Sideband suppression in magic-angle-spinning NMR by a sequence of 5 π pulses (original) (raw)
Related papers
Efficient and sideband-free 1H-detected 14N magic-angle spinning NMR
Journal of Chemical Physics, 2019
Indirect detection via sensitive spin-1/2 nuclei like protons under magic-angle spinning (MAS) has been developed to overcome the low spectral sensitivity and resolution of 14 N NMR. The 14 N quadrupolar couplings cause inefficient encoding of the 14 N frequency due to large frequency offsets and make the rotor-synchronization of the evolution time necessary. It is shown that 14 N rf pulses longer than the rotor period can efficiently encode 14 N frequencies and generate spinning sideband free spectra along the indirect dimension. Average Hamiltonian and Floquet theories in the quadrupolar jolting frame (QJF) are used to treat the spin dynamics of the spin-1 quadrupolar nucleus under long 14 N rf pulses and MAS. The results show that the rf action can be described by a scaled and phase-shifted effective rf field. The large quadrupolar frequency offset becomes absent in the QJF, therefore leads to sideband-free spectra along the indirect dimension. More importantly when a pair of long 14 N rf pulses are used, the distribution of the phase shift of the effective rf field does not affect the 14 N encoding for powder samples, thus high efficiencies can be obtained. The efficient and sideband-free features are demonstrated for three 1 H/ 14 N indirectly-detected experiments using long 14 N pulses under fast MAS.
π pulses and echo formation in magic-angle-spinning NMR
Journal of Magnetic Resonance (1969), 1989
Several theoretical and experimental aspects of echo formation in inhomogeneously broadened rotating solids are described. The timing constraints upon a n-pulse train that allow the formation of rotational echoes are derived, and the effects of the RF phase upon the phase of the echo train are examined. Several new x-pulse trains of various timings, phases, numbers of pulses, and spacings are presented. These effects are expiained. both rigorously and intuitively, using the previously developed MAS magnetization vector model of Olejniczak et al. (J. Chem. Phys. 81,4804 (1984)).
Journal of Magnetic Resonance, 1999
The quadrupolar phase-adjusted spinning sidebands (QPASS) pulse sequence has been recently demonstrated as a useful method for obtaining quadrupolar parameters with magic-angle spinning NMR. The sequence separates spinning sidebands by order in a two-dimensional experiment. A sheared projection of the 2D spectrum effectively yields the infinite spinning rate second-order quadrupolar powder pattern, which can be analyzed to determine quadrupolar coupling constants and asymmetry parameters. The RF power and spinning speed requirements of the original QPASS sequence make it an experimentally demanding technique. A new version of the sequence is demonstrated here and is shown to alleviate many problems associated with the original sequence. New solutions to the determining equations, based on the use of multiple rotor cycles in the QPASS sequence, lead to longer delays between the nine pulses, provide less chance of pulse overlap, and allow for use of weaker RF field strengths that excite only the central quadrupolar transition. A three-rotor-cycle version of the new experiment is demonstrated on the 139 La nucleus.
Journal of Magnetic Resonance, 2001
We have investigated the extent to which rotor synchronization of radiofrequency pulses leads to spectral improvement in highresolution magic angle spinning NMR experiments. Several pulse sequences were tested, and the effect was found to be maximal in homonuclear TOCSY spectra. The physicochemical nature of the sample plays a role in the phenomenon, as rotor synchronization allows the refocusing of residual anisotropic interactions. However, even in a liquid sample the effects were visible. Radial inhomogeneities of the radiofrequency field were identified as an important source of the problem. C 2001 Academic Press
Modulation-aided signal enhancement in the magic angle spinning NMR of spin-5/2 nuclei
Chemical Physics Letters, 2003
We report signal enhancement schemes using fast amplitude modulated pulses for the onedimensional (1D) NMR of spin-5/2 nuclei under magic-angle spinning. Signal enhancement by a factor of around 2.5 is observed when amplitude modulated pulses precede selective excitation of the central transition. This enhancement is a result of the redistribution of the evergy level populations through partial saturation of the satellite transitions. Results are shown for 27 Al and 17 O. The gain in signal intensity is very useful for the observation of weak signals from low abundance quadrupolar nuclei.
Chemical Physics Letters, 2004
We present a new solid-state NMR pulse sequence that accomplishes efficient broad-band dipolar recoupling in systems with small dipolar couplings and large chemical shift anisotropies. The method involves a supercycled symmetry-based recoupling sequence incorporated in a constant-interval data acquisition strategy. The supercycle removes destructive higher-order average Hamiltonian terms, and makes the method more robust at long time intervals. We demonstrate 38.4% double-quantum filtering efficiency on diammonium [1,4-13 C 2 ]-fumarate in which the internuclear distance, as estimated by X-ray diffraction, is 387.8 pm. The estimated 13 C-13 C dipolar coupling was )136.5 AE 5.1 Hz, corresponding to an internuclear distance of 382.5 AE 4 pm.