Line narrowing in 1H NMR of powdered organic solids with TOP-CT-MAS experiments at ultra-fast MAS

Federico M Paruzzo; Brennan J Walder; Lyndon Emsley

doi:10.1016/j.jmr.2019.06.015

Line narrowing in ¹H NMR of powdered organic solids with TOP-CT-MAS experiments at ultra-fast MAS

J Magn Reson. 2019 Aug:305:131-137. doi: 10.1016/j.jmr.2019.06.015. Epub 2019 Jun 27.

Authors

Federico M Paruzzo¹, Brennan J Walder¹, Lyndon Emsley²

Affiliations

¹ Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
² Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland. Electronic address: lyndon.emsley@epfl.ch.

PMID: 31271928
DOI: 10.1016/j.jmr.2019.06.015

Abstract

The residual broadening observed in ¹H spectra of rigid organic solids at natural abundance under 111 kHz magic angle spinning (MAS) is typically a few hundred Hertz. Here we show that refocusable and non-refocusable interactions contribute roughly equally to this residual at high-fields (21.14 T), and suggest that the removal of the non-refocusable part will produce significant increase in spectral resolution. To this end, we demonstrate an experiment for the indirect acquisition of constant-time experiments at ultra-fast MAS (CT-MAS) which verifies this hypothesis. The combination of this experiment with the two-dimensional one pulse (TOP) transformation reduces the experimental time to a fraction of the original cost while retaining the narrowing effects. Results obtained with TOP-CT-MAS at 111 kHz MAS on a sample of β-AspAla yield up to 30% higher resolution spectra than the equivalent one-pulse experiment, in less than 10 min.

Keywords: (1)H spectra; Constant time; Homonuclear dipolar decoupling; Solid-state NMR; Ultra-fast MAS.