Redox multiple

It is now 20 years since the first report on the electrochemistry of an electrode coated with a conducting polymer film.1 The thousands of subsequent papers have revealed a complex mosaic of behaviors arising from the multiple redox potentials and the large changes in conductivity and ion-exchange properties that accompany their electrochemistry. 

Although the redox potential of Rieske-type clusters is approximately 400 mV lower than that of Rieske clusters, it is 300 mV more positive than the redox potential of plant-type ferredoxins (approximately -400 mV). Multiple factors have been considered to be essential for the redox potential of iron sulfur proteins ... 

The electrochemical behavior of heterometallic clusters has been reviewed clsewbcre."" The interest in examining clusters stems from their potential to act as "electron sinks " in principle, an aggregate of several metal atoms may be capable of multiple redox state changes. The incorporation of heterometals provides the opportunity to tune the electrochemical response, effects which should be maximized in very mixed"-metal clusters. Few very mixed -metal clusters have been subjected to detailed electrochemical studies the majority of reports deal with cyclic voltammetry only. Table XII contains a summary of electrochemical investigations of "very mixed"-metal clusters. 

Because of their multiple oxidation states, the chalcogens, particularly sulfur, can engage in numerous redox couples participating in acid-base, oxidation-reduction, precipitation, and complexation equilibria. 

This protocol was extended to other inorganic colloids (e.g., ZnS, PbS), and it was pointed out that such extension paves the way to an electrochemical coding technology for the simultaneous detection of multiple DNA targets based on nanocrystal tags with diverse redox potentials [148]. 

Mormille MR, S Liu, JM Suflita (1994) Anaerobic biodegradation of gasoline oxygenates extrapolation of information to multiple sites and redox conditions. Environ Sci Technol 28 1727-1732. 

Figure 17.6 Redox hydrogel approach to immobilizing multiple layers of a redox enzyme on an electrode, (a) Structure of the polymer, (b) Voltammograms for electrocatalytic O2 reduction by a carbon fiber electrode modified with laccase in the redox hydrogel shown in (a) (long tether) or a version with no spacer atoms in the tether between the backbone and the Os center (short tether). Reprinted with permission fi om Soukharev et al., 2004. Copyright (2004) American Chemical Society.

Dendrimers with multiple ferrocene moieties at the surface usually show one-step multielectron redox reactions due to little internuclear interaction (141-143), while those with locally communicating ferro-cenyl groups have also been reported (141). 

Zinc is also used in biological studies to gain information about non-zinc containing systems. It can be a convenient redox inactive replacement for the study of complex systems with multiple redox centers. For example, the mechanism of quenching the triplet state of zinc cytochrome c by iron(II) and iron(III) cytochrome c has been studied. Zinc insertion has been used to get around the difficulty of studying two heme proteins with the same absorption spectra and provides rate constants for iron and iron-free cytochrome c quenching.991... 

Trigonal- and tetragonal-prismatic clusters are also characterized by redox reactions (15) and (16) changing the formal multiplicity of the M-M bonds in them (Sects 3.5 and 5.3). 

The present chapter will cover detailed studies of kinetic parameters of several reversible, quasi-reversible, and irreversible reactions accompanied by either single-electron charge transfer or multiple-electrons charge transfer. To evaluate the kinetic parameters for each step of electron charge transfer in any multistep reaction, the suitably developed and modified theory of faradaic rectification will be discussed. The results reported relate to the reactions at redox couple/metal, metal ion/metal, and metal ion/mercury interfaces in the audio and higher frequency ranges. The zero-point method has also been applied to some multiple-electron charge transfer reactions and, wheresoever possible, these results have been incorporated. Other related methods and applications will also be treated. 

Ullmann, M., The coupling of protonation and reduction in proteins with multiple redox centers theory, computational method and application to cytochrome C3, J. Phys. Chem. B 2000,104, 6293-6301... 

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