Temperature-controlled supramolecular vesicles modulated by p-sulfonatocalix[5]arene with pyrene.

Construction of vesicles is a significant topic of research in the fields of chemistry, biology, and materials science for their various applications. Recently, more and more research has been focused on “supramolecular amphiphiles”, which have emerged as a smart strategy due to their simplicity, versatility, and especially reversibility. Several kinds of noncovalent interactions have been used to tune the molecular amphiphilicity and self-assembled nanostructures, including hydrogen-bonding, charge-transfer, and p···p interactions, among others. The noncovalent interactions often employed (e.g., hydrogen bonding, coordination, and p stacking) are not always effective for designing supramolecular architectures in aqueous medium, and hence, they lack the necessary biocompatibility for applications in the fields of biotechnology. Macrocyclic receptors, such as cyclodextrins, calixarenes, and cucurbiturils, exhibit particular advantages in building water-soluble supramolecular architectures, more significantly, the three macrocyclic species are all friendly to organisms. To the best of our knowledge, supramolecular vesicles formed by host–guest interactions between macrocyclic hosts and guests have been explored less frequently. Kim et al. reported, for the first time, the spontaneous formation of vesicles triggered by the formation of a stable ternary inclusion complex that behaves as a large supramolecular amphiphile, in which cucurbituril was employed. Cyclodextrin is the macrocyclic host used most frequently in building organized amphiphiles, and the first noncovalent vesicle based on a cyclodextrin complex was reported by Chen and co-workers in 2007. Calixarenes, composed of phenolic units linked by methylene groups, represent a particularly significant class of the host molecules in supramolecular chemistry. Their intrinsic cone shape is the prerequisite for high-curvature aggregations of amphiphiles. Their relatively rigid framework can enhance the stability of amphiphilic aggregation. Consequently, calixarenes have received certain attention in constructing micellar and vesicular aggregations. The vesicles reported are uniformly formed by a covalent approach that modifies calixarenes into amphiphiles by the linkage of lipophilic groups at one rim and hydrophilic groups at the other rim, whereas no supramolecular vesicles based on host–guest complexation have been explored. Recently, Garc a-R o and Basilio found that the complexation of water-soluble calix[6]arene can tune the amphiphilicity of a cationic surfactant. Blanzat et al. reported the spontaneous formation of vesicles by combining an aminocalix[6]arene with sugar-based surfactants using an acid–base reaction to obtain a catanionic association while this manuscript was under preparation. Our particular interest herein is to fabricate calixarene-based supramolecular vesicles through host–guest complexation. The most fascinating aspect of supramolecular chemistry is that two or more components can self-assemble into higher-order structures, which exhibit particular properties and functions that the individual component cannot achieve. Herein, we report the successful construction of nanoscale supramolecular binary vesicles on the basis of host–guest complex formation between p-sulfonatocalix[5]arene (C5AS) and 1-pyrenemethylaminium (PMA) (Scheme 1). Notably, neither free C5AS nor PMA can form nanoscale aggregates themselves. Furthermore, the obtained vesicle shows thermal reversibility and it can disassemble when the temperature increases up to 35–40 8C. This temperature-responsive character makes this kind of vesicle a potential delivery model for special substrates. A simple mixture of C5AS (0.05 mm) and PMA (0.25 mm) with a charge-matching molar ratio in aqueous solution shows the Tyndall effect, which prompted us to explore the higher hierarchy aggregation based on the host–guest complexation of C5AS with PMA. The critical aggregation concentrations (CAC) of PMA in the absence and presence of C5AS were measured by monitoring the polarity of the sur[a] K. Wang, Dr. D.-S. Guo, Prof. Dr. Y. Liu Department of Chemistry State Key Laboratory of Elemento-Organic Chemistry Nankai University, Tianjin 300071 (P.R. China) Fax: (+86)22-23503625 E-mail : yuliu@nankai.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000991.