Intermediate oxidation products cystine

The dying of hair is accomplished by the action of H2O2, the persulfate of sodium or ammonia which oxidize the cystine. An analysis of this treatment reveals the presence of several intermediate oxidation products and the final transformation of 32 % of the Cystine to cysteic acid (HOOC - CH - CH - SO3H). 

The actual presence of large amounts of cysteic acid in bleached hair had at one time been in doubt [55, 56]. It had been theorized that the cysteic acid found in bleached hair hydrolysates was formed by decomposition of intermediate oxidation products of cystine during hydrolysis prior to the analytical procedure [55]. However, differential infrared spectroscopy [4] and electron spectroscopy for chemical analysis by Robbins and Bahl [5] on intact unhydrolyzed hair have conclusively demonstrated the existence of relatively large quantities of cysteic acid residues in chemically bleached hair. Evidence for other sulfur acids (e.g., sulfinic or sulfenic acids) in bleached hair has not been provided. It is unlikely that these amino acids exist in high concentrations in hair because these species are relatively unstable. 

Zahn and co-workers [2], using two-dimensional gel electrophoresis, separated up to 62 isolated protein spots from human hair. From the fluoro-gram of bleached hair, these scientists identified cystine oxides (monoxide and dioxide). Although the exact quantities of these intermediate oxidation products versus cysteic acid were not reported, the quantities were indicated to be small relative to the cysteic acid content [2]. 

To summarize, sulfonic acid is the principal established end product of the oxidative cleavage of the disulhde bond from the chemical bleaching of human hair with current hair bleach products [3,9]. The mercaptan content of bleached hair is lower than that of unbleached hair [4], The intermediate oxidation products of cystine (i.e., the disulhde monoxide, dioxide, trioxide, and tetroxide) do not exist as signihcant end products of hair bleaching using today s commercial bleach products [3,6,9]. Nevertheless, evidence has been presented demonstrating low levels of cystine oxides in bleached hair [2],... 

When cystine is irradiated at pH values below 5 in the presence of air and water, S—S fission predominates. Oxides such as CyS02SCy may be formed as intermediates, but the products isolated are mainly compounds such as cysteic acid, CySOsH. Alanine, serine, and glycine, produced in quantity in the absence of air, were formed only in minute amounts in its presence. Under all conditions of irradiation CyS02SH and CySSSCy were formed. When cystine was irradiated in the dry state cysteine, alanine, and lanthionine were formed. The results of irradiation experiments on cystine solutions are summarized in Table XXV. Savige (private communication, 1964) considers that products obtained by irradiation of cystine may arise by the following mechanisms ... 

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