Cucurbituril

Cucurbiturils are macrocyclic molecules composed of several glycoluril units and have the ability to bind other molecules in their chemically very inert cavity. The name is derived from Cucurbita, the botanical name of pumpkins, based on the similarity of the shape of the molecules with a pumpkin. The cavity of the Cucurbituril, a twelve- fold methylene -bridged " hexamer ", has a volume in nm3 area, with a height of about 9.1 Å, an outer diameter of about 5.8 Å and an inner diameter of about 3.9 Å.

Cucurbiturils were first synthesized in 1905 by R. Behrend. However, their structure was elucidated only in 1981. Currently cucurbiturils were isolated, which consist of 5, 6, 7, 8 or 10 repeating units. These have a corresponding volume of 82, 164, 279, 479 and 870 Å3 on. One of 9 units constructed Cucurbituril has not yet been isolated to date. Other well-known molecules with similar molecular shape are the cyclodextrins and calixarenes dar.

Nomenclature

Usually cucurbiturils be referred uril with cucurbit [# ], where the number of repeating units is given in brackets. A common abbreviation is CB [ #] or CB #.

Synthesis

At cucurbiturils are aminals which are prepared from two molecules of urea ( 1) and an α -dicarbonyl compound such as an α -diketone or most Glyoxal ( 2) through a nucleophilic addition wherein glycoluril (3 ) is formed as an intermediate. The intermediate is condensed with formaldehyde (4 ), whereby the Cucurbituril hexamer (5) is formed at a temperature above 110 ° C.