Redox recycling

Radical ions, 33, 44 Raman spectroelectrochemistry, 45 Randles-Sevcik equation, 31 Rate constant, 12, 18 Rate determining step, 4, 14 Reaction mechanism, 33, 36, 113 Reaction pathway, 4, 33 Reaction rate, 12 Receptor-based sensors, 186 Redox recycling, 135... 

Closely spaced band electrodes (pairs or triples), with each electrode within the diffusion layer of the other, can be used for studying reactions, in a manner analogous to ring-disk generation-collection and redox recycling experiments (131,132). Unlike with rotating ring-disk electrodes, the product of the reaction at the collector electrode can diffuse back across the narrow gap to the... 

The discovery of non-specific disulfide reductases which are labile in aerobic cellular extracts suggests that kinetic constraints of thiol/disulfide exchange in vivo are very complex. One of such proteins is thioredoxin which behaves as a non-specific protein-disulfide reductase. Thioredoxin also works as a cofactor of sulfoxide reductases. The dithiol active site of thioredoxin sits on a protrusion of the protein surface [274], Thioredoxin is an ubiquitous protein whose molecular weight is about 12 KDa [274,275], It has been found in cytosolic and mitochondrial [276] compartments of animal cells, and it is partly bound to membranes. High contents in thioredoxin have been found in neurons, secretory and epithelial cells. Redox recycling of thioredoxin is insured by thioredoxin reductase, which has been identified in a variety of mammalian cells as a symmetrical dimer with a molecular weight of 116KDa[274]. Thioredoxin reductase is NADPH-specific, but it exhibits a very wide disulfide substrate specificity. 

The last type of redox recycling is substrate recycling rather than true redox recycling. Two enzymes are used, with the product of the first enzyme reaction serving as substrate for the second enzyme. In turn, the product of the second reaction acts as the substrate for the first enzyme. Both the degradation of a co-substrate and the production of a product like hydrogen peroxide can be quantified electrochemically. This concept can be applied to other electrochemical transducers, such as ion selective electrodes, because label conversion is not accomplished with the electrode. Amplification factors of 3-48,000 were reported by Scheller and colleagues [55-58] for ampero-metric multienzyme electrodes with the appropriate substrates. 

FIG. 3 Scheme of redox recycling in the feedback mode enabling very high rates of mass transport at small distances. 

Figure 5.11 Ascorbate redox recycling contribution to oxidasejhydrolase activity...

Polyaniline has always been at the forefront of interdisciplinary research on account of its unique reversible prototropic dopability, excellent redox recyclability, chemical and environmental stabiUty, low cost and easy preparation [68], However, the intractable insolubility of polyaniline in common organic solvents is the most significant factor hampering commercial use. As a backbone modification of polyaniline, polymer 22 was synthesized by chemical polymerization of p-selenienylaniline with FeCb [69]. The polymer was soluble in THF, DMF, NMP and DMSO and exhibited a reversible prototropic doping process. Upon doping with iodine, the pellet powder sample showed a low conductivity of 8.0 x 10 S cm . ... 

Odijk M, Olthiris W, Dam VAT, van den Betg A (2008) Simulation of redox-recycling phenomena at interdigitated array (IDA) electrodes ampUflcation and selectivity. Electroanalysis 20 463 68... 

A novel wall-jet cell with parallel dual cylinder (PDC) microelectrodes was constructed and used for FIA [7]. The detector takes advantage of redox recycling between... 

Frequency analysis of NP collisions is not simple because the shape and frequency of the current transients are affected not only by the NPs but also by the material and nature of the surface of the measuring electrode. For example, the current transient frequency of citrate-stabilized IrO NPs differed by the electrode material current transients for IrO, NP collisions were frequent on bare An, rare on bare Pt, and not observed at all on carbon liber UMEs. The electrocatalytic redox recycling behavior also depends strongly on the electrode material. The current spikes are sensitive to the electrode surface, and we find that the current transient behavior can be modified with different surface treatments, for example, by immersing the Pt UME in a 10 mM aqueous NaBH4 solution for 5 min. The influence of the electrode surface properties on NP behavior is still not well understood, but the single NP collision detection techniques described here can be useful tools to study such phenomena. 

---