Octacalcium Phosphate Carboxylates. 5. Incorporation of Excess Succinate and Ammonium Ions in the Octacalcium Phosphate Succinate Structure

Octacalcium phosphate succinate, Ca8(HPO₄)_1.07(succ)_0.93(PO₄)₄·6H₂O (OCP-SUCC), has an ~50% larger hydrated layer volume than that of its parent compound, octacalcium phosphate, Ca₈(HPO₄)₂(PO₄)₄·5H₂O (OCP). The incorporation of structurally excess ions in OCP-SUCC was established by chemical analyses, X-ray powder diffraction, and infrared spectroscopy. Both excess succinate and counter ammonium ions were found to incorporate in the hydrated layer of the OCP-SUCC structure; this incorporation caused a slight expansion in the a-axis of up to 3%. Removal of these excess ions resulted in contraction of the a-axis to near that of OCP-SUCC. OCP-SUCC and particularly other OCP-carboxylates (OCPCs) that have larger hydrated layer volumes have a potential to incorporate various molecules and ions; these OCPCs could serve as vehicles to facilitate slow release of these additives into aqueous solutions.