The type and strength of the non-covalent interactions that take place in a solution of ibuprofen in a new natural deep eutectic solvent (NADES), based on L-menthol, were investigated through NMR methods. Even in acetonitrile, a hydrogen-bonding network is formed between the components of the solvent. As a result of the cooperative effect of the constituents, a molecular complex is also formed with ibuprofen.
A eutectic mixture of L-menthol and malonic acid, Me/MA (4 : 1), was characterized by calorimetry and other physical measurements. The new deep eutectic solvent (m.p. 6 °C) solvates 338 mg of ibuprofen per mL, and the solution is stable in a wide temperature range. Strategies of NMR titration used in supramolecular chemistry were employed to explore binding forces between the eutectic constituents as well as solute-solvent interaction in ibuprofen solution. Even in acetonitrile, Me
MA is formed through a hydrogen-bonding network, where the constituents act as hydrogen donors and acceptors at the same time. The estimated association constant is around 30 M−1; the binding forces are enough to build the eutectic mixture at high concentrations. The aggregate Me
MA forms a molecular complex with ibuprofen in acetonitrile as a result of the cooperative effect of the constituents. In addition, van der Waals interactions are operative between ibuprofen and menthol in the saturated IB-Me/MA (4 : 1) solution.Zum Volltext