Interaction of bile salts with calcium phosphate

Insoluble calcium salts are always observed in different types of gallstones, such as calcium phosphate, calcium carbonate and calcium bilirubinate. The major form of calcium phosphate in gallstone is calcium hydroxyapatite(HAP). Understanding of the transformation of amorphous calcium phosphate(ACP) into HAP in bile is necessary to prevent gallstones formation. The aim of this paper was to examine the interaction of bile salts, an important bio-surfactant, with ACP using vibrational spectroscopy. ACP [ (Ca9-x(HPO4)(2x)(PO4)(6-2x))], calcium hydrogen phosphate (CaHPO4 .2H(2)O) and calcium phosphate (Ca-3(PO4)(2)) precipitations were synthesized. CaHPO4 reacted with NaDC (0. 1 mol . L-1) completely in solution, and mixed complex (NamCan(DC)(2n+m)) precipitate formed. In contrast, only part of Ca-3(PO4)(2) reacted with NaDC, and the aggregate of NaDC in solution increased by Ca2+ bridge. It indicated that the micelle of NaDC bound to Ca2+ on the solid surface of both CaHPO4 and Ca-3(PO4)(2), and the reactivity of CaHPO4 Was more stronger than that of Ca-3(PO4)(2). ACP reacted with NaDC, NaTC and NaC respectively. The results demonstrated that the solubility of ACP increased with increase of bile salts content in solution. The reacting capacity of bile salts for ACP has the following order: pO(2) NaDC > NaTC > NaC. The affinity of bile salts micelle to calcium binding to HPO42- in ACP is stronger than binding to PO43-. Therefore, ACP transfers easily into HAP under bile condition.