MQMAS Multiple quantum magic angle

MQMAS multiple quantum magic angle spinning... 

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... 

Two Dimensional Multiple Quantum MAS. For non-integer spin quadrupolar nuclei a two dimensional (2D) Multiple Quantum Magic Angle Spiiming (2D MQMAS) technique emerged in 1995 that has had a profound effect on their study, and has meant that much higher resolution spectra can be produced from these nuclei in sol-gel materials. This experiment correlates the (m, -m) multiple quantum transition to the (1/2, -1/2) transition (Fig. 3-2(c)). The resolution enhancement stems from the fact that the quadrupole frequencies for both transitions are correlated. At specific times, the anisotropic parts of the quadrupole interaction are refocused and an echo forms. The amplitude of the echo is determined onlyhy isotropic interactions, so that the experiment is repeated at different echo times which forms the 2D data set where the echo amplitude is modulated only by isotropic effects. FT of the echo amplitude then produces an isotropic spectrum that... 

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