Broadband Multiple-Quantum NMR Spectroscopy

✍ Scribed by M. Feike; D.E. Demco; R. Graf; J. Gottwald; S. Hafner; H.W. Spiess

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 209 KB
• Volume: 122
• Category: Article
• ISSN: 1064-1858
• DOI: 10.1006/jmra.1996.0197

✦ Synopsis

This concept, which was first derived for static samples excitation of multiple-quantum coherences in the presence of (2,3), can also be used in the presence of fast MAS, applied fast magic-angle spinning is introduced. This sequence involves to obtain highly resolved multiple-quantum spectra. For the back-to-back ( BABA ) 90Њ radiofrequency pulse cycles timed to excitation of multiple-quantum coherences under the condispan two rotor periods. It proved to be robust and insensitive to tions of fast MAS, the double-quantum part of the dipolar off-resonance effects, to isotropic chemical shifts, and to chemi-Hamiltonian must be recoupled during the excitation and cal-shift anisotropies. This is demonstrated on crystalline phosreconversion periods. Laboratory (L)-frame pulse sequences phates, composed of Q ( 1 ) , Q (2 ) , and Q ( 3 ) groups, which are charlike DRAMA (12-14) or BABA (15), rotating (R)-frame acterized by a large chemical-shift anisotropy spanning more pulse sequences such as HORROR (16), MELODRAMA than 200 ppm. With these experiments, 31 P high-resolution dou-(17), or C7 ( 18), and combined ''R/L-driven'' techniques ble-quantum NMR spectroscopy is introduced as a tool for the direct investigation of dipolar connectivities between like or dif- (19) have been developed for this purpose. Until now, only ferent Q ( n ) units in phosphates. 31 P dipolar connectivities in two DRAMA (4,6, 12), BABA (5,[8][9][10], and C7 (9, 10) have samples, Mg 2 P 2 O 7 and MgP 4 O 11 were established. Therefore, been used for recording high-resolution MQC spectra in rodouble-quantum spectroscopy of this kind has potential for the tating dipolar solids. Also, the simple three-p/2 pulse seinvestigation of disordered solids, for instance, phosphorus quence was used for double-quantum excitation in rotating glasses.