Effect of Thiol Structures on Reduction of Hair

Our investigation on the effects of thiol structures in permanent wave solutions on reduction of hair led to following discoveries:1) Partition coefficients (P) of thiols between water and 1-octanol was measured to determine the permeability of thiols into hair. Results from this method, there was a high correlation between the hydrophobic character, logP and the efficiency of the permanent wave solutions.2) It is generally thought that the reduction of hair by thiols is strongly affected by the acidity of SH groups. The dissociation constants of SH groups was determined by spectrophotometric titrations. Using this method, we found no significant relationship between the acidity of SH groups and permanent wave efficiency. Ellman's Reagent (5, 5′-dithiobis[2-nitrobenzoic acid]:DTNB) was used to determine the reaction rate constant of thiols and DTNB. A significant correlation was found between the rate constants and SH group acidity as determined by spectrophotometric titrations, From these results, it appears that the effects of permanent wave are not solely dependent on the kinetics of homogeneous reaction in a liquid phase, and the action of thiol in permanent waving should be regarded as a diffusion controlled process.