Aggregation behavior of non-cytotoxic ester functionalized morpholinium based ionic liquids in aqueous media

Ester functionalized surface active ionic liquids (SAILs), [C(n)EMorph][Br], where n = 8, 12 and 16, comprising of long hydrophobic chain appended with ester functionality connected to N-methylmorpholine group have been synthesized and investigated for their aggregation behavior and cytotoxicity. A variety of state of art techniques viz. tensiometry, conductometry, isothermal titration calorimetry (ITC), spectrofluorometry, dynamic light scattering (DLS) and atomic force microscopy (AFM) have been employed to get insight into the various aspects of aggregation behavior. The investigated SAILS have been found to possess lower critical aggregation concentration (cac) and greater adsorption efficacy at air-solution interface as compared to earlier reported non-functionalized SAILs or conventional ionic surfactants. Further, the thermal stability of these morpholinium cationics has been evaluated by thermal gravimetric analysis (TGA). These SAILS have been found to be non-cytotoxic in the concentration range generally required for different biological applications as judged by MIT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay on the C6 glioma cell line. The dependence of characteristic properties of aggregation on alkyl chain length has been established. (C) 2015 Elsevier Inc. All rights reserved.