Cyclodextrins fullerene interactions

The advantage of using antibiotics, cyclodextrins, maltodextrins and fullerenes as chiral selectors is that the enantioselectivity of the molecular interaction takes place in two places inside the cavity (internal enantioselectivity) and outside the cavity—due to the arrangement, size and type of the radicals, atoms or ions bound on the external chain of the chiral selector (external enantioselectivity) [10]. The thermodynamics of the reaction between the enantiomers and chiral selectors plays the main role in the enantioselectivity of molecular interaction. 

Buvari-Barcza and co-workers [77] showed, by comparing several com-plexing agents, that y-CD is the best host for solubilising C6q fullerene in a water environment. The interaction of C6q and y-CD forms a C6o-(y-CD)2 inclusion complex. The analytical data and solid state NMR indicated that the essentially 1 2 complex exists as two different forms. In the violet colored form, unhydrated C60 is included, while in the brownish one, C q is also hydrated. The inner diameter of the y-cyclodextrin is only 0.95 nm while the diameter of C6q is estimated to be 1.0 nm. Because of this dimensional difference, complete inclusion is inconceivable, but the secondary hydroxyls of the y-CD rims can be connected by hydrogen bonds and possibly mediated by water molecules (Fig. 29). 

From a supramolecular perspective, cyclodextrins offer a preformed cavity of defined size within a water-soluble macrocycle. The interaction between guest molecules, or substituents to the cyclodextrin itself, leads to some useful results. Hydrophobic fluorescent substituents will be self-included by the macrocycle in aqueous solution until they are displaced by guests with even greater affinities [6]. The act of displacement will generate a fluorescent response that lends itself to sensor applications. It is also possible to use the hydrophobic core to induce rotaxane formation. This approach has been used by many groups, for example, Liu has recently used it to prepare water-soluble gold-polypseudorotaxanes that capture fullerenes such as C60 [7]. 

Carbohydrates, Recognition of, p. 169 Carbonic Anhydrase Models, p. 178 Carcerands and Hernicarcerands. p. 189 Cation-n Interactions, p. 214 Cavitands, p. 219 Chiral Guest Recognition, p. 236 Classical Descriptions of Inclusion Compounds, p. 253 Classification and Nomenclature of Supramolecular Compounds, p. 261 Clathrate Hydrates, p. 274 Conzplexation of Fullerenes, p. 302 Concepts in Ciystal Engineering, p. 319 Crown Ethers, p. 326 Cryptands, p. 334 Cryptophanes, p. 340 Cyclodextrins, p. 398... 

Kono et al. reported improvement of water-solubility of fullerene, C o by using PAMAM dendrimer modified with both poly(ethylene glycol) (PEG) and (3-cyclodextrin (CD) [28]. The authors believed that the presence of CD at the periphery of dendrimer can increase the formation of complex with fullerene, while PEG moiety can promote water-solubility and biocompatibility. The selection of p-cyclodextrin was based on its low affinity for interaction with PEG. The synthetic procedure for preparation of PEG/CD-modified dendrimer and encapsulation of fullerene is depicted in Fig. 6.9. 

Ikeda et al. and Konishi et al. reported on a supramolecular photocmrent generation system in combination with electrostatic and van der Waals interactions. In a Ceo-porphyrin bilayer prepared by electrostatic alternate adsorption (Fig. 27), the quantum yield of photocurrent generation is increased when self-aggregation of porphyrins is suppressed by host-guest interaction of cyclodextrin and porphyrin [104-106]. Cationic fullerene and tetracationic porphyrin bound on a DNA scaffold by electrostatic interactions was fabricated by conjugate polymer (Fig. 28). The quantum yield of photocurrent generation was 3.8% [107]. 

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