Distinctive spectroscopic properties and adsorption behaviors of p-sulfonatocalixarene-cetyltrimethylammonium bromide supra-amphiphilic systems

Abstract

So far, the knowledge about the properties of the calixarene-based supra-amphiphiles remain very limited. In the present study, we investigated the properties of p-sulfonatocalix[n]arene (SC[n], n = 4, 6 and 8)-cetyltrimethylammonium bromide (CTAB) supra-amphiphiles by measuring their fluorescence, UV–vis absorption, 1H NMR spectra as well as surface tension, and found that the calixarene/surfactant mixed systems exhibited special spectroscopic properties and adsorption behaviors. Although SC[n] and CTAB were both non-fluorescent, the resulting SC[n]-CTAB complexes emitted fluorescence; the strongest fluorescence intensity was observed when the molar ratio of CTAB to SC[n] reached the stoichiometry. The SC[n]-CTAB complexes and/or CTAB monomers did not adsorb at the air/water surface until the CTAB content was higher than the stoichiometry. Once CTAB began to adsorb at the surface, the surface tension decreased sharply (much faster than in the absence of SC[n]). Among SC[4], SC[6] and SC[8], SC[4] not only induced the CTAB molecules to line up most tightly at the air/water surface, but also possessed the strongest ability to promote the aggregation of the CTAB molecules in solution. Moreover, proteins did not break the binding between SC[n] and CTAB; they interacted with the complex instead and their activities were closely related to the molar ratio of CTAB to SC[n]. The present study should suggest the potential application of SC[n]/CTAB systems in fields such as fluorescent inks, encryption coding, and regulation of protein activity.