Tilted n-fold symmetric radio frequency pulse sequences:: Applications to CSA and heteronuclear dipolar recoupling in homonuclear dipolar coupled spin networks

We describe new solid-slate NMR methods for measuring the magnitude of the chemical shift anisotropy (CSA) and/or the heteronuclear dipolar coupling in the presence of homonuclear dipolar coupled spin networks under magic-angle spinning (MAS). The techniques employ 2 pi/5 phase shifts of a frequency switched Lee-Goldburg irradiation scheme which recouples the CSA and/or the heteronuclear dipolar coupling while simultaneously decoupling the homonuclear dipolar interactions. The induced spin dynamics are sensitive to the magnitude of the CSA and its asymmetry and may be implemented under conditions where the MAS rate exceeds the size of the anisotropic interactions. These approaches could find use in measurements of the magnitudes and relative orientations of CSA and/or heteronuclear dipolar couplings to extract torsion angles in uniformly labeled systems. (C) 1998 American Institute of Physics.