Complementary hydrazone-based dynamic covalent nanoparticles
Date
26/06/2019Author
Supervisor
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Abstract
The 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.
Type
Thesis, PhD Doctor of Philosophy
Rights
Embargo Date: 2022-03-20
Embargo Reason: Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 20th March 2022
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