Quantum chemical and spectroscopic analysis of calcium hydroxyapatite and related materials

Amorphous calcium hydroxyapatite was examined by vibrational spectroscopy (Raman and infra-red (IR)) and quantum chemical simulation techniques. The structures and vibrational (IR, Raman and inelastic neutron scattering) spectra of PO43− ion, Ca3(PO4)2, [Ca3(PO4)2]3, Ca5(PO4)3OH, CaHPO4, [CaHPO4]2, Ca3(PO4)2·H2O, Ca3(PO4)2·2H2O and Ca3(PO4)2·3H2O clusters were quantum chemically simulated at ab initio and semiempirical levels of approximation. A complete coordinate analysis of the vibrational spectra was performed. The comparison of the theoretically simulated spectra with the experimental ones allows to identify correctly the phase composition of the amorphous calcium hydroxyapatite and related materials. The shape of the bands in the IR spectra of the hydroxoapatite can be used in order to characterize the structural properties of the material, e.g., the PO43− ion status, the degree of hydrolysis of the material and the presence of hydrolysis products.