Characterization of doubly ionic hydrogen bonds in protic ionic liquids by NMR deuteron quadrupole coupling constants - Differences to H-bonds in amides, peptides and proteins
 

Characterization of doubly ionic hydrogen bonds in protic ionic liquids by NMR deuteron quadrupole coupling constants - Differences to H-bonds in amides, peptides and proteins


We present the first deuteron quadrupole coupling constants (DQCC) for selected protic ionic liquids (PILs) measured by solid-state NMR spectroscopy. The experimental data are supported by dispersion-corrected density functional theory (DFT-D3) calculations and molecular dynamics (MD) simulations. The DQCCs of the N-D bond in the triethylammonium cations are the lowest reported for deuterons in PILs indicating strong doubly ionic hydrogen bonds. The NMR coupling parameters are compared to those in amides, peptides, and proteins. The DQCCs show characteristic behaviour with increasing interaction strength of the counterion and variation of the H-bond motifs. We report the similar presence of the quadrupolar splitting pattern and the narrow liquid line in the NMR spectra over large temperature ranges, indicating the heterogeneous nature of PILs. The knowledge of DQCC is a prerequisite for studying the rotational dynamics by means of NMR quadrupolar relaxation time experiments.

More...