Fourier Transform and Multi Dimensional EPR Spectroscopy for the Characterization of Hydroxyapatite Gels |
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Authors: | G. Kordas C.C. Trapalis |
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Affiliation: | (1) Institute of Materials Science, National Centre of Scientific Research “Demokritos”, 153 10, Ag. Paraskevi, Athens, Greece |
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Abstract: | Calcium hydroxyapatite powder was prepared by the sol-gel method, using calcium acetate and PO(OC2H5)3 as initialcompounds, and alcohol(methyl, ethyl, and propyl-alcohol) as solvent. Homogenous solutions andgels were prepared, using a molar ratio of Ca / P = 1.67. Theevolution of the structure was followed by XRD (X-ray diffraction), IR(Infrared), and FT-n(= 1, 2, 3)D-EPR (Fourier transform Electron Paramagnetic Resonance) spectroscopy. The dried gel exhibits a signalcharacterized by a central line and two satellites. The 2D spectrum(Electron Spin Echo Envelop Modulation ESEEM vs. field sweep) showed thesame modulation for the central line. The FT-EPR spectrum vs. field sweep2D-spectrum indicated that the satellites are due to an hfs splitting withwater. The central region of this 2D spectrum is influenced by P and H in a concentration ratio of[H] / [P] = 2.5. TheESEEM spectrum was simulated, assuming the equation for two spin systems S = 1/2 andI = 1/2. This simulation gave, for m and n, the values of 2 and5, respectively. This finding suggests a–P–O–P–O–P– linear evolution of thestructure. It appears that one ethyl group does not hydrolyze in thegelation process. This result was confirmed by IRspectroscopy. |
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Keywords: | FT-EPR spectroscopy hydroxyapatite sol-gel synthesis |
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