Construction And Function Of Supramolecular Assemblies Based On Amphiphilic P-Sulfonatocalixarenes

Calixarenes are macrocyclic oligomers made of phenol units linked by methylene bridges. They can be readily functionalized at the phenolic hydroxyl groups (lower rim) and at the para positions (upper rim) and give rise to wide range of structural derivatives. Calixarene chemistry was initially directed to the design of host compounds with receptor abilities. However, the versatility of the calixarenes is not limited to this, and when properly functionalized, they can be applied in various areas such as self-assembly on monolayers and nanoparticles, sensors for enzyme assays, drug delivery systems, and construction of molecular machines, supramolecular polymers and amphiphiles.Among the various types of calixarenes described in the literature, p-sulfonatocalixarenes had attracted considerable attention due to their high water solubility, selective binding ability and excellent biological compatibility. In fact, several biological and medical potential applications that take advantage of these properties have been described. The recognition properties of p-sulfonatocalixarenes enable them to be also used as building blocks to construct supra-amphiphiles by means of calixarene-induced aggregation:complexation with p-sulfonatocalixarenes promotes the aggregation of guest molecules by lowering the CAC, enhancing the aggregate stability, and regulating the degree of order in the aggregates. In these cases, the functional segments required to provide or improve the amphiphilic properties of the molecular species are linked by means of host-guest interactions. In addition to these interesting properties, amphiphilic p-sulfonatocalixarenes can be simply obtained by attaching hydrophobic alkyl chains to the phenolic oxygen atoms. These compounds can be, in principle, included in the same category of oligomeric amphiphiles (such as dimeric, trimeric and tetrameric amphiphiles). Besides sharing some of the appellative properties of open chain oligomeric amphiphiles, such as lower critical aggregation concentration (CAC), amphiphilic p-sulfonatocalixarenes are equipped with a host-guest recognition site, able to bind guest molecules and ions, which can be explored along with their self-association properties in order to develop new soft materials. However, constructing supramolecular assemblies by non-covalent interactions between amphiphilic p-sulfonatocalixarenes and guest molecules has been explored much less frequently. Consequently, amphiphilic p-sulfonatocalixarenes were chosen as host molecules. The construction and function of supramolecular assemblies based on non-covalent interaction between them and guest molecules have been studied.