Broadband polarization transfer under magic-angle spinning: Application to total through-space-correlation NMR spectroscopy

A pulse sequence is described that leads to a broadband recoupling of the dipolar interaction in magic-angle-spinning solid-state NMR experiments of C-13 spins. The sequence is based on a combination of rotating frame and laboratory frame transfer periods. The recovered dipolar interaction is only weakly dependent on spectral parameters but is a faithful measure for the internuclear distances. Furthermore, a pure zero-quantum term is recovered (of the type found in static ''spin-diffusion'' experiments). This makes the pulse sequence particularly suited for incorporation into two-dimensional total through-space correlation experiments that deliver simultaneous information about all dipolar couplings in a single 2D experiment. It is found that the necessary decoupling from abundant protons is best performed in two steps: first, the strong homonuclear couplings between the high-gamma spins are averaged by Lee-Goldburg irradiation and, second, the heteronuclear dipolar interaction is averaged by the combined application of an RF field to the low-gamma spins and magic-angle sample spinning. Phase-inversion and amplitude attenuation in the rotating frame and refocusing pulses in the laboratory frame part of the pulse sequence are introduced to achieve an optimum chemical-shift offset-independence and for the suppression of unwanted double-quantum transitions. The design principles are explained in detail. Finally, the pulse scheme is applied to total-correlation spectroscopy of a uniformly labeled amino acid. The experimental cross-peak intensities are in qualitative agreement with the known crystal structure of the model compound. (C) 1997 Academic Press.