The reactivity of the cystine linkages in wool towards reducing agents

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Abstract
The reactivity was investigated before and after modification of the wool in various ways. Reduction and alkylation of part of the cystine, the (A + B) fraction, allows the remainder, the (C + D) fraction, to react with sodium bisulfite and thioglycollic acid under conditions where it is normally inert. The reaction products are the same as normally obtained with fraction (A + B). In contrast with this, reduction followed by cross-linking of the thiol groups from fraction (A + B) through a methylene bridge does not allow fraction (C + D) to show this induced reactivity. Acetylation of polar side chains in wool leads to a general reduction in the reactivity of cystine. Treatment of wool with phenyl isocyanate leads to blocking of all the polar side chains without affecting the cystine. Such treatment almost completely inhibits subsequent reactivity of the cystine linkages. The degree of reactivity of cystine linkages is largely governed by their accessibility to a reagent, close proximity of bulky side chains reducing reactivity through steric hindrance. Other factors such as varying structural arrangement may be responsible for the variation in the nature of the products resulting from a particular reaction.