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Kitatsuji Y.,Japan Atomic Energy Agency | Kimura T.,Japan Atomic Energy Agency | Kihara S.,Kyoto Institute for Interesting Chemistry
Electrochimica Acta

Redox reactions of U, Np and Pu ions of various oxidation states were investigated by flow electrolysis at a column electrode (CE) equipped with a platinized glassy carbon (GC) fiber working electrode (Pt/GC-WE), and compared with those observed at the CE with an ordinary activated GC fiber working electrode (GC act-WE). Since the overpotential for the reduction of NpO 2 + and PuO 2 + were decreased when Pt/GC-WE was employed, the one-electron reduction of NpO 2 + to Np 4+ followed by that of Np 4+ to Np 3+ and the one-step three-electron reduction of PuO 2 2+ to Pu 3+ proceeded at the CE with Pt/GC-WE, different from the reduction processes of NpO 2 + and PuO 2 2+ at the CE with GC act-WE. On the other hand, the redox reactions of UO 2 2+/U 4+, Np 4+/Np 3+, NpO 2 2+/NpO 2 + and Pu 4+/Pu 3+ were scarcely affected with the platinization of the GC working electrode. The reaction processes observed at the CE with Pt/GC-WE were elucidated consulting with those at the CE with GC act-WE and voltammograms at rotating platinum, platinized platinum, GC and platinized GC electrodes. A rapid and precise method for the preparation of U, Np and Pu ion of a desired oxidation state was proposed by taking advantage of the unique characteristics of the CE with Pt/GC-WE. © 2012 Elsevier Ltd. Source

Kasuno M.,Ryukoku University | Fujimoto K.,Ryukoku University | Kakitani Y.,Ryukoku University | Matsushita T.,Ryukoku University | Kihara S.,Kyoto Institute for Interesting Chemistry
Journal of Electroanalytical Chemistry

The flow cell proposed previously for the rapid and coulometric determination of cations based on the electrochemical ion transfer at the aqueous|organic solution interface was improved to be applicable to the determination of anions. The developed cell was composed of a porous poly(tetrafluoroethylene) tube (1.0 mm in inner diameter), a copper wire (0.8 mm in diameter) inserted into the tube, a platinum wire placed outside the tube, an organic solution into which the tube was immersed and a reference electrode in the organic solution. The aqueous solution containing a species of interest was flowed through the narrow gap between the tube and the copper wire. A potential difference was applied at the aqueous|organic solution interface by using the copper wire and the reference electrode in the organic solution in order to realize the ion transfer at the interface, and the current due to the interfacial ion transfer was detected by the copper and platinum wires. The developed cell was evaluated adopting the transfer of an anion such as perchlorate, picrate or alkylsulphonates from the aqueous solution to 1,2-dichloroethane (used as the organic solution), and demonstrated that the anions of 10 -4 mol dm -3 level could be determined with coefficients of variations better than 0.2% (n = 5). The applicability of the developed cell to the flow injection analysis of anions was also discussed. © 2010 Elsevier B.V. All rights reserved. Source

Okugaki T.,Kyoto Institute of Technology | Kasuno M.,Ryukoku University | Maeda K.,Kyoto Institute of Technology | Kihara S.,Kyoto Institute for Interesting Chemistry
Journal of Electroanalytical Chemistry

The oxidation of α-tocopherol (vitamin E), α-TOH, in 1,2-dichloroethane, DCE, by NO or MnO4 - in water (pH = 1-9), W, at the W/DCE interface was investigated by voltammetry for charge (ion or electron) transfer at the interface of two immiscible electrolyte solutions, VCTIES, and controlled potential difference electrolysis at the interface. A positive current wave due to the interfacial redox reaction producing α-tocopherone cation α-TO+ and H+ in DCE was observed by VCTIES. The H+ transferred to W, and a part of α-TO+ was converted to α-tocopheryl quinone, α-TQ, by the hydrolysis with the water dissolved in DCE. Even when the potential difference at the interface, E, was in the range where any faradaic current was not observed by VCTIES, the interfacial reaction proceeded and gave α-TQ in DCE. The reduction products of NO or MnO4 - in W at E in both ranges were N2O or Mn2+ and MnO2, respectively. When the oxidant in W was MnO4 - and E was available for the transfer of MnO4 - to DCE, the redox reaction between MnO4 - and α-TOH in DCE proceeded in addition to the interfacial redox reaction. α-Tocopherol spiro-dimer, α-TD, α-TQ and MnO2 were produced by the reaction in DCE. The oxidation reaction of α-TOH at the W/DCE interface was compared with that at a platinum electrode in the bulk of DCE. © 2009 Elsevier B.V. All rights reserved. Source

Kitatsuji Y.,Japan Atomic Energy Agency | Otobe H.,Japan Atomic Energy Agency | Kimura T.,Japan Atomic Energy Agency | Kihara S.,Kyoto Institute for Interesting Chemistry
Electrochimica Acta

Reduction processes of UO2 2+ in weakly acidic solutions were investigated based on electrochemical and spectrophotometric measurements. A reversible one-electron reduction of UO2 2+ to UO2 + and a further irreversible reduction of UO 2 + were observed voltammetrically at a gold microdisk electrode in weakly acidic perchlorate solutions of pH from 2.0 to 3.5. Aggregates of U(IV) were formed as a deposit on the electrode and a colloid in the bulk solution, when the controlled-potential bulk electrolysis was carried out at a gold gauze electrode, even though the potential applied was that available for the first one-electron reduction wave of UO2 2+ observed at a gold microdisk electrode. It was elucidated that the aggregate was produced by the combination of the one-electron reduction to UO2 + and the disproportionation of UO2 + producing U(IV) and UO2 2+. The aggregate enhanced the rate of the disproportionation of UO2 +, and hence the reduction current of UO2 2+ increased abruptly when a definite amount of aggregate was formed on the electrode, in the solution, or both. The aggregate of a two-electron reduction product of UO 2 2+ was determined to be poorly crystallized UO 2 of fluorite-type structure, and the characteristics of the aggregate were different from the crystalline UO2 © 2014 Elsevier Ltd. Source

Kihara S.,Kyoto Institute for Interesting Chemistry | Kasuno M.,Ryukoku University | Okugaki T.,Kyoto University | Shirai O.,Kyoto University | Maeda K.,Kyoto Institute of Technology

Some biomimetic reactions observed with the aid of aqueous/organic, W/O, two phases or liquid membrane, LM, systems were introduced. The reactions introduced were mostly those reported by the group of present authors as follows; (1) Transformations of porphyrin iron(III) complex, Fe(P), and α-tocopherol, α-TOH, derivatives in O contacted with W. (2) The oxidation of Fe(P) in O with an oxidant in W, α-TOH in O with nitric oxide in W or hydroquinone in O with oxygen in W, and the reduction of quinone in O with β-nicotinamide adenine dinucleotide in W. (3) A respiration mimetic reaction accompanied by the selective ion transfer at the W/O interface. (4) Biomimetic charge transport reactions observed by LM systems such as the oscillation of membrane current. (5) A new type of membrane transport reaction realized in the presence of an applied electrical potential gradient parallel to the W/ membrane interface. The processes of above-described reactions were elucidated based on the voltammetric methods and concepts taking into account the properties common to both artificial LMs and biomembranes. A method proposed by present authors for the elucidation of the membrane transport process was also introduced. © The Electrochemical Society of Japan All rights reserved. Source

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