240 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VII Set Stability of Hair Following Alk¾1ation with N-Hept¾1 Maleimide Hanging Lengths (cm): After Following Relaxation Time (min): Sample 0 5 7.5 I0 15 30 150 Intact (H=O set) 2 7.5 11 12 13 13 13 Intact 2 5.0 7 8 I0 11 12 Reduced/hepryl maleimid e 2.5 3.5 4 4 4.5 5.0 6 •Measured at 84 per cent RH, 85øF. Table VIII Effect of Reduction Level on the Set Stability of Alkylated Hair Hanging Lengths (cm) at Relaxation Times (min):: Treatment 3 6 9 12 20 45 Intact (H20) 2 3 5.5 8 I0 11 Intact 2.5 3 3.5 5.5 8.5 10.5 15' Reduction/hepty[ maleimide 2.5 5.0 6 7.5 9 I0 30' Reduction/hepr¾1 maleimide 2 3 3.5 4 5 6.5 60' Reduction/heptyl maleimide 2 2.5 3.0 3 5 4 5.0 tresses were air dried overnight on the rollers (alternatively, the set hair was dried with a hand held dryer). The set stability is shown in Table VII. The alkylation results in excellent set stability during a prolonged exposure to condi- tions of high humidity. Additional experiments indicated that increasing the size of the alkyl substituent above C7 offered no benefit. Optimal interaction of the hydrophobic sidechains or, indeed, the mobility of such chains, may not be possible in the case of the dodecyl residues because ofsteric factors. Thus, the maximal stabilization of the keratin would not be attained. It is of interest to note that the best results have been obtained with hair alkylated either with heptyl or with benzyl maleimides. The effect of alkylation on the set stability (measured at 84 per cent RH, 85øF) was de- termined at several reduction levels (Table VIII). It appears that alkylation of reduced hair having less than 50 per cent cleavage does not greatly improve the setting properties. An important consideration in the reduction-alkylation process is the respective bond energies of the system. As discussed earlier, disulfide bonds represent approximately 50 kcal/mol of stabilization energy. The introduction of two apolar residues (heptyl sidechain) for the blocking of a reduced disulfide will contribute only about 3 kcal/rnol of binding energy. At low reduction levels, the introduction of a few hydrophobic crosslinks cannot compete with the residual disulfides which significantly contribute to the overall setting characteristics of intact hair. At very high reduction levels, only a

HYDROPHOBIC BONDS AND HAIR TREATMENTS 241 few restraining disulfide crosslinks remain, thus, the stabilizing influence of the hydro- phobic crosslinks becomes more prevalent in maintaining the native structure of the keratin. (1) (2) ?:'' (3) .. •'•. (4) .: (5) (6) 55:: (7) (8) : ::5::'! (9) . :: '..i!:' (lO) ":': (11). ::: :::: (1.2) (1•) :.. :. REFERENCES L. J. Wolfram and M. K. O. Lindemann, Some observations on the hair cuticle, J. Soc. Cosmet. Chem., 22,839(1971). M. Harris et. al., Role of cystine in the structure of the fibrous protein, wool, J. Res. Nat. Bur. Stand., 27, 89 (1941) ..... J. B. Speakman, Mechano-chemical methods for use with animal fibers, J. Text. Inst., 38, T102 (1947). E. I. Valco and G. Barnett, A study of the swelling of hair in mixed aqueous solvents, J, Soc. Cosmet. Chem., 3,108 (1952). K. C. Tsou, R. J. Barnett, and A.M. Seligman, Preparation of some N-(l-naphthyl)-maleimides as sulfhydryl group reagents, J. Amer. Chem. Sot., 77, 4613 (1955). J. R. Heitz, C. D. Anderson, and B. M. Anderson, Inactivation of yeast alcohol dehydrogenase by N- alkyl maleimides, Arch. Biochem. Biophys., 127,627 (1968). L. E. Coleman, Jr., J. F. Bork, and H. Dunn, Jr., Reaction ofprimary aliphatic amines with maleic anhy- dride, J. Org. Chem., 24, 135 (1959). H. D. Weigmann, Reduction of disulfide bonds in keratin with 1,4-dithiothreitol. I. Kinetic investiga- tion, J. Polym. Sci. A-I, 6, 2237 (1968). L.J. Wolfram and D. L. Underwood, The equilibrmm between the disulfide linkage in hair keratin and sulfite or mercaptan, Text. Res. J., 36,947 (1966). I. M. Klotz, Role of water structure in macromolecules, Fed, Proc. Fed. Amer. Soc. Exp. BioL, 24, Suppl. 15, S-24 (1965). E. Wicke, Structure formation and molecular mobility in water and in aqueous solutions, Angew. Chem Int. Ed., 5,106 (1966). G. Nemethy, Hydrophobic interactions, Angew. Chem. Int, Ed., 6, 195 (1967). A.D. Jenkins and L. J. Wolfram, The chemistry of the reaction between tetrakis (hydroxymethyl) phos- phomum chloride and keratin, J. Soc. Dyers Colour., 79, 55 (1963).