An understanding of how electrons tunnel long distances through organic media of proteins is crucial for the characterization of many biological processes, such as photosynthesis and respiration. A broad long-range goal of the proposed research is the development of a detailed quantum mechanical picture of long-distance electron transfer reactions in complex molecular systems that involved proteins and DNA. In order to achieve this goal, computer simulations, comparison with experimental data, and systematic theoretical analysis of the dynamics of photoinduced electron transfer reactions will be carried out for a variety of novel complex molecular systems that recently have been studied experimentally. In these systems, two transition metal complexes, donor and acceptor in the reaction, are separated by a large biological molecule, such as protein or DNA, that mediates a photoinduced electron transfer reaction. Specifically, the role of inelastic tunneling, symmetry effects of the donor and acceptor states, and interplay between structural and dynamical aspects of the biological tunneling will be investigated. Systems that will be studied include modified cytochromes, such as Ru(bpy)2im(his X)-cyt-c, azurin, myoglobin, and some other metalloproteins in which a Ru complex is bound to genetically engineered histidines on the surface of the protein; similarly, variable-length DNA helices containing a bound Ru-complex will be studied theoretically. Electron transfer properties of the pi-orbital system of the complex will be investigated. The DNA and protein complexes will be used to study the distance, as well as the structure, and base pair sequence dependence of intramolecular charge transfer rates. The proposed research will provide a quantitative understanding of how structure and dynamics of biological molecules controls charge transfer at the most fundamental quantum mechanical level.