Study of the nucleation sites in collagen mineralization

By comparing IR spectra of collagen, collagen/CaCl 2 and collagen/calcium phosphate, it was found that intensities of amide Ⅰ, Ⅱ and Ⅲ bands were significantly decreased after mineralization. Band amide Ⅰ shifted to wards lower wave number. This shift indicated chemical interaction between carboxyl groups and Ca ions formed in tie mineralization. The result indicated that there was another nucleation site, i.e. carbonyl (C[ZJZS;ZX;LX,Y] O) on collagen, besides the previous reported nucleation site of carboxyl (-COOH) on collagen. The decrease of amide Ⅰ peak intensity was mainly due to blockage of CO stretch. Comparing the IR spectra of demineralized collagen and pure collagen, amide Ⅰ, Ⅱ and Ⅲ peaks intensity and position were almost the same. When the mineral dissolved, amide peaks rebounded, which indicated that the crystals nucleated on these sites enwrapped the groups and blocked the groups vibration. The decreases of peak intensity of amide Ⅰ, Ⅱ and Ⅲ were different due to their different vibration modes. The result confirmed that the carbonyl group was one kind of the nucleation site during collagen mineralization. The relationship between the process of collagen mineralization and variety of amide bonds was also studied.