Coherence selection in double CP MAS NMR spectroscopy

Applications of double cross-polarization (CP) magic-angle spinning (MAS) NMR spectroscopy, via 1H/15N and then 15N/13C coherence transfers, for 13C coherence selection are demonstrated on a 15N/13C-labeled N-acetyl-glucosamine (GlcNAc) compound. The 15N/13C coherence transfer is very sensitive to the settings of the experimental parameters. To resolve explicitly these parameter dependences, we have systematically monitored the 13C{15N/1H} signal as a function of the rf field strength and the MAS frequency. The data reveal that the zero-quantum coherence transfer, with which the 13C effective rf field is larger than that of the 15N by the spinning frequency, would give better signal sensitivity. We demonstrate in one- and two-dimensional double CP experiments that spectral editing can be achieved by tailoring the experimental parameters, such as the rf field strengths and/or the MAS frequency.