The Formation of Various Cross Linkages in Wool and Their Effect on the Supercontraction Properties of the Fibers

Abstract

Various solvent systems have been investigated for obtaining maximum alkylation of cysteine residues in reduced wool to dimethylene-S,S'-dicysteine residue. These and related amino acid residues were determined in wool hydrolyzates by means of an automatic amino acid analyzer. Cystine residues in wool were converted to both lanthionine and lysinoalanine residues by treating the wool with potassium carbonate solutions, whereas treatment with potassium cyanide solutions produced lanthionine resi dues without forming significant amounts of lysinoalanine residues in the wool. On a molar basis, lanthionine and dimethylene-S,S'-dicysteine residues had similar restrictive effects on the extent of total supercontraction in 8M LiBr, whereas one lysinoalanine residue was equivalent to about five lanthionine residues in its effect on the extent of supercontraction. The conversion of cystine to lanthionine or dimethylene-S-S'-dicysteine residues retarded the first stage of supercontraction in 4 M LiBr at pH 8.3, whereas in 6 M LiBr, only the second stage of supercontraction was retarded. Similarly, the addition of free bromine to the lithium bromide solutions retarded the first stage of supercontraction of unmodified wool fibers in 4 M LiBr but did not affect the initial rate of contraction in 6 M LiBr. It is suggested that the matrix protein molecules are unfolded in 6M LiBr, thereby obviating the need for thiol-disulfide interchange reactions in the deformation of the matrix which must accompany the contraction of the micro- fibrils. The presence of lanthionine or dimethylene-S,S'-dicysteine residues in the wool did not decrease the rate or extent of supercontraction in 4 M LiBr-N HCl at 98.5°C.