No abstract

X-ray diffraction, infrared absorption spectroscopy, and chemical investigation have been carried out on deproteinated samples of turkey leg tendon at different degrees of calcification. The inorganic phase consists of poorly crystalline B carbonated apatite. On increasing calcification, the apatite crystal size, as well as its thermal stability, increase while the relative magnesium content is reduced. On the other hand, synchrotron X-ray diffraction data clearly indicate that apatite lattice parameters do not change as the crystals get larger. At the last stage of calcification the crystal size, chemical composition, and thermal conversion of the apatite crystallites approximate those of bone samples, which have been examined for comparison. The results provide a quantitative relationship between relative magnesium content and extent of apatite conversion into B-tricalcium phosphate by heat treatment. Furthermore, they suggest that the smaller crystallites laid down inside the gap region of the collagen fibrils are richer in magnesium than the longer ones that fill the space between collagen fibrils.

No abstract

No abstract

The influence of high supersaturation on kinetic control and the importance of the polypeptide structure in the crystallization of calcium carbonate polymorphs were studied in crosslinked gelatin films containing high concentrations of the polypeptides poly-l-aspartate and poly-l-glutamate. Oriented crystallization of vaterite occurs in uniaxially deformed gelatin films containing poly-l-aspartate at concentations greater than 100 mg per gram of gelatin. The fact that no orientation of the mineral phase was observed with entrapped poly-l-glutamate at the same concentrations suggests that the oriented crystallization is controlled by the b sheet structure assumed by poly-l-aspartate in the presence of calcium ions. These results indicate that local supersaturation in the microenvironment in which nucleation and growth occur plays an important role in controlling the deposition of vaterite in cross-linked gelatin films. However, collagen bundles and the ordered and oriented polypeptide chains of poly-l-aspartate can contribute to the control of polymorphism by inducing the formation of a specific phase by epitaxial crystallization, as suggested by the preferentially oriented deposition of vaterite and aragonite. This is of potential significance in biomineralization processes and in materials science.