Frequency-Swept Ultra-Wideline Magic-Angle Spinning NMR Spectroscopy

Abstract

Recent years have witnessed the development of solid-state NMR techniques that allow the direct investigation of extremely wide inhomogeneously broadened resonance lines. To date, this typically involves the application of frequency sweeps as offered by wideband uniform rate smooth truncation (WURST) pulses. While the effects of such advanced irradiation schemes on static samples are well understood, the interference between the varying carrier frequency and the time-dependent evolution of the spin system under magic-angle spinning (MAS) conditions is more complex. Herein, we introduce the well-known WURST-Carr−Purcell−Meiboom−Gill (WCPMG) pulse sequence for spinning samples. Using numerical spin-density matrix analysis, an ideal design based on fast frequency sweeps and high truncation of the incorporated WURST pulses is presented that enables uniform excitation/refocusing under MAS conditions with low-to-moderate radio-frequency power requirements. This permits the acquisition of ultra-wideline MAS NMR lines exceeding 500 kHz with chemical shift resolution in a single transmitter step.

Pushing the Detection Limit of Static Wideline NMR Spectroscopy Using Ultrafast Frequency-Swept Pulses

“…Modern solid-state nuclear magnetic resonance (ssNMR) techniques have in recent years enabled atomic-scale, structural information on low-symmetry catalytic sites. − In particular, the direct observation of heavy nuclei, e.g., platinum often situated at the heart of the catalytic center, is addressed by the application of static ultrawideline (UW) ssNMR . This combines Carr–Purcell–Meiboom–Gill (CPMG) , acquisition with frequency-swept wideband uniform rate smooth truncation (WURST) pulses in the WURST-CPMG (WCPMG) NMR experiment. , We have recently extended WCPMG from static to magic-angle spinning (MAS) NMR conditions by applying extremely fast frequency sweeps, allowing the treatment of the rotating powder as being static (quasi stationarity) during the interaction with the rf-field . Here, we focus on optimizing the signal-enhancement properties of the static WCPMG NMR experiment, in particular when the observed nuclei have short transverse relaxation times.…”

“…10,11 We have recently extended WCPMG from static to magic-angle spinning (MAS) NMR conditions by applying extremely fast frequency sweeps, allowing the treatment of the rotating powder as being static (quasi stationarity) during the interaction with the rf-field. 12 Here, we focus on optimizing the signal-enhancement properties of the static WCPMG NMR experiment, in particular when the observed nuclei have short transverse relaxation times. The time-domain signal of the WCPMG NMR sequence shown in Scheme 1 with identical WURST-N pulses for excitation/refocusing can be described as a train of n echoes, which are equally separated by the delay…”

A Venue for Advances in Experimental and Theoretical Methods in Physical Chemistry

“…To illustrate the types of articles that meet the editorial criteria, we have collected together 41 papers recently published in section A4 in this virtual issue of The Journal of Physical Chemistry . These articles describe recent methodological advances across the breadth of physical chemistry, including experimental − and theoretical/computational − innovations.…”