Atsuo Mizukami

Effect of cations on the electrochemical behavior of p-toluenesulfonate-doped polypyrrole in various aqueous solutions

The electrochemical behavior of p-toluenesulfonate-doped polypyrrole (PPy/TsO−) in aqueous solution was analyzed by cyclic voltammetry. These films were prepared by the electropolymerization of pyrrole in aqueous solutions. It was found that in aqueous solutions containing alkali metal ions (M+), the dopant anions (TsO−) in the PPy film could be exchanged relatively easily with electrolyte anions in aqueous solutions by potential sweeping. However, PPy/TsO− was electrochemically inactivated in aqueous solutions containing alkaline earth metal ions (M2+) or tetraalkylammonium ions (R4N+). It was found that the inactivation in aqueous solutions containing M2+ or R4N+ could not be explained simply by the hypothesis that these cations were not incorporated into PPy/TsO− during the reduction process because of their large ion size. It was speculated that the anisotropic molecular organization of PPy/TsO− might play a key role in its inactivation of PPy/TsO−.

Electrochemical exchange process of dopant anions in polypyrrole

Abstract The electrochemical behavior of the exchange process for dopant anions in p-toluenesulfonate doped polypyrrole (PPy/TsO−) in aqueous solution was analyzed by cyclic voltammetry. These films were prepared by electropolymerization of pyrrole in aqueous solutions. It was found that the dopant anions (TsO−) in the PPy film could be exchanged relatively easily with electrolyte anions in aqueous solutions by potential sweeping. However, they could not be easily exchanged in acidic solutions. The electrochemical behavior of PPy/TsO− in various aqueous solutions is discussed.

Magnetron Sputtering of Bi-Ca-Sr-Cu-O Thin Films with Superconductivity above 80 K

Superconducting Bi-Ca-Sr-Cu-O thin films on (100) MgO were prepared by rf magnetron sputtering from a sintered Bi1Ca1Sr1Cu2Ox target. Post-annealing after sputtering resulted in superconducting films with a resistance anomaly around 110 K and zero resistance at 80 K. X-ray diffraction patterns indicated a preferential orientation, where the c axis of a fourfold stacked perovskite, with a lattice constant c=15.38 A, is perpendicular to the substrate plane.

Sputtered Tl-Ca-Ba-Cu-O Thin Films with Zero Resistivity at 98 K

Superconducting Tl-Ca-Ba-Cu-O thin films were prepared by rf magnetron sputtering from a sintered Tl3Ca2Ba2Cu3Ox target. After post-annealing, films grown on (100) MgO substrates exhibited the best superconducting properties with an onset temperature as high as 110 K and zero resistivity at 98 K. No resistive tails were observed at measuring current densities of 0.5–5 A/cm2. X-ray diffraction patterns indicated that the major phase of the films is Tl2Ca1Ba2Cu2Ox.

Cooling-induced retrograde amnesia reflexes Pavlovian conditioning associations in Limax flavus

The relationships between cooling-induced retrograde amnesia and associations in Pavlovian conditioning in the terrestrial mollusk Limax flavus were studied. In the first experiment, the slugs were conditioned to avoid carrot odor and the experimental conditions required for amnesia induction were studied. Memory reactivation before cooling was found to be necessary for amnesia induction and the induced amnesia was selective for the reactivated memory. In the subsequent experiments, slugs were conditioned to avoid both carrot and cucumber odors using one of three Pavlovian conditioning paradigms, namely two-independent first-order conditioning, phase-2-sequential second-order conditioning and phase-2-simultaneous second-order conditioning, after which amnesia was induced by cooling immediately after presentation of one of the conditioning odors. The amnesia pattern induced differed depending upon the conditioning procedure used, which indicated that amnesia induction was related closely to stimulus associations in slugs. The possible role of cooling-induced retrograde amnesia as a tool for studying memory associations is also discussed.

Lipid bilayer formation in a microporous membrane filter monitored by ac impedance analysis and purple membrane photoresponses

Abstract We have measured and analyzed the time-dependent variation in the ac impedance of lipid-impregnated polycarbonate membrane filters (PCMs). The results showed that the electrical characteristics of PCMs gradually changed with time. From the results, we inferred the formation of bilayer-like micromembranes within the PCM pores and presented a model of the time-dependent thinning process of a lipid + decane micromembrane system. In addition, we measured the time-dependent variation of the photoresponse of purple membrane reconstituted onto the PCM system and showed that thinning of the micromembrane proceeded in all the PCM pores. The results provided information about what is occurring within lipid-impregnated PCMs. Hence such filters will help us explore model systems simulating certain biological membrane systems. The time-dependent variations in the characteristics of such lipid-impregnated PCM systems were previously unknown, although these systems are accepted as stable and feasible candidates for simulating biological functions.

Direct transmembraneous reconstitution of bacteriorhodopsin into planar phospholipid bilayers

Abstract A new method of incorporating bacteriorhodopsin molecules into planar lipid bilayers was developed and compared with a conventional system where purple membranes were adsorbed onto planar bilayers. By the new method, purple membrane sheets were first solubilized with a detergent and the solubilized fraction was directly added to an aqueous phase of a preformed planar bilayer membranes. Then, the solubilized bacteriorhodopsin molecules were spontaneously incorporated into the planar bilayers. Upon illumination, a steady state electric current was generated and the magnitude of the current was hardly affected by the presence of an uncoupler, FCCP. Furthermore, when bacteriorhodopsin molecules were incorporated into planar bilayers in high temperature range, a transient capacitive peak current was mostly eliminated by successive perfusions with a buffer at room temperature. These properties are in contrast with those of conventional method and strongly indicate that the bacteriorhodopsin molecules are transmembraneously reconstituted into planar bilayer membranes by the new method. The new method will prove useful in quantitative investigation of the properties of active ion transport.

Time-dependent variation in a.c. impedance of lipid-impregnated membrane filters

Abstract We measured and analyzed time-dependent variation in the a.c. impedance of lipid-impregnated membrane filters. By changing the lipid concentration of the membrane and the salt concentration of the aqueous solution surrounding the filter, we could determine how the lipids in a decane solution rearange their order in lipid-impregnated membrane filters. The results showed that the electrical characteristics of such filters change gradually with time; from this we inferred the formation of bilayer-like micromembranes. In addition, we verified the effectiveness of cholesterol and octadecylamine in improving membrane stability, resulting in a longer life-span of the micromembranes. Finally, we present a scenario for the time-dependent behavior of a lipid-decane system that is within a skeleton consisting of a cellulose matrix of a membrane filter. The results yielded knowledge about what occurs within lipid-impregnated membrane filters and the mechanism for membrane stabilization. Hence, such filters will help us explore model systems that simulate certain biological membrane systems. The time-dependent variations in characteristics of such lipid-impregnated membrane systems were previously unknown, even though such systems have been recognized as stable and feasible candidates for simulating biological functions.

electrochemical behavior simulating the synaptic plasticity in the dopant exchange process of p-toluenesulfonate-doped polypyrrole

Abstract The unusual electrochemical behavior of p-toluenesulfonate-doped polypyrrole (PPy/TsO−) was studied in terms of its application to the device that can reversibly change the amplitude of the output signal according to the frequency of the input signal. The device simulates the synaptic plasticity (the efficiency of the signal transmission changes as a function of the frequency of the stimulus signal). Therefore we call this an electrically plastic device. PPy/TsO− films were prepared by electropolymerization of pyrrole in aqueous solutions. PPy/TsO− is electrochemically inactivated in aqueous solutions containing alkaline-earth metal ions or tetraalkylammonium ions. The inactivated PPy/TsO− is gradually activated however by potential sweeping or spontaneous anion exchange during immersion. Using both gradual activation by potential sweeping and preferential dopant exchange during immersion in a mixed electrolyte solution, reversible electrically plastic behavior was successfully developed. The possibility of developing a biomimetic device that uses PPy/TsO− as an artificial conducting polymer in an electrochemical system is discussed.

Electrical oscillations across polypyrrole membranes caused by electron donors and electron acceptors

Abstract Polypyrrole chemically polymerized on a polycarbonate membrane filter showed electrical oscillations when an electron donor and an electron acceptor were separately present on each side of the membrane. It was found that the oscillations were created by stirring the solutions and were amplified by salt concentration differences across the membrane. It was speculated that the oscillations reflect the differences between electron and ion transfer rates in the reduced and oxidized states of the polypyrrole membrane.