Multiple-quantum magic-angle-spinning MQMAS

In the vast majority of cases where NMR is used to localise cations in zeolites, one or both of the following techniques is used Magic Angle Spinning (MAS) or Multiple Quantum Magic Angle Spinning (MQMAS). 

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]. 

Other sensitive but less frequently occurring pharmaceutical nuclei such as phosphorus, bromine, and sodium can be used. The latter two are characterized by quadrupolar nuclear spin. Advanced experiments, such as multiple quantum magic angle spinning (MQMAS) may be required to obtain narrow signals in these instances.166,167... 

We present a solid-state nuclear magnetic resonance (NMR) experiment that allows the observation of a high-resolution two-dimensional heteronuclear correlation (2D HETCOR) spectrum between aluminum and phosphorous in aluminophosphate molecular sieve VPI-5. The experiment uses multiple quantum magic angle spinning (MQMAS) spectroscopy to remove the second order quadrupolar broadening in Al nuclei. The magnetization is then transferred to spin-1/2 nuclei of P via cross polarization (CP) to produce for the first time isotropic resolution in both dimensions. 

The multiple-quantum magic-angle spinning (MQMAS) technique is one of the most important NMR advances for half-integer quadrupolar nuclei that has been made in recent years. Through a correlation between the multiple and single-quantum coherences, the anisotropic second-order quadrupolar... 

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