Fullerenes calix arenes

The cavity of these calixarenes is usually too small to accommodate fullerenes, and is confirmed by solution, unless they have extended cavity walls as in calix[4]-naphthalenes. Nevertheless, some calix[4]arenes were shown to form stable crystalline complexes with C60 with the fullerene eno- to the calixarene cavity, and they include p-Ph-calix[4]arene, which has a toluene molecule in the cavity, the overall structure dominated by fullerene-fullerene and eso-calixarene fullerene interactions p-Br-calix[4]arene propyl ether, the structure showing very close interfullerene contacts in a columnar structure (Fig. 2d), which most likely results in opposing induced dipoles from the unidirectionally aligned calix-arenes " and /7-I-calix[4]arene benzyl ether, where the fullerenes are ordered without appreciable interfullerene interactions. There is also a calix[4]resorcinarene, R = CH2CH2Ph, 3, which has a molecular capsule derived from head-to-head hydrogen bonding of two resorcinar-enes and propan-2-01 molecules, with the fullerenes also... 

Figure 9.7 Optical micrograph (a) and TEM image (b) of the [60]fullerene calix[5]arene 4 complex. (Reproduced with permission from Reference [62]. Copyright Wiley-VCH Verlag GmbH.)...

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]. 

A range of amphiphilic dendrimers have been reported based on fullerene C60 or a calix[4]arene core with dendritic branches on one side and long aliphatic tails on the other, Figure 14.8. The amphiphiles self-assemble into micelles with the aliphatic chains buried in the micelle core and the more hydrophilic dendritic portion facing out.14... 

The calix[8]arene depicted in Fig. 2.18 can bind fullerenes (see Chap. 3) the fullerene soccer ball is trapped in the calix. Fullerenes are usually prepared as mixture of Ceo, C70, 75, and so on, and separating them is not always easy. The calix[8]arene has a cavity with an inner diameter of 1 nm, which is therefore suitable for Ceo, since it has a diameter of 0.7nm. When the calixarene is added to a toluene solution of a mixture of fullerenes, a 1 1 complex of the calixarene and Ceo selectively precipitates. Isolation of the precipitates followed by dispersion of them in chloroform results in the precipitation of dissociated Ceo. Repeating these processes results in Ceo with high purity. 

As with the calix[n]arene family, the oxacalixarenes may also be derivatized to yield compounds with deeper cavities or greater functionality. Unfortunately, unlike the calix[n]arenes, the 4-t-butyl group cannot be removed using retro-Friedel-Crafts methods as the etheric links are not robust under the conditions necessary. The best way to introduce functionality to the upper rim is to build it in at the start. This approach may be problematic as the precursor 2,6-bis(hydroxy) phenol derivatives are often formed in low yield or are impossible to prepare in a single step. Despite these difficulties a diverse range of such compounds exist in addition to the simple 4-t-butyl and 4-methyl derivatives bromo- and benzylox-acalix[3]arenes that bind fullerenes [1-3] have both been reported. 

While a monolayer of the parent calix[6]arene shows a selective response to Cs" (which increases the parallel orientation), the hexaamide shows a selective response to guanidinium ion, Similar results are reported for 8 " and its derived ester 264 (R = 1,1,3,3-tetramethylbutyl R = Et) and amide, where the order of selection for cations is Cs" > Rb > Na > K and for anions is 1 > F > Br" > Monolayers prepared from 8 and the fullerenes... 

Relatively few molecular separations have been studied from the utilitarian standpoint. One of these, the purification of fullerenes via 8 , is discussed on p. 170. In a reciprocal experiment the separation of 4 " , 6 , and 8 with a column using a chemically-bonded C o silica stationary phase has been re-ported. Chromatographic selectivity has been achieved for amino acid esters and alkali metal cations on silica-bonded calix[4]arene tetraesters, the structure of which has been explored by and Si-CP-MAS NMR. Silica-bonded calixarenes have also been used as packing materials for HPLC columns that are capable of separating disubstituted aromatics, peptides, and nucleosides. The HPLC separation of phenols using 6 ° as a constituent of the eluent has been described. ... 

Fullerene C70 does not form a complex with the same calixarene in toluene, but it does so in benzene, crystallizing as the 2 1 complex, (C7o)2(p-Bu -calix[8]arene) (structme unknown).The same fullerene also forms a 2 1 complex with / -Bu -calix[6]arene, and its precipitation from toluene solutions can be used to retrieve 87% purity C70 from Ceo-depleted fullerite. 

The fullerene-rich calix[6]arene complexes. (C60 or C7o)2calix[6]arene, were structurally authenticated as isomorphous complexes,showing the calixarene in the double-cone conformation with a fullerene perched in each of the shallow cavities, resembling the jaws of a pincer acting on two adjacent cage molecules the... 

Fig. 4 Encapsulation of fullerenes by bridged calix[5]arenes. (From Refs. [30,32].)...

Ikeda, A. Suzuki. Y. Yoshimura. M. Shinkai. S. On the prerequisites for the formation of solution complexes from [60]fullerene and calix[n]arenes A novel allosteric effect between [6]fullerene and metal cations in calix[-njaryl ether complexes. Tetrahedron 1998. 54. 2497-2508. 

Haino. T. Yamanaka, Y. Araki, H. Fukazawa. Y. MetaF induced regulation of fullerene complexation with double-calix[5]arene. Chem. Commun. 2002. 402-403. 

Asfari, Z. Thuery, P. Nierlich, M. Vicens. J. Unsym-metrical calix[4]- /5-crowns-6 with unequivalent crown loops. Tetrahedron Lett. 1999. 40. 499-502. van Axel Castelli. V. Cort, A.D. Mandoliai. L. Rein-houdt, D.N. Schiaffino. L. Catalysis of the addition of benzenethiol to 2-cyclohexen-I-ones by uranyl-salophen complexes A catalytic metallocleft with high substrate specificity. Chem. Eur. J. 2000, 6. 1193-1198. Albrecht, M. Hovestad, N.J. Boersma, J. van Koten. G. Multiple use of soluble rnetallodendritic materials as catalysts and dyes. Chem. Eur. J. 2001, 7. 1289-1294. Haino. T. Araki. H. Yamanaka. Y. Fukazawa, Y. Fullerene receptor based on calix[5]arene through metal-assisted self-assembly. Tetrahedron Lett. 2001. 42, 3203-3206. 

The association of porphyrin and fullerene electron acceptors in LB films can also proceed via a stepwise, noncovalent formation of the assembly, as demonstrated by Shinkai and Ikeda (Figure 13.88). The host-guest interaction of Ceo with homooxa-calix[3]arene is the noncovalent interaction that assists film formation The fullerene absorption in the host-guest complex is used to determine a surface concentration of 1.4 x 10 ° molcrn" in the Ceo layer, which is then further covered with the polymer-sustained porphyrins 165 or 166. Porphyrin surface concentrations are then controlled by UV-visible absorption and are found to be 7.6 X 10 and 5.5 x 10 for 165 and 166, respectively. Photocurrent measurements performed under irradiation at 420 nm, with a 1.36 mW cm for a coating of 165, and at 430 nm, with a 1.53mWcm for a coating of 166, in... 

Fig. 6 Schematic view of the photoactive multilayers of sodium 3-mercaptoethane-sulfonate (first layer), fullerene-cationic homooxa-calix[3]arene inclusion complex 2 (second layer), anionic porphyrin polymer 3 or 4 (third layer) on an ITO electrode [82].

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