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VOLUME 99 | ISSUE 4 | PAGE 223
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 different analytical methods. By means of electron 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 NO32- paramagnetic centres detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from 1H and 31P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centres and nitrate anions as the precursors of NO32- radicals preferably occupy PO43- site in the HAp structure.