Water behavior study for tailoring fructose-citric acid based natural deep eutectic solvent properties towards antibiotics solubilization

Understanding the physicochemical properties of solvents is crucial for the selection of the most appropriate medium for a specific application. In this sense, eutectic solvents give the possibility for creating design solvents, adjusting the chemical nature and the molar ratio between its components. Water incorporation is a strategy that has primarily been used to manipulate viscosity, not considering other important properties such as density, conductivity, or contact angle. This work demonstrates by means of a systematic study that water is a determining factor in the physicochemical properties of a model natural deep eutectic solvents (NADES) based on fructose, citric acid and water (1:1:5). Moreover, the moment of water incorporation, whether during preparation (structural water) or after preparation (dilution water), plays a key role. The results showed that dilution water had a more marked effect on properties such as conductivity, density, refraction index and thermal stability, contrary to fluorescence intensity in which structural water had the most notorious effect. In the case of viscosity, contact angle, intermolecular interactions and ciprofloxacin solubility, no statistical differences were observed in both types of water. From these results, it can be concluded that the moment of water addition to an eutectic system can be taken as a strategy not only to shape its physicochemical properties but also to direct its analytical, pharmaceutical and industrial applications.