Organic redox electrodes

Quinhydrone, a solid-state associate of quinone and hydroquinone, decomposes in solution to its components. The quinhy drone electrode is an example of more complex organic redox electrodes whose potential is affected by the pH of the solution. If the quinone molecule is denoted as Ox and the hydroquinone molecule as H2Red, then the actual half-cell reaction... 

Fig. 6. Band edge positions of several semiconductors ia contact with an aqueous electrolyte at pH 1 ia relation to the redox (electrode) potential regions (vs the standard hydrogen electrode) for the oxidation of organic functional groups (26,27).

While the laws governing electrode potentials in non-aqueous media are basically the same as for potentials in aqueous solutions, the standardization in this case is not so simple. Two approaches can be adopted either a suitable standard electrode can be selected for each medium (e.g. the hydrogen electrode for the protic medium, the bis-diphenyl chromium(II)/ bis-diphenyl chromium(I) redox electrode for a wide range of organic... 

Electrochemistry, organic, structure and mechanism in, 12, 1 Electrode processes, physical parameters for the control of, 10, 155 Electron donor-acceptor complexes, electron transfer in the thermal and photochemical activation of, in organic and organometallic reactions. 29, 185 Electron spin resonance, identification of organic free radicals, 1, 284 Electron spin resonance, studies of short-lived organic radicals, 5, 23 Electron storage and transfer in organic redox systems with multiple electrophores, 28, 1 Electron transfer, 35, 117... 

Electrode surfaces can be modified by redox polyelectrolytes via a sol-gel process, yielding random redox hydrogels or by layer-by-layer self-assembly of different redox and nonredox polyelectrolytes by alternate electrostatic adsorption from solutions containing the polyelectrolytes to produce highly organized redox-active ultrathin multilayers. 

In electrode reactions of the type H+/H2, 02/H20, and probably many organic redox systems, the electrode surface may be involved by virtue of the presence of adsorption sites where intermediates in the reaction mechanism, e.g. atomic hydrogen, are located. Generally, the reaction rate is higher at metals with a larger adsorptive capacity. This is a particular form of electrocatalysis, which is a subject of still-growing interest. 

In this section, we describe the fabrication of metal complex oligomer and polymer wires composed of bis(terpyridine)metal complexes using the bottom-up method.11 13 This method has an advantage in fabricating organized structures of rigid redox polymer wires with the desired numbers of redox metal complexes. We also present a new electron-transport mechanism applicable to the organized redox polymer wires-coated electrode. 

Standard electrode potentials and other free energy data for organic redox reactions 122... 

STANDARD ELECTRODE POTENTIALS AND OTHER FREE ENERGY DATA FOR ORGANIC REDOX REACTIONS... 

Organic acids, 26 Oxide OH groups, 169 Platinum redox electrode, 235, 253 Point of zero charge (PZC), 146 Clay dispersion, 146 Oxides, 131,146 Soils, 158-159... 

Monolayers and multilayers of redox enzymes (e.g., glucose oxidase [70], bilirubin oxidase [71]) have been organized on electrode surfaces using bifunctional reagents (producing covalent bonding between the layers) [70, 71] or using bioaffinity... 

The mechanisms of the electron-transfer event in such systems, involving solvational reorganization of the reactant, have been treated in much detail in the literature of complex-ion chemistry in inorganic chemistry (25) and by Marcus (26), Hush (27), and Weaver (28) for corresponding redox processes conducted at electrodes. The details of these works are outside the scope of this article, but reviews (29,30) will be useful to the interested reader. Chemisorbed intermediates, produced in two- or multistep redox reactions, are not involved except with some organic redox systems such as quinones or nitroso compounds. 

The system azobenzene-hydrazobenzene is one of the rather few organic redox couples that behave reversibly or very nearly so at the dropping mercury electrode [187]. In nonaqueous solvents, like DMF, azobenzenes are reduced in two, one-electron steps The first one produces the radical anion, whereas the second one yields a hydrazo-benzene dianion. This dianion is easily protonated it has a tendency to decompose into arylhydrazine [188]. 

By one method a relay-cofactor dyad is assembled on the electrode, and the respective apo-protein is reconstituted on the surface to yield an aligned protein that is linked to the conductive surface by the relay component. The second method involves the synthesis of the relay-cofactor unit and the reconstitution of the apo-protein in solution. The specific immobilization of the enzyme on the electrode by the relay unit provides the structurally organized enzyme electrodes. While the first method is technically easier, the second methodology that involves tedious synthetic and separation steps, permits the fundamental structural characterization of the reconstituted protein. In the two configurations, the redox enzymes are anticipated to be electrically contacted with the electrode by means of the relay, a conductive... 

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