P-31 AND H-1 POWDER ENDOR STUDY OF OZONIDE RADICALS IN CARBONATED APATITES, SYNTHESIZED FROM AQUEOUS-SOLUTIONS

An O-3(-) defect in Na+ and CO32- containing apatite powder has been i nvestigated with ENDOR after X-irradiation. The powder, synthesized by a hydrolysis of octo-calciumphosphate (OCP) and N2CO3 was dried at 25 degrees C until constant weight was reached. At low temperatures, bot h P-31 and H-1 ENDOR spectra were recorded for different settings of t he magnetic field (i.e., when the magnetic field is swept through the EPR O-3(-) spectrum). The ENDOR powder spectra were thoroughly analyze d using computer simulations based on the ''orientation selection prin ciple''. Interactions with two types of protons and two types of P-31 nuclei could be resolved. In this way, a detailed model could be estab lished for the O-3(-) ion in the hydroxyapatite lattice. The defect is located between two successive vacant hydroxyl sites. The axis connec ting the two outer oxygen atoms (g(y)-axis) of the O-3(-) ion is found to be along the hexagonal c-axis of the lattice. The twofold axis of the defect ion (g(x)-axis) is parallel to the b-axis of the lattice.