Off-resonance 13C-2H REDOR NMR for site-resolved studies of molecular motion.

We introduce a 13C-2H Rotational Echo DOuble Resonance (REDOR) technique that uses the difference between on-resonance and off-resonance 2H irradiation to detect dynamic segments in deuterated molecules. By selectively inverting specific regions of the 2H magic-angle spinning (MAS) sideband manifold to recouple some of the deuterons to nearby carbons, we distinguish dynamic and rigid residues in 1D and 2D 13C spectra. We demonstrate this approach on deuterated GB1, H/D exchanged GB1, and perdeuterated bacterial cellulose. Numerical simulations reproduce the measured mixing-time and 2H carrier-frequency dependence of the REDOR dephasing of bacterial cellulose. Combining numerical simulations with experiments thus allow the extraction of motionally averaged quadrupolar couplings from REDOR dephasing values.