2010 TRI/PRINCETON CONFERENCE 193 allows for collection of numerous spectra for one sample position. Excitation-emission spec- tra are constructed by measuring fl uorescence emission at various excitation wavelengths— from 270 nm to 450 nm in increments of 2 nm. Emission spectra were collected starting 15 nm higher than the excitation wavelength to generate a total emission scan of 200 nm. Therefore, if the excitation wavelength was set at 270 nm, the emission spectrum would be collected from 285–485 nm. Average values represent measurements from two hair tresses in which case readings were obtained 1 in. from the top of the tress. In some cases, such as photo- and thermal degradation studies, readings were obtained 1 in. from the top of the tress (unexposed area) and 2 in. further down the tress in the exposed region. Thermal exposure was conducted for 1 min. of continuous treatment in the middle of the tress using a Big Chi (Model GF1533D) fl at iron marketed and sold by Farouk Systems Group (Houston, TX). It is a variable temperature controlled iron capable of reaching a temperature of 200 °C. Hair was exposed to UV radiation in a Q-Sun weathering chamber (Q-Sun Xenon Test Chamber Model Xe-1-B Q-Panel Lab Products, Cleveland, OH) containing a full spec- trum 1800 xenon arc lamp with irradiance set at 0.35 W/m2 at 340 nm. The total expo- sure time was 96 hours at a temperature of 40 °C. Hair was mounted in frames constructed of black cardboard shielding the top and bottom portions of the hair tress and leaving only the middle portion exposed to UV light. RESULTS AND DISCUSSION Previous studies of the intrinsic fl uorescence of hair yielded information about the effects of chromophores on the fl uorescent behavior of Trp and its metabolic/degradation products: Kynurenenine, N-formylkynurenine, and 3-hydroxykynurenine (12). The effects of mela- nin on the fl uorescence of these molecules can be monitored by comparison of highly pig- mented dark brown hair with non-pigmented Piedmont hair or white hair. In the current investigation we utilized Piedmont hair, which contains higher levels of yellow pigmenta- tion than pure white hair. Gray hair may also contain yellowish coloration, presumably present due to exposure to UV radiation, which is believed to be attributed to higher levels of 3-hydroxykynurenine (11). In general, hair containing greater quantities of melanin has much lower emission characteristics, most likely because more light absorbed by melanin will result in less light available to interact with Trp and other fl uorophores. Further, Trp fl uorescence was found to be highly dependent on the moisture content of hair, with greater Trp fl uorescence occuring at higher levels of hydration (12). Trp fl uorescence is known to be extremely sensitive to its immediate environment, and may increase or decrease depending on the mobility of the Trp residues. One may even observe an increase in Trp fl uorescence when hair is subjected to damaging treatments such as permanent waving due to the cleav- age of disulfi de bonds. Although one may expect less Trp to be present after such a damag- ing treatment, such an effect may be explained by an increase in the mobility of Trp residues in the protein in the absence of disulfi de bond (13). BLEACHING OF HAIR In many cultures, hair bleaching is a widespread procedure that is employed to lighten the color of pigmented hair. It is especially popular for the formation of highlights—the

JOURNAL OF COSMETIC SCIENCE 194 artistic blending and shading of hair to produce an overall confi guration on the head containing the originally colored hair fi bers with fi bers of various degrees of lightening. The principal intention of hair bleaching is the destruction of melanin granules by oxida- tion through the action of H2O2 and persulfate salts. Dark brown and Piedmont hair were bleached for 30 min. with a commercial bleaching formulation. For both cases, photographs of virgin and bleached hair are provided in Figure 1. While dark brown hair still contains some pigmentation after the bleaching process, Piedmont hair (yellow hue in the virgin state) becomes very white after treat- ment. Excitation-emission matrices for virgin and bleached dark brown hair are provided in Figure 2. The most apparent difference between the two spectra is the large increase (as a result of bleaching) of the fl uorescence band corresponding to the principal kynurenine peak (Ikyn), which occurs at λex=366 nm, λem=433 nm. There is also a large fl uorescence increase observed at the extreme of the spectrum corresponding to λex=450 nm, λem=509 nm, which we refer to as I509 throughout the text. Trp fl uorescence (ITrp), corresponding to λex=290 nm, λem=343 nm, appears to decrease as a result of bleaching however, this is due to a difference in scale of the two spectra. In fact, Trp fl uorescence increases as a result of bleaching, probably because less melanin is available to absorb light. Figure 1. Photographs of (A) virgin dark brown hair, (B) bleached dark brown hair, (C) virgin Piedmont hair, and (D) bleached Piedmont hair.