NMR Of Quadrupolar Nuclei Research Articles

Optimization of pulses with low bandwidth for improved excitation of multiple-quantum coherences in NMR of quadrupolar nuclei.

We discuss the commonly encountered problem when optimizing nuclear magnetic resonance (NMR) pulses using optimal control that the otherwise very precise NMR theory does not provide as excellent agreement with experiments. We hypothesize that this disagreement is due to phase transients in the pulse due to abrupt phase and amplitude changes resulting in a large bandwidth. We apply the gradient optimization using parametrization algorithm that gives high fidelity pulses with a low bandwidth compared to the typical gradient ascent pulse engineering pulses. Our results obtain a better agreement between experiments and simulations supporting our hypothesis and solution to the problem.

“EASY: A simple tool for simultaneously removing background, deadtime and acoustic ringing in quantitative NMR spectroscopy. Part II: Improved ringing suppression, application to quadrupolar nuclei, cross polarisation and 2D NMR”

A simple experiment for Elimination of Artifacts in NMR SpectroscopY (EASY) was introduced in Part I, and it was shown that NMR probe background signals, spectral distortions due to deadtime effects, and acoustic ringing can be eliminated simultaneously from solid-state NMR spectra. In this Part II, it is shown that acoustic ringing suppression can be improved up to one order of magnitude compared to the original EASY pulse sequence by inserting a delay τ between the two data acquisition scans of the EASY pulse sequence. The achievable ringing suppression depends on the length of this delay and is limited by the spin-lattice relaxation time T1. Furthermore, EASY is considered in conjunction with NMR of quadrupolar nuclei. For strong second-order broadening, EASY can be used to acquire either pure central transition MAS patterns or pure satellite transition NMR spectra. Two further modifications to EASY are introduced. One concerns improved ringing artifact suppression in experiments in which the central transition NMR signal is amplified by Rotor Assisted Population Transfer (RAPT). The second EASY modification enables the acquisition of quantitative NMR spectra if signals with different quadrupole coupling constants are present. In addition, acoustic ringing and 11B stator signals are removed. Finally, it is demonstrated that the basic idea of EASY for removing ringing artifacts can be realized for heteronuclear one-dimensional and hetero- and homo-nuclear multi-dimensional NMR experiments using extended phase cycling. 15N{1H} CPMAS and 15N 2D Exchange NMR spectroscopy are considered as examples.

Ultrafast 1h and 7li Solid-State MAS NMR Studies of Materials for Next-Generation Li-Based Batteries

Li-based batteries are considered as one of the most promising advanced energy storage systems for electrical vehicles (EV) and stationary energy storage. However, their successful implementation in these emerging technologies is a significant challenge because energy requirements, system safety, and manufacturing costs are subject to more stringent demands than in current commercial batteries. Therefore, optimization of battery components such as electrode materials and electrolytes is a key step for the rational development of advanced battery systems. Solid-state magic-angle-spinning (MAS) NMR has emerged in the last decades as a unique technique for obtaining very accurate information on the atomic-level structure and dynamics of complex materials (1). This technique is sensitive to short-range order and therefore is not limited to crystalline materials. In particular, ultrafast MAS NMR (>60 kHz) generates spectral resolution enhancements that facilitate the identification of different species in complex systems (2).In this work, we present solid state NMR structural and dynamic characterizations of two highly Li-ion-conductive ceramic materials and a novel hybrid organic-inorganic composite. The results obtained by NMR were successfully applied to improve the performance of such materials.In the first part of this work, 7Li and 13C ultrafast MAS NMR were used to characterize a hybrid anode material composed of inorganic SnLi particles coated with a polymer phase based on the polymerization of vinyl-ethylene carbonate (VEC). The presence of 6 different SnLi alloy phases in the material was clearly differentiated together with some residual metallic lithium due to the different 7Li Knight shifts(3) of the individual compositions. 13C MAS NMR was used to characterize the organic phase in this compound. Results obtained provide a deeper understanding of the chemical composition and the possible synergistic interactions within this composite. In the second part of this work, ultrafast 1H and 7Li solid-state MAS NMR were applied in the study of two highly Li-ion-conductive ceramic materials. In particular, the effects of protonation by exposure to moisture on the conductivity of lithium in the perovskite Li3xLa2/3-x□1/3-2xTiO3 and the garnet Li7-3xGax□2xLa3Zr2O12were followed by NMR (where □=defect). The large grain boundary contributions to the overall Li-ion conductivity were monitored and the effects of moisture on the sintering of these electrolyte materials determined. Based on these results, an effective strategy to improve the total Li-ion conductivity of these materials was designed.(1) a) NMR of Quadrupolar Nuclei in Solid Materials, Roderick E. Wasylishen, Sharon E. Ashbrook, and Stephen Wimperis (Eds.) John Wiley & Sons Ltd, Chichester, UK (2012). b) Solid-State NMR in Materials Science: Principles and Applications, Vladimir I. Bakhmutov, CRC Press(2011). c) NMR Crystallography, Robin K. Harris, Roderick E. Wasylishen, and Melinda J. Duer (Eds.), Wiley, Chichester (2009).(2) I. Bertini, L. Emsley, M. Lelli, C. Luchinat, J. Mao, G. Pintacuda. J. Am. Chem. Soc. 2010, 132, 5558-9.(3) E. Bekaert, F. Robert, P. E. Lippens, and M. Menetrier. J. Phys Chem. C 2010, 114, 6749-6754.

ChemInform Abstract: Signal Enhancement in Solid‐State NMR of Quadrupolar Nuclei

AbstractReview: 133 refs.

NMR quadrupole liouvillians for arbitrary spin: Exact symbolic expressions and perturbation solutions

AbstractThe NMR of quadrupolar nuclei with half‐integer spins is almost always described by treating the quadrupole interaction with second‐order perturbation theory. The standard practice is to perturb the wave functions, then calculate the transitions. In this article, we elaborate on the so‐called direct method in which the transitions are calculated directly without the requirement of knowing the operators and the wavefunctions. The method is set up using a set of formulae giving fully symbolic expressions. First of all, this provides a convenient way for a full and exact numerical solution that goes beyond perturbation theory. The other possibility is that it allows us to see the effect of the quadrupole perturbation on the unperturbed transitions. The results are the same, as they must be, but this approach reveals a number of important symmetries. Perturbations will mix the unperturbed transitions, but despite the use of high‐order perturbation theory, the mixing is very simple, specific, and controlled by selection rules. This gives a clear physical picture of the physical basis of the effects of perturbation theory. The approach is systematic and general and is easily extended to an arbitrary half‐integral spin. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part 42A: 45–358, 2013.

The NMR of quadrupolar nuclei. Relationship between exact and perturbation solutions for spin 3/2

Nuclei with spin>1/2 often experience an interaction, called the quadrupole interaction, which can be very strong in NMR terms. For nuclei with half-integral spins, however, the so-called central transition in the NMR spectrum remains relatively narrow. Second-order perturbation theory provides an excellent description, but the classic derivation involves perturbing the energy levels, then constructing the transitions. Recently, we have derived a method for calculating transitions and their energies directly, without requiring any detailed knowledge of wavefunctions, operators or their commutators. This provides a simple derivation of the perturbation result that highlights important physical aspects of the equations.

Defect dynamics observed by NMR of quadrupolar nuclei in gallium nitride.

Hexagonal and cubic polytypes of bulk gallium nitride powders are characterized by 69,71Ga and 14N MAS NMR at 11.7 T. The (corrected) 71Ga chemical shifts are 333.0 and 357.5 ppm, respectively; the corresponding 14N chemical shifts are -301.8 and -297.0 ppm (all shifts referenced to 1 M gallium nitrate). The 69,71Ga nuclear quadrupole coupling constants (NQCC) in the hexagonal form are axially symmetric and agree with previous single-crystal determinations. The 71Ga MAS NMR satellite pattern envelope of the cubic form has a large Gaussian half-height width of 297 kHz, due to nonzero NQCC values induced by defects. The 14N MAS NMR spinning sideband pattern of the cubic form has a Lorentzian envelope half-height width of 17.5 kHz for the same reason. A sample containing both phases shows an unexpected marked loss of the 71Ga MAS NMR satellite transition intensity expected for the hexagonal phase. Static 71Ga-selective Hahn spin-echo measurements at the perpendicular edge of the powder pattern for the hexagonal form in this sample show a large reduction in T2, especially at higher temperatures. The partial destruction of both spin-echoes and rotational echoes is due to a chemical-exchange type process involving sites having different NQCC values.

Enhancement of the central-transition signal in static and magic-angle-spinning NMR of quadrupolar nuclei by frequency-swept fast amplitude-modulated pulses

We here report on using fast amplitude-modulated (FAM) pulse trains with constantly incremented pulse durations (SW-FAM) for signal enhancement in one-dimensional nuclear magnetic resonance spectra of quadrupolar nuclei with half-integer spin. In such systems, a FAM pulse train leads to a redistribution of populations across the spin levels, which results in a substantial gain for the central-transition signal. Compared to fixed-duration FAM pulse trains, SW-FAM delivers about the same signal enhancement for spinning samples, but gives much better performance in the static case. This is demonstrated for several compounds, observing the nuclei 23Na ( I=3/2), 27Al ( I=5/2), and 45Sc ( I=7/2).

Single- and multiple-quantum cross-polarization in NMR of quadrupolar nuclei in static samples

Cross-polarization from a spin I=1/2 nucleus (e.g., 1H) to a spin S = 3/2 nucleus (e.g., 23Na) or a spin S = 5/2 nucleus (e.g., 27A1 or nO) in static powder samples is investigated. The results of conventional (single-quantum), three-quantum, and five-quantum cross-polarization experiments are presented and discussed. Based on a generalization of an existing theory of cross-polarization to quadrupolar nuclei, computer simulations are used to model the intensity and lineshape variations observed in cross-polarized NMR spectra as a function of the radio-frequency field strengths of the two simultaneous spin-locking pulses. These intensity and lineshape variations can also be understood in terms of the spin S = 3/2 or 5/2 nutation rates determined from experimental quadrupolar nutation spectra. The results of this study are intended as a preliminary step towards understanding single- and multiple-quantum cross-polarization to quadrupolar nuclei under MAS conditions and the application of these techniques to the MQMAS NMR experiment.

Single- and multiple-quantum cross-polarization in NMR of quadrupolar nuclei in static samples

Single- and multiple-quantum cross-polarization in NMR of quadrupolar nuclei in static samples

ChemInform Abstract: Site Connectivities in Amorphous Materials Studied by Double‐Resonance NMR of Quadrupolar Nuclei: High‐Resolution 11B ↔ 27Al Spectroscopy of Aluminoborate Glasses.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Numerical Simulation of Magnetic Resonance Experiments: Concepts and Applications to Static, Rotating and Double Rotating Experiments

Abstract An object-oriented programming environment for numerical simulation of magnetic resonance spectra is introduced and applied to NQR and NMR of quadrupolar nuclei. Using a Floquet approach it is possible to perform simulations of spin systems that are described by explicitly time-dependent Hamiltonians in full analogy to simulations of time-independent systems. Applications to magic angle spinning and double rotation are discussed.

RF field inhomogeneity in a MAS probe evaluated by MAS nutation NMR of quadrupolar nuclei

RF field inhomogeneity in a MAS probe evaluated by MAS nutation NMR of quadrupolar nuclei

Quantitative analysis in MAS NMR of quadrupolar nuclei

Quantitative analysis in MAS NMR of quadrupolar nuclei

ChemInform Abstract: NMR of Quadrupolar Nuclei in the Solid State

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The second order influence of the nuclear quadrupole interaction on the central line in the NMR of quadrupolar nuclei using rapid sample spinning

Using perturbation theory it is demonstrated that the second order quadrupole broadening of the central line of the NMR spectra of half integer spins is reduced by rapid sample spinning at the magic angle down to about 1/3.6 of the original value. The centre of gravity of the central line remains unchanged. Thus, the method of rapid sample spinning at the magic angle in the NMR of nuclei with strong quadrupole couplings can be used to get directly the spatial average of the chemical shift tensor. This situation is demonstrated experimentally in the case of high-field 27Al- and 23Na-NMR of various materials.

Enhanced resolution in NMR of quadrupolar nuclei in solids: Interferometric correlation of the first- and second-order shifts

Enhanced resolution in NMR of quadrupolar nuclei in solids: Interferometric correlation of the first- and second-order shifts