A Kinetic Study of the Supercontraction of Wool Fibers in Solutions of Salts, Acids, and Alkalies

Abstract

Wool fibers contract in hot solutions of acids or alkalies, the initial rate of contraction increasing with increasing concentration of the acid or alkali. At the higher concentrations contraction is followed by elongation of the fibers to lengths which may exceed the original length. The maximum contraction obtained decreases with increasing concentration of acid or alkali used. Comparison of the rates of contraction of wool fibers in solutions of different salts in 1 or 4 N HCl shows that cations and anions fall in the following order of decreasing contraction rate: Li + > Na + > K + and I -> Br -> Cl -.Kinetic curves for the contraction of wool fibers in 1 N HCl containing salts show welldefined two-stage contraction. With 4 M LiBr or NaI this appears as a shelf in the curve at 25-30% contraction, and with many fibers the final level of contraction exceeds 70%. With 5 or 6 M LiI or 6 M NaI the fibers contract by about 25%, elongate to a length which may approach the original, and then again contract; in such solutions a considerable proportion of the wool protein is dissolved, leaving a sulfur-rich residue. Two-stage contraction kinetics have been observed only when using solutions with pH values in the lower range. As the pH is increased the rate of contraction also increases, particularly at pH values greater than about 8. The two-stage contraction kinetics have been interpreted in terms of the contraction at different rates of two structures in the wool fiber.

The Stress—Strain Characteristics of Animal Fibers After Reduction and Alkylation

“…Nlany models have been proposed [5,10,13,14,21,23,26,40,41,43,44,47 to account for the properties of the wool fiber and frequently these models have heen based on histological or subcellular structures known to be present in the fibers. C.'hieHy, their purpose has been to provide an explanation for the presence of Hookean, yield, and postyield regions in the load-extension curves for wet fibers [43] ] and for the decrease in intensity of the a-type x-ray diffraction pattern and appearance of ã 3-pattern as the fibers are stretched [ 5 ] .…”

“…9a) and a noncontractile matrix in which they are embedded. The extent of supercontraction is limited at the first stage by disulfide [ 15,10] and acid-labile covaleni bonds and -at total contraction hy acid-lalile bonds only [ 11,13,14]. These covalent cross linkages are thought to link the helices to each other or to matrix molecules (Fig.…”

Covalent acid‐labile crosslinkages in wool

“…Disulfide and sulfhydryl contents of the wool samples were determined by using the methods of Leach.5 The extent of supercontraction of single wool fibers as a function of time was measured as described previously. 1 The differences in rate of the first and second stages of supercontraction are greater when supercontraction occurs in highly concentrated solutions of LiBr a t low temperatures. The first stage of supercontraction is therefore defined as the extent of the initial rapid contraction in 81lf LiBr at 2OOC.…”

“…It is significant that the only other treatment reported to give supercontraction of comparable extent2 involved oxidation of the wool with C102 followed by boiling in dilute acid solutions; the wool contracted by 62Y0. Three general hypotheses can be considered to account for the greater extent of supercontraction which is observed when HC1 is incorporated in the LiBr solutions. (1) The presence of acid cauc'es polypeptide chains containing a given number of residues to assume a shorter end-to-end length than they do in LiBr solutions containing no acid.…”

The Effects of Disaggregating Agents on the Stress-Strain Relationship for Wool Fibers

“…These fringes could constitute a covalent link between matrix and microfibril in the manner of Model A, or they may act as anchoring points for the beaded chains in Model B. They also&dquo; provide an explanation for the effects of acids on the extent of supercontraction in solutions of LiBr [12,15]. A structure described by Model .4 would be expected to show major changes in stress-strain behavior if stretching were performed in reagents capable of destroying a-helices or side-chain interactions between the high-sulfur and low-sulfur proteins.…”