Design and characterization of novel ionic liquids (ILs) containing natural compounds such as tryptophan, fructose, and adenine; the ILs stabilized via H-bonds and anomeric effect

Abstract

Ionic liquids (ILs) are a remarkable compound class consisting entirely of ions (cations and anions) with a melting point below 100 °C. In ILs, the cation’s positive charge and the anion’s negative charge are distributed through induction and resonance effects. This distribution reduces attraction between ion pairs and balances the energy between them, facilitating the formation of an IL. In this work, we designed the ILs containing the natural anions and cations. In the designed ILs, the anions contain various amino acids and sugars, and the cation contains methylated DNA base adenine. Our study has focused on intramolecular hydrogen bonding (H-bond) within the anion and intermolecular H-bond between methylated adenine cation and the various anions. Our objective in creating these structures is to investigate H-bonds’ influence on the negative charge distribution in the anion and to explore the anomeric effect on the stability of the cation in the designed ILs. In particular, using quantum mechanics (QM) calculations, we examined how intermolecular H-bonds affect the interaction energy between the ions in our newly designed ILs. At the same time, molecular dynamics (MD) simulations were utilized to validate the QM results. The QM average interaction energy (ΔE_int) between the anion and cation of the designed ILs is −73.39 kcal/mol, consistent with the ΔE_int typically reported for the common ILs. This approach may lead to developing more efficient and environmentally friendly ILs for various applications.