Does an electron transfer really occur at the oil/water interface?

前人的研究表明，硝基苯中的二茂铁和水中的铁氰化物之间的电子转移（ET）在油/水界面上不是非均相的，而是在水相中均相的。这种反应机制被称为“离子转移（IT）机制”，因为流过界面的电流是由于产物离子的IT。由于油/水界面的ET反应是一个双分子反应，因此速率常数应该有一个上限。本文通过扩展Smoluchowski-Debye双分子反应理论，从理论上得到了界面ET的扩散控制速率常数，并利用循环伏安数字模拟、交流阻抗测量、微流电解、电子导体油水分离（ECSOW）系统、本文对氯苯胺-抗坏血酸和二甲基二茂铁-铁氰化物体系的ET反应进行了初步的研究。新发现的葡萄糖氧化酶催化的二甲基二茂铁和葡萄糖之间的ET的反应机理已经被发现是类似的IT机理。然而，已经澄清的是，当使用极疏水的氧化还原化合物如联苯二甲酸镥络合物作为油相中的氧化还原物质时，“trLte”（即，非均相）ET应发生在油/水界面处。已经报道了这种异构ET只有几个例子，因此，我们一直在寻找新的“真正的”ET系统。利用ECSOW体系，我们发现了一种新的ET体系，其中四苯基卟啉（TPP）镉配合物用于油相中的氧化还原物种。此外，还发现了Zn-TPP配合物在1，2-二氯乙烷中与质子在水中的光诱导电子转移反应。

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.