The Calixarenes

Much more recently the caeside salt [Li([2.1.1]cryptand)] Cs has been reported. The material contains as one-dimensional zigzag chain of Cs anions situated 6 A apart, shorter than the 7 A sum of the van der Waals radii. The material has interesting properties including low band gap semiconductivity that result from the overlap of the adjacent Cs wave functions.  

9 Gutsche, C. D., Calixarenes, Royal Society of Chemistry Cambridge, 1989 Gutsche, C. D., Calixarenes 2, Royal Society of Chemistry Cambridge, 1997. 

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Based on the above results they have concluded that the ligand groups circularly arranged on the lower rim of the calixarene cavity construct a novel cyclic metal receptor for selective extraction of transition metal cations. Results suggest that the fine tuning in molecular... 

In an effort to restrict the location of semiconductor nanoparticles in LB films and inhibit aggregation, the formation of CdS in LB films of calixarenes was investigated [195]. Limiting areas of 3.0 nm and 1.8 nm were obtained on 0.5 mM CdCli, compatible with the cross-sectional areas of the calixarenes. Y-type LB fdms were prepared at 25 mN m on glass, quartz, and silicon. The substrates had been made hydrophobic by treatment with a silane vapor. After H2S treatment overnight in sealed jars, UV absorbance spectra and XPS data were obtained. The absorption edge for the CdS particles formed in the calixarene LB films transferred at pH 5.5 was 3.3 eV as compared with 2.7 eV for films formed in cad-... 

In a study of mixed monolayers of C60 and p-iert-butylcalix[8]arene, different isotherm behavior was obtained [256]. The surface pressure was observed to rise at a lower molecular area (1.00 nm molecule vs. 2.30 mn molecule in the prior study). Similar isotherms were observed whether a 1 1 mixture or a solution prepared by dissolving the preformed 1 1 complex was spread. The UV spectra of the transferred LB films appeared different than that of bulk C60. It was concluded that a stable 1 1 complex could be formed by spreading the solution either of the mixture or of the complex. This was confirmed in a later study by the same group that included separate spreading of the calixarene and the C60... 

This is clearly a complex system, for it is pointed out that the calixarene-limiting area depends on the spreading solvent and is subject to a memory effect. In another study, mixed monolayers and the resulting LB films of C60 with two derivatized calix[4]resorci-nolarenes and with p-tert-butylcalix[6]arene and p-tcrt-butylcalix[8]arene were examined... 

A huge group of macrocycles which contain 2,6-disubstituted phenols are the calixarenes [51]-[53]. Their conformation has been investigated intensively (Gutsche, 1989, 1991). In most conformations, however, the phenolic rings are oriented almost vertically in relation to the plane of the macrocydic ring. Therefore the OH functions are not oriented in an intra-annular fashion. Nevertheless the pK values of calixarenes [51] differ from those of other comparable phenols. The reason for this is the... 

Applicability in biological ion assay is an important factor for biocompatible potentio-metric ion sensors. Attempts were made to determine Na" " concentrations in human blood sera by using silicone-rubber membrane Na+-ISFETs based on (5) [Fig. 17(a)] [29]. The found values for Na concentration in undiluted, 10-fold diluted, and 100-fold diluted serum samples are in good agreement with the Na" " calibration plots. Even in the undiluted serum samples, only a slight potential shift was observed from the calibration. This indicates that the calixarene-based silicone-rubber-membrane Na+-ISFETs are reliable on serum Na assay. For comparison with the silicone-rubber membrane, Na -ISFETs with corresponding plasticized-PVC membrane containing (2) or (5) were also tested for the Na assay. The found values of Na" " concentration... 

The specific structure of [(H20)5Ni(py)]2+ was observed in the complexes with the second-sphere coordination of calix[4]arene sulfonate.715 There are two different [(H20)5Ni(py)]2+ cations in the complex assembly. In one the hydrophobic pyridine ring is buried in the hydrophobic cavity of the calixarene with the depth of penetration into the calixarene cavity being 4.3 A (Figure 9). The second independent [(H20)5Ni(py)]2+ cation is intercalated into the calixarene bilayer. 

The interactions between the [W(calix)] metal fragment and the ethylene moiety has been analyzed using the extended Huckel calculations (see Chart 4).22b As supported by the structural parameters of 31, the dxz is no longer available for -it donation from the calixarene oxygens in the xz plane, thus explaining the strong C2v distortion of the [ [ Bu -cal ix 14]-(0)4 W] unit observed in the X-ray structure of 31, with the two WO bonds in the metal-ethylene plane ca. 0.2 A longer than... 

A different synthetic access to a 1 -metallacyclopropene, which can be a versatile organometallic synthon, is displayed in Scheme 33. The mono-alkyne derivatives of W(IV)-calix[4]arene are easily accessible through the thermal displacement of cyclohexene from 32 using the appropriate acetylenes. The reaction led to complexes 34 and 172-174. The proposed 3-metallacyclopropene has been confirmed from the spectroscopic and the X-ray data. The H NMR data reveal a cone conformation of the calixarene with a four-fold symmetry, for which the... 

Longer Hg-7r interactions are observed in the /> ra-/-butylcalix[4]arene mercury complex 162. The mercury atom forms primary bonds with the two sulfur atoms and engages in weaker secondary interactions with two arene rings of the calixarene whose centroids sit at 3.07-3.11 A from the metal center.201... 

A further category of cavitands are the calixarenes (Gutsche, Dhawan, No Muthukrishnan, 1981 Gutsche Levine, 1982). Structure (255) illustrates an example of this type which is readily prepared by treatment of 4-f-butylphenol with formaldehyde and base. The compound may exist in other conformations besides the saucer-shaped one illustrated by (255). Similarly, f-butyl-calix[4]arene (256 R = CH2COOH) has an enforced hydrophilic cavity in the shape of a cone the alkali and ammonium salts of this host are soluble in water (Arduini, Pochini, Reverberi Ungaro, 1984). 

A variety of other ligands, such as the calixarenes (see Chapter 5), have... 

Calixarenes, when in their cone-conformation (54), represent versatile host systems for metalated container molecules and many examples have been reported in the literature (55-61). Reinaud and coworkers have carried out extensive work concerned with calix[6]arenes that are functionalized at the small rim by nitrogen arms (62), aiming to reproduce the hydro-phobic binding site of mononuclear zinc and copper metalloen-zymes. A recent example is the calix[6]arene ligand L1 (Fig. 3), in which a tris(2-methylpyridyl)amine unit covalently caps the calixarene small rim (63). The ligand forms copper complexes of... 

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... 

Interestingly, the macrocycles can adopt two different conformations A and B (Fig. 34), which are reminiscent of the partial cone and cone conformations of the calixarenes. A detailed... 

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). 

A ferris wheel assembly involving a 1 1 complex of 19 and metallated [18]crown-6 is found in the cationic supermolecule [La(H20)3([ 18]crown-6)] (19+2H) + [48]. The lanthanum ion is coordinated by one calixarene sulfonate group, the [18] crown-6 and three aquo ligands, and the metallated crown sits inside the calixarene cavity. A helical hydrogen bonded chain structure is formed between the cationic assembly, water and chloride ions. The ferris wheel structural motif is also found in Ce3+ complex which simultaneously contains a Russian Doll assembly [44]. 

PET-17 has been designed for selective recognition of sodium (Figure 10.15). It contains four carbonyl functions, two of them being linked to pyrene and nitrobenzene at opposite sites on the calixarene lower rim. Complexation with Na+ prevents close approach of pyrene and nitrobenzene and thus reduces the probability of PET. The fluorescence quantum yield increases from 0.0025 to 0.016. 

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