Syntheses of Octacalcium Phosphate Containing Dicarboxylic Acids and Effects of the Side Groups on the Crystal Growth of Octacalcium Phosphate.

The syntheses of octacalcium phospates (OCPs) containing dicarboxylic acids, Ca8(HPO4)2-z(RC2O4)z(PO4)4⋅mH2O, were attempted. The effects of the side groups on crystal growth of these compounds were investigated. OCPs containing dicarboxylic acid were obtained from tricalcium phosphate (α-Ca3(PO4)2) in acetic acid/sodium acetate buffer solution by hydrolysis. As for dicarboxylic acids, succinic acid, methyl-succinic acid, mercaptosuccinic acid, DL-malic acid and L-aspartic acid were used. OCPs containing dicarboxylic acid obtained in this process were determined by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectrometry, thermogravimetric analyses and chemical analyses. All of these identified compounds were structurally similar to octacalcium phosphate, Ca8(HPO4)2(PO4)4⋅5H2O, with expanded a-axis unit-cell dimensions. Phosphate ions in “hydrated layer” of OCP were replaced by succinate ions with about 94% of theoretical replacement value. The percentage of replacement for OCPs containing dicarboxylic acid having the side groups were range 24 and 59%. Namely, the polarity and the size of the side groups effected on the incorporation of dicarboxylate ions into OCP interlamellar and the crystal growth.