Reaction of Wool With Potassium Cyanide

Sakamoto

Naito

et al. 1989

Self Cite

SynopsisThe crosslinking structure of keratin fibers has been investigated. The reaction of wool with aqueous KCN was studied by means of chemical and physical methods. Quantitative conversion of disulfide (SS) groups of the cystine (Cys) residues into stable thioether (S) linkages was confirmed. In terms of mechanically effective and noneffective crosslinkages, the amounts of intermolecular and intramolecular crosslink in the KCN-treated wools were determined from the analysis of the corresponding amino acids and mechanical experiment in which the shear modulus of swollen, rubberlike samples is determined from the relation between equilibrium stress and strain for simple extension of the fiber in a diluent. A modified elastic equation of state was used for the calculation of the number of intermolecular crosslink. The front factor in the equation used was determined by combining the results obtained from purely chemical kinetics and the values of shear modulus of the swollen wools. The ratio of the number of intermolecular and intramolecular SS crosslinkages in the Lincoln wool was found to be 64 : 36. The reactivity of the former is much higher than that of the latter, and these two types of SS crosslink form substantially the same type of S crosslink. The fraction of the Cys residues accessible to cyanide ions depends mainly on the reaction temperature. INTRODUCTIONThe reaction of keratins with aqueous potassium cyanide has been extensively studied.'-4 It has been postulated that the reaction proceeds via substitution mechanism of the type of reaction S, 2, in which cystine residues convert to lanthionine residues crosslinked by thioether linkage, and this causes negligible production of lysinoalanine resid~es.'-~.~ I t was decided, therefore, to investigate the crosslinking structure of keratins with particular emphasis on the use of potassium cyanide which reacts selectively with disulfide bonds in keratins and forms thioether crosslinkages.I t has been found that the rubbery conditions can be successfully achieved for swollen wools in a diluent system composed of equal volumes of 8M lithium bromide and diethylene glycol mono-n-butyl ether.6-8 From extension modulus measured in the diluent, crosslink density could be determined by using rubber elasticity theory for swollen network. Kajiyama et al.4 investigated crosslinking structure of wools treated with potassium cyanide, and the number of crosslinks was evaluated by measuring the degree of swelling in formic acid according to the method of Caldwell and Milligan.g They reported that a part of intermolecular disulfide crosslinks converts to intramolecular monosulfide crosslinks.Owing to the .complexity of keratin structure and the nonunifonnity throughout fiber structure, it is difficult to define the terms "intermolecular" and "intramolecular" crosslinkages in ~0 0 1 .~We can now differentiate only between " mechanically effective" and " noneffective" crosslinkages.This article deals with the application of the elastic equation of state derived from rubber...

Section: Introductionmentioning

confidence: 99%

Crosslinking structure of keratin. II. Intermolecular and intramolecular crosslinks in potassium‐cyanide‐treated wool fibers

Sakamoto

Naito

et al. 1989

Self Cite

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

Sasaki

Naito

et al. 1989

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.

Cross‐linking structure of keratin. IV. The number of cross‐linkages in low‐sulfur components and the volume fraction of high‐sulfur domains in various α‐keratin fibers

Hirata

Nishimura

et al. 1993

SYNOPSISVarious a-keratin fibers that had been treated with an 11 M LiBr solution containing Nethylmaleimide showed typical rubberlike elasticity in a solution composed of equal volumes of 8M LiBr and diethylene glycol mono-n-butyl ether. Stress-strain relations of the swollen fibers were treated with a two-phase model: a mechanically stable phase of higher crosslinked domains and a rubber phase with lower cross-link density. Stress-strain curves for a variety of keratins (three different human hairs, six different wools, mohair, cashmere, llama, alpaca, angora, and opossum) were analyzed by applying non-Gaussian chain statistics to the swollen keratin network, including microdomains, which act as reinforcing filler particles in rubber. The phase structures of unswollen domains and swollen rubber were considered to originate from different structural components characteristic of a-keratin, namely, the high-sulfur matrix and the low-sulfur microfibrils being randomized by swelling. It has been suggested that ( 1 ) the modulus of swollen fibers increases with increase of the content of disulfide (SS) in keratins, ( 2 ) the volume fraction of high-sulfur domains increases with increase of SS content, and ( 3 ) the number of intermolecular cross-links in the rubber region of low-sulfur proteins is virtually the same among keratins and reaches about 65-75% of the SS linkages in the corresponding proteins. Some discussion has been made on the SS bonding in situ, namely, SS linkages between the low-sulfur proteins, between the low-sulfur and the high-sulfur proteins, and between the high-sulfur proteins in keratins. 0