| Popis: |
Conversion of the disulphide bonds of wool to S-methyl groups accelerates supercontraction in solutions of LiBr, but has no appreciable effect on the level of the equilibrium contraction. Evidence is presented that the rate of supercontraction is partly determined by interchange reactions between sulphydryl and disulphide groups and that inhibition of supercontraction when free bromine is present in the solutions of LiBr is due to oxidation of the sulphydryl groups. It is concluded that the contractile structures of the fibre are not cross-linked by disulphide bonds, but are embedded in material containing inter- and intra-molecular disulphide bonds (the matrix), the rate of plastic deformation of the latter structure being affected by sulphydryl interchange with disulphide bonds. Nitration, iodination, mild oxidative treatments, and treatments with acids or alkalis accelerate the first stage of supercontraction in 6M LiBr at pH 6, but retard the second stage. This retardation is not observed with contrac... |
