312 Right-handed alpha-Helix JOURNAL OF COSMETIC SCIENCE Sulphur & Tyrosine-rich Proteins (KA-P) Nuclear Remant Low-sulphur Proteins (KIF-P) lntermacrofibrillar Material Intermediate Filament Macrofibril F-Layer A-Layer I, Para- Exo­ Endo-cuticle Para-cortical Cell Cortex I 200 I 2000 Cuticle I 20000 nm Figure 1. Graphical representation of the morphological components of a Merino wool fibre (Adapted by Zahn et al. (4) from a drawing by R. D. B. Fraser 1972). cells, the cell membrane complex (cmc), is a continuous phase of proteins, lipoproteins, and adjacent membrane lipids. During hair growth, the cortex cells assume a spindle- like shape (length: approx. 100 µm, largest diameter: approx 5 µm). The cells express proteins that form as major cell component axially oriented, partial a-helical interme- diate filaments (IF, diameter about 10 nm) embedded in an amorphous matrix of IF-associated proteins (IFAP). The IFAPs are highly cross-linked through cystine, which forms mainly inter-chain disulphide bonds. The cells that were originally at the pe- riphery of the hair root form thin, flat cuticle cells that each have a layered structure of amorphous proteins. These cells form a protective layer of overlapping cells around the cortex. In the context of mechanical or thermal investigations this complex structure can be simplified as a two-phase, filament/matrix composite, as originally proposed by Feughel- man (5 ). In this model the partly crystalline, a-helical intermediate filaments (IF) can be identified as the filamentous phase. The matrix in consequence contains as major component the IF-associated proteins (IFAP) (6) and also summarily the rest of the morphological components, such as cuticle, cell membrane complex, etc. ( 4). DSC of keratins in water was found (7) to be especially suited to analyze various aspects of the thermal stability of these main morphological components, since the helical segments in the IFs undergo denaturation between l 10°C and 160°C in water, depending on the type of keratin, and well removed from the temperature range of pyrolysis (8,9). Various aspects of this transition of fundamental as well as of practical relevance are reviewed, specifically considering the current theory on the interaction of filaments and matrix during denaturation and its relation to the effects of cosmetic, chemical treat- ments, namely, oxidation (bleaching) and reduction (perm-waving).

2006 TRI/PRINCETON CONFERENCE 313 DSC OF DIFFERENT a-KERA TINS IN WATER EXPERIMENT AL All DSC-experiments were performed on a power-compensated instrument (DSC-7, Perkin Elmer), using pressure-resistant (25 bar) stainless steel, large-volume capsules (Perkin Elmer). Prior to the measurement samples were stored under constant, ambient room conditions (approx. 22°C, 55%RH) to ensure invariant water contents. Under these conditions a given material (5-7 mg) was weighed into the sample container, 50 µL of water was added and the container was sealed. An empty container without the O-ring rubber seal was used as reference. Temperature range and heating rate were generally 70-180°C and 5°C/min, respectively. Analyses were conducted between 9- and 18-fold, depending on the complexity of the DSC-curve. Amino acid analyses were performed by the ion-exchange method on an LC6000 Amino Acid Analyzer (Biotronic). The amino acid referred to in what follows is the double amino acid cystine, containing a disulfide crosslink. Its contents in the various keratins is reported by referring to the mono amino acid, and specifically to the molar fraction of cysteine residues (Cys-R, [mol%}). The expectation value for the 95% confidence limits of the Cys-R values is ±5%. RESULTS Figure 2 shows typical DSC curves for mohair (hair of the Angora goat) and Merino (sheep) wool in water. As further materials rhinoceros horn (RH), porcupine quill (PQ), finger nail (FN), echidna quill (EQ), human hair (HH), and afro hair (NH) were investigated (7). Usually keratins show a single-peak structure for the denaturation, though double peaks were frequently observed for wool, as was to be expected from the literature (8,10). This tendency, though considerably less pronounced, was also observed for finger nails, horse hair, and rhinoceros horn. The statistical analysis of the data for the denaturation enthalpies for the various keratins supports the conclusion that for all materials the Mohair 1.6 Wool 2.0 (MO) To• 142 5°( (WOI 1.2 To2 = 142 5°[ :i 16 i ! AH• 19.8 J/g � ) ) � 12 � 0.8 0 ·� 0 :ha QI .. ::i:: 0.4 0.4 90 100 110 120 130 140 150 100 110 120 130 140 150 160 T@mperature I •c I Temperature(•[) Figure 2. DSC traces for mohair (MO) and merino wool (WO) under standard conditions (Adapted from Ref. 7). The relevant parameters are graphically defined.