Toward dipolar recoupling in macroscopically ordered samples of membrane proteins rotating at the magic angle

MAS NMR spectroscopy can be combined with the advantages of uniaxially ordered samples of membrane proteins as demonstrated in the so-called MAOSS (magic angle oriented sample spinning) experiment. Under these conditions, dipolar recoupling methods can be used to determine the orientation of internuclear vectors with respect to the MAS rotor frame. However, most approaches to measure dipolar couplings yield angle ambiguities even in the static, non-spinning case. Here, we present the possibility of overcoming these problems by deriving a new homonuclear double-quantum radio frequency pulse sequence based on an eightfold symmetry. Only dipolar Hamiltonian terms with spatial components m=±2 are recoupled with high efficiency allowing unambiguous angle determinations. Preliminary data demonstrate the applicability of this experiment to oriented samples.