EFFECT OF CURLING IRONS 231 (a) 2.50E+06 • 2.00E+06 o •- 1.50E+06 • 1.00E+06 -- 5.00E+05 O.00E+00 300 unexposed unexposed: 14•/14•o = 0.97 ._•30 rain: 14e5/1421.26= / !?•,•n .....................................I..........•,_.,.,T,:: •,i,• ........... , 30 min , , , 350 400 450 500 550 Wavelength (nm) 8. OOE+06 7. OOE+06 m 6.00E+06 o 5. OOE+06 (b) .'•' 4.00E+00 • 3.OOE+06 I 2.OOE+06 1.OOE+06 0.00E+00 330 unexposed unexposed: 14./142o = 0.79 • 30 min: 14•dl42o = 0.95 30 rnin i i i i 380 430 480 530 580 Wavelength (nm) (c) 1.80E+07 1.60E+07 1.40E+07 1.20E+07 1.00E+07 8. OOE+06 6. OOE+06 4.OOE+06 2.OOE+06 0.00E+00 360 unexposed 30 rain unexposed: 14./142o = 0.95 30 mln: 14edl42o = 1.04 f , 410 46O 510 560 Wavelength (nm) Figure 3. The emission spectra of white (unpigmented) hair, at excitation wavelengths of 290 nm (a), 320 nm (b), and 350 nm (c), before thermal exposure after 30 min of treatment. Thermal treatment was administered at 164øC. The fluorescence spectra of unpigmented hair obtained at excitation wavelengths of 320 nm (Figure 3b) and 350 nm (Figure 3c) suggest thermal decomposition of both N- formylkynurenine (emission peak at 420 nm) and l-kynurenine (emission peak at 465 nm). The extent of decomposition of these two species is not nearly as severe as in the case of Trp, judging from the emission intensity ratios for these chromophores before and

232 JOURNAL OF COSMETIC SCIENCE lOO 7o 6o 4o 3o 2o lO o 0 Bleached, k=.04 [] Piedmont, k=.05 • Asian, k=.03 X Light Brown, k=.04 O White, k=.03 0 5 10 15 20 25 30 35 Time (min) Figure 4. Decomposition of Trp for various fiber types as a function of thermal exposure time. Thermal treatment was administered at 164øC. k is reported in min 1. after thermal treatment. This may be due to the higher thermal stability of N- formylkynurenine and l-kynurenine, or may arise from the fact that kynurenines are the products of Trp decomposition. It must also be addressed that thermal treatment pro- duces a change in the relative emission intensities for the peaks corresponding to N-formylkynurenine (420 nm) and 1-kynurenine (465 nm). For the spectra obtained at