AOT vesicles as templates for the horseradish peroxidase-triggered polymerization of aniline

Abstract

In dilute aqueous solution at pH = 4.3 in the presence of 0.1 M sodium dihydrogen phosphate, AOT (bis-(2-ethylhexyl)sulfosuccinate) was found to form vesicles. The average diameter of the vesicles was adjusted to about 70 nm by polycarbonate membrane extrusion. The vesicles were applied as chemical structure-controlling templates for the horseradish peroxidase/H₂O₂-triggered polymerization of aniline to yield the green emeraldine salt form of polyaniline. The enzyme-containing vesicular reaction system was optimized with respect to obtaining a reaction product with high absorbance in the NIR region of the spectrum which is known to be a characteristic property of the conductive emeraldine salt form of polyaniline. The reaction system was analyzed by cryo transmission electron microscopy, ¹H NMR, UV/VIS/NIR, circular dichroism and fluorescence measurements. The peroxidase was found to be bound to the vesicles leading to an initiation of the reaction preferentially on the vesicles surface and not in the bulk aqueous solution. Before the reaction was started by H₂O₂ addition, the anilinium cations were found to only weakly interact with the surface of the vesicles. After polymerization, a stable suspension containing vesicles which were coated with polyaniline was obtained. The reaction product was isolated and analyzed by FTIR measurements. With respect to the vesicle system used previously, SDBS/decanoic acid (1 : 1) (Z. Guo, H. Rüegger, R. Kissner, T. Ishikawa, M. Willeke and P. Walde, Langmuir, 2009, 25, 11390–11405), the AOT system has several advantages for further explorations of this type of in situ formation of conductive vesicle-based polymer capsules.