A Method for Determining the Penetration of Reducing Agents into Wool Using Fluorescence Microscopy

Abstract

The fluorogenic reagent 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (ABD- F) has been used to label thiol groups in partially reduced wool fibers. In fibers in which 10% of the disulfide bonds were reduced with either dithiothreitol or tributyl phosphine, up to 66% of the thiol groups were specifically labeled in 2 hours at pH 8. The extent of the labeling was determined by analysis of ABD-labeled wool for cysteine- S-ABD. Specificity of labeling was confirmed by comparing the amino acid analyses of untreated wool with reduced wool before and after treatment with ABD-F. Fibers were reduced with a variety of reducing agents, and sections were examined by fluo rescence microscopy. From the distribution of the fluorescence. reduction was largely confined to the outer regions of the fiber for 10% reduction at pH 9 (40°C, 30 minutes) with dithiothreitol, tributylphosphine, and tetrakis(hydroxymethyl)-phosphonium chloride. With sodium thioglycollate, however, there was more even penetration of the fibers under the same conditions. The application of this method is discussed for assessing the effect of reducing agents used in conjunction with polymer shrink-resist treatments.