Multiple-quantum /MAS NMR

S. P. Brown and S. Wimperis, Two-dimensional multiple-quantum MAS NMR of quadrupolar nuclei a comparison of methods. /. Magn. Reson., 1997,128,42-61. 

T. Vosegaard, F. H. Larsen, H. J. Jakobsen, P. D. Ellis and N. C. Nielsen, Sensitivity-enhanced multiple-quantum MAS NMR of half-integer quadrupolar nuclei. J. Am. Chem. Soc., 1997, 119, 9055-9056. 

Most recently, the multiple quantum MAS NMR technique was applied to obtain a high resolution solid-state NMR spectrum [16-17], but it seems to need much more time before this technique becomes useful for solid-state NMR. 

J.P. Amoureux, C. Fernandez, Triple, quintuple and higher order multiple quantum MAS NMR of quadrupolar nuclei. Solid State Nucl. Magn. Reson. 10 (1998) 211-223. 

We note that optimal control is a universal tool for experiment design and has also, in solid-state NMR spectroscopy, found additional applications in the design of homonu-clear dipolar recoupling [41], broadband rf pulses and quantum gates [71], building blocks of symmetry-based recoupling experiments [129], quadrupolar multiple-quantum MAS experiments [165], and improved pulses for quadrupolar nuclei [166]. Numerous references to further applications with regard to liquid-state NMR can be found in [72]. 

Multinuclear (isocyanide)gold complexes, reactivity, 2, 287 Multi-phase organometallic catalysis, in ionic liquids, 1, 856 Multiple-quantum MAS, half-integer spin quadrupolar nuclei central transition NMR studies, 1, 466 Multistate magnetization transfer, in dynamic NMR magnetization, 1, 410 Multistep catalytic cycles... 

Another illustration of how powerful structural NMR tools can be is found in the multiple quantum MAS (MQMAS) NMR study of a G-quadruplex channel. A guanine nucleoside derivative forms tetramers, G-quar-tets. which, in the presence of monovalent cations, assemble to result in a G-quadruplex channel consisting of the stacking of four 6-quartets, coordinating in the channel four cations in this case, three Na" and one While the ID Na-MAS NMR spectrum exhibits only a broad, umesolved signal the 2D MQMAS spectrum gives a clear and neat separation for the three crystallographically distinct Na sites (Fig. 2). 

S.E. Ashbrook, S. Wimperis, Novel two-dimensional NMR methods that combine single-quantum cross-polarization and multiple-quantum Mas of quadrupolar nuclei,... 

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). 

An interesting new approach has been made possible by multiple quantum 27A1 MAS (MQMAS) NMR investigations of zeolites. Due to its nuclear electric quad-rupole moment, 27A1 exhibits broad lineshapes in distorted structural environments. 

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