5 - Time and Frequency Domain Study of Different Electron Transfer Processes in Bacterial Reaction Centers

Abstract

This chapter focuses on the time and frequency domain study of different electron transfer processes in bacterial reaction centers (RCs). Bacterial reaction centers contain three protein subunits, four bacteriochlorophylls (Bchl), two bacteriopheophytins (Bphe), two quinones, and one atom of iron. The application of excitonic theory to pigment interactions in RCs using atomic coordinates of RCs has shown that each optical transition in RCs in visible and near-infrared spectra has a contribution from the transition of all six pigments. The spectral properties of the cofactors of RCs in the optical range suggest the possibility for studying the selective changes in Bchl and Bphe molecules caused by excitation, reduction, or oxidation. This study can include the selective photoaccumulation of the cofactors in the reduced or oxidized states as well as picosecond and sub-picosecond measurements of the excitation and charge separation in time and frequency domains. The measurements in the time domain can be done in a wide range of temperatures. The study of the relaxation of P* by hole burning should be carried out at <10 K using narrow excitation lines to eliminate inhomogeneous broadening.