Design of cationic amphiphiles for generating self-assembled soft nanostructures, micelles and hydrogels

Design of amphiphiles to develop robust self-assembled soft nanomaterials, such as micelles and hydrogels is an interesting subject. A series of cationic amphiphilic compounds were synthesized comprising 1-ethoxy (3-pentadecyl) benzene as the hydrophobic tail. The second carbon of ethoxy was linked to quaternary head groups (trimethyl ammonium bromide (PEA), triethyl ammonium bromide (PETE), pyridinium bromide (PEPy),N-methyl morpholino bromide (PENM),N-methyl piperidine bromide (PENP)). Inclusion of benzene ring leads to a significant decrease in critical micellar concentration (CMC) as compared to other cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB). Interestingly, at higher concentration, these cationic amphiphiles were forming soft hydrogels with critical gelation concentration (CGC) from 3 to 10% (w/v). The small-angle X-ray scattering (SAXS) analysis of xerogel revealed the formation of self-assembled lamellar patterns of molecules. Further, the morphology of xerogels were also seen under a scanning electron microscope (SEM) which correlates with SAXS data. The SAXS and SEM data confirms the formation of worm-like micellar structures and entangle themselves to form a hydrogel. The cytotoxicity assay was done on HDFA, HeLa and HEK cell lines, haemolysis assay showed better haemocompatibility than CTAB. The synthesized surfactants exhibited up to 3-fold higher solubilization capability against hydrophobic molecules than CTAB.