Reintroduction of the quadrupolar interaction under magic-angle spinning NMR

The anisotropy in the dipole–dipole and quadrupole couplings are averaged out in magic-angle spinning (MAS) NMR experiments. Under conditions of axial symmetry (η=0), we exploit the homologous forms of the respective coupling Hamiltonians to show that the quadrupole coupling can also be resurrected by a simple adaptation of a rotor-synchronized pulse sequence previously proposed for the recovery of dipole–dipole couplings. We develop the theory for the recovery of the quadrupole couplings, and then use numerical simulations of the quadrupolar (double-quantum) dephasing observed in the 2H MAS NMR spectra of lipid systems to extract the quadrupolar splitting.