FOURIER-TRANSFORM AND MULTI DIMENSIONAL EPR SPECTROSCOPY FOR THE CHARACTERIZATION OF SOL-GEL DERIVED HYDROXYAPATITE

Calcium hydroxyapatite powder was prepared by sol-gel method using cal cium acetate and PO(OC2H5)(3) as initial compounds, and alcohol (methy l, ethyl, and propyl-alcohol) as solvent. Homogeneous solution and gel s were prepared using a molar ratio of Ca/P = 1.67. The evolution of t he structure was detected by X-ray diffraction, IR, and FT-n(= 1, 2, 3 )D-EPR spectroscopy. The dried gels exhibit a signal characterized by a central line and two satellites. The 2D spectrum (ESEEM vs. field sw eep) showed the same modulation for the central line. The FT-EPR spect rum vs. field sweep 2D-spectrum indicated that the satellites are due to an hfs splitting with water. The central region of this 2D spectrum is influenced by P and H in a concentration ratio of [H]/[P] = 2.5. T he ESEEM spectrum was simulated assuming the equation V-mod = V-mod(P) V-m(mod)(H)(n) for two spin systems S = 1/2 and I = 1/2. This simulati on gave for m and n the values of 2 and 5, respectively. This finding suggests the structure: [GRAPHICS] for the unpaired state. It appears that one ethyl group does not hydrolyse in the gelation process. The E SEEM spectra of hydroxyapatite exhibit a modulation generated by P, H and Ca atoms.