The First tetrafluorinated azobenzene-imidazolium ionic conjugates as potential thermotropic liquid crystalline drugs: Self-assembly properties and cytotoxic effects

Abstract

A new series of tetrafluorinated azobenzene-imidazolium ionic liquid crystals (ILCs) of varying alkyl chain length (n = 10–18 in even parity) in the imidazolium cationic head group was prepared and characterized using FTIR and NMR spectroscopy, and elemental microanalysis. Their thermal and phase properties were investigated using differential scanning calorimetry (DSC) and polarized optical microscope (POM). Their phase properties and morphology were influenced by fluorination and alkyl chain length. Long alkyl chains were necessary to induce liquid crystalline behaviour in these salts. All homologues were mesogenic, exhibiting stable smectic A phase with broad temperature range. Cytotoxic effects of these ILCs against human cervical cancer (HeLa) cells and normal fibroblasts was evaluated using the MTT assay. Cytotoxicity of these ILCs was dependent on the alkyl chain length in the imidazolium cationic head. All the salts were less toxic towards normal fibroblasts and exhibited 7–27-fold enhancement in cytotoxicity against HeLa cells (24hr IC50 ranged between 0.61 µM -2.84 µM) as compared to the standard therapeutic drug, Etoposide (IC50 = 25.67 µM). Long homologues (n = 16, 18) were selective towards cancer cells with selectivity index ≥ 3. These thermotropic ILCs could be doped with room-temperature mesomorphous polymers for the formulation of safe and selective anticancer drugs.