1H NMR relaxation in glycerol solutions of nitroxide radicals: Effects of translational and rotational dynamics

Abstract

(1)H spin-lattice relaxation rates in glycerol solutions of selected nitroxide radicals at temperatures between 200 K and 400 K were measured at 15 MHz and 25 MHz. The frequency and temperature conditions were chosen in such a way that the relaxation rates go through their maximum values and are affected by neither the electron spin relaxation nor the electron-nitrogen nucleus hyperfine coupling, so that the focus could be put on the mechanisms of motion. By comparison with (1)H spin-lattice relaxation results for pure glycerol, it has been demonstrated that the inter-molecular electron spin-proton spin dipole-dipole interactions are affected not only by relative translational motion of the solvent and solute molecules, but also by their rotational dynamics as the interacting spins are displaced from the molecular centers; the eccentricity effects are usually not taken into account. The (1)H relaxation data have been decomposed into translational and rotational contributions and their relative importance as a function of frequency and temperature discussed in detail. It has been demonstrated that neglecting the rotational effects on the inter-molecular interactions leads to non-realistic conclusions regarding the translational dynamics of the paramagnetic molecules.

MRI temperature and velocity measurements in a fluid layer with heat transfer

“…Concerning the longitudinal relaxation time T 1 , our results are in agreement with results given by Kruk et al [26]. We observe that two values of temperature are possible for a given T 1 .…”

Nuclear spin relaxation in liquids and gases

“…They could demonstrate in this way that the intermolecular relaxation contained contributions from both translational and rotational motions, the latter entering the model through the eccentricity effects mentioned above in connection with other work from the same group. 141 Field-cycling relaxometry of viscous liquids and polymer melts was reviewed by Kruk et al 175 Shikata and Yoshida 176 studied 17 O spin-lattice relaxation in some small ketones, studied as neat liquids. The variable-temperature NMR work was complemented by studies of frequency-dependent dielectric relaxation and viscosity measurements.…”

“…Kruk et al 141 studied 1 H relaxation in glycerol solutions of selected nitroxide radicals over a large temperature range and at two magnetic fields. The intermolecular relaxation was found to be affected not only by translational motion of the solvent and solute but also by the rotational dynamics.…”

Reactivity of Fluoro‐Substituted Bis(thiocarbonyl) Donors with Diiodine: An XRD, FT–Raman, and DFT Investigation

“…In solutions of nitroxide radicals the proton relaxation is affected by the much larger electron transition frequency and by hyperfine coupling between the electron and nitrogen nucleus 44. 47–52 Relaxation expressions accounting for these effects have been provided for solutions containing 15 N radicals48 as well as for the case of 14 N;50 because of their rather complex form we do not provide them explicitly in this Minireview. Combining the expansion of ${J_{{\rm{trans}}} \left( \omega \right)}$ with these relaxation formulae, three ranges of linearity of ${R_1 \left( \omega \right)}$ versus ${\sqrt \omega }$ have been predicted and confirmed experimentally 48.…”