Influence of proton coupling on symmetry-based homonuclear 19F dipolar recoupling experiments

Titelangaben

Zehe, Christoph S. ; Siegel, Renée ; Senker, Jürgen:
Influence of proton coupling on symmetry-based homonuclear 19F dipolar recoupling experiments.
In: Solid State Nuclear Magnetic Resonance. Bd. 65 (2015) . - S. 122-131.
ISSN 0926-2040
DOI: https://doi.org/10.1016/j.ssnmr.2014.12.002

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Abstract

We study the efficiency of two symmetry based homonuclear F-19 double-quantum recoupling sequences for moderate (R14(2)(6)) and ultra-fast (R14(4)(5)) MAS under the influence of strong H-1-H-1 and H-1-F-19 dipolar interactions and H-1 continuous wave decoupling. Simulations based on various spin systems derived from the organic solid 1,3,5-tris(2-fluoro-2-methylpropionylamino)benzene (F-BTA), used as a model system, reveal that the strong-decoupling limit is not accessible even for moderate spinning speeds. Additionally, for the no-decoupling limit improved DQ efficiencies are predicted for both moderate and ultra-fast MAS. Strong perturbations of build-up curves can be avoided by additional stabilisation through supercycling. Additional H-1 cw decoupling during F-19 recoupling rapidly reduces the maximum DQ efficiency when deviating from the no-decoupling limit. These effects were confirmed by experimental data on F-BTA. For moderate spinning the influence of H-1-H-1 and H-1-F-19 couplings is markedly stronger compared to ultra-fast MAS. For the latter case those influences reduce to a constant scaling if only short excitation times up to the first minimum are taken into account Based on this analysis the experimental build-up curves of 1,3,5-tris(2-fluoro-2-methylpropionylamino)benzene can be refined with homonuclear F-19 spin systems which allow to probe even subtle structural differences for the fluorine atoms of F-BTA. (C) 2014 Elsevier Inc. All rights reserved.