The Atomistic Structure of Amorphous Carbonate, Phosphate and Sulfate Biominerals

Biominerals are key to all life, whether they make up exoskeletons of marine organisms (amorphous calcium carbonate), human bones (amorphous calcium phosphate) or being signs of extra-terrestrial life (amorphous iron sulfate) but little is know of their atomistic structures. How they behave could be determined by this structure and knowledge of this could lead to favouring certain crystallisation pathways or indeed speeding up the process, ie. If someone breaks their arm, can we induce faster healing? In the present study, amorphous biominerals including carbonates, phosphates and sulfates are synthesised (stabilised where necessary). The proton content is reduced either via heat-treatment or deuteratation. The deuteration method is the first of its kind and enabled the materials of study to be

examined at central facilities via x-ray and neutron diffraction. For the first time, neutron diffraction experiments have been conducted on amorphous calcium and magnesium carbonates. Also, a first synthesis of deuterated amorphous biominerals including amorphous calcium carbonate (ACC), amorphous magnesium carbonate (AMC) and amorphous calcium phosphate (ACP). Diffraction data from these materials are utilised by the empirical potential structure refinement (EPSR) algorithm to generate atomistic models using Reverse Monte Carlo (RMC). These models used well defined molecular units and yielded results showing the calcium distribution throughout ACC to be uniformed, contrary to former reports on the atomistic structure of ACC.