Molecular translation, electron-transfer

K. Ando and S. Kato, Dielectric relaxation dynamics of water and methanol solutions associated with the ionization of /V,/V-dimcltiylanilinc theoretical analyses, J. Chem. Phys., 95 (1991) 5966-82 D. K. Phelps, M. J. Weaver and B. M. Ladanyi, Solvent dynamic effects in electron transfer molecular dynamics simulations of reactions in methanol, Chem. Phys., 176 (1993) 575-88 M. S. Skaf and B. M. Ladanyi, Molecular dynamics simulation of solvation dynamics in methanol-water mixtures, J. Phys. Chem., 100 (1996) 18258-68 D. Aheme, V. Tran and B. J. Schwartz, Nonlinear, nonpolar solvation dynamics in water the roles of elec-trostriction and solvent translation in the breakdown of linear response, J. Phys. Chem. B, 104 (2000) 5382-94. 

Electron transfer (ET) reaction in a polar solvent has been one of the central issues in physical chemistry and biophysics. In the presence of an immersed solute, a polar solvent around the solute continuously fluctuates due to the translational and orientational motion of its constituent molecules. The concept of a free energy profile governing these fluctuations as a function of solvent coordinates plays a central role in the theory of ET. Recently, we developed a molecular theory for obtaining the free energy profiles of ET reactions based on ex-RISM, and obtained quantitatively good results in terms of agreement with the simulation data. 

Theoretical formulations of reorganization in the course of electron-transfer processes have undergone a number of advances in recent years. The relative importance of various solvent contributions (including translational as well as orientational response, and inductive and dispersion as well as elecrostatic interactions) can depend strongly on the polarity (i.e., dipolar, higher multipolar, or nonpolar) as well as other molecular features of the solvent [21, 47-49]. Molecular-level perspectives on solvent response are of great utility in helping to parameterize effective cavity models (e.g., in conjunction with conventional [50] or spatially nonlocal [47] dielectric models). Additivity relationships traditionally assumed to pertain to sol-... 

It should be intuitively obvious (and is further clarified below) that the effect of applied potential on the electron transfer rate between the electrode M and a molecular species S in its solution neighborhood reflects the way by which this potential translates into a potential drop between M and S. This follows from the fact that the rate depends on the relative positions of electronic levels in the electrode and the molecule, which in turn depend on this drop. In much of the electrochemical literature it is assumed that when the electrode potential changes by 3 T so does this potential drop. This amounts to the assumption that the species S does not feel the potential change on M, that is, that the electrolyte solution effectively screens the electrode potential at the relevant S-M distance. Such an assumption holds at high supporting electrolyte concentration (order of 1 mole per liter). However, even... 

Figure 7-1 Current questions in biological electron transfer. A small monoheme cytochrome may pre-ori-entate by means of complementary electrostatic fields projecting from itself and its redox partner. Having formed a collision complex, it may be able to rotate and translate across part of the molecular surface of the redox partner before it finds the most favorable orientation for electron transfer.

In 1934, N. Semenov, in his book on chain reactions [2] strongly emphasized the role of the collisional energy transfer in gas-phase chemical kinetics, particularly paying attention to different kind of molecular energy, electronic, vibrational, rotational and translational. However, it was not until the work by Landau and Teller in 1936 [3] when it was realized that the collisional energy transfer should be described in terms of kinetics of populations of individual energy levels. Later on, the discussion of the energy transfer become indispensable sections of comprehensive texts on chemical kinetics as exemplified by the Kondratiev book [4]. 

---