| Research Abstract |
The previous study showed that the electron transfer (ET) between ferrocene in nitrobenzene and ferricyanide in water occurred not heterogeneously at the oil/water interface, but homogeneously in the water phase. This reaction mechanism is called "ion-transfer (IT) mechanism", as the current flowing through the interface is due to an IT of the product ion. The objective of this study is to know whether an ET really occurs at the oil/water interface.
Because an ET at the oil/water interface is a bimolecular reaction, there should be an upper limit for the rate constant. In this study the diffusion-controlled rate constant for the interfacial ET has been theoretically obtained by an extension of the Smoluchowski-Debye theory for a bimolecular reaction in solutions.
Experimental approaches have been carried out using several electrochemical techniques including digital simulation of cyclic voltammograms, ac impedance measurement, microflow electrolysis, electron-conductor separating oil-water (ECSOW) system, etc. The ET reactions in cloranil-ascorbate and dimethylferrocene-ferricyanide systems have been elucidated in terms of the IT mechanism. The reaction mechanism of a newly-found, glucoseoxydase-catalyzed ET between dimethylferrocene and glucose has been found to be an analogous IT mechanism.
However, it has been clarified that when an extremely hydrophobic redox compound such as lutetium biphtharocyanine complex is employed as the redox species in the oil phase, a "trLte" (i.e.,heterogeneous) ET should occur at the oil/water interface. There have been reported only a few examples for such heterogeneous ET, and accordingly we have searched for new "true" ET systems. By making good use of the ECSOW system, we have found a new ET system in which tetraphenylporphyrin (TPP) Cd complex is employed for the redox species in the oil phase. Furthermore, a new photoinduced ET reaction between Zn-TPP complex in 1,2-dichloroethane and proton in water has been discovered.
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