Transition temperature and enthalpy change dependence on stabilizing and destabilizing ions in the helix–coil transition in native tendon collagen

The transition temperatures tt and enthalpy changes ΔH in the helix–coil transition of solid tendon collagen soaked in a solution containing one of the following stabilizing or destabilizing agents, HCHO, NaF, NaCl, NaI, NaBr, NaOH, NH2CONH2, CaCl2, MgCl2, were measured as a function of molar concentration by a calorimetric method. The temperature and the enthalpy changes accompanying the transition behaved in a similar manner: when the tt was depressed by the presence of ions, similar behaviour was observed in ΔH. Both parameters (tt and ΔH) increased for HCHO, and decreased for NaF and NaCl at concentrations lower than 0.2 M. Above 0.2 M they increased for NaF and NaCl, and decreased in the presence of the other reagents listed above. The average tt and the ΔH observed in collagen soaked in water were 63.5°C and 12.3 cal/g, respectively. In addition to the parameters mentioned above, the molar effectiveness of the various reagents was obtained for the cases where there was a linear relationship between the tt and molar concentration of the reagent in the solution.

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