Incongruent dissolution of hydroxyapatite in the presence of phosphoserine

Abstract

Concentrations of phosphate and calcium ions, liberated from the surface of hydroxyapatite (HAP) during the adsorption of phosphoserine (PSer), were determined at 30°C. HAP showed a marked incongruent dissolution behavior in the presence of PSer. That is, the concentration of phosphate ion in solution increases with the addition of PSer due to the ion-exchange between PSer and phosphate ion on HAP (molar ratio of the former to the latter=3∶2), whereas the concentration of calcium ion decreases with this release of phosphate ion, because the solubility product of HAP restricts the concentrations of both ions in solution (calculated values of — log (Ca2+)10 (PO43−)6 (OH−)2 were 115.8±1.0). The affinity of PSer to HAP was highest at pH 5.8 where the PSer and the HAP surface had the opposite charges. This electrostatic attraction force between PSer and HAP was shielded to some extent by the addition of KCl.