Determination of the Configuration of Silk Fibroin Dissolved in Aqueous Solutions of Lithium Bromide

Abstract

FOLLOWING the discovery, made earlier in this laboratory1, that water-soluble silk fibroin is predominantly α-folded, it was natural to speculate upon the molecular configuration of this protein in the aqueous solutions of lithium bromide from which it can be isolated in the soluble form and in which inter-chain hydrogen bonds clearly do not persist. Recently, the difficulties of making the necessary measurements of the absorption of inter-red radiation were lessened significantly by the preparation of remarkably clear, stable solutions of high protein content (25–50 gm. of fibroin per 100 ml.). In agreement with observations reported by von Weimarn2 and others3, it was found that these ‘silk syrups’ could readily be made at ordinary temperatures either by dispersing fibroin in suitable solutions of lithium bromide or by a process of ‘salting-out’ (which was indistinguishable, qualitatively, from the separation of phases observable in many simpler polymer-penetrant systems).