Dynamics of the Electron Transfer Reaction in Cytochrome b_5

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Electron transfer is one of the most fundamental process in chemistry and biology. Theoretical frameworks describing non-adiabatic electron transfer process is well established through classical, semiclassical and quantum models. In all these theories, the basic assumption is that the electron transfer rate constant can be partitioned into two factors-the electronic coupling factor and the Frank-Condon factor.A new aproach is proposed in order to understand the relation between the protein modes and the electron transfer reaction, especially the Frank-Condon factor. We have presented a reduced spin-boson hamiltonian model where the bosonic bath is represented by the harmonic protein normal modes or the collective modes determined by the principal component analysis. Solvent effect is incorporated by the Tanford-Kirkwood model.The spin-boson model have been applied to the problem of electron transfer by others in previous studies. However, there are several new aspects that our work brings out. Our starting point is the normal mode analysis in the frequency domain. This allowed us to structurally identify all the bath modes in protein and solvent. This is important if one ones to correlate specific structural fluctuations of the protein to electron transfer coupling. Thus our model has all the advantages of a spin-boson model, with the added advantage that the individual bath modes are no more spatially anonymous. The present analysis is not just restricted to harmonic normal modes, but instead one can use data from a molecular dynamics run and through a principal component analysis.