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PubMed2001

Intramolecular AR--O--AR bond formation in calixarenes.

The formal dehydration of two vicinal phenol moieties of p-tert-butylcalix[6]arene was achieved in two steps by mild oxidation of the calixarene followed by treatment of the resulting monospirodienone derivative (9c) with an ionic hydrogenation mixture (Et(3)SiH/CF(3)COOH). Reaction of 9c yielded the unsubstituted xanthenocalix[6]arene 11d, while treatment of the monospirodienone derivative of a spherand-type calixarene (13) with Et(3)SiH/CF(3)COOH afforded the dibenzofuran derivative 15. The formation of the latter product indicates that, at least for 13, the rings forming the Ar--O--Ar bond in the product are not those connected by the spiro bond in the starting material. Methylation of the phenolic hydroxyl groups of 11d with methyl p-toluenesulfonate/K(2)CO(3) or dimethyl sulfate/base afforded its dimethyl and tetramethyl ether derivatives. The parent xanthone calix[6]arene derivative 17b was prepared by O-methylation of the phenol groups followed by CrO(3) oxidation of the xanthene methylene group and deprotection of the OH groups. McMurry coupling of calixanthone 17a afforded the dixanthylene 18. Calixarenes 11d and 15 (which possess a xanthene and dibenzofuran group, respectively) were structurally characterized by X-ray crystallography.

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PubMed2004

Oxygenation of calixarene phenol rings.

[structure: see text] The first examples of epoxy-p-quinol and diepoxy-p-quinol calixarene derivatives have been obtained by base-promoted direct addition of O(2)(oxygenation) to calixarene phenol rings. The regio- and stereochemistry of these derivatives was determined by 2D NMR studies, in conjunction with MM3 calculations, and X-ray crystallography. Both the oxygenation and the subsequent carbonyl reduction occur with a preferential attack to the less hindered exo face of the calixarene rings.

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PubMed2005

Quantum mechanical calculations of conformationally relevant 1H and 13C NMR chemical shifts of calixarene systems.

[graphs: see text] QM GIAO calculations of 13C and 1H chemical shift values of the ArCH2Ar group have been performed, using the hybrid DFT functional MPW1PW91 and the 6-31G(d,p) basis set, on some representative calixarenes and on a series of simplified calixarene models allowing derivation of chemical shift surfaces versus phi and chi dihedral angles. A good reproduction of experimental data was obtained. The applicability of chemical shift surfaces in the study of calixarene conformational features is illustrated.

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PubMed2006

Templating photodimerization of stilbazoles with water-soluble calixarenes.

Water soluble six and eight membered calixarenes template the dimerization of trans-stilbazoles. In the absence of calixarenes at the concentrations employed stilbazoles mainly isomerize to the corresponding cis isomers. Calixarenes help to localize the olefins and orient them in a specific geometry to yield anti-head-tail dimers. Electrostatic interaction between the sulfonate anion and the pyridinium ion of the olefin and hydrophobic interaction between the olefin and the host cavity are believed to be responsible for the observed selectivity. (1)H NMR spectra provide evidence for complexation but do not suggest the exact structure of the host-guest complex.

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PubMed2000

Preparation and characterization of calixarene-coated capillaries for capillary electrophoresis.

Preparation and characterization of calixarene-coated capillaries for capillary electrophoresis (CE) were exemplified with p-allylcalix[4]arene (pACX4) which was immobilized to the fused silica surface using gamma-methacryloxypropyl-trimethoxysilane (gamma-MAPS) as linking agent. Successful gamma-ACX4 coating was suggested by the greatly decreased electroosmotic flow (EOF), due to the introduction of phenolic hydroxyl groups on the inner surface of the capillaries. A slight slope of EOF versus pH at pH <8 would help make the separation reproducible. The coated columns also featured a low ultraviolet (UV) absorption background and long lifetime (> 6 months at 4<pH<9). Moreover, their special selectivity on phenolic compounds indicated a certain extent of selective interactions between solutes and the calixarene coating, which effected separations partially based on an electrochromatographic mechanism.

Calixarenes↗

PubMed2003

Characterization of calixarene- and resorcinarene-bonded stationary phases. I. Hydrophobic interactions.

New HPLC phases with supramolecular selectors on the basis of calixarenes and resorcinarenes were investigated for the first time by means of empirically based test mixtures. The tests, originally developed for common reversed phases, were chosen to evaluate fundamental chromatographic properties of the new materials. In the first part of these studies three descriptors (hydrophobic retention capacity--k'(hyd), hydrophobic selectivity--alpha(hyd), steric selectivity--alpha(ster)) were determined. Except of higher alpha(ster) values and alpha(hyd) values with some methods for the resorcinarene phase the phases with supramolecular selectors were classified as less hydrophobic possessing lower hydrophobic and steric selectivities compared to three RP-C18 phases and a p-tert-butyl phenyl ether phase. The results were confirmed by means of a separation of geometric isomers of thioxanthenes. In contrast, in spite of lower k'(hyd) and alpha(hyd) values calixarene phases were more selective than the Kromasil-C18 phase in the separation of gestagenic and androgenic steroids due to specific interactions with the steroids of similar lipophilicity.

Calixarenes↗

PubMed2000

New calixarene-bonded stationary phases in high-performance liquid chromatography: comparative studies on the retention behavior and on influences of the eluent.

The chromatographic behavior of six calixarene-bonded stationary phases is reported. Varying analyte selectivities (i.e., for phenols, substituted aromatics, polycyclic aromatic hydrocarbons, barbituric acid derivatives, xanthines) exist as a function of the ring-size of the calix[n]arenes (n=4, 6, 8) and the substitution at the "upper rim" with para-tert.-butyl groups. Although eluents with unusually high proportions of water were used, a comparison with conventional reversed-phase (RP) columns shows a predominantly reversed-phase character with remarkable selectivities of these phases. The influences of several organic solvents on retention variations of solutes are compared for RP-C18, phenyl and calixarene phases.

Calixarenes↗

PubMed2003

A study of the freeze-drying conditions of calixarene based solid lipid nanoparticles.

In this note, we report a study of cryoprotectant carbohydrate (glucose, fructose, mannose and maltose) effects on the reconstitution of calixarene based solid lipid nanoparticle (SLN) suspensions after freeze-drying, studied by atomic force microscopy and photon correlation spectroscopy. All carbohydrates tested showed excellent cryoprotection and redispersion properties with the calixarene based SLNs.

Absorptiometry, Photon↗

PubMedDate not supplied

Complex formation of cytochrome C with a calixarene carboxylic acid derivative: a novel solubilization method for biomolecules in organic media.

A calixarene carboxylic acid derivative has been found to form a complex with the cationic protein cytochrome c. The solubilized cytochrome c was stable and showed peroxidase activity in chloroform. The calix[6]arene and the calix[8]arene achieved quantitative extraction of the protein. The calix[6]arene, whose cavity is well-fitted to a protonated amino group, exhibited a selectivity to lysine-rich proteins due to the recognition of the epsilon-amino groups in lysine residues on the surface of the protein. This is the first report showing protein extraction by calixarenes. The solubilized cytochrome c could catalyze an oxidative reaction in organic solvents. This host compound functions as a novel solubilization tool for biomolecules and a separation tool for lysine-rich proteins.

Animals↗

PubMed2006

Ipso-chlorosulfonylation of calixarenes: a powerful tool for the selective functionalization of the large rim.

In our quest for the elaboration of supramolecular models of metallo-enzyme active sites, we became interested in developing new methodologies for the selective functionalization of the large rim of calix[6]arenes. Here, we describe a novel reaction, i.e. the ipso-chlorosulfonylation of calixarene derivatives. The process has been found to be highly efficient, selective and versatile. The regioselectivity is controlled by the nature of the O-substituents at the small rim. Indeed, when O-alkylated by a protonable imidazole group, the aromatic rings are deactivated toward an electrophilic attack and the anisol units can be selectively ipso-chlorosulfonylated under mild conditions (rt). Performing the reaction at a higher temperature allowed the per-chlorosulfonylation to take place. Hence, the synthesis of various sulfonate and sulfonamide derivatives is reported. Finally, a combination of ipso-nitration and chlorosulfonylation allows the per-functionalization of the aromatic units at the large rim in selective alternate positions. Overall, this novel methodology opens new routes to a variety of calixarenes, allowing the tuning of their physical properties without drastically altering their hydrophobic conic cavities.

Calixarenes↗

PubMed2005

Efficient synthesis of water-soluble calixarenes using click chemistry.

[reaction: see text] Several water-soluble calix[4]arenes were synthesized via Huisgen 1,3-dipolar cycloaddition between azides and alkynes. Cationic, anionic, and nonionic calixarenes were prepared from a common azidocalixarene intermediate. Azidocalixarenes performed better than alkynylcalixarenes as precursors. The aggregation behavior of the water-soluble calixarenes was studied by (1)H NMR spectroscopy.

Calixarenes↗

PubMed2004

Antimycobacterial calixarenes enhance innate defense mechanisms in murine macrophages and induce control of Mycobacterium tuberculosis infection in mice.

Tuberculosis remains the leading cause of death among infectious diseases, accounting for more than two million deaths annually. The incidence of the disease is increasing globally, partially because of the resurgence of drug-resistant strains of Mycobacterium tuberculosis. Calixarenes are macrocyclic oligomers, some of which are able to modify the growth of M. tuberculosis in infected cells. Most experimental work has been carried out with Macrocyclon, also known as HOC 12.5EO. In this study, we demonstrate that Macrocyclon is effective in controlling M. tuberculosis infections, and we provide evidence that its effect is partially mediated by an l-arginine-dependent mechanism of macrophage activation that involves the activity of the inducible nitric oxide synthase. We also show that Macrocyclon is effective in athymic and major histocompatibility complex class II-/- mice and synthesized a number of structurally related calixarenes expressing significant antimycobacterial activity.

Animals↗

PubMed2005

The effect of the process variables on the HPLC separation of tricyclic neuroleptics on a calixarene-bonded stationary phase.

The chromatographic behavior of a new HPLC-stationary phase with supramolecular selectors on the basis of calixarenes is described for the separation of nine tricyclic neuroleptics. The effects of different chromatographic conditions (buffer system, pH-value, type and content of organic modifier, injection volume) on the separation of the analytes were studied. Additionally, the effect of structural differences of the neuroleptic analytes was studied. The chemical structure and pKa of the neuroleptics highly influenced their separation on the calix[8]arene phase. The separation of all analytes on the investigated calixarene-bonded stationary phase was possible with a mobile phase of acetonitrile with 30 mM ammonium acetate buffer (pH 3.5) 30:70(v/v) using 1 ml/min flow rate.

Antidepressive Agents, Tricyclic↗

PubMed2000

Calixarenes in analytical and separation chemistry.

Discovered in the 1940's, [1n]metacyclophanes with the common name calix[n]arenes which is derived from for the molecule's shape enjoyed a remarkable interest in almost all fields of chemistry since the 1980's, which is highlighted by several books [1-8]. Over 50 reviews concerning their synthesis, properties and applicabilities were published, many of those with emphasis on organic synthesis and structural properties are cited in [P. 5-6 in 2]. Of interest for analytical chemists are reviews on calixarenes and the structurally related resorcin[n]arenes (or calix[n]resorcarenes) and calixpyrroles concerning potentiometric sensors [9-12], chromo- and fluorophores [13, 14], molecular switches [15], metal ion binding in solution [16-19], redox properties [20] and anion binding [21-24]. Other recent reviews deal with thermodynamic aspects [25], organometallic compounds [26], P-containing calixarenes [27-29], as well as molecular dynamics modeling [30-33]. It is a vital field with over 200 publications per year. Therefore, this article presents only selected results on complexation, solvent extraction and membrane transport with the emphasis on ion and molecular recognition which can be used for analytical purposes, without attempting to cover all available references.

Journal Article↗

PubMed2000

Calixarenes as scaffolds: introduction of tridentate rare earth metal binding units into calix[4]arene.

The reactions of various derivatives of chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid) with p-tert-butylcalix[4]arene have produced several new mono- and difunctionalized derivatives of the calixarene in which tridentate functional groups suitable for the binding of rare earth metal cations have been incorporated. Single-crystal X-ray structure determinations have been performed on two difunctionalized calixarenes found to adopt different "cone" and "1,2-alternate" conformations, as well as on a complex of europium(III) with the phenoxide form of a monofunctionalized ligand, this structure confirming that charge factors are dominant in determining the site of lanthanide metal binding in these ligands.

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PubMed2006

Unexpected Pt(II) migration between the calixarene oxygen atoms.

Reaction between the 1,3-bis(trimethylsilyl) ether of calix[4]arene and platinum(II) difluoro complexes unexpectedly results in the formation of the 1,2-bridging platinum(II) calixarene complex, which, upon treatment with 2 equiv of acyl chloride, reinstates the 1,3-disubstitution pattern in the calixarene moiety.

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PubMed2004

Stimuli-responsive supramolecular nanocapsules from amphiphilic calixarene assembly.

We synthesized tetrameric amphiphilic molecules based on a calixarene building block that self-assembles into a tunable and stable aggregation structure in aqueous solution. The amphiphilic calixarene molecules with a small hydrophilic part were observed to assemble into a vesicular structure that decreases significantly in diameter with only small increases in the hydrophilic chain length. Further increasing the chain length induced the collapse of the vesicles into spherical micelles. Remarkably, the vesicles were also observed to transform into small globular micelles at lower pH, which can be used to trigger the release of the encapsulated hydrophilic guest molecules.

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PubMed2001

Spirodienone derivatives of a spherand-type calixarene.

Oxidation of the spherand-type calixarene 4 with 1 or 2 equiv of phenyltrimethylammonium tribromide/base afforded mono- and bis(spirodienone) derivatives (8b and 9, respectively). The spirodienone groups are derived from the oxidation of two phenols connected by a common methylene group. NOESY data indicated that 9 possesses a "head to tail" arrangement of the spirodienone groups. Oxidation of 4 with 3 equiv of the oxidizing reagent afforded two tris(spirodienone) calixarene derivatives 11 and 10 with C(1) and C(3) symmetries, respectively. The same tris(spirodienone) products were obtained by oxidation of 9 with I(2)/aq KOH. Tris(spirodienone) 11 displayed NOE cross-peaks in the NOESY NMR spectrum consistent with a nonalternant disposition of carbonyl and ether groups. Upon heating 10 and 11 isomerize in the solid state and in solution. The major component in the equilibration mixtures is 11, indicating that this is the thermodynamically more stable tris(spirodienone) isomer.

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