posters 5th Asia-Pacific NMR Symposium 2013

Bandwidth in Double CP MAS NMR spectroscopy (#214)

Der-Lii M. Tzou 1
  1. Institute of Chemistry, Academia Sinica, Taipei, Taiwan

The signal intensity in double cross-polarization (DCP) NMR experiments is critically dependent on the experimental parameters, which include the rf field strength, carrier frequency, and magic-angle spinning (MAS) frequency. In this systematic study, we have monitored {1H}/31P/13C DCP signals from monosaccharide a-D-[UL-13C6] galactopyranosyl 1-phosphate (GalP) at a MAS frequency of 13 kHz, at which only double quantum cross-polarization (CP) coherence transfer is allowed. To lessen the stringent requirements for these experimental parameters, we have implemented linear ramp pulse, adiabatic ramp-shaped pulse, and block pulse during the period of 31P/13C CP. We unravel the CP matching profiles with respect to these parameters by monitoring the 31P/13C signal while varying the rf field strength and carrier frequency. For comparison, we extracted the selectivity bandwidth from the full width at half maximum (FWHM) of the matching profiles, in units of frequency (kHz), and found bandwidths of 1.1, 14, and 22 kHz for the matching profiles of the 13C rf field strength and the 13C and 31P carrier frequencies, respectively, for a linear ramp pulse CP. These bandwidths are broader than the measured values in an adiabatic-shaped pulse CP (0.8, 10, and 12 kHz), as well as in block CP (0.3, 7, and 10 kHz) experiments. We demonstrate that the linear ramp pulse CP is superior to both block CP and adiabatic-shaped CP in lessening the stringent requirements of the aforementioned experimental settings for DCP experiments.