Calixarenes cyclodextrins

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

Keywords CP/MAS Host-guest chemistry Molecular motion Calixarenes Cyclodextrins Cyclophosphazenes Fullerenes Solid-state NMR... 

Study of the inclusion behaviors of the cavity of many commonly known macrocyclic receptors like calixarenes, cyclodextrins and cyclic oligopeptides draws considerable interest in supramolecular chemistry. However, the construction of inclusion compounds using self-assembly of... 

Amphiphilic macrocyclic host molecules have been investigated for many years. Among others, it is known that amphiphilic crown ethers, " cryptands, calixarenes, cyclodextrins, and curcubitnrils can form bilayer vesicles in aqueous solution. However, the host-guest chemistry of such host vesicles remained largely unexplored for many years. Darcy and Ravoo prepared bilayer vesicles composed entirely of amphiphilic cyclodextrin host molecules. These vesicles have a membrane that displays a high density of embedded host molecules that bind hydrophobic guest molecules such as f-butylbenzyl and adamantane derivatives. The characteristic size-selective inclusion behavior of the cyclodextrins is maintained, even when the host molecules are embedded in a hydrophobic... 

Cage compounds Zeolites, calixarenes, cyclodextrines, crown ethers, cyclophanes, etc. Gases, vapors (membranes, supporting media)... 

Macrocycles play an important role in the development of supramolecular chemistry. Based on the traditional macrocycles such as crown ethers, calixarenes, cyclodextrins, and cucurbiturils, a great many supramolecular polymers as well as their applications have been reported. Because pillar-arenes have only had 6 years of development (from 2008), the research on pillararene-based supramolecular polymers is at a preliminary stage. However, all of the efforts made and aehievements that have been reached suggest that pillararenes as well as pillararene-based supramoleeular polymers will have a bright future. 

Numerous examples of artificial channels have been reported since the pioneering work of Tabushi using tetrachained cyclodextrin as a model. Of these examples, the macrocycles, such as crown ethers, calixarenes, cyclodextrins, and cucurbiturils, play an important role. The macrocycles provide not only the platforms for construction of whole channels but also the functional sites necessary to achieve transport selectivity and efficiency. From this viewpoint, pillararenes, new macrocycles with unique structural features, may also act as a platform for building such channels, which will give the channels new functions. This hypothesis has been systematically explored by us. 

Cyclotriveratrylene, by analogy with calixarenes, cyclodextrins and a few other cyclophane-type compounds, can be used as a matrix to preorganize coordination sites for transition metals, either at the edge of the rigid structure, or around an expanded CTV s cavity. Achiral 2- and 3-pyridine tripod ligands have been synthesized together with a bipyridine multichelate. Studies of these new ligands, both by... 

Fig. 15. Prototype examples of (a) cyclodextrins and (b) calixarenes, showing conformational stmctures and dimensions.

Calixarenes (from the Latin ca/ x) may be understood as artificial receptor analogues of the natural cyclodextrins (96,97). In its prototypical form they feature a macrocycHc metacyclophane framework bearing protonizable hydroxy groups made from condensation of -substituted phenols with formaldehyde (Fig. 15b). Dependent on the ring size, benzene derivatives are the substrates most commonly included into the calix cavity (98), but other interesting substrates such as C q have also been accommodated (Fig. 8c) (45). 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

Cylodextrins (CDs) are a class of chiral cyclic oligosaccharides that have molecule-sized cavities. They commonly comprise between six and eight D-glucopyranoside units that are linked via a-l,4-glycosidic links. Their bowl-shaped form is generally represented as a cylindrical funnel by analogy to the calixarenes family. There is a large number of cyclodextrin derivatives in the... 

It has already been mentioned that metal complexes with confined binding pockets often display unusual chemical reactivities (see Section II). Thus, complexes of substituted hydrotris (pyrazolyl)borates, in which the substituents serve to from a hydrophobic binding pocket, have already been shown to exhibit enhanced chemical reactivity when compared with their unmodified analogs (282,283). Likewise, cyclodextrin and calixarene-based metallocavitands have been used as catalysts for selective organic transformations, and even as catalysts for reactions that... 

Recently, it has been found that the outcome of some cycloadditions can be altered remarkably when performed inside the cavity of cyclodextrins (288), self-assembled molecular capsules (289), or coordination cages (290). This fact intrigued us greatly and stimulated our interest in the Diels-Alder reactivity of the calixarene-like [M2(L19)(L )]+ complexes bearing unsaturated carboxylate coligands L (215). 

Recent years have also seen the development of a variety of com-plexation reagents incorporating C-P bonds and their associated functionalities, such as phosphoryl linkages. For example, substituted calixarenes (Figure 1.4) have been developed for extraction of radionuclides, and phosphorus-derivatized cyclodextrins for stereospecific inclusion interactions. 

In principle, there are four basic strategies to compensate for the repulsive effects between the hydrophobic fullerene surface and water (a) encapsulation in the internal hydrophobic moiety of water-soluble hosts like cyclodextrins (Andersson et al., 1992 Murthy and Geckeler, 2001), calixarenes (Kunsagi-Mate et al., 2004) or cyclotriveratrylenes (Rio and Nierengarten, 2002) (b) supramolecular or covalent incorporation of fullerenes or derivatives into water-soluble polymers (Giacalone and Martin, 2006) or biomolecules like proteins (Pellarini et al., 2001 Yang et al., 2007) (c) suspension with the aid of appropriate surfactants and (d) direct exohe-dral functionalization in order to introduce hydrophilic moieties. 

Low affinity to polar solvents and fullerenes aggregation in water limit their use in biologic systems. To increase water solubility of fullerenes, few ways are used solubilization with the use of some water-soluble polymers like PDT or polyvin-ilpyrrolidone, generation of complexes with cyclodextrines or calixarenes, and... 

Based on the theory, the separation of enantiomers requires a chiral additive to the CE separation buffer, while diastereomers can also be separated without the chiral selector. The majority of chiral CE separations are based on simple or chemically modified cyclodextrins. However, also other additives such as chiral crown ethers, linear oligo- and polysaccharides, macrocyclic antibiotics, chiral calixarenes, chiral ion-pairing agents, and chiral surfactants can be used. Eew non-chiral separation examples for the separation of diastereomers can be found. 

It had been reported that fullerene Cgo forms a water-soluble complex with y-cyclodextrin by heating with an excess amount of y-cyclodextrin in water [10] or in a mixture of refluxing water and toluene for a long time, such as 30 h [ 11]. The isolated complex is considered to have the Cgo structure bicapped with y-cyclodextrin in a molar ratio of 1 2 [11], and the complex dissolved in water to give a solution of C o with a concentration of nearly 10 mol L 410,11 ]. Fullerene Qo was also solubilized in water by complexation with a sulfocalix[8] arene, i.e., calix-[8]aryloxy-49,50,51,52,53,54,55,56-octakis(propane-3-sulfonate). The concentration of this complex in water is estimated as 5x10 mol L [12]. Complex formation between fullerene and various calixarenes has also been reported [8]. 

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