Electron transfer, semiquantitative

Studies of ferredoxin [152] and a photosynthetic reaction center [151] have analyzed further the protein s dielectric response to electron transfer, and the protein s role in reducing the reorganization free energy so as to accelerate electron transfer [152], Different force fields were compared, including a polarizable and a non-polarizable force field [151]. One very recent study considered the effect of point mutations on the redox potential of the protein azurin [56]. Structural relaxation along the simulated reaction pathway was analyzed in detail. Similar to the Cyt c study above, several slow relaxation channels were found, which limited the ability to obtain very precise free energy estimates. Only semiquantitative values were... 

Of course, appropriate values of both electronic coupling elements, V3 for reaction (61) and Vct for reactions (62) and (63), are not directly available. However, semiquantitative discussion is possible in the view of data for other similar systems. For the electron transfer between anthracene and the anthracene radical anion, the corresponding coupling element Vaa = 0.05-0.10eV [128, 129] is quite large. For... 

The introduction of VB structures (the empirical nature of EVB does not matter here) makes easier the description of the process in terms of diabatic potential surfaces. The latter have been used to describe reactions in vacuo since long time, more than 30 years before the formal definition given by Smith (1969), and continue to represent an important tool for an accurate study of many chemical processes in vacuo (see e.g. the reviews given by Sidis (1992) and by Pacher et al. (1993)), and for qualitative and semiquantitative characterizations of organic reactions (see e.g. Shaik and Hiberty, 1991). Their use in solution has been spurred by Marcus model on electron transfer (ET) reactions (Marcus, 1956), and extended by the Russian school in the sixties to other chemical processes (Levich and Dogonadze, 1959 Levich, 1966 Dogonadze, 1971 German et al., 1971, Albery, 1980). 

This review is organized to cover the basic features of simple electron transfer reactions. The first three sections develop background material on the thermodynamics, kinetics, and microscopic theory of electron transfer reactions. More general, semiquantitative treatments of these topics are presented, with the objective of introducing the conceptual approaches used to characterize electron transfer processes. The fourth section describes experimental studies on two electron transfer systems, selected from both physiological and nonphysiological... 

For the investigation of the electronic character of catalytic reactions, it has been found fruitful to study not only the catalytic action of metals and semiconductors of known electron state distribution, but also the changes of this distribution by illumination during catalysis. The War-burg-Barcroft technique of biochemistry has proved to be very suitable for this purpose. It could be shown in a semiquantitative way that promotion of electrons enhances acceptor reactions, that electron traps hinder such action, and that n-type and p-type conductors behave in opposite fashion when employed as photocatalysts. Using ferrites as catalysts in an acceptor reaction, the electron transfer concept was confirmed. 

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