Cucurbit[n]uril : a new molecule in host-guest chemistry

Cucurbit[n]uril, CB[n], is made from the condensation of glycoluril and formaldehyde in concentrated acid solutions (Fig. 1). It was first made in 1905 as the six-subunit macrocycle CB[6] but its structure was not determined until 1981.[1] Over the last five years the cucurbituril family has been expanded to include cucurbiturils of different sizes (n = 5, 7, 8, 10),[2ââ"šÂ¬Ã¢â‚¬Å“5] substituted cucurbiturils, and even inverted cucurbiturils.[6] Cucurbiturils are named for their distinct shape; similar to pumpkins (Cucurbitaceae sp.), and are characterized by their hydrophobic cavity and hydrophilic portals (Fig. 2). Each CB[n] is 9.1 ÃÆ'Ã"šÃ†'ÂÃ"šÃ¢â‚¬Â¦ long with internal volumes from 82 to more than 500 ÃÆ'Ã"šÃ†'ÂÃ"šÃ¢â‚¬Â¦3, and widths between 4.4 and 12.6 ÃÆ'Ã"šÃ†'ÂÃ"šÃ¢â‚¬Â¦. Total or partial encapsulation of small guests typically results from ionââ"šÂ¬Ã¢â‚¬Å“dipole and hydrogen bonding interactions between positive charges on the guest and the carbonyl oxygen atoms of the CB[n] portals and/or hydrophobic interactions between the guest and the inner surface of the CB[n] cavity. This article examines some of the important hostââ"šÂ¬Ã¢â‚¬Å“guest applications of cucurbit[n]urils in chemistry and biochemistry.