Relaxation times and line widths of isotopically-substituted nitroxides in aqueous solution at X-band |
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Authors: | Biller Joshua R Meyer Virginia Elajaili Hanan Rosen Gerald M Kao Joseph P Y Eaton Sandra S Eaton Gareth R |
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Institution: | aDepartment of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, United States;bCenter for EPR Imaging in vivo Physiology, University of Denver, Denver, CO 80208, United States;cCenter for EPR Imaging and In Vivo Physiology, University of Maryland, Baltimore, Baltimore, MD 21201, United States;dCenter for Biomedical Engineering and Technology, University of Maryland, Baltimore, Baltimore, MD 21201, United States;eDepartment of Pharmaceutical Sciences, University of Maryland, Baltimore, Baltimore, MD 21201, United States;fDepartment of Physiology, University of Maryland, Baltimore, Baltimore, MD 21201, United States |
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Abstract: | Optimization of nitroxides as probes for EPR imaging requires detailed understanding of spectral properties. Spin lattice relaxation times, spin packet line widths, nuclear hyperfine splitting, and overall lineshapes were characterized for six low molecular weight nitroxides in dilute deoxygenated aqueous solution at X-band. The nitroxides included 6-member, unsaturated 5-member, or saturated 5-member rings, most of which were isotopically labeled. The spectra are near the fast tumbling limit with T1∼T2 in the range of 0.50–1.1 μs at ambient temperature. Both spin–lattice relaxation T1 and spin–spin relaxation T2 are longer for 15N- than for 14N-nitroxides. The dominant contributions to T1 are modulation of nitrogen hyperfine anisotropy and spin rotation. Dependence of T1 on nitrogen nuclear spin state mI was observed for both 14N and 15N. Unresolved hydrogen/deuterium hyperfine couplings dominate overall line widths. Lineshapes were simulated by including all nuclear hyperfine couplings and spin packet line widths that agreed with values obtained by electron spin echo. Line widths and relaxation times are predicted to be about the same at 250 MHz as at X-band. |
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Keywords: | Spin&ndash spin relaxation Spin&ndash lattice relaxation Spin packet line width |
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