Novel Dipolar Recoupling Sequences for Excitation of High-Order Multiple-Quantum Coherences in Magic-Angle-Spinning NMR,

M. Edén, and A. Brinkmann,
44th Experimental NMR Conference, Savannah, Georgia, USA (Mar. 2003), talk.

Multiple-quantum coherences (MQC) are used in a wide variety of solid-state NMR techniques for determining molecular structure. The dipolar couplings that are required for creating MQC vanish under magic-angle-spinning conditions, necessitating the use of dipolar recoupling techniques. Most recoupling sequences used to date, achieve "double-quantum recoupling" (e.g., C7); when applied to an ensemble of multi-spin systems at thermal equilibrium, they sequentially convert longitudinal magnetization into MQC of even orders, i.e., 2,4,6,...

Based on the CN [1] and RN [2] families of pulse sequences, we present novel recoupling methods for the following purposes:

(1) "Single-quantum recoupling" [3,4]. Such sequences create MQC orders in steps of 1, i.e., convert longitudinal magnetization into coherence orders 1,2,3,.... They are useful for spin-counting purposes.

(2) "Triple-quantum recoupling" [5], leading to excitation of MQC orders in steps of 3.

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  2. 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).
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  5. M. Edén, Order-selective multiple-quantum excitation in magic-angle spinning NMR: creating triple-quantum coherences with a trilinear Hamiltonian, Chem. Phys. Lett. 366, 469-476, (2002).
Dr. Andreas Brinkmann
NRC Metrology
National Research Council Canada
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