I I I 2700 2600 2500 Figure 5. Formation of the mercaptan groups in hair due to photodamage. The virgin hair spectrum (A) changes significantly (B) upon 165 h irradiation in a solar simulator. c c -- c Amide I I I 1700 1600 Wc•venumbers (1/cm) Figure 6. Effect of hair photodamage on the peptide backbone. The amide I region of virgin Piedmont hair (solid line) changes (dotted line) upon 165 h irradiation in the solar simulator (see text).

266 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS c c -- c Amide I I I 1700 1650 Wavenumbers (1//cm) Figure 7. The amide I region of the Raman spectra (same data as in Figure 6) were enhanced using the second derivative (13-point) technique. The virgin hair spectrum is indicated by a solid line, and after 165 h irradiation in a solar simulator by a dotted line. proteins do not show the same vibrational frequency. This frequency is modulated by the nature of hydrogen bonding (inter- or intramolecular) as well as by the milieu of the amide bond. Thus, for a complex proteinaceous structure such as human hair, a variety of bands, with slightly differing frequencies, are likely to appear in this region. The overlap of these bands leads to a broad observed band that can be resolved using analytical procedures. Comparison of the spectra obtained for the virgin and the pho- todamaged hair shown in Figure 6 reveals slight but clear changes in the amide I region as a result of light-induced damage. These spectra have been resolved in Figure 7 to enhance these differences. The largest change appears in the ratio of the bands at ca. 1653 cm- • and 1663 cm- •. Based on the data available in protein literature, the 1653 cm- • band has been assigned to the or-helical protein conformation, while the band at ca. 1665 cm- • is likely due to the disordered form. These preliminary data suggest that under these irradiation conditions, the or-helical protein is relatively unaffected and that the damage occurs mainly to the cuticles and, perhaps, to the amorphous matrix proteins. A detailed study is needed to better characterize the changes observed in this preliminary study. In summary, a relatively new technique has been evaluated for its potential application in hair research. It is shown that the vibrational bands due to disulfide bonds and their