psulfonatocalix4arene

p-sulfonatocalix[4]arene (PSC4A) is a water-soluble, anionic macrocycle derived from calix[4]arene. It carries four para-sulfonate substituents on the phenolic rings, imparting a negative charge that enhances solubility in water and stabilizes host–guest complexes with positively charged species. In solution, PSC4A often adopts a cup-shaped cone conformation, presenting a hydrophobic cavity bounded by negatively charged sulfonate rims.

PSC4A acts as a receptor for a range of cationic guests, including quaternary ammonium salts, other ammonium-containing entities, and certain dyes or drug molecules. Binding is driven by a combination of hydrophobic effects inside the cavity, electrostatic interactions with the sulfonate groups, and, in some cases, cation–π interactions with the aromatic calixarene walls. Complexes are frequently 1:1 (host:guest), though stoichiometries can vary with guest size and charge and under different solution conditions. Binding strength is influenced by ionic strength, pH, and the presence of competing cations.

Applications of PSC4A span supramolecular chemistry and analytical science. It is used as a versatile, water-soluble host to study host–guest interactions, to solubilize hydrophobic compounds in aqueous media, and in sensor and separation technologies. The derivative also serves as a building block for constructing more complex supramolecular assemblies and has been employed in studies of binding thermodynamics and kinetics.

Synthesis and availability: PSC4A derivatives are prepared by introducing sulfonate groups onto the calix[4]arene framework and are available commercially. The sulfonated form is notably stable in water and widely used as a model system in binding studies.