Dynamics of the Cleavage of Ellman's Reagent in Surfactant Vesicles

摘要

The cleavage of Ellman's reagent 5,5'-dithiobis (2-nitrobenzoic acid) (1) to 2-nitro-5-thiolatobenzoate dianion, 5, by dithionite, sulfite, and thiophenoxide ions and by zwitterion 4, was studied at pH 8 in aqueous solution and in aqueous solutions of hexadecyltrimethylammonium ion micelles or dihexadecyldimethyl-ammonium ion vesicles, 2. Excepting reagent 4, strong micellar and vesicular catalysis of the cleavage reactions was observed. When Ellman's reagent was added to the empty vesicles, followed by the addition of excess cleavage reagent, separate fast and slow reactions were observed. The relative contribution of each process varied with the aging time between the addition of the Ellman's reagent and the cleavage reagent. The results were quantitatively analyzed in terms of reversible substrate distribution between exovesicular (surface) and endovesicular (subsurface) sites. With dithionite and sulfite reagents, rapid cleavage of exovesicular substrate was followed by slow cleavage of endovesicular substrate which had permeated back to the vesicular surface to react with exovesicular dithionite or sulfite. With thiophenoxide, very rapid exovesicular cleavage was followed by slower enodvesicular cleavage of substrate by rapidly permeating thiophenoxide (thiophenol). Reagent 4 was not bound by vesicular 2, and cleavage reactions occurred only exovesicularly or off the vesicle.