Design, preparation and characterization of 7-hydroxy-4-methylcoumarin-based deep eutectic solvents

Abstract

The development of an appropriate delivery system of active pharmaceutical ingredients (APIs) is an absolute necessity in the treatment of different diseases. Recently, DESs have been intensively studied for the purpose of improved API delivery. As a part of our continuous investigations in this particular field, we have prepared and characterized two new deep eutectic solvents with pharmaceutically active ingredients. Lidocaine (Lid), 7-hydroxy-4-methylcoumarin (Cou) and lactic (La) or levulinic (Le) acid were used for the preparation of the desired DESs. Both solvents were characterized by different methods in order to determine their physical and chemical properties. The water content determined by Karl–Fischer titration is 1.02% and 1.66%, respectively, while the polarity of both solvents is between the polarity of water and methanol. NMR and IR studies indicate the presence of Cou in the deprotonated (anionic) form, Lid in both neutral and protonated forms, and acids in the neutral form. Spectroscopic studies indicate the presence of strong O–H⋯O and C–O⋯H hydrogen bonds in both DESs. In silico methods provided a deeper insight into the complex intermolecular interaction patterns between the components of the prepared deep eutectic solvents. The thermal analysis indicates that these solvents can be considered as DESs with high thermal stability.