New Epr Methods for Investigating Photoprocesses With Paramagnetic Intermediates

Abstract

Some of the significant advances in time-resolved multifrequency electron paramagnetic resonance (EPR) methods are reviewed, with the explicit focus on studies of light-driven processes and photoreactions in real time. Prominent examples are excited state electron transfer reactions with transient charge-separated radical pairs playing a central role. Paramagnetic intermediates and products are key functional states; thus EPR is the method of choice for their characterization. Photogenerated spin polarization and coherences as process-inherent features add the practical advantage of compensation in the trade-off between sensitivity and time resolution. Additionally, they provide detailed structural and dynamic information on the photoreactive system. Significance and specificity of the results achieved for charge separation in photosynthetic reaction centers and donor-acceptor model complexes indicate highly promising perspectives in photochemical research.

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

“…The fourth advantage is a high absolute sensitivity which is of special significance for biochemical research where often only small amounts of the material are available. A more detailed discussion on the HFEPR research of the photosynthetic systems can be found in the recent reviews (Stehlik and Mobius, 1997;Mobius, 2000).…”

Fourier-Transform EPR at High-Field/High-Frequency (3.4 T/95 GHz) Using Broadband Stochastic Microwave Excitation

“…This would be particularly interesting for the investigation of biradicals or light-induced radical pairs, such as those occurring in photosynthetic reaction centers (15). The nonlinear responses contain information about the correlation of the two electron spins.…”

Asymmetric perturbations of signalling oligomers

“…Among them, double site-directed spin labelling (DSDL) EPR techniques such as double electron-electron resonance (ELDOR) and its variants (Stehlik and Möbius, 1997) with the capability of the determination of intermediate and long-range distance restraints (10-70 Å) between specific sites in proteins, are the most extensively used EPR methodologies to obtain information on the extent and directionality of conformational changes in large biomolecular complexes including homooligomers (Focke et al, 2011;Rice et al, 2013).…”