58—SOME OBSERVATIONS ON THE OXIDATIVE DEGRADATION OF THE PROTEIN CHAINS OF WOOL

Abstract

A useful index of the resistance of the protein chains of wool to oxidative degradation is described. The method involves simply the measurement of time to break specimen wool fibres, yarn, or fabric exposed to an oxidizing solution, in this case, of sodium hypochlorite. The time to break is shortened when the fibres are pretreated with fine particles of carbon or clay, providing the fibres are swelled sufficiently when the particles are applied. Blocking of amino groups with isocyanates increases the time to break. The presence of the vulcanizing agent, tetramethyl thiuram disulphide, in wool affords some measure of protection against radiation damage by electron bombardment, as indicated by subsequent time-to-break tests in hypochlorite. The oxidative removal of hydrogen atoms from one of the –NH–CHR– groups of diketopiperazine, found to occur with hypobromite by Goldschmidt^1–5, is suggested as an initial step in the degradation of diketopiperazine by ultraviolet irradiation. Similar removal of hydrogen atoms from –NH–CHR– groups probably occurs in wools irradiated by ultraviolet and electron radiation, or in wools that have been heated or irradiated in the presence of the thiuram agent. Model experiments with peptides and amino acids treated with the thiuram agent suggest that a dehydrothiohydantoin ring is formed at the amino end of a peptide chain, similar to the formation of a dehydrohydantoin ring found by Goldschmidt to occur on N-terminal amino acids in peptides by treatment with HOBr. In both cases, hydrogen atoms are removed from –NH–CHR– groups. The replacement of the hydrogen atom on the carbon by a methyl group, as observed by comparing polydimethyl glycine (polyaminoisobutyric acid) and polyglycine, increases resistance to yellowing by ultraviolet light and by hypochlorite.