In aqueous solutions, disordered gelatin molecules cannot be returned to the ordered helical structure of native collagen. However, since synthetic polypeptides and some proteins can be made to go through the helix-coil transformation reversibly by the appropriate choice of solvent systems, a similar attempt has been made with gelatins. The behavior of gelatin in formic acid (FA)-dimethylformamide (DMF) and in ethylene dichloride-dichloroacetic acid has been examined. The studies cover (1) an analysis of the optical rotatory power and rotatory dispersion as a function of solvent composition; (2) the configurational changes as described by viscosity measurements; and (3) the roles of aggregation and degradation as determined by light scattering. [α]25.5D is -116° for gelatin in FA and becomes more positive as the DMF content is increased, reaching a value of -58° at 5% FA in DMF. There is a discontinuity in a plot of [α] D vs. FA_ concentration at the molar mixing ratio FA/DMF = 1. Similarly, there is a discontinuity in a plot of [η] vs. FA concentration at FA/DMF = 1, with a sharp rise in [η] when FA/DMF <1. The light-scattering data indicate that no aggregates are formed in the FA-DMF mixtures. These data are consistent with the assumption that a hydrogen-bonded helical structure is formed when FA/DMF <1 but this helix is not the same as that of native collagen. The implications of these data are discussed.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry