Redox reactions mediators

Nevertheless, there is good evidence that in all purely bluelight sensitive organisms, the photoreceptor is a flavin (flavoprotein) (Table 2), which appears to be bound to membranes (plasmalemma) in a highly dichroic manner. The mechanism of sensory transduction is probably correlated with light-induced redox reactions mediated by a flavin. This observation is consistent with the fact that nearly all physiolog-... 

Field JA, Cervantes FJ (2005) Microbial redox reactions mediated by humus and structurally related quinones. In Perminova IV, Hatfield K, Hertkom N (eds) Use of humic substances to remediate polluted environments from theory to practice, vol 52. Springer, Dordrecht, pp 343-352... 

Figure 4.3 Free energy changes in redox reactions mediated by microbes, (a) Oxidation of reduced inorganic compounds linked to reduction of O2. (b) Oxidation of organic matter CH2O linked to reduction of various organic and inorganic oxidants. pH = 7 and unit oxidant and reductant activities except (Mn +) = 0.2mM and (Fe +) = ImM...

Table 1 Examples of Redox Reactions Mediated by Nicotinamide-dependent Enzymes...

Unanticipated developments help to put known facts into place. Results from biochemistry drove home to organic chemists the message that it was not a chemical rarity for carbon-hydrogen bonds to be sources of hydride equivalents. Westheimer, Vennesland et al. established beyond doubt that in a redox reaction mediated by the coenzyme couple NAD(P)+/NAD(P)H the carbon-hydrogen bond of ethanol could serve directly as a hydride donor to an electron-deficient carbon of a pyridinium ion, and that this hydride equivalent could in turn be donated directly to the electropositive carbon of a carbonyl group. Thus the hydride donor capacities of carbon are also part and parcel of life. All this can occur under physiological conditions with the help of an enzyme, which somehow activates these reactants. The sequence is illustrated schematically in equation (1). In either direction hydride is transferred from carbon to carbon. 

Strong evidence exists for electron hopping in photoinduced transmembrane redox reactions mediated by Ceo and C70 fullerenes across planar bilayer membranes... 

Table 4 Reductive defluorination by intramolecular redox reaction mediated by NHCs ...

S.3.3 Electrocatalytic Modified Electrodes Often the desired redox reaction at the bare electrode involves slow electron-transfer kinetics and therefore occurs at an appreciable rate only at potentials substantially higher than its thermodynamic redox potential. Such reactions can be catalyzed by attaching to the surface a suitable electron transfer mediator (45,46). Knowledge of homogeneous solution kinetics is often used to select the surface-bound catalyst. The function of the mediator is to facilitate the charge transfer between the analyte and the electrode. In most cases the mediated reaction sequence (e.g., for a reduction process) can be described by... 

There has therefore been much interest in the mediation of redox reactions in solution by conducting polymer-modified electrodes. 

Mediation, and redox reactions in solution, 585 Medical dosage, 371 Mercury... 

Table 2. Analytical scale mediated redox reactions with participation of a significant layer of polymer...

In view of the extensive and fruitful results described above, redox reactions of small ring compounds provide a variety of versatile synthetic methods. In particular, transition metal-induced redox reactions play an important role in this area. Transition metal intermediates such as metallacycles, carbene complexes, 71-allyl complexes, transition metal enolates are involved, allowing further transformations, for example, insertion of olefins and carbon monoxide. Two-electron- and one-electron-mediated transformations are complementary to each other although the latter radical reactions have been less thoroughly investigated. 

In redox mediation, to have an effective electron exchange, the thermodynamic redox potentials of the enzyme and the mediator have to be accurately matched. For biocatalytic electrodes, efficient mediators must have redox potentials downhill from the redox potential of the enzyme a 50 mV difference is proposed to be optimal [1, 18]. The tuning of these potentials is a compromise between the need to have a high cell voltage and a high catalytic current. Furthermore, an obvious requirement is that the mediator must be stable in the reduced and oxidized states. Finally, for operation of a membraneless miniaturized biocatalytic fuel cell, the mediators for both the anode and the cathode must be immobilized to prevent power dissipation by solution redox reactions between them. 

During the last two decades, more studies have been conducted to explore the catalytic effects of different redox mediators on the bio-transformation processes. Redox mediators, also referred to as electron shuttles, have been shown to play an important role not only as final electron acceptor for many recalcitrant organic compounds, but also facilitating electron transfer from an electron donor to an electron acceptor, for example, azo dyes [8, 11, 12], Redox mediators accelerate reactions by lowering the activation energy of the total reaction, and are organic molecules that can reversibly be oxidized and reduced, thereby conferring the capacity to serve as an electron carrier in multiple redox reactions. 

Mediation of Redox Reactions of Organic Substances by the Hydrous Ferric Oxide Surface and Fe(II)-Surfaces... 

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