Cucurbituril-6 (CB[6]) is a macrocyclic host molecule from the cucurbituril family, composed of six glycoluril units linked by methylene bridges. It has a rigid, hydrophobic, barrel-shaped cavity that can encapsulate guest molecules, forming stable host-guest complexes. CB[6] is widely used in supramolecular chemistry, drug delivery, catalysis, and molecular recognition due to its strong binding affinity and selective interactions.