If a single glycoluril molecule is only half a brick, then the edifice built from many such bricks - cucurbituril - can be considered a masterpiece of supramolecular chemistry. Cucurbituril (abbreviated as CB[n], also known as cucurbit[n]uril) is a barrel-shaped, cage-like macromolecule formed by linking n glycoluril units through methylene bridges. Because its cavity can encapsulate guest molecules through hydrophobic interactions, it is hailed as the "fourth generation of supramolecular host compounds", succeeding crown ethers, cyclodextrins, and calixarenes.
The cucurbituril family has many members: the common CB[6] is cyclized from six glycoluril units, featuring a hydrophobic internal cavity and negatively charged portals rimmed with carbonyl oxygen atoms, much like a miniature "molecular barrel" with a smooth inner wall and narrowed ends. It can capture neutral or positively charged guest molecules with an ultra-high affinity at the femtomolar level, forming stable host-guest inclusion complexes. This property makes it show great promise in areas such as targeted drug delivery, molecular switches, and nanoreactors.
In recent years, chemists have also synthesized "handcuff-type" bis-cucurbiturils, where two cavities stand side by side, greatly expanding the complexity and functional diversity of supramolecular assemblies - playing important roles in supramolecular polymers, molecular machines, sensors, and artificial light-harvesting systems. It can be said that every "building-block world" of cucurbituril begins with a single, unassuming glycoluril molecule.