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Morphological influence of functionalized and non-functionalized α,ω-dicarboxylates on calcite crystallization

Stephen Mann, Jon M. Didymus, Nigel P. Sanderson, Brigid R. Heywood and Eliseo J. Aso Samper

Abstract

The influence of a range of α,ω-dicarboxylates on the morphology of calcite crystals grown from supersaturated bicarbonate solutions was studied by optical and scanning electron microscopy. At Ca/malonate ≈ 3, spindle-shaped crystals elongated along the c axis and with curved {110} prismatic faces were formed. This effect was reduced with increasing chain length. The unsaturated derivative, maleate, was intermediate in potency compared with the saturated malonate and succinate compounds. In contrast, the trans isomer, fumarate, had minimal morphological effect. Functionalization of the lower chain acids had a marked influence on crystal morphology. Crystals grown in the presence of aspartate (α-aminosuccinate) exhibited well defined {110} prismatic faces at Ca/additive = 17, whilst γ-carboxyglutamate had a pronounced effect at ratios as high as 85. The stabilization of the {110} faces of calcite by αω-dicarboxylate binding is described in terms of electrostatic, geometric and stereochemical recognition at the crystal/additive interface.

Modelling Biomineralization: Studies on the Morphology of Synthetic Calcite

J. M. Didymus, S. Mann, N. P. Sanderson, P. Oliver, B. R. Heywood & E. J. Aso-Samper

Conference paper

372 Accesses

5 Citations

Abstract

Many organisms possess the remarkable ability to deposit single crystals of calcite (CaCCO3) with morphologies not normally observed in the inorganic world [1]. Whilst it is true that single geological crystals of calcite can exhibit an enormous range of different habits, all these forms have common interfacial angles and symmetry as described by the R̄3c space group. By contrast, the external forms of some biological single crystals of calcite have symmetries that are non-crystallographic. The coccolith segments deposited by the unicellular marine alga Emiliania huxleyi illustrate this phenomenon particularly well:- Current theories of biomineralization suggest that calcifying organisms have adopted strategies for controlling morphology based on the deployment of functional organic molecules. For example, proteins rich in aspartate and glutamate residues and also phosphoserine, are common for molluscs [3] whilst coccoliths of E. huxleyi are deposited along with sulphated and carboxylated polysaccharides [4]. Thus, carboxylate groups and, to a lesser extent, sulphates and phosphates play an important role in the biomineralization of calcite.