Deuterium spin-lattice relaxation rates

An interesting application in porous silica glass employs deuterium spin-lattice relaxation rates in selectively deuterated pyridine (50). The pore-size dependence shown in Fig. 20 is linear in the reciprocal of the pore radius for both the para and ortho positions, but the significant difference in the relaxation at these two positions precludes analysis by an isotropic... 

The second separation method involves n.O.e. experiments in combination with non-selective relaxation-rate measurements. One example concerns the orientation of the anomeric hydroxyl group of molecule 2 in Me2SO solution. By measuring nonselective spin-lattice relaxation-rat s and n.0.e. values for OH-1, H-1, H-2, H-3, and H-4, and solving the system of Eq. 13, the various py values were calculated. Using these and the correlation time, t, obtained by C relaxation measurements, the various interproton distances were calculated. The distances between the ring protons of 2, as well as the computer-simulated values for the H-l,OH and H-2,OH distances was commensurate with a dihedral angle of 60 30° for the H-l-C-l-OH array, as had also been deduced by the deuterium-substitution method mentioned earlier. 

Figure 26.16 The temperature dependence ofthe jump rates ry for deuterium in TaViDos and TaVjDu, as determined from the spin lattice relaxation data [72], The solid lines show the fits of Eq. (26.29) to the data. The dashed line represents the behavior of Ty (l) for H in TaVjHo jj, as derived from the fit of Eq. (26.29) to the proton spin-lattice relaxation data (Ref [54]).

Overall molecular reorientations and internal motions take place in the 10 10 s time window and information about them can be accessed using relaxation rate measurements. By far the best approach is to use NMR experiments where deuterium Zeeman and quadrupolar spin-lattice relaxation times are measured on selectively deuteriated mesogens or on deuteriated probes dissolved in the mesophase. Frequency, orientation and temperature dependence of the spectral densities obtained in these relaxation studies give indications about the various motional modes and are extremely useful for testing orientational diffusion and chain dynamics models. Different deuterium relaxation experiments can be employed to extend the observable dynamic range the quadrupolar echo sequence gives spin-spin relaxation times sensitive to motions in the range s, while extremely slow motions... 

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