Single crystal nuclear magnetic resonance in spinning powders.
We present a method for selectively exciting nuclear magnetic resonances (NMRs) from well-defined subsets of crystallites from a powdered sample under magic angle spinning. Magic angle spinning induces a time dependence in the anisotropic interactions, which results in a time variation of the resonance frequencies which is different for different crystallite orientations. The proposed method exploits this by applying selective pulses, which we refer to as XS (for crystallite-selective) pulses, that follow the resonance frequencies of nuclear species within particular crystallites, resulting in the induced flip angle being orientation dependent. By selecting the radiofrequency field to deliver a 180° pulse for the target orientation and employing a train of such pulses combined with cogwheel phase cycling, we obtain a high degree of orientational selectivity with the resulting spectrum containing only contributions from orientations close to the target. Typically, this leads to the selection of between 0.1% and 10% of the crystallites, and in extreme cases to the excitation of a single orientation resulting in single crystal spectra of spinning powders. Two formulations of this method are described and demonstrated with experimental examples on [1-(13)C]-alanine and the paramagnetic compound Sm(2)Sn(2)O(7).
Université de Lyon, Centre de RMN à Très Hauts Champs, CNRS/Ecole Normale Supérieure de Lyon/Université Claude Bernard Lyon 1, 5 rue de la Doua, 69100 Villeurbanne, France.
Andrew J
AJ
Pell
Guido
G
Pintacuda
Lyndon
L
Emsley
D000409:Alanine / Q000737:chemistry*; D003198:Computer Simulation; D003460:Crystallization; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D010087:Oxides / Q000737:chemistry; D011208:Powders / Q000737:chemistry; D012493:Samarium / Q000737:chemistry; D014001:Tin / Q000737:chemistry
D010087:Oxides; D011208:Powders; D012493:Samarium; D014001:Tin; D000409:Alanine