Two-Dimensional MAS Multiple-Quantum NMR of Quadrupolar Nuclei. Removal of Inhomogeneous Second-Order Broadening

Multiple-Quantum Cross-Polarization and Two-Dimensional MQMAS NMR of Quadrupolar Nuclei

“…1a, phase cycling is used to select both p ϭ Ϯn coherences during t 1 . In order to ensure absorptive two-dimensional lineshapes, a z-filter (21,38) is included in the sequence, i.e., a pulse is used to convert the multiple-quantum coherences to populations while another pulse reads these out as observable single-quantum coherences.…”

Multiple-Quantum MAS NMR Spectroscopy of Spin-32Quadrupolar Spin Systems Using Shaped Pulses

“…For the normal two-pulse scheme employed in MQMAS NMR for quadrupolar spin- 3 2 nuclei, (0) can be chosen as I (14) ϭ ͉1͗͘4͉, and O as I x (23) . On the other hand the first pulse of the z-filtering scheme, (0), should be chosen as ͉1͗͘4͉e Ϫi 14 t 1 ϩ HC, where HC is the Hermitian conjugate.…”

“…While the MQMAS method has rapidly become a favorite experimental choice, nevertheless, VAS, DAS, and DOR are complementary techniques for some systems and can be incorporated with MQMAS (12,19,20). A time-split method (14,21) was proposed to avoid the shearing transformation of the spectral data which is usually needed as a post-data processing procedure to enhance the resolution in the first dimension of the 2D MQMAS NMR spectra. This renders data processing easier but the pure absorptivities of the resulting lineshapes are generally not as good as those obtained by the two-pulse-plus-z-filtering method (13).…”

“…This situation can be improved by application of the z-filtering method which ensures the symmetry of the intensities of the coherences before detection. The three-pulse version of the z-filtering method (13) is superior to its fourpulse counterpart (14) because the former yields higher spectral sensitivities and is more easily optimized. Further improvement of the spectral lineshapes can be achieved by synchronizing the sample spinning rate with the pulse lengths (12,15).…”

Single-Quantum NMR Spinning-Side-Band Patterns for Spin-3/2 System

“…Structural investigations have been done in the last few years [19][20][21] using MQ/SQ correlation method which proved to be insensitive to the first-and second-order quadrupolar spectral broadening. Since the above technique involves spin-space manipulation together with sample rotation at the magic angle, it can be implemented easily using an ordinary MAS probe.…”