Distance information from proton-driven spin diffusion under MAS

The measurement of small dipolar couplings, corresponding to long internuclear distances, in the presence of large couplings is investigated for proton-driven spin-diffusion (PDSD) experiments in 13C solid-state magic-angle spinning NMR. Analytical calculations and numerical simulations using coherent and incoherent models as well as measurements on a model substance indicate that dipolar truncation, the suppression of polarization transfer across small couplings by larger ones, does not strongly influence the PDSD experiments. Therefore, long internuclear distances (>3 إ) corresponding to small dipolar couplings can be measured even in the presence of larger couplings. This finding holds promise for structure determination by solid-state NMR using uniformly labelled biomolecules.