Synthesis and vesicular self-assembly of a novel asymmetric cationic and ethoxylated amphiphile

Cationic quaternary ammonium and nonionic oligo(ethylene oxide) are attractive classes of polar units for new amphiphile synthesis. However, they present distinct physical and chemical properties. We combine these two hydrophilic groups to each side of a hydrophobic segment, getting a new asymmetric cationic ethoxylated amphiphile (EO(12)BphC(10)NC(12)). Different from common amphiphiles, EO(12)BphC(10)NC(12) not only connects different hydrophilic units on both ends of hydrophobic spacers but also integrates the structural characters of bola- and gemini-form amphiphiles together, which brings interesting properties to the new building block. We studied its surface activity and self-assembly behavior in aqueous solution. It turns out that EO(12)BphC(10)NC(12) can reduce the surface tension of aqueous solution and self-assembly into vesicles above the critical aggregation concentration. More importantly, the strong nuclear Overhauser effect between quaternary ammonium cation and the first oxyethylene group indicates that the two headgroups locate at the vesicle surface together randomly, other than selectively occupy inner or outer vesicle surface. The synergistic effect of molecular size and hydration of different hydrophilic groups leads to the interdigitated packing state of alky chains in the vesicle with symmetric membrane.