Spin-lattice relaxation line-shape analysis

Hagen, W.R. and Albracht, S.P.J. 1982. Analysis of strain-induced EPR-line shapes and anisotropic spin-lattice relaxation in a [2Fe-2S] ferredoxin. Biochimica et Biophysica Acta 702 61-71. 

NMR is a powerful technique for providing information about the distribution and dynamics of local RFs, characteristic of such systems. While the quadrupole-perturbed NMR line shape analysis gives details about the distribution of local RFs, spin-lattice relaxation (SLR) studies can give information on the dynamics in the frustrated state of these systems. From the literature, it can be seen that most of the NMR experiments have been carried out in RADP mixed systems and its deuterated analogues. ETFI group published a number of results21-23 on various mixed crystals. 

Spin-Lattice Relaxation and Line-Shape Analysis... 

Investigating molecular dynamics using NMR, in contrast to DS and LS, involves the application of several conceptually quite different techniques. For example, in spin-lattice relaxation studies one is concerned with familiar time correlation functions that are probed as spectral density point by point (Section II.D.2). In the case of line-shape analysis, usually a two-pulse echo sequence is applied, and the... 

The 13C-NMR line-shape analysis at T < TN in (TMTTF)2Br has proved that the periodicity of the magnetic modulation is commensurate with the underlying lattice [52]. The spin lattice relaxation is activated in the SDW ground state since there exists a finite energy gap in the phason modes of this commensurate SDW phase (Fig. 8). 

When the H- H dipole-dipole interaction can be measured for a specific pair of H nuclei, studies of the temperature dependence of both the H NMR line-shape and the H NMR relaxation provide a powerful way of probing the molecular dynamics, even in very low temperature regimes at which the dynamics often exhibit quantum tunnelling behaviour. In such cases, H NMR can be superior to quasielastic neutron scattering experiments in terms of both practicality and resolution. The experimental analysis can be made even more informative by carrying out H NMR measurements on single crystal samples. In principle, studies of both the H NMR lineshape and relaxation properties can be used to derive correlation times (rc) for the motion in practice, however, spin-lattice relaxation time (T measurements are more often used to measure rc as they are sensitive to the effects of motion over considerably wider temperature ranges. 

The attractiveness of surface/pore characterization via NMR spin-lattice relaxation measurements of pore fluid lies in the potential advantages this technique has as compared to the conventional approaches. These include rapid analysis, lower operating costs, analysis of wet materials, no pore shape assumption, a wide range of pore sizes can be evaluated (0.5 nm to >1 /im), no network/percolation effects and the technique is non-destructive. When determining specific surface areas, NMR analysis does not require out-gassing and has the potential for on-line analysis of slurries. 

Muller and coworkers have recently reported the molecular behavior of 1,3,5-trioxane in a cyclophosphazene inclusion compound using H-2 NMR [68]. The experimental data were obtained by variable-temperature line shape analysis, spin-spin and spin-lattice relaxation time measurements and by 2D exchange between 30 and 370 K. At room temperature, highly mobile trioxane guests were observed. They undergo various overall and conformational motions which give rise to substantial orientational disorder within the hexagonal cyclophosphazene channels. 

Solid-state NMR of the Rb has been employed to investigate the phase transitions in polycrystalline LiRbS04. The spin-lattice relaxation time Ti and the NMR line shape have been measured using MAS and MQ MAS methods between 373 and 488 K. The QCC, %, the asymmetry parameter, r, and the isotropic chemical shift, 5, have been determined from the analysis of MAS and MQ MAS spectra. The anomalies of x near the phase transition were associated with the deformation of the local environment of the Rb ions in the crystal lattice. 

Relaxation, CIDNP, and N.Q.R.—Relaxation. Phosphorus-31 and carbon-13 relaxation times are reported for dimethyl methylphosphonate. The mobility of phosphazene polymers has been studied using P spin-lattice relaxation parameters. The structure and mobility of polycrystalline nitrilotrimethylphos-phonic acid was estimated by line shape analysis. Molecular interactions of guanosine monophosphate and ATP have been studied through their relaxation properties. ... 

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