Quinones electrochemistry

The quinone electrochemistry story becomes even more complex, and the role of adsorption and solution chemical reactions are still being actively investigated this topic has been reviewed by Chambers. ... 

Polypyrrole shows catalytic activity for the oxidation of ascorbic acid,221,222 catechols,221 and the quinone-hydroquinone couple 223 Polyaniline is active for the quinone-hydroquinone and Fe3+/Fe2+ couples,224,225 oxidation of hydrazine226 and formic acid,227 and reduction of nitric acid228 Poly(p-phenylene) is active for the oxidation of reduced nicotinamide adenine dinucleotide (NADH), catechol, ascorbic acid, acetaminophen, and p-aminophenol.229 Poly(3-methylthiophene) catalyzes the electrochemistry of a large number of neurotransmitters.230... 

Skibo, E. B. Gilchrist, J. H. Synthesis and electrochemistry of pyrimidoquinazoline-5,10-diones. design of hydrolytically stable high potential quinones and new reductive alkylation systems. J. Org. Chem. 1988, 53, 4209 -218. 

The characterization of the semiquinone radical anion species of PQQ in aprotic solvents was undertaken to provide information about the electrochemistry of coenzyme PQQ and to give valuable insight into the redox function of this coenzyme in living systems <1998JA7271>. The trimethyl ester of PQQ and its 1-methylated derivative were examined in aprotic organic solvents by cyclic voltammetry, electron spin resonance (ESR), and thin-layer UV-Vis techniques. The polar solvent CH3CN was found to effectively solvate the radical anion species at the quinone moiety, where the spin is more localized, whereas the spin is delocalized into the whole molecule in the nonpolar solvent CH2CI2. 

The electrochemistry of quinones is surprisingly similar to that of dioxygen. It is as if a conjugated carbon link is inserted between two oxygen atoms ... 

The azo function [e.g., azobenzene (PhN=NPh)] is reduced in a manner that is similar to that for quinones (discussed above). The electrochemistry for azo groups is a part of the discussion of the nitrogen compounds in Chapter 11 (Figure 11.10 illustrates the cyclic voltammogram for azobenzene). 

Reaction 5.1 is meant to represent a nonspecific electrostatic interaction (presumably responsible for double-layer charge accumulation) Reaction 5.2 symbolizes specific adsorption (e.g., ion/dipole interaction) Reaction 5.3 represents electron transfer across the double layer. Together, these three reactions in fact symbolize the entire field of carbon electrochemistry electric double layer (EDL) formation (see Section 5.3.3), electrosorption (see Section 5.3.4), and oxidation/reduction processes (see Section 5.3.5). The authors did not discuss what exactly >C, represents, and they did not attempt to clarify how and why, for example, the quinone surface groups (represented by >CxO) sometimes engage in proton transfer only and other times in electron transfer as well. In this chapter, the available literature is scrutinized and the current state of knowledge on carbon surface (electrochemistry is assessed in search of answers to such questions. 

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Dimmel, D. R., Perry, L. F., Palasz, P. D., and Chum, H. L., Electron-transfer reactions in pulping systems. 2. Electrochemistry of anthraquinone lignin model quinone methides. J Wood Chem Technol 1985, 5 (1), 15-36. 

Redox catalysis is the catalysis of redox reactions and constitutes a broad area of chemistry embracing biochemistry (cytochromes, iron-sulfur proteins, copper proteins, flavodoxins and quinones), photochemical processes (energy conversion), electrochemistry (modified electrodes, organic synthesis) and chemical processes (Wacker-type reactions). It has been reviewed altogether relatively recently [2]. We will essentially review here the redox catalysis by electron reservoir complexes and give a few examples of the use of ferrocenium derivatives. 

Adsorbed from solutions of 10-25% electroactive component compared with total adsorbate where no diluent is indicated, none was used. Electron-transfer rates were determined by electrochemistry (CV, chronoamperometry or ACIS) using aqueous electrolyte except where noted in parentheses. Fc = ferrocenyl pyr = pyridyl azo = azobenzenyl Q = quinone Converted to per CH2 using 1.27 A per (sp- C)-(sp- C) bond [114]. 

The electrochemistry of both NAD+ and NADH at clean electrodes occurs at high overvoltages (of the order of 1V) and hence causes imwanted side reactions, which tend to foul the electrode [142-144]. One way around this problem is to use mediators (two electron-proton acceptor/donors) such as o-quinone [145-147] or p-phenylenediamine derivatives [148], arylnitro derivative such as 2-nitro-9-fluorenone [149], PQQ with Ca " [150] and polyaromatic dye molecules, i.e., phenazine, phenoxazine and phenothiazine derivatives [11] that substantially lower the voltage for needed NADH oxidation. 

The first mechanism is often found in the electrochemical reduction and oxidation of quinones and flavins in aprotic media.Using cyclic voltammetry (CV) and simultaneous electrochemistry and electron paramagnetic resonance (SEEPR),... 

The formation of carbon surface oxides, phenols, quinones, lactones, and car-boxyhc acids upon the electrooxidation of carbon has been detected by physical methods such as infrared spectroscopy [262], ellipsometry [263], x-ray photoelectron spectroscopy [262,264,265], thermal desorption, and electrochemistry (see refs. [8, 96, 248, and 261] and references therein). Cyclic voltammograms of oxidized carbons exhibit increased charge in the potential interval from 0.4 to... 

An attempt to follow by direct electrochemistry the red-ox reactions involving the cofk tors of the RC embedded in lipid films on pyrolytic graphite electrodes has been recendy carried out, allovdng the evaluation of the peaks relative to quinones and the primary donor. Direct electrochemistry of cofactors was also realized for RC in a lipid film on graphite and ITO or sandvdched between polycation layers on gold, permitting the determination of their midpoint potentials by cyclic and square wave voltammetry. In this case evidence of the presence of peaks relative to the bacteriopheophytin was reported for the first time. ... 

C6IT4O2) A yellow crystalline organic compound with a pungent odor. Its molecules contain a non-aromatic six-carbon ring and it behaves as an unsaturated diketone with conjugated double bonds. It is used in making dyestuffs. A platinum electrode in an equimolar solution of quinone and hydroquinone (benzene-l,4-diol, CgH4(OH)2) is used as a standard electrode in electrochemistry. The reaction is ... 

The electrochemistry and biological redox behavior of members of four classes. of compounds will be considered. These are catecholamines, phenothiazines, biological quinones, and purines. 

The relationship between the electrochemistry of tocopherols and toco-pherylquinones and their biological redox reactions is not as obvious as with the other systems discussed in this chapter. However, the electrochemistry serves to show the complexity of their redox behavior and to point out some important points in the redox mechanisms of quinones. 

The electrochemistry of the PQQ (pyrrolo-quinoline quinone) prosthetic group has been investigated at poly(pyrrole)-coated electrodes, and PQQ has been entrapped within poly(pyrrole) films " good electrochemistry was observed in both cases. Poly(pyrrole) has also been used to entrap adenosine triphosphate (ATP) anions, again by growing the film in the presence of the anion, " and as an electrode material for oxidizing ascorbate. " In the latter case the oxidation... 

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