DNA stability in ionic liquids and deep eutectic solvents

DNA molecules are known as the genetic information carriers. Recently, they have been explored as a new generation of biocatalysts or chiral scaffolds for metal catalysts. There is also growing interest in finding alternative solvents for DNA preservation and stabilization, including two unique types of solvents: ionic liquids (ILs) and deep eutectic solvents (DES). Therefore, it is important to understand how DNA molecules interact with these novel ionic solvent systems (i.e. ILs and DES). It is well known that inorganic divalent and monovalent ions preferentially bind with major and minor grooves of DNA structures. However, in the case of ILs and DES, organic cations may intrude into the DNA minor grooves; more importantly, electrostatic attraction between organic cations and the DNA phosphate backbone becomes a predominant interaction, accompanied by hydrophobic and polar interactions between ILs and DNA major and minor grooves. In addition, anions may form hydrogen bonds with cytosine, adenine and guanine bases. Despite these strong interactions, DNA molecules maintain a double helical structure in most ionic solvent systems, especially in aqueous IL solutions. The exciting advances of G-quadruplex DNA structures in ILs and DES are also discussed.