Time-Resolved High-Frequency and Multifrequency EPR Studies of Spin-Correlated Radical Pairs in Photosynthetic Reaction Center Proteins

Abstract

In this chapter we demonstrate the potential of high-frequency and multifrequency time-resolved electron paramagnetic resonance (EPR) to reveal unique information on the electron-transfer processes in the photosynthetic systems, where spectra exhibit spin-polarization phenomena. A precise determination of the magnetic resonance parameters of the radicals in the spin-correlated radical pairs with high-frequency EPR facilitates an analysis of more sophisticated models and methods, such as sequential electron transfer spin-polarization and quantum beats oscillations. These approaches help to describe dynamics, structure and electron transfer pathways in the photosynthetic proteins. In the first part of the manuscript we concentrate on the study of the dynamics of the sequential electron-transfer in deuterated photosynthetic bacterial reaction center proteins. High-frequency EPR spectroscopy reveals the influence of the relationship between structure and dynamics on the rate of charge separation. In the second part of the chapter we demonstrate how the three-dimensional structure of the electron intermediates in green plant photosystem I can be determined by high time-resolution multifrequency and high-frequency EPR techniques.