Electron relay, redox reaction between

Actually, one of the most important applications of metal nanoparticles is in the field of catalysis. Catalysts should offer large specific area in order to accelerate the access of reactants to the active sites. Nanoparticles, such as those synthesized by radiolysis, are thus particularly efficient in a number of reactions. However, catalyzed reactions are controlled not only by the kinetics, but also by the thermodynamics. Thus, due to their redox properties, nanoparticles with small sizes and low polydispersities are able to play a role as intermediate electron relays in an overall electron transfer between a donor and an acceptor. 

Although conducting polymers have demonstrated direct electrochemical communication with nitrate reductases, the incorporation of electron relay groups within the polymer matrix provides a more efficient pathway for electron hopping between the enzyme and the electrode surface. Several artificial electron donors can shuttle electrons to the oxidized form of nitrate reductase with methyl viologen being the best choice due to its very negative redox potential [214-216]. The electron transfer reactions can be represented as follows ... 

The redox properties of Ru(bipy)5 " (ground state and excited state) have been taken advantage of Ru(bipy)3 is able to transfer an electron to a relay (MV, or a rhodium(III) complex or another electron acceptor) whose reduced form reacts with water to yield hydrogen the latter reaction might be accelerated by the presence of a heterogeneous redox catalyst. The ruthenium(II) complex is regenerated in the reaction between Ru(bipy) " and an electron donor D. This compound D is irreversibly converted to an oxidation product. An ideal system would, of course, use H2O as electron donor, with formation of O2. This remains to be done, but model systems for H2O oxidation have also been proposed [20] ... 

Other examples of electron transfer reactions in surfactant assemblies are those between pyrene and dimethylaniline in micelles, between viologen derivative and zinc porphyrin as an electron relay, and between chlorophyll a and methylviologen in microemulsions the photoinduced reduction of duroquinone by zinc porphyrin in micellar solution the photoinduced redox reaction of proflavine in aqueous and micellar solutions retardation of back reactions in micellar systems light-driven electron transfer from tetrathiafulvalene to porphyrin and tris a, a -bipyridine)... 

A direct electron transfer from entrapped quinohemoprotein alcohol dehydrogenase (QH-ADH) to a Pt electrode, via chains of the polypyrrole, acting as immobilization matrix, was demonstrated [152]. QH-ADH is able to translocate in a fast inner-enzymatic reaction, the electrons primarily accepted by PQQ to heme units located close to the outer protein shell, from where they can be transferred on the conducting-polymer chains (Fig. 13). A similarity between the electron-transfer pathway in multicofactor proteins and that of mediator-modified electroenzymes is apparent, if one considers that a multicofactor enzyme can be regarded as a combination of a primary redox site and protein-integrated electron-transfer relays. 

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