Spin-diffusion lattice relaxation, rotating frame

Spin-lattice relaxation of C nuclei is, in principle, very attractive for it is determined by local fluctuations at to c or cuof (rotating or lab frame respectively) spin diffusion among nuclei does not average relaxation rates among chemically distinct carbons. In solids one must append a cautionary note. 

Molecular motions in low molecular weight molecules are rather complex, involving different types of motion such as rotational diffusion (isotropic or anisotropic torsional oscillations or reorientations), translational diffusion and random Brownian motion. The basic NMR theory concerning relaxation phenomena (spin-spin and spin-lattice relaxation times) and molecular dynamics, was derived assuming Brownian motion by Bloembergen, Purcell and Pound (BPP theory) 46). This theory was later modified by Solomon 46) and Kubo and Tomita48 an additional theory for spin-lattice relaxation times in the rotating frame was also developed 49>. 

A cured epoxy synthesised from a mixture of the diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylenediamine was studied by NMR spectroscopy including multiple pulse techniques and spin-lattice relaxation in the rotating frame. Tip. The study [28] focused on the water distribution based upon possible variation in the cross-link density measured by spin diffusion. From the analysis involving a combination of Tip and multiple... 

Similar interpretations of the crystal size of zinc salts of ethylene ionomers were obtained in discussions about H spin-diffusion with ]H spin-lattice relaxation times in the laboratory (Tf3) and rotating (T ) frames. Table 3... 

The NMR rotating frame spin-lattice relaxation time (Tjp) method, which has been used successfully in our laboratory in studies of pressure effects on diffusion in highly viscous liquids, was used in this study to measure lateral diffusion of the phospholipid molecules in DPPC and POPC vesicles. An advantage of this method is that the diffusion coefficient is found directly from measured quantities without estimations of molecular parameters or the effects of the addition of spin or fluorescence probes to... 

In contrast to nematics, a helical twist of the molecular director takes place in the chiral nematic phase. Studies of the spin-lattice relaxation in chiral nematics have shown that the relaxation mechanisms are essentially the same as in pure nematics [141, 142]. At high Larmor frequencies the relaxation is diminished by molecular self-diffusion and by local molecular rotations, whereas director fluctuations determine the relaxation rate at low Larmor frequencies. This can be easily understood because the spin-lattice relaxation rate in the MHz region is dominated by orientational fluctuations with wavelength much smaller than the period of the helix. The influence upon the rotating frame spin-lattice relaxation time Tip of the rotation of the molecules due to diffusion along the helix, an effect specific for twisted structures, has not been observed in COC [143]. 

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