Cyclodextrins fullerene complexation

Belgorodsky et al. (2006) studied the binding of pristine fullerene complexed with cyclodextrin on bovine serum albumin protein demonstrating that the binding is a multistep process. First, the cyclodextrin dissociation from C60 takes place, exposing a fullerene hydrophobic portion, than this portion binds to the protein. 

Murthy CN, Geckeler KE (2001) The water-soluble beta-cyclodextrin-[60]fullerene complex. Chem. Commun. 1194-1195. 

Braun T, Buvari-Barcza A, Barcza L, Konkoly-Thege I, Fodor M, Migali B (1994) Mechanochemistry a novel approach to the synthesis of fullerene compounds. Water soluble Buckminster fullerene - gamma- cyclodextrin inclusion complexes via solid-solid reaction. Solid State Chem. 74 47-51. 

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... 

Literature data on cytotoxic effects of photoexcited fullerene C60 are controversial. In the studies on transformed B-lymphocytes of Raji fine, phototoxic action of water-soluble carboxy-C60 was not revealed even upon its concentration of 5 x 10 5 M (Irie et al., 1996). In the study (Kamat et al., 2000) damaging effect of fullerenes C60 in dependence on intensity of irradiation toward CHO cells has been demonstrated. Using microsomal fraction of rat liver that was treated with C -cyclodextrin complex, it was shown that already in 5-30 min after UV-irradiation the accumulation of LPO products occurs that is suppressed by antioxidants like ascorbic acid and a-tocopherol. Similar effect of fullerenes C60 has been revealed in microsomal fraction of the cells of ascitic sarcoma 180 (Kamat et al., 2000). 

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]. 

The complexation of fullerenes and y-cyclodextrin was found to take place more efficiently by the use of a HSVM. Thus, when Cgo was vigorously shaken with 4 molar equivalents of y-cyclodextrin for only 10 min by HSVM and the resulting mixture dissolved in 4 mL of water, a magenta-colored solution of Cgo was obtained by filtration with a membrane filter (Scheme 1) [16]. The concentration of Cgo was 1.4x10 mol L which is the highest value for Cgo dissolved in water. When this aqueous solution was let stand for 2 weeks, the Cgo-y-cy-clodextrin 1 2 complex was obtained as purple crystals. 

The main components of the membrane of the enantioselective, potentiometric electrode are chiral selector and matrix. Selection of the chiral selector may be done accordingly with the stability of the complex formed between the enantiomer and chiral selector on certain medium conditions, e.g., when a certain matrix is used or at a certain pH. Accordingly, a combined multivariate regression and neural networks are proposed for the selection of the best chiral selector for the determination of an enantiomer [17]. The most utilized chiral selectors for EPME construction include crown ethers [18-21], cyclodextrins [22-35], maltodextrins 136-421, antibiotics [43-50] and fullerenes [51,52], The response characteristics of these sensors as well as their enantioselectivity are correlated with the type of matrix used for sensors construction. 

Pulse radiolysis of 2-propanol has also been used to investigate elementary redox and radical reactions of fullerenes in solution [18]. For example, reduction of Ceo to C6o by Cs (k > 10 dm mol" s ) and (CH3)2 COH [k = (5 2) x 10 dm mor s ] was observed, and Ceo " was found to be stable for hours in the absence of oxygen. Ceo is insoluble in water, but its reduction in this solvent by (CH3)2 C0H was achieved by imbedding the fullerene in y-cyclodextrin to form a soluble guest-host complex in a 9 1 (vol %) water 2-propanol mixture. In this case, the reaction rate was two times slower than that in neat 2-propanol. Information was also obtained [18] on the addition of CH3 to Ceo in 2-propanol by the follow-... 

Abstract New applications of ID and 2D solid state (SS) NMR spectroscopy in structural studies of inclusion complexes (ICs) formed by organic host lattices (cyclodextrins, calixarenes, cyclophosphazenes, and fullerenes) are described. Each section of the review gives short characteristics of host molecules and recent applications of SS NMR. Less common systems, which are interesting as models for SS NMR studies, (bis[6-0,6-0 -(l,2 3,4-diiso-propylidene-a-D-galactopyranosyl) thiophosphoryl] disulfide (DGTD) and 1,2-dichloro-ethane/tris(5-acetyl-3-thienyl) methane (TATM)), are also discussed. 

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). 

In addition to the radical-induced reduction of the y-CD incorporated [60]fullerene, even the formation of Ceo-radical adducts were demonstrated to occur. Considering the configuration of the y-CD/Ceo/y-CD complex, a reaction with radical species is only possible through the two caps of the cyclodextrin moieties and should thus be restricted to small radicals. In light of this aspect, a reaction with a bulky radical species such as "CH2(CH3)2COH should be made more difficult or even be ruled out. In fact, the lack of any spectral evidence for a (C6o-CH2(CH3)2COH) adduct supports this view. 

The incorporation of the functionalized fullerene into a host molecule, such as a y-cyclodextrin or surfactants is an elegant way to bypass the aggregation of C6oC(COO )2-As demonstrated in studies with [60]fullerene this host can accommodate only a single fullerene molecule, which still has access to the solvent phase. The ground state spectrum of this guest-host complex shows the same narrow bands as, for example, monomeric C6oC(COOEt)2 or Cgo/Y-CD and clearly differs from the presumed CeoCfCOO )2 n cluster. 

Complexation of fuUerene C o with y-cydodextrin was attained by employment of high-speed vibrational milling (HSVM) by Komatsu et al. (Scheme 8.6) [14], Fullerene Cso was complexed within 10 min milling with fourfold excess of cyclodextrin, forming a 1 2 complex 25 with a bicapped structure. The solid-state... 

Equally effective was the complexation of C70 by HSVM (lOmin, Cjq j-cyclodextrin 1 8), while the other functionalized C50 derivatives afforded water-soluble 1 1 complexes, since functional groups prevent the formation of the bicapped 1 2 complexes. By mechanochemical treatment, fullerene 50 also complexes with sulfocalix[8]arene (lOmin, equimolar amounts), and the obvious advantage of the solid-state complexation is illustrated by the complexation of sulfocalix [8]arene with fullerene dimer (also prepared by mechanosynthesis, see chapter Applications of Ball Milling in Nanocarbon Material Synthesis). Dimer is hardly soluble in most common organic solvents, but the mechanochemical treatment of an equimolar mixture of sulfocalix[8]arene and fullerene dimer for lOmin afforded bicapped complex, which is about twice more soluble in water than in commonly used ODCB. 

With the knowledge that cyclodextrins (CDs) of appropriate dimensions and correct stoichiometries can complex Ceo and C70 fullerenes in water, Star et al. reported that common starch, of which CD is a macrocyclic analog, dispersed SWNTs in aqueous environments provided the starch molecule was activated toward complexation by wrapping itself helically around small molecules. - ... 

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. 

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