TRYPTOPHAN FLUORESCENCE IN HAIR 303 CONCLUSIONS The following conclusions can be drawn based on the fi ndings presented above: (1) The fl uorescence data obtained at several excitation wavelengths and for different types of hair, including white, Piedmont, bleached, blonde, brown, curly black, and Chinese, revealed major evidence for the presence of three major chromophores includ- ing Trp and its three photo-oxidation products: N-formylkynurenine, kynurenine, and 3-hydroxykynurenine. (2) While melanin itself does not seem to contribute signifi cantly to hair fl uorescence, the presence of melanin in pigmented hair was shown to reduce the fl uorescence intensity of other keratin chromophores. (3) Photo and thermal exposure of hair was shown to decompose protein chromophores and reduce fl uorescence intensity of Trp and, to a lesser extent, kynurenines. The data also point to a photoprotective infl uence of melanin on kynurenines. Externally applied mela- nin was also shown to exert a photoprotective effect for other hair chromophores. (4) Chemical reduction of hair by thioglycolates was shown to increase Trp fl uorescence. It was proposed that the effect is caused by softening of the keratin matrix accompanied by an increase in the mobility of protein chains and a consequent decrease in Trp quenching by di- sulfi des. Re-oxidation of thiol groups into disulfi des by hydrogen peroxide was demonstrated to decrease Trp fl uorescence to prereduction levels. A similar effect is produced by hair hydra- tion, with the magnitude of Trp fl uorescence reversibly increasing with water content. REFERENCES (1) J. Strassburger and M. M. Breuer, Quantitative Fourier transform infrared spectroscopy of oxidized hair, J. Soc. Cosmet. Chem., 36, 61–74 (1985). (2) C. Pande and J. Jachowicz, Hair photodamage—Measurement and prevention, J. Soc. Cosmet. Chem., 44, 109–122 (1993). (3) C. Pande, FT-Raman spectroscopy—Applications in hair research, J. Soc. Cosmet. Chem., 45, 257–268 (1994). (4) C. R. Robbins and S. K. Bahl, Analysis of hair by electron spectroscopy for chemical analysis, J. Soc. Cosmet. Chem., 35, 379–390 (1984). (5) J. R. Lakowicz, Principles of Fluorescence Spectroscopy (Plenum Press, New York, 1983), pp. 496. (6) C. R. Robbins, Chemical and Physical Behavior of Human Hair (Springer-Verlag, New York, 1994). (7) R. S. Asquith, L. Hirst, and D. E. Rivett, Effects of ultraviolet radiation as related to the photoyellowing of wool, Appl. Polym. Symp., 18, 333–335 (1971). (8) F. G. Lennox, M. G. King, I. H. Leaver, G. C. Ramsay, and W. E. Savige, Mechanisms of prevention and correction of wool photoyellowing, Appl. Polym. Symp., 18, 353–369 (1971). (9) Z. Yoshida and M. Kato, On the photooxidation products of tryptophan, J. Am. Chem. Soc., 76, 311–312 (1954). (10) P. Walrant and R. Santus, Ultraviolet and N-formyl-kynurenine-sensitized photoinactivation of bovine carbonic anhydrase: An internal photodynamic effect, Photochem. Photobiol., 20, 455–460 (1974). (11) R. K. Borkman, Ultraviolet action spectrum for tryptophan destruction in aqueous solution, Photochem. Photobiol., 26, 163–166 (1977). (12) A. Pirie and K. J. Dilley, Photo-oxidation of N-formylkynurenine and tryptophan peptides by sunlight or simulated sunlight, Photochem. Photobiol., 19, 115–118 (1974). (13) T. B. Truong, Charge transfer to a solvent state. 5. Effect of solute-solvent interaction on the ionization potential of the solute. Mechanism for photoionization, J. Phys. Chem., 84, 964–970 (1980). (14) S. Daly, R. Bianchini, T. Polefka, L. Jumbelic, and J. Jachowicz, Fluorescence and coloration of grey hair, Int. J. Cosmet. Sci., 31, 347–359 (2009).

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