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

前人的研究表明，二茂铁在硝基苯中与水中的铁氰化物之间的电子转移不是在油/水界面上非均相发生的，而是在水相中均匀发生的。这种反应机理被称为“离子转移(IT)机理”，因为流经界面的电流是由于产物离子的离子转移(IT)。这项研究的目的是要知道在油/水界面上是否真的发生了ET，因为油/水界面上的ET是一个双分子反应，所以速率常数应该有一个上限。本文将Smoluchowski-Debai理论推广到溶液中的双分子反应，从理论上得到了界面ET的扩散控制速率常数，并用循环伏安数字模拟、交流阻抗测量、微流电解、电子导体分离油水体系等电化学方法进行了实验研究，从理论上阐明了Cloranil-抗坏血酸和二甲基二茂铁-铁氰化铁体系中的ET反应机理。一种新发现的葡萄糖加氧酶催化的ET与二甲基二茂铁和葡萄糖之间的反应机理被发现是类似的IT机理，但已被澄清的是，当油相中的氧化还原物种采用极端疏水的氧化还原化合物如联苯四氮杂菁化合物时，在油/水界面上应该出现一个“trLte”(即非均相)ET。关于这种异质ET的报道还很少，因此我们一直在寻找新的“真正的”ET系统。通过利用ECSOW体系，我们发现了一种新的ET体系，在该体系中，四苯基卟啉(TPP)Cd络合物被用于油相中的氧化还原物种。此外，在1，2-二氯乙烷中发现了锌-TPP络合物与水中质子的新的光诱导ET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.