This work explores the utility of simple rotary resonance experiments for the determination of the magnitude and orientation of 13C chemical shift tensors relative to one or more 13C–14N internuclear axes from 13C magic-angle-spinning NMR experiments. The experiment relies on simultaneous recoupling of the anisotropic 13C chemical shift and 13C–14N dipole–dipole coupling interactions using 2D rotary resonance NMR with RF irradiation on the 13C spins only. The method is demonstrated by experiments and numerical simulations for the 13Cα spins in powder samples of l-alanine and glycine with 13C in natural abundance. To investigate the potential of the experiment for determination of relative/absolute tensor orientations and backbone dihedral angles in peptides, the influence from long-range dipolar coupling to sequential 14N spins in a peptide chain (14Ni–13Cαi–14Ni+1 and 14Ni+1–13C′i–14Ni three-spin systems) as well as residual quadrupolar–dipolar coupling cross-terms is analyzed numerically.
Document Type: Research Article
Department of Molecular and Structural Biology 2:
Department of Molecular and Structural Biology, Department of Chemistry, University of Aarhus, Aarhus C, DK-8000, Denmark