144 JOURNAL OF COSMETIC SCIENCE 0.10 0.08 0.06 C 0.04 0.02 -- 0 5300 5200 5100 5000 4900 4800 4700 Wavenumber/ cm- 1 Figure 3. NIR spectra in the 5300-4700 cm- 1 region corrected on the basis of the intensity of the CH stretching band around 5900 cm -l. Thin solid line: untreated hair. Dotted line: hair treated with MA/ BOE/ethanol solution for 20 min. Dashed line: treated for 40 min. thick solid line: treated for 60 min. some water despite being dried under vacuum overnight and measured in the dry condition. The absorbance of the water band decreases with increasing treatment time in the acid solution, suggesting that the bound water is replaced by substances in the acid solution. PEAK SHIFT OF PROTEIN BAND BY ACID In Figure 3, the peak of the NH stretching and amide II combination band (protein band) appears to be shifted toward lower wavenumbers by the acid treatment. To display it in more detail, the second derivatives of the spectra in the range of 49 5 0-4 7 5 0 cm - 1 are shown in Figure 5, showing clearly a peak shift toward lower wavenumbers with the acid treatment. In contrast, little shift was observed for the combination band in the case of the hair treated with an aqueous solution of HCl/BOE/ethanol (data not shown). Therefore, the peak shift should be caused by malic acid. For the stretching mode, it is known that the band shifts toward lower wavenumbers if the bond is affected by the hydrogen bond. On the contrary, the amide II band, NH in-plane deformation mode, may shift toward higher wavenumbers by the hydrogen bond. The effect of the hydrogen bond on the peak shift is, however, generally higher for stretching modes than for deformation modes. Therefore, the peak shift toward lower wavenumbers for the combination band of NH stretching and amide II means that the hydrogen bond is strengthened. A similar trend for the peak shift and that of set durability improvement was also found for bleached Japanese hair (6). Thus it seems that malic acid works in the same manner for damaged hair, although all kinds of damaged hair have not been investigated.

INTERACTION BETWEEN HAIR PROTEIN AND ORGANIC ACID 145 T""" I 0.03 E 0.025 u 0 "- � LO � co Q) u C co ..c L.. 0 en ..c ( 0.02 0.015 0.01 0.005 0 0 20 40 60 TI min Figure 4. Absorbance of the water band (5170 cm - 1 ) plotted against the treatment time, T. THE SYNCHRONOUS 2D CORRELATION MAP 80 Figure 6 displays a synchronous 2D NIR correlation map of the hair, constructed from the treatment time-dependent (0, 20, 40, and 60 min) spectral variations in the 5 300- 4750 cm- 1 region. The one-dimensional spectra drawn at the top and at the left side of the 2D map are reference spectra obtained by averaging the spectra set. The synchronous correlation spectrum represents the simultaneous or coincidental change of spectral intensity variations measured at v 1 and v 2 : here, v 1 and v 2 are spectral variables (wavenumbers in this paper). A synchronous spectrum is symmetrical with respect to the diagonal line (dashed line). The obtained synchronous correlation map is characterized by two autopeaks ( on the diagonal line) near 5170 and 4890 cm - 1 and cross peaks located at the off-diagonal positions between them. The intensity of autopeaks of a synchronous correlation spec- trum represents the overall extent of dynamic fluctuations of spectral signals (12,16). Therefore, it is found that the change in the water band and the protein band is large. The cross peaks shows the relation between the 5170 cm- 1 and 4890 cm -l bands. The 51 70 cm - l is almost at the center of the water band, but 4890 cm - l is a little deviated