INVESTIGATING PREVENTION OF UV DAMAGE 359 crucial for understanding the potential protective effects of treatment materials A–F on hair fi ber protein structure because these materials have Raman spectra of their own. An example of peak fi tting for 440–600 1/cm for a Material B–treated, irradiated hair fi ber is shown in Figure 3. Material B has a strong peak near 488 1/cm which overlaps with the disulfi de signature from the hair fi ber. Peak fi tting was important for separating the potential effect of the treatment material from the hair fi ber structure. RESULTS AND DISCUSSION Baselined, normalized spectra for the cuticle of untreated, nonirradiated unpigmented hair fi bers and unpigmented hair fi bers subjected to 24 h of 62 W/m2 UV radiation (5.4 MJ/m2) are shown in Figure 4. Tentative peak assignments from literature (5–14) are also given Figure 2. Approaches to quantifying Raman peak information. Figure 3. E xample peak fi tting for Material B.
JOURNAL OF COSMETIC SCIENCE 360 in the fi gure. Key differences appear with disulfi de and amide III. Disulfi de content decreases on 24-h UV exposure, indicating damage to the hair fi ber cuticle. The infl uence of UV on amide III was less clear and is not addressed in this work. As discussed in the Methods section, Raman spectra were normalized to peaks that did not change signifi cantly on 24 h of UV exposure. Because of its importance to hair fi ber structure, normalized disulfi de peak height was investigated for all treatments. Figure 5 shows the disulfi de peak height normalized to the peak height values for Phe, CH2 bending, amide I, and CH signature around 2,920 1/cm. Using all available peaks for normalization allows for analysis of hair fi bers treated with materials even if the treat- ment material Raman signature overlaps with some of the hair fi ber peaks used for normalization. Comparing the nonirradiated versus irradiated hair fi bers in Figure 5 shows a clear decrease in normalized disulfi de bond intensity, consistent with Figure 4. The treatment materials, with the exception of Material B, showed disulfi de content consistent with or lower than disulfi de content of the untreated, irradiated hair. Mate- rial B appears to show some promise for disulfi de protection. However, this protection needs to be verifi ed with a secondary method because of the peak fi tting required to separate the contribution from hair fi ber disulfi de from the raw material signature at 488 1/cm. In addition, materials A–F could potentially provide benefi ts if delivered from formulations, which were not evaluated in this work. They could potentially also have a protective effect on other measures of UV damage to hair, which were also not evaluated as part of this work. Figure 4. Ra man spectra of the cuticle of unpigmented hair fi bers that have not undergone irradiation (non- irradiated hair fi bers) and that have undergone 24 h of 62 W/m2 UV irradiation (5.4 MJ/m2).
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