BROAD-BAND 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 experi ments of C-13 spins. The sequence is based on a combination of rotatin g frame and laboratory frame transfer periods. The recovered dipolar i nteraction is only weakly dependent on spectral parameters but is a fa ithful measure for the internuclear distances. Furthermore, a pure zer o-quantum term is recovered (of the type found in static ''spin-diffus ion'' 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 c ouplings in a single 2D experiment. It is found that the necessary dec oupling from abundant protons is best performed in two steps: first, t he strong homonuclear couplings between the high-gamma spins are avera ged 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 a chieve an optimum chemical-shift offset-independence and for the suppr ession of unwanted double-quantum transitions. The design principles a re explained in detail. Finally, the pulse scheme is applied to total- correlation spectroscopy of a uniformly labeled amino acid. The experi mental cross-peak intensities are in qualitative agreement with the kn own crystal structure of the model compound. (C) 1997 Academic Press.