Room-temperature ionic liquid cations act as short-chain surfactants and disintegrate a phospholipid bilayer

The effect of room-temperature ionic liquids (RT-ILs) cations made of 1-alkyl-3-methylimidazolium (alkyl group of C-4-C-8) and anions (commonly found in RT-ILs) on the structural integrity of large unilamellar vesicles (LUVs) of 1,2-dielaidoylphosphocholine were studied. Vesicle integrity was determined by monitoring the release of calcein quenched by cobalt ions and vesicle size distribution after incubation in the presences of each cation or anion. Results demonstrated that the instability of a fluid bilayer increased as the length of alkyl group of the cation increased. LUVS were mostly stable in the presence of the anions as evidenced by Continued retention of encapsulated materials. Size measurements revealed, in the case of 1-butyl-3-methylimidazolium cation (100-1500 mM), encapsulated material was released through small holes in the bilayer. However, total vesicle disruption was the release mechanism in the case of 1-hexyl or octyl-3-rnethylimidazolium above 200 mM. (c) 2005 Elsevier B.V. All rights reserved.