Zinc incorporation into hydroxylapatite.

By theoretical modeling and X-ray absorption spectroscopy, the local coordination structure of Zn incorporated into hydroxylapatite was examined. Density function theory (DFT) calculations show that Zn favors the Ca2 site over the Ca1 site, and favors tetrahedral coordination. X-ray absorption near edge structure (XANES) spectroscopy results suggest one dominant coordination environment for the incorporated Zn, and no evidence was observed for other Zn-containing phases. Extended X-ray absorption fine structure (EXAFS) fitting of the synthetic samples confirms that Zn occurs in tetrahedral coordination, with two P shells at approximately 2.85-3.07A, and two higher Ca shells at approximately 3.71-4.02A. These fit results are consistent with the most favored DFT model for Zn substitution in the Ca2 site.