Local Environment in Biomimetic Hydroxyapatite−Gelatin Nanocomposites As Probed by NMR Spectroscopy

The local environment in biomimetic hydroxy-apatite (HAp) nanocomposites containing 0 and 33 wt % gelatin was characterized by 31 P solid-state NMR spectroscopy. The presence of crystalline HAp and amorphous calcium phosphate phases was found in both materials. The latter can appear at the grain surfaces or at the boundaries of the crystalline phases. In the 31 P cross-polarization MAS NMR spectra of HAp containing 33 wt % of built-in gelatin, an additional signal at 0.9 ppm was observed, which demonstrates the spatial correlation to hydrogen atoms of nonmineral origin, as indicated by 31 P− 1 H heteronuclear correlation (HETCOR) NMR spectroscopy. This site is identified as a phosphate species present at the surfaces of the mineral component (HAp) interacting with the surrounding organic matrix.