Cucurbituril

Computer models of CB[5], CB[6], and CB[7]. Top row is the view into the cavity and the bottom is the side view

In host-guest chemistry, cucurbiturils are macrocyclic molecules made of glycoluril (=C4H2N4O2=) monomers linked by methylene bridges (−CH2−). The oxygen atoms are located along the edges of the band and are tilted inwards, forming a partly enclosed cavity (cavitand). 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.[1]

Cucurbiturils were first synthesized in 1905 by Robert Behrend, by condensing glycoluril with formaldehyde,[2] but their structure was not elucidated until 1981.[3] The field expanded as CB5, CB7, and CB8 were discovered and isolated by Kim Kimoon in the year 2000.[4] To date cucurbiturils composed of 5, 6, 7, 8, 10, and 14 repeat units have all been isolated,[5][6] which have internal cavity volumes of 82, 164, 279, 479, and 870 Å3 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.

  1. ^ 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
  2. ^ Ueber Condensationsproducte aus Glycoluril und Formaldehyd, Robert Behrend, Eberhard Meyer, Franz Rusche, Justus Liebig's Annalen der Chemie 1905, 339, 1–37. doi:10.1002/jlac.19053390102
  3. ^ Cucurbituril W. A. Freeman, W. L. Mock, and N.-Y. Shih J. Am. Chem. Soc., 1981, 103, 7367. doi:10.1021/ja00414a070
  4. ^ Kim, Jaheon; Jung, In-Sun; Kim, Soo-Young; Lee, Eunsung; Kang, Jin-Koo; Sakamoto, Shigeru; Yamaguchi, Kentaro; Kim, Kimoon (2000). "New Cucurbituril Homologues: Syntheses, Isolation, Characterization, and X-ray Crystal Structures of Cucurbit[n]uril(n=5, 7, and 8)". Journal of the American Chemical Society. 122 (3): 540–541. doi:10.1021/ja993376p.
  5. ^ Cucurbituril Homologues and Derivatives: New Opportunities in Supramolecular Chemistry Acc. Chem. Res., 36 (8), 621 -630, 2003. doi:10.1021/ar020254k
  6. ^ Cheng, Xiao-Jie, et al. "Twisted Cucurbit[14]uril." Angewandte Chemie International Edition 52.28 (2013): 7252–7255. Web. doi:10.1002/ange.201210267