Extreme narrowing region

Kovacs H, Bagley S and Kowalewski J 1989 Motional properties of two disaccharides in solutions as studied by carbon-13 relaxation and NOE outside of the extreme narrowing region J. Magn. Reson. 85 530 1... 

Usually, nuclear relaxation data for the study of reorientational motions of molecules and molecular segments are obtained for non-viscous liquids in the extreme narrowing region where the product of the resonance frequency and the reorientational correlation time is much less than unity [1, 3, 5]. The dipolar spin-lattice relaxation rate of nucleus i is then directly proportional to the reorientational correlation time p... 

Ionic liquids, however, are often quite viscous, and the measurements are thus beyond the extreme narrowing region. The relaxation rates hence become frequency-dependent. Under these conditions, the equation for the spin-lattice relaxation rate becomes more complex ... 

The measurement of correlation times in molten salts and ionic liquids has recently been reviewed [11] (for more recent references refer to Carper et al. [12]). We have measured the spin-lattice relaxation rates l/Tj and nuclear Overhauser factors p in temperature ranges in and outside the extreme narrowing region for the neat ionic liquid [BMIM][PFg], in order to observe the temperature dependence of the spectral density. Subsequently, the models for the description of the reorientation-al dynamics introduced in the theoretical section (Section 4.5.3) were fitted to the experimental relaxation data. The nuclei of the aliphatic chains can be assumed to relax only through the dipolar mechanism. This is in contrast to the aromatic nuclei, which can also relax to some extent through the chemical-shift anisotropy mechanism. The latter mechanism has to be taken into account to fit the models to the experimental relaxation data (cf [1] or [3] for more details). Preliminary results are shown in Figures 4.5-1 and 4.5-2, together with the curves for the fitted functions. 

Given the specific, internuclear dipole-dipole contribution terms, p,y, or the cross-relaxation terms, determined by the methods just described, internuclear distances, r , can be calculated according to Eq. 30, assuming isotropic motion in the extreme narrowing region. The values for T<.(y) can be readily estimated from carbon-13 or deuterium spin-lattice relaxation-times. For most organic molecules in solution, carbon-13 / , values conveniently provide the motional information necessary, and, hence, the type of relaxation model to be used, for a pertinent description of molecular reorientations. A prerequisite to this treatment is the assumption that interproton vectors and C- H vectors are characterized by the same rotational correlation-time. For rotational isotropic motion, internuclear distances can be compared according to... 

The Ti value for the TMPS moiety decreased as the temperature increased from —90 to 80 °C. This indicates that the molecular motion is in the slow-motion region in this temperature range. However, the T value for the DMS moiety is increased as the temperature is increased from —67 to 80 °C, becomes a minimum at —67 °C and is increased again as the temperature is decreased from —67 to —90 °C. This indicates that the molecular motion is in the extreme narrow region above —67 °C. The copolymer retains both rigid and soft parts in the main chain. 

Similarly, the limits of the broader areas having three solid phases are fairly certain, whereas those of extremely narrow regions such as the yi + y2 + uranium in the 675° C. section and the delta hydride + yi + -uranium in the 675° and 750° C. sections are subject to question. Additional x-ray data would be helpful in defining these phase fields. 

Results of Bo dependency were applied to the two models 1) Static model We assumed a homogeneous population of Na" " in the intracellular fluid, 2) Exchange model We assumed an exchange between Na+ under the slow-motion condition and the Na+ in the extreme narrowing region. Results obtained in this study can be fitted with the two-site exchange... 

As shown in Eq. 2, the observed diffusion coefficient should be time-averaged value of and Db. However, the observed value is virtually equal to since values of Db and Pb are so small compared with values of Df j and (1 - Pb). Therefore, observed diffusion coefficient of Na ion in the agar gel mainly represents the motion of Na ion in the extreme narrowing region. 

The proportional counter is essentially a very fast counter and has a linear counting curve up to about 10,000 cps. This ability to separate closely spaced pulses is due to the fact that the avalanche triggered by the absorption of an x-ray quantum is confined to an extremely narrow region of the counter, 0.1 mm or less, and does not spread along the counter tube (Fig, 7-17). The rest of the counter volume is still sensitive to incoming x-rays. 

In the extreme narrowing region of correlation times for molecular rotations, i.e. very fast molecular rotations with respect to the resonance frequency, the following applies ... 

BPP theory of NMR relaxation [12]. Therefore, an increase in q means an increase in the inverse of temperature. According to the BPP theory, Ti decreases with increasing temperature and increases after passing through a minimum as the temperature is increased further. As shown in Fig. 20.11, the decrease in Ti for the C—O (rr) and CH3 (rr) carbons of PM A A in the gel with the increase in <7 means that the motion of the side chain carbons is in the extreme narrowing region at the lefthand side of the BPP... 

From these spectra, the carbons contributing to the peak at 15.8 ppm have a longer Ti value than those at 16.7 ppm. This indicats that the former carbons are more mobile than the latter carbons, because the Ala Ca-helix carbons in tropomyosin have correlation times in the extreme narrowing region at room temperature. The distance between the two a-helical axes in... 

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