Oxygen/dioxygen reduction/reaction

Instead of the dioxygen-reductant pair, one can employ oxo componds containing an oxygen atom which is already partly reduced H2O2 [68], ROOH [69], PhIO [70], NaOCl [71], KHSO. [72], amine Af-oxides [73], and magnesium monoperoxyphtalate [74] (see also Chapter X). One of the most efficient (in terms of reaction rate and turnover number) systems is the combination of ruthenium porphyrin and 2,6-dichloropyridine A-oxide [73]. A simplified mechanism of alkane oxidation with iodosylbenzene catalyzed by iron porphyrinate is demonstrated in Scheme XI. 17. 

Any of these ROS could oxidize an organic substrate with the net insertion of an oxygen atom. In each case, reductive reactions are required for activation of dioxygen to one of the ROS from electrons supplied by NADPH. The generation of a carbon-... 

The oxidized catalytic site of cytochrome oxidase composed of cytochrome <23 and Cub is reduced via the bridge mechanism by two electrons supplied from the electron reservoir of the respiratory chain to form a reduced complex, which then binds an oxygen molecule. The reaction center is oxidized to the initial state in a 2-electron reaction with the formation of a peroxide bridge between <23 and Cub. The partially reduced (to peroxide) oxygen molecule must be bound in the reaction center since cytochrome oxidase is known to reduce dioxygen to water without the release of any intermediates from the membrane. After that, the catalytic complex accepts two electrons in turn from the electron reservoir Fe(c) a3. At the next step, the peroxide bridge undergoes 1 1-electron reduction and protonation to water. 

Shi Z, Zhang J. Density functional theory study of transitional metal macrocyclic complexes dioxygen-binding abilities and their catalytic activities toward oxygen reduction reaction. J Phys Chem C 2007 111 7084-90. 

As in the above section, the reader is referred to Part III where details of the biologically oriented reactions of dioxygen are described. Several reviews - have been published relating to the inorganic and bio-inorganic aspects of oxygenation and redox reactions. Recent studies indicate that the primary electron-transfer step for the reduction of O2 is a one-electron process which is followed under acidic conditions by chemical disproportionation to yield HgOa (an overall 2e process) and under basic conditions by production of OH (a 4e process overall). The primary reaction reduction potential is —0.33 V and is independent of pH. 

Finally, why are oxgyen reactions, such as dioxygen reduction or hydrocarbon oxidation, slow compared with hydrogen reactions for materials at the top of the volcano relation. This is clear from Figure 4. Oxygen intermediates... 

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