MICRORAMAN SPECTRAL STUDY OF THE PO4 AND CO3 VIBRATIONAL-MODES IN SYNTHETIC AND BIOLOGICAL APATITES

The carbonate and phosphate vibrational modes of different synthetic a nd biological carbonated apatites were investigated by Raman microspec troscopy, and compared with those of hydroxyapatite. The nu(1) phospha te band at 960 cm-(1) shifts slightly due to carbonate substitution in both A and B sites. The spectrum of type A carbonated apatite exhibit s two nu(1) PO43- bands at 947 and 957 cm-(1). No significant change w as observed in the nu(2) and nu(4) phosphate mode regions in any carbo nated samples. The nu(3) PO43- region seems to be more affected by car bonation: two main bands were observed, as in the hydroxyapatite spect rum, but at lower wave numbers. The phosphate spectra of all biominera ls apatite were consistent with type AB carbonated apatite. In the ena mel spectrum, bands were observed at 3513 and at 3573 cm(-1) presumabl y due to two different hydroxyl environments. Two different bands due to the carbonate nu(1) mode were identified depending on the carbonate substitution site A or B, at 1107 and 1070 cm(-1) respectively, Our r esults, compared with the infrared data already reported, suggest that even low levels of carbonate substitution induce modifications of the hydroxyapatite spectrum. Increasing substitution ratios, however, do not bring about any further alteration. The spectra of dentine and bon e showed a strong similarity at a micrometric level. This study demons trates the existence of acidic phosphate, observable by Raman microspe ctrometry, in mature biominerals. The HPO42- and CO32- contents increa se from enamel to dentine and bone, however, these two phenomena do no t seem to be correlated.