Applicability of the protein environment equilibrium approximation for describing ultrafast biophysical processes

Abstract

The theoretical description of ultrafast processes in biological systems, in particular, electron transfer in photosynthetic reaction centers, is an important problem in modern biological physics. Because these processes occur in a protein medium with which an energy exchange is possible, methods of the quantum theory of open systems must be used to describe them. But because of a high process rate and the specifics of the protein environment, basic approximations of this theory might be inapplicable. We study the applicability of the approximation of the protein environment (bath) state invariance for the dissipative dynamics of charge transfer between molecule-pigments contained in reaction centers. For this, we use model systems whose parameters are close to real ones. We conclude that this approximation can be used to describe both the monotonic and the oscillating dynamics of the reaction subsystem in large biological molecules. We consider various mechanisms for bath thermalization and show that the bath thermalization occurs not because of the intramolecular redistribution of the vibrational energy in it but because of its coupling to the reaction subsystem.