| Résumé : |
Tanning, the multi-step process whereby complex salts of Cr(III) crosslinking collagen fibrils, is more an art form than a science and the mechanism of the chromium-collagen interaction is poorly understoos. The long range goal of this research is to develop an experimental model with which to study the interactions of Cr(III) with collagen that are characteristic of tanning. In the present study, the thermal stability of acid soluble collagen from bovine skin is studied by circular dichroism spectropolarimetry. The melting curve for the triple helix of calf skin collagen in 0.05 M acetic acid was analyzed in terms of a pre-transition followed by complete denaturation, with a characteristic Tp=34.0°C Td=40.7°C. For pepsin solubilized, adult bovine dermal collagen, slightly lower denaturation temperatures were observed - Tp=31.0°C, Td=37.7°C probably due to the removal of the nonhelical telopeptides in the solubilization of adult skin collagen. The addition of salts, NaCl or KCl, initially had a destabilizing effect on the triple helix, lowering both Tp and Td nearly in parallel. At low concentrations of Nacl, preferential binding occured with apparent dissociation constants Kd(Tp)=0.034 M and K(Td)=0.017 M for calf skin collagen at 1 mg/mL in 0.05 M acetic acid, suggesting the possibility of site preferential interactions contributing to the observed melting behavior. As the salt concentration was increased between 0.1 M and 0.5 M, little further destabilization was observed, Tp and Td became indistinguishable. At 0.4 M NaCl (0.5 M KCl)the samples began to gel. Here, water-structuring effects may play a role. In contrast, under conditions of the model tanning system, where Cr(III) was added at pH 2 and the pH was then adjusted to 4.5 with bicarbonated, the "tanned" collagen gelled at a salt concentration of 0.1 M. |
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Effects of neutral salts on collagen structure and chromium-collagen interactions in JOURNAL OF THE AMERICAN LEATHER CHEMISTS ASSOCIATION (JALCA), Vol. XCIV, N° 2 (02-03/1999)
