1. Measurement of Accurate Interfluorine Distances in Crystalline Organic Solids: A High-Frequency Magic Angle Spinning NMR Approach
- Author
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Ivan V. Sergeyev, Jochem Struppe, Tatyana Polenova, Matthew Fritz, Angela M. Gronenborn, Glenn P. A. Yap, Caitlin M. Quinn, and Jodi Kraus
- Subjects
Models, Molecular ,Materials science ,Magnetic Resonance Spectroscopy ,010304 chemical physics ,Solid-state ,Analytical chemistry ,Molecular Conformation ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,Fluorine ,Solid material ,010402 general chemistry ,Crystallography, X-Ray ,01 natural sciences ,Article ,0104 chemical sciences ,Surfaces, Coatings and Films ,chemistry ,0103 physical sciences ,Materials Chemistry ,Magic angle spinning ,Physical and Theoretical Chemistry ,Organic Chemicals ,Density Functional Theory - Abstract
Long-range interatomic distance restraints are critical for the determination of molecular structures by NMR spectroscopy, both in solution and in the solid state. Fluorine is a powerful NMR probe in a wide variety of contexts, owing to its favorable magnetic properties, ease of incorporation into biological molecules, and ubiquitous use in synthetic organic molecules designed for diverse applications. Due to the large gyromagnetic ratio of the 100% naturally abundant (19)F isotope, interfluorine distances as long as 20 Å are accessible in magic angle spinning (MAS) dipolar recoupling experiments. Herein, we present an approach for the determination of accurate interfluorine distances in multi-spin systems, using the finite pulse RFDR (fpRFDR) at high MAS frequencies of 40–60 kHz. We use a series of crystalline “molecular ruler” solids, difluorobenzoic acids and 7F-L-tryptophan, for which the intra- and intermolecular interfluorine distances are known. We describe the optimal experimental conditions for accurate distance determinations, including the choice of a phase cycle, the relative advantages of selective inversion 1D vs. 2D correlation experiments, and the appropriate numerical simulation protocols. A best strategy for the analysis of RFDR exchange curves in organic solids with extended spin interaction networks is presented, which, even in the absence of crystal structures, can be potentially incorporated into NMR structure determination.
- Published
- 2019