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

Abstract

The spin-boson model is applied to describe the coupling between protein motion and electron transfer for the primary electron transfer in the photosynthetic reaction center of Rps. viridis, a coupling which involves a very large number of degrees of freedom of the protein.For this purpose the relationship between the spectral function J(ω) characterizing the protein motion and the fluctuations of the protein contribution to the energy gap is derived. The relationship allows one to determine a suitable J(ω) from classical Molecular Dynamics simulations. Furthermore, we provide also an efficient numerical method to determine electron transfer rates in the framework of the spin-boson model. We also derive a high temperature approximation for the transfer rate which connects the spin-boson description with the well-known descriptions by Marcus and Hopfield. We determine then electron transfer rates both as a function of the redox energy difference and of temperature. The results show that for the system considered, the Marcus theory holds well at physiological temperatures. The low temperature behavior of the electron transfer rates is in qualitative agreement with observations in that electron transfer can accelerate with lowering the temperature, and that transfer rates can also slightly decrease with decreasing temperature.

The temperature dependence of radiationless transition rates from ab initio computations

“…More refined models for radiationless rates based on the spin-boson theory have also been developed, and widely applied to the study of ET in condensed media. [16][17][18] A significant improvement has been provided by Warshel and coworkers, who introduced the dispersed polaron model which, combined with the quantum mechanical consistent force field method (QCFF/PI), and its extensions, has allowed to determine rate constants from classical trajectory simulations. [19][20][21] Indeed, that methodology has provided deep insights into the role of protein motion on their chemical activity.…”

Superradiance Transition and Nonphotochemical Quenching in Photosynthetic Complexes

“…(See also [32,33,34], and references therein.) Then, one can write, λmn(t) = λnδmnξ(t), where λn is the coupling constant at site, n, and ξ(t) is a random process.…”

Non-Markovianity during the quantum Zeno effect

“…It is well known [63][64][65] that several chemical and physics systems can be modeled using a reaction coordinate linked to an effective potential energy function with two distinct minima points, and which is amenable to analysis in terms of exchange of quantum correlations between the system under study and its immediate environment. The light harvesting complex is an important system where the observed long lived coherences, lasting several picoseconds, may be linked to quantum information processing features inherent in the propagating exciton (or correlated electronhole pair).…”