Redox system reduction mechanism

Redox systems, organic, with multiple electrophores, electron storage and transfer in, 28, 1 Reduction.of C—X and X—X bonds (X = 0, S), kinetics and mechanism of the dissociative, 36, 85... 

Again it seems not necessary to discuss the considerations of the chemical versus electrochemical reaction mechanism. It is clear from the extremely negative standard potential of silicon, from Eqs. (2) and (6), that the Si electrode is in all aqueous solutions a dual redox system, characterized by its OCP, which is the resultant of an anodic Si dissolution current and a simultaneous reduction of oxidizing species in solution. The oxidation of silicon gives four electrons that are consumed in the reduction reaction. Experimental results show clearly that the steady value of the OCP is narrowly dependent on the redox potential of the solution components. In solutions containing only HF, alternatively alkaline species, the oxidizing component is simply the proton H+ or the H2O molecule respectively. 

Malmslrom, B. G. The mechanism of dioxygen reduction in cytochrome c oxidase and laccase. In Oxidases and Related Redox Systems (King, T. E., Mason, H. S., Morrison, M., eds.), Oxford-New York, Pergamon Press, 1981... 

Organic Systems. The photooxidation and reduction reactions for most organic compounds require two electron processes and are generally irreversible. However, several phenothiazine dyes, such as Thionine and Methylene Blue, function as reversible two electron redox systems. The reversible photobleaching of chlorophyll may also involve a one or two electron process although the exact mechanism is still in doubt. One electron redox processes for organic molecules are possible... 

The redox system does not depend on endosomal acidification but needs TfR. Fe2Tf first binds to TfR which is located in close proximity to the proton-and electron-pumping NADHiTf oxidoreductase. The Fe—Tf bond is destabilized by proton efflux, making Fe3+ susceptible to reduction. Fe2+ is trapped by a plasma membrane binder and can be transported by a translocator [4]. As Al is a simple trivalent cation incapable of redox changes, it may be theoretically impossible that Al bound to Tf is taken up by a redox mechanism. Actually, no reports on a redox-mediated process of Al bound to Tf have been made. 

Proton-coupled electron transfer is a prominent theme in biological redox systems. There are three basic mechanisms for these processes (Figure 18). In the first mechanism (path A), electron transfer occurs prior to proton transfer. This mechanism is commonly observed for the electrochemical reduction and oxidation of quinones and flavins in protic media [52], In this interfacial environment, proton transfer is manifested as an ECE (E represents an electron transfer at the electrode surface and C represents a homogeneous chemical reaction) two-electron reduction of these systems to their fully reduced states (Figure 19). As electron transfer occurs prior to the proton transfer event, proton transfer does not affect either the redox potential or the electron transfer rate to or from the cofactor. 

When a mixture of tetrachloromethane and benzaldehyde in DMF was treated, at room temperature, with a catalytic amount of lead(ll) bromide and a shght excess of aluminum as a stoichiometric reductant the coupled product was obtained in good yield (Scheme 13.69) [86]. Subsequent reductive 1,2-elimination of trichloromethyl carbinol by means of the Pb/Al bimetal system could be readily achieved by changing the reaction media. The mechanism of the Pb/Al bimetal redox system presumably involves lead(O) reduction of polyhalomethane to provide an organolead complex which then reacts wifh an aldehyde to give the couphng product. Regenerahon of lead(O) by reduchon of lead(ll) with aluminum metal would complete the catalyhc cycle. 

All of these considerations of O2 reduction mechanisms suggest that the four-electron reduction of O2, with its very favorable potential, overestimates the oxidative power of O2 in chemical systems. This should be kept in mind in the following discussions of redox reactions if O2 is the oxidant. 

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