4‑Sulfonatocalix[6]arene-Induced Aggregation of Ionic Liquids Ve ́ ronique Wintgens, † Cle ́ mence Le Coeur, † Catherine Amiel, † Jean-Michel Guigner, ‡ Jó zsef G. Harangozó , § Zsombor Miskolczy, § and La ́ szló Biczó k* ,§ † Syste ̀ mes Polyme ̀ res Complexes, ICMPE, 2 rue Henri Dunant, 94320 Thiais, France ‡ Institut de Miné ralogie et de Physique des Milieux Condense ́ s, IMPMC, Universite ́ Pierre et Marie Curie, CNRS, 4 Place Jussieu, 75005 Paris, France § Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, P.O. Box 17, 1525 Budapest, Hungary * S Supporting Information ABSTRACT: The interaction of 4-sulfonatocalix[6]arene (SCX6) macrocycle with 1- alkyl-3-methylimidazolium type of ionic liquids possessing dodecyl, tetradecyl, or hexadecyl substituent was studied in aqueous solution at 298 K. Host-guest complexation promoted the spontaneous self-assembly into nanoparticles of 7:1 ionic liquid:SCX6 stoichiometry. Positively charged and stable nanoparticles were produced in solutions of 7-200-fold excess of ionic liquid as compared to the amount of SCX6. The negatively charged nanoparticles formed in solutions having 2-7 ionic liquid:SCX6 molar ratios evolved into larger species. The stability of the nanoparticles increased with the lengthening of aliphatic chain of the ionic liquid. Cryo-TEM experiments showed dense particles generally with spherical shape and multilayered structure, which has been confirmed by small-angle neutron scattering. 1. INTRODUCTION Noncovalent interactions between hydrophobic and hydro- philic compounds can lead to supramolecular amphiphiles with diverse topology. 1 The advantages of such associates over conventional surfactants based on covalent bonds are the easy preparation, facile tuning of the properties, and efficient response to various stimuli. Supramolecular amphiphiles can serve as building blocks for well-defined nanostructures, functional materials, and layers. 2,3 4-Sulfonatocalix[n]arenes (SCXn), the cavitands comprised of n =4-8 phenolic units linked by methylene groups, have become popular constituents for construction of various self- assembled architectures. 4-7 The 1:1 binding of hexamethylated SCX6 (HMSCX6) and dodecyltrimethylammonium bromide (C 12 TAB) was found to promote micelle formation much below the critical micelle concentration (cmc) of the pure surfactant. 8 NMR measurements showed that the interaction between the oxygen atoms in the OMe substituent of the macrocycle and the cationic headgroup of the surfactant plays an important role in the stabilization of HMSCX6-C 12 TAB supramolecular amphiphile. 9 These associates barely changed when C 12 TAB concentration was raised, and the majority of C 12 TAB remained free until its concentration was below the cmc. 10 A smaller macrocycle, SCX4, and a longer chain surfactant, tetradecyltrimethylammonium bromide (C 14 TAB), produced unilamellar vesicle after sonication, which could be lyophilized and rehydrated without alteration of size or shape. 11 The confinement of the cationic head of gemini surfactants in SCX4 led to supramolecular vesicles, whose inner- and outer- layer surfaces consisted of the hydrophilic phenolic hydroxyl groups of the macrocycles, whereas the hydrophobic alkyl chains of the gemini surfactants were packed together in the middle of the layer. 12 The inclusion complexes of 1- pyrenemethylammonium and SCXn spontaneously organized to vesicle by the stacking of the aromatic segment of the guests. 13 Fluorescence decay measurements provided evidence for SCXn-promoted interaction among coralyne molecules. SCXn hosts were capable of binding as many coralyne molecules as the number of their hydroxybenzenesulfonate units. 14 Enzyme-responsive vesicle was fabricated from myristoylcholine-SCX4 complex. When the guest was cleaved to myristic acid and choline by cholinesterase, the vesicle disintegrated, permitting the release of the entrapped drugs. 15 The sensitivity of the vesicle composed of N,N′-dodecyl- dimethyl-4,4′-bipyridinium and SCX4 to reduction, temper- ature variation, and cyclodextrin addition was exploited to deliver doxorubicin in a controlled manner. 16 SCXn complexes had a variety of structural motifs in the solid phase depending on the characteristics of the components. 17 Multicomponent bilayer systems were constructed in the solid state 18 involving 1:1 SCX4 complex of decyl- or dodecyl-substituted imidazo- lium cations bound to large tetra-aryl phosphonium cations, along with aquated Y 3+ or Gd 3+ . Bilayer type arrangement of Received: March 29, 2013 Revised: May 15, 2013 Article pubs.acs.org/Langmuir © XXXX American Chemical Society A dx.doi.org/10.1021/la401185p | Langmuir XXXX, XXX, XXX-XXX