Ionotropic Nucleation of Calcium Carbonate by Molluscan Matrix

TLDR: The hydrophilic, sulfated fraction of the organic matrix found in molluscan shells appears to be involved in crystal nucleation, and is located primarily at the sites of initial nucleation.

Abstract: The hydrophilic, sulfated fraction of the organic matrix found in molluscan shells appears to be involved in crystal nucleation. It is located primarily at the sites of initial nucleation. The hydrophilic fraction favors in vitro formation of calcified deposits, when it is fixed in place on the hydrophobic fraction. Calcium is bound by the hydrophillic fraction with high affinity and selectivity. Enzymatic desulfation reduces the calcium binding. However, the binding stoichiometry of one calcium for every two ester sulfates is not altered. The calcium binding induces local anion binding, which induces secondary calcium binding. This coordinated ion binding is known as ionotropy. The resultant local high concentration of ions is thought to bring about nucleation.