Helix-coil transition of gelatin: helical morphology and stability

By combining optical rotation with thermal characterization and rheological measurements, we have studied triple helix formation in water and ethylene glycol solutions of gelatin. We find the enthalpy change per unit helix required for the transition from triple helix to random coil is independent of the concentration of helices in solution and the temperature at which the helices form. Helices formed in ethylene glycol are less stable than those formed in water solutions as, unlike water, ethylene glycol is too large a molecule to mediate interchain hydrogen bonds. The storage modulus has a universal dependence on helix concentration in both solvents but, due to a reduction in helix length, the critical concentration at which an elastic gel forms is smaller in ethylene glycol.