Dynamic solvent effects on outer-sphere electron transfer

Abstract

In this paper we present the results of a theoretical study of outer-sphere electron transfer (ET) in a polar solvent, with the modification of the nuclear states by the change in the charge distribution originating solely from the response of the exterior medium. The model Hamiltonian for the system corresponds to two parabolic diabatic potential surfaces with adiabatic coupling between them. The real-time path integral formalism is utilized to derive the general expressions for the influence functional of the medium in the Gaussian approximation and for the ET rate. The ET rate is explicitly evaluated for the particular case of a medium characterized by the Debye dielectric relaxation function. We explore the relation between the dynamics of the reaction coordinate and the character of the ET process, deriving an expression for the ET rate, which bridges between the nonadiabatic and the solvent-controlled adiabatic limits. We establish simple criteria for the validity range of various descriptions of ET dynamics, i.e., the transition state theory, the solvent-controlled ET as well as the adiabatic and nonadiabatic limits. The results are applied to intramolecular ET in alkanols, establishing the adiabatic nature of these processes, whose dynamics is dominated by the (slow) longitudinal dielectric relaxation rate of the solvent.with € "" and €s being the optical and the static dielectric 2090

Coupling of protein motion to electron transfer in a photosynthetic reaction center: investigating the low temperature behavior in the framework of the spin—boson model

“…This relationship has been stated before in [13,33] without detailed derivation. For the sake of completeness we provide the derivation here employing a different, simple approach.…”

“…But as Bader et al pointed out [33], the dispersed polaron method is a semiclassical approximation, which assume [Ê R ,Ê P ] = 0, whereÊ R andÊ P are explained in (13) and (14), so that it only gives good results in the classical limit i.e., at high temperatures, but overestimates the tunneling correction at low temperatures. As a matter of fact, one can show that Warshel et al's treatment is an approximation of the spin-boson model at high temperature.…”

“…This form of J(ω) is so-called Debye function, and has been used also in several studies mentioned above [13,14]. In [3] the values of τ and σ obtained from the simulation of the photosynthetic reaction center Rps.…”

Fundamental signatures of short- and long-range electron transfer for the blue copper protein azurin at Au/SAM junctions

“…As a decisive development of the preceding work (19,20,25,26), we offer unique kinetic data obtained through temperature-and pressure-variation and the mechanistic analysis through a unique global fitting procedure accounting for ET at different SAM thickness, temperature, and pressure conditions that provided the variation of the reduced ET rate constant over almost five orders of magnitude. Importantly, our previous work demonstrated that Au-deposited SAMs can withstand pressure-related stress within 5 to 150 MPa (27, 28, 34).The rate constant, k et , for nonbiological and biological ET may be cast in a thermally activated Arrhenius form that is valid within the range of commonly used temperatures (1,3,(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45):where ΔG Ã a is an activation free energy for reaching the transition state, which arises from the complete Franck-Condon weighted density of states and is connected with the medium's dielectric (cumulative sum) response, and A is a preexponential factor whose form is specific for the ET mechanism (see below) (1,3,(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45). Previous studies that exploited SAM-coated electrodes revealed two kinds of phenomenological behavior (17)(18)(19)(20)(21)(22)(24)(25)(26)…”

Picosecond time-dependent Stokes shift studies of fluoroprobe in liquid solution

“…The conjecture that this reaction takes place in the strongly adiabatic limit [26][27][28] has partly motivated us to undertake this research. For jet-cooled derivative compounds of fluoroprobe, the excitation spectra have recently been published [29].…”