Selective pulse experiments in high-resolution solid state NMR (original) (raw)
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High-Performance Selective Excitation Pulses for Solid and Liquid-State NMR Spectroscopy
Chemphyschem, 2004
Computer-optimized selective pulses are routinely used in solution-state NMR spectroscopy. At the same time, their utility and importance for solid-state applications has yet to be fully realized. We suggest a new computational approach that makes the design of soft selective pulses with desired properties relatively straightforward. By applying this technique to the generic selective excitation problem, we have arrived at a family of high performance selective excitation pulses, dubbed E-Family, that allows more flexibility and better performance than analogous pulses previously reported in the literature. The new pulses have been successfully tested in both solid- and solution-state NMR experiments. A theoretical treatment of the effects of chemical shift anisotropy (CSA) on the selective excitation in magic-angle spinning (MAS) experiments in solids is presented. The set of heuristics that comprise our new strategy were incorporated into a general NMR simulation program SPINEVOLUTION.
A new concept for selective excitation in NMR
Chemical Physics Letters, 1996
The new NMR concept of selective excitation generated by pulses whose envelope is slaved to that of a signal originating from the sample is described. It is shown that these kinds of pulses exhibit interesting features such as a sort of auto-calibration of the pulse length and phase. These particular features are discussed and experimental evidence is given. Illustration of the use of slaved pulses is demonstrated in the case of ID transient NOE by selective inversion.
Improvement of NMR experiments by employing semiselective half-Gaussian-shaped pulses
Half-Gaussian-shaped pulses yield an almost ideal excitation profile, if the relatively broad dispersion component is eliminated by a simple nonselective 90" purge pulse. In contrast to Gaussian-shaped pulses, the half-Gaussian excitation scheme does not create significant amounts of antiphase components, but leads almost quantitatively to in-phase magnetization of the excited signal. This feature is especially useful in experiments where a semiselective excitation is followed by a mixing of in-phase components (e.g., in NOESY, ROESY, or TOCSY type experiments). In such a case even signals with large or numerous couplings give rise to a very efficient transfer. In addition, the magnetization vectors in the transverse plane show an almost perfect alignment after semiselective excitation with a purged half-Gaussian pulse. Thus it can be employed advantageously in all experiments where a semiselective excitation is directly followed by the I, evolution period. In such experiments the use of Gaussian pulses leads to very large first-order phase gradients, the correction of which causes severe distortions of the baseline. The alternative use of purged half-Gaussian-shaped pulses results only in very small phase gradients, comparable to those in experiments with nonselective excitation. C 1489 Academy Press. Inc.
Solid State Nuclear Magnetic Resonance, 2004
It is demonstrated that the use of fast amplitude-modulated RF pulse trains with constant (FAM-I) and incremented pulse durations (SW-FAM) leads to considerable sensitivity enhancement for the central-transition signal (via spin population transfer from the satellite transitions) for solid-state NMR spectra of titanium, 47 Ti ðI ¼ 5 2 Þ and 49 Ti ðI ¼ 7 2 Þ: For the magic-angle spinning spectra of TiO 2 and BaTiO 3 ; the intensity of the 49 Ti central-transition line was more than doubled compared to simple Hahn-echo acquisition, while for the static case, enhancement factors of 1.6 ðTiO 2 Þ and 1.8 ðBaTiO 3 Þ were obtained. No lineshape distortions are observed in either MAS or static spectra of both compounds. Employment of the FAM and SW-FAM sequences should be useful in the routine acquisition of 47;49 Ti spectra, as the NMR signal can be detected much faster. r
Journal of magnetic resonance (San Diego, Calif. : 1997), 2015
A selective saturation pulse at fast magic angle spinning (MAS) frequencies (60+kHz) suppresses t1 noise in the indirect dimension of two-dimensional (1)H MAS NMR spectra. The method is applied to a synthetic nucleoside with an intense methyl (1)H signal due to triisopropylsilyl (TIPS) protecting groups. Enhanced performance in terms of suppressing the methyl signal while minimising the loss of signal intensity of nearby resonances of interest relies on reducing spin diffusion - this is quantified by comparing two-dimensional (1)H NOESY-like spin diffusion spectra recorded at 30-70kHz MAS. For a saturation pulse centred at the methyl resonance, the effect of changing the nutation frequency at different MAS frequencies as well as the effect of changing the pulse duration is investigated. By applying a pulse of duration 30ms and nutation frequency 725Hz at 70kHz MAS, a good compromise of significant suppression of the methyl resonance combined with the signal intensity of resonances g...
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.
High-resolution 1 H NMR in solids with frequency-switched multiple-pulse sequences
Solid State Nuclear Magnetic Resonance, 1993
A new pulse sequence for abundant-spin NMR in solids, called FSLG240W, is demonstrated. The sequence employs phase-coherent frequency-switching of the rf irradiation to induce opposite rotations around the magic-angle axis in the rotating frame. Three 4~/3 rotations in one sense are followed by three 4~/3 rotations in the opposite sense. Observation windows separate each rotation. The pulse sequence cancels out the average dipolar Hamiltonian, the first-order correction terms, and the most deliterious second-order terms. The pulse sequence has a short cycle time and a high scaling factor K = 1,/a, but is sensitive to rf inhomogeneity. We demonstrate slightly better resolution than either MREV8 or BR24 on a small spherical sample of L-alanine.