OCP crystals were hydrolyzed in solutions containing Ca2+, Mg2+, HPO42-, CO32-, F-, citrate or P2O7 ions. Products of hydrolysis were analyzed using scanning (SEM) and transmission (TEM) electron microscopy, infrared spectroscopy and x-ray diffraction.
Results demonstrated that the OCP to Apatite (AP) transformation is influenced by: (1) types of ions in solution: inhibited by Mg2+, citrate or P2O74-; facilitated by F-, CO32-, HPO42- or Ca2+ ions; (2) ionic concentrations; (3) solution pH; (4) OCP crystal size. SEM showed needle-like micro-crystals on the surfaces and ends of OCP macrocrystals. TEM showed side-to-side and end-to-end arrangements and presence of central defects in the apatite crystals. IR spectra showed the incorporation of CO3, or HPO4, the HPO4 incorporation being least from F-containing solutions. These results suggest that OCP to AP transformation occurred by the process of dissolution of OCP and subsequent precipitation of Ca-deficient apatites, incorporating CO32-, HPO42- or F- present in solution.
These results indicate that the observed stabilty of OCP in pathological calcifications may be due to the presence of Mg2+, citrate and/or P2O74- and/or low levels of CO32-, F-, Ca2+, HPO42- ions in the biological fluids.
LeGeros, R. Z.; Daculsi, G.; Orly, I.; Abergas, T.; and Torres, W.
"Solution-Mediated Transformation of Octacalcium Phosphate (OCP) to Apatite,"
Scanning Microscopy: Vol. 3
, Article 16.
Available at: https://digitalcommons.usu.edu/microscopy/vol3/iss1/16