2006 TRI/PRINCETON CONFERENCE 343 + - C-tenn N-term Figure 2. Schematic representation of the position of the positive and negative charges on the peptides. net positive charge occur more frequently and net positive charge appears to favour higher hydrophobic moment, compared to net negative charge. Observing the peptide structure it is possible to deduce some performances of these two peptides in solution. The distribution of the positive and the negative charges are important for understanding its penetration, since they allow for an orientation of the peptide at the hair surface, like a screw (Figure 2). The presence of a negative charge at the C-terminus suggests that the C-terminus will point away from the anionic surface and that adsorption will occur in a specific orientation driven by electrostatic comple- mentarity' s (17 ,20). The positive charges on the N-term peptide are located at the larger part of its structure, while C-term peptide shows a much more uniform size. Since hair surface is negatively charged, the electrostatic interaction between the peptide and hair surface will allow for the cationic part of the peptide to orientate into the hair surface. Because in the C-term peptide this cationic part is thinner, the penetration of the peptide inside the hair negatively charged membrane would be easier. To corroborate these assumptions, the visualization of the penetration of the peptides inside hair structure was carried out either by visual inspection (Figure 3) or by fluo- rescence microscopy on hair transversal cuts (Figure 4). The penetration of the peptides inside hair structure was first seen visually and notably the C-term peptide with the bleaching pre-treatment was more coloured than the others (Figure 3). These results were also confirmed by fluorescence microscopy. For only water washed Control W Control B C-Term W C-Term B N-TermW N-Term B Figure 3. Hair samples after treatment with the coloured peptides, comparing with the control samples. W refers to water washed samples while B refers to bleached samples.

344 JOURNAL OF COSMETIC SCIENCE (Control) (C-Term) (N-Term) Figure 4. Flourescence micrographs of cross sections of bleached virgin white hair after treatment with the peptides. hair no changes could be observed (data not shown), comparing to the control. Con- trarily, for bleached hair, which as previously stated has the surface damaged and is therefore more negatively charged, the penetration was only attained for the C-term peptide (Figure 4). It was also observed that the peptides were layered around the hair surface and did not penetrate completely inside its structure (ring-dyeing). It is believed that if longer penetration times and higher temperatures were used, the migration of the peptides could reach the cortical cells (9). Since the virgin hair that was only water washed lacks chemical or mechanical damages, its hydrophobic layer remains intact. Therefore, water and other substances are hardly adsorbed (or desorbed) and penetrate into the hair surface. This explains the fact that there was no penetration of the peptide structures inside hair when it was only water washed. On the other hand, the hydrophobic lipid layer of damaged hair surface may be depleted or damaged therefore, inner cellular structures of hair, which consists of many hydrophilic molecules, such as cystines, are now exposed to water. Several authors relate the increase in the adsorption of several compounds, such as polymers or proteins hydrolysates, with hair damage (bleaching), which has been described as a "self- adjusting" system, while reporting also an increase of protein adsorption with a decrease in the molecular size of the com pounds (7, 9, 13). The physical characteristics of the hair fibres after treatment were also determined. The tensile strength resistance and elongation for the hair samples are presented in Figure 5. 250 70 l 200 150 cii C: 60 .2 50 40 "iii 100 30 20 50 10 Cont, W Cont, B C-tenn, W C-lenn. B N-tenn, W N-tenn, B Cont, W Cont, B C-lerm, W C-tenn, B N-term, W N-tenn, B Figure 5. Tensile strength resistance (MPa) and Elongation(%) for the controls and for the hair samples after peptide treatment.