Fluorescent Probe Study of AOT Vesicle Membranes and Their Alteration upon Addition of Aniline or the Aniline Dimer p-Aminodiphenylamine (PADPA)

Artificial vesicles formed from sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in aqueous solution are used successfully as additives for enzymatic oligomerizations or polymerizations of aniline or the aniline dimer p-aminodiphenylamine (PADPA) under slightly acidic conditions (e.g., pH 4.3 with horseradish peroxidase and hydrogen peroxide as oxidants). In these systems, the reactions occur membrane surface-confined. Therefore, (i) the physicochemical properties of the vesicle membrane and (ii) the interaction of aniline or PADPA with the AOT membrane play crucial roles in the progress and final outcome of the reactions. For this reason, the properties of AOT vesicles with and without added aniline or PADPA were investigated by using two fluorescent membrane probes: 1,6-diphenyl-1,3,5-hexatriene (DPH) and 6-lauroyl-2-dimethylaminonaphthalene (Laurdan). DPH and Laurdan were used as “sensors” of the membrane fluidity, surface polarity, and membrane phase state. Moreover, the effect of hexanol, alone or in co...