Imidazolium Salts Mimicking the Structure of Natural Lipids Exploit Remarkable Properties Forming Lamellar Phases and Giant Vesicles

Tailor-made ionic liquids based on imidazolium salts have recently attracted a large amount of attention because of their extraordinary properties and versatile functionality. An intriguing ability to interact with and stabilize membranes has already been reported for 1,3-dialkylimidazolium compounds. We now reveal further insights into the field by investigating 1,3-dimethyl-4,5-dialkylimidazolium (Cn-IMe·HI, n = 7, 11, 15) and 1,3-dibenzyl-4,5-dialkylimidazolium (Cn-IBn·HBr, n = 7, 11, 15) salts. Diverse alkyl chain lengths and headgroups differing in their steric demand were employed for the membrane interface interaction with bilayer membranes imitating the cellular plasma membrane. Membrane hydration properties and domain fluidization were analyzed by fluorescent bilayer probes in direct comparison to established model membranes in a buffered aqueous environment, which resembles the salt content and pH of the cytosol of living cells. Membrane binding and insertion was analyzed via a quartz crystal microbalance and confocal laser scanning microscopy. We show that short-chain 4,5-dialkylimidazolium salts with a bulky headgroup were able to disintegrate membranes. Long-chain imidazolium salts form bilayer membrane vesicles spontaneously and autonomously without the addition of other lipids. These 4,5-dialkylimidazolium salts are highly eligible for further biochemical engineering and drug delivery.