Kinetic studies of hair reduction using a single fiber technique

A technique for investigating reduction kinetics of hair using single hair fibers is described. The method is based on stress relaxation caused by disulfide bond breakage, and can be used for fundamental studies of parameters affecting hair reduction rates. Analysis of our data in light of mathematical models indicates that under conditions where reduction is fast compared to diffusion into the hair, the reaction proceeds as a sharp front or moving boundary, and when reaction is slow compared to diffusion, the reaction front is diffuse and pseudo first-order kinetics are followed. We have used the method to investigate he effects of pH, temperature, and reactant concentration with a monothiol reducing agent, sodium thioglycolate (TG), and with two dithiol reducing agents, dithiothreitol (DTT) and sodium dihydrolipoate (6-8 dithiooctanoate). The two dithiol reducing agents displayed moving boundary kinetics under all conditions investigated, while SFTK data obtained with TG was characteristic of pseudo first-order kinetics except at pH values of 10 or greater. We have also observed that while different hairs from the same individual generally have a fairly narrow distribution of reaction rates, hair from different individuals may vary significantly insusceptibility to reductive treatment