Cucurbituril complexes

CYCLODEXTRIN AND CUCURBITURIL COMPLEXATION OF REDOX-ACTIVE GUESTS... 

The real power and attraction of cucurbituril complexes in payload delivery is twofold. First, they can be triggered to release payload in a variety of ways, but in particular, by the... 

Gadde S, Kaifer AE. Cucurbituril complexes of redox active guests. Curr Org Chem 2011 15 27-38. 

Buschmann H-J, Jansen K, Schollmeyer E. The formation of cucurbituril complexes with amino acids and amino alcohols in aqueous formic acid studied by calorimetric titrations. Thermochim Acta 1998 317 95-8. 

Template effects have been used in rotaxane synthesis to direct threading of the axle through the wheel. Since macrocycHc compounds such as cyclodextrins, crown ethers, cyclophanes, and cucurbiturils form stable complexes with specific guest molecules, they have been widely used in the templated synthesis of rotax-anes as ring (wheel) components. Here, we briefly discuss macrocycles used in the synthesis of rotaxane dendrimers and their important features. 

The presence in dyehouse effluents of typical dye-complexing metal ions is an environmentally sensitive issue, such metallic contamination arising mostly from the decomposition of metal-complex dyes [26]. The synthetic complexing agent cucurbituril (section 10.3.2) can be used to selectively extract such metal ions from the effluent. 

The encapsulation of classical and organometallic transition-metal complexes to yield molecules of the type complex in a complex is a very attractive research area. A variety of inclusion complexes of this type has been reported. Of relevance for this review are reports on the encapsulation of coordinatively unsaturated transition-metal complexes inside self-assembled coordination cages (120), cyclodextrins (121,122), and cucurbiturils (123). 

Inclusion complexation, 77 552-553 Inclusion compounds, 74 159-190, 170-182 amylose, 74 168 anionic guest, 74 170 cailixarene, 74 165-166 categories of, 74 160 crown macroring, 74 160-161 cucurbituril, 74 168-169 cyclodextrin, 74 166-167... 

Buschmann HJ, Schollmeyer E (1997) Cucurbituril and P-cyclodextrin as hosts for the complexation of organic dyes. J Incl Phenom Macrocycl Chem 29 167-174... 

Gadde S, Batchelor EK, Weiss JP, Ling Y, Kaifer AE (2008) Control of H- and J-aggregate formation via host-guest complexation using cucurbituril hosts. J Am Chem Soc 130 17114-17119... 

The article by Kim et al. (2002) give an opportunity to compare the cations depicted in Scheme 2.45 and iV,iV -dimethyl-4,4 -bipyridinium as guests to cucurbituril. The inclusion complex of N,N -... 

Besides Scheme 3.45, one more case of ferrocenylammoninm oxidation deserves to be considered. That is, the chemical oxidation of the confined species. fV-(ferrocenylmethylene)-A/,A/,Af-trimethylam-monium forms a remarkably stable inclnsion complex with cucurbituril (Jeon et al. 2005). Yuan and Macartney (2007) used aqueous solution of the bis(2,6-pyridinedicarboxylato)cobaltate(III) ion for comparative oxidation of free and included compounds. This oxidant does not bind to curcubituril. As it turned out, the inclusion significantly reduces the rate constants for the ferrocenyl-ferroceniumly transition. One of the important causes of the retardation observed is the steric hindrance due to close approach of the oxidant to the encapsulated ferrocene (Yuan and Macartney 2007). 

Fig. 2. HNMR induced shifts (ppm) of methylene groups of al-kanediammonium ions upon complexation with cucurbituril (DjO-HCOjH solution) from [7] with permission...

This NMR technique has been applied to a series of alkanediammonium ions, and the results (induced shifts of proton resonances) are summarized in Fig. 2. It may be seen that the shielding region extends for approximately 4.5 methylene units, or 6 A, which coincidentally is the interatomic distance axially spanning the cavity of cucurbituril. Similar induced chemical shift effects are found in CNMR spectra, and UV spectral perturbations are noted upon encapsulation of certain aromatic-ring bearing ammonium ions (particularly 4-methyl-benzylamine). Conclusive evidence for internal complexation with cucurbituril has been secured by crystallography [3]. 

Table I. Affinity data for ligand-receptor complexes of cucurbituril [7]...

Fig. 4. Conjectured cross-sectional representation of complexes of cucurbituril plus n-butylam-monium ion, as well as with cyclopentanemethylammonium ion. Outlines are drawn to van der Waals radii (maximum projection for all atoms upon axial rotation of the rewptor, crystallographi-cally determined interatomie distances for cucurbituril). Two N-H- 0=C hydrogen bonds may form, but the third projects incorrectly for coordination to the receptor from [7] with...

Binding of arylamines constitutes the most sensitive test of the internal capacity of cucurbituril. A complex is formed with P-CH3C6H4CH2NH3, but... 

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