Dynamic-angle spinning technique

In order to remove the anisotropic effects of quadrupolar interactions which can obscure MAS spectra other techniques such as Double Rotation (DOR) [18, 19], Dynamic Angle Spinning (DAS) [18] or Multiple Quantum Magic Angle Spinning (MQMAS) have to be employed. Of these the most simple to apply practically is MQMAS, which can be conducted on a standard MAS-equipped NMR spectrometer. A number of texts and review papers discuss MQMAS in significant technical detail [20, 21]. 

In this review, we shall introduce some basic concepts about sohd-state NMR of half-integer quadrupolar nuclei and discuss the most useful and promising methods presently available to study them. These include older methods, such as Double Rotation (DOR) and Dynamic Angle Spinning (DAS), and novel techniques including MQMAS, Quadrupolar Phase Adjusted Spinning Sidebands QPASS, SateUite Transition (ST) MAS and Inverse-STMAS NMR, and Fast Amplitude Modulation (FAM). We also discuss several techniques based on dipolar interactions between quadrupolar and spin-1/2 nuclei, such as Cross-Polarization (CP) MQMAS, MQ Heteronuclear Correlation Spectroscopy... 

A major recent advance in the study of quadrupolar nuclei by solid-state NMR is the development of double-rotation (DOR) and dynamic-angle spinning (DAS) [ 158,159,163). These techniques are capable of removing not only the first-order effects such as chemical shift anisotropy, but also the second-order quadrupolar interaction, which, as we have seen above, affects all quadrupolar nuclei. The second-order interaction can be expanded as a function of Wigner rotation matrices D " , so that the shift of the central transition is... 

The complete suppression of the influence of second-order quadrupole broadening requires the application of double rotation (DOR) [34-36] or dynamic angle spinning (DAS) [37-39] techniques. 

In another related article Jerschow has reviewed new high-resolution NMR techniques for the study of quadrupolar nuclei. This article also includes theoretical description of the NMR techniques. A number of topics that are often left out in other review articles, such as nuclear quadrupole resonance, overtone spectroscopy and the ionic model for the calculation of electric field gradients, have also been considered. In addition, high-resolution techniques, such as double rotation, dynamic-angle spinning, MQ MAS, and satellite transition MAS have also been reviewed. 

The technique known as dynamic-angle spinning (DAS) adopts an alternative approach to DOR the sample is rotated sequentially about two different axes, jS/ and 82 which are chosen so that... 

Other relevant methods are (1) quadrupole nutation spectroscopy, a two-dimensional technique which allows the projection of the conventional spectrum in one dimension, and only quadrupolar information in the second frequency axis, (2) dynamic-angle spinning (DAS), in which the sample is spun sequentially rather than simultaneously (as in DOR) about two different magic axes and (3) satellite transition spectroscopy (SATRAS), which monitors... 

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