Abstract
Octacalcium phosphate (OCP) has a layered structure composed of apatitic and hydrated layers. HPO42− in the hydrated layer can be substituted by dicarboxylate ions. We investigated formation of OCP with incorporated dicarboxylate ions, namely octacalcium phosphate carboxylate (OCPC), under synthetic conditions with various concentrations of benzenedicarboxylic acids (BDCAs) such as 1,2-benzenedicarboxylic acid (1,2BDCA, phthalic acid), 1,3-benzenedicarboxylic acid (1,3BDCA, isophthalic acid), and 1,4-benzenedicarboxylic acid (1,4BDCA, terephthalic acid). 1,3BDCA or a small amount of 1,2BDCA could be incorporated into OCP, but 1,4BDCA could not be incorporated into OCP. When the added amount of 1,3BDCA was larger than 2 mmol, OCPC with 1,3BDCA (1,3BDCA-OCPC) was formed with dicarboxylate-free OCP (Pure-OCP). The fractions of 1,3BDCA-OCPC with respect to Pure-OCP increased with increasing amounts of 1,3BDCA. When excessive amounts of 1,3BDCA, namely 25 times with respect to the stoichiometric composition of OCPC, were used for formation of OCPC, 1,3BDCA-OCPC was formed as a single phase. Addition of excessive amounts of 1,3BDCA prevented formation of Pure-OCP and had an advantage in formation of 1,3BDCA-OCPC.
