Using nutation-frequency-selective pulses to reduce radio-frequency field inhomogeneity in solid-state NMR

Abstract

Abstract. Radio-frequency (rf) field inhomogeneity is a common problem in NMR which leads to non-ideal rotations of spins in parts of the sample. Often, a physical volume restriction of the sample is used to reduce the effects of rf-field inhomogeneity, especially in solid-state NMR where spacers are inserted to reduce the sample volume to the centre of the coil. We show that band-selective pulses in the spin-lock frame can be used to apply B1-field selective inversions to spins that experience selected parts of the rf-field distribution. Any frequency band-selective pulse can be used for this purpose, but we chose the family of I-BURP pulses (Geen and Freeman, 1991) for the measurements demonstrated here. As an example, we show that the implementation of such pulses improves homonuclear frequency-switched Lee–Goldburg decoupling in solid-state NMR.

Optimisation of 1H PMLG homonuclear decoupling at 60 kHz MAS to enable 15N–1H through-bond heteronuclear correlation solid-state NMR spectroscopy

“…In addition, nutation-frequency-selective pulses that reduce rf inhomogeneity could also be explored. 103 The CP-refocused INEPT pulse sequence is complementary to dipolar coupling-based double CP or the use of symmetry-based decoupling to establish 15 N-1 H heteronuclear correlation under fast MAS. 26,29,30,104 Note that the use of symmetry-based recoupling is more prone to t 1 noise.…”

Rapid Quantification of Pharmaceuticals via 1H Solid-State NMR Spectroscopy

“…Thus, we expect the performance of CRAMPS–MAR to decline as the analytes’ structures and/or the mixture becomes more complex. Nonetheless, the resolution of CRAMPS is continuously being improved. ,,,, With the recent progress, we believe that CRAMPS–MAR can still advance, allowing complex, multi-component pharmaceutical mixtures to be quantified with ease.…”

“…Nonetheless, the resolution of CRAMPS is continuously being improved. 49,51,53,70,71 With the recent progress, we believe that CRAMPS−MAR can still advance, allowing complex, multi-component pharmaceutical mixtures to be quantified with ease. ■ CONCLUSIONS In this work, we proposed a novel SSNMR approach, CRAMPS−MAR, for rapid quantification of APIs.…”

Effects of radial radio-frequency field inhomogeneity on MAS solid-state NMR experiments

“…Data availability. The experimental NMR data, the simulation data, and the processing and plot scripts for all figures are available at https://doi.org/10.3929/ethz-b-000488476 (Aebischer et al, 2021).…”

“…used for a virtual sample restriction (Charmont et al, 2000), but since gradients are not very common in solid-state NMR probes, this approach is rarely used. Another possibility is radio or nutation-frequency-selective pulses that can be used for the same purpose (Charmont et al, 2002;Aebischer et al, 2020). All these methods, however, are accompanied by a reduction in signal due to the restriction of the measured sample volume to a smaller part of the coil volume.…”