Are ionic liquids and deep eutectic solvents the same?: Fundamental investigation from DNA dissolution point of view

From the very first day of the introduction of deep eutectic solvents (DESs) as an alternative to the ionic liquids (ILs), it has been claimed that both the solvents enjoy similar physiochemical properties. The claim was found not to be correct when the dissolution phenomenon of DNA in the ILs and DESs consisting of a few selected similar cations and anions was investigated. Upon investigation of eight different sets of solvents (ILs and DESs) with similar constituents, it was observed that ILs were able to provide a better medium for the dissolution and stability of DNA whereas the DESs neither help in dissolution nor provide the structural and chemical stability to the solute. The study of the physicochemical properties such as viscosity, ionic conductivity, polarity, hydrogen bond donation/acceptance ability, and density helped to understand how the solution properties affect the dissolution. Interestingly, studies on ionic conductivities suggested that the higher the conductivity higher the dissolution. Further, the ionic species provide electrostatic interaction with the charges on phosphate present in the DNA along with hydrogen bonding. The other properties studied also supported favourable interaction of the IL ions with DNA in comparison to the DESs. The molecular docking studies indicated the ability of both the ILs and DESs to promote hydrogen bond with nucleic acids and this appears to be the major driving force to solubilize DNA in the solvents. The anions [Pyruvate]−, [Glycolate]−, [Acetate]− and [Formate]− which are constituent of ILs display the ability to promote more hydrogen bond interactions in comparison to the corresponding acids such as Pyruvic acid, Glycolic acid, Acetic acid, and Formic acid which are constituent of the DESs. It was concluded that the higher ability of the ILs to form hydrogen bonds with DNA was responsible for the better solubilization of the macromolecule in the solvent systems.