Superoxide, electrochemistry

AlNashef IM, Leonard ML, Matthews MA, Weidner JW (2002) Superoxide electrochemistry in an ionic liquid. Ind Eng Chem Res 41 4475 478... 

D.T. Sawyer and J.L. Roberts, Electrochemistry of oxygen and superoxide ion in dimethyl sulfoxide at platinum, gold, and mercury electrodes. J. Electroanal. Chem. 12, 90-101 (1966). 

R.N. Iyer and W.E. Schmidt, Observations on the direct electrochemistry of bovine copper-zinc superoxide dismutase. Bioelectrochem. Bioenerg. 27, 393 104 (1992). 

Y. Tian, L. Mao, T. Okajima, and T. Ohsaka, Electrochemistry and electrocatalytic activities of superoxide dismutases at gold electrodes modified with a self-assembled monolayer. Anal. Chem. 76, 4162-4168 (2004). 

I 76 Electrochemistry of the Group 7 Elements Manganese, Technetium, and Rhenium Tab. 6 Redox potentials of manganese superoxide dismutase... 

Cathodic reduction of oxygen is the most convenient method of production of the superoxide radical-anion,. The properties of this important species have been well reviewed and key references to the extensive work on the electrochemistry of oxygen are contained therein. Of immediate significance is the large cathodic shift in E° for the 0 /0 couple which accompanies a change from aqueous to aprotic solvent (e.g. DMF, DMSO, and MeCN) this is interpreted in terms of relatively weak solvation in aprotic media which enhances the nucleophilicity of the superoxide anion. However, in the presence of acids the chemistry of superoxide is dominated by the disproportionation shown in equation 1. 

As a first example of the use of reaction mechanism graphs, consider the electrochemistry of molten carbonate fuel cell (MCFC) cathodes. These cathodes are typically nickel-oxide porous electrodes with pores partially filled with a molten carbonate electrolyte. Oxygen and carbon dioxide are fed into the cathode through the vacant portions of the pores. The overall cathodic reaction is 02 + 2C02 + 4e / 2C03=. This overall reaction can be achieved through a number of reaction mechanisms two such mechanisms are the peroxide mechanism and the superoxide-peroxide mechanism, and these are considered next. 

This represents electrodeless electrochemistry, whereby the only process is electron transfer and the only product is the one-electron adduct of 02, the superoxide ion (02). Through the use of redox mediator dyes and spectrophotometry, the electron-transfer thermodynamic reduction potential for 02 has been evaluated ... 

Several applications of electrochemistry to medical and biological matters were presented. For example, the possibility that Oj (a superoxide ), which is an intermediate in some mechanisms of the reduction of oxygen, could cause degenerative diseases by adsorbing on cell surfaces and decomposing DNA was examined. The idea was turned down, but a related one emphasized Oj can combine with protons and other radicals, and these (e.g., peroxy radicals) are very reactive and may indeed cause trouble. 

An interesting aspect of csdochrome c electrochemistry is the possibility to couple it with other redox reactions such as enzymes [25,26,43] or short-lived species [25,147]. Analytical apphcation of this bioelectrochemical process has been reported for the determination of superoxide anion, hydrogen peroxide and antioxidants (see below). 

CJ McNeil, KA Smith, P Bellavite, JV Bannister. Application of the electrochemistry of cytochrome-c to the measurement of superoxide radical production. Free Radical Res Commun 7 89-96, 1989. 

Zhang C, Fan FRF, Bard AJ. Electrochemistry of oxygen in concentrated NaOH solutions solubility, diffusion coefficients, and superoxide formation. JAm Chem Soc 2009 131(1) 177-81. 

The first reported work on the electrochemistry of the ORR in quaternary ammonium-based ionic liquids was in 2003 by Buzzeo et al. [19] who aimed to clarify the asymmetry observed in the cyclic voltammograms corresponding to the O2/O2" redox couple for some ionic liquids. The diffusion coefficients of oxygen and the electrogenerated superoxide anion (02 ) in [N2226][N(Tf)2] (Scheme 18.5) were determined by chronoamperometric measurements at 20 °C and, interestingly, were found to differ by a factor of over 30 (e.g. = 1.48 x 10 m s , Dq ... 

Thus, it seems at that time that the electrochemistry of oxygen in quaternary phosphonium ILs is not straightforward, given the number of species involved and the unknown nature of those species. On the contrary, a few years later the generation of a stable superoxide was reported by Hayyan et al. [24] in [P666i4][N(Tf)2]. 

After the first steps in the area of electrochemistry towards the end of nineteenth century, the beginning of twentieth century brought increased activity of Czech chemists. The mysterious electrolytic silver superoxide still attracted attention of V. Novak, O. Sulc, J. Baborovsky (1875-1946) (Fig. 3.1.2), and B. Kuzma (1873-1943) [4, 5]. Experiments to determine the voltage of anodic decomposition of sodium hydroxide were carried out by F. Plzak (1877-1944). The papers on the abovementioned topics were published in Czech or in German. 

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