenzoates by oxygen transfer in the carbene formed by extrusion of Ph3P. The first three examples of arenesulphinyl benzylidenetriphenylphosphoranes have been prepared. FVP of these at 500°C gives a mixture containing aryl thiolobenzoates formed as above together with ketones, sulphides, thiols, disulphides and stilbene. Mechanisms are suggested for the formation of these products. Four new alkyl sulphonyldiazoacetates have been prepared. FVP of these at 600°C gives vinyl sulphones, while at lower temperatures, products resulting from transfer of oxygen in the carbenes formed by extrusion of N₂ predominate.Studies in organophosphorus chemistryMaynard, Judith Annhttps://hdl.handle.net/10023/152302019-03-29T11:22:07Z1966-01-01T00:00:00ZVarious methods of alkylation of the >PO₂⁻,>-PS₂⁻ and >POS⁻ ions have been investigated. Ethyl miethylphosphonate reacted with 2-methyloxiran to give ethyl 2-hydroxypropyl methylphosphonate and with p-nitrobenaonitrile oxide to give ethyl 0a-hydroxyimino-4-nitrobenzyl methylphosphonate, a new type of organophosphorus ester, which was shown to hydrolyse in acid solution about 10⁷ times faster than a simple phosphonate ester. A kinetic study of this remarkably fast hydrolysis suggests a mechanism involving neighbouring group participation of the hydroximino- moiety. Alkylation of ethyl methylphosphonate was not achieved by reaction with oxasiridines. Reaction of dihgxylphosphinic acid with p-nitrobenzonitrile oxide gave a-hydroxyimino-4-nitrobenzyl dihexylphosphinate. This ester was stable in acid solution but both the a-hydroxyimino-4-nitrobenzyl dihexylphosphinate and phosphinate esters decomposed at pH5 to give p-nitroaniline. A possible route of decomposition involving a Lossen rearrangement is suggested. Alkylation products were not isolated when OO-diethyl phosphoro-thioate and -dithioate reacted with p-nitrobenzo-nitrile oxide; the products obtained indicate that an alkylation, similar to that of the >PO₂⁻ ion, had occurred but subsequent facile decomposition of the neutral anhydrous esters had taken place. A possible application of the realkylation and subsequent decomposition of the >PO₂⁻ ion, brought about by reaction with nitrile oxide, in the reactivation of "aged" phosphonylated cholinesterase is discussed. The reaction of propyl iodide with dialkyl phosphoramidates has been shown to cause an alkyl exchange process on both oxygen and nitrogen atoms, together with P-N bond fission. The phosphorylation of phenol to give triphonyl phosphate was accomplished by heating with diphenyl N-propylphosphoramidate in the presence of propyl iodide.
1966-01-01T00:00:00ZMaynard, Judith AnnVarious methods of alkylation of the >PO₂⁻,>-PS₂⁻ and >POS⁻ ions have been investigated. Ethyl miethylphosphonate reacted with 2-methyloxiran to give ethyl 2-hydroxypropyl methylphosphonate and with p-nitrobenaonitrile oxide to give ethyl 0a-hydroxyimino-4-nitrobenzyl methylphosphonate, a new type of organophosphorus ester, which was shown to hydrolyse in acid solution about 10⁷ times faster than a simple phosphonate ester. A kinetic study of this remarkably fast hydrolysis suggests a mechanism involving neighbouring group participation of the hydroximino- moiety. Alkylation of ethyl methylphosphonate was not achieved by reaction with oxasiridines. Reaction of dihgxylphosphinic acid with p-nitrobenzonitrile oxide gave a-hydroxyimino-4-nitrobenzyl dihexylphosphinate. This ester was stable in acid solution but both the a-hydroxyimino-4-nitrobenzyl dihexylphosphinate and phosphinate esters decomposed at pH5 to give p-nitroaniline. A possible route of decomposition involving a Lossen rearrangement is suggested. Alkylation products were not isolated when OO-diethyl phosphoro-thioate and -dithioate reacted with p-nitrobenzo-nitrile oxide; the products obtained indicate that an alkylation, similar to that of the >PO₂⁻ ion, had occurred but subsequent facile decomposition of the neutral anhydrous esters had taken place. A possible application of the realkylation and subsequent decomposition of the >PO₂⁻ ion, brought about by reaction with nitrile oxide, in the reactivation of "aged" phosphonylated cholinesterase is discussed. The reaction of propyl iodide with dialkyl phosphoramidates has been shown to cause an alkyl exchange process on both oxygen and nitrogen atoms, together with P-N bond fission. The phosphorylation of phenol to give triphonyl phosphate was accomplished by heating with diphenyl N-propylphosphoramidate in the presence of propyl iodide.The reaction of aromatic nitro-compounds with tervalent phosphorus reagentsTodd, Michael Jameshttps://hdl.handle.net/10023/152262019-03-29T11:22:45Z1967-01-01T00:00:00ZAs a synthetic procedure, the deoxygenation of aromatic nitro-compounds by tervalent organophosphorus compounds has been extended to include new routes to the anthranil and phenothiazine nuclei. Synthesis of anthranils from 2-nitrophenyl ketones has been exemplified by the preparation of 3-Phenylanthranil, 3-styrylanthranil and 5-chloro-3-methylanthranil from 2-nitro-benzophenone, 2 -nitrochalcone and 5-Chloro-2-nitroacetophenone respectively. The preparation of phenothiazines from 2-nitro-biaryl sulphides has been studied more extensively. It was found that when successful, this ring closure gave the cyclised product in about 55% yield. Rather more than half the sulphides used, however, gave no products or only a very low yield, and no rational means of predicting the success of a given ring closure could be found. Triethyl phosphite was the only phosphorus compound found to be capable of effecting this cyclisation. The use of several other phosphorus compounds was investigated, but although deoxygenation of the nitro-group undoubtedly took place, as evidenced by the large amounts of tar formed, no cyclised products could be isolated. Although a comprehensive investigation was not undertaken, the results of two experiments suggested that a considerable improvement in the yields of the phenothiazines could be achieved by carrying out the deoxygenations in a solvent (as opposed to pure phosphorus compound) and thus, reducing the extent of tar-forming side reactions. In addition, an unidentified product has been obtained from the reaction of 3-(o-nitrophenyl)coumarin with triethyl phosphate. Several unsuccessful attempts were made to synthesise a seven membered ring system. As part of an examination of the mechanism of the deoxygenation, the rate of reaction of a series of phosphorus compounds with 2-nitrobiphenyl was studied. It was found that phosphorus compounds with electron donating groups attached to the phosphorus atom reacted more rapidly, suggesting that the rate determining step involved a nucleophilic attack by phosphorus. No adequate explanation could be advanced for the finding that of all the phosphorus compounds studied, diethyl methylphosphonite reacted most rapidly. While the reactions of triethyl and triisopropyl phosphites were first order with respect to nitrobiphenyl, the reactions of hexaethyl phosphorous triamide and diethyl methylphosphonite appeared to be second order. A detailed kinetic study would be necessary to confirm this observation and investigate the fundamental change in mechanism which it implies. The possibility of the formation of nitroso-compounds as intermediates in the deoxygenation of the nitro-compounds has been discussed, and an unsuccessful attempt to trap such an intermediate has been made. Further attempts ought to be made in this direction and should be concentrated on finding a compound which will react more rapidly with the nitroso-compound than does triethyl phosphite. Such a trapping agent must also be capable of operating in the presence of an excess of nitro-compound. Much of the work in this thesis has been directed towards establishing whether an electron deficient nitrene intermediate is formed during the course of the deoxygenation of an aromatic nitro-compound. Although no one experiment could be regarded as conclusive, the overall weight of evidence argued convincingly in favour of this type of intermediate.
1967-01-01T00:00:00ZTodd, Michael JamesAs a synthetic procedure, the deoxygenation of aromatic nitro-compounds by tervalent organophosphorus compounds has been extended to include new routes to the anthranil and phenothiazine nuclei. Synthesis of anthranils from 2-nitrophenyl ketones has been exemplified by the preparation of 3-Phenylanthranil, 3-styrylanthranil and 5-chloro-3-methylanthranil from 2-nitro-benzophenone, 2 -nitrochalcone and 5-Chloro-2-nitroacetophenone respectively. The preparation of phenothiazines from 2-nitro-biaryl sulphides has been studied more extensively. It was found that when successful, this ring closure gave the cyclised product in about 55% yield. Rather more than half the sulphides used, however, gave no products or only a very low yield, and no rational means of predicting the success of a given ring closure could be found. Triethyl phosphite was the only phosphorus compound found to be capable of effecting this cyclisation. The use of several other phosphorus compounds was investigated, but although deoxygenation of the nitro-group undoubtedly took place, as evidenced by the large amounts of tar formed, no cyclised products could be isolated. Although a comprehensive investigation was not undertaken, the results of two experiments suggested that a considerable improvement in the yields of the phenothiazines could be achieved by carrying out the deoxygenations in a solvent (as opposed to pure phosphorus compound) and thus, reducing the extent of tar-forming side reactions. In addition, an unidentified product has been obtained from the reaction of 3-(o-nitrophenyl)coumarin with triethyl phosphate. Several unsuccessful attempts were made to synthesise a seven membered ring system. As part of an examination of the mechanism of the deoxygenation, the rate of reaction of a series of phosphorus compounds with 2-nitrobiphenyl was studied. It was found that phosphorus compounds with electron donating groups attached to the phosphorus atom reacted more rapidly, suggesting that the rate determining step involved a nucleophilic attack by phosphorus. No adequate explanation could be advanced for the finding that of all the phosphorus compounds studied, diethyl methylphosphonite reacted most rapidly. While the reactions of triethyl and triisopropyl phosphites were first order with respect to nitrobiphenyl, the reactions of hexaethyl phosphorous triamide and diethyl methylphosphonite appeared to be second order. A detailed kinetic study would be necessary to confirm this observation and investigate the fundamental change in mechanism which it implies. The possibility of the formation of nitroso-compounds as intermediates in the deoxygenation of the nitro-compounds has been discussed, and an unsuccessful attempt to trap such an intermediate has been made. Further attempts ought to be made in this direction and should be concentrated on finding a compound which will react more rapidly with the nitroso-compound than does triethyl phosphite. Such a trapping agent must also be capable of operating in the presence of an excess of nitro-compound. Much of the work in this thesis has been directed towards establishing whether an electron deficient nitrene intermediate is formed during the course of the deoxygenation of an aromatic nitro-compound. Although no one experiment could be regarded as conclusive, the overall weight of evidence argued convincingly in favour of this type of intermediate.N-NitrosoacylarylaminesThomson, Jemima Birrellhttps://hdl.handle.net/10023/152252019-03-29T11:24:50Z1968-01-01T00:00:00ZThe decompositions of N-nitrosoacylarylamines in benzene and in carbon tetrachloride have been investigated. The reaction products of N-nitrosobenzanilldes parallel those of N-nitrosoacetanilides, carboxylic acids being the major products from almost all reactions carried out in both benzene and carbon tetrachloride. Carboxylic anhydrides, hitherto unreported products, have been isolated from reactions in carbon tetrachloride. The observed displacement of a bromo or uitro substituent in o- or p-positions in the amino moiety of the nitrosoamide by a chloride or benzoate ion during the formation of aryl halides and substituted phenyl benzoates is in contrast to Suschitsky's results. In general, the major part of the reaction appears to be abstraction by a carboxylate anion of hydrogen from the o-position in the amino moiety of the nitrosoamide to form the carboxylic acid. However, when both o-positions in the amino moiety of the nitrosoamide are substituted, the reaction proceeds primarily by nucleophilic displacement of a substituent by the carboxylate anion. The decomposition of N-nitrosoacetanilide in carbon tetrachloride gives a benzynoid-type adduct with 2,3,4,5-tetraphenylcyclopentadienone, with consequent suppression of the formation of chlorobenzene, which is a major product from a reaction carried out in the absence of the above diene. Appropriate benzynoid-type adducts are also formed in reactions of N-nitrosobenzanilides with 2,3,4,5 tetraphenylcyclopentadienone and with anthracene, but not with furan. By the use of substituted N-nitrosobenzanilides, it has been shown that, for appreciable adduct formation with 2,3,4,5-tetraphenylcyclopentadienone, a substituent must be in the m-position in the amino moiety, i.e. o- or p- to the hydrogen which is being removed in the formation of the carboxylic acid. The nature of the acyl moiety of the molecule has some influence on the formation of the adduct, but the nature of the solvent appears to have little influence on the yield of adduct formed. In reactions in which high yields of benzynoid-type adducts are obtained, the only other major product isolated is the appropriate carboxylic acid. True aryne intermediates are discounted, and it is suggested that the intermediate is dipolar in nature. A reaction scheme involving radicals, previously suggested by Riichardt et al. can be modified to account for the reaction in benzene. The reaction in carbon tetrachloride, however, appears to follow a different reaction path, and probably involves radicals to a slight extent only, the main reaction being ionic.
1968-01-01T00:00:00ZThomson, Jemima BirrellThe decompositions of N-nitrosoacylarylamines in benzene and in carbon tetrachloride have been investigated. The reaction products of N-nitrosobenzanilldes parallel those of N-nitrosoacetanilides, carboxylic acids being the major products from almost all reactions carried out in both benzene and carbon tetrachloride. Carboxylic anhydrides, hitherto unreported products, have been isolated from reactions in carbon tetrachloride. The observed displacement of a bromo or uitro substituent in o- or p-positions in the amino moiety of the nitrosoamide by a chloride or benzoate ion during the formation of aryl halides and substituted phenyl benzoates is in contrast to Suschitsky's results. In general, the major part of the reaction appears to be abstraction by a carboxylate anion of hydrogen from the o-position in the amino moiety of the nitrosoamide to form the carboxylic acid. However, when both o-positions in the amino moiety of the nitrosoamide are substituted, the reaction proceeds primarily by nucleophilic displacement of a substituent by the carboxylate anion. The decomposition of N-nitrosoacetanilide in carbon tetrachloride gives a benzynoid-type adduct with 2,3,4,5-tetraphenylcyclopentadienone, with consequent suppression of the formation of chlorobenzene, which is a major product from a reaction carried out in the absence of the above diene. Appropriate benzynoid-type adducts are also formed in reactions of N-nitrosobenzanilides with 2,3,4,5 tetraphenylcyclopentadienone and with anthracene, but not with furan. By the use of substituted N-nitrosobenzanilides, it has been shown that, for appreciable adduct formation with 2,3,4,5-tetraphenylcyclopentadienone, a substituent must be in the m-position in the amino moiety, i.e. o- or p- to the hydrogen which is being removed in the formation of the carboxylic acid. The nature of the acyl moiety of the molecule has some influence on the formation of the adduct, but the nature of the solvent appears to have little influence on the yield of adduct formed. In reactions in which high yields of benzynoid-type adducts are obtained, the only other major product isolated is the appropriate carboxylic acid. True aryne intermediates are discounted, and it is suggested that the intermediate is dipolar in nature. A reaction scheme involving radicals, previously suggested by Riichardt et al. can be modified to account for the reaction in benzene. The reaction in carbon tetrachloride, however, appears to follow a different reaction path, and probably involves radicals to a slight extent only, the main reaction being ionic.The reactions of tervalent phosphorus reagents with aromatic nitro-compoundsSears, David Johnhttps://hdl.handle.net/10023/152232019-03-29T11:23:35Z1968-01-01T00:00:00ZThe reactions of tervalent phosphorus reagents with a number of aromatic nitro-compounds have been investigated. While it was expected that such reactions would give further examples of the deoxygenation and further reaction of the nitro-group, possibly via a reactive nitrene intermediates in fact, two, different, novel displacements of the nitro-group were found. In the first case, reaction of o-dinitrobenzene and related compounds with tervalent phosphorus reagents gave a series of phosphonates, phosphinates and phosphine oxides, in high yield, with the phosphorus atom bonded directly to the aromatic system, generally with an o-nitro-group still present in the final product. A mechanism involving nucleophilic aromatic substitution by the phosphorus reagent, with the displacement of the nitro-group as ethyl nitrite, was suggested. In the second case, reaction of p-nitrotoluene and p-ethylnitrobenzene, for example, with triethyl phosphite, gave low yields of diethyl p-tolyl- and p-ethylphenylphosphonate. As there is no activation of this nitro-group towards aromatic nucleophilic substitution, a mechanism involving attack on an oxygen of the nitro-group by the phosphorus reagent, with sub- sequent rearrangement through a four-membered intermediate was proposed. The other products of the reactions of o-alkyl-nitrosobenzenes and alkylnitrobenzenes with trialkyl phosphites were, in general, indicative of the participation, in the reaction, of a nitrene intermediate. The similarity of the products formed to those found in established examples of the reactions of nitrene intermediates, was noticed. The mechanism of this reaction was discussed in detail.
1968-01-01T00:00:00ZSears, David JohnThe reactions of tervalent phosphorus reagents with a number of aromatic nitro-compounds have been investigated. While it was expected that such reactions would give further examples of the deoxygenation and further reaction of the nitro-group, possibly via a reactive nitrene intermediates in fact, two, different, novel displacements of the nitro-group were found. In the first case, reaction of o-dinitrobenzene and related compounds with tervalent phosphorus reagents gave a series of phosphonates, phosphinates and phosphine oxides, in high yield, with the phosphorus atom bonded directly to the aromatic system, generally with an o-nitro-group still present in the final product. A mechanism involving nucleophilic aromatic substitution by the phosphorus reagent, with the displacement of the nitro-group as ethyl nitrite, was suggested. In the second case, reaction of p-nitrotoluene and p-ethylnitrobenzene, for example, with triethyl phosphite, gave low yields of diethyl p-tolyl- and p-ethylphenylphosphonate. As there is no activation of this nitro-group towards aromatic nucleophilic substitution, a mechanism involving attack on an oxygen of the nitro-group by the phosphorus reagent, with sub- sequent rearrangement through a four-membered intermediate was proposed. The other products of the reactions of o-alkyl-nitrosobenzenes and alkylnitrobenzenes with trialkyl phosphites were, in general, indicative of the participation, in the reaction, of a nitrene intermediate. The similarity of the products formed to those found in established examples of the reactions of nitrene intermediates, was noticed. The mechanism of this reaction was discussed in detail.E.S.R. studies of the decomposition of acylarylnitrosaminesPaton, Robert Michaelhttps://hdl.handle.net/10023/152192019-03-29T11:23:42Z1969-01-01T00:00:00ZThe E. S. R. spectra observed during the decomposition of acylarylnitrosamines in four series of solvents have been investigated, and the mechanisms of the reactions discussed in terms of the radicals involved. For aromatic hydrocarbons two signals were detected. The first was that due to the (N-phenylacetamido)phenyl-nitroxide pi-radical, as reported by Chalfont and Perkins), while the second was attributed to the phenyldiazotate o-radical. The structure of these radicals is discussed in the light of a study of the spectra resulting from variation of the acyl and aryl groups of the nitrosamide and of theoretical calculations using the McLachlan and CNDO methods. The mechanism originally proposed by Ruchardt and Freudenberg is preferred to that of Perkins, in view of the failure to detect the chain-carrier radical of the latter scheme in some of the solvents, the intensity of the phenyldiazotate signal remaining constant throughout. For ethers the two signals observed were assigned to (N-phenylacetamido) phenylnitroxide and (N-phenylacetamido)-1-alkoxyalkylnitroxide resulting from the addition of phenyl and 1-alkoxyalkyl radicals to the nitroso group of the nitrosamide. The mechanism proposed, which is also applicable to the reaction in alcohols, is based on that currently acceptable for the decomposition of diazonium salts in ethers. Whenever possible assignments have been made for the various other signals detected and the mode of formation of the radicals discussed.
1969-01-01T00:00:00ZPaton, Robert MichaelThe E. S. R. spectra observed during the decomposition of acylarylnitrosamines in four series of solvents have been investigated, and the mechanisms of the reactions discussed in terms of the radicals involved. For aromatic hydrocarbons two signals were detected. The first was that due to the (N-phenylacetamido)phenyl-nitroxide pi-radical, as reported by Chalfont and Perkins), while the second was attributed to the phenyldiazotate o-radical. The structure of these radicals is discussed in the light of a study of the spectra resulting from variation of the acyl and aryl groups of the nitrosamide and of theoretical calculations using the McLachlan and CNDO methods. The mechanism originally proposed by Ruchardt and Freudenberg is preferred to that of Perkins, in view of the failure to detect the chain-carrier radical of the latter scheme in some of the solvents, the intensity of the phenyldiazotate signal remaining constant throughout. For ethers the two signals observed were assigned to (N-phenylacetamido) phenylnitroxide and (N-phenylacetamido)-1-alkoxyalkylnitroxide resulting from the addition of phenyl and 1-alkoxyalkyl radicals to the nitroso group of the nitrosamide. The mechanism proposed, which is also applicable to the reaction in alcohols, is based on that currently acceptable for the decomposition of diazonium salts in ethers. Whenever possible assignments have been made for the various other signals detected and the mode of formation of the radicals discussed.Base-induced cyclisations of ortho-substituted nitro-aromaticsMcFarlane, Michael Davidhttps://hdl.handle.net/10023/152092019-03-29T11:21:51Z1988-01-01T00:00:00ZIn Chapter I some of the chemical, biological and physical properties of purine analogues, particularly benzimidazole N-oxides, are briefly discussed. In Chapter II, the preparations of 4-, 5-, 6-, and 7-amino-1H-benzimidazole 3-oxides are described. The methods employed involve base-induced cyclisation of suitably protected aminonitrophenyl glycine derivatives (esters or nitriles) followed by hydrolysis of the ester or nitrile and decarboxylation. In Chapter III, attempts are made to prepare imidazopyridine N-oxides, an area of N-oxide chemistry little explored. Although few derivatives of this class of compound are synthesised, the preparation of the parent 3H-imidazo[4 ,5-b]pyridine 1-oxide is accomplished. In Chapter IV, the possibility of preparing 1-methylbenzimidazole 3-oxides by the methods used in Chapters II and III is investigated, but unexpected results are obtained e.g. cyclisation of O-nitropheny1-sarcosine esters gives 1-hydroxy-4-methylquinoxaline-2, 3-diones. These reactions have instigated an investigation into the general mechanism for the base-induced cyclisations discussed in this thesis.
1988-01-01T00:00:00ZMcFarlane, Michael DavidIn Chapter I some of the chemical, biological and physical properties of purine analogues, particularly benzimidazole N-oxides, are briefly discussed. In Chapter II, the preparations of 4-, 5-, 6-, and 7-amino-1H-benzimidazole 3-oxides are described. The methods employed involve base-induced cyclisation of suitably protected aminonitrophenyl glycine derivatives (esters or nitriles) followed by hydrolysis of the ester or nitrile and decarboxylation. In Chapter III, attempts are made to prepare imidazopyridine N-oxides, an area of N-oxide chemistry little explored. Although few derivatives of this class of compound are synthesised, the preparation of the parent 3H-imidazo[4 ,5-b]pyridine 1-oxide is accomplished. In Chapter IV, the possibility of preparing 1-methylbenzimidazole 3-oxides by the methods used in Chapters II and III is investigated, but unexpected results are obtained e.g. cyclisation of O-nitropheny1-sarcosine esters gives 1-hydroxy-4-methylquinoxaline-2, 3-diones. These reactions have instigated an investigation into the general mechanism for the base-induced cyclisations discussed in this thesis.Nitrene-induced aromatic rearrangementsKulik, Stanleyhttps://hdl.handle.net/10023/152072018-07-10T15:45:24Z1970-01-01T00:00:00ZIt has been shown in this investigation that thermal decomposition of mono-substitutedaryl 2-azidophenyl sulphides and deoxygenation of mono-substitutedaryl 2-nitrophenyl sulphides both proceed via a re-arrangement involving five-membered ring attack of the first-formed nitrene followed by a sigmatropic sulphur shift to give the corresponding phenothiazines. By using deuterium labelling, it has been further shown that the rearrangement occurs even in the unsubstituted 2-nitrophenyl phenyl sulphide. Decomposition of 2,6-disubatitutedaryl 2-azidophenyl sulphides and deoxygenation of 2,6-disubstitutedaryl 2-nitrophenyl sulphides led to some very interesting chemistry. For example, 2,6-dimethyl-phenyl 2-azidophenyl sulphide and 2,6-dimethylphenyl 2-nitrophenyl sulphide gave 5,11-dihydro-4-methyldibenzo[b,e][1,4] thiazepine rather than the isomeric 10,11-dihydro-4-methyldibenzo[b,f][1,i4] thiazepine, while 2,6-dimethoxyphenyl 2-azidophenyl sulphide and 2,6-dimethoxy-phenyl 2-nitrophenyl sulphide both gave 1-methoxyphenothiazine and 1,2-dimethoxyphenothiazine via a rearrangement involving a novel l,4-methoxyl shift. That these and the other examples described herein may be explained by a mechanism analogous to that postulated for the phenothiazine rearrangement was shown by the isolation of 1,4a-dicarbethoxy-4H-phenothiazine, a product analogous to the intermediate postulated, from the deoxygenation of 2,6-dicarbethoxy-phenyl 2-nitrophenyl sulphide.
1970-01-01T00:00:00ZKulik, StanleyIt has been shown in this investigation that thermal decomposition of mono-substitutedaryl 2-azidophenyl sulphides and deoxygenation of mono-substitutedaryl 2-nitrophenyl sulphides both proceed via a re-arrangement involving five-membered ring attack of the first-formed nitrene followed by a sigmatropic sulphur shift to give the corresponding phenothiazines. By using deuterium labelling, it has been further shown that the rearrangement occurs even in the unsubstituted 2-nitrophenyl phenyl sulphide. Decomposition of 2,6-disubatitutedaryl 2-azidophenyl sulphides and deoxygenation of 2,6-disubstitutedaryl 2-nitrophenyl sulphides led to some very interesting chemistry. For example, 2,6-dimethyl-phenyl 2-azidophenyl sulphide and 2,6-dimethylphenyl 2-nitrophenyl sulphide gave 5,11-dihydro-4-methyldibenzo[b,e][1,4] thiazepine rather than the isomeric 10,11-dihydro-4-methyldibenzo[b,f][1,i4] thiazepine, while 2,6-dimethoxyphenyl 2-azidophenyl sulphide and 2,6-dimethoxy-phenyl 2-nitrophenyl sulphide both gave 1-methoxyphenothiazine and 1,2-dimethoxyphenothiazine via a rearrangement involving a novel l,4-methoxyl shift. That these and the other examples described herein may be explained by a mechanism analogous to that postulated for the phenothiazine rearrangement was shown by the isolation of 1,4a-dicarbethoxy-4H-phenothiazine, a product analogous to the intermediate postulated, from the deoxygenation of 2,6-dicarbethoxy-phenyl 2-nitrophenyl sulphide.Reactive intermediates in the chemistry of acetylarylnitrosaminesHarger, Martin James Proctorhttps://hdl.handle.net/10023/152042019-03-29T11:22:41Z1968-01-01T00:00:00ZThe role of aryne intermediates in the reactions of acetylarylnitrosamines in solution has been investigated. Participation by 3-t-butylbenzyne in the decomposition of o-t-butyl-N-nitrosoacetanilide in benzene, leading to m-t-butylphenyl acetate, has been confirmed, although the major product, o-t-butylphenyl acetate, is formed predominantly from o-t-butylphenyl carbonium ions, 5-t-Butyl 1,4-dihydronaphthalene-1,4-endoxide has been isolated from the decomposition in the presence of furan. In common with the o-isomer, m- and p-t-butyl-N-nitroso-acetanilides yield 'aryne adducts' with 2,3,4,5-tetra- phenylcyclopentadienone in benzene. They do not, however, form t-butyl-l,4-dihydronaphthalene-l,4-endoxides with furan, and participation by a true aryne in their reactions and in those of unsubstituted N-nitrosoacetanilide, is discounted. The nature of the arynoid intermediato has not, in spite of the elimination of many possibilities, been conclusively established, but it is probably the dipolar conjugate base formed by removal of an o-proton from the arenediazonium cation. Anomalies similar to those observed in the decomposition of o-t-butyl-N-nitrosoacetanilide are exhibited by 2,5-di-t-butyl-N- nitrosoacetanilide, which affords aryne adducts with both furan and anthracene in greater yield than does the mono-substituted nitrosamide. Aryne participation was not evident in the highly complex decompositions in benzene of 1,4-di-t-butyl-2,5-di-(N-nitrosoacetamido) benzene, 2,5-di-t-butyl-2,5-di-(N-nitrosoacetamido)benzene, and 4-acetoxy-2,5-di-t-butyl-N-nitrosoacetanilide, Formation of 2,5-di-t-butylphenol, 2,5-di-t-butyl-2-benzoquinone, and acetic anhydride in the last-named reaction indicates deacetylation of the intermediate acetoxybenzenediazonium acetate, and suggests that complications in the reactions of the dinitrosamides arise from interaction between the N-nitrosoacetamido substituents. The decompositions of diphenyl[o-(N-nitrosoacetamido)phenyl] phosphine oxide and diethyl o-(N-nitrosoacetamido)phonyl]phosphonate have been studied, and evidence of aryne intermediacy obtained. The results are discussed in terms of currently acceptable mechanisms for the decomposition of N-nitroso- acetanilide and, where necessary, modifications to these are suggested.
1968-01-01T00:00:00ZHarger, Martin James ProctorThe role of aryne intermediates in the reactions of acetylarylnitrosamines in solution has been investigated. Participation by 3-t-butylbenzyne in the decomposition of o-t-butyl-N-nitrosoacetanilide in benzene, leading to m-t-butylphenyl acetate, has been confirmed, although the major product, o-t-butylphenyl acetate, is formed predominantly from o-t-butylphenyl carbonium ions, 5-t-Butyl 1,4-dihydronaphthalene-1,4-endoxide has been isolated from the decomposition in the presence of furan. In common with the o-isomer, m- and p-t-butyl-N-nitroso-acetanilides yield 'aryne adducts' with 2,3,4,5-tetra- phenylcyclopentadienone in benzene. They do not, however, form t-butyl-l,4-dihydronaphthalene-l,4-endoxides with furan, and participation by a true aryne in their reactions and in those of unsubstituted N-nitrosoacetanilide, is discounted. The nature of the arynoid intermediato has not, in spite of the elimination of many possibilities, been conclusively established, but it is probably the dipolar conjugate base formed by removal of an o-proton from the arenediazonium cation. Anomalies similar to those observed in the decomposition of o-t-butyl-N-nitrosoacetanilide are exhibited by 2,5-di-t-butyl-N- nitrosoacetanilide, which affords aryne adducts with both furan and anthracene in greater yield than does the mono-substituted nitrosamide. Aryne participation was not evident in the highly complex decompositions in benzene of 1,4-di-t-butyl-2,5-di-(N-nitrosoacetamido) benzene, 2,5-di-t-butyl-2,5-di-(N-nitrosoacetamido)benzene, and 4-acetoxy-2,5-di-t-butyl-N-nitrosoacetanilide, Formation of 2,5-di-t-butylphenol, 2,5-di-t-butyl-2-benzoquinone, and acetic anhydride in the last-named reaction indicates deacetylation of the intermediate acetoxybenzenediazonium acetate, and suggests that complications in the reactions of the dinitrosamides arise from interaction between the N-nitrosoacetamido substituents. The decompositions of diphenyl[o-(N-nitrosoacetamido)phenyl] phosphine oxide and diethyl o-(N-nitrosoacetamido)phonyl]phosphonate have been studied, and evidence of aryne intermediacy obtained. The results are discussed in terms of currently acceptable mechanisms for the decomposition of N-nitroso- acetanilide and, where necessary, modifications to these are suggested.N-Oxides from substitued o-nitroanilinesFrench, Colin Stuarthttps://hdl.handle.net/10023/152002019-03-29T11:23:19Z1998-01-01T00:00:00ZThe aim of this project was to investigate the cyclisation reactions of some o-nitroaryl derivatives of amino acids, with a view to the synthesis of potentially biologically active heterocyclic compounds. Chapter one is concerned with an overview of the synthesis of heterocyclic N-oxides, mainly via the cyclisations of ortho-substituted nitroaromatics. Firstly, the properties of heterocyclic N-oxides are considered, then both reductive and non-reductive methods of their synthesis by cyclisation reactions are explored. After a discussion of intramolecular condensations leading to cyclisation, the possibilities for alternative mechanisms for these reactions are deliberated. Chapter Two begins with an introduction to the specific cyclisation reactions of o-nitroaryl- and 2, 4-dinitrophenyl-amino acids. The preparation and cyclisation reactions of o-nitrophenyl derivatives of amino acid esters are then described with emphasis on the implications for the mechanism of these cyclisation reactions. Chapter Three discusses the related cyclisations of N-alkyl-o-nitroanilines which have no activating group (for example, an ester) on the N-alkyl chain. The mechanistic implications of this are explored, in the context of the cyclisations discussed in Chapter Two. In Chapter Four, the synthesis of benzimidazole and quinoxaline acyclic nucleoside analogues is briefly described. These have the potential to be biologically active compounds.
1998-01-01T00:00:00ZFrench, Colin StuartThe aim of this project was to investigate the cyclisation reactions of some o-nitroaryl derivatives of amino acids, with a view to the synthesis of potentially biologically active heterocyclic compounds. Chapter one is concerned with an overview of the synthesis of heterocyclic N-oxides, mainly via the cyclisations of ortho-substituted nitroaromatics. Firstly, the properties of heterocyclic N-oxides are considered, then both reductive and non-reductive methods of their synthesis by cyclisation reactions are explored. After a discussion of intramolecular condensations leading to cyclisation, the possibilities for alternative mechanisms for these reactions are deliberated. Chapter Two begins with an introduction to the specific cyclisation reactions of o-nitroaryl- and 2, 4-dinitrophenyl-amino acids. The preparation and cyclisation reactions of o-nitrophenyl derivatives of amino acid esters are then described with emphasis on the implications for the mechanism of these cyclisation reactions. Chapter Three discusses the related cyclisations of N-alkyl-o-nitroanilines which have no activating group (for example, an ester) on the N-alkyl chain. The mechanistic implications of this are explored, in the context of the cyclisations discussed in Chapter Two. In Chapter Four, the synthesis of benzimidazole and quinoxaline acyclic nucleoside analogues is briefly described. These have the potential to be biologically active compounds.Reactions of acylarylnitrosaminesCook, Johnhttps://hdl.handle.net/10023/151982019-03-29T11:24:22Z1970-01-01T00:00:00ZThe decomposition of acylarylnitrosamines in benzene and halogenomethanes has been studied. "Benzyne adducts" are formed in yields up to 82% in the decomposition of N-nitrosoacetanilide in the presence of various 2,3,4,5-tetraarylcyclopenta- dienones and anthracenes, and competition reactions using mixtures of arynophiles gave competition constants identical to those from similar reactions using authentic sources of benzyne, W-Nitroso- acetanilide did not, however react with furan to form l,4-dlhydronaphthalene-l,4-endoxide, and the yield of 1,2,3,4-tetraphenylnaphthalene formed in the reaction with 2,3,4,5-tetraphenylcyclopenta- dienone in benzene was gradually reduced from 22% to 1.4% on addition of furan, N-Nitrosoacetanilide has been shown to react with dimethylacetylene- dicarboxylate in benzene to give cis-, and trans- dimethyl diphenylmaleates and 1,2,3,4-tetracarbo- methoxynaphthalene in good yield, in addition to the expected biphenyl. The reaction of benzyne from pentyl nitrite and anthranllic acid, however, gave only 5,6,11,12-tetracarbomethoxydlbenzo [a,ej cyclooctatetraene. These results are discussed, and the suggestion made that the intermediate leading to the formation of "aryne adducts" need not be a true aryne. An arynoid species, the dipolar conjugate base of the aryldlazonium cation, formed by removal of the o-proton, is suggested as a possible alternative. The reactions of acylarylnitrosamines with halogenomethanes have also been studied, and the results compared with those of similar reactions of arylazotriphenylmethanes and aryldlazonium halides and fluoroborates. The participation of diazoniam halides and acetate has been demonstrated in the reactions of N-nitrosoacetanilide, and possible mechanisms involving formation of diazonium halides have been suggested. The decomposition of o-t-butyl-N-nitroso-acetanilide in halogenomethanes led to the formation of the o-, and m-t-butylphenyl halides, in addition to the o-, and m-t-butylphenyl acetates. Participation of 3-t-butylbenzyne was confirmed by the isolation of 5-t-butyl-l,4-dihydronaphthalene-1,4-endoxide when o-t-butyl-N-nitrosoacetanilide was allowed to decompose in bromotrichloromethane in the presence of furan; this was accompanied by a suppression of formation of the m-t-butylphenyl halides and acetate, A reaction scheme is suggested involving participation of diazonium halides and acetate. The reaction of N-nitroso-N-formylanthranilic acid and N-nitroso-N-acetylanthranilic acid with 2,3,4,5-tetraphenylcyclopentadlenone in benzene led to the formation of 1,2,3,4-tetraphenylnaph- thalene, but the principal products in these reactions were 3,1-benzoxazin-4-one and 2-methyl-3,1-benzoxazin-4-one respectively.
1970-01-01T00:00:00ZCook, JohnThe decomposition of acylarylnitrosamines in benzene and halogenomethanes has been studied. "Benzyne adducts" are formed in yields up to 82% in the decomposition of N-nitrosoacetanilide in the presence of various 2,3,4,5-tetraarylcyclopenta- dienones and anthracenes, and competition reactions using mixtures of arynophiles gave competition constants identical to those from similar reactions using authentic sources of benzyne, W-Nitroso- acetanilide did not, however react with furan to form l,4-dlhydronaphthalene-l,4-endoxide, and the yield of 1,2,3,4-tetraphenylnaphthalene formed in the reaction with 2,3,4,5-tetraphenylcyclopenta- dienone in benzene was gradually reduced from 22% to 1.4% on addition of furan, N-Nitrosoacetanilide has been shown to react with dimethylacetylene- dicarboxylate in benzene to give cis-, and trans- dimethyl diphenylmaleates and 1,2,3,4-tetracarbo- methoxynaphthalene in good yield, in addition to the expected biphenyl. The reaction of benzyne from pentyl nitrite and anthranllic acid, however, gave only 5,6,11,12-tetracarbomethoxydlbenzo [a,ej cyclooctatetraene. These results are discussed, and the suggestion made that the intermediate leading to the formation of "aryne adducts" need not be a true aryne. An arynoid species, the dipolar conjugate base of the aryldlazonium cation, formed by removal of the o-proton, is suggested as a possible alternative. The reactions of acylarylnitrosamines with halogenomethanes have also been studied, and the results compared with those of similar reactions of arylazotriphenylmethanes and aryldlazonium halides and fluoroborates. The participation of diazoniam halides and acetate has been demonstrated in the reactions of N-nitrosoacetanilide, and possible mechanisms involving formation of diazonium halides have been suggested. The decomposition of o-t-butyl-N-nitroso-acetanilide in halogenomethanes led to the formation of the o-, and m-t-butylphenyl halides, in addition to the o-, and m-t-butylphenyl acetates. Participation of 3-t-butylbenzyne was confirmed by the isolation of 5-t-butyl-l,4-dihydronaphthalene-1,4-endoxide when o-t-butyl-N-nitrosoacetanilide was allowed to decompose in bromotrichloromethane in the presence of furan; this was accompanied by a suppression of formation of the m-t-butylphenyl halides and acetate, A reaction scheme is suggested involving participation of diazonium halides and acetate. The reaction of N-nitroso-N-formylanthranilic acid and N-nitroso-N-acetylanthranilic acid with 2,3,4,5-tetraphenylcyclopentadlenone in benzene led to the formation of 1,2,3,4-tetraphenylnaph- thalene, but the principal products in these reactions were 3,1-benzoxazin-4-one and 2-methyl-3,1-benzoxazin-4-one respectively.Some studies on the formation and interconversion of iron-sulfur nitrosyl complexesBlyth, Debra F.https://hdl.handle.net/10023/151932019-03-29T11:18:58Z1996-01-01T00:00:00ZStudies on the effect of substituting iron(III) for iron(II) or nitrate for nitrite in the reaction of cysteine with iron(II) salts and nitrite with and without sodium ascorbate present demonstrated the formation of the tetranuclear Na[Fe₄S₃(NO)₇] complex when iron(III) is substituted for iron(II), albeit in smaller yield; but no iron-sulfur-nitrosyl clusters were detected when nitrite was replaced with nitrate. Similarly in the case of reaction of methionine with iron(II) salts and nitrite in the presence of sodium ascorbate, the dinuclear complex Fe₂(SMe)₂(NO)₄ is formed in reduced yield when iron(III) is substituted for iron(II) and no iron-sulfur-nitrosyl complexes are detected when nitrite is replaced with nitrate. The effect of pH on the reactions of cysteine and methionine with iron(II) salts and nitrate, with and without sodium ascorbate present in the case of cysteine, were studied. The cysteine reactions showed that in the presence of sodium ascorbate, the yield of Na[Fe₄S₃(NO)₇] fell slightly as pH was decreased due to formation of the less soluble ascorbic acid from acidification of sodium ascorbate. At very low pH both cysteine reactions with and without sodium ascorbate present did not yield Na[Fe₄S₃(NO)₇] due to the formation of nitric oxide from nitrite, which would rapidly oxidise to give nitrogen dioxide, and to the instability of the Na[Fe₄S₃(NO)₇] complex itself at very low pH. The dinuclear complex Fe₂(SMe)₂(NO)₄ is very stable to conditions of low pH but its formation at very acidic conditions was hindered, again due to the formation of nitric oxide from nitrite. A range of iron-sulfur containing amino acid complexes of the general type [Fe₃o(amino acid)₆(H₂0)₃]X₇, were synthesised and their reactions with nitrite studied. In the presence of sodium ascorbate, when the amino acid is methylcysteine, both [Fe₄S₃(NO)₇]' and Fe₂(SMe)₂(NO)₄ were isolated after reaction with nitrite. However no identified iron-sulfur-nitrosyl complexes could be detected when the amino acid was methionine. In the absence of sodium ascorbate both the methylcysteine and methionine complexes yielded a range of unidentified complexes which infra-red spectroscopy demonstrated absorbed strongly in the nitrosyl stretching region and it was postulated that the species observed were inorganic nitrosyl complexes. FTIR analysis of Fe₄S₄(NO)₄ in the polar coordinating solvents THF, DMF and DMSO demonstrated conversion to [Fe₄S₃(NO)₇]⁻. No such conversion was observed using the solvents diethyl ether or dichloromethane. An intermediate species was observed in THF and DMSO using FTIR spectroscopy which was postulated to be a [Fe(solvent)₆][Fe₄S₄(NO)₄]₂ complex. Another peak observed in the latter stages of the conversion was believed to be that of a dinuclear Fe(SR)₂(NO)₄ type complex. ESR analysis of Fe₄S₄(NO)₄ in THF and DMSO however demonstrated formation of a mononuclear species of type [Fe(NO)₂(X)₂]ⁿ⁺. Thus in the dilute solutions required for ESR analysis, mononuclear species of the type [Fe₂(NO)₂(X)₂]ⁿ⁺ are favoured but in the more concentrated solutions needed for FTIR analysis polynuclear species of the type [Fe₄S₄(NO)₄] are predominant.
1996-01-01T00:00:00ZBlyth, Debra F.Studies on the effect of substituting iron(III) for iron(II) or nitrate for nitrite in the reaction of cysteine with iron(II) salts and nitrite with and without sodium ascorbate present demonstrated the formation of the tetranuclear Na[Fe₄S₃(NO)₇] complex when iron(III) is substituted for iron(II), albeit in smaller yield; but no iron-sulfur-nitrosyl clusters were detected when nitrite was replaced with nitrate. Similarly in the case of reaction of methionine with iron(II) salts and nitrite in the presence of sodium ascorbate, the dinuclear complex Fe₂(SMe)₂(NO)₄ is formed in reduced yield when iron(III) is substituted for iron(II) and no iron-sulfur-nitrosyl complexes are detected when nitrite is replaced with nitrate. The effect of pH on the reactions of cysteine and methionine with iron(II) salts and nitrate, with and without sodium ascorbate present in the case of cysteine, were studied. The cysteine reactions showed that in the presence of sodium ascorbate, the yield of Na[Fe₄S₃(NO)₇] fell slightly as pH was decreased due to formation of the less soluble ascorbic acid from acidification of sodium ascorbate. At very low pH both cysteine reactions with and without sodium ascorbate present did not yield Na[Fe₄S₃(NO)₇] due to the formation of nitric oxide from nitrite, which would rapidly oxidise to give nitrogen dioxide, and to the instability of the Na[Fe₄S₃(NO)₇] complex itself at very low pH. The dinuclear complex Fe₂(SMe)₂(NO)₄ is very stable to conditions of low pH but its formation at very acidic conditions was hindered, again due to the formation of nitric oxide from nitrite. A range of iron-sulfur containing amino acid complexes of the general type [Fe₃o(amino acid)₆(H₂0)₃]X₇, were synthesised and their reactions with nitrite studied. In the presence of sodium ascorbate, when the amino acid is methylcysteine, both [Fe₄S₃(NO)₇]' and Fe₂(SMe)₂(NO)₄ were isolated after reaction with nitrite. However no identified iron-sulfur-nitrosyl complexes could be detected when the amino acid was methionine. In the absence of sodium ascorbate both the methylcysteine and methionine complexes yielded a range of unidentified complexes which infra-red spectroscopy demonstrated absorbed strongly in the nitrosyl stretching region and it was postulated that the species observed were inorganic nitrosyl complexes. FTIR analysis of Fe₄S₄(NO)₄ in the polar coordinating solvents THF, DMF and DMSO demonstrated conversion to [Fe₄S₃(NO)₇]⁻. No such conversion was observed using the solvents diethyl ether or dichloromethane. An intermediate species was observed in THF and DMSO using FTIR spectroscopy which was postulated to be a [Fe(solvent)₆][Fe₄S₄(NO)₄]₂ complex. Another peak observed in the latter stages of the conversion was believed to be that of a dinuclear Fe(SR)₂(NO)₄ type complex. ESR analysis of Fe₄S₄(NO)₄ in THF and DMSO however demonstrated formation of a mononuclear species of type [Fe(NO)₂(X)₂]ⁿ⁺. Thus in the dilute solutions required for ESR analysis, mononuclear species of the type [Fe₂(NO)₂(X)₂]ⁿ⁺ are favoured but in the more concentrated solutions needed for FTIR analysis polynuclear species of the type [Fe₄S₄(NO)₄] are predominant.Some studies of biologically active S-nitrosothiolsAskew, Stuart Clivehttps://hdl.handle.net/10023/151892019-03-29T11:23:33Z1995-01-01T00:00:00ZS-nitrosothiols are effective NO-donating drugs which can elicit vasodilation of vascular tissue and disaggregate or inhibit the aggregation of platelets in blood. The chemistries of two S-nitrosothiols, S-nitroso-N-acetyl-DL-penicillamine (SNAP) and S-nitrosoglutathione (GSNO) have been investigated in an attempt to identify the chemical and physiological mechanisms which underlie their biological actions as vasodilators and modulators of platelet behaviour. Although SNAP and GSNO have been found to be susceptible to decomposition by similar chemical mechanisms, such as by thermal and photochemical means, evidence is presented to suggest that they are both capable of NO transfer to other thiol containing compounds such as cysteine. This produces a very unstable S-nitrosothiol, S-nitrosocysteine, which readily produces NO. However, they can both be decomposed by different, distinctive mechanisms. Metal ion catalysis by copper is shown to greatly accelerate the decomposition of SNAP, but has little effect on GSNO. Instead, NO release from GSNO is effected by enzymatic cleavage of the glutamyl-cysteinyl peptide bond by the enzyme glutamyl transpeptidase (γ-GT). The resulting S-nitrosothiol, S-nitrosocysteinylglycine, would be expected to be more susceptible to release of NO by metal (copper) ion catalysis. It is concluded that transnitrosation (NO-transfer) between thiol groups, or enzymatic cleavage are obligatory steps in the mechanism of NO release from GSNO, whereas SNAP requires only the presence of trace amounts of metal ions like copper to effect this process. The different modes of NO production may go some way towards explaining the different physiological effectiveness of these S-nitrosothiols as vasodilators and inhibitors of platelet aggregation.
1995-01-01T00:00:00ZAskew, Stuart CliveS-nitrosothiols are effective NO-donating drugs which can elicit vasodilation of vascular tissue and disaggregate or inhibit the aggregation of platelets in blood. The chemistries of two S-nitrosothiols, S-nitroso-N-acetyl-DL-penicillamine (SNAP) and S-nitrosoglutathione (GSNO) have been investigated in an attempt to identify the chemical and physiological mechanisms which underlie their biological actions as vasodilators and modulators of platelet behaviour. Although SNAP and GSNO have been found to be susceptible to decomposition by similar chemical mechanisms, such as by thermal and photochemical means, evidence is presented to suggest that they are both capable of NO transfer to other thiol containing compounds such as cysteine. This produces a very unstable S-nitrosothiol, S-nitrosocysteine, which readily produces NO. However, they can both be decomposed by different, distinctive mechanisms. Metal ion catalysis by copper is shown to greatly accelerate the decomposition of SNAP, but has little effect on GSNO. Instead, NO release from GSNO is effected by enzymatic cleavage of the glutamyl-cysteinyl peptide bond by the enzyme glutamyl transpeptidase (γ-GT). The resulting S-nitrosothiol, S-nitrosocysteinylglycine, would be expected to be more susceptible to release of NO by metal (copper) ion catalysis. It is concluded that transnitrosation (NO-transfer) between thiol groups, or enzymatic cleavage are obligatory steps in the mechanism of NO release from GSNO, whereas SNAP requires only the presence of trace amounts of metal ions like copper to effect this process. The different modes of NO production may go some way towards explaining the different physiological effectiveness of these S-nitrosothiols as vasodilators and inhibitors of platelet aggregation.Nitrosothiols as no-donor drugs: Synthesis, mechanistic studies, chemical stability, pharmacological and physiological activityAl-Sa'doni, Haitham H.https://hdl.handle.net/10023/151872019-03-29T11:19:24Z1996-01-01T00:00:00ZS-Nitrosothiols (RSNO) are an important class of NO-donor drugs. They have been used clinically and occur naturally where they may have a role in several biological and physiological processes in the human body. The medical importance of S-nitrosothiols has been highlighted recently by several reports which describe the clinical use of GSNO (13) to inhibit platelet aggregation during coronary angioplasty and also to treat a form of preeclampsia, a high blood pressure condition suffered by some pregnant women. We set out to extend the range of compounds of this type by synthesising a novel series of biologically active S-nitrosothiols (1-13) and to look for a correlation between structure, chemical stability, and physiological activity. The situation has been complicated by the recent discovery that the main route for the release of NO from S-nitrosothiols is a copper- catalysed process. A detailed kinetic study of copper ions, and thiols on the stability of the compounds we synthesised has shown that the dominant pathway for the decomposition of S-nitrosothiols in most circumstances is one catalysed by Cu⁺ ions. We suggest that Cu⁺ ions are formed by the reaction of Cu²⁺ ions with thiol, present in the S-nitrosothiols as an impurity. The implications of this discovery for an understanding of the biological action of S-nitrosothiols is suggested. All the new S-nitrosated dipeptides (2-12) examined show less susceptibility to copper (I)- catalysed release of NO than SNAP (1) but are more reactive than GSNO (13). We found that S-nitrosated dipeptides are potent vasodilators and suitable inhibitors of platelet aggregation but are chemically very stable in the absence of copper ions. All thirteen compounds combine the favoured property of chemical stability with a high level of biological activity. We found that copper(I)-chelation induced reduction of the biological activity of S- nitrosothiols in smooth muscle relaxation. The results show that responses to both SNAP and GSNO are reversibly inhibited by neocuproine. We conclude that relaxation of vasodilator smooth muscle by SNAP and GSNO is caused in part by NO released into solution via a Cu⁺-dependent catalytic reaction, and provide evidence that endogenous Cu⁺ ions may also contribute to the maintenance of vasodilator 'store' in vivo by catalysing the decomposition of naturally-occurring S-nitrosothiols. A particularly interesting finding recently by Gordge et al. (1995) shows that the inhibition of platelet aggregation activity shown by GSNO is much reduced in the presence of neocuproine and the closely related bathocuproine, both specific Cu⁺-chelating agent. However, it was shown very recently (Schrammel et al, 1996) that copper ions inhibit basal and NO-stimulated recombinant soluble guanylate cyclase activity and that Cu⁺ is more effective than Cu²⁺ in this regard. L-Ascorbic acid (vitamin C) could play a role in the in vivo release of NO from naturally occurring and exogenous S-nitrosothiols and so play a part in smooth muscle relaxation and in inhibition of platelet aggregation. All thirteen compounds examined show the ability to release NO in vitro. The inhibitory effect of Hb, a recognised NO scavenger, was investigated. In smooth muscle, responses to intermediate doses of S-nitrosothiols were significantly inhibited by Hb, though not abolished entirely. In platelet, we found that the inhibitory activity of these S-nitrosothiols was reversed by haemoglobin, indicating the involvement of NO in the process. We found that the solution stability of the S-nitrosothiols did not correlate with relaxation of vascular smooth muscle or inhibition of platelet aggregation, again suggesting that the tissue specificity is a function of the R- group. We conclude that the biological activity of S-nitrosothiols depends upon the release of NO in a process catalysed by Cu(I), and that the decomposition may occur inside or outside the cell, depending upon the structure of RSNO.
1996-01-01T00:00:00ZAl-Sa'doni, Haitham H.S-Nitrosothiols (RSNO) are an important class of NO-donor drugs. They have been used clinically and occur naturally where they may have a role in several biological and physiological processes in the human body. The medical importance of S-nitrosothiols has been highlighted recently by several reports which describe the clinical use of GSNO (13) to inhibit platelet aggregation during coronary angioplasty and also to treat a form of preeclampsia, a high blood pressure condition suffered by some pregnant women. We set out to extend the range of compounds of this type by synthesising a novel series of biologically active S-nitrosothiols (1-13) and to look for a correlation between structure, chemical stability, and physiological activity. The situation has been complicated by the recent discovery that the main route for the release of NO from S-nitrosothiols is a copper- catalysed process. A detailed kinetic study of copper ions, and thiols on the stability of the compounds we synthesised has shown that the dominant pathway for the decomposition of S-nitrosothiols in most circumstances is one catalysed by Cu⁺ ions. We suggest that Cu⁺ ions are formed by the reaction of Cu²⁺ ions with thiol, present in the S-nitrosothiols as an impurity. The implications of this discovery for an understanding of the biological action of S-nitrosothiols is suggested. All the new S-nitrosated dipeptides (2-12) examined show less susceptibility to copper (I)- catalysed release of NO than SNAP (1) but are more reactive than GSNO (13). We found that S-nitrosated dipeptides are potent vasodilators and suitable inhibitors of platelet aggregation but are chemically very stable in the absence of copper ions. All thirteen compounds combine the favoured property of chemical stability with a high level of biological activity. We found that copper(I)-chelation induced reduction of the biological activity of S- nitrosothiols in smooth muscle relaxation. The results show that responses to both SNAP and GSNO are reversibly inhibited by neocuproine. We conclude that relaxation of vasodilator smooth muscle by SNAP and GSNO is caused in part by NO released into solution via a Cu⁺-dependent catalytic reaction, and provide evidence that endogenous Cu⁺ ions may also contribute to the maintenance of vasodilator 'store' in vivo by catalysing the decomposition of naturally-occurring S-nitrosothiols. A particularly interesting finding recently by Gordge et al. (1995) shows that the inhibition of platelet aggregation activity shown by GSNO is much reduced in the presence of neocuproine and the closely related bathocuproine, both specific Cu⁺-chelating agent. However, it was shown very recently (Schrammel et al, 1996) that copper ions inhibit basal and NO-stimulated recombinant soluble guanylate cyclase activity and that Cu⁺ is more effective than Cu²⁺ in this regard. L-Ascorbic acid (vitamin C) could play a role in the in vivo release of NO from naturally occurring and exogenous S-nitrosothiols and so play a part in smooth muscle relaxation and in inhibition of platelet aggregation. All thirteen compounds examined show the ability to release NO in vitro. The inhibitory effect of Hb, a recognised NO scavenger, was investigated. In smooth muscle, responses to intermediate doses of S-nitrosothiols were significantly inhibited by Hb, though not abolished entirely. In platelet, we found that the inhibitory activity of these S-nitrosothiols was reversed by haemoglobin, indicating the involvement of NO in the process. We found that the solution stability of the S-nitrosothiols did not correlate with relaxation of vascular smooth muscle or inhibition of platelet aggregation, again suggesting that the tissue specificity is a function of the R- group. We conclude that the biological activity of S-nitrosothiols depends upon the release of NO in a process catalysed by Cu(I), and that the decomposition may occur inside or outside the cell, depending upon the structure of RSNO.Modification of polydienes via homogenous catalysisNicol, Mairihttps://hdl.handle.net/10023/151832019-03-29T11:23:05Z1998-01-01T00:00:00ZOur investigations into the synthesis of polyketones have involved the catalytic functionalisation of polydienes with particular emphasis on routes via a polyepoxide and a polyalcohol. Initially, a route via the polyepoxide was studied, in which polybutadiene (various micro structures and molecular weights) and polyisoprene were epoxidised (equation 1) in high conversion using a [MoO₂CI₂ [(lR)-endo]-(+)-3(diethoxyphosphoryl) camphor] catalyst (MoCI₂O₂L) and subsequently isomerised to the polyketone using lithium bromide [(equation 2), see Scheme 1 in thesis].
Lithium bromide requires a solublising agent in reactions carried out in dichloromethane, however this is not the case for reactions carried out in tetrahydrofuran as lithium bromide is readily dissolved in this solvent. (See abstract in full thesis for equation).
Polybutadiene and polyisoprene can be easily converted to their respective polyepoxide. The backbone double bonds of the polydienes show from ¹H nmr 100% conversion to the epoxide with greater than 95% selectivity. The polyepoxides are easily purified after the removal of HCl (produced by the catalyst) as this causes crosslinking. Subsequent isomerisation of the purified poly epoxides show from ¹³C and ir that characteristic ketone units can be formed along with the ketal resonances attributed to brevicomin type moeties, formed from the reaction of a ketone with a neighbouring epoxide group.
Problems with the insolubility of the polyketone led to the preparation of a polyalcohol, via hydroboration using 9-borabicyclononane (equation 3) followed by oxidation using an alkaline solution of hydrogen peroxide (equation 4). The attempted dehydrogenation of the polyalcohol to give the resultant polyketone using various oxidants was studied, see Scheme 2.
Conversion of the polybutadiene to the alcohol via hydroboration-oxidation using 9-BBN/NaOH-H₂O₂ showed by ¹H and ¹³C nmr a 50% conversion of the backbone double bonds at a low temperature and 100% conversion at a high temperature. The microstructure of the resultant polyalcohol showed 1,4: 1,5: 1,6 segments in a 1:2:1 ratio, these different segment impart irregularity into the polymer chain and could consequently be carried through to the polyketone giving rise to lower crystallinity and a more processable polymer. Although various oxidants has been investigated for the dehydrogenation of the polyalcohol a suitable oxidant has not yet been found.
1998-01-01T00:00:00ZNicol, MairiOur investigations into the synthesis of polyketones have involved the catalytic functionalisation of polydienes with particular emphasis on routes via a polyepoxide and a polyalcohol. Initially, a route via the polyepoxide was studied, in which polybutadiene (various micro structures and molecular weights) and polyisoprene were epoxidised (equation 1) in high conversion using a [MoO₂CI₂ [(lR)-endo]-(+)-3(diethoxyphosphoryl) camphor] catalyst (MoCI₂O₂L) and subsequently isomerised to the polyketone using lithium bromide [(equation 2), see Scheme 1 in thesis].
Lithium bromide requires a solublising agent in reactions carried out in dichloromethane, however this is not the case for reactions carried out in tetrahydrofuran as lithium bromide is readily dissolved in this solvent. (See abstract in full thesis for equation).
Polybutadiene and polyisoprene can be easily converted to their respective polyepoxide. The backbone double bonds of the polydienes show from ¹H nmr 100% conversion to the epoxide with greater than 95% selectivity. The polyepoxides are easily purified after the removal of HCl (produced by the catalyst) as this causes crosslinking. Subsequent isomerisation of the purified poly epoxides show from ¹³C and ir that characteristic ketone units can be formed along with the ketal resonances attributed to brevicomin type moeties, formed from the reaction of a ketone with a neighbouring epoxide group.
Problems with the insolubility of the polyketone led to the preparation of a polyalcohol, via hydroboration using 9-borabicyclononane (equation 3) followed by oxidation using an alkaline solution of hydrogen peroxide (equation 4). The attempted dehydrogenation of the polyalcohol to give the resultant polyketone using various oxidants was studied, see Scheme 2.
Conversion of the polybutadiene to the alcohol via hydroboration-oxidation using 9-BBN/NaOH-H₂O₂ showed by ¹H and ¹³C nmr a 50% conversion of the backbone double bonds at a low temperature and 100% conversion at a high temperature. The microstructure of the resultant polyalcohol showed 1,4: 1,5: 1,6 segments in a 1:2:1 ratio, these different segment impart irregularity into the polymer chain and could consequently be carried through to the polyketone giving rise to lower crystallinity and a more processable polymer. Although various oxidants has been investigated for the dehydrogenation of the polyalcohol a suitable oxidant has not yet been found.The pyrolysis of methyl iodideBoyd, Robert Kinnearhttps://hdl.handle.net/10023/151792019-03-29T11:20:27Z1963-01-01T00:00:00ZThere is an extensive literature on the pyrolysis and photolysis of organic iodides. The main reason for the popularity of these substances as subjects for kinetic investigations is the relative weakness of the carbon-iodine bonds, the comparatively ready-splitting of these bonds providing a possible initiating process for the decomposition.
The object of the present work was to establish the kinetics of the pyrolysis of methyl iodide in the presence of hydrogen iodide, with a view to determining the carbon-iodine bond dissociation energy. Ogg¹ carried out a kinetic investigation into the pyrolysis of methyl, ethyl, and n-propyl iodides in the presence of hydrogen iodide. However, apart from the fact that the bond dissociation energies derived from Ogg’s analysis of his data are about 12 k.cals per mole lower than values from other sources, work done in St. Andrews, on the pyrolysis of trifluoromethyl iodide² and benzyl iodide⁵, suggested that a mechanism different from that postulated by Ogg was operative.
In the light of these considerations, it seemed that a reinvestigation of the thermal reaction between methyl iodide and hydrogen iodide was necessary. Before describing this present work, a summary is given of published work on the decompositions of iodides, and on carbon-iodine bond dissociation energies.
1963-01-01T00:00:00ZBoyd, Robert KinnearThere is an extensive literature on the pyrolysis and photolysis of organic iodides. The main reason for the popularity of these substances as subjects for kinetic investigations is the relative weakness of the carbon-iodine bonds, the comparatively ready-splitting of these bonds providing a possible initiating process for the decomposition.
The object of the present work was to establish the kinetics of the pyrolysis of methyl iodide in the presence of hydrogen iodide, with a view to determining the carbon-iodine bond dissociation energy. Ogg¹ carried out a kinetic investigation into the pyrolysis of methyl, ethyl, and n-propyl iodides in the presence of hydrogen iodide. However, apart from the fact that the bond dissociation energies derived from Ogg’s analysis of his data are about 12 k.cals per mole lower than values from other sources, work done in St. Andrews, on the pyrolysis of trifluoromethyl iodide² and benzyl iodide⁵, suggested that a mechanism different from that postulated by Ogg was operative.
In the light of these considerations, it seemed that a reinvestigation of the thermal reaction between methyl iodide and hydrogen iodide was necessary. Before describing this present work, a summary is given of published work on the decompositions of iodides, and on carbon-iodine bond dissociation energies.Glyceride studies of selected seed oilsQureshi, Muhammad Ilyashttps://hdl.handle.net/10023/151752019-03-29T11:19:15Z1966-01-01T00:00:00Z1. The component glycerides of J. curcas, J. inultifida, J. gossypifolla and sunflower seed oils are determined by a new method of crystallisation and column chromatography on silica-silver nitrate. 2. The component glycerides of nine seed oils (safflower, tobacco, A. mexieana, maize, cotton, gi-oundnut, M. ternifolia, G. asiatica and M. latifolia) are determined by thin layer argentation procedure. 3. The results agree with those obtained by lipolysis on" calculated directly from the component acids on the basis of the theory of positional distribution. Moreover, the distribution of oleic, linoleic, hexadec-9 and 11-enoic, lauric and myristic acids in vegetable triglycerides are studied by hydrolysis with pancreatic lipase. The results, discussed in terms of a "selectivity factor", indicate that these unsaturated acids do not compete equally for the secondary hydroxyl group of glycerol.
1966-01-01T00:00:00ZQureshi, Muhammad Ilyas1. The component glycerides of J. curcas, J. inultifida, J. gossypifolla and sunflower seed oils are determined by a new method of crystallisation and column chromatography on silica-silver nitrate. 2. The component glycerides of nine seed oils (safflower, tobacco, A. mexieana, maize, cotton, gi-oundnut, M. ternifolia, G. asiatica and M. latifolia) are determined by thin layer argentation procedure. 3. The results agree with those obtained by lipolysis on" calculated directly from the component acids on the basis of the theory of positional distribution. Moreover, the distribution of oleic, linoleic, hexadec-9 and 11-enoic, lauric and myristic acids in vegetable triglycerides are studied by hydrolysis with pancreatic lipase. The results, discussed in terms of a "selectivity factor", indicate that these unsaturated acids do not compete equally for the secondary hydroxyl group of glycerol.The formulae and structures of some aromatic amine and hydrocarbon complexes of antimony trichlorineMullen, Donald Joseph Edgarhttps://hdl.handle.net/10023/151722019-03-29T11:19:53Z1970-01-01T00:00:00ZThe crystal structure of the complex 2SbCl₃.p-xylene (space group: P2₁/c; a=9.13Å, b=8.44Å, c=12.79A, β=125°21') was investigated at low temperatures, and it proves to be a layer structure with packing p-xylene molecules. The compound C₅H₅NH⁺ Sbcl₄⁻ (space group; C2/c; a=13.12Å, b=13.07Å, c= 7.44Å, β =122°19') was identified as a hydrolysis product of' the Sbcl₃/pyridine system by means of a partial structure analysis. The complex 2Sbcl₃.C₅H₅N (space group: Pca2₁; a=26.14Å, b=11.93Å, o=7.51Å) was prepared and its structure elucidated. Its general structural features include an infinite Sb - C1 chain, pyridine ligands attached to the antimony atom, and the presence, in addition, of a "solvating" pyridine molecule.
The complex 2Sbcl₃.C₅H₅N (space group; P1; a=10.93A, b=8.92Å, c=9.30Å, ∝ = 106°48’, β = 192°48’, ⋈ = 116 °36’) was prepared. This has an extensively bridged Sb - Cl system and non-bonding pyridine molecules, occurring in alternate layers. The complex SbCl₃.C₅H₅N (space group: P2₁/c; a=13.00Å., b=17.87Å, c=12.17Å, β=121°11') was prepared.
1970-01-01T00:00:00ZMullen, Donald Joseph EdgarThe crystal structure of the complex 2SbCl₃.p-xylene (space group: P2₁/c; a=9.13Å, b=8.44Å, c=12.79A, β=125°21') was investigated at low temperatures, and it proves to be a layer structure with packing p-xylene molecules. The compound C₅H₅NH⁺ Sbcl₄⁻ (space group; C2/c; a=13.12Å, b=13.07Å, c= 7.44Å, β =122°19') was identified as a hydrolysis product of' the Sbcl₃/pyridine system by means of a partial structure analysis. The complex 2Sbcl₃.C₅H₅N (space group: Pca2₁; a=26.14Å, b=11.93Å, o=7.51Å) was prepared and its structure elucidated. Its general structural features include an infinite Sb - C1 chain, pyridine ligands attached to the antimony atom, and the presence, in addition, of a "solvating" pyridine molecule.
The complex 2Sbcl₃.C₅H₅N (space group; P1; a=10.93A, b=8.92Å, c=9.30Å, ∝ = 106°48’, β = 192°48’, ⋈ = 116 °36’) was prepared. This has an extensively bridged Sb - Cl system and non-bonding pyridine molecules, occurring in alternate layers. The complex SbCl₃.C₅H₅N (space group: P2₁/c; a=13.00Å., b=17.87Å, c=12.17Å, β=121°11') was prepared.The reaction between toluene and deuterium catalysed by some metals of group VIIIMoyes, Richard Bellhttps://hdl.handle.net/10023/151672019-03-29T11:21:52Z1964-01-01T00:00:00ZCatalysis action is usually held to be preceeded by some form of chemical interaction of one reactant, or of both, with the catalyst. Toluene has certain distinctive features from this point of view. The carbon-hydrogen bond dissociation energy for the side chain bonds is about 84kcal. Mol ⁻¹ while the ring carbon-hydrogen bond energy is probably greater than 103 kcal. Mole⁻¹.¹ The side chain gives aliphatic characteristics while the aromatic ring of toluene adds the further possibility of interaction with the catalyst through its unsaturated properties and, as a special aromatic feature, through the T-ring system. It was the possible interplay of these features which suggested this research.
The brief literature survey deals with general features of the exchange reactions of maturated hydrocarbons, unsaturated and aromatic compounds only in so far as the main features are judged to have a bearing on the toluene problem and to show the development of features common to most exchange reactions.
The catalyst metal was varied in the experimental part of this work and since this can be viewed as altering the nature of toluene’s reaction partner some relevant similar work in the literature is summarised. Evaporated films of metal were chosen as catalytic agents in order to avoid possible complications arising from supporting materials and differing preparatory methods from metal to metal. Wherever possible work on metal film catalysts will therefore be used to provide the examples is the following literature survey.
1964-01-01T00:00:00ZMoyes, Richard BellCatalysis action is usually held to be preceeded by some form of chemical interaction of one reactant, or of both, with the catalyst. Toluene has certain distinctive features from this point of view. The carbon-hydrogen bond dissociation energy for the side chain bonds is about 84kcal. Mol ⁻¹ while the ring carbon-hydrogen bond energy is probably greater than 103 kcal. Mole⁻¹.¹ The side chain gives aliphatic characteristics while the aromatic ring of toluene adds the further possibility of interaction with the catalyst through its unsaturated properties and, as a special aromatic feature, through the T-ring system. It was the possible interplay of these features which suggested this research.
The brief literature survey deals with general features of the exchange reactions of maturated hydrocarbons, unsaturated and aromatic compounds only in so far as the main features are judged to have a bearing on the toluene problem and to show the development of features common to most exchange reactions.
The catalyst metal was varied in the experimental part of this work and since this can be viewed as altering the nature of toluene’s reaction partner some relevant similar work in the literature is summarised. Evaporated films of metal were chosen as catalytic agents in order to avoid possible complications arising from supporting materials and differing preparatory methods from metal to metal. Wherever possible work on metal film catalysts will therefore be used to provide the examples is the following literature survey.The thermal reaction of toluene and iodine and some related processesAlexander, Williamhttps://hdl.handle.net/10023/151632019-03-29T11:24:06Z1957-01-01T00:00:00ZThe work reported in this thesis arose from some observations made by R.B. Cundall¹ in the laboratories at St Andrews while he was investigating the pyrolysis of methyl iodide. An attempt to use toluene as a radical acceptor resulted in the production of some hydrogen iodide, and Cundall attempted a brief investigation into its source. The reaction of iodine with toluene was suspected, and in some initial experiments, the reaction was investigated in a flow system.
In these experiments it was shown that stilbene and dibenzyl condensed out at the furnace exit, and that benzyl iodide, hydrogen iodide and unreacted toluene and iodine condensed out in the analysis traps.
The only other reference to this reaction are recorded in Beilstein², where it is noted that the prolonged heating of toluene and iodine vapours together yields hydrogen iodide and other products. Other investigations have shown that the prolonged refluxing of toluene, to which iodine has been added, produced no hydrogen iodide.
The aim of the work described in this thesis was to investigate the products and kinetics of the reaction. It was hoped that additional data on the question of the bond strength of the side chain (C-H) link in toluene might be obtained since a study of the bromination of the latter had recently yielded a new value for this bond dissociation energy. The results quoted in later sections of this thesis on the reaction of toluene with iodine are explained by a primary reaction between the hydrocarbon and an atom of iodine. This step produces a benzyl radical and hydrogen iodid, and appears to be markedly inhibited by the addition of excess hydrogen iodide. The presence of dibenzyl and stilbene in the products rendered it necessary to investigate the reaction of dibenzyl with iodine, and which hydrogen iodide. The results of these investigations are given in later sections.
Before dealing with the experimental work of this thesis, and discussing it, a brief survey is given of some relevant themes and studies reported in the literature, and which form a background against which this present investigation has to be considered.
1957-01-01T00:00:00ZAlexander, WilliamThe work reported in this thesis arose from some observations made by R.B. Cundall¹ in the laboratories at St Andrews while he was investigating the pyrolysis of methyl iodide. An attempt to use toluene as a radical acceptor resulted in the production of some hydrogen iodide, and Cundall attempted a brief investigation into its source. The reaction of iodine with toluene was suspected, and in some initial experiments, the reaction was investigated in a flow system.
In these experiments it was shown that stilbene and dibenzyl condensed out at the furnace exit, and that benzyl iodide, hydrogen iodide and unreacted toluene and iodine condensed out in the analysis traps.
The only other reference to this reaction are recorded in Beilstein², where it is noted that the prolonged heating of toluene and iodine vapours together yields hydrogen iodide and other products. Other investigations have shown that the prolonged refluxing of toluene, to which iodine has been added, produced no hydrogen iodide.
The aim of the work described in this thesis was to investigate the products and kinetics of the reaction. It was hoped that additional data on the question of the bond strength of the side chain (C-H) link in toluene might be obtained since a study of the bromination of the latter had recently yielded a new value for this bond dissociation energy. The results quoted in later sections of this thesis on the reaction of toluene with iodine are explained by a primary reaction between the hydrocarbon and an atom of iodine. This step produces a benzyl radical and hydrogen iodid, and appears to be markedly inhibited by the addition of excess hydrogen iodide. The presence of dibenzyl and stilbene in the products rendered it necessary to investigate the reaction of dibenzyl with iodine, and which hydrogen iodide. The results of these investigations are given in later sections.
Before dealing with the experimental work of this thesis, and discussing it, a brief survey is given of some relevant themes and studies reported in the literature, and which form a background against which this present investigation has to be considered.Indolizines: with special reference to the action of electrophilic reagentsFraser, Martinhttps://hdl.handle.net/10023/151572019-03-29T11:20:10Z1962-01-01T00:00:00ZIndolizine was first synthesised by Scholts¹ in 1912 who proposed at that time the presently accepted ring structure (1). A number of alternative names and systems of numbering have been suggested for the heterocycle. These include pyrindole, pyrroline, pyrrosoline, 9 pyrrolopyridine and pyrrolo [1,2-a] pyridine. It is proposed to use the name indolozine and the numbering as shown in (1), in accordance with the recommendations of the I.U.P.A.C. Direct support for Scholts’ formulation of the structure of indolizine followed from its catalytic reduction² showing the presence of four double bonds, to a derivative identical with d-coniceine (a) (ostahydtoindolizine) which on degradation with ayanogen bromide yielded a1 condine (9-n-gropylpieridine). Further evidence substantiating this formulation of indolizine arises from consideration of numerous syntheses described below.
1962-01-01T00:00:00ZFraser, MartinIndolizine was first synthesised by Scholts¹ in 1912 who proposed at that time the presently accepted ring structure (1). A number of alternative names and systems of numbering have been suggested for the heterocycle. These include pyrindole, pyrroline, pyrrosoline, 9 pyrrolopyridine and pyrrolo [1,2-a] pyridine. It is proposed to use the name indolozine and the numbering as shown in (1), in accordance with the recommendations of the I.U.P.A.C. Direct support for Scholts’ formulation of the structure of indolizine followed from its catalytic reduction² showing the presence of four double bonds, to a derivative identical with d-coniceine (a) (ostahydtoindolizine) which on degradation with ayanogen bromide yielded a1 condine (9-n-gropylpieridine). Further evidence substantiating this formulation of indolizine arises from consideration of numerous syntheses described below.Triphenyl- and tetraphenyl cyclopentadienylidesSinger, Michael Inglis Campbellhttps://hdl.handle.net/10023/151552019-03-29T11:24:15Z1968-01-01T00:00:00ZThe thermal decomposition of 2,3,4,5-tetraphenyldiazo cyclopentadiene in pyridine and methyl pyridines has been found to provide a route to the corresponding pyridinium 2,3,4,5-tetraphenyl-cyclopentadienylide. This procedure has been extended to include decomposition of the diazo compound in derivatives of Group V and VI elements and a route to a series of hitherto unreported tetraphenyloyclopentadienylides has been established. Triphenyl-phosphonium, triphenylarsonium, and triphenyIstibonium 2,3,4,5-tetraphenylcyclopentadienylides have been isolated as stable crystalline solids and evidence has been Sound for the existence of the triphenylbismuthonium analogue. Diphenylsulphoniumi methyIphenylsulphonium, and diphenylselenonium 2,3,4,5-tetra-phenyloyclopentadienylides have also been shown to have unusual stability. The mechanism of the decomposition reaction of 2,3,4,5- tetraphenyldiazocyclopentadiene is discussed and is considered to proceed by initial decomposition of the diazo compound to tetraphenyloarbenacyclopentadiene followed by eleotrophilic attack on a suitable heteror-atem group, containing a lone pair of electrons. A comparative study of the properties and the reactivities of the tetraphenylcyclopentadienylides with carbonyl compounds and nitrosobenzene has been made. The pKa's of some of the ylide conjugate acids were determined in 95% ethanol solution and it appears that for the similarly substituted ylidos there is no: consistent parallel between nucleophilicity and basicity. The thermal decomposition of other diazocyclopentadienes, including the 2,3,4,5-tetrachlora-, 2,3,4-tripheny1-1 5-bromo-2,3,4-triphenyl-, and 5-chloro-2,3,4-triphenyl- derivatives, occurred uncontrollably and attempts to obtain ylides failed when these diazo compounds were subjected to analogous conditions employed for 2,3,4,5-tetraphenyldiazocyclopentadiene. Phosphines were found to couple readily with substituted diazocyolopentadienes to form the corresponding phosphazines with the exception of the reaction between triphenylphosphine and 2,3,4,5-tetraphenyldiazocyclopentadiene. Evidence suggests that: these phosphazines, in acidic media, are protonated at the nitrogen atom rather than at the five-membered ring. Pyridinium 2,3,4-triphenyIcyclopentadienylide was prepared by alkylation of pyridine with 5-bromo-2,3,4-triphonyloyclo-pentadiene in a solution of nitromethane and subsequent basi-fication. In an attempt to prepare the analogous phosphomium ylide it was found that: triphonylphosphine in nitromethane led to reduction of the bromo compound. However when this reaction was carried out: in the absence of solventtriphenyl-(2,3,4-triphenyIcyclopentadienyl)phosphonium bromide was isolated. It has been found that tmiphenylarsine oxide and 2,3,4-triphenyloyclopentadiene undergo a reaction in triethylamine and phosphorus pentoxide to form triphenylarsonium 2,3,4- triphenyIeyclopentadienylide, and that' when the reaction is carried out in acetic anhydride the 5-acetyl ylide is formed. Some electrophilic substitution reactions on the triphenyl-phosphonium and triphenylarsonium 2,3,4-triphonyloyolopenta-dienylides have been done and the properties and nucleophilioity of these ylides have been investigated. A comparison has also been drawn between these ylides and their totmaphenylcyclopenta-dienylide analogues.
1968-01-01T00:00:00ZSinger, Michael Inglis CampbellThe thermal decomposition of 2,3,4,5-tetraphenyldiazo cyclopentadiene in pyridine and methyl pyridines has been found to provide a route to the corresponding pyridinium 2,3,4,5-tetraphenyl-cyclopentadienylide. This procedure has been extended to include decomposition of the diazo compound in derivatives of Group V and VI elements and a route to a series of hitherto unreported tetraphenyloyclopentadienylides has been established. Triphenyl-phosphonium, triphenylarsonium, and triphenyIstibonium 2,3,4,5-tetraphenylcyclopentadienylides have been isolated as stable crystalline solids and evidence has been Sound for the existence of the triphenylbismuthonium analogue. Diphenylsulphoniumi methyIphenylsulphonium, and diphenylselenonium 2,3,4,5-tetra-phenyloyclopentadienylides have also been shown to have unusual stability. The mechanism of the decomposition reaction of 2,3,4,5- tetraphenyldiazocyclopentadiene is discussed and is considered to proceed by initial decomposition of the diazo compound to tetraphenyloarbenacyclopentadiene followed by eleotrophilic attack on a suitable heteror-atem group, containing a lone pair of electrons. A comparative study of the properties and the reactivities of the tetraphenylcyclopentadienylides with carbonyl compounds and nitrosobenzene has been made. The pKa's of some of the ylide conjugate acids were determined in 95% ethanol solution and it appears that for the similarly substituted ylidos there is no: consistent parallel between nucleophilicity and basicity. The thermal decomposition of other diazocyclopentadienes, including the 2,3,4,5-tetrachlora-, 2,3,4-tripheny1-1 5-bromo-2,3,4-triphenyl-, and 5-chloro-2,3,4-triphenyl- derivatives, occurred uncontrollably and attempts to obtain ylides failed when these diazo compounds were subjected to analogous conditions employed for 2,3,4,5-tetraphenyldiazocyclopentadiene. Phosphines were found to couple readily with substituted diazocyolopentadienes to form the corresponding phosphazines with the exception of the reaction between triphenylphosphine and 2,3,4,5-tetraphenyldiazocyclopentadiene. Evidence suggests that: these phosphazines, in acidic media, are protonated at the nitrogen atom rather than at the five-membered ring. Pyridinium 2,3,4-triphenyIcyclopentadienylide was prepared by alkylation of pyridine with 5-bromo-2,3,4-triphonyloyclo-pentadiene in a solution of nitromethane and subsequent basi-fication. In an attempt to prepare the analogous phosphomium ylide it was found that: triphonylphosphine in nitromethane led to reduction of the bromo compound. However when this reaction was carried out: in the absence of solventtriphenyl-(2,3,4-triphenyIcyclopentadienyl)phosphonium bromide was isolated. It has been found that tmiphenylarsine oxide and 2,3,4-triphenyloyclopentadiene undergo a reaction in triethylamine and phosphorus pentoxide to form triphenylarsonium 2,3,4- triphenyIeyclopentadienylide, and that' when the reaction is carried out in acetic anhydride the 5-acetyl ylide is formed. Some electrophilic substitution reactions on the triphenyl-phosphonium and triphenylarsonium 2,3,4-triphonyloyolopenta-dienylides have been done and the properties and nucleophilioity of these ylides have been investigated. A comparison has also been drawn between these ylides and their totmaphenylcyclopenta-dienylide analogues.DiacylcyclopentadienesPreston, Nigel Wilkeshttps://hdl.handle.net/10023/151522019-03-29T11:22:12Z1968-01-01T00:00:00ZA property of aromatic compounds is their preference for reaction with electrophiles by substitution rather than by addition. A number. of substituted cyclopentadienes have been prepared by electrophilic substitution of the cyclopentadienide anion, a 6pi-electron aromatic species. When the substituents are electron- withdrawing groups, the result is increased acidity of the cyclopentadienes, and deactivation of their anions towards further electrophilic attack.
Reaction of cyclopentadienide anion with acyl chlorides gives rise to 1,2-diacyicyclopentadienes, which appear to exist, in the solid phase and in non-polar solvents almost entirely as the hydrogen-bonded enol tautomers, which are 2-acyl-6-hydroxyfulvenes. These enols have considerable acidity, since the negative charge of their anions is delocalised (See abstract in thesis for diagram).
The time-averaged structure of the enol molecule is symmetrical, and it is not possible spectroscopically to distinguish the hydrogen atom at C-3 from that at C-5.
The electrophilic substitution of the 2-acyl-6-hydroxy- fulvenes or their anions is of interest because of the deactivating influence of the acyl groups, together with the fact that, there are three different possible sites for electrophilic substitution, viz. 0-5(5), C-4 and 0.
Nitrated, brominated and azo-coupled derivatives have been prepared from 2-benzoyl-6-phenyl-6-hydroxyfulvene and 2-acetyl-6-raethyl-6-hydroxyfulvene. Bromination and nitration give C-4 substituted products; the monobrominated derivatives readily undergo further bromination at C-3 and C-5, since the presence of one bromine atom has little, if any, deactivating effect. The reaction between 1,2-dibenzoyl- or 1,2-diacetylcyclopenta-dienide anion and aryl diazonium salts gives products substituted at G-5j which are tautomeric with 2,3-diacylcyclopentadienone arylhydrazones. An O-substituted compound has been obtained from the' reaction of dibenzoylcyclopentadienide anion with methyl chloroformate. Attempts to prepare triacylated cyclopentadienes by the action of acyl chlorides (without a Friedel-Crafts catalyst), or by Vilsmeier formylation of 2-acyl-6-hydroxyfulvenes, were unsuccessful.
Some possible pathways to diacylcyclocyclopentadienylides and pyridinium diacylcyclopentadienylides were explored, but yielded no ylides. However, triphenylarsonium 3,4-dibenzoylcyclopenta-dienylide was prepared by the reaction of 2-benzoyl-6-phenyl-6- hydroxyfulvene with triphenylarsine oxide in acetic anhydride, Triphenylarsonium 3,4-dipivaloylcyclopentadienylide was similarly prepared from 2-pivaloyl-6-t-butyl-6-hydroxyfulvene. Linn and Sharkey reported the reaction of 2-benzoyl-6- phenyl-6-hydroxyfulvene with hydrazine and with hydroxylamine to give the compounds 1,4-di]phenyl-2H-cyclopenta[d]pyridazine and 1,4-diphenylcyclopentaC d]-2,3-oxazine. (See abstract in thesis for diagram).
Analogues have been prepared from 2-acetyl-6-methyl-6-hydroxy- fulvene. These heterocyclic systems are iso-pi-electronic with azulexie. The 2H,-cyclopenta[d]pyridaaines were found to resemble azulenes in their reaction with electrophiles on the five- membered ring, Brominated and formylated derivatives were prepared, the substituents occupying the 5- or 7-position, Protonation takes place at C-5 or G-7 and the resulting methylene group is reactive. Condensation with carbonyl compounds such as p-dimethyl- aminobenaaldehyde and diphenylcyclopropenone was found to occur readily.
The cyclopenta[d]-2,3-oxazines' appear to be' somewhat less reactive towards electrophiles than the 2H-cyclopentaCd]pyrid- azines, and formylation was successful, Brominated derivatives were nevertheless obtained. It is concluded, on the basis of their reactions, and the K.M.R, coupling constants of the five- membered ring protons of the brominated derivatives, that a lesser degree of n-electron delocalisation exists in the cyclo- penta[d]-2,3-oxazines than in the 2-substituted cyclopenta[d]-pyridazines.
The appendix to this thesis contains an account of some reactions of the cyclononatetraenide anion, including the attempted preparation of ylides incorporating the 10 n-electron cyclonona-tetraenide ring.
1968-01-01T00:00:00ZPreston, Nigel WilkesA property of aromatic compounds is their preference for reaction with electrophiles by substitution rather than by addition. A number. of substituted cyclopentadienes have been prepared by electrophilic substitution of the cyclopentadienide anion, a 6pi-electron aromatic species. When the substituents are electron- withdrawing groups, the result is increased acidity of the cyclopentadienes, and deactivation of their anions towards further electrophilic attack.
Reaction of cyclopentadienide anion with acyl chlorides gives rise to 1,2-diacyicyclopentadienes, which appear to exist, in the solid phase and in non-polar solvents almost entirely as the hydrogen-bonded enol tautomers, which are 2-acyl-6-hydroxyfulvenes. These enols have considerable acidity, since the negative charge of their anions is delocalised (See abstract in thesis for diagram).
The time-averaged structure of the enol molecule is symmetrical, and it is not possible spectroscopically to distinguish the hydrogen atom at C-3 from that at C-5.
The electrophilic substitution of the 2-acyl-6-hydroxy- fulvenes or their anions is of interest because of the deactivating influence of the acyl groups, together with the fact that, there are three different possible sites for electrophilic substitution, viz. 0-5(5), C-4 and 0.
Nitrated, brominated and azo-coupled derivatives have been prepared from 2-benzoyl-6-phenyl-6-hydroxyfulvene and 2-acetyl-6-raethyl-6-hydroxyfulvene. Bromination and nitration give C-4 substituted products; the monobrominated derivatives readily undergo further bromination at C-3 and C-5, since the presence of one bromine atom has little, if any, deactivating effect. The reaction between 1,2-dibenzoyl- or 1,2-diacetylcyclopenta-dienide anion and aryl diazonium salts gives products substituted at G-5j which are tautomeric with 2,3-diacylcyclopentadienone arylhydrazones. An O-substituted compound has been obtained from the' reaction of dibenzoylcyclopentadienide anion with methyl chloroformate. Attempts to prepare triacylated cyclopentadienes by the action of acyl chlorides (without a Friedel-Crafts catalyst), or by Vilsmeier formylation of 2-acyl-6-hydroxyfulvenes, were unsuccessful.
Some possible pathways to diacylcyclocyclopentadienylides and pyridinium diacylcyclopentadienylides were explored, but yielded no ylides. However, triphenylarsonium 3,4-dibenzoylcyclopenta-dienylide was prepared by the reaction of 2-benzoyl-6-phenyl-6- hydroxyfulvene with triphenylarsine oxide in acetic anhydride, Triphenylarsonium 3,4-dipivaloylcyclopentadienylide was similarly prepared from 2-pivaloyl-6-t-butyl-6-hydroxyfulvene. Linn and Sharkey reported the reaction of 2-benzoyl-6- phenyl-6-hydroxyfulvene with hydrazine and with hydroxylamine to give the compounds 1,4-di]phenyl-2H-cyclopenta[d]pyridazine and 1,4-diphenylcyclopentaC d]-2,3-oxazine. (See abstract in thesis for diagram).
Analogues have been prepared from 2-acetyl-6-methyl-6-hydroxy- fulvene. These heterocyclic systems are iso-pi-electronic with azulexie. The 2H,-cyclopenta[d]pyridaaines were found to resemble azulenes in their reaction with electrophiles on the five- membered ring, Brominated and formylated derivatives were prepared, the substituents occupying the 5- or 7-position, Protonation takes place at C-5 or G-7 and the resulting methylene group is reactive. Condensation with carbonyl compounds such as p-dimethyl- aminobenaaldehyde and diphenylcyclopropenone was found to occur readily.
The cyclopenta[d]-2,3-oxazines' appear to be' somewhat less reactive towards electrophiles than the 2H-cyclopentaCd]pyrid- azines, and formylation was successful, Brominated derivatives were nevertheless obtained. It is concluded, on the basis of their reactions, and the K.M.R, coupling constants of the five- membered ring protons of the brominated derivatives, that a lesser degree of n-electron delocalisation exists in the cyclo- penta[d]-2,3-oxazines than in the 2-substituted cyclopenta[d]-pyridazines.
The appendix to this thesis contains an account of some reactions of the cyclononatetraenide anion, including the attempted preparation of ylides incorporating the 10 n-electron cyclonona-tetraenide ring.Excited state reactions of some aromatic carbonyl compoundsIreland, John Framehttps://hdl.handle.net/10023/151512019-03-29T11:22:03Z1972-01-01T00:00:00ZThe pK values for xanthone protonation in the S₀, S₁ and T₁ states have been determined by direct measurement and by Forster Cycle calculation. Both methods for determining pK give the order for xanthone of pK(T₁) > pK(S₁) > pK(S₀). A study of benzophenones and acetophenones showed this pK order to be a common one for aromatic carbonyl compounds. The pK order for these compounds has been explained in terms of the type of transitions involved and the S₁-T₁ splitting of these transitions. In the case of substituted aromatic carbonyl compounds the pK order reflects the effect of substitution on the lowest S₀-S₁ and transitions. Results are also presented on the effect of inorganic anions solvenli and temperature on xanthone fluorescence. Spectral details are reported for several xanthones, benzophenones, acetophenones, and anthraquinones.
1972-01-01T00:00:00ZIreland, John FrameThe pK values for xanthone protonation in the S₀, S₁ and T₁ states have been determined by direct measurement and by Forster Cycle calculation. Both methods for determining pK give the order for xanthone of pK(T₁) > pK(S₁) > pK(S₀). A study of benzophenones and acetophenones showed this pK order to be a common one for aromatic carbonyl compounds. The pK order for these compounds has been explained in terms of the type of transitions involved and the S₁-T₁ splitting of these transitions. In the case of substituted aromatic carbonyl compounds the pK order reflects the effect of substitution on the lowest S₀-S₁ and transitions. Results are also presented on the effect of inorganic anions solvenli and temperature on xanthone fluorescence. Spectral details are reported for several xanthones, benzophenones, acetophenones, and anthraquinones.Studies in the pyrolysis of some benzyl bromidesMearns, Alexander H.https://hdl.handle.net/10023/151472019-03-29T11:23:51Z1961-01-01T00:00:00ZThe work described in subsequent pages arose from certain difficulties in the current knowledge of the bond dissociation energies (D) of compounds of the type C₆H₅CH₂-X. For the reaction
C₆H₅CH₂-X → C₆H₅CH₂ - + X – D k.cals. (1)
we can write
D(C₆H₅CH₂-X) = ΔHf(C₆H₅CH₂-) + ΔHf(X-) - ΔHf(C₆H₅CH₂-X) (2)
where ΔHf is the heat of formation of a chemical entity. It has been the task of many recent researches to evaluate (D) for different compounds. Since the last two terms in the thermochemical equation are often known, a determination of D(C₆H₅CH₂-X) permits the heat of formation of the benzyl radical to be evaluated. It is obviously necessary that a consistent scheme should produce a single value for ΔHf(C₆H₅CH₂-) and one which is independent of the nature of X. Early work in this field by Szwarc had produced such agreement, but recent more detailed work, threw doubt on his findings for D(C₆H₅CH₂-H). Since his values were claimed to be cross-checked through (2), it was clear that his work on the determination of D(C₆H₅CH₂-H). Since his values were claimed to be cross-checked through (2), it was clear that his work on the determination of D (C₆H₅CH₂-Br)⁴ might also be in error, for it was claimed to agree with his toluene results.
The pyrolysis of bromides in the presence of excess toluene has been the main kinetic practised by Szwarc, and benzyl bromide is one of many bromides which have been investigated by him.
In theory the method requires that the primary dissociation R – Br → R- + Br- (3) shall be followed by the inhibition of secondary processes by reactions
R- + C₆H₅CH₃ → RH + C₆H₅CH₂- (4)
Br- + C₆H₅Ch₃ → HBr + C₆H₅CH₂- (5)
2C₆H₅CH₂- → C₆H₅CH₂CH₂C₆H₅ (6)
Swarc claimed that the method showed the decompositions to have a first order dependence on RBr concentration, and that the temperature dependence of the velocity constant followed an equation
log₁₀k = log₁₀A – E/4.57T
for the most extensively investigated cases. He laid stress on the fact that the values of A he obtained were close to 10¹³ sec⁻¹, which is the expected value for a first order reaction, and hence that he was observing the dissociation process (3). As usual in this field the energy of activation E was taken as the bond dissociation energy. Justification for this assumption will be considered in the next section.
Benzyl bromide was one of the compounds Szwarc investigated more extensively and the results conformed with the above generalisations. In case of several other bromides the published results do not justify his assumption that the temperature independent factor would be found to have the value 10¹³ sec⁻¹ under a more exhaustive scrutiny. These items prompted a re-examination of the whole toluene carrier gas technique as applied to benzyl bromide. In one form of this technique, and probably the most widely used version, a stream of toluene vapour entrains the halide Rbr by passage over the surface of the latter. Although temperatures above the dew point of toluene were advocated by Szwarc, elementary considerations suggested that solution of toluene in the Rbr could not be prevented by this and uniformity of entrainment would suffer greatly. Varying concentrations of reactant would result and kinetic deductions would be invalidated. As described in later pages, some simple experiments showed this suspicion about the toluene carrier gas technique to be correct. In view of this end and the chemical uncertainties quoted earlier, there seemed a need to re-investigate the pyrolysis of benzyl bromide fairly extensively. In later pages the details of such work are given together with work on the chlorobenzyl bromides. Before dealing with the practical aspects of the work a short survey of the relevant previous investigations and kinetic techniques used is given.
1961-01-01T00:00:00ZMearns, Alexander H.The work described in subsequent pages arose from certain difficulties in the current knowledge of the bond dissociation energies (D) of compounds of the type C₆H₅CH₂-X. For the reaction
C₆H₅CH₂-X → C₆H₅CH₂ - + X – D k.cals. (1)
we can write
D(C₆H₅CH₂-X) = ΔHf(C₆H₅CH₂-) + ΔHf(X-) - ΔHf(C₆H₅CH₂-X) (2)
where ΔHf is the heat of formation of a chemical entity. It has been the task of many recent researches to evaluate (D) for different compounds. Since the last two terms in the thermochemical equation are often known, a determination of D(C₆H₅CH₂-X) permits the heat of formation of the benzyl radical to be evaluated. It is obviously necessary that a consistent scheme should produce a single value for ΔHf(C₆H₅CH₂-) and one which is independent of the nature of X. Early work in this field by Szwarc had produced such agreement, but recent more detailed work, threw doubt on his findings for D(C₆H₅CH₂-H). Since his values were claimed to be cross-checked through (2), it was clear that his work on the determination of D(C₆H₅CH₂-H). Since his values were claimed to be cross-checked through (2), it was clear that his work on the determination of D (C₆H₅CH₂-Br)⁴ might also be in error, for it was claimed to agree with his toluene results.
The pyrolysis of bromides in the presence of excess toluene has been the main kinetic practised by Szwarc, and benzyl bromide is one of many bromides which have been investigated by him.
In theory the method requires that the primary dissociation R – Br → R- + Br- (3) shall be followed by the inhibition of secondary processes by reactions
R- + C₆H₅CH₃ → RH + C₆H₅CH₂- (4)
Br- + C₆H₅Ch₃ → HBr + C₆H₅CH₂- (5)
2C₆H₅CH₂- → C₆H₅CH₂CH₂C₆H₅ (6)
Swarc claimed that the method showed the decompositions to have a first order dependence on RBr concentration, and that the temperature dependence of the velocity constant followed an equation
log₁₀k = log₁₀A – E/4.57T
for the most extensively investigated cases. He laid stress on the fact that the values of A he obtained were close to 10¹³ sec⁻¹, which is the expected value for a first order reaction, and hence that he was observing the dissociation process (3). As usual in this field the energy of activation E was taken as the bond dissociation energy. Justification for this assumption will be considered in the next section.
Benzyl bromide was one of the compounds Szwarc investigated more extensively and the results conformed with the above generalisations. In case of several other bromides the published results do not justify his assumption that the temperature independent factor would be found to have the value 10¹³ sec⁻¹ under a more exhaustive scrutiny. These items prompted a re-examination of the whole toluene carrier gas technique as applied to benzyl bromide. In one form of this technique, and probably the most widely used version, a stream of toluene vapour entrains the halide Rbr by passage over the surface of the latter. Although temperatures above the dew point of toluene were advocated by Szwarc, elementary considerations suggested that solution of toluene in the Rbr could not be prevented by this and uniformity of entrainment would suffer greatly. Varying concentrations of reactant would result and kinetic deductions would be invalidated. As described in later pages, some simple experiments showed this suspicion about the toluene carrier gas technique to be correct. In view of this end and the chemical uncertainties quoted earlier, there seemed a need to re-investigate the pyrolysis of benzyl bromide fairly extensively. In later pages the details of such work are given together with work on the chlorobenzyl bromides. Before dealing with the practical aspects of the work a short survey of the relevant previous investigations and kinetic techniques used is given.Some dihydrodiazapepinium salts and related compounds.Tucker, Kanwaljit S.https://hdl.handle.net/10023/151412019-03-29T11:24:31Z1978-01-01T00:00:00ZA wide variety of 6-aryl-2, 3-dihydro-1, 4-diazepinium salts has been prepared by reaction of 1,2-diamines with 1, 5-diaza-3- aryl-pentadienium salts. The latter compounds were readily accessible by Vilsmeier formylation of the appropriate arylacetic acid. Some dianil salts were also prepared via chlorovinyl- aldehydes.
Cyclisation of the 3-aryl substituted vinamidinium compounds is sensitive to the effects of substituents adjacent to the reactive centres. The reaction of the open-chain vinamidinium salts with piperidine suggests that the formation of the 7-membered ring compounds is a two step process, with the rate of cyclisation determined by the second-step. For sterically hindered aryl-vinamidinium salts and/or diamines cyclisation to diazepines was accomplished either by initial treatment of the vinamidinium salt with ammonia followed by addition of the diamin or by using the sodium salts of arylmalondialdehydes obtained by alkaline hydrolysis of the vinamidinium salts.
Some 6-unsubstituted dihydrodiazepinium salts were also prepared from β-diketones.
The studies of the reactions of 6-aryl-2, 3-dihydrodiazepinium salts with electrophiles showed that bromination and nitration occurs at the p-position of the 6-phenyl ring, and that the phenyl ring is activated by its diazepine substituent. A substituent adjacent to the bond linking the two rings alters the geometry of the two rings and consequently affects the chemistry of these compounds by diminishing the conjugation between the two rings.
Kinetic studies indicate that substituents at the 2-position and N-positions of the diazepine ring also affect reactions at the P-position of the 6-phenyl ring; the rate of bromination is lowered by the introduction of methyl substituents at the 2-position.
The halogen atom of a 6-(p-halogenophenyl) dihydrodiazepinium salt is not replaced by nucleophiles. 5, 7-Unsubstituted-6-aryl- dihydrodiazepines undergo 'transdiazepination' on treatment with substituted ethylenediamine.
The 6-phenyldihydrodiazepinium salt forms a free radical on addition of concentrated sulphuric acid.
The mass spectral fragmentation of these compounds indicates the primary loss of an N₁-C₂ species; other fragmentation patterns are also described.
Some 1, 5-benzodiazepines were also studied. They also contain the vinamidinium system, but it is perturLed by a complicated interaction between the two rings. Bromination of these compounds takes place at the 2, 4-methyl substituents. Their mass spectra differ from those of the 6-aryldihydrodiazepines; quinoxaline and benzimidazole species are the predominant breakdown products. Some simple macrocycles were prepared from β- diketones and diamines. They also differ from the 2, 3-dihydro- diazepines; for example no electrophilic substitution products could be isolated.
The effect of electronic perturbation on the 1, 5-diazapenta- dienium system when it is contained in 1, 2-dihydro-2-oxo- and 2-thioxo-5-arylpyrimidinium salts was also investigated. They formed adducts with piperidine at their 4-position. Their syntheses were carried out by reactions of arylmalondialdehydes with dimethyl substituted urea and thiourea. Some of these compounds showed fluorescence.
The electronic structures of 2, 3-dihydro-6-aryl-1, 4-diazepinium salts, and of the other related salts containing the vinamidinium system which are considered in this thesis, were investigated by ¹³C n.m.r. spectroscopy.
1978-01-01T00:00:00ZTucker, Kanwaljit S.A wide variety of 6-aryl-2, 3-dihydro-1, 4-diazepinium salts has been prepared by reaction of 1,2-diamines with 1, 5-diaza-3- aryl-pentadienium salts. The latter compounds were readily accessible by Vilsmeier formylation of the appropriate arylacetic acid. Some dianil salts were also prepared via chlorovinyl- aldehydes.
Cyclisation of the 3-aryl substituted vinamidinium compounds is sensitive to the effects of substituents adjacent to the reactive centres. The reaction of the open-chain vinamidinium salts with piperidine suggests that the formation of the 7-membered ring compounds is a two step process, with the rate of cyclisation determined by the second-step. For sterically hindered aryl-vinamidinium salts and/or diamines cyclisation to diazepines was accomplished either by initial treatment of the vinamidinium salt with ammonia followed by addition of the diamin or by using the sodium salts of arylmalondialdehydes obtained by alkaline hydrolysis of the vinamidinium salts.
Some 6-unsubstituted dihydrodiazepinium salts were also prepared from β-diketones.
The studies of the reactions of 6-aryl-2, 3-dihydrodiazepinium salts with electrophiles showed that bromination and nitration occurs at the p-position of the 6-phenyl ring, and that the phenyl ring is activated by its diazepine substituent. A substituent adjacent to the bond linking the two rings alters the geometry of the two rings and consequently affects the chemistry of these compounds by diminishing the conjugation between the two rings.
Kinetic studies indicate that substituents at the 2-position and N-positions of the diazepine ring also affect reactions at the P-position of the 6-phenyl ring; the rate of bromination is lowered by the introduction of methyl substituents at the 2-position.
The halogen atom of a 6-(p-halogenophenyl) dihydrodiazepinium salt is not replaced by nucleophiles. 5, 7-Unsubstituted-6-aryl- dihydrodiazepines undergo 'transdiazepination' on treatment with substituted ethylenediamine.
The 6-phenyldihydrodiazepinium salt forms a free radical on addition of concentrated sulphuric acid.
The mass spectral fragmentation of these compounds indicates the primary loss of an N₁-C₂ species; other fragmentation patterns are also described.
Some 1, 5-benzodiazepines were also studied. They also contain the vinamidinium system, but it is perturLed by a complicated interaction between the two rings. Bromination of these compounds takes place at the 2, 4-methyl substituents. Their mass spectra differ from those of the 6-aryldihydrodiazepines; quinoxaline and benzimidazole species are the predominant breakdown products. Some simple macrocycles were prepared from β- diketones and diamines. They also differ from the 2, 3-dihydro- diazepines; for example no electrophilic substitution products could be isolated.
The effect of electronic perturbation on the 1, 5-diazapenta- dienium system when it is contained in 1, 2-dihydro-2-oxo- and 2-thioxo-5-arylpyrimidinium salts was also investigated. They formed adducts with piperidine at their 4-position. Their syntheses were carried out by reactions of arylmalondialdehydes with dimethyl substituted urea and thiourea. Some of these compounds showed fluorescence.
The electronic structures of 2, 3-dihydro-6-aryl-1, 4-diazepinium salts, and of the other related salts containing the vinamidinium system which are considered in this thesis, were investigated by ¹³C n.m.r. spectroscopy.Azulenes - with special reference to the action of electrophilic reagentsKirby, Edward Cameronhttps://hdl.handle.net/10023/151362019-03-29T11:21:05Z1961-01-01T00:00:00Z1961-01-01T00:00:00ZKirby, Edward CameronThe reactions of thiophens and furans with 2,4-dinitrobenzene diazonium compoundsGore, Suresh Trimbakhttps://hdl.handle.net/10023/151322019-03-29T11:22:53Z1976-01-01T00:00:00ZThe reaction of several thiophens and furans with 2, 4-dinitrobenzene diazonium sulphate in glacial acetic acid/water mixture has been studied. Thiophen and its 2-and 3-monomethyl derivatives gave arylated products with the liberation of nitrogen. Although there is a strong indication that free radicals are involved, the reaction mechanism remains uncertain. Various likely paths are discussed. 2, 4-Dimethyl, 2-t-butyl, and 2-phenyl thiophens yielded the azo compounds with the same diazonium salt. 2-Methylbenzo(b) thiophen, and 3-methylbenzo (b) thiophen also gave the azo coupled products. 2, 5-Dimethylthiophen yielded an equal proportion of the 3-azo- compound and the 2, 4-dinitrophenylhydrazone of 5-methylthiophen-2- aldehyde. Both the 2, 3, 5-trimethylthiophen and the tetramethylthiophen underwent side chain substitution in the 5-and 2-position respectively to give the corresponding 2, 4-dinitrophenylhydrazones. Dinitrophenylhydrazones of various polyalkyl thiophen aldehydes were prepared and characterised. ¹H. n. m. r. spectra of polyalkyl thiophens in deuteriotrifluoroacetic acid showed the proton exchange in methyl groups. However, acelylation of polymethyl thiophens and diazocoupling of polyalkyl benzenoid hydrocarbons failed to give any side chain substitution products. The reaction of furan, 2-methylfuran and 3-methylfuran with the 2, 4-dinitrobenzene diazonium solution in acetic acid yielded substituted N-(2, 4 dinitroanilino) - 2-oxo-2, 5-dihydropyrroles. Initial azo coupling with the furan followed by ring opening and subsequent rearrangement is thought to be the likely path for this reaction. Benzo(b) furan gave arylated products under similar conditions while 2-methylbenzo(b) furan gave a small amount of the azo coupled product in addition to the arylated product. Several primary aromatic amines including the weakly basic mono and dinitro anilines were diazotised in trifluoroacetic acid. Short reaction periods were required for the completion of the diazotisation and high yields of azo coupled products were obtained by subsequent coupling reactions. ¹H and ¹³C n.m.r. data on these benzene diazonium ions in trifluoroacetic acid was also obtained.
1976-01-01T00:00:00ZGore, Suresh TrimbakThe reaction of several thiophens and furans with 2, 4-dinitrobenzene diazonium sulphate in glacial acetic acid/water mixture has been studied. Thiophen and its 2-and 3-monomethyl derivatives gave arylated products with the liberation of nitrogen. Although there is a strong indication that free radicals are involved, the reaction mechanism remains uncertain. Various likely paths are discussed. 2, 4-Dimethyl, 2-t-butyl, and 2-phenyl thiophens yielded the azo compounds with the same diazonium salt. 2-Methylbenzo(b) thiophen, and 3-methylbenzo (b) thiophen also gave the azo coupled products. 2, 5-Dimethylthiophen yielded an equal proportion of the 3-azo- compound and the 2, 4-dinitrophenylhydrazone of 5-methylthiophen-2- aldehyde. Both the 2, 3, 5-trimethylthiophen and the tetramethylthiophen underwent side chain substitution in the 5-and 2-position respectively to give the corresponding 2, 4-dinitrophenylhydrazones. Dinitrophenylhydrazones of various polyalkyl thiophen aldehydes were prepared and characterised. ¹H. n. m. r. spectra of polyalkyl thiophens in deuteriotrifluoroacetic acid showed the proton exchange in methyl groups. However, acelylation of polymethyl thiophens and diazocoupling of polyalkyl benzenoid hydrocarbons failed to give any side chain substitution products. The reaction of furan, 2-methylfuran and 3-methylfuran with the 2, 4-dinitrobenzene diazonium solution in acetic acid yielded substituted N-(2, 4 dinitroanilino) - 2-oxo-2, 5-dihydropyrroles. Initial azo coupling with the furan followed by ring opening and subsequent rearrangement is thought to be the likely path for this reaction. Benzo(b) furan gave arylated products under similar conditions while 2-methylbenzo(b) furan gave a small amount of the azo coupled product in addition to the arylated product. Several primary aromatic amines including the weakly basic mono and dinitro anilines were diazotised in trifluoroacetic acid. Short reaction periods were required for the completion of the diazotisation and high yields of azo coupled products were obtained by subsequent coupling reactions. ¹H and ¹³C n.m.r. data on these benzene diazonium ions in trifluoroacetic acid was also obtained.The reactions of aromatic amines with 1,2-quinonesSmith, Peter Irvinehttps://hdl.handle.net/10023/151302019-03-29T11:23:25Z1971-01-01T00:00:00Z1971-01-01T00:00:00ZSmith, Peter IrvineNew variations of the 1, 6, 6aλ⁴-triheterapentalene structureMitchell, James Alexanderhttps://hdl.handle.net/10023/151242019-03-29T11:19:20Z1979-01-01T00:00:00ZThe reaction between 3-substituted-5-phenyl-1, 2-dithiolium salts and various aminoheterocycles was investigated. Substituted 2-aminopyridines gave, in most cases, a mixture of two isomeric products, formulated as dithiadiazacyclopent [a] indenes. Similarly, 2-amino-2-thiazoline and 2-aminothiazole gave a mixture of products. The effect of using different solvents and leaving groups in these reactions was studied. 4-Aminopyridine, 2-aminopyrimidine and 2-aminobenzimidazole each gave only one product, whereas 2,6-diaminopyridine produced a mixture of two disubstitution products- N-Phenylbenzamidine gave a small quantity of 5-phenyl-3-phenylimino- 3H-1, 2-dithiole, while 2-methylpyridine produced no useful material. Two byproducts, 5-phenyl-1, 2-dithiole-3-thione and 5-phenyl-1, 2- dithiole-3-one were formed in each reaction which was investigated. 2-Amino-4-methylpyridine reacted with perchloromethyl mercaptan to give a sulphenamide. Reaction of this compound with benzoylacetic acid, followed by thionation, provided an alternative route to one of the dithiadiazacyclopent [a] indene isomers. The sulphenamides of 2-amino-2-thiazoline and 2-aminothiazole failed to react with benzoylacetic acid. 1, 2, 4-Thiadiazoles were used to synthesise compounds formulated as 1H- and 6H-triheterapentalenes. 4, 5-Dihydro-5-imino-1, 2, 4-thiadiazoles reacted with arenediazonium fluoroborates to give 6H-3aλ⁴ -thia-1, 2, 3, 4 , 6-pentaazapentalehes. 4, 5-Dihydro-5-imino - 1,2,4-thiadiazoles formed Vilsmeier salts which reacted with aqueous methylamine or sodium hydrogen sulphide solution, producing 1H-3aλ⁴ thia-1,3,4,6-tetraazapentalenes and 6H-3, 3aλ⁴ -dithia-1, 4 , 6-triazapentalenes respectively. Sodium hydroxide and sodium hydrogen selenide solutions failed to react with these Vilsmeier salts. 6H-3-oxa-3aλ⁴ -thia-1, 4, 6-triazapentalenes were prepared from 5-acetamino-3-methyl-1, 2, 4 -thiadiazole, 5-formamino- 3-methyl- 1, 2, 4 - thiadiazole,3,6-dimethyl-5-methyl- thio-6H-3aλ⁴ -thia-1, 3, 4, 6-tetraazapentalene and from 4, 5-dihydro- 5-imino- 3, 4 - dimethyl-1, 2, 4 - thiadiazole. 6H-3, 3aλ⁴ -Dithia-1,4,6-triazapentalenes were prepared by thionating oxathiaazapentalenes, and by allowing carbon disulphide to react with 1, 2, 4-thiadiazolium salts. An attempted synthesis of 5,6-dimethyl-6H-3, 3aλ⁴ -dithia- 1, 2, 4 , 6-tetraazapentalene from 5-amino-3, 4-dimethyl-4H-1, 2, 4- thiadiazolium iodide proved unsuccessful. 4, 5-Dihydro-5-imino-3,4-dimethyl- 1, 2, 4-thiadiazole reacted with phenylisocyanate giving 2-aminophenyl-5, 6-dimethyl- 6H-3-oxa-3aλ4-thia-1, 4 , 6-triazapentalene. Phenylisothiocyanate gave 2-aminophenyl-5, 6-dimethyl-6H-3, 3aλ4-dithia-1, 4 , 6-triaza- pentalene. Thiophosgene gave 1, 3-bis(3, 4-dimethyl-1, 2, 4- thiadiazol-5-ylidene)acetone.
1979-01-01T00:00:00ZMitchell, James AlexanderThe reaction between 3-substituted-5-phenyl-1, 2-dithiolium salts and various aminoheterocycles was investigated. Substituted 2-aminopyridines gave, in most cases, a mixture of two isomeric products, formulated as dithiadiazacyclopent [a] indenes. Similarly, 2-amino-2-thiazoline and 2-aminothiazole gave a mixture of products. The effect of using different solvents and leaving groups in these reactions was studied. 4-Aminopyridine, 2-aminopyrimidine and 2-aminobenzimidazole each gave only one product, whereas 2,6-diaminopyridine produced a mixture of two disubstitution products- N-Phenylbenzamidine gave a small quantity of 5-phenyl-3-phenylimino- 3H-1, 2-dithiole, while 2-methylpyridine produced no useful material. Two byproducts, 5-phenyl-1, 2-dithiole-3-thione and 5-phenyl-1, 2- dithiole-3-one were formed in each reaction which was investigated. 2-Amino-4-methylpyridine reacted with perchloromethyl mercaptan to give a sulphenamide. Reaction of this compound with benzoylacetic acid, followed by thionation, provided an alternative route to one of the dithiadiazacyclopent [a] indene isomers. The sulphenamides of 2-amino-2-thiazoline and 2-aminothiazole failed to react with benzoylacetic acid. 1, 2, 4-Thiadiazoles were used to synthesise compounds formulated as 1H- and 6H-triheterapentalenes. 4, 5-Dihydro-5-imino-1, 2, 4-thiadiazoles reacted with arenediazonium fluoroborates to give 6H-3aλ⁴ -thia-1, 2, 3, 4 , 6-pentaazapentalehes. 4, 5-Dihydro-5-imino - 1,2,4-thiadiazoles formed Vilsmeier salts which reacted with aqueous methylamine or sodium hydrogen sulphide solution, producing 1H-3aλ⁴ thia-1,3,4,6-tetraazapentalenes and 6H-3, 3aλ⁴ -dithia-1, 4 , 6-triazapentalenes respectively. Sodium hydroxide and sodium hydrogen selenide solutions failed to react with these Vilsmeier salts. 6H-3-oxa-3aλ⁴ -thia-1, 4, 6-triazapentalenes were prepared from 5-acetamino-3-methyl-1, 2, 4 -thiadiazole, 5-formamino- 3-methyl- 1, 2, 4 - thiadiazole,3,6-dimethyl-5-methyl- thio-6H-3aλ⁴ -thia-1, 3, 4, 6-tetraazapentalene and from 4, 5-dihydro- 5-imino- 3, 4 - dimethyl-1, 2, 4 - thiadiazole. 6H-3, 3aλ⁴ -Dithia-1,4,6-triazapentalenes were prepared by thionating oxathiaazapentalenes, and by allowing carbon disulphide to react with 1, 2, 4-thiadiazolium salts. An attempted synthesis of 5,6-dimethyl-6H-3, 3aλ⁴ -dithia- 1, 2, 4 , 6-tetraazapentalene from 5-amino-3, 4-dimethyl-4H-1, 2, 4- thiadiazolium iodide proved unsuccessful. 4, 5-Dihydro-5-imino-3,4-dimethyl- 1, 2, 4-thiadiazole reacted with phenylisocyanate giving 2-aminophenyl-5, 6-dimethyl- 6H-3-oxa-3aλ4-thia-1, 4 , 6-triazapentalene. Phenylisothiocyanate gave 2-aminophenyl-5, 6-dimethyl-6H-3, 3aλ4-dithia-1, 4 , 6-triaza- pentalene. Thiophosgene gave 1, 3-bis(3, 4-dimethyl-1, 2, 4- thiadiazol-5-ylidene)acetone.Some hydrolytic reactions of beta-lactamsFreeman, Keithhttps://hdl.handle.net/10023/151202019-03-29T11:20:44Z1976-01-01T00:00:00ZThis thesis describes the synthesis and alkaline ring fission of some β-lactams. Three series of β-lactams were studied: those of type (A) bearing a substituent on the ring nitrogen; 1,3,4-trisubstituted 3-lactams (B); and the spiro-3-lactams of type (C).
[See diagrams within thesis - Abstract.]
Three synthetic routes were used for the synthesis of the p-lactams, namely (a) the Reformatsky Reaction using an imine and a bromoacetate ester, (b) the cyclization of a 3-bromopropionamide, and (c) the addition of an acid chloride across an imino group. In the acid chloride-imine reaction it was shown that, contrary to previous reports, the reaction will proceed successfully with an U-benzyloxycarbonylaminoacyl chloride, and that conditions of high-dilution are not necessary in order to obtain high yields. The results of hydrolytic studies indicate that intramolecular assistance by an amido-group alpha to the β-lactam carbonyl is not of significance in the hydrolysis of these β-lactams in the conditions employed (0.1-1.0 M sodium hydroxide). Hydrolyses were also conducted in the presence of micelle forming agents and the results obtained show that the effect of these upon the rate of hydrolytic fission is dependent upon the nature of the substituenis present on the β-lactam ring.
1976-01-01T00:00:00ZFreeman, KeithThis thesis describes the synthesis and alkaline ring fission of some β-lactams. Three series of β-lactams were studied: those of type (A) bearing a substituent on the ring nitrogen; 1,3,4-trisubstituted 3-lactams (B); and the spiro-3-lactams of type (C).
[See diagrams within thesis - Abstract.]
Three synthetic routes were used for the synthesis of the p-lactams, namely (a) the Reformatsky Reaction using an imine and a bromoacetate ester, (b) the cyclization of a 3-bromopropionamide, and (c) the addition of an acid chloride across an imino group. In the acid chloride-imine reaction it was shown that, contrary to previous reports, the reaction will proceed successfully with an U-benzyloxycarbonylaminoacyl chloride, and that conditions of high-dilution are not necessary in order to obtain high yields. The results of hydrolytic studies indicate that intramolecular assistance by an amido-group alpha to the β-lactam carbonyl is not of significance in the hydrolysis of these β-lactams in the conditions employed (0.1-1.0 M sodium hydroxide). Hydrolyses were also conducted in the presence of micelle forming agents and the results obtained show that the effect of these upon the rate of hydrolytic fission is dependent upon the nature of the substituenis present on the β-lactam ring.The nature, origin and mechanism of development off-flavour in frozen cod (Gadus morhus)McGill, Alister Smithhttps://hdl.handle.net/10023/151152019-03-29T11:19:43Z1976-01-01T00:00:00ZFish is a highly perishable foodstuff best preserved by low temperature storage but even under these conditions deterioration still occurs and off-flavours are produced. This thesis describes an investigation into the nature, origin and mechanism of development of the components responsible for this off-flavour in cod (Gadus morhua). An understanding of these matters may make it possible to prevent the development of this flavour or at least minimise the effect. In Chapter I the current theories of the perception and mechanism of taste and alfaction are described, as are the complexities of the chemical nature of flavour in food and especially fish. The causes of off-flavour development in fish are discussed and the background to the cold storage phenomenon introduced. The characterisation of the compounds responsible for the off-flavour is described in Chapter II. By using dinitrophenylhydrasone derivatisation it was found that carbonyls are largely responsible but these derivatives could not be used for a complete analysis. The technique that was finally used to fractionate the mixture was that of gas liquid chromatography supported by organoleptic assessment. In this chapter, the experimental procedures adopted in the investigation are described. In Chapter III the major component responsible for the cold storage flavour is shown to be present at extremely low concentrations in the fish and is identified as hept-cis-4-enal. Details of other volatile components present in cod flesh are also presented including two other aldehydes, hept-trans-2-enal and hepta-trans-2-cis-4-dienal which possess some of the off-flavour character. Chapter IV presents the evidence for the production of those compounds by an autoxidative pathway and gives information on their rate of production with temperature. Taste panel assessments carried out during the latter work showed that there was a positive correlation between increase in hept-cis-4-enal concentration and cold storage flavour. A more detailed study indicated that hept-cis-4-enal is produced by to 3 polyenoic fatty acid oxidation but it was not possible to resolve whether a specific fraction or the total lipid was involved in this production. The results show that in white fish the rate of oxidation in cold storage is slow despite the unsaturated nature of the lipids and an explanation for this is advanced in Chapter V where the general mechanism of autoxidation is discussed. Some consideration is also given to the method of formation of hept-cis-4-enal from the w 3 polyenoic acids. A number of possible routes have been identified but the most probable pathway is via one of the major peroxide Intermediates in the autoxidation
1976-01-01T00:00:00ZMcGill, Alister SmithFish is a highly perishable foodstuff best preserved by low temperature storage but even under these conditions deterioration still occurs and off-flavours are produced. This thesis describes an investigation into the nature, origin and mechanism of development of the components responsible for this off-flavour in cod (Gadus morhua). An understanding of these matters may make it possible to prevent the development of this flavour or at least minimise the effect. In Chapter I the current theories of the perception and mechanism of taste and alfaction are described, as are the complexities of the chemical nature of flavour in food and especially fish. The causes of off-flavour development in fish are discussed and the background to the cold storage phenomenon introduced. The characterisation of the compounds responsible for the off-flavour is described in Chapter II. By using dinitrophenylhydrasone derivatisation it was found that carbonyls are largely responsible but these derivatives could not be used for a complete analysis. The technique that was finally used to fractionate the mixture was that of gas liquid chromatography supported by organoleptic assessment. In this chapter, the experimental procedures adopted in the investigation are described. In Chapter III the major component responsible for the cold storage flavour is shown to be present at extremely low concentrations in the fish and is identified as hept-cis-4-enal. Details of other volatile components present in cod flesh are also presented including two other aldehydes, hept-trans-2-enal and hepta-trans-2-cis-4-dienal which possess some of the off-flavour character. Chapter IV presents the evidence for the production of those compounds by an autoxidative pathway and gives information on their rate of production with temperature. Taste panel assessments carried out during the latter work showed that there was a positive correlation between increase in hept-cis-4-enal concentration and cold storage flavour. A more detailed study indicated that hept-cis-4-enal is produced by to 3 polyenoic fatty acid oxidation but it was not possible to resolve whether a specific fraction or the total lipid was involved in this production. The results show that in white fish the rate of oxidation in cold storage is slow despite the unsaturated nature of the lipids and an explanation for this is advanced in Chapter V where the general mechanism of autoxidation is discussed. Some consideration is also given to the method of formation of hept-cis-4-enal from the w 3 polyenoic acids. A number of possible routes have been identified but the most probable pathway is via one of the major peroxide Intermediates in the autoxidationExploratory testing of current and new lubricant antioxidantsBurton, Alanhttps://hdl.handle.net/10023/151102019-03-29T11:25:16Z1995-07-01T00:00:00ZChapter one is a general introduction to lubricant degradation. Subjects discussed include the problems associated with oil degradation, the mechanism of the autoxidation process, products generated by autoxidation, methods used for controlling the autoxidation process, the reasoning for constant lubricant development and the conventional industrial screening tests. The concept of the radical clock, and the rationale for testing an antioxidants ability to trap alkyl radicals, are also introduced. Chapter two deals with the measurement of the rate constant, kH, at which the aminyl hydrogen is removed by alkyl radicals from 4,4'-disubstituted diphenylamines. The method used was based on the ability of some radicals to rearrange irreversibly. The radical clocks employed for this study were the 5-hexenyl and the neophyl rearrangements. Results indicated that the 5-hexenyl radical rearrangement was too fast so all the quantitative results were obtained using the neophyl rearrangement. The alkyl radicals were generated by the decomposition of a diacyl peroxide. Problems encountered with this source were radical disproportionation and heterolytic scission, both of which form 2-methyl-2-propenylbenzene. Various methods of overcoming these problems were discussed and, by taking into account the alkene formation, kH was obtained for a variety of diarylamines at differing temperatures. From these results the Arrhenius pre-exponential factors and activation energies were obtained. Log kH was found to correlate with op+ values for the para substituents. The experimental results show that diphenylamines with electron releasing substituents in the para position were the most efficient at trapping alkyl radicals; this was found to correlate with kinetic studies involving peroxyl radicals. Chapter three describes the measurement of the rate constant, kH, at which the phenolic hydrogen is removed by alkyl radicals from 2,6-di-t-butyl-4-substituted phenols. For this study the neophyl radical rearrangement was used. Solutions to problems associated with radical disproportionation and heterolytic scission are again suggested. The experimental results show that phenols with electron withdrawing substituents in the para-position were the most efficient at trapping alkyl radicals. Kinetic studies with peroxyl radicals give the opposite result in that phenols with electron releasing substituents in the para position were the most efficient. Chapter four deals with the testing of 4,4'-disubstituted diphenylamines with existing industrial screening tests. The results show that in general diphenylamines with electron releasing substituents in the para position were the most efficient antioxidants. The effect that the lubricant basestock has on these results was also investigated. Chapter five deals with slow release antioxidants. These compounds were designed to release a fresh supply of antioxidant as the original materials are consumed. Compounds under consideration were the N-amides, N-silyl diphenylamines, N-oxides and N-alkyl diphenylamines. Of these only the N-alkyl diphenylamines were further investigated using flash vacuum pyrolysis (FVP) and the industrial screening tests. The FVP results indicated that the N-alkyl diphenylamines were decomposing by cleavage of the N-C bond, although other mechanisms were probably important. The industrial screening tests indicated that the decomposition involved the oxidation of the nitrogen to the N-oxide which easily decomposed to the hydroxylamine, an active antioxidant. Chapter six gives a brief summary of the experimental results and the conclusions derived from them.
1995-07-01T00:00:00ZBurton, AlanChapter one is a general introduction to lubricant degradation. Subjects discussed include the problems associated with oil degradation, the mechanism of the autoxidation process, products generated by autoxidation, methods used for controlling the autoxidation process, the reasoning for constant lubricant development and the conventional industrial screening tests. The concept of the radical clock, and the rationale for testing an antioxidants ability to trap alkyl radicals, are also introduced. Chapter two deals with the measurement of the rate constant, kH, at which the aminyl hydrogen is removed by alkyl radicals from 4,4'-disubstituted diphenylamines. The method used was based on the ability of some radicals to rearrange irreversibly. The radical clocks employed for this study were the 5-hexenyl and the neophyl rearrangements. Results indicated that the 5-hexenyl radical rearrangement was too fast so all the quantitative results were obtained using the neophyl rearrangement. The alkyl radicals were generated by the decomposition of a diacyl peroxide. Problems encountered with this source were radical disproportionation and heterolytic scission, both of which form 2-methyl-2-propenylbenzene. Various methods of overcoming these problems were discussed and, by taking into account the alkene formation, kH was obtained for a variety of diarylamines at differing temperatures. From these results the Arrhenius pre-exponential factors and activation energies were obtained. Log kH was found to correlate with op+ values for the para substituents. The experimental results show that diphenylamines with electron releasing substituents in the para position were the most efficient at trapping alkyl radicals; this was found to correlate with kinetic studies involving peroxyl radicals. Chapter three describes the measurement of the rate constant, kH, at which the phenolic hydrogen is removed by alkyl radicals from 2,6-di-t-butyl-4-substituted phenols. For this study the neophyl radical rearrangement was used. Solutions to problems associated with radical disproportionation and heterolytic scission are again suggested. The experimental results show that phenols with electron withdrawing substituents in the para-position were the most efficient at trapping alkyl radicals. Kinetic studies with peroxyl radicals give the opposite result in that phenols with electron releasing substituents in the para position were the most efficient. Chapter four deals with the testing of 4,4'-disubstituted diphenylamines with existing industrial screening tests. The results show that in general diphenylamines with electron releasing substituents in the para position were the most efficient antioxidants. The effect that the lubricant basestock has on these results was also investigated. Chapter five deals with slow release antioxidants. These compounds were designed to release a fresh supply of antioxidant as the original materials are consumed. Compounds under consideration were the N-amides, N-silyl diphenylamines, N-oxides and N-alkyl diphenylamines. Of these only the N-alkyl diphenylamines were further investigated using flash vacuum pyrolysis (FVP) and the industrial screening tests. The FVP results indicated that the N-alkyl diphenylamines were decomposing by cleavage of the N-C bond, although other mechanisms were probably important. The industrial screening tests indicated that the decomposition involved the oxidation of the nitrogen to the N-oxide which easily decomposed to the hydroxylamine, an active antioxidant. Chapter six gives a brief summary of the experimental results and the conclusions derived from them.Synthesis of new microporous solids by template designNoble, Graham Williamhttps://hdl.handle.net/10023/151082019-03-29T11:22:33Z1999-01-01T00:00:00ZThe rational design and synthesis of organic templates for the synthesis of new microporous materials has resulted in the production of five new materials, three of which are known to be microporous, the other two being better described as being open framework materials. The first three microporous materials are named STA-1, -2 and -3 (for St. Andrews) and have structural compositions of the form MgxAl1-xPO4 x/n Rn+.yH2O (Mg0.18Al0.82PO4.R0.094-0.22H2O, as determined by EDX for STA-1). The fourth novel microporous solid is a boron aluminophosphate (BAlPO) and the fifth an aluminophosphate solid containing its organic template intact. All of the new materials were synthesised following a systematic study over a wide range of templates including 5 homologous series designed specifically to be used as templates in the production of alumino-silicates and -phosphates. The structure of the first two magnesium aluminophosphates (STA-1, STA-2) to be solved by single microcrystal diffraction at the ESRF at Grenoble on crystals approximately 30 x 30 x 30 mum in size is described. The in situ location of the template was determined directly from x-ray diffraction in the second of these materials and has formed part of a combined experimental and computational study into template location within novel frameworks. The study shows how the encapsulation of the template is directly responsible for the similarity in pore architecture between MAPO-56 and STA- 2 (which co-crystallise) since the template adopts the same orientation in both materials Polymeric / oligomeric templates have also formed part of this study. These templates are shown to influence the phase, crystallinity, particle size and catalytic performance of the product magnesio-aluminophosphate MAPO-31. Computer modelling has also been utilised to interpret the experimental data obtained from the systematic study on the use of polymeric templates. The in situ synthesis and subsequent encapsulation of two coordination complexes inside the supercage of zeolite-Y, including the 3-methyl-1,3,5,8,12- pentaazacyclotetradecane macrocycle is also described.
1999-01-01T00:00:00ZNoble, Graham WilliamThe rational design and synthesis of organic templates for the synthesis of new microporous materials has resulted in the production of five new materials, three of which are known to be microporous, the other two being better described as being open framework materials. The first three microporous materials are named STA-1, -2 and -3 (for St. Andrews) and have structural compositions of the form MgxAl1-xPO4 x/n Rn+.yH2O (Mg0.18Al0.82PO4.R0.094-0.22H2O, as determined by EDX for STA-1). The fourth novel microporous solid is a boron aluminophosphate (BAlPO) and the fifth an aluminophosphate solid containing its organic template intact. All of the new materials were synthesised following a systematic study over a wide range of templates including 5 homologous series designed specifically to be used as templates in the production of alumino-silicates and -phosphates. The structure of the first two magnesium aluminophosphates (STA-1, STA-2) to be solved by single microcrystal diffraction at the ESRF at Grenoble on crystals approximately 30 x 30 x 30 mum in size is described. The in situ location of the template was determined directly from x-ray diffraction in the second of these materials and has formed part of a combined experimental and computational study into template location within novel frameworks. The study shows how the encapsulation of the template is directly responsible for the similarity in pore architecture between MAPO-56 and STA- 2 (which co-crystallise) since the template adopts the same orientation in both materials Polymeric / oligomeric templates have also formed part of this study. These templates are shown to influence the phase, crystallinity, particle size and catalytic performance of the product magnesio-aluminophosphate MAPO-31. Computer modelling has also been utilised to interpret the experimental data obtained from the systematic study on the use of polymeric templates. The in situ synthesis and subsequent encapsulation of two coordination complexes inside the supercage of zeolite-Y, including the 3-methyl-1,3,5,8,12- pentaazacyclotetradecane macrocycle is also described.The regioselective hydrogenation of acrylic acids using rhodium-mixed anhydride catalyst precursorsFairfax, Neil Roberthttps://hdl.handle.net/10023/151042019-03-29T11:23:31Z1993-01-01T00:00:00ZComplexes of general composition [RhCl(PPh₃)n(Ph₂P0₂CCR = CR'R'')] (n=2 R = H, R' =R" =Me; R = R' =H, R'' =CH = CHMe; R = Me, R' =H, R'' =Ph; n=l, R = R'=H, R'' =Me or CH = CHMe) have been used as precursors for the catalytic hydrogenation of various substituted acrylic acids, [HO₂CCR = CR' R'']. The reactions of [RhCl(PPh₃)(Ph₂P0₂CCH = CHMe)] and '[0₂CCH = CHMe] and [RhCl(PPh₃)₂(Ph₂P0₂CCMe = CHPh)] and '[0₂CCIVIe = CHPh] give [Rh(0₂CCH = CHMe)(PPh₃)(Ph₂P0₂CCH = CHMe)] and [Rh(0₂CCMe = CHPh)(PPh₂)(Ph₂P0₂CCMe = CHPh)] accordingly and these complexes are the respective active species in the catalytic hydrogenation of but-₂- enoic acid and ₂-methyl-₃-phenylpropenoic acid. The crossed reactions between [RhCl(PPh₃)(Ph₂P0₂CCH = CHMe)] and [0₂CCMe = CHPh], [RhCl(PPh₃)₂(Ph₂P0₂CCMe = CHPh)] and [0₂CCH = CHMe], [RhCl(PPh₃)(Ph₂P0₂CCH = CHMe)] and '[09CCH = CMe₂] and [RhCl(PPh₃)₂(Ph₂P0₂CCH = CMe₂)] and '[0₂CCH = CHMe] predominantly yield products in which the chelate mixed anhydride ligand is but-2-enoic acid derived, on account of its lesser substituted carbon-carbon double bond. Attempts at isolating hydride intermediates in the catalytic cycle have proved unsuccessful. However, investigations of the step by which the product carboxylic acid anion is released from the metal complex (transesterification reaction) have involved the synthesis of [RhCl(PPh₂)₂(Ph₂P07CCH₂CH₂Me)] (₂ isomers) from [RhCl(PPh₃)₃] and [Ph₂PO₂CCH₂CH₂Me] and [Rh(PPh₃)₂(Ph₂P0₂CCH₂CH₂Me)]+ from [RhCl(PPh₃)₂(Ph₂P0₂CCH₂CH₂Me)] and TlPFg. The reactions of both these products with '[0₂CCH = CHMe] yield the active species [Rh(0₂CCH = CHMe)(PPh₃)(Ph₂P0₂CCH = CHMe)]. Prior to transesterification the most likely intermediate in the catalytic cycle is [Rh(0₂CCH₂CH₂Me)(PPh₃)n(Ph₂P0₂CCH₂CH₂Me)] (n = l or ₂) in which both the mixed anhydride and the coordinated anion have been hydrogenated. The reaction of [RhCl(PPh₃)₂(Ph₂P0₂CCH₂CH9CH₃)] with K[0₂CCH₂CH₂CH₃)] affords the fluxional, square-planar species, [Rh(0₂CCH₂CH₂CH₃)(PPh₃)₂(Ph₂P0₂CCH₂CH₂CH₃)]. The hydrogenation of hexa-4-dienoic acid, [H0₂CCH = CHCH = CHMe], using rhodium-mixed anhydride complexes yields both hexanoic and hex-₄-enoic acids via two concurrent mechanisms, since the active species, [Rh(0₂CCH = CHCH = CHMe)(PPh₃)(Ph₂P0₂CCH = CHCH = CHMe)] exists in two forms; one containing a chelate mixed anhydride, the other a chelate hexa-4- dieonate ligand. The production of hexanoic acid is brought about by the active involvement of the chelate hexa-4-dienoate ligand in the catalytic cycle. Attempts to prevent this involvement have centred around the replacement of the chloride ligand in the catalyst precursor with non-labile fluoride and trifluoromethyl anions. [RhF(PPh₂)₃l reacts with mixed anhydride ligands to give ₅-coordinate species, [RhF(PPh₂)₂(Ph₂P0₂CCR = CR' R' ' )], in which the mixed anhydride is bound via phosphorus and carbonyl oxygen, however these precursors show no increased regioselectivity. The reaction of [RhCl(PPh₃)₂] with [Hg(CF₃)₂] does not yield [RhCF₂(PPh₂)₃] but [RhCl(PF₂)(PPh₃)₂], and in the presence of excess PPh₃ yields [RhCl(CF₃)₂(PPh₃)₂]. Other attempts to prevent the involvement of the bidentate hexa-4-dienoate ligand in the catalytic cycle have involved the addition of PPh₃ or CH₃CO₂H to the catalytic solution, and to a certain degree increased regioselectivity towards the production of hex-₄-enoic acid has been achieved. NOTE: All ³¹P NMR spectra presented, have their chemical shifts quoted relative to H₃PO₄, whilst all ¹⁹F NMR shifts are relative to CCI₃F.
1993-01-01T00:00:00ZFairfax, Neil RobertComplexes of general composition [RhCl(PPh₃)n(Ph₂P0₂CCR = CR'R'')] (n=2 R = H, R' =R" =Me; R = R' =H, R'' =CH = CHMe; R = Me, R' =H, R'' =Ph; n=l, R = R'=H, R'' =Me or CH = CHMe) have been used as precursors for the catalytic hydrogenation of various substituted acrylic acids, [HO₂CCR = CR' R'']. The reactions of [RhCl(PPh₃)(Ph₂P0₂CCH = CHMe)] and '[0₂CCH = CHMe] and [RhCl(PPh₃)₂(Ph₂P0₂CCMe = CHPh)] and '[0₂CCIVIe = CHPh] give [Rh(0₂CCH = CHMe)(PPh₃)(Ph₂P0₂CCH = CHMe)] and [Rh(0₂CCMe = CHPh)(PPh₂)(Ph₂P0₂CCMe = CHPh)] accordingly and these complexes are the respective active species in the catalytic hydrogenation of but-₂- enoic acid and ₂-methyl-₃-phenylpropenoic acid. The crossed reactions between [RhCl(PPh₃)(Ph₂P0₂CCH = CHMe)] and [0₂CCMe = CHPh], [RhCl(PPh₃)₂(Ph₂P0₂CCMe = CHPh)] and [0₂CCH = CHMe], [RhCl(PPh₃)(Ph₂P0₂CCH = CHMe)] and '[09CCH = CMe₂] and [RhCl(PPh₃)₂(Ph₂P0₂CCH = CMe₂)] and '[0₂CCH = CHMe] predominantly yield products in which the chelate mixed anhydride ligand is but-2-enoic acid derived, on account of its lesser substituted carbon-carbon double bond. Attempts at isolating hydride intermediates in the catalytic cycle have proved unsuccessful. However, investigations of the step by which the product carboxylic acid anion is released from the metal complex (transesterification reaction) have involved the synthesis of [RhCl(PPh₂)₂(Ph₂P07CCH₂CH₂Me)] (₂ isomers) from [RhCl(PPh₃)₃] and [Ph₂PO₂CCH₂CH₂Me] and [Rh(PPh₃)₂(Ph₂P0₂CCH₂CH₂Me)]+ from [RhCl(PPh₃)₂(Ph₂P0₂CCH₂CH₂Me)] and TlPFg. The reactions of both these products with '[0₂CCH = CHMe] yield the active species [Rh(0₂CCH = CHMe)(PPh₃)(Ph₂P0₂CCH = CHMe)]. Prior to transesterification the most likely intermediate in the catalytic cycle is [Rh(0₂CCH₂CH₂Me)(PPh₃)n(Ph₂P0₂CCH₂CH₂Me)] (n = l or ₂) in which both the mixed anhydride and the coordinated anion have been hydrogenated. The reaction of [RhCl(PPh₃)₂(Ph₂P0₂CCH₂CH9CH₃)] with K[0₂CCH₂CH₂CH₃)] affords the fluxional, square-planar species, [Rh(0₂CCH₂CH₂CH₃)(PPh₃)₂(Ph₂P0₂CCH₂CH₂CH₃)]. The hydrogenation of hexa-4-dienoic acid, [H0₂CCH = CHCH = CHMe], using rhodium-mixed anhydride complexes yields both hexanoic and hex-₄-enoic acids via two concurrent mechanisms, since the active species, [Rh(0₂CCH = CHCH = CHMe)(PPh₃)(Ph₂P0₂CCH = CHCH = CHMe)] exists in two forms; one containing a chelate mixed anhydride, the other a chelate hexa-4- dieonate ligand. The production of hexanoic acid is brought about by the active involvement of the chelate hexa-4-dienoate ligand in the catalytic cycle. Attempts to prevent this involvement have centred around the replacement of the chloride ligand in the catalyst precursor with non-labile fluoride and trifluoromethyl anions. [RhF(PPh₂)₃l reacts with mixed anhydride ligands to give ₅-coordinate species, [RhF(PPh₂)₂(Ph₂P0₂CCR = CR' R' ' )], in which the mixed anhydride is bound via phosphorus and carbonyl oxygen, however these precursors show no increased regioselectivity. The reaction of [RhCl(PPh₃)₂] with [Hg(CF₃)₂] does not yield [RhCF₂(PPh₂)₃] but [RhCl(PF₂)(PPh₃)₂], and in the presence of excess PPh₃ yields [RhCl(CF₃)₂(PPh₃)₂]. Other attempts to prevent the involvement of the bidentate hexa-4-dienoate ligand in the catalytic cycle have involved the addition of PPh₃ or CH₃CO₂H to the catalytic solution, and to a certain degree increased regioselectivity towards the production of hex-₄-enoic acid has been achieved. NOTE: All ³¹P NMR spectra presented, have their chemical shifts quoted relative to H₃PO₄, whilst all ¹⁹F NMR shifts are relative to CCI₃F.Occurence and reactions of long-chain epoxy acidsConacher, Henry Brown Stewarthttps://hdl.handle.net/10023/151032019-03-29T11:25:00Z1968-01-01T00:00:00ZThe possibility that long-chain epoxy acids may be key intermediates in the biosynthesis of acids with conjugated unsaturation has been investigated. By isomerisation of several epoxy acids with acidic and basic catalysts it was hoped to provide a chemical model to support this postulate. Acid-catalysed rearrangement of methyl vernolate, although giving no support for the above hypothesis, yielded a novel oxo-cyclopropane ester, identified by degradative and synthetic techniques as methyl 12-oxo-9,10-methyleneheptadecanoate. This reaction was studied in two solvents under different conditions, and a mechanism has been proposed for the formation of this unusual ester. Under optimum conditions the ester was obtained in yield. Base-catalysed rearrangement of suitably activated epoxy esters provided useful support for the biosynthetic postulate. By this means partial syntheses were effected of methyl coriolate from vernolate, racemio methyl L-dimorphecolate from 9,10-epoxy-octadec-12-enoate, and racemic methyl helenynolate from methyl 9,10-epoxyoctadec-12-ynoate. A synthesis of methyl parinarate from methyl linolenate via an epoxy intermediate was also attempted. Re-examination of three seed oils for unknown epoxy acids which would be biosynthetic intermediates, led to the discovery of a new epoxy acid, cis-9,10-epoxyoctadec-12-ynoic acid, in Helichrysum bracteatum seed oil. Finally, the inter- and intraglyceride distribution of vernolic acid in six seed oils was examined. It was shown that vernolic acid, like oleic and linoleic acids, competes effectively for the 2-position in the triglycerides.
1968-01-01T00:00:00ZConacher, Henry Brown StewartThe possibility that long-chain epoxy acids may be key intermediates in the biosynthesis of acids with conjugated unsaturation has been investigated. By isomerisation of several epoxy acids with acidic and basic catalysts it was hoped to provide a chemical model to support this postulate. Acid-catalysed rearrangement of methyl vernolate, although giving no support for the above hypothesis, yielded a novel oxo-cyclopropane ester, identified by degradative and synthetic techniques as methyl 12-oxo-9,10-methyleneheptadecanoate. This reaction was studied in two solvents under different conditions, and a mechanism has been proposed for the formation of this unusual ester. Under optimum conditions the ester was obtained in yield. Base-catalysed rearrangement of suitably activated epoxy esters provided useful support for the biosynthetic postulate. By this means partial syntheses were effected of methyl coriolate from vernolate, racemio methyl L-dimorphecolate from 9,10-epoxy-octadec-12-enoate, and racemic methyl helenynolate from methyl 9,10-epoxyoctadec-12-ynoate. A synthesis of methyl parinarate from methyl linolenate via an epoxy intermediate was also attempted. Re-examination of three seed oils for unknown epoxy acids which would be biosynthetic intermediates, led to the discovery of a new epoxy acid, cis-9,10-epoxyoctadec-12-ynoic acid, in Helichrysum bracteatum seed oil. Finally, the inter- and intraglyceride distribution of vernolic acid in six seed oils was examined. It was shown that vernolic acid, like oleic and linoleic acids, competes effectively for the 2-position in the triglycerides.Epoxidation of unsaturated estersSchuler, Hermann Roberthttps://hdl.handle.net/10023/151002019-03-29T11:24:00Z1974-01-01T00:00:00ZEight isomeric 9,12-diunsaturated c₁₈ methyl esters and seven isomers from two series of positionally isomeric methyl octadecacis, cis-dienoates, ie. 18:2 (5c12c - 8c12c) and (6c9c - 6c11c) were epoxidised to furnish monounsaturated monoepoxy esters and diepoxy esters. The monoepoxides and diepoxides were separated in pure form by column and thin layer chromatography, A comparative study was made of the chromatographic (TLC and GLC) behaviour and the NMR spectra of the unsaturated epoxy esters. TLC gave some indication of the position and geometry of the epoxy group and the nature of the unsaturated centre. The geometry of the epoxy group and the olefinic or acetylenic nature of the unsaturated centre were also revealed by GLC. 220 MHz NMR spectra, recorded for all unsaturated epoxy esters and diepoxy esters, exhibited up to nine more or less resolved signals which showed the long range deshielding influences of the ester group, the unsaturated centre, and the epoxy group. These influences were noticeable even when five methylene groups separated the deshielding group and the proton under consideration. Even though the NMR spectra did not give a complete structural analysis of the epoxy esters, they nevertheless revealed the geometry of the epoxy group as well as the nature of the unsaturated centre. The epoxides were convened to vicinal diether derivatives the mass spectrometric examination of which allowed the unambiguous location of the epoxy group and therefore also of the original double bond. Melting points of the vicinal dihydroxy acids, derived from all the twenty-six unsaturated epoxy esters by acetolysis and hydrolysis, were determined. The melting point differences between the various Isomers reflected such structural features as the geometry and position of the alpha-diol group and of the accompanying unsaturated centre. Two diepoxy esters, methyl cis-6,7, cis-9,10-diepoxystearate and methyl cis-8,9, cis-12,13 diepoxystearate, were reacted with boron trifluoride etherate. Instead of the expected dioxo derivatives, various cyclic ethers were obtained. A minor study was concerned with the hydroboration of various unsaturated long chain esters. The intermediate organoboranes were subjected to oxida.tion, protonolysis and coupling reactions to give in good yields hydroxy, oxo and hydroperoxy esters as well as hydrogenated and coupled products.
1974-01-01T00:00:00ZSchuler, Hermann RobertEight isomeric 9,12-diunsaturated c₁₈ methyl esters and seven isomers from two series of positionally isomeric methyl octadecacis, cis-dienoates, ie. 18:2 (5c12c - 8c12c) and (6c9c - 6c11c) were epoxidised to furnish monounsaturated monoepoxy esters and diepoxy esters. The monoepoxides and diepoxides were separated in pure form by column and thin layer chromatography, A comparative study was made of the chromatographic (TLC and GLC) behaviour and the NMR spectra of the unsaturated epoxy esters. TLC gave some indication of the position and geometry of the epoxy group and the nature of the unsaturated centre. The geometry of the epoxy group and the olefinic or acetylenic nature of the unsaturated centre were also revealed by GLC. 220 MHz NMR spectra, recorded for all unsaturated epoxy esters and diepoxy esters, exhibited up to nine more or less resolved signals which showed the long range deshielding influences of the ester group, the unsaturated centre, and the epoxy group. These influences were noticeable even when five methylene groups separated the deshielding group and the proton under consideration. Even though the NMR spectra did not give a complete structural analysis of the epoxy esters, they nevertheless revealed the geometry of the epoxy group as well as the nature of the unsaturated centre. The epoxides were convened to vicinal diether derivatives the mass spectrometric examination of which allowed the unambiguous location of the epoxy group and therefore also of the original double bond. Melting points of the vicinal dihydroxy acids, derived from all the twenty-six unsaturated epoxy esters by acetolysis and hydrolysis, were determined. The melting point differences between the various Isomers reflected such structural features as the geometry and position of the alpha-diol group and of the accompanying unsaturated centre. Two diepoxy esters, methyl cis-6,7, cis-9,10-diepoxystearate and methyl cis-8,9, cis-12,13 diepoxystearate, were reacted with boron trifluoride etherate. Instead of the expected dioxo derivatives, various cyclic ethers were obtained. A minor study was concerned with the hydroboration of various unsaturated long chain esters. The intermediate organoboranes were subjected to oxida.tion, protonolysis and coupling reactions to give in good yields hydroxy, oxo and hydroperoxy esters as well as hydrogenated and coupled products.Some reactions of methyl octadecenoates and related compoundsPerera, Buvipali Srimahttps://hdl.handle.net/10023/150982019-03-29T11:21:33Z1972-01-01T00:00:00ZPart I: The Methyl trans-Methyleneoctadecanoates. The sixteen isomeric methyl trans-methyleneoctadecanoates have been synthesised from the corresponding methyl trans alkenoates by the Simmons-Smith reaction, and some of their physical properties examined. Only one isomer (methyl trans-9,10-methyleneoctadecanoates) has previously been reported. The gas liquid chromatographic data are interesting in that on both polar and non-polar columns the cis and trans isomers are well separated. The methyl trans-methyleneoctadecanoates show diagnostic nuclear magnetic resonance signals around 9.8 to 9.6r. The 2,3-; 3,4-; 5,6-; 16,17-; and 17,18- isomers differ from one another, but the remainder are very similar to each other. The mass spectra of some of the isomers were examined but they do not provide much useful information. Our data, along with that previously reported for the corresponding cis isomers (see ref 21), should assist in the recognition of these compounds. For complete identification, however it may be necessary, in addition to examine the mass spectrum of the hydrogenated ester.
Part II: Halogenation of Unsaturated Long-chain Hydroxy Compounds. Neighbouring group participation in unsaturated hydroxy compounds occurring during reaction at the unsaturated centre has already been observed in appropriate long-chain compounds during various oxidation reactions and during oxymercuration. The halogenation of certain hydroxyalkenoates, octadecenols and octadecenoic acids has now been examined with a view to finding out if neighbouring group participation occurs during these reactions. The halogenating agents employed were iodine monochloride, bromine and chlorine giving rise to the electrophilic reagents I+, Br+ and C1+ respectively. In most reactions only the simple addition products (vic-dihalides) were observed and these were converted into ene-halides by dehydro- halogenation since the latter have been reported previously in only a few cases. The hydroxyl group was involved in halogenation in only a few instances - mainly in iodochlorination - to give substituted tetrahydrofurans (1,4-epoxides). Lactones were obtained during the halogenation of some unsaturated acids. Attempts to obtain N-heterocyclic compounds by the reaction of long-chain amines were less successful but the conversion of methyl ricinoleate to methyl 12-amino-oleate was satisfactorily achieved.
1972-01-01T00:00:00ZPerera, Buvipali SrimaPart I: The Methyl trans-Methyleneoctadecanoates. The sixteen isomeric methyl trans-methyleneoctadecanoates have been synthesised from the corresponding methyl trans alkenoates by the Simmons-Smith reaction, and some of their physical properties examined. Only one isomer (methyl trans-9,10-methyleneoctadecanoates) has previously been reported. The gas liquid chromatographic data are interesting in that on both polar and non-polar columns the cis and trans isomers are well separated. The methyl trans-methyleneoctadecanoates show diagnostic nuclear magnetic resonance signals around 9.8 to 9.6r. The 2,3-; 3,4-; 5,6-; 16,17-; and 17,18- isomers differ from one another, but the remainder are very similar to each other. The mass spectra of some of the isomers were examined but they do not provide much useful information. Our data, along with that previously reported for the corresponding cis isomers (see ref 21), should assist in the recognition of these compounds. For complete identification, however it may be necessary, in addition to examine the mass spectrum of the hydrogenated ester.
Part II: Halogenation of Unsaturated Long-chain Hydroxy Compounds. Neighbouring group participation in unsaturated hydroxy compounds occurring during reaction at the unsaturated centre has already been observed in appropriate long-chain compounds during various oxidation reactions and during oxymercuration. The halogenation of certain hydroxyalkenoates, octadecenols and octadecenoic acids has now been examined with a view to finding out if neighbouring group participation occurs during these reactions. The halogenating agents employed were iodine monochloride, bromine and chlorine giving rise to the electrophilic reagents I+, Br+ and C1+ respectively. In most reactions only the simple addition products (vic-dihalides) were observed and these were converted into ene-halides by dehydro- halogenation since the latter have been reported previously in only a few cases. The hydroxyl group was involved in halogenation in only a few instances - mainly in iodochlorination - to give substituted tetrahydrofurans (1,4-epoxides). Lactones were obtained during the halogenation of some unsaturated acids. Attempts to obtain N-heterocyclic compounds by the reaction of long-chain amines were less successful but the conversion of methyl ricinoleate to methyl 12-amino-oleate was satisfactorily achieved.Internal rotation about c-c and c-n bondsHamlin, Sally-Annehttps://hdl.handle.net/10023/150942019-03-29T11:22:24Z1978-01-01T00:00:00ZA study of the historical and more recent work on rotation about carbon-carbon and carbon-nitrogen bonds was the basis for the further investigation of three series of compounds: 1. 2,2'-disubstituted biphenyls, 2. N-benzyl-N-tosyl substituted anilines, 3. substituted quinone-anils. From this work it was established that, in certain compounds, the free energy (ΔG*) for hindered rotation cannot be discussed solely in steric terms but that electronic influences should also be considered. In. the substituted aniline series, it was concluded that a Hammett type correlation existed between the electronegativity of the substituents para to the amino group and the value of ΔG*. This correlation was extrapolated to explain the electronic influence of the substituents ortho to the amino group. Consideration was paid to the possibility that, for the ortho substituents, steric factors may outweigh electronic factors. An attempt was made to extend this correlation to explain the electronic influence of 2'- and 4'-substituents upon the ΔG* values and rates of racemization of-substituted biphenyls. However, it was found that the simple Hammett correlation was not followed and that, for the racemization studies, the entropy of activation (ΔS*) became a significant factor. The values of ΔG* for hindered rotation were obtained from the analysis of 100MHz n.m.r. spectra. The validity of these ΔG* values was discussed with respect to their accuracy and with respect to the effect of entropy. The synthetic routes used to obtain the three series of compounds were also discussed. The discussion of the synthetic routes includes the attempted preparations of a number of quinone-anils via the condensation of 2,6-di-t-butyl-l,4-benzoquinone with 4-substituted 2-benaylanilines. This was complicated by the production of impure samples of 2-benzylaniline and 2-benayl-4-chloroaniline. The synthesis of 2-benzyl-4-nitroaniline was not reproducible. The condensation reaction resulted in a number of products. These were separated by crystallization techniques and identified by high pressure liquid chromatography, I.R. spectroscopy, -13C and proton n.m.r. The structure of a new compound based on a dihydroindole containing one spiro carbon joined to a substituted quinone ring is proposed.
1978-01-01T00:00:00ZHamlin, Sally-AnneA study of the historical and more recent work on rotation about carbon-carbon and carbon-nitrogen bonds was the basis for the further investigation of three series of compounds: 1. 2,2'-disubstituted biphenyls, 2. N-benzyl-N-tosyl substituted anilines, 3. substituted quinone-anils. From this work it was established that, in certain compounds, the free energy (ΔG*) for hindered rotation cannot be discussed solely in steric terms but that electronic influences should also be considered. In. the substituted aniline series, it was concluded that a Hammett type correlation existed between the electronegativity of the substituents para to the amino group and the value of ΔG*. This correlation was extrapolated to explain the electronic influence of the substituents ortho to the amino group. Consideration was paid to the possibility that, for the ortho substituents, steric factors may outweigh electronic factors. An attempt was made to extend this correlation to explain the electronic influence of 2'- and 4'-substituents upon the ΔG* values and rates of racemization of-substituted biphenyls. However, it was found that the simple Hammett correlation was not followed and that, for the racemization studies, the entropy of activation (ΔS*) became a significant factor. The values of ΔG* for hindered rotation were obtained from the analysis of 100MHz n.m.r. spectra. The validity of these ΔG* values was discussed with respect to their accuracy and with respect to the effect of entropy. The synthetic routes used to obtain the three series of compounds were also discussed. The discussion of the synthetic routes includes the attempted preparations of a number of quinone-anils via the condensation of 2,6-di-t-butyl-l,4-benzoquinone with 4-substituted 2-benaylanilines. This was complicated by the production of impure samples of 2-benzylaniline and 2-benayl-4-chloroaniline. The synthesis of 2-benzyl-4-nitroaniline was not reproducible. The condensation reaction resulted in a number of products. These were separated by crystallization techniques and identified by high pressure liquid chromatography, I.R. spectroscopy, -13C and proton n.m.r. The structure of a new compound based on a dihydroindole containing one spiro carbon joined to a substituted quinone ring is proposed.Studies in polymer alloys for applications in prostheticsSmith, John Storrar Gunnhttps://hdl.handle.net/10023/150342018-07-06T09:15:52Z1996-07-01T00:00:00ZThis study relates to the preparation of polymer composites with properties of interest in dental and medical fields. These applications concern, bone cements which are used in total hip replacement operations, tooth filler composites, radiopaque composites and high impact materials used in the manufacturing of denture bases. A bone cement comprising apatite copolymer was prepared with properties which allow direct bonding to the poly(methyl methacrylate)(PMMA) polymer matrix and promotes bone ingrowth into the cement. Novel radiopaque materials were prepared and analysed by x-ray which revealed values greater or similar to those found with dentine or enamel. These radio-adjustable materials have the potential to be useful filling materials and to impart radiopacity to PMMA which is used in the manufacture of acrylic teeth and denture bases. In the case of high impact materials, preparation was carried out by suspension polymerisation and the impact strengths and modulus calculated. A formulation is shown with improved characteristics than those found for commercially available materials. The aim throughout has been the ability to transfer reaction conditions from bench to plant scale. Combinations of poly(butyl methacrylate) (PBMA), poly(ethyl methacrylate) (PEMA) and PMMA were re-examined for compatibility using DSC and NMR (solid state). It was found that limited compatibility exists in the solid state. In solution, agreeing with previous studies, incompatibility was shown.
1996-07-01T00:00:00ZSmith, John Storrar GunnThis study relates to the preparation of polymer composites with properties of interest in dental and medical fields. These applications concern, bone cements which are used in total hip replacement operations, tooth filler composites, radiopaque composites and high impact materials used in the manufacturing of denture bases. A bone cement comprising apatite copolymer was prepared with properties which allow direct bonding to the poly(methyl methacrylate)(PMMA) polymer matrix and promotes bone ingrowth into the cement. Novel radiopaque materials were prepared and analysed by x-ray which revealed values greater or similar to those found with dentine or enamel. These radio-adjustable materials have the potential to be useful filling materials and to impart radiopacity to PMMA which is used in the manufacture of acrylic teeth and denture bases. In the case of high impact materials, preparation was carried out by suspension polymerisation and the impact strengths and modulus calculated. A formulation is shown with improved characteristics than those found for commercially available materials. The aim throughout has been the ability to transfer reaction conditions from bench to plant scale. Combinations of poly(butyl methacrylate) (PBMA), poly(ethyl methacrylate) (PEMA) and PMMA were re-examined for compatibility using DSC and NMR (solid state). It was found that limited compatibility exists in the solid state. In solution, agreeing with previous studies, incompatibility was shown.Reactive intermediates in the reactions of aryl halides with basesHall, Julia Kathleen Aylmerhttps://hdl.handle.net/10023/150172019-03-29T11:20:23Z1969-01-01T00:00:00ZThe reaction of a series of 2,6-dimethylaryl halides with strong base has been investigated. Debromination to give polymethylbenzenes has been found to occur in all the systems studied and varying amounts of higher-boiling products, mainly polymethyl-bibenzyls, have also been obtained. Various mechanisms for these new reactions are discussed and the participation of an unusual triplet carbene intermediate is suggested. The related thermal decomposition of sodium o-halophenates has also been investigated. The participation of a similar carbene intermediate in this reaction appears to be unlikely. Possible mechanisms for the formation of diphenylmethanes obtained in the decomposition of sodium pentachlorophenate in methylbenzenes, are discussed.
1969-01-01T00:00:00ZHall, Julia Kathleen AylmerThe reaction of a series of 2,6-dimethylaryl halides with strong base has been investigated. Debromination to give polymethylbenzenes has been found to occur in all the systems studied and varying amounts of higher-boiling products, mainly polymethyl-bibenzyls, have also been obtained. Various mechanisms for these new reactions are discussed and the participation of an unusual triplet carbene intermediate is suggested. The related thermal decomposition of sodium o-halophenates has also been investigated. The participation of a similar carbene intermediate in this reaction appears to be unlikely. Possible mechanisms for the formation of diphenylmethanes obtained in the decomposition of sodium pentachlorophenate in methylbenzenes, are discussed.