Water in termally treated bioapatites and their synthetic analogues: 1H NMR Data

Abstract

The molecular water incorporation in bioapatites obtained by bone pyrolysis at temperatures of 600–1100 °C has been investigated using in situ solid 1H nuclear magnetic resonance (solid 1H NMR) method in the temperature range of T = 25–300 °C and, in addition, 1H magic-angle spinning NMR, X-ray diffraction and infrared spectroscopy at room temperature. For comparison, synthetic analogues of bioapatite, precipitated hydroxyapatite (HA), HA with La impurity and carbonate fluorapatite were investigated as well. It was established that there are water molecules adsorbed on crystallites surfaces and bound in structure (H2Os) in studied apatites. More rigid H2Os1 molecules cause the doublet under normal conditions and the wide singlet at T ≥ 150 °C in situ 1H solid NMR spectra. In addition, H2Os3 molecules with reorientation mobility at T = 150–300 °C are presented in bioapatite and HA annealed at lower temperatures and La-HA. Water incorporation into structure of bioapatite annealed at 600–1100 °C and its synthetic analogues HA is established to be zeolite-like. Presumably, the configuration of cavities is formed in the apatite crystal scaffold during annealing of studied apatites. These cavities are related with vacancy clusters in original structures and connected between themselves and with surface by the channels with a diameter of not more than 0.3 nm. Water molecules trapped in smaller (H2Os2) and larger cavities (H2Os1) cause the doublet and singlet, respectively; water molecules in OH vacancies in channels (H2Os3) are due to narrow lines.