The Reaction of Thiol and Disulphide Groups with Mercuric Chloride and Methylmercuric Iodide. II. Fibrous Keratins

Abstract

The reaction of HgCl2 with wool has been studied polarographically over the pH range 1 to 9 under various conditions. At pH 1 to 6 the salt appears to be bound in the un-ionized form probably at amide and peptide group sites. The binding is greatly suppressed in the presence of complexing anions such as Cl- and S2O3=. SO3= also has this complexing effect but in addition produces new -SH binding sites by reversibly splitting -SS- bonds. This splitting proceeds to completion at pH 7 to 10 in the presence of an excess of mercurial, HgCl2 requiring several days and MeHgI several hours. The reaction of keratins with SO3= and mercurials may be followed polarographically and has provided a convenient method of preparing keratins with zero or decreased -SS- bond contents. The reaction rate increases in the presence of 8~ urea and then forms the basis for new analytical methods of measuring the -8s- content of intact keratins. The keratin (7.5 mg or more) is reacted with Na2SO3 in 8M urea (5 ml) for at least 24 hr (with excess HgCl2) or 2 hr (with excess MeHgI) at 20 �C. Single current readings at -1 0 and -0.8 V (v. S.C.E.) respectively at the dropping mercury electrode indicate the residual mercurial and hence by difference the (-SS- plus -SH) content. The -SH content of intact keratins is estimated by reacting say 25 mg with excess MeHgI at pH 7 for at least 4 hr at 20 �C in the absence of SO3=. This mercurial reacts much more rapidly with the -SH sites in keratin than do other mercurials.