A simple method for hyperfine-selective heteronuclear pulsed ENDOR via proton suppression

Doan, Peter E.; Fan, Chaoliang; Davoust, Clark E.; Hoffman, Brian M.

doi:10.1016/0022-2364(91)90338-t

Cited by 16 publications

(16 citation statements)

References 5 publications

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“…The hyperfine contrast selectivity provided by the properties of the inversion pulse can be exploited for the assignment of ENDOR peaks to weakly or strongly coupled nuclei in X-band spectra where overlap of ENDOR signals due to strongly coupled heteronuclei and weakly coupled protons occurs [6, 7, 26]. We explored the hyperfine contrast selectivity provided by shaped band-selective inversion pulses and found that overlapping ENDOR spectra could be separated more efficiently compared to experiments with rectangular pulses.…”

Section: Resultsmentioning

confidence: 99%

“…Comparison of ENDOR spectra recorded with different lengths of the inversion pulse and therefore different relative intensities of small and large hyperfine couplings can allow assignment of the different ENDOR peaks to different types of nuclei. The optimum inversion pulse bandwidth for suppression of proton hyperfine couplings was found to also maximize the ENDOR signal for larger heteronuclear hyperfine couplings and led to the proposal of the POSHE (PrOton Suppression and Heteronuclear Enhancement) ENDOR technique for selectively recording heteronuclear ENDOR spectra [6, 7]. …”

Section: Introductionmentioning

confidence: 99%

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ENDOR with band-selective shaped inversion pulses

Tait

Stoll

2017

Journal of Magnetic Resonance

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Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity. Band-selective inversion pulses are characterized by almost rectangular inversion profiles, leading to full inversion for spin packets with resonance offsets within the pulse excitation bandwidth and leaving spin packets outside the excitation bandwidth largely unaffected. Here, we explore the consequences of using different band-selective amplitude-modulated pulses designed for NMR as the inversion pulse in ENDOR. We find an increased sensitivity for small hyperfine couplings compared to rectangular pulses of the same bandwidth. In echo-detected Davies-type ENDOR, finite Fourier series inversion pulses combine the advantages of increased absolute ENDOR sensitivity of short rectangular inversion pulses and increased sensitivity for small hyperfine couplings of long rectangular inversion pulses. The use of pulses with an almost rectangular frequency-domain profile also allows for increased control of the hyperfine contrast selectivity. At X-band, acquisition of echo transients as a function of radiofrequency and appropriate selection of integration windows during data processing allows efficient separation of contributions from weakly and strongly coupled nuclei in overlapping ENDOR spectra within a single experiment.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

ENDOR with band-selective shaped inversion pulses

Tait

Stoll

2017

Journal of Magnetic Resonance

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“…Spectra can be compared quantitatively to detect changes in hyperfine couplings or isotopic content without the scaling or shifting needed for spectra obtained by the Davies ENDOR sequence. In addition, Mims ENDOR can be simulated by de facto standard software like EasySpin [29, 30] without arbitrary corrections (as in Davies ENDOR) for pulse-width artifacts [31, 32]. Two-dimensional hyperfine sublevel correlation (HYSCORE) spectra were measured with a 4-pulse microwave sequence, π/2-τ-π/2- t 1 -π- t 2 -π/2-τ- echo with a four-step phase cycle, where τ, t 1 , and t 2 indicate independently-incremented delays that produce a two-dimensional dataset [27, 28, 33, 34].…”

Section: Methodsmentioning

confidence: 99%

The tetrahydrobiopterin radical interacting with high- and low-spin heme in neuronal nitric oxide synthase – A new indicator of the extent of NOS coupling

Krzyaniak

Cruce

Vennam

et al. 2016

Free Radical Biology and Medicine

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Reaction intermediates trapped during the single-turnover reaction of the neuronal ferrous nitric oxide synthase oxygenase domain (Fe(II)nNOSOX) show four EPR spectra of free radicals. Fully-coupled nNOSOX with cofactor (tetrahydrobiopterin, BH4) and substrate (l-arginine) forms the typical BH4 cation radical with an EPR spectrum ~4.0 mT wide and hyperfine tensors similar to reports for a biopterin cation radical in inducible NOSOX (iNOSOX). With excess thiol, nNOSox lacking BH4 and l-arg is known to produce superoxide. In contrast, we find that nNOSOX with BH4 but no l-arg forms two radicals with rather different, fast (~ 250 µs at 5 K) and slower (~ 500 µs at 20 K), electron spin relaxation rates and a combined ~7.0 mT wide EPR spectrum. Rapid freeze-quench CW- and pulsed-EPR measurements are used to identify these radicals and their origin. These two species are the same radical with identical nuclear hyperfine couplings, but with spin-spin couplings to high-spin (4.0 mT component) or low-spin (7.0 mT component) Fe(III) heme. Uncoupled reactions of nNOS leave the enzyme in states that can be chemically reduced to sustain unregulated production of NO and reactive oxygen species in ischemia-reperfusion injury. The broad EPR signal is a convenient indicator of uncoupled nNOS reactions producing low-spin Fe(III) heme.

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“…This suppression of ENDOR transitions for nuclei with A«~a>1 has been referred to as a self-ELDOR (30] effect and also as a spin-alignment hole [31]. This selective suppression of ENDOR signal amplitudes has also been used as a spectral editing tool [32][33][34][35]. Since the effect on the ENDOR amplitudes depends only on the relation between the magnitude of the hyperfine coupling and the excitation bandwidth of the microwave preparation pulse, this spectral editing mechanism has been referred to as a hyperfine contrast selectivity mechanism [28,36].…”

Section: Davies Endormentioning

confidence: 99%

Spin dynamics in continuous wave and pulsed ENDOR spectroscopy of coals

1994

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ENDOR experiments on coals recorded using continuous wave (CW) and pulsed techniques appear to give qualitatively different spectra. A matrix proton signal dominates the ENDOR spectrum of coals recorded in the CW ENDOR experiment while both a matrix and local proton ENDOR signals with hyperfine couplings of up to 20 MHz are observed in spectra recorded using pulsed excitation techniques. Analysis of these spectra lead to different implications for the structure of the molecules that host the unpaired electron. Using a combination of pulsed EPR (Electron Spin Echo, FID detected hole burning) and pulsed Electron Nuclear Multiple Resonance (Sub-level relaxation, hyperfine selective ENDOR, EPR sub-spectra) experiments, we investigate the electron and nuclear spin dynamics in order to reconcile the different signal amplitudes observed in the CW and pulsed ENDOR spectra. In the CW ENDOR experiment, the results of the Fill detected hole burning experiments prove that the low ENDOR signal intensity can not be attributed to spectral diffusion mechanisms competing with ENDOR mechanisms. Instead, we find that an unfavorable ratio of the electron and nuclear spin relaxation rates results in small local ENDOR signals. The matrix line dominates the spectrum because of the large number of matrix protons. In the pulsed ENDOR experiment, the hyperfine contrast selectivity mechanism suppresses the intensity of the matrix ENDOR signal and enhances the amplitudes of the local ENDOR signals. In addition, the ENDOR signal is not a function of the ratio of the electron and nuclear relaxation rates.

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A simple method for hyperfine-selective heteronuclear pulsed ENDOR via proton suppression

Cited by 16 publications

References 5 publications

ENDOR with band-selective shaped inversion pulses

ENDOR with band-selective shaped inversion pulses

The tetrahydrobiopterin radical interacting with high- and low-spin heme in neuronal nitric oxide synthase – A new indicator of the extent of NOS coupling

Spin dynamics in continuous wave and pulsed ENDOR spectroscopy of coals

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