  Pathologies associated with calcified tissue, such as osteoporosis, demand in
vivo and/or in situ spectroscopic analysis to assess the role of chemical
substitutions in the inorganic component. High energy X-ray or NMR
spectroscopies are often impractical or damaging in biomedical conditions. Low
energy spectroscopies, such as IR and Raman techniques, are often the best
alternative. In apatite biominerals, the vibrational signatures of the
phosphate group are generally used as fingerprint of the materials although
they provide only limited information. Here, we have used first principles
calculations to unravel the complexity of the complete vibrational spectra of
apatites. We determined the spectroscopic features of all the phonon modes of
fluor-apatite, hydroxy-apatite, and carbonated fluoroapatite beyond the
analysis of the phosphate groups, focusing on the effect of local corrections
induced by the crystalline environment and the specific mineral composition.
This provides a clear and unique reference to discriminate structural and
chemical variations in biominerals, opening the way to a widespread application
of non-invasive spectroscopies for in vivo diagnostics, and biomedical
analysis.
