Properties of the HYSCORE Spin Echo Signal

Astashkin, Andrei V.; Raitsimring, Arnold M.

doi:10.1006/jmre.2000.2264

Cited by 6 publications

(5 citation statements)

References 16 publications

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“…In addition, all spectra show diagonal lines at about 18 MHz and at 9.4 MHz ( g z ), 7.4 MHz ( g y ), and 7.0 and 8.2 MHz ( g x ). Regarding the diagonal features, we can mention that they can originate from the usual stimulated ESEEM due to the incomplete inversion of the electron spins by the third mw pulse . While this does not change the interpretation of the 18 MHz line as belonging to one of the interdoublet transitions, we will not attempt to reproduce the diagonal lines in our HYSCORE simulations.…”

Section: Resultsmentioning

confidence: 98%

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using ³³S Labeling and ESEEM Spectroscopy

et al. 2007

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Sulfite oxidase from Arabidopsis thaliana has been reduced at pH = 6 with sulfite labeled with 33 S (nuclear spin I = 3/2), followed by reoxidation by ferricyanide to generate the Mo(V) state of the active center. To obtain information about the hyperfine interaction (hfi) of 33 S with Mo(V), continuous wave EPR and electron spin echo envelope modulation (ESEEM) experiments have been performed. The interpretation of the EPR and ESEEM spectra was facilitated by a theoretical analysis of the nuclear transition frequencies expected for the situation of the nuclear quadrupole interaction being much stronger than the Zeeman and hyperfine interactions. The isotropic hfi constant of 33 S determined in these experiments was about 3 MHz, which demonstrates the presence of coordinated sulfate in the sulfite-reduced low-pH form of the plant enzyme.

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Section: Resultsmentioning

confidence: 98%

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using ³³S Labeling and ESEEM Spectroscopy

et al. 2007

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“…In the hyperfine sublevel correlation (HYSCORE) spectra of 33 S-SDH R55Q (Fig. 4) the off-diagonal correlation lines were only seen at g z and g x , whereas the HYSCORE spectra obtained at the inner parts of the EPR spectrum only showed weak diagonal lines that might have originated from the contribution of a stimulated electron spin echo (ESE) signal to the HYSCORE ESE signal [35]. …”

Section: Resultsmentioning

confidence: 99%

Pulsed EPR investigations of the Mo(V) centers of the R55Q and R55M variants of sulfite dehydrogenase from Starkeya novella

et al. 2010

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Continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopy have been used to characterize two variants of bacterial sulfite dehydrogenase (SDH) from Starkeya novella in which the conserved active-site arginine residue (R55) is replaced by a neutral amino acid residue. Substitution by the hydrophobic methionine residue (SDH R55M ) has essentially no effect on the pH dependence of the EPR properties of the Mo(V) center, even though the X-ray structure of this variant shows that the methionine residue is rotated away from the Mo center and a sulfate anion is present in the active-site pocket (Bailey et al. in J Biol Chem 284:2053-2063). For SDH R55M only the high-pH form is observed, and samples prepared in H 2 17 O-enriched buffer show essentially the same 17 O hyperfine interaction and nuclear quadrupole interaction parameters as SDH WT enzyme. However, the pH dependence of the EPR spectra of SDH R55Q , in which the positively charged arginine is replaced by the neutral hydrophilic glutamine, differs significantly from that of SDH WT . For SDH R55Q the blocked form with bound sulfate is generated at low pH, as verified by 33 S couplings observed upon reduction with 33 S-labeled sulfite. This observation of bound sulfate for SDH R55Q supports our previous hypothesis that sulfite-oxidizing enzymes can exhibit multiple pathways for electron transfer and product release (Emesh et al. in Biochemistry 48:2156-2163). At pH ≥ 8 the high-pH form dominates for SDH R55Q .

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“…The echo intensity is measured at each t 1 and t 2 value, which are varied stepwise at constant t. This two-dimensional set of echoes gives, after a Fourier transformation along t 1 and t 2 , a two-dimensional HYSCORE spectrum. [30] The lengths of the p/2 and p pulses were 16 and 32 ns, respectively, and a delay of t = 128 ns between the first two p/2 pulses gave the best sensitivity and resolution for the detection of 1 H, 14 N, and 19 F peaks, with no blind-spot effect. HYSCORE spectra were recorded with 256 256 data points for both t 1 and t 2 time domains.…”

Section: Methodsmentioning

confidence: 99%

Radical Localization in a Series of Symmetric Ni^IIComplexes with Oxidized Salen Ligands

Chiang¹,

Kochem²,

Jarjayes³

et al. 2012

Chemistry A European J

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Square-planar nickel(II) complexes of salen ligands, N,N'-bis(3-tert-butyl-(5R)-salicylidene)-1,2-cyclohexanediamine), in which R=tert-butyl (1), OMe (2), and NMe(2) (3), were prepared and the electronic structure of the one-electron-oxidized species [1-3](+·) was investigated in solution. Cyclic voltammograms of [1-3] showed two quasi-reversible redox waves that were assigned to the oxidation of the phenolate moieties to phenoxyl radicals. From the difference between the first and second redox potentials, the trend of electronic delocalization 1(+·) >2(+·) >3(+·) was obtained. The cations [1-3](+·) exhibited isotropic g tensors of 2.045, 2.023, and 2.005, respectively, reflecting a lower metal character of the singly occupied molecular orbital (SOMO) for systems that involve strongly electron-donating substituents. Pulsed-EPR spectroscopy showed a single population of equivalent imino nitrogen atoms for 1(+·), whereas two distinct populations were observed for 2(+·). The resonance Raman spectra of 2(+·) and 3(+·) displayed the ν(8a) band of the phenoxyl radicals at 1612 cm(-1), as well as the ν(8a) bands of the phenolates. In contrast, the Raman spectrum of 1(+·) exhibited the ν(8a) band at 1602 cm(-1), without any evidence of the phenolate peak. Previous work showed an intense near-infrared (NIR) electronic transition for 1(+·) (Δν(1/2) =660 cm(-1), ε=21,700 M(-1) cm(-1)), indicating that the electron hole is fully delocalized over the ligand. The broader and moderately intense NIR transition of 2(+·) (Δν(1/2) =1250 cm(-1) , ε=12,800 M(-1) cm(-1)) suggests a certain degree of ligand-radical localization, whereas the very broad NIR transition of 3(+·) (Δν(1/2) =8630 cm(-1), ε=2550 M(-1) cm(-1)) indicates significant localization of the ligand radical on a single ring. Therefore, 1(+·) is a Class III mixed-valence complex, 2(+·) is Class II/III borderline complex, and 3(+·) is a Class II complex according to the Robin-Day classification method. By employing the Coulomb-attenuated method (CAM-B3LYP) we were able to predict the electron-hole localization and NIR transitions in the series, and show that the energy match between the redox-active ligand and the metal d orbitals is crucial for delocalization of the radical SOMO.

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Properties of the HYSCORE Spin Echo Signal

Cited by 6 publications

References 16 publications

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using ³³S Labeling and ESEEM Spectroscopy

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using ³³S Labeling and ESEEM Spectroscopy

Pulsed EPR investigations of the Mo(V) centers of the R55Q and R55M variants of sulfite dehydrogenase from Starkeya novella

Radical Localization in a Series of Symmetric Ni^IIComplexes with Oxidized Salen Ligands

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Properties of the HYSCORE Spin Echo Signal

Cited by 6 publications

References 16 publications

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using 33S Labeling and ESEEM Spectroscopy

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using 33S Labeling and ESEEM Spectroscopy

Pulsed EPR investigations of the Mo(V) centers of the R55Q and R55M variants of sulfite dehydrogenase from Starkeya novella

Radical Localization in a Series of Symmetric NiIIComplexes with Oxidized Salen Ligands

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Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using ³³S Labeling and ESEEM Spectroscopy

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using ³³S Labeling and ESEEM Spectroscopy

Radical Localization in a Series of Symmetric Ni^IIComplexes with Oxidized Salen Ligands