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Chlorinating Silk with Methanesulfonyl Chloride in Dimethylformamide and Treating Chlorinated Silk with Mercaptans

Silk fibers were chlorinated with methanesulfonyl chloride in dimethylformamide under mild conditions. The chlorination occurred mainly at serine residues, and β-chloroalanine was found in the hydrolyzates of the chlorinated silk samples using gas chromatography-mass spectrometry, and was quantified using high performance liquid chromatography. About 30% of serine residues could be converted into β-chloroalanine residues. Chlorinated silk fibers reacted under alkaline conditions with mercaptans containing other functional groups, that is, thioglycollic acid, 3-mercaptopropionic acid, β-mercaptoethylamine, and cysteine, which yielded S-carboxymethyl, S-2-carboxyethyl, S-2-aminoethyl, and S-2-amino-2-carboxyethylcysteine residues, respectively. The amino group contents of the samples treated with β-mercaptoethylamine were higher than ten times that of the original silk. The amino group-enriched silk fibers were treated with methyl gluconates, yielding silk fibers containing pendant oligosaccharide groups. No interaction was observed between these modified silk fibers and a lectin, concanavalin A.