Synthesis for obtaining Natural Deep Eutectic Solvents (NADESs) and their Physicochemical Characterizations

Natural Deep Eutectic Solvents (NADESs) are formed through hydrogen bonding interactions between a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), resulting in a stable, homogeneous liquid. In this work, preliminary analyses were conducted to evaluate the influence of the synthesis method on the physicochemical properties of NADESs. Two preparation techniques, mechanical agitation and ultrasound, were applied to four NADES systems composed of choline chloride (ChCl), urea (Ur), citric acid (CA), and glycerol (Gly): N1 (CA: Gly, 1:3 M), N2 (ChCl: Ur, 2:1 M), N3 (ChCl: CA, 1:1 M), and N4 (ChCl: Gly, 1:1 M), all with 20% (w/w) water. Properties assessed included pH, electrical conductivity, density, and refractive index. Results showed variable pH values without a consistent trend. Electrical conductivity was higher in NADESs synthesized via agitation, notably in N2 (37.7 mS/cm vs. 16.4 mS/cm with ultrasound), suggesting enhanced ionic mobility. Ultrasound-assisted synthesis generally yielded NADESs with greater density, as observed in N1 and N4 (1.155 vs. 1.084 g/cm³ and 1.154 vs. 1.138 g/cm³, respectively), potentially due to improved molecular packing. Refractive index values remained relatively stable across methods, though slight deviations were observed. These findings indicate that mechanical agitation favors higher conductivity, whereas ultrasound may promote greater homogeneity and compactness. Therefore, the choice of synthesis method should be tailored to the targeted physicochemical profile for specific applications.