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

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Abstract
Measurements of shrinkage temperatures (TS) 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 TS and increasing both v−1 and [η] (generally, for increasing salting in) is F− < SO2- 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 (CS) is controlled by the amount of diluent in equilibrium swelling with the molten network, and the shape of TS vs. CS 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.