SORPTION OF PEPTIDES BY HAIR Percent Peptide Sorbed 605 0.6 0.4 0.2 5 min 10 min 20 min Virgin hair I I I 1 2 3 4 5 6 7 8 9 pH 10 11 12 Figure 5. $orption of peptides from solutions of different pH values by thioglyeolate- damaged hair. (The curves are identified by the time the hair was reduced) Effect of Ammonium Thioglycolate on Peptide Sorption at Various pH Levels The curves in Figs. 5 and 6 show the effect of treatment of the hair coils with ammonium thioglycolate, followed by rinsing and treat- ment in 5% solutions of peptides at various pH levels. Figure 5 shows the curves for the five, ten, and twenty minute thioglycolate treatments. Peptide sorption remains at a relatively low value to pH 4-5 and then increases rapidly. It is remarkable that maximum absorption over most of the range is observed with hair treated for the shortest time (five minutes) with ammonium thioglycolate. After a treatment time of ten minutes, sorption decreases slightly and is sharply reduced after twenty minutes. At this stage, with the exception of a slight divergcnce above pH 10, the hair behaves very much like virgin hair. Treatment of the hair for one hour or more with ammonium thio- glycolate again changes the character of the curves. Sorption begins to increase with a longer time period of treatment following the absorp-

606 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Percent Peptide Sorbed 1.2-- 1.0 0.8 0.6 . . 0 t I I I I I I I I I I 2 3 4 5 6 7 8 9 10 11 12 pH Figure 6. Sorption oF peptides from solutions of different pH values by thioglycolate- damaged hair. (The curves are identified by the time the hair was reduced) tion minimum observed after twenty minutes of reduction. This is shown in Fig. 6, which includes the twenty minute curve again for reference. The peptide is sorbed more readily at the lower pH values of 5 to 9, and sorption increases very rapidly after two hours' treat- ment in ammonium thioglycolate at pH values from 10 to 12. A suggested explanation for the results is that only a short period of treatment with thioglycolate is necessary to open up the cutide and increase the protein area for sorption of the peptide. The cuticle is rapidly separated from the hair strands, and in 20 minutes it has ap- parently been removed almost completely. The cortex then reacts but here the action is much slower, so that after one hour of treatment the sorption over the entire pH range has not increased markedly above that obtained after twenty minutes of treatment. It is only after additional treatment that the great increase in peptide sorption occurs.