Reaction of Silk Fibroin with Diazomethane

Abstract

The reactive groups in silk are intimately related to the absorp tion of moisture, acids, alkalies, or dyes, and to physical properties such as extensibility and tensile strength. A large proportion of these gorups are present in silk fibroin in the form of hydroxyl groups of the amino acid tyrosine. The latter groups are of special interest, partly because of their preponderance, but principally be cause there are divergent views as to whether they are free in the untreated fibres. As an approach to the problem it appeared ad visable to attempt to inactivate these groups by suitable chemical treatment and then to study the properties of the modified protein. Several methods have been tried for this purpose by different in vestigators but they were found to be too drastic, and generally resulted in severe physical deterioration of the fibre. In the present investigation, the silk was treated with an ethereal solution of the methylating agent diazomethane. The treatment resulted in a rapid decrease in tyrosine content of the silk with no appreciable decrease in tensile strength of the fibres, and the results led to the conclusion that the hydroxyl groups of tyrosine are free in the untreated fibres. The total methoxyl con tent after treatment of the fibre for 25 hours or longer was greater than could be accounted for by assuming that only phenolic hy droxyl groups had reacted. The "extra" methoxyl was not on either the primary amino or the serine hydroxyl groups, but appears to have resulted from the reaction of diazomethane with groups, tentatively assumed to be carboxyl, to form the methyl esters.