Fourier Transform and Multi Dimensional EPR Spectroscopy for the Characterization of Sol-Gel Derived Hydroxyapatite |
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Authors: | G Kordas CC Trapalis |
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Institution: | (1) National Centre of Scientific Research “Demokritos”, Institute of Materials Science, Ag. Paraskevi, 153 10 Athens, Greece |
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Abstract: | Calcium hydroxyapatite powder was prepared by sol-gel method using calcium acetate and PO(OC2H5)3 as initial compounds, and alcohol (methyl, ethyl, and propyl-alcohol) as solvent. Homogeneous solution and gels were prepared
using a molar ratio of Ca/P=1.67. The evolution of the 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 sweep) showed the same modulation for the central line. The FT-EPR spectrum 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. The ESEEM spectrum was simulated assuming the equation Vmod=Vmod(P)mVmod(H)n for two spin systems S=1/2 and I=1/2. This simulation gave form andn the values of 2 and 5, respectively. This finding suggests the structure:
for the unpaired state. It appears that one ethyl group does not hydrolyse in the gelation process. The ESEEM spectra of
hydroxyapatite exhibit a modulation generated by P, H and Ca atoms. |
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Keywords: | sol-gel hydroxyapatite FT-EPR |
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