Frequency dependence of electron spin relaxation times in aqueous solution for a nitronyl nitroxide radical and perdeuterated-tempone between 250 MHz and 34 GHz.
Joshua R Biller, Virginia M Meyer, Hanan Elajaili, Gerald M Rosen, Sandra S Eaton, Gareth R Eaton
Index: J. Magn. Reson. 225 , 52-7, (2012)
Full Text: HTML
Abstract
Electron spin relaxation times of perdeuterated tempone (PDT) 1 and of a nitronyl nitroxide (2-(4-carboxy-phenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) 2 in aqueous solution at room temperature were measured by 2-pulse electron spin echo (T(2)) or 3-pulse inversion recovery (T(1)) in the frequency range of 250 MHz to 34 GHz. At 9 GHz values of T(1) measured by long-pulse saturation recovery were in good agreement with values determined by inversion recovery. Below 9 GHz for 1 and below 1.5 GHz for 2,T(1)~T(2), as expected in the fast tumbling regime. At higher frequencies T(2) was shorter than T(1) due to incomplete motional averaging of g and A anisotropy. The frequency dependence of 1/T(1) is modeled as the sum of spin rotation, modulation of g and A-anisotropy, and a thermally-activated process that has maximum contribution at about 1.5 GHz. The spin lattice relaxation times for the nitronyl nitroxide were longer than for PDT by a factor of about 2 at 34 GHz, decreasing to about a factor of 1.5 at 250 MHz. The rotational correlation times, τ(R) are calculated to be 9 ps for 1 and about 25 ps for 2. The longer spin lattice relaxation times for 2 than for 1 at 9 and 34 GHz are due predominantly to smaller contributions from spin rotation that arise from slower tumbling. The smaller nitrogen hyperfine couplings for the nitronyl 2 than for 1 decrease the contribution to relaxation due to modulation of A anisotropy. However, at lower frequencies the slower tumbling of 2 results in a larger value of ωτ(R) (ω is the resonance frequency) and larger values of the spectral density function, which enhances the contribution from modulation of anisotropic interactions for 2 to a greater extent than for 1.Copyright © 2012 Elsevier Inc. All rights reserved.
Related Compounds
Related Articles:
2012-03-22
[J. Phys. Chem. A 116(11) , 2855-66, (2012)]
2010-09-01
[Free Radic. Res. 44(9) , 1036-43, (2010)]
2006-06-20
[Brain Res. 1095(1) , 190-9, (2006)]
Nitroxide spin exchange due to re-encounter collisions in a series of n-alkanes.
2008-08-14
[J. Chem. Phys. 129(6) , 064501, (2008)]
2009-04-30
[J. Phys. Chem. A 113(17) , 4930-40, (2009)]