J. Cosmet. Sci.) 58, 339-346 CTuly/August 2007) Peptide structure: Its effect on penetration into human hair CARLA J. S. M. SILVA, ANDREIA VASCONCELOS, and ARTUR CAVACO-PAULO, Department of Textile Engineering, Minho University, 4800-058 Guimaraes, Portugal. Synopsis The influence of the peptide structure on its penetration inside hair was studied, together with the effect of hair bleaching (oxidation). For that reason, the outcome of positioning a charged sequence (KAKAK) either at the N or C terminal on hair penetration has been studied for peptides with 1 7 residues each. It was observed that the penetration of these peptides into hair was driven by electrostatic interactions, where the position of the charged group at the peptide structure was of major importance. The penetration was only achieved for damaged hair due to its higher negative charge at the membrane surface. It was also observed that the peptides were able to restore the original tensile strength of bleached hair. Consequently, the knowledge of hair surface properties is of extreme importance when designing peptides directed for hair treatment. INTRODUCTION The desire for products that improve the look and feel of hair has created a huge industry for hair care which is constantly in quest of new products and finishing treatments. Beauty care technology has advanced the cleaning, protection and restoration of desirable hair and skin properties by altering its surface. Therefore, the characterization of hair structure and the knowledge of physical and mechanical properties of hair are essential (1,2). Human hair is a fibrous tissue, comprised of keratin. The main morphological compo- nent is the fibrous cortex (about 80%) surrounded by the multicellular flat cuticle sheath (about 15 % ), with the additional feature of a central medulla for some types, especially coarser fibres. These main morphological components consist of distinct chemical con- stituents. In the amorphous cuticle, the outer exocuticle layer is composed mainly of high-sulphur proteins and is therefore rich in disulphide cross-link bonds, leading to its high mechanical properties (tough and resilient layer) and creating a trans-cellular barrier to the penetration of various compounds to the hair structure (3-6). Because of this, penetration of chemicals into hair occurs mainly through intercellular diffusion. Unaltered human hair has an isoelectric point near 3.67. Hence, under most pH con- ditions the surface of hair carries a negative charge. For this reason, most conditioning Address all correspondence to A. Cavaco-Paulo. 339

340 JOURNAL OF COSMETIC SCIENCE polymers are cationic, since electrostatic interactions are believed to play a determining role in the adsorption mechanism (7). The exposure of the hair to sun, wind and modern hair styling products and techniques (e.g. shampooing, combing, blow-drying, bleaching, colouring and shaping of hair with wave preparations) imparts significant and unwanted damage to the cuticle and cortex of the hair shaft. This damage results in a loss in body, lustre, and smooth texture. Such damage is also reflected in poor wet and dry combability, increased electrostatic charg- ing, reduced tensile strength and breaking of the hair and in the poor appearance of hair styles. The main objectives of hair care product development are then to inhibit or reduce the damage caused by the factors described previously and to create an improved feel of the hair (8). The cosmetic industry also takes an interest in the penetration of several substances into hair fibres in order to improve the knowledge of diffusion processes in hair (9,10). To study the diffusion of molecules into hair, fluorescence dyes are often used and in this case the penetration can be investigated by conventional fluorescent microscopy. The use of protein materials in the formulation of modern hair care products to provide shine, strength, softness, smoothness and good combing properties is well known and began more than 50 years ago. Several patents disclose compositions capable of perme- ating into shampooed hair to impart hair with moistness and to provide excellent finishing effects by including proteins or proteins hydrolizates, like for example a water-soluble compound derived from a vegetable protein derivative (11), non-naturally occurring keratin proteins (12), a mixture of a hydrolysed protein and an amino acid with aliphatic side chain (13) and several hydrolysed proteins (14,15). The present study describes how the structure of two peptides, which differ only in their conformation from the N to the C-terminal, influences in their penetration inside human hair. It was verified that their penetration inside hair was structure dependent and it was essentially driven by electrostatic charging. These peptides were capable of restoring the tensile strength of bleached hair, thus compensating for its damage, which could rep- resent a new methodology for hair treatment. EXPERIMENT AL DETAILS/MATERIAL AND METHODS HAIR SAMPLES AND PEPTIDE STRUCTURES European virgin white hair samples were received from IMHAIR Ltd. (Italy). The peptide structures were synthesized by JPT Peptide Technologies GmbH (Berlin, Ger- many). The two synthesized peptides, with 17 amino acids each, were: C-term: 11111 LCLCL LLKAK AK N-term: KAKAK LLLCL CLLLL LL where L, C, K and A is the one-letter code to the amino acids Leucine, Cysteine, Lysine and Alanine. All the peptides were covalently linked by the N-terminal to a fluorescent dye, (5(6)-carboxytetramethylrhodamine, succinimidyl ester) i.e. 5(6)-TAMRA, with spectral properties of Absmax = 544 nm and Emmax = 572 nm, to facilitate the analysis of peptide penetration. The peptides molecular weight was 2292.67 g/mol and they were supplied as a lyophilized material. They were analysed by HPLC and MS, and their