OXYRADICALS FROM PHOTOIRRADIATED HAIR 177 12 10 a b c Figure 5. Effects of additives on HTA production from irradiated bleached hair: 0.2 g bleached hair (1-mm long) in 2 mM TA at pH 7.6, irradiated for 90 min. a. Ethanol added (1 M). b. Azide added (10 mM). c. No additives. metal-sulfur complexes, which have considerable reactivity, and thus provide another pathway for oxyradical production (20,37). The sequence given in Scheme 2 has been suggested to explain the fate of thiyl radicals produced during the autoxidation of cysteine (38,39). In our spin trapping studies, irradiation was not carried out in the ESR cavity, and we find no evidence for the presence of transient sulfur radicals. Among the free radicals involved in these reactions, superoxide, hydroxyl, and hydrogen peroxide are most cytotoxic species induced by ionizing radiation and photosensitized

178 JOURNAL OF COSMETIC SCIENCE 10 Gauss Figure 6. ESR spectrum of the DMPO-OH adduct from irradiated hair. A 0.015-g sample of hair was irradiated for 10 min in 1 ml 20 mM DMPO, after which the sample solution phase was transferred to the quartz fiat cell. Spectrometer settings: microwave power, 20 mw sweep width, 100 G modulation am- plitude, 1 G receiver gain, 1.25 x 104 number of scans, 5. a. DMPO blank (no hair). b. Brown hair. c. Red hair. d. Bleached hair. oxidations. Additional reactions result in the oxidation of amino acids, most notably tryptophan, within the hair matrix. Thus, photodamaged hair (and wool) is characterized by reduced tryptophan and increased cysteic acid (5,6,50,41). The reduced fiber strength of weathered hair appears to be the consequence of the scission of disulfide bonds and their conversion to cysteic acid residues. Tryptophan photodamage appears to precede disulfide photooxidation. In cysteine-containing protein such as keratin, the disulfide bond contributes strongly to the overall stability and integrity of the structure. With the destruction of disulfide bonds, the hair may lose its natural elasticity, become more porous, and, hence, become more sensitive to changes in humidity. Degradation of