Supercontraction of Wool in Aqueous LiBr; In hibition by Free Br2 and its Relation to Sulfhydryl- Disulfide Interchange

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Abstract
Wool treated with N-ethylmaleimicle (NEMI) to decrease the sulfhydryl content by 70% supercontracts much more slowly than untreated wool at 98.5° C. in 6 M LiBr at pH 6, whereas in 4 M LiBr/l N HCl the contraction rates of treated and untreated fibers are equal. Pretreatment of wool with dilute bisulfite solutions accelerates supercontrac tion much more in 4 M LiBr at pH 8 than in 4 M LiBr/1 N HCl. It is concluded that interchange reactions between sulfhydryl and disulfide groups facilitates supercontraction. The presence of Br2 in the solutions of LiBr used for supercontracting wool fibers causes different effects according to the pH of the LiBr solutions. In 1 N HCl the 118 supercontraction is accelerated at all levels of contraction; at pH 4 to 5 the initial stage of supercontraction is accelerated and the second stage of contraction retarded; at pH > 6 supercontraction is retarded at all levels of contraction. Wool fibers super- contract in solutions of Br2 in dilute HCl even at low temperatures. Evidence is presented that Br2 reacts with sulfhydryl groups of wool during super contraction in solutions of LiBr and that it acts at a site in the wool fibers affected by pretreatment with NEMI. Wool fibers which have been reduced with thioglycollate and either cross-linked with ethylene dibromide or reacted with methyl iodide show no change in contraction kinetics when Br2 is added to the LiBr solutions. It is concluded that Br2 inhibits supercontraction in solutions of LiBr by reacting with sulfhydryl groups and so interfering with interchange reactions between sulfhydryl and disulfide groups in the wool.