Dibenzo-18-crown-6 (DB18C6) is a monofunctional, crown ether that acts as a host for a guest molecule. This system acts as a model for ligand binding to a protein and aids in higher understanding of binding processes. To support this study, density functional theory (DFT) calculations were utilized to determine the binding energy of DB18C6 with ammonium chloride in gas-phase as well as in the solvents water and methanol. All calculations were done with implicit and explicit solvent. Additionally, optimized structures of six conformers were found. Gas-phase calculations were done with the B3LYP, B3LYP-D, B3LYP-D3, M05-2X, and ωB97X-D DFT functionals and carried out with the open-source computational program package PSI4. Further DFT calculations of the gas-phase and solvated DB18C6 were done with M05-2X by using the computational program packages Gaussian 09 and Gaussian 16. Basis Set Superposition Error (BSSE) was accounted for in all binding energy calculations. The gas-phase lowest energy conformer was found to lie approximately ~2 kcal mol<sup>−1</sup> lower than the next lowest energy structure. This resulting lowest energy conformer, with a closed conformation, is consistently the lowest energy conformer among all DFT functionals employed. A reordering of the relative energies of conformers resulted due to DB18C6 seeming to prefer a more open conformation when complexed or solvated. Furthermore, as supported by Molecular Dynamic (MD) simulations and DFT calculations, higher energy conformations transition to an open conformation when complexed and/or solvated. Low affinity of ammonium to DB18C6 is suggested by the DFT binding energy calculations and MD simulations. The study resulted in finding the lowest energy conformers of DB18C6 and the binding energy of the ammonium ligand to the crown ether as well as the respective geometry for each species.

Ammonium ligand binding to dibenzo-18-crown-6 in solvent

255th National Meeting (2018)

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