MAS solid state NMR of proteins: simultaneous ¹5N- ¹³CA and ¹5N- ¹³CO dipolar recoupling via low-power symmetry-based RF pulse schemes.

The generation of efficient RN n (ν)s,(ν)k symmetry-based low-power RF pulse schemes for simultaneous (15)N-(13)CA and (15)N-(13)CO dipolar recoupling is demonstrated. The method involves mixing schemes employing phase and amplitude-modulated dual band-selective 180° pulses as basic "R" element and tailoring of the RF field-modulation profile of the 180° pulses so as to obtain efficient magnetisation transfer characteristics over the resonance offset range of the nuclei involved. Mixing schemes leading to simultaneous (15)N-(13)CA and (15)N-(13)CO dipolar recoupling would permit the one-shot acquisition of different chemical shift correlation spectra that are typically utilized for protein backbone resonance assignments and thereby save data acquisition time. At representative MAS frequencies the efficacies of the mixing schemes presented here have been experimentally demonstrated via the simultaneous acquisition of {3D CONH and 3D CANH}, {3D CONH and 3D CO(CA)NH} and {3D CONH, 3D CANH, 3D CO(CA)NH and 3D CA(CO)NH} spectra generated via the magnetisation transfer pathways (1)H → (13)CO → (15)N → (1)H (CONH), (1)H → (13)CA → (15)N → (1)H (CANH) and (1)H → (13)CO → (13)CA → (15)N → (1)H (CO(CA)NH) and (1)H → (13)CA → (13)CO → (15)N → (1)H (CA(CO)NH).