Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

Synthesized by the wet chemical precipitation technique, hydroxyapatite (HAp) powders with the sizes of the crystallites of 20�50 nm and 1 µm were analyzed by dierent analytical methods. By means of el ectron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (by-products) could incorporate into the HAp structure. The relaxation times and EPR parameters of the stable axially symmetric NO 2− 3 paramagnetic centres detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from 1 H and 31 P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centres and nitrate anions as the precursors of NO 2− 3 radicals preferably occupy PO 3− 4 site in the HAp structure. DOI: 10.7868/S0370274X14040055