Techniques for EPR spectroscopy of pulsed electron double resonance (PELDOR): A review

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Techniques for electron paramagnetic resonance (EPR) spectroscopy of pulsed electron double resonance (PELDOR) are reviewed, and the features of the EPR spectroscopy procedure are considered. Basic theoretical results demonstrating the capabilities of the method in investigating paramagnetic particles are presented. It is shown that distances between paramagnetic particles in chaotically oriented systems—pairs and supramolecular ensembles—can be determined in the range of 1.5–8.0 nm. By analyzing the kinetics of the PELDOR signal decay, it is possible, apart from the distance, to determine the distance distribution function, mutual orientation of particles, and number of paramagnetic particles in formation of aggregates. A general block diagram of the PELDOR spectrometer, as well as cm- and mm-wave band spectrometers available in Russian and foreign laboratories, is described. The PELDOR sensitivity and resolution are discussed, and the range of distances measurable using this method is determined. Methods and procedures for determining the experimental parameters used to interpret the kinetics of PELDOR signal decay and estimate the structural parameters of a system of paramagnetic centers under investigation are considered. The PELDOR method with a magnetic field jump is described. The PELDOR technique and its advantages and drawbacks are analyzed in comparison with other methods for determining distances.