Chiral electrodes of magneto- electropolymerized polyaniline films

Abstract

Introduction. Magnetic fields induce chiral structures through the Lorentz force acting on currents in electrolytic solutions. Two-dimensional spiral structures were found in the electrodeposition of metals [1, 2] and conducting polymers [3], and three-dimensional helical structures in silicate membrane growth [4], though both structures were on the millimeter scale. If chiral structures on the molecular scale are induced on the surface of the films formed under magnetic fields, such film surfaces would serve as enantioselective catalysts. Enantioselective recognition of chiral molecules is one of the most important processes in biochemistry; in most cases, it is realized by enzymes. Chiral surfaces of heterogeneous catalysts have the enantioselective properties, and thus considerable effort has been devoted to preparing chiral surfaces by adsorbing chiral molecules [5, 6] or slicing single crystals [7]. Chirality was also introduced into conducting polymers by doping chiral molecules [8, 9, 10], and chiral polyaniline films exhibited enantioselective recognition for several amino acids [9]. We attempted to prepare polyaniline films with a chiral surface by magnetoelectropolymerization (MEP), which is electropolymerization under magnetic fields [11]. Polyaniline is one of the most promising materials for electronic devices, and its films are easily prepared by the oxidative electropolymerization of aniline in acidic aqueous solutions. Aniline monomers are stoichiometrically oxidized in front of the polymer chain, and then electrons are transported from the front to the substrate electrode within the chain. Under magnetic fields, the Lorentz force is expected to act on currents within the polymer chain and induce helical growth. Thus, it is interesting to examine whether the MEP films exhibit chiral electrode properties. Here, we show the voltammetric responses of the MEP polyaniline films to vitamin C (L-ascorbic acid) and its enantiomer, erythorbic acid (D-ascorbic acid).