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Resolution Enhancement in Multiple-Quantum MAS NMR Spectroscopy

1998; Elsevier BV; Volume: 133; Issue: 1 Linguagem: Inglês

10.1006/jmre.1998.1432

1096-0856

Ingo Schnell, Adonis Lupulescu, S. Hafner, Dan E. Demco, H. W. Spieß,

Advanced MRI Techniques and Applications

Two techniques for resolution and sensitivity enhancement are introduced in multiple-quantum (MQ) MAS spectroscopy of rigid solids. The first makes use of ultrafast MAS with spinning frequencies of up to 35 kHz, while the second combines MAS at moderately fast spinning frequencies of about 13 kHz with multiple-pulse (MP) dipolar decoupling. For the latter approach, a semiwindowless WHH-4 sequence is applied during the MQ evolution period (MQ dimension) and/or detection period (single-quantum dimension). In the MQ dimension, the MP sequence has to be supplemented by two bracketing pulses in order to preserve the order and the intensities of the evolving MQ coherences. Double-quantum1H NMR spectra ofl-alanine recorded using both decoupling techniques are shown and compared to each other. Triple-quantum1H NMR spectra under ultrafast MAS conditions are also presented.