3D N-15-C-13-C-13 chemical shift correlation spectroscopy in rotating solids

We describe 3D solid state MAS NMR experiments which separate chemical shifts in one N-15 and two C-13 dimensions. The polarization transfer from H-1 to N-15, and subsequently to C-13, is accomplished with recently developed techniques which overcome the shortcomings of constant amplitude Hartmann-Hahn cross polarization. Homonuclear (C-13-C-13) recoupling is performed with the MELODRAMA sequence. In the 2D C-13-C-13 spectra of adenosine monophosphate (AMP), successive MELODRAMA transfers propagate C-13. magnetization around the five C-13's of the ribose ring, and the cross-peaks from successive transfer steps exhibit the netative/positive/negative... pattern expected from the double-quantum polarization transfer process. The 3D N-15-C-13-C-13 spectrum of uniformly-N-15,C-13-labeled histidine consists of C-13-C-13 planes separated by N-15 chemical shifts. The 2D planes are asymmetric since in many cases the polarization giving rise to each cross-peak originates on only one nuclear spin of the coupled pair. 3D N-15-C-13-C-13 spectra of this type should be useful for dispersing overlapping spectra of peptides, proteins, and nucleic acids.