Multiple-Channel Rotor-Synchronized Pulse Sequences: Application to Heteronuclear Recoupling and Decoupling in Magic Angle Spinning NMR,

A. Brinkmann, and M. H. Levitt,
41st Experimental NMR Conference, Asilomar, California, USA (Apr. 2000), poster.

Recently a new class of rotor-synchronized pulse sequences, denoted RNnν has been reported [1]. The sequences consist of N elements, each of which rotates the spins by an angle π around the x-axis. The phases of the elements are alternated by ±πν/N. The sequence of N elements span n rotational periods. Earlier on the concept of C7 [2] was generalized to sequences denoted by CNnν [3,4], consisting of N cycles, with phases incremented in steps of 2πν/N. The sequence of N cycles spans n rotational periods. These types of sequences might be used simultaneously using multiple-channel rf irradiation. We present symmetry theorems for this application, which allow the construction of rf sequences to recouple and/or decouple certain spin interactions in heteronuclear spin systems in the presence of magic angle rotation of the sample.

We present solutions for decoupling homonuclear dipolar and CSA interactions on two rf channels while recoupling the heteronuclear dipolar couplings. The sequences are used to measure heteronuclear 15N-13C distances and to obtain two dimensional correlation spectra. Possibilities for improving heteronuclear decoupling during homonuclear recoupling are also discussed.

  1. M. Carravetta, M. Edén, X. Zhao, A. Brinkmann, and M. H. Levitt, Symmetry Principles for the design of radiofrequency pulse sequences in the nuclear magnetic resonance of rotating solids, Chem. Phys. Lett. 321, 205-215, (2000). Abstract, Full text (PDF).
  2. Y. K. Lee, N. D. Kurur, M. Helmle, O. G. Johannessen, N. C. Nielsen, and M. H. Levitt, Efficient dipolar recoupling in the NMR of rotating solids. A sevenfold symmetric radiofrequency pulse sequence, Chem. Phys. Lett. 242, 304-309, (1995).
  3. M. Edén, and M. H. Levitt, Pulse sequence symmetries in the nuclear magnetic resonance of spinning solids: Application to heteronuclear decoupling, J. Chem. Phys. 111, 1511-1519, (1999).
  4. A. Brinkmann, M. Edén, and M. H. Levitt, Synchronous helical pulse sequences in magic-angle spinning nuclear magnetic resonance: Double quantum recoupling of multiple-spin systems, J. Chem. Phys. 112, 8539-8554, (2000). Abstract, Full text (PDF).
Dr. Andreas Brinkmann
National Research Council Canada
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