Theoretical Calculations of Segregation Behavior of Zinc and Magnesium at Hydroxyapatite Surface in Contact with Water

Abstract

Density functional theory (DFT) calculations were performed to investigate atomic structures and segregation behavior of Zn²⁺ and Mg²⁺ ions at a (10\bar{1}0) surface of hydroxyapatite (HAp). In order to take account of aqueous solution environment surrounding the HAp surface, the conductor-like screening model (COSMO) was used. Ionic exchange energies of Zn²⁺ and Mg²⁺ at Ca sites around the surface were evaluated, under an assumption of chemical equilibrium between HAp and aqueous solution. It was found that Zn²⁺ can segregate energetically more favorably at the HAp surface, as compared to Mg²⁺. This may correspond to Zn²⁺ effects on inhibition of HAp crystal growth, as suggested by experiment.