- EPR and ELDOR Studies on Spin Relaxation in Perdeuterated 2,2,6,6-Tetramethyl-4-piperidone-N-oxyl in Liquid Solutions. The Slowly Relaxing Local Structure Mechanism
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The spin relaxation of perdeuterated 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (PDT) in various solvents was studied via EPR line width and saturation and ELDOR.Saturation and ELDOR results are incompatible with the line-width result when the latter are analyzed in the standard manner: rotational diffusion (RD) with temperature invariance of the anisotropy factor N and of the non-Debye parameter ε in the nonsecular spectral densities j(ω0).In a more general approach, first all relevant intramolecular relaxation terms are obtained independently from the combined T2, T1, and ELDOR data.Further analysis of these terms suggests that, in general, the rotational relaxation of PDT may arise from rotational diffusion (RD) and a slowly relaxing local structure mechanism (SRLS).Separation of RD and SRLS contributions seems possible via the electron spin relaxation rate, more particularly via the spin-rotational interaction part WeSR.This is most clearly shown by the results on PDT in methylcyclohexane (MCH) and in the isotropic phase of the liquid crystalline solvent 4'-n-octyl-4-cyanobiphenyl (8CB).Particularly, by virtue of the results on 8CB the combined T2-T1-ELDOR method seems promising in spin label/spin probe research on ordering media by its option to yield directly the ordering dynamics of the nearby environment.
- Drift, E. van der,Rousseeuw, B. A. C.,Smidt, J.
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- Synthesis of nitroxyl radicals for overhauser-enhanced magnetic resonance imaging
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Non-invasive measurement and visualization of free radicals in vivo would be important to clarify their roles in the pathogenesis of free radical-associated diseases. Nitroxyl radicals can react with free radicals and be derivatized to achieve specific cellular / subcellular localizing capabilities while retaining the simple spectral features useful in imaging. Overhauser-enhanced magnetic resonance imaging (OMRI), which is a double resonance technique, creates images of free radical distributions in small animals by enhancing the water proton signal intensity via the Overhauser Effect. In this study, we synthesized various nitroxyl probes having 15N nuclei and deuterium, and measured the enhancement factor for Overhauser-enhanced magnetic resonance imaging experiments. 15N-D-4- Oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (15N-D-oxo-TEMPO) has the highest enhancement factor compared with other nitroxyl probes. The proton signal enhancement was higher for 15N-labeled nitroxyl probes when compared to the 14N-labeled analogues because of the reduced spectral multiplicity of the I = 1/2 nucleus. Furthermore, this enhancement is proportional to the line width and number of electron spin resonance lines of nitroxyl radicals. Finally, we compared the Overhauser-enhanced magnetic resonance image of 15N-labeled, deuterated 4-Oxo-2,2,6,6- tetramethylpiperidine-1-oxyl with that of 14N-H-TEMPOL. These results suggested that the selective deuteration of the nitroxyl probes enhanced the signal-to-noise ratio and thereby improved spatial and temporal resolutions.
- Yamada, Ken-Ichi,Kinoshita, Yuichi,Yamasaki, Toshihide,Sadasue, Hiromi,Mito, Fumiya,Nagai, Mika,Matsumoto, Shingo,Aso, Mariko,Suemune, Hiroshi,Sakai, Kiyoshi,Utsumi, Hideo
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experimental part
p. 548 - 553
(2009/04/11)
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