| Superoxide ion ( O2·- ) is one kind of reactive oxygen species, which is characteristic, of paramagnetic, strong reactivity, short-life and so on. Many evidences show that superoxide ion is related to many human diseases such as diabetic, cancer and sapremia. More and more people have known that it is important to scavenge excess superoxide ion in human body, so the investigation on superoxide ion has attracted much attention in many fields, especially in biology, clinical medicine, pharmaceuticals, chemistry. Being a univalent reduction product of oxygen, in principle, superoxide ion can function as one-electron reductant, complexation ligand, nucleophile, a base and an oxidizing agent. And it can react with many biological substances in biological milieu. In this dissertation, the reactivity of superoxide ion was studied by the electrochemical methods and the reaction mechanisms were elucidated in detail. The explorations on the reactivity of superoxide ion will be useful in understanding the metabolism process of some compounds in biological system. We have developed three types of powder microelectrodes and studied the voltammetric response of O2 / O2·- and the one-electron reduction kinetic process at the powder microelectrodes. We also found a new media system (acetone + 0.1mol/L n-Bu4NBr) which is suitable for examining the electrode reaction of one-electron reduction of O2 as well as the reactivity of O2·-. Concurrently, the scavenging activity of several antioxidants with low molecular weight towards O2·-in lipophilic solvent were evaluated by cyclic voltammetry (CV) in our work. It is very important to evaluate the scavenging activity of antioxidants for protecting biological systems against reactive oxygen species (ROS). The main content of this dissertation is as follows:( i ): The voltammetric responses of the reduction of O2 as a function of the aprotic solvents were investigated , the results suggesting that acetone was a suitable solvent for examining the electrode reaction of the O2 /O2·-couple as well as scavenge of O2·-. The electrochemical behaviors of O2 / O2·- at the different electrodes in acetone was compared by cyclic voltammetry (CV). The result indicated that not only the reversibility of O2 / O2·- couple but the redox peak currents at the glassy carbon electrode (GCE) were better than that at Au electrode and Pt electrode. The influence of the supporting electrolyte on the electrochemical response of O2 / O2·- was studied, which suggesting that 0.1mol/L n-Bu4NBr was suitable for our experiment. Theone-electron reduction of oxygen was further certified by Chronocoulometry and Rotating ring-disk electrode technique. The kinetic parameters (the electron transfer rate constant, ko and the cathodic transfer coefficient , a) of the reduction of oxygen to superoxide ion (O2 ) were evaluated using normal pulse voltammetry. The obtained values of koand a were as follows: (1.95±0.05)X 104cm ?s'I,0.34±0.01 ? Additionally, the scavenging activities of ascorbic acid , bilirubin were examined, and the experimental results confirmed that ascorbic acid was the better scavenger toward O2 between them.(ii): An acetylene black powder microelectrode (AB-PME) is developed by filling acetylene black powder in the cavity at the tip of a microelectrode. Cyclic voltammetric response of O2 / O2 "shows a nearly reversible redox process at a AB-PME in N, N — dimethylformamide (DMF). And a well-developed steady state current plateau for the electrochemical reduction of oxygen was obtained in this system. The electron transfer number (n) and heterogeneous electron transfer rate constant (ks) were measured by steady-state voltammetric response. The one-electron reduction of the dissolved oxygen in this aprotic media was further examined by using chronocoulometry. In additional, the interaction of O2with pyrogallol was investigated by cyclic voltammetry and the reaction mechanism was discussed in detail.(iii) Multi-wall carbon nanotubes (MWCNTs) are filled in the cavity at the tip of a microelectrode to form a carbon nanotubes powder microelectrode (CNTs-PME). CNTs-PME was used to study electrochemical properties of superoxide ion in aprotic media. The reversibility of the O2 / O2 "couple at the different powder microelectrode in different aprotic media was compared by cyclic voltammetry (CV). The result indicated that the nearly reversible redox process of O2 / C^was obtained at a CNTs-PME. The effect of water on the voltammetric response of the O2 / O2 "couple and reproducibility of the powder microelectrode were also investigated . The heterogeneous electron transfer rate constant (ks) can be measured by steady-state voltammogram and the result is 4.7* 10"3cm ? s"1, suggesting that the electrode reaction is a nearly reversible process as expected. The scavenging activities of bilirubin, a-tocopherol (Vitamin E) are examined, and the experimental results confirm that a-tocopherol is the better scavenger toward O2 between them.(iv) The electrochemical response of the reduction of O2 to O2" at glassy carbon electrode in N, N—dimethylformamide (DMF) was investigated by cyclic voltammetry (CV), the result indicated that it was the quasi-reversible electrochemical process(AEp=200mV). The electrode reaction mechanisms of superoxide ion with hydroquinone, ethyl acetate and benzoic acid were discussed in detail. Based on Nicholson's procedure, the heterogeneous charge transfer rate constant was calculated and the result was (1.33 ± 0.05)xl(T3 cm ? s'1 (n=8, P=0.95, RSD=4.9%)<, The macro scale generation of superoxide ion was carried out by means of controlled potential electrolysis. The UV-spectrum of superoxide ion in DMF was obtained, which exhibited a single absorption band with A max at 273 nm within the range of 190—500nm.(v ) Superoxide ion was generated by the electrochemical reduction of oxygen at a platinum electrode in dimethylsulphoxide (DMSO). Chorocoulometry was employed to examine the one-electron reduction process in this system. The heterogeneous charge transfer rate constant could be obtained by Cyclic voltammetry and the result was (1.07 + 0.06)xl0"3 cm ? s"1 (n=5, P=0.95, RSD=5.2%)c This work was focused on the nucleophilicity and scavenge of electrogenerated-superoxide ion by cyclic voltammetry. The comparative studies on the nucleophilic displacement reactions of superoxide ion with ester (ethyl acetate and diethyl adipate) and alkyl halide (carbon tetrachloride and 1,2—dichloroethane) were carried out. The scavenging activity of ascorbic acid and indole-acetic acid were evaluated and the result allowed the conclusion that the scavenging ability of ascorbic acid was better than that of indole-acetic acid. UV-spectrum of electrogenerated superoxide ion in DMSO was obtained in our work, which certified further that the method of electrogeneration was reliable and superoxide ion was stable in DMSO.
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