Cucurbituril

Catalyzing 1,3-dipolar cycloadditions may be the most unusual feature of this supramolecular ligand, though by far not the only one. The size of cucurbituril 

Buschmann et al. were the first to prepare a polyrotaxane containing cucurbituril by cleverly adapting interfacial polymerization conditions to the requirements of the water-soluble pseudorotaxane monomer. Polymers in which cucurbituril has been threaded onto the side chain in a pseudorotaxane fashion have been reported by Kim et al. Cucurbituril has also been integrated into a branched polymer structure. Through the functionalization of the surface of a dendrimer with a diamine motif, Kim et al. achieved the threading of CB[6] onto it, leading to a pseudorotaxinated surface architecture.  

Our interest in cucurbituril as a macrocyclic component ( bead ) in polyrotaxane synthesis originates from our interest in the synthesis of well-defined poly- 

Variations in monomer and catalyst stoichiometry, reaction time or temperature all proved unsuccessful in triggering the formation of the dipolar cycloaddition product. The use of excess cucurbituril led only to quantitative isolation of the pseudorotaxanes derived from 1 and 2 (Fig. 1.38). We speculated that our initial monomer design must have been flawed. The choice of a six-carbon spacer to maximize recognition of the monomer by cucurbituril may be the cause of the catalytic inhibition. We hypothesized that the pseudorotaxanes derived from cucurbituril and monomers 1 and 2 must form much faster than any possible ternary complex and that the essentially perfect fit of each monomer inside cucurbituril would prevent the simultaneous encapsulation of alkyne and azide moieties by a third cucurbituril with the correct conformation required for catalysis. 

In order to find evidence for this hypothesis we decided to prepare a polyro-taxane that would mimic the chain dimensions and therefore not only the electronic but also steric factors imposed by the growing polymer chain via a post-threading route. As the simplest model we selected a poly(hexamethylene amine) and its corresponding protonated form (Fig. 1.39).  

Although Meschke et al. claimed that the pseudopolyrotaxane was obtained, the existence of pseudopolyrotaxane structure is still unclear because of the lack of the attractive interaction between polymer and cucurbituril. 

3-Dipolar cycloaddition reaction of propargyl ammonium salt and 2-azidoethylammonium salt is greatly enhanced in the presence of cucurbituril because the hydrophobic cavity of cucurbituril is an excellent reaction field for the cyclocondensation [175]. Mock et al. obtained [2]rotaxane consisting 

Sauvage et al. have synthesized a variety of oligorotaxanes utilizing 1,10-phenanthroline-copper(I) complex [179]. Stable bis(l,10-phenanthroline) copper(I) complex has a tetrahedral coordination structure, and two 

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Fig. 9. Cucurbituril inclusion chemistry (a) tridimensional stmcture of cucurbit[6]uril (b) conjectured cross-sectional representation of a host—guest...

This entry to supramolecular chemistry allows one, at the same time, to develop a host-guest chemistry because the space inside the cucurbituril barrel is sufficient to confine small "guesf molecules. This is illustrated with the crystallization of the supramolecular adduct [W3S4(H20)8Cl](pyH ccuc) Cl4a 5.5 H2O with a pyridinium cation inside the cucurbituril cavity [48]. The introduction of guest molecules may vary the net charge on the assembly and consequently the whole packing in the solid state. 

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. 

Fig. 3. Rotaxane dendrimers incorporating cucurbituril threaded on l,6-di(bipyridmium)hex-ane with Fr chet dendrons as stoppers...

Each factor may affect the others, depending on relative concentrations and pH. Cucurbituril requires quite strongly acidic conditions for solubilisation, hence its use in textile processing is likely to be very limited. It has mostly been investigated in connection with the removal of colour from textile effluents [46,48-53]. 

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). 

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

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... 

An evaluation of the macrocyclic ligand cucurbituril in powder form as a precipitant for direct dyes varying in molecular size, including Cl Direct Red 79 (disazo), Blue 71 (trisazo) and Red 80 (tetrakisazo), established the influence of pH and ligand concentration on adsorption [60]. The cucurbituril molecule contains six acetylenediurein units linked in... 

The network structures to be discussed will all involved hydrogen bonding as the supramolecular synthon. It should be noted however that other interactions such as coordinate bonds and host-guest interactions may also organise host molecules into network structures. Coordination polymers constructed from molecular hosts may involve functionalised calixarenes [8-11], cyclotriveratrylene [12], or cucurbituril [13]. Calixarenes have also been used to build up network structures via host-guest interactions [14,15]. It is also notable that volatile species may be trapped within the solid state lattice of calix[4] arene with a structure entirely composed of van der Waals interactions [16]. 

Nau WM, Ghale G, Hennig A et al (2009) Substrate-selective supramolecular tandem assays monitoring enzyme inhibition of arginase and diamine oxidase by fluorescent dye displacement from calixarene and cucurbituril macrocycles. J Am Chem Soc 131 11558-11570... 

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... 

Gadde S, Batchelor EK, Kaifer AE (2009) Controlling the formation of cyanine dye H- and J-aggregates with cucurbituril hosts in the presence of anionic polyelectrolytes. Chem Eur J 15 6025-6031... 

Koner AL, Nau WM (2007) Cucurbituril encapsulation of fluorescent dyes. Supramol Chem 19 55-66... 

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