150 JOURNAL OF COSMETIC SCIENCE protein-water because they are not so strong. In the case of acid-treated hairs, an organic acid penetrating into the same area occupies the position where water originally existed (Figure Sc). Consequently, the band of water and band A of the protein band in the NIR spectra decrease simultaneously as described above. The anionic carboxyl group of the organic acid makes stronger hydrogen bonds with protein NH than protein-water (A) and protein-protein (B) hydrogen bonds. Even under high humidity, water mol- ecules also permeate, but the strong hydrogen bonds with the organic acid are not easily replaced by water, and they prevent proteins from moving. As a result, the hair shape is maintained. It is known that treatment with some acids decreases the water uptake of wool (19) and that naphthalenesulfonic acid improves hair-set durability (20). It is seen from Figure 4 that MA/BOE/ethanol treatment also reduces the water uptake of hair. The present NIR results suggest, however, a new, additional, mechanism of set durability improvement in the strengthening of hydrogen bonds by carboxyl groups of acids such as malic acid. CONCLUSIONS Hair-set durability against high humidity is improved by treatment with malic acid. From the fact that the improvement was confirmed even for single hair fibers, it is concluded that this improvement is due to internal changes in the hair fiber. This makes natural setting possible, and not due to the common technologies based on adhesion or fixing by oils or polymers. By the analysis of 2D NIR correlation spectroscopy, the behavior of organic acid was determined. It adsorbs at the site where water originally binds, prevents water penetra- tion, and makes strong and stable hydrogen bonds with hair proteins. The formation of such strong and stable hydrogen bonds suppresses the exchange of hydrogen bonds that is the cause of the breakage of set durability. ACKNOWLEDGMENTS The authors thank Dr. Daisuke Adachi for his kind offer of software for the generalized 2D correlation analysis. The authors are also grateful to Professor Yukihiro Ozaki (Kwansei-Gakuin University) for his kind and valuable discussions and advice on NIR measurement and 2D correlation analysis. The authors also thank Dr. Naohisa Kure, Director of Hair Care Research Laboratories, Kao Corporation, for helpful discussions and guidance. REFERENCES (1) S. Nagase, S. Shibuichi, K. Ando, E. Kariya, and N. Sarah, Influence of internal structures of hair fiber on hair appearance. I. Light scattering from the porous structure of the medulla of human hair,]. Cosmet. Sci., 53, 89-100 (2002). (2) S. Nagase, N. Satoh, and K. Nakamura, Influence of internal structure of hair fiber on hair appearance. II. Consideration of the visual perception mechanism of hair appearance,]. Cosmet. Sci., 53, 387--402 (2002). (3) M. Okamoto, R. Yakawa, A. Mamada, S. Inoue, S. Nagase, S. Shibuichi, E. Kariya, and N. Satoh,

INTERACTION BETWEEN HAIR PROTEIN AND ORGANIC ACID 151 Influence of internal structures of hair fiber on hair appearance. III. Generation of light-scattering factors in hair cuticles and the influence on hair shine,]. Cosmet. Sci., 54, 353-366 (2003). (4) S. Nagase, S. Shibuichi, K. Ando, E. Kariya, M. Okamoto, R. Yakawa, A. Mamada, and N. Satoh, Light-scattering control at the medulla enhances human hair shine. Internal structures of hair fiber and its shine (I), Proceedings of 21st IFSCC Congress, 2000, p. 153. (5) C.R. Robbins, Chemical and Physical Behavior of Human Hair, Fourth Edition (Springer-Verlag, New York, 2002), pp. 133-134. (6) M. Nojiri, T. Itou, M. Asami, K. Ueyama, and K. Nakamura, A novel technology for improving hair setting ability and its mechanism,]. Cosmet. Sci., 55, Sl51-S153 (2004). (7) Y. Liu, Y. Ozaki, and I. Noda, Two-dimensional Fourier-Transform near-infrared correlation spec- troscopy study of dissociation of hydrogen-bonded N-methylacetamide in the pure liquid state,]. Phys. Chem., 100, 7326-7332 (1996). (8) B. G. Osborne and T. Fearn, Ne,1r Infrared Spectroscopy in Food Analysis (Longman Scientific & Technical, UK, 1986), pp. 28-42. (9) R. D. B. Fraser, Side-chain orientation in fibrous proteins, Nature, 176, 358-359 (1955). (10) R. D. B. Fraser and T. P. MacRae, Hydrogen- deuterium exchange reaction in a-keratin,]. Chem. Phys., 28, 1120-1125 (1958). (11) E.G. Bendit, M. Feughelman, R. D. B. Fraser, and T. P. MacRae, The hydrogen - deuterium exchange reaction in stretched keratin, Textile Res.]., 29, 284-285 (1959). (12) I. Noda, Generalized two-dimensional correlation method applicable to infrared, Raman, and other types of spectroscopy, Appl. Spectrosc., 47, 1329-1336 (1993). (13) K. Murayama, B. Czarnik-Matusewicz, Y. Wu, R. Tsenkova, and Y. Ozaki, Comparison between conventional spectral analysis methods, chemometrics, and two-dimensional correlation spectroscopy in the analysis of near-infrared spectra of protein, ApjJ!. Spectrosc., 54, 978-985 (2000). (14) B. Czarnik-Matusewicz, K. Murayama, Y. Wu, and Y. Ozaki, Two-dimensional attenuated total reflection/infrared correlation spectroscopy of adsorption-induced and concentration-dependent spec- tral variations of f3-lactoglobulin in aqueous solutions,]. Phys. Chem. B, 104, 7803-7811 (2000). (15) K. Murayama, Y. Wu, B. Czarnik-Matusewicz, and Y. Ozaki, Two-dimensional/attenuated total reflection infrared correlation spectroscopy studies on secondary structural changes in human serum albumin in aqueous solutions: pH-dependent structural changes in the secondary structures and in the hydrogen bondings of side chains,]. Phys. Chem. B, 105, 4763-4769 (2001). (16) Y. Ozaki, K. Murayama, Y. Wu, and B. Czarnik-Matusewicz, Two-dimensional infrared correlation spectroscopy studies on secondary structures and hydrogen bondings of side chains of proteins, Spec- troscopy, ] 7, 79-100 (2003). (17) A. Elliott, Infra-red dichroism and chain orientation in crystalline ribonuclease, Proc. Royal Soc. (London), A21 l, 490-499 (1952). (18) G. A. Jeffrey, An Introduction to Hydrogen Bonding (Oxford University Press, New York, 1997), pp. 11-15. (19) C.H.Nicholls and J.B. Speakman, The influence of combined acid on the affinity of wool for water, ]. Text. Inst., 45, T267-T271 (1954). (20) L. J. Wolfram and L. Albrecht, Torsional behavior of human hair,]. Soc. Cosmet. Chem., 36, 87-99 (1985).