Phase-adjusted spinning sidebands

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... 

An alternative means by which the isotropic and anisotropic chemical shift interactions can be separated is the 2D PASS (phase-adjusted spinning sidebands) experiment due to Levitt and co-workers [115]. By changing the timings of the application of five 71 pulses in the tj dimension, it is possible to separate the spinning sidebands by order. As a specific example, Fig. 9.24 shows the 2D PASS spectrum for the antibiotic, penidUin-V. [116] An analysis of this spectrum allowed the determination of the CSA prindpal values for aU the resonances. A distinct advantage of this approach is that only very few (typically 16) increments must be made in the indirect dimension. 

Another technique, enabling a complete separation of isotropic and anisotropic chemical shift was introduced and developed by Antzutkin and Levitt with coworkers [116,117]. This sequence, called 2D PASS (phase adjusted spinning sidebands), consist of a r/2 pulse followed by a train of five n pulses (see Fig. 2.16) The timings between the pulses are modulated to satisfy the PASS equations. The PASS equations are complex and wiU not be discussed here timings for the pulses are shown in paper published by Antzutkin (see Ref [116]). 

The quadrupole phase adjusted spinning sideband pulse sequence has been applied to the observation of Ga. Ga and Ga single crystal NMR spectra of P-Ga203 have been reported. The environments of gallium in MFI-type gallium silicates have been studied using Ga NMR spectroscopy. " P and Ga NMR spectroscopy has been used to characterize gaUium... 

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