Deuteron Quadrupole Coupling Constants and Reorientation Correlation Times of Cations in Amino Acid Ionic Liquids
Year: 2025
Type: article
Abstract: The deuteron quadrupole coupling constants and reorientation correlation times of imidazolium cations in amino acid ionic liquids (AAILs) from NMR spin‐lattice relaxation times, T 1 , are determined. A proper determination of the reorientation correlation times τ c of the acidic C(2)─H groups on the imidazolium rings requires knowledge of reliable NMR deuteron quadrupole coupling constants χ D . For that purpose, a relation between the deuteron quadrupole coupling constants χ D and the proton chemical shifts δ 1 H from density functional theory (DFT) calculated properties of differently sized clusters of the AAILs is first derived. Using this relation, the simple measurement of proton chemical shifts δ 1 H provides an accurate estimate for χ D , which can then be used for determining the reorientation correlation times τ c . This method is applied to AAILs including the same imidazolium cation but differently functionalized anions. The obtained χ D values range between 180 and 210 kHz, depending on the differently strong cation–anion interaction further enhanced by hydrogen bonding. The resulting reorientation correlation times τ c indicate that the extreme narrowing condition is fulfilled for this type of IL. Using the Stokes–Einstein–Debye relation, the correlation times τ c and the additionally measured viscosities η provide an estimate for the volume/size of the clusters present in solution.
Source: ChemPhysChem
Authors: David Kotwica, Dirk Michalik, Ralf Ludwig
Institutions: University of Rostock, Leibniz Institute for Catalysis
Language: English
Subfield: Catalysis
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,550
Funder: Deutsche Forschungsgemeinschaft
OpenAlex ID: W4415559504