High-field EPR

Abstract

Among the numerous spectroscopic techniques utilized in photosynthesis research, high-field/high-frequency EPR and its pulse extensions ESE, ENDOR, ESEEM, and PELDOR play an important role in the endeavor to understand, on the basis of structure and dynamics data, dominant factors that control specificity and efficiency of light-induced electron- and proton-transfer processes in primary photosynthesis. Short-lived transient intermediates of the photocycle can be characterized by high-field EPR techniques, and detailed structural information can be obtained even from disordered sample preparations. The chapter describes how multifrequency high-field EPR methodology, in conjunction with mutation strategies for site-specific isotope or spin labeling and with the support of modern quantum-chemical computation methods for data interpretation, is capable of providing new insights into the photosynthetic transfer processes. The information obtained is complementary to that of protein crystallography, solid-state NMR and laser spectroscopy.

Field and frequency modulated sub-THz electron spin resonance spectrometer

“…Significant developments of high-field quasi-optical ESR are ongoing, 32,33,[36][37][38][39][40] where cw ESR has evolved up to f hν = 750 GHz 41 and free electron lasers (FEL) can provide highest irradiation power (several kW) in pulsed or quasi-cw high-field ESR. [42][43][44][45] However, these spectrometers are highly specialized and operate in one dedicated high-field environment, 41 and a very recent commercial system provides a high ESR sensitivity but narrow (0.2 T) field sweep range.…”

EPR Spectroscopy

“…Due to space limitations only a selected range of systems can be covered. Recent good reviews exist about EPR spectroscopic studies on photosynthesis [20][21][22] and metalloproteins [23][24][25][26]. Strongly physics-related application fields, such as quantum computing [27], electrically detected [28] and optically [29] detected EPR spectroscopy of dopants and defects in solids are left out.…”

X-Ray Detected Magnetic Resonance at Sub-THz Frequencies Using a High Power Gyrotron Source

“…Whereas the precession cone angles θ 0 are quite small in ferrimagnets, pulsed EPR spectrometers typically require the magnetization to be rotated by 90 • or even 180 • in the rotating frame [22][23][24]. Recall, however, that XMCD signals of paramagnetic phases were detected so far only under high magnetic bias fields (B 0 ≥ 5T) and at fairly low temperatures (T ≤ 20K): XDEPR spectra should thus be pumped at sub-THz frequencies [25].…”

“…(ii) resonances affected by orientational anisotropy and hyperfine structures can be better resolved [24,30].…”