Cucurbit urils

Keywords Cobaltocenium, Cucurbit[ ]urils, Cyclodextrins, Dendrimers, Ferrocene, Host-guest complexation, Inclusion complexes, Viologens... 

The functionalization chemistry of the CD s has been extensively developed at this time [15,16], Synthetic methodology is available to either mono-functionalize or perfunctionalize either the primary or secondary hydroxyl portal of these hosts. Derivatization is still a pending subject in the chemistry of cucurbit[ ]uril hosts. Kim and coworkers have reported a procedure that allows the equatorial functionalization of the periphery of CB6 [17], but the same procedure is highly inefficient with either CB7 or CB8. Further developments in this area may be of great significance to extend the range of applications of these compounds. 

Interest in the host binding properties of the cucurbit[ ]urils (CBs) is increasing very quickly. As a result of this growing interest, several reports on the binding interactions between CB hosts and dendrimers are available. However, although very promising, the chemistry of CBs is still less developed than that of CDs and the body of work is much smaller in the former case. Furthermore, the lack of practical synthetic methods for CB functionalization limits the possibilities of structural elaboration around CB hosts. While the CDs have been used as scaffolds for the construction of dendrimers or covalently attached to dendritic structures, similar research work with CBs is still in its infancy. 

Lagona J, Mukhopadhyay P, Chakrabartri S, Isaacs L (2005) The cucurbit[ ]uril family. Angew Chem Int Ed 44 4844-4870... 

For a time one managed by choosing new descriptions and used intricate contractions and modifications of the available terms Some examples being clathrate complex, clathrate hydrate, hydrocarbon clathrate, gas hydrate, interlamellar sorbent, molecular compoimd, addition compound, loose addition complex, cascade complex, lock-and-key complex, super molecular complex, molecular complex associate, tweezer molecule complex, soccer molecule complex, hexapus molecule complex, octopus molecule complex as well as complexes or inclusion compounds of spherands, sepulchrands, coronands, cyclidenes, cryptands, cryptophanes, calixarenes, cucurbit-uril, annelides etc. 

Figure 1.11 (a) Chemical and X-ray crystal structure of cucurbit[ ]uril. (b) X-ray crystal structure of a charge-transfer complex stabilized by CB[8]. 

Various eueurbit[n]uril derivatives have been synthesized (Figure 1.14). Miyahara et al. reported half-eueurbit[ ]urils, hemicucurbit[n]urils by eondensation of ethyleneurea and paraformaldehyde in the presence of aeid catalyst. The reaetion at 25 °C in 4 N HCl afforded the hexamer hemi-cueurbit[6]uril (1.26), in high yield (94%). In contrast, hemicucurbit[12]uril (1.27) was obtained in high yield (93%) when the reaction was conducted at 55 °C in 1 N HCl. Bambus[6]uril (1.28), which combines the structural features of both cucurbit[ ]urils and hemicucurbit[ ]urils, was introduced by... 

Reaction at the lower temperature gave a family of cucurbit[n]urils from pentamer to 11-mer, although their yields, except for cucurbit[6]urils, were low (10-25%). Fortunately, the new synthetic receptors, smaller or larger than cucurbit[6]uril, show good solubility (CB[5] ca. 420 mM CB[7] ca. 370 mM). Therefore, their discovery was a breakthrough in cucurbit[ ]uril chemistry, and has led to a rapid increase in research in this... 

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