Crosslinking structure of keratin. I. Determination of the number of crosslinks in hair and wool keratins from mechanical properties of the swollen fiber

Abstract

SynopsisHair and wool keratin fibers which had been treated with an 11 M LiBr solution containing N-ethyl maleimide showed typical rubberlike elasticity in a solution composed of equal volumes of 8 M LiBr and diethylene glycol mono-n-butyl ether. Stress-strain curves and equilibrium force-temperature relations were measured for swollen hair and wool fibers. The non-Gaussian effects on deformation and the energy component in retractive forces were analyzed. On the basis of rubber elasticity theory, a method for estimation of the number of mechanically effective crosslinks in keratin fibers was proposed. A linear relationship between the crosslink density and the disulfide content was obtained from the data for a variety of keratin fibers (i.e., two different human hairs, horse hair, and 17 different wools). From the results of thermodynamical and non-Gaussian treatments for swollen keratin, it was suggested that the swollen fiber consists of a two-phase structure: a mechanically stable phase of higher crosslinked domains and rubbery phase with lower crosslink density. It was further found that considerable amounts of nondisulfide covalent crosslinks are present in wool and hair keratins.

Composite Materials from Natural Resources: Recent Trends and Future Potentials

“…The quantity and positioning of metal atoms (sodium, calcium, manganese, magnesium, iron (II), iron (III) and aluminium) differentiate amphiboles from one another (Virta, 2002). The serpentine group of minerals have the formula Mg 3 Si 2 O 5 (OH) 4 . Serpentine structure is a bending sheet.…”

Disulfide Cross-Linked Network Structure of Intermediate Filament and Matrix in Hair and Wool Cortices

“…The reduced and NEM-treated fibers thus obtained were thoroughly washed with water and then air-dried. Blocking the free SH groups is necessary at this stage to stabilize the network structure by inhibiting the SH/SS interchange reactions during swelling and extension [12,15].…”

“…The diameter of the swollen fibers and any significant deviation in ellipticity was measured under a microscope at approximately 20 places randomly selected over the length of the fiber (20 mm). This procedure was performed at room temperature because the diameter of the swollen fibers in the mixed solution was approximately constant irrespective of temperature [12]. The average cross-sectional area of the swollen fibers was calculated from the average value of the swollen fiber diameter Ds.…”

“…This method is based on the application of a nonGaussian elastic equation of state to the stress-strain curve of a swollen fiber. The swollen fiber samples were prepared by treating with an 11 M LiBr aqueous solution containing 10 −2 M N -ethylmaleimide (NEM) to block the free SH groups in the fibers and stabilize the disulfide crosslinked network even at the extension state of the fiber [12]. The swollen samples thus obtained exhibit typical rubber elasticity in a 55 : 45 (v/v) mixed solution of 8 M aqueous LiBr solution and pure diethylene glycol monon-butyl ether (BC).…”

Chemical Reactions Occurring in Curing Treatment for Permanent Hair Straightening Using Thioglycolic and Dithioglycolic Acids

“…(3), k'1 is much smaller than the value of k1, since the reactions proceeding by the collisions between the side chain groups of cysteine and mixed disulfide residues depend largely on the ease of the molecular motion of the protein chains. The chain mobility will be affected by either the water content, which depends on Tg [9] or the cross-link density of hair [10]. On the contrary, the values of k2 and k'2 are considered to be probably a similar magnitude, because of the reactions between the protein side chain groups and low molecular weight species.…”