Dynamic Angle Spinning DAS

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 Dynamic Angle Spinning (DAS) [53-55], the sample is rotated sequentially about two different axes, ffi and ff2, which are chosen so that... 

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. 

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