Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9587614 | Journal of Magnetic Resonance | 2005 | 8 Pages |
Abstract
Electron spin relaxation times for four triarylmethyl (trityl) radicals at room temperature were measured by long-pulse saturation recovery, inversion recovery, and electron spin echo at 250Â MHz, 1.5, 3.1, and 9.2Â GHz in mixtures of water and glycerol. At 250Â MHz T1 is shorter than at X-band and more strongly dependent on viscosity. The enhanced relaxation at 250Â MHz is attributed to modulation of electron-proton dipolar coupling by tumbling of the trityl radicals at rates that are comparable to the reciprocal of the resonance frequency. Deuteration of the solvent was used to distinguish relaxation due to solvent protons from the relaxation due to intra-molecular electron-proton interactions at 250Â MHz. For trityl-CD3, which contains no protons, modulation of dipolar interaction with solvent protons dominates T1. For proton-containing radicals the relative importance of modulation of intra- and inter-molecular proton interactions varies with solution viscosity. The viscosity and frequency dependence of T1 was modeled based on dipolar interaction with a defined number of protons at specified distances from the unpaired electron. At each of the frequencies examined T2 decreases with increasing viscosity consistent with contributions from T1 and from incomplete motional averaging of anisotropic hyperfine interaction.
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Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Rikard Owenius, Gareth R. Eaton, Sandra S. Eaton,