Electron-Electron Double Resonance

A reference-arm W-band (94 GHz) microwave bridge with two sample-irradiation arms for saturation recovery (SR) EPR and ELDOR experiments is described. Frequencies in each arm are derived from 2 GHz synthesizers that have a common time-base and are translated to 94 GHz in steps of 33 and 59 GHz. Intended applications are to nitroxide radical spin labels and spin probes in the liquid phase. An enabling technology is the use of a W-band loop-gap resonator (LGR) (J.W. Sidabras et al., Rev. Sci. Instrum. 78 (2007) 034701). The high efficiency parameter (8.2 GW −1/2 with sample) permits the saturating pump pulse level to be just 5 mW or less. Applications of SR EPR and ELDOR to the hydrophilic spin labels 3-carbamoyl-2,2,5,5-tetra-methyl-3-pyrroline-1-yloxyl (CTPO) and 2,2,6,6,-tetramethyl-4-piperidone-1-oxyl (TEMPONE) are described in detail. In the SR ELDOR experiment, nitrogen nuclear relaxation as well as Heisenberg exchange transfer saturation from pumped to observed hyperfine transitions. SR ELDOR was found to be an essential method for measurements of saturation transfer rates for small molecules such as TEMPONE.

show abstract

“…(1) (2) Here, N is the spin-label concentration. I 1 is a constant to be defined by initial conditions.…”

Section: Summary Of the Theory Of Sr Epr And Eldor Of Spin Labelsmentioning

confidence: 99%

“…If a saturation transfer mechanism is active, the observed signal decreases at a saturation transfer rate and subsequently recovers with a time constant T 1e . Several reviews of ELDOR and SR EPR have been written [1][2][3][4].…”

Section: Introduction Overview Of Saturation Recovery Epr and Eldor Amentioning

confidence: 99%

Saturation recovery EPR and ELDOR at W-band for spin labels

Froncisz

Camenisch

Ratke

et al. 2008

Journal of Magnetic Resonance

View full text Add to dashboard Cite

show abstract

“…It turned out that ELDOR-detected NMR (EDNMR) is the method of choice. The microwave double-resonance method electron–electron double resonance (ELDOR) [ 106 ] was introduced more than 50 years ago for investigating relaxation processes in paramagnetic systems [ 107 – 112 ]. In continuous-wave realization this method was soon recognized, in particular by Jim Hyde [ 10 ], to be applicable also for obtaining information about the distance between paramagnetic centers.…”

Section: Selected High-field Frozen-solution Endor Ednmr and Peldor mentioning

confidence: 99%

Jim Hyde and the ENDOR Connection: A Personal Account

2017

View full text Add to dashboard Cite

In this minireview, we report on our year-long EPR work, such as electron–nuclear double resonance (ENDOR), pulse electron double resonance (PELDOR) and ELDOR-detected NMR (EDNMR) at X-band and W-band microwave frequencies and magnetic fields. This report is dedicated to James S. Hyde and honors his pioneering contributions to the measurement of spin interactions in large (bio)molecules. From these interactions, detailed information is revealed on structure and dynamics of macromolecules embedded in liquid-solution or solid-state environments. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultra-fast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy and its multi-frequency extensions to new horizons concerning sensitivity of detection, selectivity of molecular interactions and time resolution. Among the most important advances is the upgrading of EPR to high magnetic fields, very much in analogy to what happened in NMR. The ongoing progress in EPR spectroscopy is exemplified by reviewing various multi-frequency electron–nuclear double-resonance experiments on organic radicals, light-generated donor–acceptor radical pairs in photosynthesis, and site-specifically nitroxide spin-labeled bacteriorhodopsin, the light-driven proton pump, as well as EDNMR and ENDOR on nitroxides. Signal and resolution enhancements are particularly spectacular for ENDOR, EDNMR and PELDOR on frozen-solution samples at high Zeeman fields. They provide orientation selection for disordered samples approaching single-crystal resolution at canonical g-tensor orientations—even for molecules with small g-anisotropies. Dramatic improvements of EPR detection sensitivity could be achieved, even for short-lived paramagnetic reaction intermediates. Thus, unique structural and dynamic information is revealed that can hardly be obtained by other analytical techniques. Micromolar concentrations of sample molecules have become sufficient to characterize stable and transient reaction intermediates of complex molecular systems—offering exciting applications for physicists, chemists, biochemists and molecular biologists.

show abstract

“…Relaxation enhancement of nuclear spins by paramagnetic species that may be native or added as probes or labels can complicate NMR spectra, but can be used to measure distances in substances studied. Similarly, nuclear spins couple to electron spins and via these couplings report the near environment of the electron spins which can be revealed by ENDOR [123,124] and by spin-echo methods such as ESEEM and HYSCORE. Coupling of the electron spins to the nuclear spins in the environment reciprocally affects the electron spin relaxation time, including in some cases sufficiently to affect the EPR linewidth, as is often demonstrated by changing solvents from normal isotopic abundance to deuterated solvents.…”

Section: Applications That Drive Innovationmentioning

confidence: 99%

The world as viewed by and with unpaired electrons

Eaton,

Eaton

2012

Journal of Magnetic Resonance

View full text Add to dashboard Cite

Recent advances in electron paramagnetic resonance (EPR) include capabilities for applications to areas as diverse as archeology, beer shelf life, biological structure, dosimetry, in vivo imaging, molecular magnets, and quantum computing. Enabling technologies include multifrequency continuous wave, pulsed, and rapid scan EPR. Interpretation is enhanced by increasingly powerful computational models.

show abstract

Electron-Electron Double Resonance

Cited by 10 publications

References 129 publications

Saturation recovery EPR and ELDOR at W-band for spin labels

Saturation recovery EPR and ELDOR at W-band for spin labels

Jim Hyde and the ENDOR Connection: A Personal Account

The world as viewed by and with unpaired electrons

Contact Info

Product

Resources

About