Redox mediators benzoquinone

A further possibility is the use of a mediated amperometric biosensor incorporating activated sludge to provide rapid determination of toxicity [79]. The respiratory activity of this biosensor is determined by using the redox mediator p-benzoquinone. 

In all of the examples considered, Ei/2 of the acceptor was much more negative than that of the donor. However, in liquid phase one-electron transfer from a donor to an acceptor can proceed even with an unfavorable difference in the potentials if the system contains a third component, the so-called mediator. The mediator is a substance capable of accepting an electron from a donor and sending it instantly to an acceptor. Julliard and Chanon (1983), Chanon, Rajzmann, and Chanon (1990), and Saveant (1980, 1993) developed redox catalysis largely for use in electrochemistry. As an example, the reaction of ter-achloromethane with /V,/V,/V ,Af-tetramethyl-p-phenylenediamine (TMPDA) can be discussed. The presence of p-benzoquinone (Q) in the system provokes electron transfer (Sosonkin et al. 1983). Because benzoquinone itself and tetrametyl-p-phenylenediamine interact faintly, the effect is evidently a result of redox catalysis. The following schemes reflect this kind of catalysis ... 

Electron mediators are usually organic molecules that are redox active, such as ferrocene derivatives, benzoquinone, N-methylphenazium, and 2,6-dichlorophenolindophenol (DCPIP). Ferricyanide has also been used as an electron mediator. They offer the advantages of non-... 

A way to reduce interferences by cooxi-dizable sample constituents is by keeping the applied electrode potential as low as possible. Therefore, a reaction partner is chosen to be electrochemically indicated that is converted at low potential. For this purpose, the natural electron acceptors of many oxidoreductases have been replaced by redox-active dyes or other reversible electron mediators. Among them are the ferricyanide/ferrocyanide couple, V-methylphenazinium sulfate, fer-rocenes, and benzoquinone. With these mediators an electrode potential around -1-200 mV can be applied, which decreases... 

A significant advance in whole-cell biosensor technology accompanied the development by Rawson et al, [372] of a mediated electrochemical sensor employing a layer of blue-green algae (cyanobacteria). These authors demonstrated that a low molecular mass redox-active mediator, such as Fe(CN)ft or benzoquinone, could accept electrons from the photosynthetic energy chain of a cyanobacterium and relay them, via diffusion, to an electrode. The sensor proved capable of detecting aqueous herbicides on the basis of their inhi-... 

A combination of PQQ derivatives with transition metals leads to form the efficient redox systems. Dropwise addition of terminal olefin to the solution of PdCl2 (0.1 molar equiv.), trimethyl ester of PQQ, (PQQTME, 0.1 molar equiv.) and H2O in DMF under molecular oxygen results in the formation of 2-alkanone (Scheme 3.2). It should be noted that PQQTME constitutes a catalytic redox cycle. The orthoqui-none function appears to reoxidize the reduced palladium species generated in situ. Use of 1,7- or 1,10-phenanthrolinequinone gives a poor result maybe due to the coordination of paUadium(II) species towards the pyridine moiety opposite to the quinone group [5]. Mediation ofp-benzoquinone in the palladium-catalyzed oxidation reactions has been reported to require electrochemical or cobalt porphyrin catalyzed oxidation of the quinol [6-8]. The above-mentioned results provide an example for efficient redox systems of coenzyme derivatives with transition metals, which is demonstrated to be synthetically useful. 

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