Compensating the asymmetric probe response in broad MAS NMR spectra of quadrupolar nuclei

Groszewicz, Pedro B.; Breitzke, Hergen; Buntkowsky, Gerd

doi:10.1016/j.ssnmr.2017.06.006

Cited by 6 publications

(3 citation statements)

References 29 publications

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“…These enhancements owe to the shorter refocusing pulse length, τ ref , as well as the higher RF field for ν ref in each case (again, this might not always be feasible for low-γ nuclei and large coil diameters). The SSB manifold appears lopsided in comparison to the ideal pattern such that some of the high frequency SSBs are more intense than the lower ones; this likely results from an asymmetric response from the probe . The CPMG-π/4 sequence results in a uniform SSB manifold for all RF fields (Figure iii).…”

Section: Results and Discussionmentioning

confidence: 96%

“…The SSB manifold appears lopsided in comparison to the ideal pattern such that some of the high frequency SSBs are more intense than the lower ones; this likely results from an asymmetric response from the probe. 85 The CPMG-π/4 sequence results in a uniform SSB manifold for all RF fields (Figure 7iii). This sequence allows for lowpower uniform excitation and refocusing with increased S/N ratios over conventional acquisition methods.…”

Section: Resultsmentioning

confidence: 97%

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Practical Aspects of Recording Ultra-Wideline NMR Patterns under Magic-Angle Spinning Conditions

et al. 2020

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Many NMR-active nuclei give rise to solid-state NMR spectra that span extremely large frequency regions due to the effects of large anisotropic NMR interactions; such spectra, which can range from 250 kHz to several MHz in breadth, have been termed ultrawideline (UW) NMR spectra. UWNMR spectra are often too broad to be uniformly excited by conventional pulse sequences that implement rectangular radiofrequency (RF) pulses. Therefore, they are typically acquired with specialized pulse sequences and frequencyswept (FS) pulses; however, such experiments are conducted predominantly upon stationary samples (i.e., static NMR with no magic-angle spinning, MAS). Herein, we demonstrate how to implement Carr−Purcell Meiboom−Gill (CPMG) type pulse sequences that utilize rectangular pulses to acquire high-quality wideline and UWNMR spectra under MAS conditions, which are useful for providing uniformly excited patterns with substantial signal enhancements in comparison to conventional MAS NMR spectra and identifying peaks and/or patterns corresponding to magnetically nonequivalent sites. We discuss the pulse timings, delays, and the duration of windowed acquisition periods that are necessary for using CPMG-type pulse sequences for T 2 -dependent enhancement under MAS conditions while allowing for chemical shift resolution and maintaining a conventional spinning-sideband (SSB) manifold, as well as protocols for processing these spectra. Careful consideration is given to pulse lengths and RF amplitudes used in these pulse sequences. Using several spin-1 / 2 (i.e., 119 Sn, 207 Pb, 195 Pt) nuclei and one integer-spin quadrupolar nucleus (i.e., 2 H), we show how sensitivity-enhancing protocols, including CPMG and cross-polarization (CP), can be used to deliver high-quality MAS NMR spectra, which feature high signal-to-noise (S/N) ratios and uniformly excited SSB manifolds. The methods outlined herein are facile to implement and offer the potential to open up MAS NMR experiments to a wide variety of elements from across the periodic table.

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Section: Results and Discussionmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 97%

Practical Aspects of Recording Ultra-Wideline NMR Patterns under Magic-Angle Spinning Conditions

et al. 2020

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“…However, the relative intensity of the highfrequency half of the powder pattern is greater than the low-frequency half. Experimentally, this is often attributed to the asymmetric probe response of the pulses [45] ; however, in these numerical simulations, this would not be the case, and the reason for this augmented signal intensity is still unknown. There is also a noticeable depletion of signal in the middle of the skyline projected powder pattern.…”

Section: Spin-1 Brain-cp Spin Dynamicsmentioning

confidence: 89%

Broadband adiabatic inversion cross‐polarization to integer‐spin nuclei with application to deuterium NMR

Altenhof

Schurko

2021

Magnetic Reson in Chemistry

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Solid-state NMR (SSNMR) spectroscopy of integer-spin quadrupolar nuclei is important for the molecular-level characterization of a variety of materials and biological solids; of the integer spins, 2 H (S = 1) is by far the most widely studied, due to its usefulness in probing dynamical motions. SSNMR spectra of integer-spin nuclei often feature very broad powder patterns that arise largely from the effects of the first-order quadrupolar interaction; as such, the acquisition of high-quality spectra continues to remain a challenge. The broadband adiabatic inversion cross-polarization (BRAIN-CP) pulse sequence, which is capable of cross-polarization (CP) enhancement over large bandwidths, has found success for the acquisition of SSNMR spectra of integer-spin nuclei, including 14 N (S = 1), especially when coupled with Carr-Purcell/Meiboom-Gill pulse sequences featuring frequency-swept WURST pulses (WURST-CPMG) for T 2 -based signal enhancement. However, to date, there has not been

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From Ultraslow to Extremely Fast Dynamics in Sodium Nitrate: an 17O NMR Study

et al. 2020

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Increasing dynamics in solids featuring nuclei subjected to second-order quadrupolar interactions lead to central-transition spectra that undergo two consecutive line-shaped transitions. Conventional motional narrowing occurs when the molecular exchange rate is on the order of the strength of the dominant interaction. In a second step, the resulting intermediately narrowed spectra change further when the motion becomes faster than the Larmor precession rate, leading to terminally narrowed spectra that can display a residual quadrupolar shift. We derive analytic expressions for this shift and analyze the quadrupolar central-transition spectra in terms of CN symmetrical cone models. Increasing the number of sites to N ≥ 3, the terminally narrowed spectra remain unaltered, while the intermediately narrowed spectra remain unaltered only for N ≥ 5. This finding relates to the different (cubic vs. icosahedral) symmetries that are required to average out the spatial second- and fourth-rank terms in the second-order quadrupolar interaction. Following recent work (Hung et al., Solid State Nucl Magn Reson 84:14–19, 2017), 17O NMR is applied to examine the three-site rotation of the nitrate group in NaNO3. Line shapes are measured and analyzed, and in addition to prior work, satellite-transition and stimulated-echo experiments are carried out. The final-state amplitudes extracted from the latter are reproduced using model calculations. It is shown how two-dimensional exchange spectra relating to N-site cone motions can be decomposed in terms of effective two-site-jump spectra. This latter approach is successfully tested for NaNO3.

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Compensating the asymmetric probe response in broad MAS NMR spectra of quadrupolar nuclei

Cited by 6 publications

References 29 publications

Practical Aspects of Recording Ultra-Wideline NMR Patterns under Magic-Angle Spinning Conditions

Practical Aspects of Recording Ultra-Wideline NMR Patterns under Magic-Angle Spinning Conditions

Broadband adiabatic inversion cross‐polarization to integer‐spin nuclei with application to deuterium NMR

From Ultraslow to Extremely Fast Dynamics in Sodium Nitrate: an 17O NMR Study

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