The carbonate group is an important constituent of bioapatite, a calcium phosphate close to hydroxyapatite, main constituent of bone and dental enamel. [CO3] can occupy two different sites in the structure (type A and B), and seems to control the growth, evolution, morphology, and physical properties of synthetic nano-carbonated hydroxyapatite. Infrared and Raman spectroscopy were used to evaluate the carbonate substitution in pathological bioapatite from patients undergoing valvular replacement because of severe aortic and mitral stenoses. FTIR spectra were collected in the 4000-400 cm-1 spectral range using a PerkinElmer System 2000, while Raman spectra in the range 4000-200 cm-1 using a Horiba Jobin-Yvon LabRam Confocal Microscope at a resolution of about 3 cm-1. The PO4 asymmetric stretching IR mode appears as an intense band at 1023 cm-1, a shoulder at 1059 cm-1, and a third band at 1104 cm-1. The CO3 asymmetric stretch vibration mode is represented by four bands at 1418, 1450, 1471, 1503 cm-1 while the CO3 out-of-plane bending mode by the band at 872 cm-1. This characteristic IR signature seems to be typical of Na-bearing type A-B carbonate apatite. The band at 1503 cm-1 could indicate the accommodation of the carbonate group in a second channel position (Type A2) usually present in carbonate apatite synthesized at high-pressure. On the contrary the Raman band at 1071 cm-1 due to CO3 symmetric stretching mode is specific of [CO3] substituting [PO4] (type B) and the band observed at 961 cm-1 due to symmetric stretching mode of PO4 is in agreement with the shift assigned to PO4 symmetric stretch mode for bone and synthetic type B carbonate apatite with different carbonate contents. The Raman peaks’ height and area are strongly correlated with weight percent carbonate. The ratio of peak area at 1071 cm-1 and peak area at 961 cm-1 was used to determine the percentage of carbonate in the analyzed samples. Values obtained (4.5-7.0 %) are in good agreement with those of biological apatite from bone.
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|Titolo:||Infrared and Raman studies of bioapatite deposits in human heart valves|
|Data di pubblicazione:||2011|
|Appartiene alla tipologia:||04a Atto di comunicazione a congresso|