Takeo Ohsaka

Adsorption behavior of viologen derivatives on hanging mercury electrode surfaces

Abstract The adsorption behavior of N , N ′-dialkyl-4,4′-bipyridinium dications (viologens) on hanging mercury electrode surfaces was investigated as a function of the alkyl chain length (C n V 2+ , n = 1–8). Monolayer adsorbed viologens give a pair of very narrow spike-like peaks on cyclic voltammograms, which can be attributed to the redox electrode reaction. The peak location was found to depend on both the alkyl chain length and the bulk concentration, and is shifted to a more positive potential with increasing chain length. These facts suggest strongly that the lateral interaction between alkyl chains of viologen molecules plays an important role in the stabilization of the structure of adsorbed layers.

Mediated electron transfer of polyethylene oxide-modified superoxide dismutase by methyl viologen

Abstract Methyl viologen was found to efficiently mediate the electron transfer between polyethylene oxide-modified superoxide dismutase and the electrode in dimethyl sulphoxide media. Based on the potential-step chronoamperometric experiments, the rate constant for the mediated electron transfer was estimated to be ≈ (1−2) × 10 3 M −1 s −1 .

Electrocatalysis of poly(thionine)-modified electrodes for oxidation of reduced nicotinamide adenine dinucleotide

A poly(thionine)-modified basal-plane pyrolytic graphite electrode, which can be prepared by a potential-sweep electrolysis of the corresponding monomer in acetonitrile media, shows an excellent electrocatalytic activity for NADH oxidation in phosphate buffer solutions (pH 6.9), with an activation overpotential which is ca. 400 mV lower than that of the bare electrode.

AC voltammetry at microcylinder electrodes

Abstract Current responses to an alternating potential perturbation of small amplitude for a reversible redox reaction occurring at a cylindrical electrodes of radius a are treated theoretically. Simple approximate equations are presented for the ac amplitude and the phase shift as functions of a single parameter ω a 2 D , where ω is the angular frequency and D is the diffusion coefficient. The validity of the resulting equations is examined experimentally using cylindrical electrodes with diameters ranging from 2 to 800 μm for the redox couple [Fe(CN) 6 ] 3− [Fe(CN) 6 ] 4− in 0.1 dom dm −3 K 2 SO 4 aqueous solutions. Good agreement between the theoretical and experimental results is obtained.

An excellent electrocatalysis of poly(phenosafranine)-modified electrode for oxidation of reduced β-nicotinamide adenine dinucleotide

A poly(phenosafranine)-modified electrode, which can be prepared by a potential-sweep oxidative electrolysis of the corresponding monomer in both aqueous and acetonitrile media, shows excellent electrocatalytic activity for NADH oxidation in phosphate buffer solutions (pH 7), with an activation overpotential which is more than 1 V lower than that of the bare electrode.

Piezoelectric admittance-based sensing of electrolyte solutions by montmorillonite clay film-coated quartz-crystal oscillators

Abstract The piezoelectric admittance of quartz-crystal oscillators coated with a montmorillonite clay film or a clay/ poly(vinyl alcohol) (PVA) composite film in contact with an aqueous electrolyte solution has been measured and the possibility of applying the technique to chemical sensing examined. The resistance of the equivalent circuit, which has been conventionally accepted for a piezoelectric quartz crystal, of the clay film-coated oscillator evaluated from the admittance measurement increases with decreasing Na2SO4 concentration, though the dependency is not linear. This change in resistance may be ascribed to changes in the density and/or the viscosity of the clay film, which result from the structural change of the film induced by the cation. The sensitivity is suppressed by composition of the clay film with PVA. The clay/PVA composite film-coated oscillator exhibits lower resistance for a cation with higher valence; the oscillator can measure the equivalent concentration or ionic strength of a cation