890 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table V Ri Values of the Components of the Decolorized Melanin Rf Relative Intensity of Fluorescence 0.00 Strong 0.02 Medium, very narrow band 0.02 Strong 0.04 Medium 0.08 Strong 0.16 Weak 0.23 Medium 0.35 Weak-medium 0.41 Weak-medium 0.43 Medium 0.51 Weak of the reactions occurring during the solubilization of the pigment and its subsequent decolorization. In the former process, the solubility re- straining cross links are eliminated and the chromophoric groups ap- pear to be left virtually intact. There is a good case to argue that these cross links are much more labile and thus different from the residues which undergo much slower reaction in the decolorization step. The bleaching proper, on the other hand, relies upon oxidative destruction of the highly conjugated system of the indole residues. It is likely that the oxidation is centered initially on the benzenoid portion of the ring. The acceleration of the decolorization process observed with both permanganate and peracids is in accordance with such a view (29). Some additional support for the postulated path of oxidative breakdown can also be derived from the results of qualitative chroma- tographic analysis of the products of the decolorization reaction. All the resolved components (Table V) were identified as acids but no aromatic derivatives were present. The test for pyrrolic acids was also negative. The latter were detected by Piattelli (16) in the permanganate- oxidized melanin. It appears, therefore, that under ordinary bleaching conditions, which we have employed for the preparation of decolorized melanin, even the indole nucleus undergoes complete degradation upon fission of the benzenoid portion of the ring to yield smaller fragments with acidic functions, such as oxalic acid which was identified as one of the decolorization products. We were unable, however, to identify posi- tively the remaining components. The oxidation of melanin by peroxide is accompanied by develop- ment of fluorescence which increases in intensity with the progress of

HAIR BLEACHING 891 the reaction. All the decolorization products are strongly fluorescent and indeed it was this property which greatly assisted their chromato- graphic separation. To our knowledge this has been the first report of the phenomenon. The only other relevant report was the observation by Binns and Swan (30) of the purple fluorescence from the synthetic melanins. Reaction of Hair Keratin with Hydrogen Peroxide The fact that the reactivity of melanin with regard to hydrogen per- oxide happens to be so much higher than that of keratin almost auto- matically connotes the bleaching process as a commercial success. How- ever, the melanin pigment represents only a very small fraction of the fiber weight (usually about 2%) and thus it is reasonable to expect that some oxidative modification of the fiber matrix will occur. Conven- tional bleaching processes utilize hydrogen peroxide in alkaline media at pH 10 and above the perhydroxy anion (HO2-) is the predominant reactive species. The abundance of sites in keratin which might yield to a nucleophilic attack by this ion precludes any firm prior assignment of a specific interaction. In addition, the presence of some radicals derived from H202, the reactivity of which is not particularly sensitive to pH changes, adds to the uncertainty concerning the type of reactions involved. The physical methods used to detect damage associated with bleaching are satisfactory for measuring the extent of deterioration, but are of little value for elucidating the chemical character of the damage. The latter can best be ascertained by chemical analysis, and such a method was used as a starting point of this investigation. Chemical Composition of Bleached Hair Tresses of brown hair were bleached with 3% Haaat pH 10 (0.5M NH3) and 35øC for 4 hours. The bleached tresses were sampled, the samples were hydrolyzed, and the hydrolyzates were analyzed on the Phoenix M-7800 Micro Analyzer. The results presented in Table V1 show convincingly that, under the conditions studied, the reaction be- tween keratin and H202 is confined mainly to the cystine residues. The decrease in cystine is almost quantitatively matched by a corresponding increase in cysteic acid. The amino acid analysis does not reveal any intermediate oxidation products of cystine which might be formed during the bleaching process. These compounds are, however, very unstable under alkaline condiitons, and any remaining would dis- proportionate to cystine and cysteic acid during the hydrolysis.