Thiol–Disulphide Interchange Reactions in the Setting of Single Wool Fibres

Wool fibres pretreated with fluoro–2, 4–dinitrobenzene, N –ethylmaleimide, peracetic acid, or nitrous acid set less readily than untreated fibres when stretched for 1 h at 100C in water or acetate buffer at pH 5. Incorporation of sodium bisulphite in the setting solution at concentrations greater than 0005 M eliminated these differences, except for fibres that had been treated with nitrous acid. The set retained by both untreated and modified fibres was increased by the addition of bisulphite to the setting solution. The presence of bisulphite in the solution used for releasing (1 h at 100C) the fibres set in the absence of bisulphite decreased the set retained, but had no effect if the fibres were set in the presence of bisulphite. Treatment of the unmodified wool fibres with solutions of bromine, peracetic acid, or methyl mercuric iodide before and during release at 100C greatly increased the set retained in an acetate buffer. Similar aftertreatments of the modified fibres caused a relatively small increase in set. Setting in buffer solutions at pH 9, when followed by release in the same solution, was only slightly decreased in extent by pretreatment of the fibres with N –ethylmaleimide or peracetic acid, whereas setting was prevented by pretreatment with fluoro–2, 4–dinitrobenzene or nitrous acid. The presence of sulphite in the solutions used for setting or releasing the fibres did not affect the result. It is suggested that rearrangement of disulphide bonds by a thiol–disulphide interchange reaction is chiefly responsible for setting of wool fibres at pH 5 in the absence of a reducing agent, but that a second type of interaction, possibly the formation of β–keratin, assumes great importance when the fibres are set in bisulphite solution. Setting at pH 9 probably takes place by the formation of new covalent linkages. Lysine side–chain groups may participate in the formation of these linkages.