Reversible electron transfer between

Arenediazonium ions can, of course, bring about electrophilic aromatic substitution giving aromatic azo-compounds. Using PhN=N and PhO , polarized signals have been observed in the N-spectrum (6 MHz) of the coupled product (A, A) and reactant, suggesting that the reaction proceeds, at least in part, by a mechanism involving preliminary reversible electron transfer between the reactants (Bubnov et al., 1972). 

However, modification of the electrode surface is not the only way in which one can facilitate reversible electron transfer between an electrode and a protein site. The indispensable condition is that the electrode surface is electrostatically compatible with the protein surface. 

Extension of this treatment to pulse techniques can, in principle, be made for several cases. In the case of square-wave voltammetry, theoretical current-potential curves for reversible electron transfer between species in solution are given by [184, 185]... 

The net result of a photochemical redox reaction often gives very little information on the quantum yield of the primary electron transfer reaction since this is in many cases compensated by reverse electron transfer between the primary reaction products. This is equally so in homogeneous as well as in heterogeneous reactions. While the reverse process in homogeneous reactions can only by suppressed by consecutive irreversible chemical steps, one has a chance of preventing the reverse reaction in heterogeneous electron transfer processes by applying suitable electric fields. We shall see that this can best be done with semiconductor or insulator electrodes and that there it is possible to study photochemical primary processes with the help of such electrochemical techniques 5-G>7>. 

The question remains open whether or not there is a direct contact between flavin and metal in a le -accepting binuclear iron cluster as, for example, in plant ferredoxin. Outer sphere le -transfer through flavin position 8 remains the alternative. On the other hand, there can no longer be a question about direct and reversible electron transfer between dihydronicotinamide and metal proteins. Any such claims (49) must be taken with greatest reservation and require careful independent confirmation. 

Absorbance attributed to the CT state decayed with a lifetime of 20 ps (Figure 26d) to leave a residual species having the characteristic differential absorption spectrum of the Au porphyrin neutral radical (Figure 26a and b). Deactivation of the CT state may involve direct reverse electron transfer between porphyrinic species ... 

The reduction potentials for the heme and FMN prosthetic groups of flavocytochromes 62 from S. cerevisiae and H. anomala are listed in Table I. Values for various modified forms of the enzyme, such as the flavin-free (deflavo) derivative, and the isolated cytochrome domain (the cytochrome 62 core) are also reported in Table I (64-69). The reduction potentials for the heme group are as expected for a 65-type cytochrome (70), with little difference in the values for different forms of protein, e.g., the deflavo-derivative of the holoenzyme and the isolated cytochrome 62. The reduction potentials for the FMN group are not too different from those of the heme (about 50 mV difference), consistent with reversible electron transfer between the two prosthetic groups (10). 

The same workers found significantly smaller volume effects for reversible electron transfer between xanthene dyes and transition metal cyanides, Eq. 

In 1993, we reported [19] reversible electron transfer between electrodes and the iron heme protein myoglobin imbedded in cast multi-lameUar liquid crystal films of didodecyldimethylammonium bromide (DDAB). Heretofore, reversible electron transfer from electrodes to myoglobin in solution had been accomplished only for highly purified myoglobin solutions on specially cleaned indium tin oxide electrodes [20,21]. If enhanced electron transfer for proteins in surfactant or lipid films were to prove general, it might help solve longstanding problems in protein electrochemistry. 

Adsorption film formed by cellulose triacetate (TAC) can also be used for immobilization of a biological system at the surface of the glassy carbon or gold electrodes [222-224]. For instance, it is possible to dissolve microperoxidase (MPO) in this film to simulate a membrane-entrapped microperoxidase. A direct, reversible electron transfer between this enzyme and the electrode is observed in nonmodified electrodes without the TAC film [224] and also when MPO is dissolved in the TAC film [85]. Fast electrochemical reaction of cytochrome c and azurin at the electrodes can be observed if the electrode covered by the TAC film containing MPO is immersed in the solution of these proteins. Thus, the immobilized film containing microperoxidase behaves like a solid state promoter of protein electrochemistry [223, 224]. 

Oxidation-Reduction Reactions. As already mentioned, iron-sulfur proteins are the group of electron-transfer substances most numerous and widely distributed in biological organisms. The most important property of these proteins is therefore their ability to undergo reversible electron transfers between different oxidation states of the active sites. 

Reversible electron transfer between FDH and the electrode through PP interface The differential pulse... 

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