The Effect of Spin Relaxation on ENDOR Spectra Recorded at High Magnetic Fields and Low Temperatures

Epel, Boris; Pöppl, Andreas; Manikandan, P.; Vega, Shimon; Goldfarb, Daniella

doi:10.1006/jmre.2000.2261

Cited by 71 publications

(88 citation statements)

References 12 publications

(26 reference statements)

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“…However, at 240 GHz the nuclear Zeeman interaction is dominant and brings the ENDOR signals out to a much more accessible frequency range. The interpretation is also simplified by the fact that the EPR level splitting is larger than the thermal energy (gµ B B 0 > kT), and that the sign of the ENDOR signal changes across the spectrum due to nuclear polarization 18,19,27 . This also leads to a straightforward determination of the sign of the hyperfine splitting.…”

Section: Resultsmentioning

confidence: 99%

A multifrequency high-field pulsed electron paramagnetic resonance/electron-nuclear double resonance spectrometer

Morley

Brunel

Tol

2008

Review of Scientific Instruments

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We describe a pulsed multi-frequency electron paramagnetic resonance spectrometer operating at several frequencies in the range of 110-336 GHz. The microwave source at all frequencies consists of a multiplier chain starting from a solid state synthesizer in the 12-15 GHz range. A fast PIN-switch at the base frequency creates the pulses. At all frequencies a FabryPérot resonator is employed and the π/2 pulse length ranges from ~100 ns at 110 GHz to ~600 ns at 334 GHz. Measurements of a single crystal containing dilute Mn 2+ impurities at 12 T illustrate the effects of large electron spin polarizations. The capabilities also allow for pulsed electron nuclear double resonance experiments as demonstrated by Mims ENDOR of 39 K nuclei in Cr:K 3 NbO 8 .

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Section: Resultsmentioning

confidence: 99%

A multifrequency high-field pulsed electron paramagnetic resonance/electron-nuclear double resonance spectrometer

Morley

Brunel

Tol

2008

Review of Scientific Instruments

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“…When t r T 1n the echo signal of conventional Davies ENDOR at the second repeat of the pulse sequence can become almost equal to the signal obtained without a π RF pulse and the ENDOR difference signal becomes about zero [12]. An example of this effect is shown in Figure 1(h) for the two-spin system.…”

Section: Cp-endor At Low Temperaturesmentioning

confidence: 89%

“…This low sensitivity leads to the requirement of sample concentrations in ENDOR of one or two orders of magnitude larger than in an EPR experiment and dramatically aggravates the application potential of this technique in studies of biological systems (available only in concentrations on the order of 100 μM). The pulsed ENDOR efficiency and the related issues have been analysed in the past in experimental and theoretical work [3,4,[11][12][13][14]. A sequence, called Tidy ENDOR, has been recently proposed to circumvent relaxation bottlenecks [13].…”

Section: Introductionmentioning

confidence: 99%

Cross-polarisation edited ENDOR

et al. 2013

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Electron-nuclear double resonance (ENDOR) is a fundamental technique in electron paramagnetic resonance (EPR) spectroscopy that directly detects hyperfine transitions of nuclei coupled to a paramagnetic centre. Despite its wide use, spinsensitivity and restricted spectral resolution in powder samples pose limitations of this technique in modern application fields of EPR. In this contribution, we examine the performance of an ENDOR pulse sequence that utilises a preparation scheme different from conventional Davies ENDOR. The scheme is based on electron-nuclear cross-polarisation (eNCP), which requires concomitant microwave (MW) and radio-frequency (RF) irradiation satisfying specific matching conditions between the MW and RF offsets and the hyperfine coupling. Changes in nuclear polarisation generated during eNCP can be detected via a conventional ENDOR read-out sequence consisting of an RF π -pulse followed by EPR-spin echo detection. Using 1 H-BDPA as a standard sample, we first examine the CP matching conditions by monitoring the depolarisation of the electron spin magnetisation. Subsequently, so-called CP-edited ENDOR spectra for different matching conditions are reported and analysed based on the provided theoretical description of the time evolution of the spin density matrix during the experiment. The results demonstrate that CP-edited ENDOR provides additional information with respect to the sign of the hyperfine couplings. Furthermore, the sequence is less sensitive to nuclear saturation effects encountered in conventional ENDOR.

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“…The W-band MIMS 13 C ENDOR spectra were measured at 15 K with the mw pulse sequence p/2-s-p/2-T-p/2-s-echo, with mw pulses of length t p/2 = 24 ns, s = 300-500 ns as indicated, and a radiofrequency pulse of length 48 ls and with variable frequency m rf applied for a time T = 50 ls. The variable mixing time W-band MIMS ENDOR experiments [33,34] (see Figure S1 in the Supplementary material) with the mw sequence p/2-s-p/2-T-t mix -p/2-s-echo were performed at 10 K with a repetition time of 20 ms and with mixing times t mix = 0 ms, 1.5 ms (all other parameters were the same as for the W-band MIMS ENDOR measurements). The asymmetry of the ENDOR peaks as the time t mix is increased can then be used to determine the absolute sign of the hyperfine interaction.…”

Section: Purification Of Active Mcrmentioning

confidence: 99%

“…3b). A variable mixing time ENDOR experiment [33,34] (see Fig. S1) performed at 10 K shows that the hyperfine interaction from the major component is negative.…”

Section: Ch 3 -S-commentioning

confidence: 99%

Coordination and binding geometry of methyl-coenzyme M in the red1m state of methyl-coenzyme M reductase

et al. 2008

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Methane formation in methanogenic Archaea is catalyzed by methyl-coenzyme M reductase (MCR) and takes place via the reduction of methyl-coenzyme M (CH 3 -S-CoM) with coenzyme B (HS-CoB) to methane and the heterodisulfide CoM-S-S-CoB. MCR harbors the nickel porphyrinoid coenzyme F 430 as a prosthetic group, which has to be in the Ni(I) oxidation state for the enzyme to be active. To date no intermediates in the catalytic cycle of MCR red1 (red for reduced Ni) have been identified. Here, we report a detailed characterization of MCR red1m (''m'' for methyl-coenzyme M), which is the complex of MCR red1a (''a'' for absence of substrate) with CH 3 -S-CoM. Using continuous-wave and pulse electron paramagnetic resonance spectroscopy in combination with selective isotope labeling ( 13 C and 2 H) of CH 3 -S-CoM, it is shown that CH 3 -S-CoM binds in the active site of MCR such that its thioether sulfur is weakly coordinated to the Ni(I) of F 430 . The complex is stable until the addition of the second substrate, HS-CoB. Results from EPR spectroscopy, along with quantum mechanical calculations, are used to characterize the electronic and geometric structure of this complex, which can be regarded as the first intermediate in the catalytic mechanism.

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The Effect of Spin Relaxation on ENDOR Spectra Recorded at High Magnetic Fields and Low Temperatures

Cited by 71 publications

References 12 publications

A multifrequency high-field pulsed electron paramagnetic resonance/electron-nuclear double resonance spectrometer

A multifrequency high-field pulsed electron paramagnetic resonance/electron-nuclear double resonance spectrometer

Cross-polarisation edited ENDOR

Coordination and binding geometry of methyl-coenzyme M in the red1m state of methyl-coenzyme M reductase

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