Dipolar and chemical shift

Finally, dipolar and chemical shift correlation (DIPSHIFT) NMR was used to investigate the molecular motion and dynamics of the immobilized alkyl ligands of poly(ethylene-co-acrylic acid) stationary phases [164]. Through the measurement of the dipolar couplings, it was possible to discern the geometry of motion of... 

Fig. 3. Example spectra from the one-dimensional dipolar-shift experiment taken from reference 7. (a) (Top) Experimental l3C chemical shift anisotropy powder pattern for Ru(C5H5)2 and (below) for comparison, the dipolar shift l3C spectrum for the same compound, (b) Calculated dipolar-shift lineshapes for different angles (indicated) between the lH-13C dipolar and chemical shift anisotropy tensor principal z-axes.

Fig. 20. Experimental setup for applications of the SPECIFIC CP experiment in the context of triple-resonance solid-state NMR experiments. After an initial broadband adiabatic CP step from protons to the I nuclei, SPECIFIC transfer to the observed 5 nucleus occurs during the mixing time tm. The resulting signal represents a dipolar and chemical shift-filtered spectrum and can be controlled by variation of the carrier frequencies and the radiofrequency during the SPECIFIC transfer. A conventional HETCOR experiment is obtained by the introduction of an evolution time t. (Adapted from Baldus et al.215 with permission.)...

Figure 8 depicts PISA wheels in which the helix tilt angle r varies from 15 to 90°. The magnitudes of the principal components of the 5-spin CSA tensor (533 = 64, 522 = 11, and 5n = 217 ppm) and the angles defining the relative orientations of the dipolar and chemical shift tensors (a = 0° and (1=17 ) were used in the simulations of PISA wheels presented in Fig. 8. The centers of the wheels as a function of helix tilt angle from both the peaks of the dipolar-coupling doublet are also shown as dashed lines in Fig. 8. The centers of the chemical shift and dipolar coupling tensors intersect at the isotropic values of the chemical shift (119.3 ppm) and the 4l " N dipolar coupling (0 Hz). The PISA wheel patterns can also be used to determine p-strand structures in lipid bilayers as the loop-like shapes of these p-strand resonances are very different from the wheel-like patterns of a-helices. It is clear from the...

Fig. 8. PISA wheel patterns for the helix tilt (r) varying from 15 to 90° simulated using Eq. (8) in the text. The chemical shift tensor values of 533 = 64, 522 = 77, and 5 =2I7 ppm, an N-H bond length of 1.07 A, and the relative orientations of the dipolar and chemical shift tensors of a = Q°, fi= T were used in the simulations. Variation of the PISA wheel with respect to the tilt angle of the helix is shown for one peak of the dipolar-coupling doublet as the spectrum is symmetric with respect to the zero frequency. The centers (shown in dashed lines) of the wheels as a function of the helix tilt angle for both dipolar transitions are linear and intersect at the isotropic N chemical shift frequency (119.3 ppm) and 0 Hz H °N dipolar coupling [Eq. (9)].

Fig. 5. (a) Two-dimensional 1SN- H dipolar/chemical shift spectrum obtained from [lSN]acetylvaline showing the dipolar and chemical shift projections. Linewidths are typically 50-150 Hz for the dipolar and 0.5-1.0 ppm for the chemical shift dimension. vR = 1.07 kHz. (b) Dipolar cross-sections taken from the 2D spectrum. Each trace runs parallel to ivh through a particular rotational sideband in u>2. (i) Experimental i5N-H spectra from [15N]acetylvaline, vR = 1.07 kHz. The two simulations (ii and iii) assume two different orientations of the dipolar and shielding tensors, (ftD = 22°, D = 0°) and (Ai = 17°, aD = 0°), respectively, and illustrate the subtle differences in orientation which can be detected in the spectra. 

In view of the dominant quadrupolar interaction of deuterium, its weak dipolar and chemical shift interactions can be neglected, which simplifies the theoretical analysis of the quadrupolar lineshapes and relaxation data (see Sections 6.2.2 and 6.2.3). 

The amplitudes of ring- and main-chain motions of a variety of polystyrenes have been established from the 13C NMR magic-angle spinning sideband patterns of dipolar and chemical shift tensors. The frequencies of the same motions have been determined by TiCC) and TjpCC) experiments. The most prevalent motion in these polymers is restricted phenyl rotation with an average total displacement of about 40°. Both the amplitude and frequency of this motion vary from one substituted polystyrene to another, and from site to site within the same polystyrene. A simple theory correlates the observed ring dipolar patterns with s. 

Spin-spin relaxation, also called transverse relaxation, is a process in which the magnetization in the x-y plane, perpendicular to the static laboratory field, decays. In section III.C.l., we will write down expressions for 1/ as they relate to the corresponding T s for dipolar and chemical shift anisotropy relaxations. It will be pointed out that, in the presence of extreme narrowing due to rapid molecular motion, T -Tg, with the consequence that these two relaxation rates do not contain different information in this limit, which almost always occurs in liquids. 

In general, the longitudinal relaxation rate of a hydride resonance is dominated by dipolar and chemical shift anisotropy contributions, the former being by far the most important in determining the observed relaxation time.[14] Thus a first look to the T value may provide a useful tool for structural assignments, since it immediately reports on the distances with respect to other magnetically active... 

Kay LE, Nicholson LK, Delaglio F, Bax A, Torchia DA (1992) Pulse sequences for removal of the effects of cross correlation between dipolar and chemical-shift anisotropy relaxation mechanisms on the measurement of heteronuclear Tl and T2 values in proteins. J Magn Reson 97 359-375... 

The dipolar and chemical shift anisotropy spin-lattice relaxation rates for those carbons bonded to hydrogen may be obtained by iterations of the following steps (1) through (4), followed by step (5). 

Double-resonance Experiments. - TROSY-type experiments have been traditionally based on the cross-correlation between dipolar and chemical shift anisotropy relaxation mechanisms. Tugarinov et al. extended the application of the relaxation compensation principles to cancellation of the intra-methyl H- H and dipole-dipole interactions. The analysis of the relaxation of the... 

For nuclei such as H with a spin of unity the strong quadrupolar interaction ( 100 kHz) dominates over the dipolar and chemical shift interactions and helps to simplify the analysis of the lineshapes. Selective deuterium labeling of ligands and/or proteins therefore offers considerable potential, not only for molecular distance information but also for studying the dynamics of the interactions. 

The two-dimensional spin-echo experiment has found applications for static samples of compounds containing homonuclear spin pairs, where dipolar and chemical shift interactions could be separated allowing the determination of internuclear distances." " It was also shown that a considerable improvement in resolution could be obtained for samples rotated in the magic angle, thus allowing the determination of the magnitude of relatively smsdl homonuclear scalar coupling constants, e.g., P)ds in Wilkinson s-type rhodium complexes. ... 

Considering the symmetry of the magnetic interactions (dipolar and chemical shift anisotropy) contributing to the spin Hamiltonian of the system for the probe,... 

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