Electron paramagnetic resonance spectra of semiquinones. VII. Long-range electron paramagnetic resonance coupling in bridged anthracenes

1968 ◽  
Vol 90 (25) ◽  
pp. 7168-7170 ◽  
Author(s):  
Karl E. Anderson ◽  
D. Kosman ◽  
C. J. Mayers ◽  
B. P. Ruekberg ◽  
Leon M. Stock
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Long Range ◽  
Paramagnetic Resonance ◽  
Resonance Coupling ◽  
Electron Paramagnetic

scholarly journals Coupling of [33S]sulphur to molybdenum(V) in different reduced forms of xanthine oxidase

1981 ◽  
Vol 199 (3) ◽  
pp. 629-637 ◽  
Author(s):  
J P G Malthouse ◽  
G N George ◽  
D J Lowe ◽  
R C Bray
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Xanthine Oxidase ◽  
The Other ◽  
Reduced Form ◽  
Sulphur Atom ◽  
Paramagnetic Resonance ◽  
Different Types ◽  
Resonance Coupling ◽  
Electron Paramagnetic ◽  
Reduced Forms

Different reduced forms of xanthine oxidase, labelled specifically in the cyanide-labile site with 33S, were prepared and examined by electron paramagnetic resonance. Coupling of this isotope to molybdenum(V) was quantified with the help of computer simulations and found to differ markedly from one reduced form to another. The xanthine Very Rapid signal shows strong, highly anisotropic, coupling with A(33S)av. 1.27 mT. For this signal, axes of the g- and A(33S)-tensors are rotated relative to one another. One axis of the A-tensor is in the plane of gxx ang gyy, but rotated by 40 degrees relative to the gxx axis, whereas the direction of weakest coupling to sulphur deviates by 10 degrees from the gzz axis. In contrast with this signal, only rather weaker coupling was observed in different types of Rapid signal [A(33S)av. 0.3--0.4 mT], and in the Inhibited signal coupling was weaker still [A(33S)av. 0.1--0.2 mT]. Clearly, there must be substantial differences in the structures of the molybdenum centre in the different signal-giving species, with the sulphur atom perhaps in an equatorial type of ligand position in the Very Rapid species but in a more axial one in the other species. Structures are discussed in relation to the mechanism of action of the enzyme and the nature of the proton-accepting group that participates in turnover.

The first 1H and 14N ENDOR spectra of an oxygen-centered radical adduct of DMPO-type nitrones

1988 ◽  
Vol 66 (9) ◽  
pp. 2395-2402 ◽  
Author(s):  
D. Larry Haire ◽  
Uwe M. Oehler ◽  
H. Duane Goldman ◽  
Robert L. Dudley ◽  
Edward G. Janzen
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Long Range ◽  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Spectral Signatures ◽  
Radical Adduct ◽  
Sequence Patterns ◽  
Hyperfine Splittings ◽  
Electron Paramagnetic

We report the first 1H and 14N electron nuclear double resonance (ENDOR) spectra of oxygen-centered radical adducts (i.e., derived from the addition of tert-butoxyl radicals) of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as well as the related cyclic nitrones: 4-phenyl-5,5-dimethyl-1-pyrroline-N-oxide (4-Ph-DMPO) and 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO). Features of the electron paramagnetic resonance (EPR) and ENDOR spectra of these cyclic (pyrrolidine) aminoxyl (nitroxide) species along with some deuterated analogues in liquid toluene solutions are highlighted. For instance, we found several long-range γ-H hyperfine splittings (HFS's) detectable by ENDOR that provide unique spectral signatures for these radical adducts. Conformational assignments of the pyrrolidine aminoxyl structures based upon the EPR and ENDOR findings are also discussed. Signs of the various hyperfine splittings (i.e., aN, [Formula: see text]) investigated by cross-relaxation intensity sequence patterns (CRISP) in the ENDOR spectra are also presented.

Electron Paramagnetic Resonance as a Probe of Conformational Flexibility in Cyclic Alkanes

1980 ◽  
Vol 34 (3) ◽  
pp. 268-275 ◽  
Author(s):  
Marsha J. Heinig ◽  
G. R. Eaton ◽  
S. S. Eaton
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Long Range ◽  
Hyperfine Coupling ◽  
Nitroxyl Radical ◽  
Nitroxyl Radicals ◽  
Epr Spectra ◽  
Paramagnetic Resonance ◽  
Cyclic Alkanes ◽  
Temperature Spectra ◽  
Electron Paramagnetic

Electron paramagnetic resonance (EPR) spectra of a homologous series of nitroxyl radicals derived from cyclic alkanones with 6 to 15 carbons in the ring have been obtained as a function of temperature. Long-range hyperfine coupling (0.7 to 2.2 G) was observed in the low-temperature spectra for rings with 6, 7, and 9 to 15 carbons. Deuteration of the 11- to 14-membered rings indicated that the long-range coupling was to one of the protons on the carbons adjacent to the point of attachment of the nitroxyl radical. For the 9- to 15-membered rings, there was a temperature region in which the hyperfine coupling decreased rapidly. This decrease is attributed to rapid conformational averaging on the EPR time scale. For the 12-, 13-, and 15-membered rings, the high temperature spectra exhibited resolved hyperfine coupling which can be computer-simulated, assuming four equivalent protons. The activation energies estimated from the coalescence temperatures in the EPR spectra fall in the range estimated by nuclear magnetic resonance and show similar influences of ring size on rigidity.

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