The characteristics and biological relevance of inorganic amorphous calcium carbonate (ACC) precipitated from seawater
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The importance of amorphous calcium carbonate (ACC) as a precursor phase in the biomineralization of marine calcifiers is increasingly being reported, particularly as the presence of ACC has been observed or inferred in several major groups. Here, we investigate the structure of ACC and the conditions required for its precipitation from seawater-based solutions, with an emphasis on the coinfluence of the carbonate system (pH, dissolved inorganic carbon (DIC) concentration), seawater Mg/Ca ratio, and presence of amino acids. We find that Mg2+ and the presence of aspartic acid, glutamic acid, and glycine strongly inhibit ACC precipitation. Moreover, we were unable to precipitate ACC from seawater with a carbonate chemistry within the range of that thought to characterize the calcification site of certain marine calcifiers (i.e., DIC < 6 mM, pH < 9.3), although substantial modification of the seawater Mg/Ca ratio (Mg/Casw) allowed precipitation at a reduced DIC with the implication that this could be an important component of utilizing an ACC pathway. In addition, the degree to which Mg/Casw and the presence of amino acids influences the structure of ACC and the necessary seawater [CO32–] for precipitation is strongly pH dependent. At lower, more biologically relevant pH than that typical of much inorganic work, decreasing Mg/Casw can result in greater long-range order and less water of crystallization but facilitates precipitation at a considerably lower [CO32–] than at higher pH.
Evans , D , Webb , P B , Penkman , K , Kroger , R & Allison , N 2019 , ' The characteristics and biological relevance of inorganic amorphous calcium carbonate (ACC) precipitated from seawater ' , Crystal Growth & Design , vol. 19 , no. 8 , pp. 4300-4313 . https://doi.org/10.1021/acs.cgd.9b00003
Crystal Growth & Design
Copyright © 2019 American Chemical Society. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1021/acs.cgd.9b00003
DescriptionThis work was supported by the Leverhulme Trust (Research Project Grant 2015-268 to N.A., R.K., and K.P.). The Royal Society is gratefully acknowledged for the award of an Industry Fellowship to P.B.W.
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