What is "cucurbituril"

n. (context organic compound English) Any of a class of macrocyclic molecules consisting of glycoluril repeat units.

Cucurbiturils are macrocyclic molecules made of glycoluril (=CHNO=) monomers linked by methylene bridges (-CH-). The oxygen atoms are located along the edges of the band and are tilted inwards, forming a partly enclosed cavity. The name is derived from the resemblance of this molecule with a pumpkin of the family of Cucurbitaceae.

Cucurbiturils are commonly written as cucurbit[n]uril, where n is the number of glycoluril units. Two common abbreviations are CB[n], or simply CBn.

These compounds are particularly interesting to chemists because they are suitable hosts for an array of neutral and cationic species. The binding mode is thought to occur through hydrophobic interactions, and, in the case of cationic guests, through cation-dipole interactions as well. The dimensions of cucurbiturils are generally on the ~ 10 Å size scale. For instance, the cavity of cucurbit[6]uril has a height ~ 9.1 Å, an outer diameter ~ 5.8 Å, and an inner diameter ~ 3.9 Å.

Review: The Cucurbit[n]uril Family Jason Lagona, Pritam Mukhopadhyay, Sriparna Chakrabarti, Lyle Isaacs Angewandte Chemie International Edition Volume 44, Issue 31, Pages 4844 - 4870 2005 Abstract

Cucurbiturils were first synthesized in 1905 by Behrend, by condensing glycoluril with formaldehyde,

Ueber Condensationsproducte aus Glycoluril und Formaldehyd, Robert Behrend, Eberhard Meyer, Franz Rusche, Justus Liebig's Annalen der Chemie 1905, 339, 1–37.

but their structure was not elucidated until 1981.

Cucurbituril W. A. Freeman, W. L. Mock, and N.-Y. Shih J. Am. Chem. Soc., 1981, 103, 7367. Article

To date cucurbiturils composed of 5, 6, 7, 8, 10, and 14 repeat units have all been isolated, which have internal cavity volumes of 82, 164, 279, 479, and 870 Å respectively. A cucurbituril composed of 9 repeat units has yet to be isolated (as of 2009). Other common molecular capsules that share a similar molecular shape with cucurbiturils include cyclodextrins, calixarenes, and pillararenes.