Solid-state phosphorus-31 nuclear magnetic resonance studies of synthetic solid phases of calcium phosphate: potential models of bone mineral

Abstract

Phosphorus-31 NMR spectra have been obtained from a variety of synthetic, solid calcium phosphate mineral phases by magic angle sample spinning. The samples include crystalline hydroxyapatite, two type B carbonatoapatites containing 3.2 and 14.5% CO3(2-), respectively, a hydroxyapatite in which approximately 12% of the phosphate groups are present as HPO4(2-), an amorphous calcium phosphate, monetite, brushite, and octacalcium phosphate. Spectra were observed by the standard Bloch decay and cross-polarization techniques, as well as by a dipolar suppression sequence, in order to distinguish between protonated and unprotonated phosphate moieties. The spectra of the synthetic calcium phosphates provide basic information that is essential for interpreting similar spectra obtained from bone and other calcified tissues.