The Effect of Aqueous Salt Solutions on the Melting of Collagen and the Viscosity of Gelatin

Measurements of shrinkage temperatures (T_S) for fibrous collagen, of equilibrium degree of swelling (v^?1) for the same in the amorphous state, and of intrinsic viscosity ([η]) for randomly coiled gelatin are reported. The data were obtained for a large variety of salts which are typical representatives of lyotropic series. The order of anions and cations for decreasing T_S and increasing both v^?1 and [η] (generally, for increasing salting in) is F^? < SO^2- ₄ < acetate < Cl^? < Br^? < NO^? ₃ < I^? < SCN^? and K⁺ < Mg²⁺ < Na⁺ < Cs⁺ < Li⁺ < Ca²⁺. For salts of ions at the extreme left of the series (salting-out agents) the shrinkage temperature in solutions of different salt concentration (C_S) is controlled by the amount of diluent in equilibrium swelling with the molten network, and the shape of T_S vs. C_S curves can be represented by conventional theories valid for binary polymer diluent systems based on a lattice model with a single interaction parameter. In such cases the salt-water solution behaves as a single component diluent and its effect on the measured properties is described as a diluent effect.