Supercontraction of Iodinated Wools

Abstract

Haly and Feughelman¹ have shown that iodination of wool, when using ethyl alcohol as the solvent, causes a large reduction in the rate of second-stage supercontraction. They express the opinion that “it does seem possible that iodination of tyrosine (or other) residues could, through steric hindrance, make movement of groups, and therefore disruption, more difficult”. Leveau et al.² attributed the lowering of the urea–bisulphite solubility of the iodinated wools to a strengthening of the hydrogen bonds of the phenolic hydroxyl groups by the substitution of the halogens on the tyrosine molecules. In a recent publication the explanation was offered by me³ that the decrease in supercontraction of the second stage by iodination was due to the steric hindrance caused by the two bulky iodine atoms substituted in the 3,5 positions on the tyrosine molecule, whereby the partially hydrated lithium ion, with its comparatively large volume, is prevented from reaching the hydrogen bonds formed by the hydroxyl group. These hydrogen bonds will therefore remain intact during the supercontraction reactions and the subsequent restriction of the movement of the chains will reduce the rate of disulphide interchange taking place, thus reducing the rate of second-stage supercontraction.