Electron transfer non-adiabatic

Figure 2.2 Adiabatic and non-adiabatic electron transfer (schematic). The splitting at the intersection has been exaggerated.

Ab initio thermodynamics, 129-155 Acetaldehyde oxidation, 196-197, 624 Acetic acid, 192-198, 394-395 Active sites in electrocatalysis, 93-124, 159-198, 237,250,253 Adiabatic and non-adiabatic electron transfer, 34... 

Thus, from equation (63), the magnitude of the electronic coupling matrix element may finally be estimated, leading to values of 21 and 24 meV for EDA and perylene, respectively. That these values are quite reasonable derives from the observation that they correspond to moderately non-adiabatic electron transfer at the ground state (with electronic factors of 2 /(1 + P) - 0.5 and 0.6 with EDA and perylene, respectively). 

Although their conceptual basis is now firmly established, non-adiabatic electron transfer processes are still the subject of intensive theoretical studies. Nevertheless, the framework provided by the standard formalism presented in this section seems sufficiently general to be used for the interpretation of kinetic data obtained in biological systems. Owing to the great number of parameters involved in the theoretical expressions, attainment of useful information requires obtaining numerous data by elaborate experiments. The next section is devoted to a review of the different approaches that have been developed over the last few years. 

It was shown in Sect. 2 that the standard formalism appropriate for non-adiabatic electron transfer processes leads to the definition of an electronic and a nuclear factor in the rate expression. This separation into factors of quite different physical origin is conceptually very useful. As a matter of fact, it is systematically emphasized throughout this presentation to clarify the nature of the different parameters involved in biological electron transfers. It happens also to be very useful when the relation between the kinetics and the biochemical function of these processes is considered. This is illustrated below by a few examples. 

The essentials of quantum kinetics were in place by 1954, Weiss having added to the Gurney theory a comprehensive theory of redox reactions. By this date, tunneling, adiabatic and non-adiabatic electron transfer, the simplicity introduced by considering redox reactions between isotopes, the separate contribution from outer sphere and inner sphere, and in particular the equation for the reorganization energy involving and stat had all been published. 

Non-adiabatic (diabatic) process (quantum mechanics) — In quantum mechanics a process is called non-adiabatic (diabatic) if one or more electrons fail to equilibrate with nuclei as they move. In a widely-used extension of this terminology, non-adiabatic electron transfer is said to occur when an electron tunnels out of one electronically non-equilibrated state into another. Due... 

The theory of non-adiabatic electron transfer was developed by Levich, Dogonadze and Kuznetsov (Levich and Dogonadze, 1959 Levich et al. 1970). These authors, utilizing the Landau-Zener theory for the intersection area crossing suggesting harmonic onedimensional potential surface, proposed a formula for non-adiabatic ET... 

Diabatic electron transfer Electron transfer process in which the reacting system has to cross over between different electronic surfaces in passing from reactants to products. For diabatic electron transfer the electronic transmission factor is 1 (see Marcus equation.) The term non-adiabatic electron transfer has also been used and is in fact more widespread, but should be discouraged because it contains a double negation. 

Non-adiabatic electron transfer See diabatic electron transfer. 

A strict quantum mechanical calculation of a tunneling system the size of a protein quickly becomes intractably complex. Fortunately, relatively simple theory has been successful at organizing and predicting electron tunneling rates in proteins. When the donor and acceptor redox centers are well separated, non-adiabatic electron transfer theory applies Fermiis Golden Rule, in which the rate of electron transfer is proportional to two terms, one electronic. Hah, and the other nuclear, FC (Devault, 1980). 

Although the two-fold symmetry displayed by the reaction centre is striking, it is only a pseudo-symmetry, because differences in the amino aeid sequences of the L and M subunits result in small differences in the positions and relative orientations of equivalent cofactors on the two branehes, and in differences of the protein environment of equivalent cofactors. The root cause of the functional asymmetry that is observed when electron transfer is monitored is therefore asymmetry in the detailed structure of the cofactor protein system on the two branches. Assuming that the transmembrane electron transfer process can basically be described as a non-adiabatic electron transfer reaction according to the Marcus equation, this... 

The dynamical theory also provides a framework for the study of the diabatic free energy profiles as functions of the reaction coordinate required in the theory of non-adiabatic electron transfer reactions. We illustrate this new application by calculating the free energy profiles in solvents covering a wide range of polarity. 

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