The Study Of Multi-step Electon Transfer At Liquid/Liquid Interface By Thin-Layer Cyclic Voltammetry

The liquid-liquid interface is the simplest and most promising model for understanding charge-transfer processes in biological systems, which is in close touch with the metabolic process of complex biologic organization. For example, the release of drugs, the simulated biologic membrane and so on. Thus, in the past few decade years, the interface between two immiscible interfaces (ITIES) has attracted wide attention. The thermodynamics and dynamics for the charge transfer across the liquid/liquid interface are the core problem of liquid/liquid electrochemistry. Electron transfer at the liquid/liquid interface is particularly important for understanding the metabolic process of complex biologic organization and the secret of the life. The multi-step electron transfer of biological intermolecular is an important chemical reaction for the developing of living beings. In nature, almost every life cycle involves the process of multi-step electron transfer. For example, photosynthesis, respiratory chain, free-radical scavenging antioxidants. However, there is a few reports concerning multi-step electron transfer. As a result, Research is urgently needed into the studies of the multi-step electron transfer.The thin-layer cyclic voltammetry (TLCV) is reported by Anson etal in 1998, which is a useful method for studying the electron transfer across the liquid/liquid interface. It is easily operational and practicable. The TLCV application plays an significant role in enlarging the research field of charge transfer.The main contents of the thesis are as fo11ows:1 As a brief introduction to the development of liquid/liquid interface electrochemistry, the papers shows the basic principle and the research method of the liquid/liquid interface chemistry. Meanwhile, the fundamental theory and the application of thin-layer cyclic voltammetry are elaborated clearly.2 The consecutive two-step electron transfer across the ZnTPP(NB)/(water)K4Fe(CN)6 was investigated. The results show that the multi-step electron transfer also obeys the Bulter-Volmer theory that the rate constants gradually increased with the increasing of driving force. Similarly, the anodic plateau current gradually increased with the increasing of the concentration ratio of the electroactive substance in the two phases. However, when the concentration ratio reached to the certain value, the anodic current would no longer rise. The phenomenon indicates the electron transfer is controlled by the diffusion of the electronactive substance in the thin-layer. In addition, the appearance of the peak current instead of plateau current gradually decreases with the volumes of the organic phase increased from 1 to 4μL, which shows the steady-state concentration pro?le in the thin layer is not achieved with the thin-layer becoming thicker.3 The consecutive two-step electron transfer between metalloporphyrin species containing different substitutes in nitrobenzene and Fe(CN)₆^4- in the aqueous phase was studied by TLCV, which showed the process was affected by the presence of the distinguished substitutes in the molecules of the three types of porphyrin zinc. Because as electron-with-drawing substitutes,–NO2 was induced in the molecule of ZnTPP, results in the ZnTPP(NO₂)₂ oxidation at a more positive potential due to the decreased density of electron cloud in the porphyrin rings, However, as the electron-donating substitutes,–OCH₃, playing the opposite role, let ZnTPP(NO₂)₂ oxidized at a more positive potential.4 The consecutive two-step electron transfer between CoTPP and K₄ Fe(CN)₆ was studied by TLCV. The results show that the two reversible couples near 0.5 and 0.8V correspond to the two step electron oxidations of CoTPP: CoTPP→CoTPP⁺→CoTPP²⁺. According to the TLCV theory, the rate constants of two-step electron transfer obtained is 0.066 cm·s^-1·M^-1 and 0.080 cm·s^-1·M^-1, respectively. The rate constant is also qualitative with the coventional Bulter-Volmer theory that the rate constant is become larger with the increasing of driving force. The study is contributed to understand the Electrode Reaction Mechanism and the electron transfer process of the Vitamin B₁₂ better. Also, it is significant to the study the drug realease and the physiological processes mechanism for the Vitamin ₁₂.