W- and X-Band Pulsed Electron Nuclear Double-Resonance Study of a Sodium−Nitric Oxide Adsorption Complex in NaA Zeolites

2000 ◽  
Vol 122 (41) ◽  
pp. 10194-10200 ◽  
Author(s):  
Andreas Pöppl ◽  
Thomas Rudolf ◽  
Palanichamy Manikandan ◽  
Daniella Goldfarb
Keyword(s):  
Nitric Oxide ◽  
Double Resonance ◽  
Adsorption Complex ◽  
Electron Nuclear Double Resonance ◽  
X Band ◽  
Nitric Oxide Adsorption

Solution Tetrahydrobiopterin Radical vs. the Enzyme-Bound Radical: A Paramagnetic Reconciliation

2021 ◽  
Vol 16 ◽  
Author(s):  
Yaser Nejaty Jahromy
Keyword(s):  
Nitric Oxide ◽  
Density Functional ◽  
Double Resonance ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Cation Radical ◽  
Spectral Simulation ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Isotropic Hyperfine Coupling ◽  
The 1960S

Background: Nitric oxide synthase (NOS) catalyzes the formation of nitric oxide (NO) and citrulline from L-arginine, dioxygen (O2), and nicotinamide adenine dinucleotide phosphate (NADPH) in a two-step reaction, with the enzyme-bound intermediate Nω-hydroxy-L-arginine (NHA). Previous electron paramagnetic resonance (EPR) studies of NOS reaction have shown that (6R, 1'R, 2'S)-6-(l',2'-dihydroxypropyl)-5,6,7,8-tetrahydropterin (H4B) acts as a single electron donor in both steps of the reaction, resulting in the transient generation of a tetrahydropterin cation radical (H4B•+). Results: H4B•+ can also be chemically generated in strongly acidic solutions. EPR studies of chemically generated H4B•+ and similar pterin radicals date back to the 1960s. However, the reported paramagnetic parameters of H4B•+ in NOS do not seem to match the corresponding reported parameters for either H4B•+ or other pterin centered radicals chemically generated in solution. In particular, the rather isotropic hyperfine coupling of ca. 45 MHz for 1H6 of H4B•+ in NOS is at least 15 MHz larger than that of H4B•+ or any other previously studies pterin solution radical. In the work reported here, a combination of 9.5 - 9.8 GHz contentious wave (cw-) EPR, 34GHz 1H electron nuclear double resonance (ENDOR), spectral simulation and Density Functional Theory (DFT) calculations were used to investigate this seeming discrepancy. Conclusion: We demonstrated that the differences in the paramagnetic parameters of the chemically generated H4B radicals in solutions and those of the H4B radicals in NOS are consistent with the presence of two different conformers of the same cation radical in the two media.

Mo(V) co-ordination in the periplasmic nitrate reductase from Paracoccus pantotrophus probed by electron nuclear double resonance (ENDOR) spectroscopy

2002 ◽  
Vol 363 (3) ◽  
pp. 817-823 ◽  
Author(s):  
Clive S. BUTLER ◽  
Shirley A. FAIRHURST ◽  
Stuart J. FERGUSON ◽  
Andrew J. THOMSON ◽  
Ben C. BERKS ◽  
...  
Keyword(s):  
Nitrate Reductase ◽  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
Time Resolved ◽  
Strongly Coupled ◽  
Periplasmic Nitrate Reductase ◽  
Weakly Coupled ◽  
Endor Spectroscopy ◽  
X Band ◽  
Paracoccus Pantotrophus

The first electron nuclear double resonance (ENDOR) study of a member of the Mo-bis-molybdopterin guanine dinucleotide family of molybdoenzymes is presented, using the periplasmic nitrate reductase from Paracoccus pantotrophus. Rapid freeze-quenched time-resolved EPR revealed that during turnover the intensity of a Mo(V) EPR signal known as High-g [resting] increases. This signal is split by two interacting protons that are not solvent-exchangeable. X-band proton-ENDOR analysis resolved broad symmetrical resonance features that arose from four classes of protons weakly coupled to the Mo(V). Signals from two of these were lost upon exchange into deuterated buffer, suggesting that they may originate from OH− or H2O groups. One of these signals was also lost when the enzyme was redox-cycled in the presence of azide. Since these protons are very weakly coupled OH/H2O groups, they are not likely to be ligated directly to the Mo(V). This suggests that protonation of a Mo(VI)=O group does not occur on reduction to Mo(V), but most probably accompanies reduction of Mo(V) to Mo(IV). A resonance feature from a more strongly coupled proton, that was not lost following exchange into deuterated buffer, could also be resolved at 22–24MHz. The anisotropy of this feature, determined from ENDOR spectra collected at a range of field positions, indicated a Mo—proton distance of approx. 3.2Å, consistent with this being one of the β-methylene protons of a Mo—Cys ligand.

A Q- and X-Band Pulsed Electron Nuclear Double Resonance Study of the Structure and Location of the Vanadyl Ions in the Cs Salt of Heteropolyacid PVMo11O40

2004 ◽  
Vol 126 (9) ◽  
pp. 2905-2911 ◽  
Author(s):  
Marlen Gutjahr ◽  
Joachim Hoentsch ◽  
Rolf Böttcher ◽  
Oksana Storcheva ◽  
Klaus Köhler ◽  
...  
Keyword(s):  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
X Band

Electron–Nuclear Double Resonance of 53Cr3+ in Aluminum Alums

1974 ◽  
Vol 52 (18) ◽  
pp. 1731-1738 ◽  
Author(s):  
A. Manoogian ◽  
B. Auger
Keyword(s):  
Double Resonance ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Electron Nuclear Double Resonance ◽  
Microwave Frequencies ◽  
Straight Line ◽  
Zero Field Splitting Parameter ◽  
X Band ◽  
Splitting Parameter ◽  
D Values

Electron–nuclear double resonance (ENDOR) studies are reported for the isotope 53Cr3+ enriched to 96% in the aluminum alums RbAl(SO4)2∙12H2O and CsAl(SO4)2∙12H2O. The measurements were made at 4.2 K and X-band microwave frequencies (~9.4 GHz). The values of the spin Hamiltonian hyperfine parameters A, B, and Q′ are found to be quite similar to those obtained previously in the corresponding gallium alums even though the zero field splitting parameter D is significantly different. A plot of A − B vs. Q′ indicates that the amount of distortion existing at a chromium site can be related to the type of monovalent ion present, i.e. Rb or Cs. It is possible to draw straight line curves relating the parameters Q′ vs. D, A − B vs. D, and Vzz vs. D which account quite well for all the ENDOR data obtained so far in the alums and GAISH and which could be generally true for chromium magnetic complexes in crystals with D values not too close to zero.

scholarly journals Q-band Electron Nuclear Double Resonance (ENDOR) and X-band EPR of the Sulfobetaine 12 Heat-treated CytochromecOxidase Complex

1997 ◽  
Vol 272 (1) ◽  
pp. 203-209 ◽  
Author(s):  
Siegfried M. Musser ◽  
Yang-Cheng Fann ◽  
Ryszard J. Gurbiel ◽  
Brian M. Hoffman ◽  
Sunney I. Chan
Keyword(s):  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
Band Electron ◽  
Heat Treated ◽  
X Band

A Q- and X-Band Pulsed Electron Nuclear Double Resonance Study of the Structure and Location of the Vanadyl Ions in the Cs Salt of Heteropolyacid PVMo11O40.

ChemInform ◽  
2004 ◽  
Vol 35 (19) ◽  
Author(s):  
Marlen Gutjahr ◽  
Joachim Hoentsch ◽  
Rolf Boettcher ◽  
Oksana Storcheva ◽  
Klaus Koehler ◽  
...  
Keyword(s):  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
X Band
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