Hydroxyl groups in bone mineral

The subjects that will be presented in this chapter are: (1) The nature of the mineral phase in bone; that is, the chemical composition and crystal structure of the solid calcium-phosphate (Ca-P) mineral phase in bone, and the changes that occur in the mineral phase per se with time and maturation; (2) the relationship of these maturational changes which occur with time to the biological, physiological, and mechanical functions of the crystals and to Ca and P mineral metabolism; and (3) the ultrastructural location of the mineral phase and its relationship to the basic underlying physical chemical mechanism responsible for the initiation of calcification.

The Nature of the Mineral Phase in Bone: Biological and Clinical Implications

Chemical structure of human bone mineral was studied by solid-state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS). Trabecular and cortical bone samples from adult subjects were compared with mineral standards: hydroxyapatite (HA), hydrated and calcined, carbonatoapatite of type B with 9 wt% of CO
 3
 2−
 (CHA-B), brushite (BRU) and mixtures of HA with BRU. Proton spectra were acquired with excellent spectral resolution provided by ultra-high speed MAS at 40 kHz. 2D 1H-31P NMR heteronuclear correlation was achieved by cross-polarization (CP) under fast MAS at 12 kHz. 31P NMR was applied with CP from protons under slow MAS at 1 kHz. Appearance of 31P rotational sidebands together with their CP kinetics were analyzed. It was suggested that the sidebands of CP spectra are particularly suitable for monitoring the state of apatite crystal surfaces. The bone samples appeared to be deficient in structural hydroxyl groups analogous to those in HA. We found no direct evidence that the HPO
 4
 2−
 brushite-like ions are present in bone mineral. The latter problem is extensively discussed in the literature. The study proves there is a similarity between CHA-B and bone mineral expressed by their similar NMR behavior.

1H MAS and 1H --> 31P CP/MAS NMR study of human bone mineral.

https://hal.archives-ouvertes.fr/hal-00835892/document

Accurate characterization of pure silicon-substituted hydroxyapatite powders synthesized by a new precipitation route

Producing a P fertilizer from sewage sludge ash (SSA) is a strategy to efficiently recycle P from a secondary raw material. The P speciation in four SSAs was characterized before and after the removal of heavy metals by a thermo-chemical treatment that involved CaCl addition. We chose complementary techniques to determine the direct P speciation, including X-ray powder diffraction, solid-state P direct-polarization magic-angle spinning nuclear magnetic resonance, and X-ray absorption near edge structure. Results from these techniques were compared with operational and functional speciation information obtained from a sequential P extraction and a plant biotest with Italian ryegrass grown on a soil-sand mixture with little available P. The speciation of P in untreated and thermo-chemically treated SSAs depended on their elemental composition. At a molar ratio of Ca:P ≤ 2, SSAs contained combinations of polymorphs of AlPO, β-tricalcium phosphate, and apatite-like P species. In SSAs with a molar ratio of Ca:P > 2, an apatite-like molecular environment was predominant. The thermo-chemical process induced an increase in crystalline phases and enhanced the crystallinity of the P species. The structural order of the bulk sample was the most decisive parameter in controlling the P availability of the studied SSAs to plants. We conclude that, to produce a high-quality fertilizer and despite of the successful heavy metal removal, the thermo-chemical process requires further development toward enhanced P bioavailability.

X. Marchandise

Papers

Characterisation and conversion study into natural living bone of calcium phosphate bioceramics by solid state NMR spectroscopy