Determination of peptide φ angles in solids by relayed anisotropy correlation NMR

A solid state NMR method is presented for determination of a backbone dihedral angle phi in peptides, being based on the previously reported method, relayed anisotropy correlation (RACO) NMR [Y. Ishii et al., Chem. Phys. Lett. 256 (1996) 133]. In the present method, the N-15-H-1 and the C-13-H-1 dipolar tensors in the H-1-N-15-C-13-H-1 system are two-dimensionally (2D) correlated via polarization transfer from N-15 to C-13 under magic angle spinning (MAS). This method was applied to N-acetyl[1,2-C-13,N-15]D,L-valine, and the H-C-N-H dihedral angle was determined to be 154.0 +/- 1.4 degrees or 206.0 +/- 1.4 degrees, the former agreeing with the X-ray value of 154 +/- 5 degrees. (C) 1998 Elsevier Science B.V. All rights reserved.