Direct determination of a peptide torsional angle ψ by double-quantum solid-state NMR,
We introduce a new solid-state NMR method for directly estimating the molecular torsional angle of an isotopically-labelled 15N-15C-13C-13N molecular fragment. The method is demonstrated on an isotopically-labelled polycrystalline sample of gly-gly-gly.HCl. The value of ψ is determined to be 162°±5°, in good agreement with the X-ray structure.