Se. Ashbrook et S. Wimperis, Novel two-dimensional NMR methods that combine single-quantum cross-polarization and multiple-quantum MAS of quadrupolar nuclei, CHEM P LETT, 340(5-6), 2001, pp. 500-508
A new approach to combining cross-polarization with multiple-quantum MAS in
a two-dimensional NMR experiment is demonstrated, involving cross-polariza
tion from H-1 to the single-quantum coherences of a quadrupolar nucleus. Th
ese coherences are then converted directly to multiple-quantum coherences r
ather than via a population state. In two separate methods, pure-absorption
lineshapes are obtained using a z-filter and a shined echo, respectively,
with the latter, a 'reversed split-t(1)' method, demonstrated to be particu
larly effective. The efficiency of both sequences may be improved by incorp
orating 'fast-amplitude-modulation' (FAM) pulses for both the conversion an
d excitation of triple-quantum coherences. (C) 2001 Elsevier Science B.V. A
ll rights reserved.