Cross polarization in the tilted frame: assignment and spectral simplification in heteronuclear spin systems

A frequency selective heteronuclear polarization transfer technique is intr oduced for rotating solids. In this method, radiofrequency fields comparabl e with the frequency offsets are applied to establish Hartmann-Hahn cross p olarization that therefore depends explicitly on the resonance offset of th e nuclei involved. Under these conditions, spectrally induced filtering in combination with cross polarization (SPECIFIC CP) can be achieved and is de monstrated to be useful for spectral simplification or assignment in hetero nuclear spin pairs. The design principles are outlined and demonstrated exp erimentally on C-13, N-15 labelled amino acids.