Synthesis, redox and electrochemical properties of new anthraquinone-attached micelle- and vesicle-forming cationic amphiphiles
Three new cationic amphiphiles bearing anthraquinone moieties at the polar headgroup region were synthesized. The single-chain amphiphile, N,N-dimethyl-N-octadecyl-N-(9,10-dihydro-9,10-dioxoanthracen-2-ylmethyl)ammonium bromide 1, in the presence of cetyltrimethylammonium bromide upon dispersion in water gave co-micellar aggregates containing covalently attached anthraquinone residues at the polar aqueous interfaces. The other two double-chain amphiphiles, N,N-dioctadecyl-N-methyl-N-(9,10-dihydro-9,10-dioxoanthracen-2-ylmethyl)ammonium bromide 2 and N,N-dimethyl-N-(1, 2-bispalmitoyloxypropanyl)-N-(9,10-dihydro-9,10-dioxanthracen-2-ylmethyl)ammonium bromide 3, however, on dispersion in aqueous media produced vesicular aggregates. The critical temperatures for the gel to liquid-crystalline-like phase transition processes for the vesicular systems were determined by following temperature-dependent changes in the ratios of keto–enol tautomeric forms of benzoylacetanilide doped within respective vesicular assemblies. The redox chemistry of the these supramolecular assemblies was also studied by following the time-dependent changes in the UV–VIS absorption spectroscopy in the presence of exogenous reducing or oxidizing agents. Electrochemical studies using glassy carbon electrodes reveal that redox-active amphiphiles adsorb on to the glassy carbon surfaces to form electroactive deposits when dipped into aqueous suspensions of either of these aggregates irrespective of the micellar or vesicular nature of the dispersions.