Beyond Simply Spinning: Improving 1H Resolution at Fast Magic-Angle-Spinning Frequencies Using Combined Rotation and...

Rapid developments in magic-angle-spinning (MAS) hardware over the past two decades have made possible the acquisition of high-resolution spectra of protons in solids, fuelling studies of small and large molecules alike. Nevertheless, proton resolution, limited by the strong dipole-dipole coupling network, remains a bottleneck even at MAS frequencies exceeding 100 kHz. We present here techniques based on phase-modulated homonuclear decoupling that dramatically improve proton coherence times and resolution compared to those of 60-95 kHz MAS alone using low average radiofrequency amplitudes (<100 kHz). A relatively high sensitivity (40-70%) and a straightforward optimization procedure performed directly on the sample being studied allow these gains to be realized in large biomolecules, as demonstrated here on a 326-residue cytoskeletal protein in its filamentous state. These techniques enable experiments with improved resolution on biomolecules while simultaneously taking advantage of the higher sensitivity available on probes with relatively large rotor volumes that cannot reach higher MAS frequencies.