ENDOR study of CO sub(2) super(-) radicals in hydroxyapatite of gamma -irradiated bone

ENDOR spectra and ENDOR-induced EPR spectra (dependences of ENDOR signals vs. the value of magnetic field B) of gamma -irradiated bone plates and powders are studied. Typical ENDOR spectrum consisted of two signals centred at the Larmor frequencies of super(1)H and super(31)P nuclei, respectively. The ENDOR signals were found to be the superposition of the signals of axial (oriented) and orthorhombic (disordered) CO sub(2) super(-) radicals. Changes of the ratio between the ENDOR signal intensities for g and g at the rotation of the plate in the magnetic field is explained by the orientation-dependent redistribution of the EPR spectral density. EI-EPR spectra satisfactorily coincide with the spectra of conventional EPR absorption. Changes of ENDOR spectrum at the annealing of a sample before gamma -irradiation (T sub(ann) = 400 degree C) are explained by Larmor ENDOR mechanism. Larmor ENDOR mechanism is associated with diffusive polarization of distant (far from a paramagnetic center) "free" nuclei under the conditions of EPR signal saturation and their depolarization by radio-frequency field in ENDOR.