Anion-Based pH Responsive Ionic Liquids: Design, Synthesis, and Reversible Self-Assembling Structural Changes in Aqueous Solution

Abstract

The creation of pH responsive materials that undergo morphological transitions between micelle and vesicle induced by solution pH change is of great importance for their potential application in drug delivery and biochemical engineering. Here, we have developed a series of 18 pH responsive ionic liquids composed of 1-alkyl-3-methylimidazolium cation, [C(n)mim](+) (n = 4, 6, 8, 10, 12, 14), and different pH responsive anions such as potassium phthalic acid ([C6H4COOKCOO](-)), sodium sulfosalicylic acid ([C6H3OHCOOSO3Na](-)), and sodium m-carboxylbenzenesulfonate ([C6H4COOSO3Na](-)). The aggregation behavior and self-assembly structures of the ILs in aqueous solution have been investigated by surface tension, dynamic light scattering, transmission electron microscopy, small-angle X-ray scattering, and nuclear magnetic resonance spectroscopy. It was found for the first time that single tail ionic liquids, [C(n)mim]X (n = 12 and 14, X = [C6H4COOKCOO], [C6H3OHCOOSO3Na], and [C6H4COOSO3Na]) could form vesicles without any additives, and reversible transition was observed between spherical micelles and vesicles with the change of solution pH value. The transition in self-assembly structures is suggested to be driven by the variation in molecular structure and hydrophilicity/hydrophobicity of anions of the ILs.

Micellar transitions in catanionic ionic liquid–ibuprofen aqueous mixtures; effects of composition and dilution

“…As the cmc of a surface active substance is best regarded as a measure of its industrial utility, we here in investigated the behavior of aqueous mixtures of C 12 Figure S4, Supporting Information) and were found to be in good agreement with the fluorescence measurements. Table 2 clearly depicts very high micellization tendency of C 12 mimCl + Ibu mixtures in aqueous solution on account of quite low cmc values in comparison to that of the individual components.…”

“…The formation of highly surface active catanionic complexes (C 12 length of imidazolium moiety is observed to produce significant changes. We conclude that hydrophobic interactions also play a very important role along with electrostatic interactions in the formation of these complexes.…”

“…[6][7][8][9] The journey of these ILs started with the first generation ILs 9,10 possessing unique physical properties such as decreased vapor pressure and high thermal stability, progressing to the second stage with advanced functional materials called second generation ILs 11,12 produced through a modification of both physical and chemical properties. easily tunable behavior and essentially to their 'greener' aspects.…”

pH-Responsive Anionic Wormlike Micelle Based on Sodium Oleate Induced by NaCl

“…A downfield shift manifests a weaker electron density of the system. 31 Therefore, when pH is 9.53, WLMs are formed because the ionized carboxylate has a strong combination with Na + . On the contrary, with the decrease of pH value, nonionic carboxylic group displaces the ionized carboxylate group in NaOA.…”

Reversible Switching of Amphiphilic Self-Assemblies of Ionic Liquids between Micelle and Vesicle by CO2

“…25 Thus obtained CMC values were listed in Table 2. In addition, the CMC values of these ILs were also determined through the plots of surface tension versus IL concentrations, 20 and the results were also included in Table 2. Generally, the CMC values determined by surface tension were in reasonable agreement with those determined by conductivity.…”