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

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.