One- and two-dimensional C-13-H-1/N-15-H-1 dipolar correlation experimentsunder fast magic-angle spinning for determining the peptide dihedral anglephi

A recently proposed C-13-H-1 recoupling sequence operative under fast magic -angle spinning (MAS) [K. Takegoshi, T. Terao, Solid State Nucl. Magn. Reso n. 13 (1999) 203-212.] is applied to observe C-13-H-1 and N-15-H-1 dipolar powder patterns in the H-1-N-15-C-13-H-1 system of a peptide bond. Both pat terns are correlated by N-15-to-C-13 cross polarization to observe one- or two-dimensional (1D or 2D) correlation spectra, which can be simulated by u sing 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-C-13,N-15] DL-vali ne, and the peptide phi 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 ex periment provided the value of phi = + 156.0 degrees +/- 0.8 degrees. (C) 2 000 Elsevier Science B.V. All rights reserved.