Studies On The Electron Transfer Of Metal Porphyrin And Other Compounds At Interface

The process of electron transfer (ET) is the basic movement in life activities. Moreover, most of life activities in organisms are closely related to the electron transfer process, such as oxygen transport of heme proteins, photosynthesis in chloroplasts, and respiration in mitochondria, which mainly happened on biomembrane. Therefore, the research of electron transfer on biomembrane is meaning for us to realize and understand many important physiological processes, and to open the secret of substance and energy metabolism in biological systems. A liquid/liquid (L/L) interface has been considered as the simplest model for biological membranes. In addition, the development of chemically modified electrode (CME) has provided a suitable microenvironment for biomolecules to take place the direct electron transfer (DET). Based on this, the paper takes porphyrin and metal complexes as the research object, a class of biomolecules that is playing an important role in the biological processes, and then systematically investigates their ET processes and direct electrochemical behavior across the simulative biomembrane interface (liquid/liquid and solid/liquid). The study also has the potential significance for constructing new biosensors.With the accelerated development of scientific technology and the mutual infiltration among various disciplines, investigation of interfacial electrochemistry may encounter more and more chance and challenge. However, recent precise technologies and more reasonable methods will be destined to exploit the broad foreground of nature. The thesis applied scanning electrochemical microscopy (SECM) which was developed by Bard and co-workers in 1989 and electrochemical impedance spectroscopy (EIS) to investigate the electron transfer of metal pophyrins across interface. There are four parts in this paper, and the main contents are as follows:1. A short review was given on the development background, the basic model and principle of L/L interface. The outlines of TLCV and SECM which are the major study methods for L/L interface were summarized. Especially, the working-principle, the quantitative analysis theory, and the applications of the two technologies in L/L interfacial electrochemistry were discussed in detail. Additionally, the thesis not only reviews the development, preparation methods, and application in biosensors and electrocatalysis fields for chemically modified electrode, but also reviews the properties and applications in modified electrode field as for room temperature ionic liquids (RTILs) and carbon nanotubes (CNTs).2. SECM was applied to study electron transfer processes between decamethyferrocene (DMFc) in nitrobenzene (NB) and ferric ion in aqueous phase, for discussing the relationship between the driving force and ET reaction at L/L interface. The experiment results showed that the obtained ET rate declined in spite of larger driving force, when Fe(CN)63- was substituted by Fe3+. Both the reason of the phenomenon and effect of the common ion on ET rate, were then described.3. ET processes of Tetraphenyl porphyrin zinc and its isomer (N-confused porphyrin zinc) were studied by SECM across the simulative membrane. Comparison of their molecular configuration, the thermodynamic energy and MOs orbitals, we discussed the effect of substance structure on interface reaction. On the other hand, different substitutes were introduced to iron porphyrin in order to alter their stability, and finally influenced the electron transfer process. A detailed discussion was carried out to study the effect of different substitutes on the kinetics of electron transfer and biological activity of iron porphyrin.4. Hematin is an important iron porphyrin compound. Considering the favorable properties of room temperature ionic liquids (RTILs) and multi-walled carbon nanotubes (MWCNTs), hematin was immobilized on the surface of ionic liquid modified carbon paste electrode (CILE) which was further modified with MWCNTs, subsequently fixed by a layer of polyvinyl alcohol (PVA). Then the direct electrochemistry behavior of hematin was achieved on the modified electrode surface. The experiment indicated that the ability of hematin ET was enhanced obviously and exhibited a quasi-reversible redox peaks on the modified electrode. The corresponding parameters were also calculated. The hematin modified electrode interestingly showed electrocatalytic activity for nitrite to a certain extent. The study was beneficial to the development of the third-generation biosensors.