Media reorganization

This fact was explained in the framework of two models. The first model is based on the concept of dynamic adaptation of a protein matrix in every step of an enzymatic reaction. Concerning the QA — QB transition, fast reversible conformational transitions can provide dipolar relaxation favourable for the media reorganization process (Likhtenshtein, 1976, 1979 a, 1988 a). Such reorganization is necessary to release... 

Further development of theory of reorganization energy consists in taking to consideration the properties of medium and manner in which it interfaces with the solute (Newton, 1999). These properties must include both size and shape of the solute and solvent molecules, distribution of electron density in reagents and products and the frequency domain appropriate to medium reorganization. 

Newton, M.D. (1999) Control of electron transfer kinetics models for medium reorganization and donor-acceptor coupling, in. Fortner, J., Bixon, M. (eds.), Advances in Chemical Physics 107, Part 1 John Wiley Sons. NY., pp. 303- 376. 

Models for Medium Reorganization and Donor-Acceptor Coupling. 

The activation free energy AG is dehned by two terms. One term is the reaction free energy [AG ], which is derived from the redox potential difference of the donor and acceptor. The second term is the medium reorganization energy (k), which is the energy stored in the solvent inertial degrees of freedom when the electron is shifted suddenly from donor to acceptor (1-5). Marcus theory predicts the activation free energy ... 

M. D. Newton, S. W. Feldberg, and J. F. Smalley, Theory and Computational Modeling Medium Reorganization and Donor-Acceptor Coupling in Electron Transfer Processes, in Interfacial Electrochemistry Theory, Experiment, and Applications, A. Wieckowski, Ed., Marcel Dekker, New York, p. 97 (1999). 

In reactions of outer-sphere electron transfer between the ions in polar liquids, the main role is played by the low-frequency polarization vibrations with typical energies much smaller than KgT. In the case of classical nuclear motions the medium reorganization energy is the sum of reorganization energies of the set of normal classical oscillators (hco < Kg T) formed by shifts similar to the one shown in Figure 2 ... 

Here 2 is the Einstein frequency, is the energy of the medium reorganization, I It,n is ihe Bessel function of imaginary argument, and pj- is the final-state density. 

Attempts have been made to estimate quantitatively the various effects possible from the theoretical viewpoint on an electrochemical interface for superconductors have been made. For example, it was established [154, 156, 158] that the probability of the electron-pair tunneling is, in principle, always substantially lower than that for usual electrons (all other factors being equal), a result that implies the prediction of inhibition near 7. Kuznetsov [158] considered in detail the mechanisms of the processes with the participation of Cooper pairs. For instance, the energy barriers were estimated for a variety of mechanisms, including the transfer to one and the same particle (capable of multielectron transformation) to two spatially separated particles, and also the transfer of the pair to one particle with the simultaneous transition of one of the pair s electrons to the normal state. It was found that the properties of the system can vary substantially, depending on the relationship between the band gap, the medium reorganization energy, and the overpotential. 

The water reorganization energy is mainly determined by the size of the water clusters between which the proton is transferred (H30+, H9C>4+) and the effective distance over which the proton is shifted during the process. The contribution of the medium reorganization outside the reactant water clusters (outer-sphere contribution) is calculated in Ref. 43, 44 as a function of reactant cluster sizes, transfer distance, pore size, and dielectric properties of the contacting media (water, polymer). 

Kharkats, Y.I. and Krishtahk, L.L (1985) Medium reorganization energy and enzymatic-reaction activation energy. Journal of Theoretical Biology, 112, 221-249. 

Newton M. D. (1997), Medium reorganization and electronic coupling in long-range electron transfer , J. Electroanal. Chem. 438, 3-10. ... 

Newton M. D., Feldberg S. W. and Smalley J. F. (1999), Theory and computational modeling medium reorganization and donor-acceptor coupling in electron transfer... 

Up to this point in time, 10 s, the electron-medium interactions have led to little, if any, medium reorganization, but at longer times the induced orientational polarization develops and contributes to the stabilization energy of the electron. We then observe the appearance of a solvated electron in a fully configurationally relaxed ground state (ef) whose mobility of 10 to 10 V cm s is more reminiscent of an... 

Figure 4 shows how the dielectric constant of the organic phase Sj and the distance from the interface or between reagents affect the medium reorganization energy. A decrease in /z or dramatically decreases Eg (Fig. 4), which reaches a minimum value as... 

Equation (1) lays down conditions for the structure of cytochrome c oxidase catalytic sites necessary for dioxygen reduction to occur by the concerted n-electron mechanism. To lower the medium reorganization energy and thus activation energy, it is necessary that ... 

The stepwise transfer of electrons from cytochrome c to cytochrome via cytochrome a is kinetically favorable due to a substantial decrease in the medium reorganization energy for direct electron transfer from cytochrome c to cytochrome a. The redox potential of FOc may not be smaller, but even greater than the redox potential of FOg. It is essential that only the minimum of the intermediate term on the reaction energy diagram be below the cross-point of the initial and final terms. 

The corresponding medium reorganization energy, obtained from Equation (58) in the usual manner, is given by... 

The nuclear term F(AE,Ej, o q,T) is essentially determined by the (free) energy gap AE between the minima of the DA and D+A potential surfaces, the medium reorganization... 

Energetic constraints on the medium reorganization energy. E is a local property, which is essentially determined by the interaction of cofactors and their ions with the amino acid residues in their vicinity. 

As seen from Eqs. (7) and (8), the free activation energy is determined to a considerable degree by the value of the medium reorganization energy This value is an important... 

Fig. 3. Scheme of the process for calculating the medium reorganization energy... 

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