Protein Charge Transfer – an Atomistic Perspective

Abstract

As photosynthesis and respiration are key biochemical reactions essential to life on this planet, the understanding and quantitative description of these processes has always been a central issue in experimental and theoretical work. In this work, we approach ground state charge transfer reactions in proteins from a theoretical and numerical perspective. The electronic structure of model polypeptides and their coordinating electron donors and acceptors is described by an atomistic, chemically specific tight-binding Hamiltonian, which has been extended by a frequency-independent reaction field to take dielectric polarization effects into account. The emerging potential energy surface is analyzed using Marcus’ theory of charge transfer reactions. The dependence of the thus computed charge-transfer rates upon the donor–acceptor separation is compatible with phenomenological concepts like through-space, through-bond and through-hydrogen bond charge transfer. Which of these mechanisms dominates the charge transfer kinetics crucially depends on the secondary structure of the protein and the relative orientation of the donor and the acceptor complex.