Homonuclear dipolar decoupling with very large scaling factors for high-resolution ultrafast magic angle spinning 1H solid-state NMR spectroscopy

We present a new phase modulated radio-frequency pulse sequence for homonuclear dipolar decoupling in proton solid-state NMR spectroscopy, eDUMBO-PLUS-1, with a chemical shift scaling factor of 0.73. This sequence was determined by screening random sequences, and experimentally optimizing the best candidates directly on 1H NMR spectra with 60 kHz magic angle spinning. It yields efficient decoupling with linewidths as little as 150 Hz for 1.3 mm MAS probes on different spectrometers. Experiments and calculations support the hypothesis of a radio-frequency and MAS joint averaging regime, in which the large scaling factor contributes significantly to the overall performance of the decoupling sequence.