Calcium phosphates and hydroxyapatite. Solid-state NMR experiments and first-principles calculations

Various calcium phosphates and hydroxyapatite (HAp) have been fully characterized by one- and two-dimensional solid-state nuclear magnetic resonance (NMR) experiments and first principles calculations of NMR parameters, such as chemical shift anisotropy (CSA) and electric field gradient tensors for all nuclei. Such compounds act as useful biocompatible materials. The projector augmented wave (PAW) and gauge including PAW methods allowed the complete assignment of spectra, including (1)H magic-angle spinning (MAS) spectra for which ultimate resolution is not attained experimentally. (1)H CSA tensors and orientation of the principal axes systems have been also discussed. (17)O parameters have been calculated for a large variety of oxo-bridges and terminal oxygen atoms, including P-O-Si fragments characteristic for silicophosphate phases. The (delta(iso), C (Q)) sets of values allowed the clear distinction between the various oxygen atoms in a calculated (17)O 3-quantum MAS experiment. Such an approach should be of great help for the description of interfaces in complex materials, in terms of structure and chemical composition.