REDUCTION OF HUMAN HAIR 225 pKa• = 8.6 (7a) cysteamine (7b) H3N S- + pKa2 = 10.75 S- '- u •,•• S- O pKal = 3.7 O pKal = 10.4 HS'.PLOH _ -- HS'./LO_ _ ammonium thioglycolate (7C) _ Figure 7. Cysteamine and ATG species present in aqueous solutions: cysteamine five-membered ring formed via hydrogen bonding in solution (7a), chemical equilibria for cysteamine solutions (7b), and chemical equilibria for ammonium thioglycolate solutions (7c). results of stress-relaxation data, which do not present evidence of a delayed reaction for ATG. CONCLUSIONS 1. SFTK measurements and amino acid analysis indicate that the rate of reduction of both stress-supporting and whole-fiber disulfide bonds by 1 M ammonium thiogly- colate solution at pH 9.4, 23øC, is faster than the rate of reduction by a 1 M cysteamine solution at pH 7.6, 23øC, both solutions having an equivalent percent of active-reducing species present. 2. Comparison of the results of amino acid analysis and SFTK measurements indicate that stress-relaxation data represent not only the removal of stress-supporting disul- fide bonds, but correlate with disulfide reduction in general. ACKNOWLEDGMENTS We thank Dr. Robert Hammer and Dr. William Daly for their suggestions on this manuscript. Mr. Patrick Hanavan is gratefully acknowledged for his assistance with the amino acid analysis procedure. Finally, we would like to express our appreciation to Dr. D. Weigmann, Dr. M. Tate, Dr. L. Salce, and Mr. A. Savaides for their valuable discussions. REFERENCES (1) R. R. Wickett, Kinetic studies of hair reduction using a single fiber technique, J. Soc. Cosmet. Chem., 34, 301-316 (1983).

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