Action of Nucleophilic Reagents on Hair Keratin

Abstract

We studied the degradation of the cystine bonds in hair keratin caused by nucleophilic reagents. The effects of alkylamines, amines containing aromatic rings, amino acids and amine-thiol combinations were investigated. The reactions were conducted in aqueous media at a high alkalinity (pH 13) and moderate temperature (40 °C).

The study ascertained that the alkaline degradation of hair follows a mechanism similar to that reported for wool, i.e., one leading to the formation of dehydroalanine residues via β-elimination. The dehydroalanine moieties undergo additional reactions with amino and thiol groups in the fiber or alkaline medium to yield lysinoalanine, lanthionine and β-(N-alkylamino)alanines.

Although the major pathways of the nucleophilic degradation processes in hair are similar to those reported for wool, the relative ratios of reaction products differ. Under our reaction conditions the amines in the treatment bath competed less effectively for dehydroalanine sites; the result was less amine adduct and more lanthionine and lysinoalanine residues.