Recoupling by Helical Pulse Sequences in Magic-Angle-Spinning NMR,

A. Brinkmann, M. Edén, and M. H. Levitt,
1st Alpine Conference on Solid-State NMR, Chamonix-Mont Blanc, France (Sep. 1999), talk.

Solid State NMR is rapidly developing as a tool for determining local structure in isotopically labelled biomolecules. Technologies have been developed which allow temporary recoupling of the nuclear spin system in the presence of magic angle spinning. Recoupling is used for measuring internuclear distances, and for generating multiple-quantum coherences which can be used for angular estimations.

Pulse schemes based on the seven fold symmetric C7 sequence are now widely used. They generate a double-quantum average Hamiltonian for the recoupled spin pairs.

We present pulse sequences based on a more general concept, involving synchronous helical modulations of the sample rotation angle and the rf phase. The "winding numbers" of the helices may be chosen according to simple rules in order to select desirable terms while recjecting others [1,2].

The new pulse sequences allow the use of a lower rf field on the recoupled spins, which permits operation at higher spinning frequencies.

Applications to double quantum dynamics in multiple-spin systems are shown. Heteronuclear applications will also be discussed.

  1. 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).
  2. 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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