J. Soc. Cosmetic Chemists, 18,599-608 (Sept. 16, 1967) The Effect of pH on the Sorption of Collagen-Derived Peptides by Hair S. A. KARJALA, Ph.D., A. KARLER, Ph.D., and J. E. WILLIAMSON, B.S.* Presented November 30, 1966, New York City Synopsis--Sorption of peptides increases very rapidly during the first few minutes to one-half hour of peroxide or thioglycolate treatment, after which sorption is essentially constant for a period, increasing rapidly again as the hair is damaged more extensively. The conclusion is drawn that the first action is on the cuticle which is readily removed by chemical treatment, and that increased sorption occurs after removal of the cuticle, only after extensive damage to the cortex. Oxidizing agents cause a maximum sorption of peptide at neutral pH values, while thioglycolate causes maximum sorption at high pH levels. Sorption appears to be an equilibrium phenomenon governed by the pH value of the peptide solution. INTRODUCTION A procedure for the objective evaluation of sorption of peptides to human hair was described in a previous publication (1). The method is based on the fact that collagens and peptides derived from collagen or gelatin contain hydroxyproline which is not present in keratin or in any of the other common proteins which at one time or another have been suggested in cosmetic formulations. The presence of hydroxyproline in hydrolyzed samples of hair after immersion in collagen-derived peptide solution and rinsing is definite proof of sorption of the peptide on the hair. This analytical method used is applicable only to collagen and to pep- tides derived from collagen. Different procedures, based on the use of radioactive peptides or some dye-binding procedure, would have to be * Wilson & Co., Inc., Research and Technical Div., Chicago, Ill. 60609. 599

600 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS used for peptides other than those from collagen. The method is sensi- tive, and analytical differences arise primarily from the high variability of the hair itself. In a further study of the parameters affecting sorption (2), it was shown that, in general, protein sorption is rapid for the first fifteen min- utes of treatment of virgin or bleached hair thereafter the sorption in- creases more slowly over a one-hour period. Peptide sorption is in- creased markedly by two one-hour bleach periods, while a third one-hour bleach has relatively little effect. Within the concentration range of 5- 20% of peptide there is relatively little difference in the amount of pep- tide sorbed. Weight increases of the hair strands demonstrated that there was considerable water sorption along with peptide sorption. Some preliminary investigations which have been made relative to the binding and elution of dyes at high and low pH levels led to the present study on the effect of pH on peptide sorption by human hair. A few rather limited studies have been made on the effect of pH on several aspects of hair treatment. Heiling6tter (3) studied the effect of thioglycolate solutions on the swelling of hair in the pH range 7.0 to 9.8, and Freytag (4) extended this type of study to bleached hair as well as virgin hair over the pH range 3 to 10. Swelling was found to increase with increase in pH and was greater for bleached hair than for virgin hair. Laden and Finkelstein (5), using dye solutions, showed that the rate and extent of sorption could be modified by changing the pH of the system from which sorption occurs: An acid pH induces a positive charge on keratin favoring the uptake of anionic materials, whereas a basic pH value favors the sorption of eationic materials. METHODS AND RESULTS The hair used in all of the tests was dark brown DeMeo Blue String* virgin human hair. It was shampooed in a nonionic detergent (Triton X-100 t) at 1% concentration, after which the hair was rinsed thoroughly in distilled water and dried. For the bleach treatments, 100 mg tresses of the shampooed hair were immersed for varying periods of time in 6,070 hydrogen peroxide, prepared by treating 50 parts of 6% H202 with 1 part of concentrated ammonium hydroxide. * DeMeo Company, 135 Fifth Ave., New York, N.Y. 10010. } A product of Rohm and Haas, Philadelphia, Pa.