Theoretical study of electron transfer reactions in biological and chemical systems

In this thesis, new theoretical and computational methods are presented that have been developed for the analysis of long-range electron transfer reactions in chemical and biological redox systems with complex structural organization. Applications are given for electron transfer reactions in proteins and in "molecular wires". In part I, we give an introduction to the general theory of electron transfer reactions. In part II, we discuss a series of novel theoretical methods and their computational implementation for the calculation of the electronic coupling matrix element in proteins within a one-electron picture. Further, results of molecular dynamics simulations of the protein medium during the tunneling event are presented which show that the tunneling matrix element is a sensitive function of the atomic configuration of the part of the protein matrix in which tunneling currents are localized (non-Condon effects). This finding indicates a strong coupling between the tunneling electron and protein vibrations, and leads to a modification of the conventional Marcus picture of electron transfer in proteins. These results provide insights into a question of how structure and dynamics of the protein medium regulates rates of biological electron transfer reactions. In Part III, we apply the method of tunneling currents for study of electron tunneling dynamics in a series of quasi-one-dimensional Donor-Bridge-Acceptor systems ("molecular wires"). The method consists of an ab initio electronic structure calculation of the spatial distribution of tunneling currents occurring during the tunneling transition in the system and allows for a direct examination of the reaction of the valence electrons in the bridge to the tunneling charge. We conclude this thesis with ab initio calculations of the tunneling current along a model 25-angstrom-long polypeptide chain and show that in the tunneling flow there exist topological defects which result in the formation of quantized vortices. In summary, the results presented in this thesis provide new insights into the nature of long-distance electron tunneling in organic media.