Dioxygen reduction reaction

In addition to the mechanism of dioxygen reduction, an understanding of how Cco pumps protons is also desirable. Models have been proposed that allow for linkage of the proton pumping to the dioxygen reduction reaction (50). One attractive model involves the CuA site and is shown in Figure 6 (10). In this mechanism, the CuA center is ligated to two histidines and two thiolates and receives the initial electron from... 

Enthalpies, Entropies, and Gibb s Energies of the Oxidation-Reduction Reactions of the Transition Metal Ions with Dioxygen in Aqueous Solution (T = 298 K) [23]... 

In earlier studies [5,6] superoxide detection in mitochondria was equated to hydrogen peroxide formation. However, while it is quite possible that superoxide is a stoichiometric precursor of mitochondrial hydrogen peroxide, it is understandable that the level of hydrogen peroxide may be decreased due to the reactions with various mitochondrial oxidants. Moreover, superoxide level can be underestimated due to the reaction with mitochondrial MnSOD. Several authors [7,8] assumed that mitochondrial superoxide production may be estimated through cyanide-resistant respiration, which supposedly characterizes univalent dioxygen reduction. This method was applied for the measurement of superoxide production under in vitro normoxic and hyperoxic conditions, in spite of the finding [7] that cyanide-resistant respiration reflects also the oxidation of various substrates (lipids, amino acids, and nucleotides). Earlier,... 

The standard potential of the 02/02 pair is equal to -0.15 V in water and -0.60 V in DMF. Usually, dioxygen easily captures two electrons in the stepwise reaction O2 + e —> O2 , then O2 + e 02 . In DMSO, dioxygen reductions into the superoxide ion and then into the dioxygen dianion are characterized by Ey2 = -0.5 V and Ey = -1.5 V in regard to the saturated calomel electrode (Sawyer and Gibian 1979). The superoxide ion occupies an intermediate position in the following redox triad O2 —> 02 —> In accordance with such a position, the superoxide ion... 

The molecule is very stable and can be sublimed [i]. Numerous metal phthalocyanines can reversibly bind molecules like, e.g., dioxygen at the metal ion. This can result in activation of internal bonds and subsequent facilitation of chemical reaction, in this case of dioxygen -> electroreduction. Thus these molecules have attracted attention as catalysts for various reactions, in particular dioxygen reduction in, e.g., fuel cells [ii], in general -> electrocatalysis [iii] and in -> sensors [iv]. Their strong coloration, which can be modified electrochemically by reduction/oxidation, suggests use in -> electrochromic devices [v]. 

The value [H202](ss) = 1.2 10 4 M measured in air-saturated solutions ([02](ss) = 2.4 10 4 M) suggests that Reaction 7 is about twice as efficient as the initial dioxygen reduction. 

Cytochrome c is the sole physiological source of electrons for dioxygen reduction at cytochrome c oxidase 11). It is crucial to a discussion of the mechanism of dioxygen reduction to know whether the binding of cytochrome c to the oxidase is to a single site or to more than one site. This will determine whether the reduction reaction can occur symmetrically (e.g., two sites) or asymmetrically (one site). 

Herrmann and co-workers showed that the 17-electron complex 62 may be subjected to electrochemical oxidation as well as reduction (54.55). The redox potentials of the respective halo complexes follow the expected trend for change in the halide ligands. In accordance with these electrochemical studies, both chemical oxidation and reduction reactions of 62 were found [Eqs. (49) and (50)]. Oxidation of the rhenium complex Re(CCMe3)(// -C5Me5)Cl2 by dioxygen results in cleavage of the neopentylidyne ligand from the metal center as pivalic anhydride and pivaloyl chloride. 

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