Spin-lattice relaxation studies

Al3+-exchanged synthetic hectorite is a good catalyst for these conversions, and the 13C NMR spectrum obtained in the interlamellar, proton-catalyzed addition of water to 2-methylpropene is indistinguishable (Fig. 79) from that of f-butanol. Doubtless studies of this kind, where natural-abundance, 3C NMR signals are used to probe the chemical identity and motional freedom of reactant and product species situated in the interlamellar spaces of clays or pillared clays (see below), will become increasingly popular. Using l3C NMR linewidths and spin-lattice relaxation studies, Matsumoto et al. (466) have succeeded in discriminating between the internal and external surfaces of pillared montmorillonites. 

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... 

Flere (1 - f) and (1 - S) are the losses brought about by the corresponding process and gfastj/3 (t -> oo) = 0 (see Fig. 6). The factor / can be regarded as a generalized non-ergodicity parameter and, hence, it is expected to show a similar anomaly as the Debye-Waller factor /g (see Fig. 5). Such decomposition of the correlation function is useful in spin-lattice relaxation studies, as will be discussed in Section 3.2.4. 

Returning to the spin-lattice relaxation studies, the relaxation behavior of type A and B glasses was systematically compared only recently.3,100,101 It turned out that, at least down to T 0.5 Tg, the spin-lattice relaxation in molecular glasses (without internal relaxing degrees of freedom) is essentially determined by the slow dynamics , namely the NCL contribution and the /1-process.70,73,100,101,115 Next, we shall briefly review these studies. 

In NMR work, spin-lattice relaxation measurements indicated a non-exponential nature of the ionic relaxation.10,11 While this conclusion is in harmony with results from electrical and mechanical relaxation studies, the latter techniques yielded larger activation energies for the ion dynamics than spin-lattice relaxation analysis. Possible origins of these deviations were discussed in detail.10,193 196 The crucial point of spin-lattice relaxation studies is the choice of an appropriate correlation function of the fluctuating local fields, which in turn reflect ion dynamics. Here, we refrain from further reviewing NMR relaxation studies, but focus on recent applications of multidimensional NMR on solid-ion conductors, where well defined correlation functions can be directly measured. 

Finally, it is interesting whether local relaxation processes of the glassy matrix facilitate ionic diffusion. For phosphate glasses and borate glasses, 31P and nB NMR spin-lattice relaxation studies gave evidence for some coupling of ion and matrix dynamics below Tg. Moreover, it was reported that local rearrange-... 

Deslauriers, R., McGregor, W. II., Sarantakis, D., and Smith, I. . P. (1974). Biochemistry 13, 3443. Carbon-13 Nuclear Magnetic Resonance Studies of Structure and Function in Thyrotropin-Releasing Factor. Determination of the Tautomeric Form of Histidine and Relationship to Biology Activity. Deslauriers, R., Paiva, A. . M., Schaumburg, K., and Smith, I. . P. (1975). Biochemistry 14, 878. Conformational Flexibility of Angiotensin II. A Carbon-13 Spin-Lattice Relaxation Study. 

Fossel, E. T., Easwaran, K. R. K., and Blout, E. R. (1975). Biopolymers 14, 927. A 1 3C Spin-Lattice Relaxation Study of Dipeptides Containing Glycine and Proline Mobility of the Cyclic Proline Side Chain. 

Levy, G. C., Komoroski, R. A., and Halstead, J. A. (1974)./. Amer. Chem. Soc. 96, 5456. Solvation and Segmental Motions of n-Alkylammonium Ions. A 1 3 C Spin-Lattice Relaxation Study. 

Spin-lattice relaxation studies on PBzE dendrimers show a similar behavior, with constant Ti values for the peripheral phenyls suggesting that the steric congestion does not increase at the surface with generation. Decreasing relaxation times for the internal layers indicate a radial increase of density with generation, consistent with the de Gennes and Hervet model. ... 

Deslauriers, R., 1. C. P. Smith, and R. Walter Conformational flexibility of the Neurohypophyseal Hormones oxytocin and Lysine-Vasopressin. A Carbon-13-Spin-Lattice Relaxation Study of back-bone and side chain. J. Amer. Chem. Soc. 96, 2289 (1974). 

Studies of amorphous hydrogenated carbon films and diamond films, using CRAMPS, spin-lattice relaxation measurements, etc. Measurements on hydrogen-fuUerene complexes, using various advanced solid-state NMR methods and spin-lattice relaxation studies... 

A C n.m.r. spin-lattice relaxation study of solvent effects on the rotational dynamics of methyl a- and /9-glycosides has been reported. Rotation rates for both anomers follow the order Me0H-DMF-D20molecular weights of the solvents. 

A.G. Avent and R. Freeman, NMR spin-lattice relaxation studied by magnetization transfer, J. Magn. Resonance 39, 169 (1980). 

Ribeiro, A. A., E. A. Dennis, Carbon-13 spin-lattice relaxation study on p-tert-OPE, J. Phys. Chem., 1976,80,1746-1753. 

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