78 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 2A. Control hair stained with silver methenamine. Mag. 16200 X. The results in Figures 1 and 2 are strong evidence that it is the high equilibrium constant between DHL and cystine, resulting from the ability of DHL to form a dithiane ring on oxidation, that causes it to reduce hair at a much faster rate than monothiol compounds with otherwise similar structures.

KINETICS OF HAIR DISULFIDE BOND REDUCTION 79 Figure 2B. Thioglycolate-treated hair stained with silver methenamine. Mag. 16200 X. COMPARISON OF DTT, DTP, AND DTB SFTK curves for dithiothreitol (DTT), dithiopropanol (DTP), and 1,4 dithio 2-butanol (DTB) under identical reaction conditions are shown in Figure 3. Rate constants ob- tained from fitting the data to equation 1 are shown in Table I. These rate constants are extremely sensitive to differences in the SFTK curves due to the dependence of the

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