High-dimensional solid-state NMR facilitated by transverse-mixing optimal control.

Owing to fast magic-angle spinning, solid-state nuclear magnetic resonance has evolved as a versatile method to decipher protein structure, dynamics, and chemical properties. While higher-dimensional approaches such as 4D and 5D correlation spectra are generally capable of exceeding the established molecular-weight limitations by ameliorating signal overlap, their intrinsic implications for sensitivity and measurement times required have severely limited these important prospects in practice. Here we show that the extensive use of dedicated transverse-mixing optimal control pulses (TROPs) in high-dimensional experiments to enable concomitant transfer of complex signals along complex magnetization transfer pathways can reduce the necessary measurement time by an order of magnitude. Owing to the multiplicative benefits of the enhancement for successive indirect chemical-shift dimensions, combined with non-linear benefits upon spectral reconstruction, the combination of non-uniformly sampled, higher-dimensional approaches with an extensive use of TROPs hence presents itself as transformative for the conventional limitations of solid-state NMR.