First determination of the spin relaxation properties of a nitronyl nitroxide in solution by electron spin echoes at X-band: A comparison with Tempone

Frequency dependence of electron spin relaxation times in aqueous solution for a nitronyl nitroxide radical and perdeuterated-tempone between 250MHz and 34GHz

“…Since τ R is proportional to a 3 , the difference in radii predicts a ratio of τ R values for 3 to that for tempone of ~3, which is in good agreement with the ratio of τ R values for 2 and 1 = 2.8. Based on these differences in τ R our modeling indicates that the longer values of T 1 and T 2 for 3 than for tempone in toluene at 300 K [18] are due predominantly to the slower tumbling of 3 than of tempone, analogous to what was observed in our studies in water. We predict that if both a nitroxyl and a nitronyl had τ R of 5 to 10 ps, the relaxation rates at X-band would be faster for the nitronyl than for tempone by up to 20%, due to the dominant effect of spin rotation.…”

“…Nitronyl nitroxides are used in identifying nitric oxide [12], dynamic nuclear polarization [13–15], and spintronics [16,17]. After the completion of this work, we received a pre-publication copy of [18], which reports the temperature dependence of relaxation for another nitronyl nitroxide in toluene at X-band, which complements the work reported here.…”

“…In ref. [18] the relaxation rates for nitronyl nitroxide 3 which is analogous to 2 but without the carboxyl group, were studied in toluene as a function of temperature. Based on analysis of the temperature dependence of 1/T 2 – 1/T 1 , the hydrodynamic radius of 3 was found to be 1.5 times larger than for tempone [18].…”

“…[18] the relaxation rates for nitronyl nitroxide 3 which is analogous to 2 but without the carboxyl group, were studied in toluene as a function of temperature. Based on analysis of the temperature dependence of 1/T 2 – 1/T 1 , the hydrodynamic radius of 3 was found to be 1.5 times larger than for tempone [18]. Since τ R is proportional to a 3 , the difference in radii predicts a ratio of τ R values for 3 to that for tempone of ~3, which is in good agreement with the ratio of τ R values for 2 and 1 = 2.8.…”

A slow relaxing species for molecular spin devices: EPR characterization of static and dynamic magnetic properties of a nitronyl nitroxide radical

“…We reasonably attribute this behaviour to the different magnitudes of the dipolar hyperfine coupling tensors, which affects the secular and pseudosecular spin relaxation rates. 60 In summary, at high temperatures, where the spin rotational term dominates the spin relaxation, nitroxides with similar dimensions can in general be competitive with NitSAc, due to their smaller g anisotropy; at lower temperatures, where secular and pseudosecular terms dominate, nitroxides are relaxing much faster than NitSAc, reasonably due to their larger A anisotropy.…”