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

前人的研究表明，硝基苯中的二茂铁与水中的氰化铁之间的电子转移（ET）在油/水界面上不是非均匀发生的，而是在水相中均匀发生的。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引起的。本研究的目的是了解ET是否真的发生在油水界面。因为油/水界面的ET是双分子反应，所以速率常数应该有一个上限。本文通过对溶液中双分子反应的Smoluchowski-Debye理论的推广，从理论上得到了界面ET的扩散控制速率常数。实验方法采用了循环伏安图的数字模拟、交流阻抗测量、微流电解、电子导体分离油水（ECSOW）系统等电化学技术。对氯兰尼-抗坏血酸盐体系和二甲基二茂铁-铁氰化物体系中ET反应的IT机理进行了阐述。新发现的葡萄糖脱氧酶催化的二甲基二茂铁与葡萄糖之间的ET反应机制与IT反应机制类似。然而，已经澄清的是，当一种极疏水的氧化还原化合物，如双酞菁镥配合物作为油相的氧化还原物质时，“trLte”（即异相）ET应该在油/水界面发生。对于这种异构ET，只有少数几个例子被报道过，因此我们寻找新的“真正的”ET系统。通过充分利用ECSOW体系，我们发现了一种以四苯基卟啉（TPP） Cd配合物为油相氧化还原物的ET体系。此外，在1,2-二氯乙烷中发现了锌- tpp配合物与水中质子的光诱导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.