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Titolo:
Orientation dependence of electric field effects on the g factor of nitroxides measured by 220 GHz EPR
Autore:
Gulla, AF; Budil, DE;
Indirizzi:
Northeastern Univ, Dept Chem, Boston, MA 02115 USA Northeastern Univ Boston MA USA 02115 iv, Dept Chem, Boston, MA 02115 USA
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY B
fascicolo: 33, volume: 105, anno: 2001,
pagine: 8056 - 8063
SICI:
1520-6106(20010823)105:33<8056:ODOEFE>2.0.ZU;2-4
Fonte:
ISI
Lingua:
ENG
Soggetto:
SPIN-RESONANCE; PARAMAGNETIC-RESONANCE; AMINO-TERMINUS; ALPHA-HELIX; PROTEINS; SPECTROSCOPY; RADICALS; LABELS; DYNAMICS; PEPTIDES;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
38
Recensione:
Indirizzi per estratti:
Indirizzo: Budil, DE Northeastern Univ, Dept Chem, Boston, MA 02115 USA Northeastern Univ Boston MA USA 02115 hem, Boston, MA 02115 USA
Citazione:
A.F. Gulla e D.E. Budil, "Orientation dependence of electric field effects on the g factor of nitroxides measured by 220 GHz EPR", J PHYS CH B, 105(33), 2001, pp. 8056-8063

Abstract

The spectroscopic properties of stable nitroxide radicals, including the magnetic properties of the impaired electron, are known to be sensitive to local electric fields. The most accessible parameter has been the isotropic N-14 hyperfine splitting a(N), which is readily measured using conventionalelectron paramagnetic resonance (EPR) spectroscopy. High-frequency, high-field EPR may be used to gain additional information about the electrostaticmicroenvironment of a nitroxide by revealing subtle influences on the nitroxide g tensor. In the present work, two nitroxide radicals with a local electric field E-loc provided by internal ionizable groups are studied as a function of pH by 220 GHz EPR. The three principal g values are resolved by immobilizing the probes in pH-adjusted poly(vinyl alcohol) films. Both nitroxides exhibit observable shifts in g(x) and g(y) as a function of pH, fromwhich the g shifts may be calibrated with respect to E-loc The calibrationshows that nitroxide probes are sensitive to field magnitudes that are typically found in proteins, and may provide a useful means to measure such fields quantitatively. In addition, differences between the two probes in therelative effect of E-loc upon g(y) are observed, which suggests that that the g tensor may be sensitive to the orientation of the local field as wellas its magnitude. Finally, the measured sensitivity to internal electric fields implies that high-field EPR of nitroxides should also be sensitive toexternally applied electric field, i.e., should exhibit a linear electric field effect (LEFE). Although the LEFE at conventional EPR Fields is well characterized for metal centers, our results suggest that high-field EPR should enable its observation in organic radicals as well.

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Documento generato il 15/07/20 alle ore 13:47:22