calix4arene

Calix[4]arene is a macrocyclic compound belonging to the calixarenes family. It comprises four phenolic units linked by methylene bridges at the para positions, forming a cup- or vase-shaped cavity capable of hosting guest molecules. The name reflects the cup-like shape and the classical calix origin.

The parent calix[4]arene features a lower rim with phenolic OH groups and an upper rim that can be derivatized to tune solubility, reactivity, and guest binding. The molecule is conformationally flexible and exists in several interconvertible forms, including cone, partial cone, 1,3-alternate, and 1,2-alternate. Substitution on the phenyl rings, such as tert-butyl groups at the lower rim, can stabilize particular conformations and influence binding properties.

Calix[4]arenes act as host molecules in supramolecular chemistry. Their hydrophobic cavities can encapsulate small organic guests, especially hydrocarbons and aromatic compounds. Binding can be modulated by upper-rim functionalization, which also enables coordination to metal ions, hydrogen bonding, and electrostatic interactions. Water-soluble derivatives, such as sulfonatocalix[4]arenes, extend applicability to aqueous environments and enable binding of cationic species.

Applications of calix[4]arene derivatives span host–guest chemistry, sensing, extraction, and catalysis. They serve as scaffolds for constructing supramolecular assemblies and for developing selective receptors. Synthesis typically involves condensation of substituted phenols with formaldehyde under basic conditions, followed by functional group transformations to install desired upper- or lower-rim substituents.