Caught in the act – novel approaches to preventing the crystallisation of amorphous materials

Mark Hodson – Project Lead (York)
Liane G. Benning  (Leeds)
John Harding (Sheffield)

Crystallisation and the transition from amorphous to crystalline states is an intriguing problem with important implications for the natural and engineered world. Many amorphous materials are inherently unstable; when synthesised in the laboratory they transform rapidly to stable crystalline phases. However, there are many environmental and engineering advantages to halting this transition and maintaining materials in their amorphous state.
We have recently shown that:
• earthworms secrete calcium carbonate granules that are largely crystalline (calcite) but that contain significant amounts of unusually stable amorphous calcium carbonate (ACC) (Hodson, Benning);
• granule trace element chemistry reflects that of the soil ingested by granule-producing earthworms (Hodson);
• granules collected from different soils contain different amounts of ACC (Hodson, Benning);
• concentrations of glutamic acid/glutamine in earthworm granules are the highest in any biomineral yet analysed in the NEaar laboratory (Penkman);
• organic molecules interact strongly with amorphous calcium carbonate surfaces in simulations (Freeman, Harding & Warwick collaborators).
Thus we hypothesise that the quantity and stability of granule ACC is controlled by the inorganic and organic trace composition of the granules. This project aims to provide initial data to elucidate the chemical and crystallographic mechanism for this unusual stabilisation of the ACC. Understanding the fundamental processes that stabilize such amorphous phases will inform biomimetic and industrial mineral synthesis processes.
With this funding we will carry out preliminary experiments to test our hypothesis thereby producing pilot data for a large EPSRC application. Earthworms will be cultured in soil of differing compositions (Hodson). The organic (Penkman) and inorganic (Hodson, Benning) chemistry of the granules and their crystallography (Benning, Brown) will be determined and compositional information related to the proportions of ACC present. These initial findings will be incorporated into computational modelling of the formation and crystallisation of calcium carbonate (Freeman, Harding) and our existing protocols for synthesising short-lived ACC (Benning).

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