Cucurbituril-8 (CB[8]) is a macrocyclic host molecule belonging to the cucurbituril family, composed of glycoluril units linked by methylene bridges. It has a large, rigid, barrel-shaped cavity that can encapsulate two guest molecules simultaneously, making it useful in supramolecular chemistry, drug delivery, and molecular recognition. CB[8] is known for its strong binding affinity and selective host-guest interactions, enabling applications in nanotechnology and biomedical research.