Tensor quadrupolar

Nitrogen-14, with its natural abundance of 99.6%, is one of the most ubiquitous and, until recently, least studied NMR-active nuclei. Due to the integer spin number (/ = 1), its single-quantum transitions are affected by first-order quadrupolar broadening, which in most materials is on the order of a few megahertz. A new class of 2D HETCOR protocols has been recently developed, which makes it possible to indirectly observe well-resolved 14N sites via their spin-1/2 neighbors and obtain the related parameters of the quadrupolar tensors. 

Here, the two Euler angles ak and flk define the orientation of the quadrupolar tensor with respect to the static magnetic field ... 

The potential of other nuclei for the study of surfaces is yet to be explored. Gottlieb and Luz (388) measured 2H spectra of a number of perdeuterated molecules adsorbed on active alumina and interpreted the results in terms of quadrupolar tensors. Yesinowski and Mobley (369) have shown that 19F MAS NMR can provide useful information about fluorinated surfaces of calcium hydroxyapatite, Cas(0H)(P04)3. In particular, l9F, 2H, and H MAS NMR may become powerful techniques for the study of interface systems in general. 

In this work, it has been demonstrated that periodic modulation of the Hamiltonian describing a dynamic process introduces spectral effects that depend upon the nature of the modulations. For both MAS and QCPMG experiments, sidebands are broadened in the intermediate dynamic regime and a significant narrowing of the sideband manifold is observed for higher order jump processes due to averaging of the anisotropic part of the quadrupolar tensor. 

A comprehensive single-crystal Cs NMR study of Cs2Cr04 has yielded the magnitude and orientations of the Cs chemical shielding and quadrupolar tensors for the 2 crystallographically distinct Cs sites in this compound, indicating that the chemical shielding and quadrupolar interactions are not coincident for the 2 distinct caesium positions (Power et al. 1994). 

The quadrupolar interaction arises from the coupling of the EFG surrounding the nucleus with that of its nuclear quadrupole moment, as described by Cohen and Reif." The EFG tensor (or the quadrupolar tensor) is defined in its PAS by three Cartesian elements, Q > with the quadrupolar tensor in the PAS notated as Q pas- Like any other... 

Peptides. The correlation of deuterium quadrupolar tensors by spin diffusion under slow magic-angle-spinning conditions can provide accurate measurements of their relative orientation. This work showed the technique applied to the cyclo-P-peptide cyclo[(5)- 3-homoalanyl-(R)-P-homoalanyl-(S)-P-homoalanyl-(i )-P-homoalanyl] with its amide hydrogens labeled by deu-terons. From the 2D spin-diffusion spectrum, the mutual orientation of the amide deuteron quadrupolar coupling tensors were found. Eight conformations that are all consistent with the NMR measurement were determined. 

Angle A indicates the Euler angles between the principal axes of the quadrupolar tensor and the chemical shift tensor. A5 = - 633. 

XX, YY, ZZ component of quadrupolar tensor q universal gas constant 8.31432 J/mol K radius of a curvature (Ch. 3) of a spherical particle or an atom (Ch. 15) of a capillary mid-point radius in Couette geometry Bjerrum radius... 

S-labelled Molybdenum Cofactor. The possibility of direct incorporation of S into PPT using controlled in vitro synthesis with purified proteins was recently used to reconstitute a S-labelled cofactor into the apoenzyme. While no spectral difference could be detected on the X-band CW-EPR spectra of the IpH samples prepared with S- and S-labelled MPT, the use of primary and refocused primary ESEEM at 35 GHz allowed the detection of the interdoublet transition from a S nucleus with strong nuclear quadrupole interaction. The estimated hfi and nqi parameters (Aj o ( S) = 3 MHz, Ti,2,3 ( S) = [1, -1, 0] MHz, (e qQ/h, t]) ( S) = (25 MHz, 0.5) and Euler angles of the quadrupolar tensor in the g-frame (a, p, y) = (0°, 40°, 0°)) are in good agreement with those predicted by DFT for the two indistinguishable... 

Relaxation measurements can be conducted both under static and MAS condition. MAS technique was introduced by Pines and coworkers [119] and further developed by others [120-122]. Application MAS results in splitting of the quadrupolar tensor into system of the spinning sidebands separated by the spinning frequency. The shape of the envelope is comparable with the shape of the static spectrum but the S/N ratio is significantly higher. Except ID techniques, 2D experiments can be applied. Spiess and coworkers [123] introduced 2D NMR approach to study the slow motions, in the 1 ms up to 1 s regime. Very detailed, concise and comprehensive review of techniques applied in MAS SS NMR of peptides and proteins was published by Reif and coworkers [82,124]. 

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