Chemical shift anisotropy tensors

It is worth mentioning that parameter p is insensitive, to first order approximation, to modulation of the residue-specific 15N chemical shift anisotropy tensor and/or dipolar interaction, as the (d2 + c2) term in the R) / R ratio is canceled out. The noncollinearity of the CSA and dipolar tensors will require corrections to Eqs. (10) and (12) for high degrees of rotational anisotropy (D /D > 1.5), as described in detail in Ref. [22]. 

As seen from Fig. 15, in the case of unprotonated aromatic para carbons, a phenyl ring yr-flip does not change the orientation of the chemical shift anisotropy tensor components and, thus, this yr-flip does not affect the NMR response of such para carbons, whereas phenyl ring oscillations do. 

In contrast, for protonated ortho and meta aromatic carbons, both phenyl ring yr-flips and oscillations affect the orientation of the chemical shift anisotropy tensor components and, consequently, their NMR response. The change in the amplitude of the oscillations with temperature for protonated and unprotonated aromatic carbons is shown in Fig. 16. For the two types of carbons the amplitudes of the oscillations are quite similar. 

Fig. 15 Effect of a phenyl ring yr-flip on the orientation of the chemical shift anisotropy tensor components for unprotonated and protonated aromatic carbons...

Fig. 152 Geometry of the chemical shift anisotropy tensors of C = O groups in MGIM units...

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.

The nitrogen-15 nmr spectra (Figure 3) of sodium exchanged Alaskan and HB33 mordenites were analyzed for the chemical shift anisotropy tensors. The chemical shift anisotropy tensors have been measured for solid nitrogen at 4.2K(23) and calculated to be 603 28 ppm for the static molecule. The observed chemical shift tensors can be used to calculate an orientational parameter , where... 

Yao LS et al (2010) Site-specific backbone amide chemical shift anisotropy tensors in a small protein from liquid crystal and cross-correlated relaxation measurements. J Am Chem Soc 132(12) 4295 309... 

These angles were determined in turn from distances between backbone carbonyl spins, measured with the DQ filtered dipolar recoupling with a windowless sequence experiment, and by determination of the mutual orientation of chemical shift anisotropy tensors of carbonyl spins on adjacent peptide planes, obtained from the DQ CP MAS spectrum. It was found that peptides composed of periodic sequences of leucines and lysines were bound along the length of the peptide sequence and displayed a tight a-helical secondary structure on the gold nanoparticles. 

Proton chemical shifts are a rich probe of structure and hydrogenbonding environments in organic and biological molecules. Until recently, measurements of chemical-shift tensors have been restricted to either solid systems with sparse proton sites or were based on the indirect determination of anisotropic tensor components from crossrelaxation and liquid-crystal experiments. A MAS approach has been introduced that permits site-resolved determination of chemical shift anisotropy tensors of protons forming chemical bonds with labelled spin 1/2 nuclei in fully protonated solids with multiple sites, including organic molecules and proteins. This approach, originally introduced for the measurements of chemical shift tensors of amide protons, is based on... 

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