title: Solution-mediated transformation of octacalcium phosphate (OCP) to apatite.
abstract: OCP crystals were hydrolyzed in solutions containing Ca2+, Mg2+, HPO4(2-), CO3(2-), 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 P2O7(4-); facilitated by F-, CO3(2-), HPO4(2-) 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 CO3(2-), HPO4(2-) or F- present in solution. These results indicate that the observed stability of OCP in pathological calcifications may be due to the presence of Mg2+, citrate and/or P2O7(4-) and/or low levels of CO3(2-), F-, Ca2+, HPO4(2-) ions in the biological fluids.
authors.affiliation: New York University College of Dentistry, New York 10010.
authors.forename: R Z
authors.initials: RZ
authors.lastname: LeGeros
authors.forename: G
authors.initials: G
authors.lastname: Daculsi
authors.forename: I
authors.initials: I
authors.lastname: Orly
authors.forename: T
authors.initials: T
authors.lastname: Abergas
authors.forename: W
authors.initials: W
authors.lastname: Torres
mesh_terms: D001031:Apatites / Q000493:pharmacokinetics*; D002130:Calcium Phosphates / Q000493:pharmacokinetics*; D003460:Crystallization
chemical_list: D001031:Apatites; D002130:Calcium Phosphates; C022045:octacalcium phosphate