Artefact-free ultra-low temperature DNP-enhanced NMR of molecular assemblies at natural isotopic abundance

Dynamic Nuclear Polarization (DNP) has greatly increased solid-state NMR sensitivity, enabling multidimensional correlation experiments (e.g., 13C–13C, 13C–15N) at natural isotopic abundance. Yet, such experiments often suffer from t1-noise, an artefact that obscures weak cross-peaks. Here, we present a method to suppress t1-noise in 13C–13C correlation spectra. This so-called zz-filter markedly improves the spectral quality on both commercial (100 K) and custom-built helium-spinning (30 K) DNP set-ups, with up to a fivefold increase in signal-to-noise ratio in the indirect experimental dimension.