Potent Natural Inhibitors of CaCO3 Crystallization From Chalk Deposits

Fossilized calcareous structures in chalk collected from exposures of the Selma formation in Alabama yielded organic components comparable to the organic matrices of the calcium carbonate (CaCO3) shells of sea urchin and oyster. The organic matrix of the chalk was composed of 0.05% soluble protein and 0.17% soluble carbohydrate per dry weight. The possible role of the organic matrix as a regulator of CaCO3 formation was tested by use of two crystallization assays, the nucleation assay and constant composition assay. Results of the nucleation assay showed total inhibition of crystallization at 0.25 ug protein/ml and partial inhibition at 0.025 ug protein/ml. However, the Selma extract was not an inhibitor of the rate of crystal growth, once crystals had already formed, as shown by use of the constant composition assay. Analysis of the chalk extract by high performance liquid chromatography yielded distinct peaks in UV absorbance, indicating that it may contain more than one presumably protein component. In addition, the relatively high content of carbohydrates in the chalk extract suggests that some of the inhibitory activity may be due to the presence of these materials. OHIOJ. SCI. 86 (3): 106-109, 1986