Hyperfine Interactions
Mostrando 13-24 de 25 artigos, teses e dissertações.
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13. VECTOR MODEL FOR INDIRECT PROTON HYPERFINE INTERACTIONS IN π-ELECTRON RADICALS*
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14. Magnetism in dense hexagonal iron
The magnetic state of hexagonal close-packed iron has been the subject of debate for more than three decades. Although Mössbauer measurements find no evidence of the hyperfine splitting that can signal the presence of magnetic moments, density functional theory predicts an antiferromagnetic (afm) ground state. This discrepancy between theory and experiment
National Academy of Sciences.
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15. Iron-sulfur proteins: spin-coupling model for three-iron clusters.
Recent Mössbauer and EPR studies of two ferredoxins and of aconitase have given evidence for a three-iron cluster, probably of a [3Fe-3S] type. The studies of the oxidized EPR-active centers have shown that the three iron sites are characterized by significantly different magnetic hyperfine coupling constants. For the ferredoxin from Azotobacter vinelandii,
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16. Electron-Nuclear Double Resonance of a Protein That Contains Copper: Evidence for Nitrogen Coordination to Cu(II) in Stellacyanin
Electron-nuclear double resonance has been used to study ligand hyperfine interactions of the copper (II) complex in a frozen solution of the blue protein stellacyanin. It is shown that the copper ion coordinates with at least one nitrogen ligand, and probably more than one, and that the copper ion is in a hydrophobic environment.
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17. PROTON MAGNETIC RESONANCE STUDIES OF PORPHYRIN IRON (III) CYANIDES*
The nuclear magnetic resonance (NMR) spectra at 220 Mc of cyanodeuteroporphyrin IX dimethyl ester iron (III), cyanoprotoporphyrin IX diethyl ester iron (III), and cyanoprotoporphyrin IX iron (III) in a mixed solvent of 80 per cent d5-pyridine and 20 per cent D2O have been measured. The resonances are assigned and, except for the ester alkoxy groups, are show
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18. Magnetoreception through Cryptochrome May Involve Superoxide
In the last decades, it has been demonstrated that many animal species orient in the Earth magnetic field. One of the best-studied examples is the use of the geomagnetic field by migratory birds for orientation and navigation. However, the biophysical mechanism underlying animal magnetoreception is still not understood. One theory for magnetoreception in bir
The Biophysical Society.
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19. Anisotropic magnetic interactions in the primary radical ion-pair of photosynthetic reaction centers
The quantum yield of triplets formed by ion-pair recombination in quinone-depleted photosynthetic reaction centers is found to depend on their orientation in a magnetic field. This new effect is expected to be a general property of radical pair reactions in the solid state. For 0 < H < 1,000 G, the quantum yield anisotropy is caused by anisotropic electron d
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20. A Comparative Spin-Label Study of Isolated Plasma Membranes and Plasma Membranes of Whole Cells and Protoplasts from Cold-Hardened and Nonhardened Winter Rye
Lipid-lipid and lipid-protein interactions in the plasma membranes of whole cells and protoplasts and an isolated plasma membrane fraction from winter rye (Secale cereale L. cv Puma) have been studied by spin labeling. Spectra were recorded between −40°C and 40°C using the freely diffusing spin-label, 16-doxyl stearic acid, as a midbilayer membrane probe
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21. Interaction of Bee Venom Melittin with Zwitterionic and Negatively Charged Phospholipid Bilayers: A Spin-Label Electron Spin Resonance Study
Electron spin resonance (ESR) spectroscopy was used to study the penetration and interaction of bee venom melittin with dimyristoylphosphatidylcholine (DMPC) and ditetradecylphosphatidylglycerol (DTPG) bilayer membranes. Melittin is a surface-active, amphipathic peptide and serves as a useful model for a variety of membrane interactions, including those of p
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22. Mössbauer and EPR studies of activated aconitase: development of a localized valence state at a subsite of the [4Fe-4S] cluster on binding of citrate.
During activation of aconitase a ferrous ion is incorporated into a [3Fe-4S] cluster to yield a structure with a [4Fe-4S] core. Using 57Fe or 56Fe for activation we have studied with Mössbauer spectroscopy the beef heart enzyme in the presence of citrate. Our studies show that the environment of one iron site (Fea) of the [4Fe-4S] cluster is drastically alt
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23. An electron spin resonance study of interactions between gramicidin A' and phosphatidylcholine bilayers.
The model of microscopic order and macroscopic disorder was used to stimulate electron spin resonance spectra of spin-labeled lipids, 5-PC, 10-PC, and 16-PC in multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) containing gramicidin A' (GA) at temperatures above the gel-to-liquid crystal transition of DPPC. The simulations show that at a lower c
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24. Electron nuclear double resonance evidence supporting a monomeric nature for P700+ in spinach chloroplasts
Proton electron nuclear double resonance (ENDOR) spectra of P700+ in spinach chloroplasts and in photosystem I particles have been obtained and compared with the corresponding ENDOR spectrum of monomeric chlorophyl a+ (Chla+) cation radical. The hyperfine couplings for P700+ can be interpreted in terms of those expected for a monomer Chla+ radical. The reduc