Abstract
Factors affecting the performance of 1H heteronuclear decoupling sequences for magic‐angle spinning (MAS) NMR spectroscopy of organic solids are explored, as observed by time constants for the decay of nuclear magnetisation under a spin‐echo (T2' ). By using a common protocol over a wide range of experimental conditions, including very high magnetic fields and very high radio‐frequency (RF) nutation rates, decoupling performance is observed to degrade consistently with increasing magnetic field. Inhomogeneity of the RF field is found to have a significant impact on T2' values, with differences of about 20 % observed between probes with different coil geometries. Increasing RF nutation rates dramatically improve robustness with respect to RF offset, but the performance of phase‐modulated sequences degrades at the very high nutation rates achievable in microcoils as a result of RF transients. The insights gained provide better understanding of the factors limiting decoupling performance under different conditions, and the high values of T2' observed (which generally exceed previous literature values) provide reference points for experiments involving spin magnetisation refocussing, such as 2D correlation spectra and measuring small spin couplings.
Highlights
Effective decoupling of 1H nuclear spins is essential for achieving high-resolution 13C and 15N solid-state NMR spectra from typical organic molecules, and is important for correlation experiments that use J couplings to determine molecular connectivity
Factors affecting the performance of 1H heteronuclear decoupling sequences for magic-angle spinning (MAS) NMR spectroscopy of organic solids are explored, as observed by time constants for the decay of nuclear magnetisation under a spinecho (T20 )
Determining the optimal decoupling parameters across a range of experimental set-ups involved acquiring a large number of detailed parameter maps for both T2* and T20
Summary
Effective decoupling of 1H nuclear spins is essential for achieving high-resolution 13C and 15N solid-state NMR spectra from typical organic molecules, and is important for correlation experiments that use J (or scalar) couplings to determine molecular connectivity. Such experiments are central to the use of NMR spectroscopy for establishing molecular structure and dynamics. Kentgens Institute for Molecules and Materials Radboud University, Heyendaalseweg 135 6525 ED Nijmegen (The Netherlands)
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