Keratins reaction with ions

Disulfide bonds present in the keratin of hair are potential binding sites for many nucleophilic molecules. Tolgyesi and Fang investigated the structural changes which occur in keratin as a result of alkaline treatments of hair. They reported that hydroxide ions initiated a p-ehmination reaction, resulting in cleavage of the disulfide bonds of cystine to produce dehydroalanine intermediates. Cysteine and lysine may react with dehydroalanine to form new cross links in keratin. Nucleophilic amines such as ethylamine and n-pentylamine may also react with dehydroalanine to form... 

All cleavages of simple disulfides by mercaptans that have been studied kinetically are bimolecular ionic reactions of the SN 2 type, involving direct displacement by mercaptide ion on disulfide [20]. Because the active species in this disulfide scission process is the mercaptide ion [21] rather than the unionized mercaptan, pH is a critical factor. As a consequence, pH can determine the rate-controlling step in the reductive cleavage of cystinyl residues in keratin fibers by mercaptans. For example, in the reaction of wool fiber with dithiothreitol, Weigmann [22] has shown that the ratecontrolling step at pH 7.0 and above is diffusion of the reducing species into... 

Salts of hydrogen cyanide have also been found to be capable of nucleophilic cleavage of the disulfide bond in keratin fibers [72]. In addition, nearly quantitative conversion of cystinyl residues to lanthionyl residues can be achieved in this reaction [73]. The most plausible mechanism is given in Equations G and H [65]. This mechanism consists of two nucleophilic displacement reactions the first by cyanide on sulfur and the second by mercaptide ion on carbon. The following mechanism is consistent with the observed formation of thioether from the reaction of N-(mercaptomethyl)polyhexamethyleneadipamide disulfide (XV) with cyanide, but not with alkali [65]. 

The salt bridges that hold hair protein (keratin) strands together rely on —NH3+ groups. Write an equation for the reaction of this group with OH ions. 

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