Determination of peptide phi 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 15N-1H and the 13C-1H dipolar tensors in the 1H-15N-13C-1H system are two-dimensionally (2D) correlated via polarization transfer from 15N to 13C under magic angle spinning (MAS). This method was applied to N-acetyl[1,2-13C,15N]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.