Electron Dipole–Dipole ESEEM in Field-Step ELDOR of Nitroxide Biradicals

Author： Kulik L.V. Grishin Y.A. Dzuba S.A. Grigoryev I.A. Klyatskaya S.V. Vasilevsky S.F. Tsvetkov Y.D.

ISSN： 1090-7807

Source： Journal of Magnetic Resonance, Vol.157, Iss.1, 2002-07, pp. : 61-68

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Abstract

The use of a rapid stepping of the magnetic field for investigation of electron dipole–dipole ESEEM in pulsed X-band ELDOR is described. The magnetic field jump, synchronized with a microwave pumping pulse, is positioned between the second and the third pulses of the stimulated echo pulse sequence. This echo is measured as a function of the delay between the first and the second pulses. The data are analyzed for a Fourier transform resulting in a Pake resonance pattern. To remove the electron-nuclear contributions to ESEEM, time traces with pumping were divided by those without. This resulted in complete elimination of electron-nuclear contributions, which is seen from the absence of peaks at nuclear frequencies and the similarity of results for protonated and deuterated solvents. For increasing the electron–electron modulation depth, a scanning of the magnetic field during the microwave pumping is proposed. The interspin distances and their distribution are determined for two long-chained (ca. 2 nm) nitroxide biradicals in glassy toluene and in frozen nematic liquid crystal 4-cyano-4′-pentyl-biphenyl. For the latter solvent, the alignment of the axis connecting two nitroxides in biradicals is quantitatively analyzed. © 2002 Elsevier Science (USA).