From gene delivery agents to ionic liquids: The impacts of cation structure and anion identity on liquefaction

Fundamental to the field of ionic liquids is the understanding that structure begets function. In this work, we reported the development of thioether-based ionic liquids, with enhanced hydrophobicity and low melting point (T-m), via the thiol-yne reaction. Cationic lipids can simply be converted to macroscopically hydrophobic ionic liquids by replacing their native chloride counteranion with Tf2N. Features that specifically increase or decrease fluidity are identified by juxtaposing the wide-ranging Tm values of these highly lipophilic salts with elements of their cation structures. Most importantly, when these T-m-increasing and -decreasing features are incorporated into the same cation, an "averaged" T-m value is observed. These findings may prove to be elements of the "know-how" needed to design functional ionic liquids that liquefy within relatively predictable temperature ranges. (C) 2019 Elsevier B.V. All rights reserved.