Reduction of dioxygen

Porphyrinic co-complexes as novel multinuclear catalysts for the reduction of dioxygen directly to water 97ACR437. 

The mechanism of reduction of dioxygen by fully reduced cytochrome oxidase. Correlation of room and low temperature studies. G. M. Clore, Rev. Inorg. Chem., 1980,2, 343-360 (52). 

Complexes III and IV have Fe-porphyrin prosthetic groups (hemes), complex IV also contains copper atoms which are involved in electron transport. Complexes I, III, and IV use the energy of electron transport to pump protons out of the matrix so as to maintain a pH gradient and an electrical potential difference across the inner membrane required for ATP synthesis (see below and Appendix 3). It is important to remember that all dehydrogenations of metabolic substrates remove two protons as well as two electrons and that a corresponding number of protons are consumed in the final reduction of dioxygen (Figures 5, 6). 

Complex IV consists of 13 peptides, two heme A groups (cytochrome a and a3> and two or three Cu atoms (Table 2). It spans the inner membrane and protrudes into the intermembrane space. Complex IV catalyzes the reduction of dioxygen by oxidized cytochrome c, and four protons derived from the matrix are consumed in the reaction. 

Pahnore GTR, Kim H-H. 1999. Electro-enzymic reduction of dioxygen to water in the cathode compartment of a biofuel cell. J Electroanal Chem 464 110-117. 

Anson FC, Ni CL, Saveant JM. 1985. Electrocatalysis at redox polymer electrodes with separation of the catalytic and charge propagation roles. Reduction of dioxygen to hydrogen peroxide as catalyzed by cobalt(II) tetrakis(4-A-methylpyridyl)porphyrin. J Am Chem Soc 107 3442. 

Buttry DA, Anson FC. 1984. New strategies for electrocatalysis at polymer-coated electrodes. Reduction of dioxygen by cobalt porphyrins immobilized in Nalion coatings on graphite electrodes. J Am Chem Soc 106 59. 

Collman JP, Hendricks NH, Kim K, Bencosme CS. 1987. The role of Lewis acids in promoting the electtocatal3dic four-electron reduction of dioxygen. J Chem Soc Chem Commun 1537. 

Collman JP, Hendricks NH, Leidner CR, Ngameni E, L Her M. 1988. Multilayer activity and implications of hydrogen peroxide in the catal3dic reduction of dioxygen by a dicobalt cofacial bis(porphyrin) (C02FTF4). Inorg Chem 27 387. 

Collman JP, Ennis MS, Offord DA, Chng LL, Griffin JH. 1996. Electrocatal)4ic reduction of dioxygen by diruthenium cofacial diporphyrins axiaUy-bound to a gold-supported, self-assembled monolayer. Inorg Chem 35 1751. 

Durand RR Jr, Bencosme CS, Collman JP, Anson FC. 1983. Mechanistic aspects of the catalytic reduction of dioxygen by cofacial metalloporphyrins. J Am Chem Soc 105 2710. 

Fukuzumi S, Okamoto K, Gros CP, Guilard R. 2004. Mechanism of four-electron reduction of dioxygen to water by ferrocene derivatives in the presence of perchloric acid in benzonitrile, catalyzed by cofacial dicobalt porphyrins. J Am Chem Soc 126 10441. 

Le Mest Y, Inisan C, Laouenan A, L Her M, Talarmin J, El Khalifa M, Saillard J-Y. 1997. Reactivity toward dioxygen of dicobalt face-to-face diporphyrins in aprotic media. Experimental and theoretical aspects. Possible mechanistic implication in the reduction of dioxygen. J Am Chem Soc 119 6095. 

Ni CL, Abdalmuhdi I, Chang CK, Anson FC. 1987. Behavior of four anthracene-linked dimeric metalloporphyrins as electrocatalysts for the reduction of dioxygen. J Phys Chem 91 1158. 

Park GJ, Nakajima S, Osuka A, Kim K. 1995. Electrocatalytic four-electron reduction of dioxygen by 1,2-phenylene-bridged dicobalt diporphyrins. Chem Lett 255. 

Shi C, Mak KW, Chan K-S, Anson EC. 1995. Enhancement by surfactants of the activity and stability of iridium octaethyl porphyrin as an electrocatalyst for the four-electron reduction of dioxygen. J Electioanal Chem 397 321. 

Shigehara K, Anson EC. 1982. Electrocatal3dic activity of three iron porphyrins in the reduction of dioxygen and hydrogen peroxide at graphite cathodes. J Phys Chem 86 2776. 

Wan G-X, Shigehara K, Tsuchida E, Anson EC. 1984. Virtues of a copolymer containing pyr-rolidone and iron porphyrin groups in the catalysis of the reduction of dioxygen at graphite electrodes. J Electroanal Chem 179 239. 

Anson and co-workers have shown that two Co ions were not necessary for four-electron 02 reduction.266 The mew-substituted complex porphyrin Co(TPyP) (42) complex bears four active pyridyl donors which readily react with four equivalents of [Ru(NH3)5(OH2)]2+ to produce the tetra-ruthenated derivative. The four Ru centers are sufficiently remote that their RuIII/n potentials coincide. Under steady state conditions [Co(TPyP)] Ru(NH3)5 4]8+ (43) adsorbed onto a pyrolytic graphite working electrode catalyzes the reduction of dioxygen (Figure 6). 

Electrocatalysis employing Co complexes as catalysts may have the complex in solution, adsorbed onto the electrode surface, or covalently bound to the electrode surface. This is exemplified with some selected examples. Cobalt(I) coordinatively unsaturated complexes of 2,2 -dipyridine promote the electrochemical oxidation of organic halides, the apparent rate constant showing a first order dependence on substrate concentration.1398,1399 Catalytic reduction of dioxygen has been observed on a glassy carbon electrode to which a cobalt(III) macrocycle tetraamine complex has been adsorbed.1400,1401... 

ELECTROCATALYTIC REDUCTION AND ACTIVATION OF DIOXYGEN 9.10.7.1 Electrocatalytic Four-electron Reduction of Dioxygen... 

The four-electron reduction of dioxygen in water (Equation (70)) is an essential reaction carried out by aerobic organisms during the energy production cycle in the mitochondria. 

How does nature prevent the release of hydrogen peroxide during the cytochrome oxidase-mediated four-electron reduction of dioxygen It would appear that cytochrome oxidase behaves in the same manner as other heme proteins which utilize hydrogen peroxide, such as catalase and peroxidase (vide infra), in that once a ferric peroxide complex is formed the oxygen-oxygen bond is broken with the release of water and the formation of an oxo iron(IV) complex which is subsequently reduced to the ferrous aquo state (12). Indeed, this same sequence of events accounts for the means by which oxygen is activated by cytochromes P-450. 

D. Dolphin Collman and Anson have found with their five-atom bridged amide systems that the reduction of dioxygen is partitioned roughly one third undergoing a four-electron reduction to water and the rest a two-electron reduction to peroxide. We see the same result indeed the 5-5 systems of ours and that of Collman-Anson are indistinguishable. Neither type of cofacial dimers with chains greater than five show any four-electron reduction. 

In a subsequent study of this type (Durand, Bencosme, Collman Anson, 1983), dimers of type (143) were investigated as potential redox catalysts for the four-electron reduction of dioxygen to water (via peroxide). The Co(ii)/Co(ii) dimer is an effective catalyst for the electrochemical reduction of dioxygen once again the dioxygen binds... 

Cytochrome c oxidase. Cytochrome c oxidase is an enzyme that occurs in the inner mitochondrial membrane and, as we have seen, catalyzes the four-electron reduction of dioxygen to water as the final reaction in the... 

It is extremely important that the interaction of quinones with XO (Reaction (3)) is reversible that can lead to receiving erroneous results at the measurement of superoxide production by SOD-inhibitable cytochrome c reduction [28,29] (see also Chapter 27). Lusthof et al. [30] demonstrated that 2,5-bis(l-aziridinyl)-l,4-benzoquinones are directly reduced by XO. Interestingly at quinone concentrations greater than 25pmol I 1, quinones entirely suppressed one-electron reduction of dioxygen, and cytochrome c was completely reduced by the semiquinones formed. It is well known that cytochrome c and lucigenin are effective superoxide scavengers and due to that, these compounds are widely used in the quantitative assays of superoxide detection. Nonetheless, under certain experimental conditions they can be directly reduced by XO [31]. 

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