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PubMed2006

p-tert-Butylcalix[4]arene complexes of molybdenum and tungsten: reactivity of the calixarene methylene C-H bond and the facile migration of the metal around the phenolic rim of the calixarene.

p-tert-Butylcalix[4]arene, [CalixBut(OH)4], reacts with Mo(PMe3)6 and W(PMe3)4(eta2-CH2PMe2)H to yield compounds of composition {[CalixBut(OH)2(O)2]M(PMe3)3H2} which exhibit unprecedented use of a C-H bond of a calixarene methylene group as a binding functionality in the form of agostic and alkyl hydride derivatives. Thus, X-ray diffraction studies demonstrate that, in the solid state, the molybdenum complex [CalixBut(OH)2(O)2]Mo(PMe3)3H2 exists as an agostic derivative with a Mo...H-C interaction, whereas the tungsten complex exists as a metallated trihydride [Calix-HBut(OH)2(O)2]W(PMe3)3H3. Solution 1H NMR spectroscopic studies, however, provide evidence that [Calix-HBut(OH)2(O)2]W(PMe3)3H3 is in equilibrium with its agostic isomer [CalixBut(OH)2(O)2]W(PMe3)3H2. Dynamic NMR spectroscopy also indicates that the [M(PMe3)3H2] fragments of both the molybdenum and tungsten complexes [CalixBut(OH)2(O)2]M(PMe3)3H2 migrate rapidly around the phenolic rim of the calixarene on the NMR time scale, an observation that is in accord with incorporation of deuterium into the methylene endo positions upon treatment of the isomeric mixture of [CalixBut(OH)2(O)2]W(PMe3)3H2 and [Calix-HBut(OH)2(O)2]W(PMe3)3H3 with D2. Treatment of {[CalixBut(OH)2(O)2]W(PMe3)3H2} with Ph2C2 gives the alkylidene complex [CalixBut(O)4]W=C(Ph)Ar [Ar = PhCC(Ph)CH2Ph].

Journal Article↗

PubMed2004

A general and high yielding fragment coupling synthesis of heteroatom-bridged calixarenes and the unprecedented examples of calixarene cavity fine-tuned by bridging heteroatoms.

A number of aza- and/or oxo-bridged calix[2]arene[2]triazines have been synthesized through an unusually high yielding and efficient fragment coupling approach starting from cyanuric chloride and resorcinol, 3-aminophenol, m-phenylenediamine, and N,N'-dimethyl-m-phenylenediamine. These novel macrocycles, which belong to the next generation of calixarenes or cyclophanes, form a unique cavity that is resulted from two isolated benzene planes and two bis-heteroatom-conjugated triazine planes in a 1,3-alternate fashion. The nature of the bridging heteroatoms, i.e., combination of the electronic, conjugative, and steric effects of the nitrogen and oxygen atoms, strongly regulates the cavity size, generating a set of fine-tuned cavities in which the distance between two benzene rings at the upper rim ranges from 5.011 to 7.979 A. The multiple intermolecular hydrogen bond interactions among N,N'-dimethylated tetraazacalix[2]arene[2]triazines and among tetraazacalix[2]arene[2]triazines lead to the formation of infinite one-dimensional chain structure and two-dimensional zigzag layered structure, respectively, in the solid state. The ease of preparation and further chemical manipulations, and the readily tunable cavity structures render these aza- and/or oxo-bridged calix[2]arene[2]triazines the unique platforms in the study of supramolecular chemistry.

Journal Article↗

PubMed2000

Regioselective Monoalkylation of Calixarenes. Synthesis of Homodimer Calixarenes.

The selective monoalkylation at the smaller (lower) rim of the p-tert-butylcalix[4]- and -[6]arenes using bis(butyltin)oxide and different alkylating agents is described. The procedure is remarkable for the mild conditions used allowing an efficiently access to monoalkylated calixarene derivatives in moderate to good yields. Monoalkynylcalix[4]arene and monoalkynylcalix[6]arene have been synthetically exploited for the synthesis of bis-calix[n]arenes (n = 4, 6) with a diyne bridge by oxidative coupling of alkynes. In addition, intermolecular methathesis of the obtained monoalkenyl-calix[4]arene allowed the preparation of bis-calix[4]arene that are single bridged at the smaller (lower) rim with a 2-butenyl moiety.

Journal Article↗

PubMed2004

A new convergent strategy for the synthesis of calixarenes via a triple annulation of Fischer carbene complexes.

A new method for the synthesis of unsymmetrical calix[4]arenes is described which involves the reaction of a diyne with a bis-carbene complex of chromium. This synthesis of calixarenes is unique in that it involves the formation of two of the four benzene rings of the calixarene and the macrocyclic ring of the calixarene in the same step. Thus, two of the four benzene rings of the calixarene are identical, but the other two rings may each be different, giving a general method for the synthesis of calixarenes in which there are either two or three differently substituted benzene rings. This protocol gives access to a large family of unsymmetrical calixarenes by the proper choice of arene substitution in the starting diyne and the starting carbene complex. Nine examples are presented in which the yields in the key triple annulation step range from 22 to 41%. The overall yields of calixarenes from commercially available starting materials compare favorably with those from existing methods for the synthesis of unsymmetrical calix[4]arenes.

Alkynes↗

PubMedDate not supplied

[Effect of calixarene-phosphonic acid on Na+, K+-ATPase activity in plasma membranes of the smooth-muscle cells].

Effect of calix[4]arenes C-97, C-99, C-107, functionalized by fragments of alpha-hydroxy-phosphonic, alpha-aminophosphonic- and methylene-bisphosphonic acid on enzymatic activity of oubaine-sensitive Na+, K+-ATPase and oubaine-resistant basal Mg2+- ATPase (specific activity - 10.6 +/- 0.9 and 18.1 +/- 1.2 micromol Pi/h per 1 mg of protein, respectively; n = 7) was studied in experiments made on the suspension of myometrium cell plasma membranes treated by 0.1% solution of digitonin. It was found that calixarene-phosphonic acids in concentration of 100 microM inhibited enzymatic activity of Na+, K+-ATPase by 86-98% and did not practically affect activity of Mg2+-ATPase. These calixarenes were more efficient than oubaine in suppressing enzymatic activity of the sodium pump: in case of the effect of calixerenes the value of the appearence constant of inhibition I0.5 was < 0.1 microM. Calixarene-methylene-bisphosphonic acid (calixarene C-97; I0.5 =33 +/- 4 microM (n = 6) takes the most efficient inhibitory effect on Na+,K+-ATPase activity among the studied calixarenes. A phenomenon of negative cooperation: the Hill coefficient value etaH =0.1-0.5<1 is characteristic of both the inhibiting effect of calixarenes and oubaine. Reguliarities of calixarenes C-97 effect on enzymatic activity of Na+,K+-ATPase were studied. As it appeared its inhibiting effect cannot be caused by trivial factors - potentially possible binding of Mg ions by it and (or) this substance effect on Mg2+ interaction with ATP4- in the incubation medium. Calixerene C-97 does not also decrease the enzyme affinity for Mg ions or ATP. However this calixerenes decreases the affinity of Na+,K+-ATPase for Na ions (the value of activation constant K(Na+)) from 50 +/- 4 (control) to 76 +/- 6 microM in the control and under the effect of calixerene, respectively). A conclusion is made that calixerene C-97 is highly-efficient (with respect to oubaine) and selective (with respect to lack of its effect on basal Mg2+-ATPase) inhibitor of Na+,K+-ATPase of plasma membrane. In the practical aspect it may be used in concentration of 1-10 microM in biochemical membranology when testing and studying kinetic and catalytic properties of the sodium pump in case of such experimental model, as the plasma membrane fraction.

Animals↗

PubMed2006

Energetics of small molecule and water complexation in hydrophobic calixarene cavities.

Calixarenes grafted on silica are energetically uniform hosts that bind aromatic guests with 1:1 stoichiometry, as shown by binding energies that depend upon the calixarene upper rim composition but not on their grafted surface density (0.02-0.23 nm(-2)). These materials are unique in maintaining a hydrophilic silica surface, as probed by H2O physisorption measurements, while possessing a high density of hydrophobic binding sites that are orthogonal to the silica surface below them. The covalently enforced cone-shaped cavities and complete accessibility of these rigidly grafted calixarenes allow the first unambiguous measurements of the thermodynamics of guest interaction with the same calixarene cavities in aqueous solution and vapor phase. Similar to adsorption into nonpolar protein cavities, adsorption into these hydrophobic cavities from aqueous solution is enthalpy-driven, which is in contrast to entropy-driven adsorption into water-soluble hydrophobic hosts such as beta cyclodextrin. The adsorption thermodynamics of several substituted aromatics from vapor and liquid are compared by (i) describing guest chemical potentials relative to pure guest, which removes differences among guests because of aqueous solvation and van der Waals contacts in the pure condensed phase, and (ii) passivating residual guest binding sites on exposed silica, titrated by water during adsorption from aqueous solution, using inorganic salts before vapor adsorption. Adsorption isotherms depend only upon the saturation vapor pressure of each guest, indicating that guest binding from aqueous or vapor media is controlled by van der Waals contacts with hydrophobic calixarene cavities acting as covalently assembled condensation nuclei, without apparent contributions from CH-pi or other directional interactions. These data also provide the first direct quantification of free energies for interactions of water with the calixarene cavity interior. The calixarene-water interface is stabilized by approximately 20 kJ/mol relative to the water-vapor interface, indicating that water significantly competes with the aromatic guests for adsorption at these ostensibly hydrophobic cavities. This result is useful for understanding models of water interactions with other concave hydrophobic surfaces, including those commonly observed within proteins.

Journal Article↗

PubMed2004

Novel urea-linked cinchona-calixarene hybrid-type receptors for efficient chromatographic enantiomer separation of carbamate-protected cyclic amino acids.

Two novel diastereomeric cinchona-calixarene hybrid-type receptors (SOs) were synthesized by inter-linking 9-amino(9-deoxy)-quinine (AQN)/9-amino(9-deoxy)-epiquinine (eAQN) and a calix[4]arene scaffold via an urea functional unit. Silica-supported chiral stationary phases (CSPs) derived from these SOs revealed, for N-protected amino acids, complementary chiral recognition profiles in terms of elution order and substrate specificity. The AQN-derived CSP showed narrow-scoped enantioselectivity for open-chained amino acids bearing pi-acidic aromatic protecting groups, preferentially binding the (S)-enantiomers. In contrast, the eAQN congener exhibited broad chiral recognition capacity for open-chained as well as cyclic amino acids, and preferential binding of the (R)-enantiomers. Exceedingly strong retention due to nonenantioselective hydrophobic analyte-calixarene interactions observed with hydro-organic mobile phases could be largely suppressed with organic mobile phases containing small amounts of acetic acid as acidic modifier. With the eAQN-calixarene hybrid-type CSP particularly high levels of enantioselectivity could be achieved for tert-butoxycarbonyl (Boc)-, benzyloxycarbonyl (Z)- and fluorenylmethoxycarbonyl (Fmoc)-protected cyclic amino acids using chloroform as mobile phase, e.g. an enantioselectivty factor alpha >5.0 for Boc-proline. Increasing amounts of acetic acid compromised enantioselectivity, indicating the crucial contributions of hydrogen bonding to chiral recognition. Comparison of the performance characteristics of the urea-linked eAQN-calixarene hybrid-type CSP with those of structurally closely related mutants provided evidence for the active involvement of the urea and calixarene units in the chiral recognition process. The urea linker motif was shown to contribute to analyte binding via multiple hydrogen bonding interactions, while the calixarene module is believed to support stereodiscrimination by enhancing the shape complementarity of the SO binding site.

Amino Acids↗

PubMed2001

Complex formation analysis of water-soluble calixarenes by capillary zone electrophoresis.

The equilibria of complex formation reactions between various kinds of cations and anionic calixarenes in an aqueous solution were analyzed by capillary zone electrophoresis on the basis of the change in electrophoretic mobility of the calixarenes. The apparent electrophoretic mobility of the calixarenes decreased with increasing concentrations of alkali metal ions and quaternary ammonium ions. Equilibrium constants were determined by a non-liner least-squares analysis using the changes in apparent electrophoretic mobility. The complex formation constants obtained with alkali metal ions were in the order of 10(2.3) - 10(3.0), and those with quaternary ammonium ions were 10(2.9) - 10(4.2), providing less selectivity among them. The selectivity of the calixarene toward alkali metal and quaternary ammonium ions in aqueous solution involves flexible structure, and compensative interactions of electrostatic and hydrophobic interactions. From the results obtained in this work, the electrophoretic method has proved to be useful for analyzing the reactivity of anionic calixarene in aqueous solution.

Alkalies↗

PubMed2001

Photophysical properties and photoinduced electron transfer within host-guest complexes of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin with water-soluble calixarenes and cyclodextrins.

We report the formation of host-guest complexes between water-soluble calix[n]arene-p-tetrasulfonates (n = 4, 6, 8) or 2-hydroxypropyl-cyclodextrins (alpha-, beta-, gamma-) and the tetratosylate salt of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP). The binding constants ranging between 10(2) and 10(5) M-1 were calculated from the absorption and fluorescence changes. Calix[4]arene-p-tetrasulfonate has a high binding affinity and forms with TMPyP a 1:1 complex, whereas other calixarenes bind two molecules of TMPyP. Electrostatic attraction is the dominating binding mode. Binding to calixarenes leads to a considerable decrease of the quantum yields of the triplet and excited singlet states and to shortening of the singlet and triplet lifetimes of TMPyP. The quenching mechanism is attributed to electron transfer between calixarene phenolates and excited TMPyP. Photoinduced electron transfer within a novel supramolecular complex calixarene/TMPyP (electron donor)/methyl viologen (electron acceptor) has been proven by absorption and fluorescence measurements. Electrostatic attraction between the cationic donor and cationic acceptor, on the one hand, and the anionic host, on the other, overcomes the electrostatic repulsion forces. In contrast, the interaction of cyclodextrin with TMPyP is hydrophobic in nature and only slightly influences the photophysical properties of TMPyP. The different behavior of TMPyP bound to either of the hosts has been assigned to the specific effects of the dominant binding modes, viz. the electrostatic attraction for calixarenes and the hydrophobic interactions for inclusion complexes with cyclodextrins.

Calixarenes↗

PubMed2005

Structural and binding features of cofacial bis-porphyrins with calixarene spacers: pac-man porphyrins that can chew.

Based on the efficient combination of calixarene spacers and acetylenic porphyrin derivatives, a new generation of cofacial bis-porphyrins has been synthesized. The first crystal structure of a cofacial bis-porphyrin-calixarene conjugate is reported. Their unique architectural features, analogous to those of pac-man-type bis-porphyrins, allow these calixarene-porphyrin conjugates to adapt their shape to the size of bidentate guests, such as diazabicyclo[2.2.2]octane (dabco) and 1,4-pyrazine. The predefined, cofacial arrangement of the porphyrin moieties observed in the solid state and in solution results in extremely high affinities (in the range of 10(9) M(-1)) for these guests. The 1,3-alternate calixarene conformations afford "open-mouth" pac-man structures whose ability to bite on nitrogen bidentates depends on their functionalization. A cone conformer provides a much more flexible structure that exhibits the highest affinity for dabco and pyrazine.

Journal Article↗

PubMed2001

Extraannular fluorinated calixarenes: regiospecificity of the deoxofluorination reactions of bis(spirodienol) derivatives.

A new route for the partial displacement of OH groups of p-tert-butylcalixarene via spirodienol derivatives is described. NaBH(4) reduction of the bis(spirodienone) calixarene derivatives 2a-2c afforded the corresponding bis(spirodienols) 3a-3c in stereospecific fashion. (1)H NMR NOESY spectroscopy indicated that in the case of 2a, the reaction proceeds by attack at the exo face of the two carbonyls (the face located anti to the spiro C-O bond). The spirodienols readily revert to p-tert-butylcalix[4]arene when heated. The reaction of 3a with the deoxofluorinating agent DAST (Et(2)NSF(3)) afforded a mixture of extraannular substituted calixarenes possessing one or two fluoro-substituted dehydroxylated rings. The bisfluorinated calixarene 6a adopts in the crystal a conformation (1,3-alternate) similar to that adopted in solution by the di-dehydroxylated calixarene 6b. An experiment conducted with a selectively deuterated spirodienol derivative indicated that the deoxofluorination reaction involves regiospecific nucleophilic attack at the gamma position of the pentadienol subunit.

Journal Article↗

PubMed2003

Unprecedented selective ipso-nitration of calixarenes monitored by the O-substituents.

The electrophilic ipso-reactions of a tBu-calix[6]arene that presents alternate O-methyl and O-2-methylen-N-methyl-imidazolyl groups (1) at the small rim have been studied. Whereas 1 underwent per-sulfonation in sulfuric acid, it selectively reacted with nitric acid to yield a tris-nitro derivative. The ipso-nitration occurred regioselectively on the calixarene anisol units. The reaction has been studied with various tBu-calixarenes (2-11) presenting alternate anisol and phenol ether units. The regioselectivity of the process appeared to be correlated to the presence of a protonable site on the O-substituent. It is proposed that the corresponding protonated heteroatom (N for the amines, O for the amides and the carboxylic acid), situated in the gamma or epsilon position of the phenoxy moieties, deactivates the corresponding aromatic ring by removing electron density through intramolecular hydrogen bonding. The high control operated by the O-substituents at the small rim even allowed the selective ipso-nitration of partially detertiobutylated calixarene 1(H3). Hence, these findings open new routes to a wide range of nonsymmetrically substituted calixarenes at the large rim.

Journal Article↗

PubMed1996

Annelated Calixarenes Composed of Calix[4]arenes with Hydroxy Groups in the Endo and Exo Position.

Various phenol-derived calix[4]arenes (3) bearing four hydroxy groups in the exo position have been prepared by uncatalyzed condensation of suitable dimers or tetramers with formaldehyde in xylene in yields up to 44%. The tetra-tert-butyl compound (3a) has been shown by X-ray analysis to adopt a regular cone conformation (nearly identical in shape with the endo isomer) with two intramolecular O-H.O hydrogen bonds, while the corresponding dimer (6c) prefers a conformation (not possible in the calixarene) with two intramolecular O-H.pi(arene) interactions. Condensation of exo-calix[4]arenes 3f,g with free ortho positions (easily available by debutylation) with bisbromomethylated dimers gave annelated double (9) and triple (10) calixarenes consisting of endo- and exo-calix[4]arene substructures in yields up to 24% and 10%, respectively. Molecular dynamics calculations suggest that the exo-calixarene part in 9 is less mobile than the entirely flexible 3, while the endo-calixarene part shows a higher mobility than usual. A complete interconversion cone --> cone is impossible, however, which enables the construction of inherently chiral molecules.

Journal Article↗

PubMed2002

Separation of cis- and trans-isomers of thioxanthene and dibenz[b,e]oxepin derivatives on calixarene- and resorcinarene-bonded high-performance liquid chromatography stationary phases.

The chromatographic behavior of six calix[n]arene phases (n=4, 6, 8) and one calix[4]resorcinarene phase is described for the separation of cis- and trans-isomers of three thioxanthene (flupentixol, clopenthixol, chlorprothixene) and one benz[b,e]oxepin derivative (doxepin). The influences of two different organic modifiers (MeOH, MeCN) for the separation of the isomers on every column are described. Different selectivities of the stationary phases exist as a function of the ring size of the calixarenes and their substitution at the "upper rim" with p-tert.-butyl groups. Furthermore, the influence of free phenol groups on the resorcinarene phase is discussed. Relations between structural elements of the analytes and the retention behavior on the stationary phases are found. The selectivity of the calixarene and resorcinarene stationary phases is compared with a RP-C18 phase containing the same base silica. Advantages of the resorcinarene as well as of the calixarene columns exist for the separation of cis- and trans-isomers of three compounds dependent from the substitution in position 2 of the thioxanthenes, respectively the kind of the basic side chain of all substances.

Calixarenes↗

PubMed2005

MD simulations of the binding of alcohols and diols by a calixarene in water: connections between microscopic and macroscopic properties.

We report results of molecular dynamics (MD) simulations of the complexes of p-sulfonatocalix[4]arene with linear alcohols from ethanol to heptanol in water at 25 degrees C. We show that these complexes are of the inclusion type and are governed by van der Waals interactions between the calixarene cavity and the inserted alkyl chain of the alcohol. We establish a correlation between the experimental Delta(r)H degrees values and the number of atoms inserted into the calixarene cavity. We also focus on the desolvation of the host and guest to establish the importance, at the enthalpic level, of the formation of hydrogen bond bridges between the calixarene and the alcohol molecule. The fact that methanol is not complexed by p-sulfonatocalix[4]arene is explained by calculating the cost of the desolvation of the guest upon complexation. We complete this study by modeling the complexes formed with 1,4-butanediol and 1,5-pentanediol. To explain the difference between the thermodynamic properties for the binding of 1,4-butanediol and butanol, we examine the insertion rate and the solvation of each hydroxy group. We show a specific behavior of one of the two hydroxy groups at the structural and energetic levels.

Alcohols↗

PubMed2004

Synthesis and lectin binding ability of glycosamino acid-calixarenes exposing GlcNAc clusters.

Novel calix[4 or 8]arene-based glycoconjugates exposing terminal N-acetyl-D-glucosamine clusters have been synthesized using amino acid-calixarenes as building blocks. The obtained glycosamino acid-calixarenes 9b-14b have lectin-binding ability and amplified inhibitory effects on erythrocyte agglutination induced by wheat germ (Triticum vulgaris) agglutinin (WGA). The inhibitory ability is dependent on the presence of the spacer and on the shape and rigidity of the calixarene skeleton.

Acetylglucosamine↗

PubMed2004

Light-induced electron transfer in porphyrin-calixarene conjugates.

The fluorescence from a set of porphyrin-calixarene complexes is quenched upon addition of benzo-1,4-quinone (BQ) in fluid solution. In N,N-dimethylformamide solution, fluorescence quenching involves both static and dynamic interactions but there are no obvious differences between porphyrins with or without the appended calixarene. Under such conditions, the static quenching behaviour is attributed to pi-complexation between the reactants and it is concluded that the calixarene cavity does not bind BQ. An additional static component is apparent in dichloromethane solution. This latter effect involves partial fluorescence quenching, for which the intramolecular rate constant can be obtained by time-resolved fluorescence spectroscopy. The derived rate constants depend on molecular structure in a manner consistent with fluorescence quenching being due to electron transfer. In all cases, however, the dominant quenching step involves diffusional contact between the porphyrin nucleus and a non-bound molecule of BQ.

Benzoquinones↗

PubMed2006

Use of electrospray ionization mass spectrometry for the study of Ln(III) complexation and extraction speciation with calixarene-CMPO in the fuel partitioning concept.

The calixarene-bearing CMPO groups belong to a family of extracting agents recently developed for nuclear reprocessing. These molecules exhibit specific properties to separate actinides(III) from lanthanides(III) in nitric acid solution. Speciation of two distinct calixarene-CMPO (carbamoyl phosphine oxide), substituted either in the wide rim or in the narrow rim with lanthanides (La, Eu, Yb), was undertaken. The complexation behaviour in single phase or in liquid-liquid extraction was examined with two different electrospray spectrometer source geometries. The stoichiometries of the different complexes were reported and the selectivity of these calixarenes towards lanthanides was determined. The results obtained were concordant for the two spectrometers and confirm that electrospray mass spectrometry is a useful tool to study non-covalently bonded complexes.

Journal Article↗