Role of orbital overlap and local dynamics in long-distance electron transfer in photosynthetic reaction centres and model systems

The following approaches have been developed to estimate the factors affecting electron transfer (ET) in proteins: (1) an analysis of the correlation between the rate constants of ET (κ_ET) in a donor-acceptor (DA) pair and the dynamic parameters of various modes of relaxation of media traced by spin, fluorescent, triplet and Mössbauer labelling methods; (2) the use of spin exchange (SE) data in biradicals and complexes of transition metals with paramagnetic ligands and triplet-triplet energy transfer (TTET) data, which are considered as simple models of ET, for the estimation of the attenuation parameter (γx) of superexchange through an individual chemical group X and through homogeneous "conducting" and "non-conducting" media. The application of the aforementioned approaches to ET in photosynthetic reaction centres (RCs) and DA pairs in simple liquids and proteins is reviewed. The mechanism of ET in the systems under consideration is discussed. A new procedure of analysis of kinetic-thermodynamic relationships, including predictions by Marcus theory, is proposed.