On the mechanism behind the enhanced solubility of glibenclamide in aqueous ionic liquid solution

The aim of the present study was to dissect the nature of intermolecular interactions leading to the improved solubility of glibenclamide in an aqueous solution of the choline tryptophanate, [Cho][Trp], ionic liquid. To this end, experimental [Figure presented] NMR measurements and computational modeling employing classical molecular dynamics (MD) simulations and combined quantum mechanics/molecular mechanics (QM/MM) models were carried out. Samples of glibenclamide dissolved in water and in an aqueous mixture of [Cho][Trp] were scrutinized both experimentally and computationally. MD simulations revealed that the constituent ions of the ionic liquid condensed around the drug molecule pushing water molecules away. Nevertheless, virtually no specific hydrogen bonding interactions between glibenclamide and the ions were formed. The hydrotropic activity of the [Cho][Trp] ionic liquid thus occurs through the formation of dynamic aggregates between the solute and the ions, which screen the hydrophobic glibenclamide from polar water molecules. Experimental [Figure presented] NMR measurements have shown that the largest changes in chemical shifts were registered for protons in the benzene rings of glibenclamide, implying that these are the main sites of interaction with the ions of the ionic liquid – a conclusion well-corroborated by the results of MD simulations. The good qualitative agreement between the computational QM/MM-based and experimental NMR spectra of glibenclamide in an aqueous solution and in aqueous mixture of [Cho][Trp] provides support to the structural results.