INTERACTION BETWEEN HAIR PROTEIN AND ORGANIC ACID 147 800 900 5000 5100 . ..... .... 5200 L-----�1---........--1,----,------,,---�---,--5300 5300 5200 5100 5000 4900 4800 Wavenumber/ cm-1 T""" I E (.) ..._ L... Q) ..c E ::::J C Q) m s Figure 6. Synchronous 2D NIR correlation spectrum in the 5300-4750 cm- 1 region constructed from treatment-time-dependent spectral changes in hair. Dotted lines through the tops of the cross peaks show which bands correlate with each other. All the correlation peaks are positive. peaks, it can be clearly seen that the protein band, which is apparently one peak, is composed of more than three bands. The three bands, around 4890, 4850, and 4810 cm- 1 are referred to as band A, band B and band C, respectively. The map shows clear correlations between A and B, and A and C. These three bands seem to be different in the strength of their hydrogen bonds with the NH of the protein amides. According to the consideration described before, it can be said that band A is the band having no or the weakest hydrogen bond, band B is in the middle, and band C is the strongest. ASSIGNMENT OF THE DECONVOLUTED PROTEIN BANDS The wavenumber of band A, 4890 cm - l, is the same as that of the band correlating with the water band in the synchronous correlation map (Figure 6). The sign of the cross peaks

148 JOURNAL OF COSMETIC SCIENCE V 1 C V 2 750 I' I' ,. ,. .,. I' 800 () 850 .................. ,. I' 900 I' ._ ____________________�::_::_::_::__::_:::_::_.._··-··-·-------+-=509:._::..: 4950 4900 4850 4800 Wavenumber/ cm- 1 4750 T""" I E (.) ..._ L... Q) ..c E :::J C: Q) ro � Figure 7. Asynchronous 2D NIR correlation spectrum in the 495 0-4 7 5 0 cm- 1 region constructed from treatment-time-dependent spectral changes of hair. Dotted lines through the tops of the cross peaks show components A, B, and C of the protein band. Shaded peaks are negative. in the synchronous correlation map are positive, indicating that the NIR spectral in- tensities of the water band and band A are either increasing or decreasing together. By taking into account the finding that the spectral intensity of the water band decreases with the treatment time, as shown in Figure 4, it can be said that band A decreases with the treatment time together with the decrease in the water band. As a result, band A is assigned to the NH protein linked by a hydrogen bond to water. The other two bands cannot be clearly assigned by the data of these measurements, but band B is the most abundant and can be identified as the protein NH group interacting with other protein residues. Finally, band C seems to arise from the protein NH group interacting with the anionic carboxylic group of MA, because band C relates to the strongest hydrogen bond (18).