In the spirit of circular economy and sustainable chemistry, the use of environmentally friendly chemical products in pharmacy has become a hot topic. In recent years, organic solvents have been the subject of a great range of restriction policies due to their harmful effects on the environment and toxicity to human health. In parallel, deep eutectic solvents (DESs) have emerged as suitable greener solvents with beneficial environmental impacts and a rich palette of physicochemical advantages related to their low cost and biocompatibility. Additionally, DESs can enable remarkable solubilizing effect for several active pharmaceutical ingredients (APIs), thus forming therapeutic DESs (TheDESs). In this work, special attention is paid to DESs, presenting a precise definition, classification, methods of preparation, and characterization. A description of natural DESs (NaDESs), i. e., eutectic solvents present in natural sources, is also reported. Moreover, the present review article is the first one to detail the different approaches for judiciously selecting the constituents of DESs in order to minimize the number of experiments. The role of DESs in the biomedical and pharmaceutical sectors and their impact on the development of successful therapies are also discussed.

The physico-chemical properties of the levo- and dextrorotatory menthol isomers as well as the corresponding racemic compound were studied using X-ray single-crystal or powder diffraction and differential scanning calorimetry experiments. As a result, the not yet determined crystal structure of DL-menthol was solved. Moreover, the stable and metastable experimental temperature-composition phase diagrams of the L-menthol/D-menthol binary system were determined. The thermodynamic relative stability of the different menthol polymorphs was also established. The present paper provides new physical, chemical and thermodynamic data of L-, D- and DL-menthol and offers new insight into their polymorphism as well as into the levorotatory–dextrorotatory menthol interactions. Both the thermodynamic and crystallographic approaches demonstrate unambiguously that racemic menthol is a racemate.

We present the synthesis, structure determination, and thermodynamic properties of a never reported cocrystal prepared with lidocaine and l-menthol. The temperature−composition phase diagram of the lidocaine/l-menthol binary system was achieved using differential scanning calorimetry and X-ray diffraction experiments. The present study demonstrates that the only way to perform a phase equilibrium survey of the lidocaine/l-menthol system is to prepare the binary mixtures from the cocrystal, an equimolar stoichiometric compound of l-menthol and lidocaine. We describe a process that is crucial to elaborate pharmaceutical agents that remain in their thermodynamical stable state throughout their preparation, manufacture, and storage for effective use.