Transformation of dicalcium phosphate dihydrate into octacalcium phosphate with incorporated dicarboxylate ions

抄録

Octacalcium phosphate (OCP) has a layered structure consisting of apatitic and hydrated layers. The hydrogen phosphate ions in the hydrated layer can be replaced by dicarboxylate ions resulting in the formation of OCP with incorporated dicarboxylate ions. We herein report the transformation behaviour of dicalcium phosphate dihydrate (DCPD), which is used as starting material for the synthesis of OCP in acetic acid (Ace), succinic acid (Suc), suberic acid (Sub), and isophthalic acid (Isp) solutions at a pH of approximately 5.5 at 60°C. We found that DCPD with a small crystal size (specific surface area: 4.9 m²·g⁻¹) completely transformed into OCP within 1 h in Ace solution, whereas DCPD with a large crystal size (specific surface area: 0.62 m²·g⁻¹) did not form the OCP phase even when treated for 3 h. OCP incorporating Suc and Isp was formed from DCPD with a small crystal size in solutions of these dicarboxylic acids. On the other hand, Sub was not incorporated into OCP although Sub is a typical dicarboxylic acid that could be incorporated into the OCP structure. We concluded that although the dicarboxylic acids that are adaptable to these experimental conditions are limited, DCPD can be used as a starting material for OCP with incorporated dicarboxylate ions.