Takayasu Sugihara

Electron-conductor separating oil–water (ECSOW) system: a new strategy for characterizing electron-transfer processes at the oil/water interface

Abstract A new electrochemical method for studying the electron transfer (ET) at the oil (O)/water (W) interface (or the liquid/liquid) interface has been devised, in which the O- and W-phases are separated by an electron conductor (EC; e.g. Pt). For the EC separating O–W (ECSOW) system, the ET across the EC phase can be observed voltammetrically in a similar manner to the O/W interface, however, no ion-transfer (IT) process can be taken place. Although the ECSOW system is thermodynamically equivalent to the corresponding O/W interface, they may be different from a kinetic viewpoint. In practice, the cyclic voltammograms obtained with the nitrobenzene NB/W interface and the ECSOW system in the presence of ferrocene in NB and hexacyanoferrate in W have shown quite different features, when the concentrations of both redox species are lower. The voltammograms for the NB/W interface have strongly supported the IT mechanism which involves an interfacial transfer of ferricenium ion. Also, the ECSOW system has been shown to be promising for clarification of complicated charge-transfer processes involving biological compounds such as l -ascorbic acid.

Electrochemical control of glucose oxidase-catalyzed redox reaction using an oil/water interface

Glucose oxidase (GOD)-catalyzed electron transfers between some oxidants in nitrobenzene (NB) and glucose in water (W) were studied by cyclic voltammetry. When an electrically neutral compound, chloranil (CQ), was employed as the oxidant in NB, the enzymatic reaction could not be regulated because of the spontaneous transfer of CQ from NB to W. In this case, the voltammetric wave observed for the enzyme-catalyzed electron transfer was increased depending on the standing time until the voltage scan was started. However, when an ionic oxidant, dimethylferricenium ion (DiMFc+), was employed as the oxidant, the electrochemical control of the enzymatic reaction was achieved by controlling the interfacial transfer of DiMFc+, so that well-reproducible voltammograms could be obtained for different concentrations of DiMFc+ and for different scan rates. The voltammetric behaviors were successfully explained by a digital simulation based on the ion-transfer mechanism, which involves the interfacial transfer of DiMFc+ and the succeeding GOD-catalyzed electron transfer which occurs not heterogeneously at the interface, but homogeneously in the W phase.