Cucurbituril molecules

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... 

Known examples involving OD motifs, i.e. molecular beads (cucurbituril molecules), threaded by coordination polymers of different topology have been described by Kim and coworkers [80],... 

Whang. D. Jeon. Y.-M. Heo, J. Kim. K. Self-assembly of a poly rotaxane contaning a cyclic bead" in every structural unit in the solid state Cucurbituril molecules threaded on a one-dimensional coordination polymer. J. Am. Chem. Soc. 1996, 118 (45). 11333-11334. 

The progress of the reaction was again monitored by NMR spectroscopy. Our criterion for catalytic turnover was that each cucurbituril molecule would lead to the formation of more than one triazole ring. This ratio was calculated from the integration of the sum of all triazole proton resonances (encapsulated and free) divided by 1/12 of the integration arising from a cucurbituril resonance. In an exploratory effort the effect of catalyst concentration, temperature and type of solvent, as shown in Table 1.2, were investigated. ... 

Figure 3.38 The cyclic cucurbituril molecule and the formation of a [4]-MN around a platinum-templated central ring.

The first new cucurbituril molecule to be synthesized and characterized was decamethylcucurbit[5]uril, reported by Stoddart et al. in 1992 [32]. However, the small cavity size of the n = 5 ring was not particnlarly useful for the inclusion of guests. The real breakthrough in expanding the CB[n] families came in 2000, when Kim et al. [33] reported a useful synthesis method for obtaining the... 

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. 

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). 

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]. 

On the contrary, cucurbiturils preferentially coniine charged, but not neutral, species. Cucurbiturils also possess cylindrical cavities suitable for the inclusion of organic molecules. Cucurbiturils are a family of macrocyclic host molecules consisting of methylene-bridged glucouril units (see Scheme 2.44). 

A special technique proposed in the literature for the removal of dyes is the inclusion of dye into cave molecules such as crown-ethers/cucurbituril, but developments with regard to regeneration and disposal of the crown ether have to be performed to permit introduction into full-scale application [116]. 

One of the major applications of glycolurils is in the preparation of the cucurbituril family of molecular receptors. Despite being known for a number of years the popularity of this molecule has grown significantly in the last decade. The most common member of the cucurbituril family is cucurbit[6]uril containing six glycoluril units linked by methylene units 149 (Figure 6). 

The cavity inside cucurbituril can hold small organic molecules. This has been established crystallographically [3], and is easily investigated in solution by... 

Glycoluril 1 is a rigid, concave molecule, which can be easily functionalized via its four ureido nitrogen atoms. The two carbonyl groups in 1 are potential hydrogen bond acceptor sites. These features make 1 an excellent building block for synthetic host molecules. Glycoluril is the monomeric unit of cucurbituril,... 

Cucurbit [6] uril and increasingly its higher homologues have been used extensively in a variety of host-guest chemistry and nanostructure assemblies. Of particular appeal are rotaxanes and molecular necklaces, mechanically interlocked assemblies of molecules based on CB [6]. Efficient synthesis of ID, 2D and 3D polyrotaxanes and molecular necklaces (cucurbituril beads linked by a macrocyclic molecule string ) has been achieved by a combination of self-assembly and coordination chemistry. We discuss rotaxanes and molecular necklaces in Section 10.7, and cucurbil-based systems are summarised in a recent review.23... 

Kim, K., Mechanically interlocked molecules incorporating cucurbituril and their supramolecular assemblies. Chem. Soc. Rev. 2002, 31, 96-107. 

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