ydroxyapatite, Ca10(PO4)6(OH)2, is the primary mineral component of bone. Bone growth begins as amorphous calcium phosphate crystallizes into hydroxyapatite. As the bone matures, the size, crystallinity, and stoichiometry of the hydroxyapatite crystals change. For example, the phosphate and hydroxide sites are often substituted by other anions such as acid phosphate (HPO42-), carbonate (CO32-), and fluoride (F-). The nature of the phosphate environment in bone can be characterized through analysis of a series of four phosphate bands in the far-infrared region (500 - 650 cm-1). The intensities and peak positions of these modes are sensitive to the hydroxyapatite crystal size, structure, and stoichiometry. Thus, we have obtained a series of bone samples from rats and rabbits of various ages. We have also grown a series of hydroxyapatite crystals, varying in (1) the initial solution concentration of calcium phosphate, (2) the initial solution concentrations of non-stoichiometric components such a carbonate and fluoride, and (3) the time of crystal growth. The far-infrared spectra of these samples were collected in the form of potassium bromide pellets. X-ray powder Hdiffraction data has also been collected on these samples to provide a Hmeasure of average crystal size. Currently, curve-fitting and Hintegration analysis are being applied to the infrared data to correlate the peak positions and intensities of these modes as a function of bone age and crystal size. These results will be valuable Hfor the interpretation of far-infrared spectra from in situ infrared Hmicrospectroscopic measurements on bone samples.
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