NMR and computational studies of ammonium ion binding to dibenzo-18-crown-6

Brielle Shope, D. Brandon Magers, István Pelczer, David Řeha, Babak Minofar, Jannette Carey

Research output: Contribution to journalArticlepeer-review


Dibenzo-18-crown-6 (DB18C6) is a single-crown ether that can act as a host for a guest ion. In an effort to illuminate the relationships among structure, dynamics, and thermodynamics of ligand binding in a simple model for understanding the affinity and specificity of ligand interactions, nuclear magnetic resonance (NMR) experiments and density functional theory (DFT) were used to study the interaction of DB18C6 with ammonium ion. 1H-NMR was used to follow the titration of DB18C6 with ammonium chloride in deuterated methanol, a solvent chosen for its amphipathic character. Ammonium ion binds strongly to DB18C6 with a dissociation equilibrium constant at least as low as ~ 10 - 6 M. DFT calculations were used to identify optimized conformations of bound and free DB18C6 and to estimate its binding energy with ammonium ion in implicit solvent. An approach is described that accounts for geometry relaxation in addition to solvation correction and basis set superposition error; to our knowledge, this is the first such report that includes the energy difference from optimizing species geometry. The lowest-energy conformer of free DB18C6 in implicit methanol acquires an open, W-shaped structure that is also the lowest-energy conformer found for the DB18C6-ammonium ion complex. These results form a foundation for further studies of this system by molecular dynamics simulations.

Original languageEnglish (US)
Pages (from-to)713-722
Number of pages10
JournalStructural Chemistry
Issue number2
StatePublished - Apr 2023

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry


  • Conformational transitions
  • Forward and reverse titration
  • Host–guest systems
  • Ligand-binding affinity
  • Molar ratio of binding
  • Stoichiometric titration
  • Synergy of experiment and computation


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