A novel high-field/high-frequency EPR and ENDOR spectrometer operating at 3 mm wavelength

Burghaus, Olaf; Rohrer, Martin; Gotzinger, T; Plato, M.; Möbius, K.

doi:10.1088/0957-0233/3/8/013

Cited by 181 publications

(200 citation statements)

References 18 publications

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“…To facilitate field calibration and maximize sensitivity, the echo detected spectra were acquired with 10 G, 300 Hz square-wave field modulation, yielding the derivative presentation directly from the spectrometer without further need for data manipulation. The magnetic field was calibrated to an accuracy of ∼ 3 G using a sample of Mn doped into MgO (24). The temperature of the sample was maintained to an accuracy of approximately ± 0.3° using an Oxford Spectrostat continuous-flow cryostat and ITC503 temperature controller.…”

Section: High-field Epr Spectroscopymentioning

confidence: 99%

EPR Spectroscopic and Computational Characterization of the Hydroxyethylidene-Thiamine Pyrophosphate Radical Intermediate of Pyruvate:Ferredoxin Oxidoreductase

et al. 2006

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The radical intermediate of pyruvate:ferredoxin oxidoreductase (PFOR) from Moorella thermoacetica was characterized using electron paramagnetic resonance (EPR) spectroscopy at Xband and D-band microwave frequencies. EPR spectra obtained with various combinations of isotopically labeled substrate (pyruvate) and coenzyme (thiamine pyrophosphate (TPP)), were analyzed by spectral simulations. Parameters obtained from the simulations were compared with those predicted from electronic structure calculations on various radical structures. The g-values and 14 N/ 15 N-hyperfine splittings obtained from the spectra are consistent with a planar, hydroxyethylidene-thiamine pyrophosphate (HE-TPP) π-radical, in which spin is delocalized onto the thiazolium sulfur and nitrogen atoms. The 1 H-hyperfine splittings from the methyl group of pyruvate and the 13 C-hyperfine splittings from C2 of both pyruvate and TPP are consistent with a model in which the pyruvate-derived oxygen atom of the HE-TPP radical forms a hydrogen bond. The hyperfine splitting constants and g-values are not compatible with those predicted for a nonplanar, σ/n-type cation radical.Pyruvate:ferredoxin oxidoreductase (E.C.1.2.7.1) (PFOR 1 ) is a member of the 2-keto acid oxidoreductase family. This enzyme plays a central role in anaerobic fermentative metabolism by catalyzing the reversible, CoA-dependent, oxidative decarboxylation of pyruvate to acetylCoA and CO 2 (3). The two electrons generated in the oxidative reaction are transferred through [4Fe-4S] clusters in PFOR to an oxidized ferredoxin (4). PFOR is found in microbes lacking mitochondria from all three kingdoms (5). PFOR enzymes from different species have been grouped into three types depending on subunit composition (6). The different types of PFOR enzymes have between one and three [4Fe-4S] clusters. clusters are electron transfer cofactors serving as way-stops for electrons exiting the active site in the forward † This work was supported by grants from the National Institutes of Health: GM35752 G.H.R.; GM39451 S.W.R.; DK44083 T.P.B.; and Center Grant 1P20RR17675 to the University of Nebraska. S.O.M was supported by an NIH Predoctoral Training Grant T32 GM 08293. *To whom correspondence should be addressed. Telephone: (608) 262-0509; Fax: (608) 265-2904; Email: reed@biochem.wisc.edu. ‖ Current address: Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520-8066 1 Abbreviations: PFOR, pyruvate:ferredoxin oxidoreductase; CoA, coenzyme A; TPP, thiamine pyrophosphate; HE-TPP, hydroxyethylidene-thiamine pyrophosphate; EPR, electron paramagnetic resonance; ENDOR, electron nuclear double resonance; CW continuous wave; DFT, density functional theory; S/N, signal-to-noise ratio; RMSD, root mean square deviation; POX, pyruvate oxidase. to an acetyl radical followed by radical recombination with a CoA-thiyl radical (11). Elucidation of the structure of the HE-TPP radical intermediate is essential to an eventual understanding of the subsequent steps in the overall reacti...

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Section: High-field Epr Spectroscopymentioning

confidence: 99%

EPR Spectroscopic and Computational Characterization of the Hydroxyethylidene-Thiamine Pyrophosphate Radical Intermediate of Pyruvate:Ferredoxin Oxidoreductase

et al. 2006

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“…Recent developments in Gunn oscillator technology enabled the development of devices matching the performance of klystrons with the additional advantage of solid-state operation (low power consumption) and low replacement costs. Up to 150 GHz, both klystrons [22] and Gunn oscillators [22,50,51] can be employed in high-frequency CW-EPR spectrometers. For pulsed operation, however, they are less well suited.…”

Section: Klystron and Gunn Oscillatormentioning

confidence: 99%

“…In the following, we will describe the most widely used probe heads and their applications in some detail. [22,24], who applied a bi-confocal FP resonator at W-band. Also, Schmidt et al [19,75] selected an FP resonator for their first W-band experiments.…”

Section: Probe Headsmentioning

confidence: 99%

“…Several coupling schemes are described. The iris in the cylinder wall can be adjusted using a metal tip on a dielectric slab [22]; alternatively, the iris can be placed in the plunger wall and the coupling can be adjusted using a sliding short [83]. A convenient way to adjust the coupling is by rotating the resonator around the waveguide coupling to the iris hole in the cylinder wall.…”

Section: Single-mode Resonators (Te 011 )mentioning

confidence: 99%

“…In this sense, they built the first ''quasi-optical'' EPR spectrometer. CW and pulsed EPR as well as ENDOR at 95 GHz (W-band) was realized for the first time by Schmidt et al [19][20][21] and Möbius et al [22][23][24]. In 1996, the Bruker company introduced the first commercial pulsed (and CW) EPR spectrometer at 95 GHz [25,26].…”

Section: Introductionmentioning

confidence: 99%

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High-Frequency EPR Instrumentation

Reijerse¹

2009

Appl Magn Reson

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An overview of the most recent developments in high-frequency highfield electron paramagnetic resonance (EPR) instrumentation is given. In particular, the practical choices concerning sources, detectors, resonators, propagation systems as well as magnet technology are discussed in the light of various possible applications. Examples of particular homodyne and heterodyne quasi-optic EPR systems illustrate the potential for future developments in EPR technology.

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Continuous-Wave EPR

Est

2016

eMagRes

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A novel high-field/high-frequency EPR and ENDOR spectrometer operating at 3 mm wavelength

Cited by 181 publications

References 18 publications

EPR Spectroscopic and Computational Characterization of the Hydroxyethylidene-Thiamine Pyrophosphate Radical Intermediate of Pyruvate:Ferredoxin Oxidoreductase

EPR Spectroscopic and Computational Characterization of the Hydroxyethylidene-Thiamine Pyrophosphate Radical Intermediate of Pyruvate:Ferredoxin Oxidoreductase

High-Frequency EPR Instrumentation

Continuous-Wave EPR

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