One- and two-dimensional 13C-1H/15N- 1H dipolar correlation experiments under fast magic-angle spinning for determining the peptide dihedral angle phi.

A recently proposed 13C-1H recoupling sequence operative under fast magic-angle spinning (MAS) [K. Takegoshi, T. Terao, Solid State Nucl. Magn. Reson. 13 (1999) 203-212.] is applied to observe 13C-1H and 15N-1H dipolar powder patterns in the IH-15N- 3C- H system of a peptide bond. Both patterns are correlated by 15N-to-13C cross polarization to observe one- or two-dimensional (1D or 2D) correlation spectra, which can be simulated by using a simple analytical expression to determine the H-N-C-H dihedral angle. The 1D and 2D experiments were applied to N-acetyl[1,2-13C,15N] DL-valine, and the peptide q angle was determined with high precision by the 2D experiment to be +/- 155.0 degrees +/- 1.2 degrees. The positive one is in good agreement with the X-ray value of 154 degrees +/- 5 degrees. The 1D experiment provided the value of phi = +/- 156.0 degrees +/- 0.8 degrees.