The chemical and structural properties of hydrolyzed octacalcium phosphate (OCP) appear to be of high relevance to tooth, bone and pathological bioapatites. Hydrolysis of synthetic well-crystallized OCP was studied at constant pH by using the pH stat method over the 6.1 to 8.6 range at 50°C and to a lesser extent at 37°C. Hydrolytic transformation proceeds according to thermodynamic requirements except for some retardation at the highest pH value as a consequence of decreased solubility of OCP which may be rate determining. The product of hydrolysis, OCP-hydrolyzate (OCPH), was characterized by chemical analysis, scanning electron microscopy, x-ray diffraction, electron microprobe (x-ray microanalysis, EDX) and solubility measurements under static and dynamic conditions. Even after prolonged hydrolysis at 50°C, the resulting product was a "calcium deficient apatite" with chemical composition and thermodynamic solubility properties differing from those of well-crystallized hydroxyapatite. Our overall findings provide new evidence that OCP may be a precursor phase in the formation of pathologic calcified deposits and normal biomineral, which appear to be complex hydrolyzates of OCP.
Tomazic, B. B.; Tung, M. S.; Gregory, T. M.; and Brown, W. E.
"Mechanism of Hydrolysis of Octacalcium Phosphate,"
Scanning Microscopy: Vol. 3
, Article 15.
Available at: https://digitalcommons.usu.edu/microscopy/vol3/iss1/15