Dioxygen reduction chemistry

Interpreting these results on a detailed molecular basis is difficult because we have at present no direct structural data proving the nature of the split Co(IIl/lI) voltammetry (which seems critical to the electrocatalytic efficacy). Experiments on the dissolved monomeric porphyrin, in CH-C solvent, reveal a strong tendency for association, especially for the tetra(o-aminophenyl)porphyrin. From this observation, we have speculated (3) that the split Co(III/II) wave may represent reactivity of non-associated (dimer ) and associated forms of the cobalt tetra(o-aminophenyl)porphyrins, and that these states play different roles in the dioxygen reduction chemistry. That dimeric cobalt porphyrins in particular can yield more efficient four electron dioxygen reduction pathways is well known (24). Our results suggest that efforts to incorporate more structurally well defined dimeric porphyrins into polymer films may be a worthwhile line of future research. 

Vasudevan P, Santosh, Mann N, Tyagi S. 1990. Transition metal complexes of porphyrins and phthalocyanines as electiocatalysts for dioxygen reduction. Transition Metal Chemistry, 15, 81-90. 

The reduced form of RNR reacts with dioxygen to generate the p-oxo diferric core (crystallographically defined (3)) and a tyrosyl radical necessary for the production of a reactive species responsible for the reduction of ribonucleotides. The intimate details of this dioxygen-based chemistry and the structure of the reduced enzyme are still unknown. Despite intensive spectroscopic characterization of the active site of MMO and the recent X-ray structural analysis of the hydroxylase component (4), even less is known concerning its mechanistic pathways responsible for the conversion of methane and other alkanes to their corresponding oxygenated products. 

Appleby, A.J. (1993) Electrocatalysis of aqueous dioxygen reduction. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 357,117-179. 

Estabrook, R.W., Hildebrandt, A.G., Baron, J., Netter, K.J. and Leibman, K. (1971) A new spectral intermediate associated with cytochrome P-450 function in liver microsomes. Biochemical and Biophysical Research Communications, 42 (1), 132-139. Pompon, D. and Coon, M.J. (1984) On the mechanism of action of cytochrome P-450. Oxidation and reduction of the ferrous dioxygen complex of liver microsomal cytochrome P-450 by cytochrome b5. Journal of Biological Chemistry, 259 (24), 15377-15385. Hildebrandt, A. and Estabrook, R.W. (1971) Evidence for the participation of cytochrome b 5 in hepatic microsomal mixed-function oxidation reactions. Archives of Biochemistry and Biophysics, 143 (1), 66-79. 

Hill, H. A. O. The chemistry of dioxygen and its reduction products. In Oxygen Free Radicals and Tissue Damage. Ciba Found. Symp. 65. Amsterdam-Oxford-New York Excerpta Medica, 1979, pp. 5-17... 

The main application of dioxygen electrochemistry has been and continues to be in the realm of analytical chemistry. The preceding sections of this chapter provide ample evidence that for carefully controlled conditions the current (i ) for the reduction of 02 is directly proportional to its concentration [which is directly proportional to its partial pressure (P )] ... 

The redox chemistry of dioxygen and its reduction products is heavily dependent on mechanistic pathway, substrate, and solution acidity. For those circumstances that are limited by direct electron transfer, the redox mechanisms... 

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