Solid state31NMR studies of the conversion of amorphous tricalcium phosphate to apatitic tricalcium phosphate

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Abstract
The hydrolytic conversion of a solid amorphous calcium phosphate of empirical formula Ca9(PO4)6 to a poorly crystalline apatitic phase, under conditions where Ca2+ and PO4 3− were conserved, was studied by means of solid-state magic-angle sample spinning31P-NMR (nuclear magnetic resonance). Results showed a gradual decrease in hydrated amorphous calcium phosphate and the formation of two new PO4 3−-containing components: an apatitic component similar to poorly crystalline hydroxyapatite and a protonated PO4 3−, probably HPO4 2− in a dicalcium phosphate dihydrate (DCPD) brushite-like configuration. This latter component resembles the brushite-like HPO4 2− component previously observed by31P-NMR in apatitic calcium phosphates of biological origin. Results were consistent with previous studies by Heughebaert and Montel [18] of the kinetics of the conversion of amorphous calcium phosphate to hydroxyapatite under the same conditions.