Kazuko Tanaka

Amperometric determination of superoxide anions generated from phytoplankton Chattonella antiqua

Superoxide anions (0;) now attract much attention in many fields of biology since it is realized that superoxide anions are produced in significant quantities in various parts of biological systems from micro-organisms to mammals [ 11. However, in most cases the biological significance and mechanism of the generation of 0; are not yet understood. Chattonellu antiqua is a highly toxic phytoplankton which is harmful to ‘fish, especially in fish farms. On the basis of morphological and histochemical observations of the cells, it is proposed that 0; might be involved in the toxic mechanism responsible for mortality in fish exposed to a large population of C. antiqua [2-61. The inhibitory effects of superoxide dismutase (SOD) on the ability of C. antiqua to reduce ferricytochrome c to ferrrocytochrome c support this assumption [51. This communication provides direct evidence, obtained electrochemically, for the generation of 0; by C. antiqua. In a previous paper we demonstrated that the electrochemical detection of 0; generated from a single stimulated neutrophil (human and porcine) could be achieved using a microelectrode technique in which a single cell was brought into contact with a working electrode of size similar to that of the cell [71. We have used this technique, with a slight modification, for C. antiqua since the size and the nature of the cell are rather different from those of neutrophils. C. antiqua was obtained from the Akashio Research Institute of Kagawa Prefecture, and cultured in an Erd-Schreiber Modified (ESM) medium of pH 8.2 with constant illumination at around 23°C. Cultures contained ca. 1 X lo5 cells/ml after l-2 weeks under these conditions. Figure 1 shows photomicrographs of C. antiqua cells. When motile, they are spindle shaped and propel themselves by the

Mediating effects of ferric chelate compounds in microbial fuel cells

Abstract The performance of bio-fuel cells containing Escherichia coli, glucose and a series of ferric chelate reagents was studies. The measured coulombic outputs indicate that the most of the compounds work effectively as electron-transfer mediators in the fuel cells. These outputs were compared with measured rate constants for the reduction of ferric chelates by E. coli and the electrochemical reaction of these compounds at a carbon electrode. The results suggest that a good mediator for microbial fuel cells is one which shows fast reduction by E. coli, together with a fast electrode reaction. In regenerative fuel cells which were run for 5 days, coulombic yields over 70 % were obtained on the basis of complete oxidation of added glucose.

7Li-MR Studies on Molecular Motion of Hydrated Lithium Ions in Concentrated Aqueous Solutions of LiCl, LiBr, and LiSCN at Low Temperatures

Abstract Nuclear spin-lattice relaxation times, T1, of 7Li in 13.8mol/kg LiCl-H2O and 12.3 mol/kg LiCl-D2O solutions have been measured in the temperature range 80K-313K. They showed similar temperature dependences with the same minimum values (27 ± 1 ms) which proved that the electric quadrupole interaction is dominant for the relaxation of 7Li-NMR. The T1 and T2 values of 7Li-NMR in concentrated aqueous solutions of LiCl (8-14 mol/kg), LiBr (8-10 mol/kg) and LiSCN (8-14 mol/kg) at 80 K to 300 K have been studied to obtain information concerning the dynamic properties of Li+ ions and the effect of anions. T1 at temperatures higher than the glass transition point is governed by a tumbling motion of the hydrated lithium ions.

Nuclear magnetic resonance and thermal studies of concentrated aqueous solutions of lithium chloride

The nuclear spin relaxation times, T1 and T2, of 7Li nuclear magnetic resonance have been investigated over a wide range of temperatures in 14 mol kg–1 aqueous lithium chloride solution, whose thermal behaviour was examined with differential thermal analysis. The relaxation is mainly attributed to dipolar coupling between water protons and lithium ions, and T1 and T2 at temperatures higher than the glass transition point are governed by the translational motion of the hydrated lithium ions. The activation parameters of the motion were found to be Ea= 33.5 ± 0.8 kJ mol–1, τ0=(1.2 ± 0.5)× 10–17 s. The Ea values are similar to those for molecular self-diffusion in a plastic-crystalline phase of globular molecules.

A Physico-Chemical Study of Concentrated Aqueous Solutions of Lithium Chloride

Abstract The experimental values of density, viscosity, electric conductivity and diffusion coefficients of trace ions in aqueous solutions of lithium chloride in wide ranges of concentration and temperature are collected and discussed. The thermal expansivity and the activation energies of viscous flow, electric conductance and diffusion of trace ions show significant changes at a molality around 12 mol/kg, beyond which the hydration requirement is not satisfied

In vivo voltammetry with an ultramicroelectrode

Studies of the transport properties of various substances through biomembranes give useful information in many aspects, particularly when they are made in vivo. Recent developments in electrochemistry have enabled us to observe translocation of molecules and ions across a living cell membrane. Ultramicroelectrodes fabricated from a single carbon fiber of micrometer dimemsions have received much attention from both the perspective of fundamental electrochemical work and their use as in vivo voltammetric probes1,2,3. They possess unique and advantageous properties for in vivo application, including extremely low capacitive current, high rates of mass transport and much reduced ohmic effects. Previouly we reported the suitability of carbon fiber electrodes for the in vivo monitoring of the uptake of electrochemically active substances such as an electron transfer mediator, methoxy-phenaziniummethylsulphate4. In this paper we report uptake behaviours of cadmium and mercury ions into living cells measured by the ultramicroelectrode technique.

Acidic dissociation constants of weak bases in D2O from measurements with ion-selective electrodes

Abstract Little information concerning the strengths of weak bases in D 2 O is available, in part because of the difficultiis associated with the use of deuterium gas electrodes and the reaction of many bases with the commonly used Ag/AgCl electrode. An emf method described recently by Tanaka and Bates avoids these problems by use of pH glass electrodes and sodium-selective electrodes in a cell without liquid junction. At the same time, improvements in the extrapolation can be realized and a precision of ±0.01 p K unit or better can be achieved. This method has now been applied to a determination of the dissociation constants of five deuterated weak bases, namely tris(hydroxymethyl)aminomethane (Tris), hydrazine, morpholine, ammonia and cyclohexylamine, at several temperatures in the range 15–45°C. Tris is a useful standard for the determination of the p K a of other bases in D 2 O. The p K a of this reference (Tris·D + ) was determined by the Harned method and is given by p K a =5914.26/ T −74.229+11.0674 ln between thermodynamic temperatures ( T ) of 288.15 and 318.15 K. Deuterium isotope effects on protonated weak bases are consistent with those found earlier for inorganic acids, carboxylic acids and phenols.

Effect of methylviologen on the hydrogen evolution at mercury electrodes in aqueous buffer solutions

Abstract Methylviologen reduces the hydrogen overvoltage and gives a catalytic hydrogen wave at the dropping mercury electrode in aqueous buffer solutions (pH 3–7). The electrochemical behaviour of the catalytic hydrogen evolution was studied by dc and pulse polarography, potential-step chronoamperometry, and constant potential electrolysis. A possible reaction scheme has been proposed to explain the experimental results, in which the reduced neutral form of methylviologen MV 0 is assumed to be oxidized to a monocation radical MV ·+ by the weak acid component in the buffer solution. Generation of MV ·+ during the hydrogen evolution is supported by the visual observation of a blue colour appearing at the surface and also in the vicinity of the electrode when a large catalytic current is flowing in dc polarography and constant potential electrolysis.

Limiting current increase of oxidation of ferrocyanide anions in water and electrolyte solutions during freezing

Normal pulse voltammograms of the oxidation of ferrocyanide to ferricyanide were investigated in water and aqueous solutions of various electrolytes at temperatures above and below the freezing point of the solvent using a platinum microdisc electrode. A significant increase in the limiting current was observed on freezing, particularly in water without added electrolyte, and, in most cases, current vs. t−12 plots gave a straight line, suggesting a diffusion-controlled mechanism. The concentration of ferrocyanide in the liquid phase localized at the electrode area in partially frozen solution was estimated from the slope by applying the diffusion coefficient of the ion in complete liquid at the freezing point or in the supercooled state, and this was compared with the concentration averaged in the bulk determined from the free induction decay (FID) signals of 1H-NMR measured under similar conditions to those of voltammetry. The degree of concentration determined from the limiting current was much higher than that estimated from the FID signals, particularly just before freezing was complete. Such a result indicates that a liquid microphase which concentrates solutes exists at or near the electrode in low temperature freezing solutions.

Faraday communications. Nuclear spin relaxation of 7Li in aqueous solutions of LiCl

Spin–lattice relaxation times, T1, of 7Li NMR have been measured for 12.3 mol kg–1 LiCl–D2O and 13.8 mol kg–1 LiCl–H2O samples at temperatures of 80 K to 313 K. The temperature dependence of T1 for both samples was very similar over the whole temperature range. The minimum of T1 was found to be 27 ± 1 ms for both samples. From the experimental results, it is concluded that the quadrupole interaction is responsible for the relaxation of 7Li NMR.