Thermal Transitions in Keratin

Abstract

Simple methods for the observation of thermal transitions in keratin fibers are dis cussed and some typical results are described. For wool fibers or human hair stretched in water by approximately 0.5% (Hookean region), transitions were detected by bends in the force-temperature curve at points A. D. and E. occurring at approximately 30°. 80°, and 90° C. respectively. In addition, a transition region BC was shown up by a "smeared" curvature of the force-temperature curve over the approximate range 50- 60° C. This region BC corresponds to previously reported transitions in mechanical behavior and in thermal expansion: it is shown to be associated with crystalline micro- fibrils.

Reduction of the cystine in human hair, followed by methylation, widened the region BC but produced little change in the other transitions. Reduction of wool fibers without methylation produced a significant decrease in temperature of the whole region BC. but again there was little change in the other transition temperatures. By contrast, the transition A was lowered by using dilute alcoholic solutions, showing that hydrophobic bonding makes a contribution to the stability of the wool structure.