Solid-state NMR study of the role of H and Na in AB-type carbonate hydroxylapatite

Solid-state nuclear magnetic resonance (NMR) techniques, combined with Fourier transform infrared (FT-IR) spectroscopy, were used to study synthetic AB-type carbonate hydroxylapatite (CHAp). ¹³C{¹H) heteronuclear correlation (HetCor) experiments indicate that the two carbonate environments represented by the peaks at δ_C = 169.8 and 170.8 ppm are associated with three H environments with one environment represented by a peak centered about δ_H = 0.0 ppm and two additional peaks located at 1.3 and 5.5 ppm. The peaks near δ_H = 0.0 ppm correspond to hydroxyl environments within the channels of the CHAp, whereas those at 1.3 and 5.5 exhibit spectral characteristics consistent with bicarbonate ions that donate moderate to weak hydrogen bonds. Possible methods by which bicarbonate incorporation can be accommodated by the apatite structure are discussed. The Na/carbonate ratio and ²³Na NMR spectroscopy indicate that Na plays an important role in the carbonate incorporation in these materials.