Radiation-Induced Stable Radicals in Calcium Phosphates: Results of Multifrequency EPR, EDNMR, ESEEM, and ENDOR Studies

This article presents the results of a study radiation-induced defects in various synthetic calcium phosphate (CP) powder materials (hydroxyapatite—HA and octacalcium phosphate—OCP) by electron paramagnetic resonance (EPR) spectroscopy at X, Q, W-bands (9, 34, 95 GHz for microwave frequencies, respectively). Currently, CP are widely used orthopedics dentistry owing to their high biocompatibility physico-chemical similarity with human hard tissue. It is shown that addition classical EPR techniques, other experimental approaches such as ELDOR-detected NMR (EDNMR), spin echo envelope modulation (ESEEM), electron-nuclear double (ENDOR) can be analyze electron–nuclear interactions powders. We demonstrated value angular dependence quadrupole interaction 14N nuclei nitrate radical determined EDNMR method room temperature. The ESEEM technique has allowed rapid analysis nuclear environment estimation structural positions centers crystal matrices. ENDOR spectra provide information about distribution radicals OCP structure.