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PubMed2004

Lanthanide crown ether complexes of p-sulfonatocalix[5]arene.

Two types of arrays are formed in water involving aza-crown ethers, p-sulfonatocalix[5]arene and europium(III) ions. One is a co-ordination polymer connecting calixarenes, sodium ions and lanthanide ions based on "ferris wheel" moieties incorporating aza-18-crown-6 and sodium ions. The second structure is a host-guest arrangement with di-protonated diaza-18-crown-6 in the cavity of the calixarenes as part of secondary coordination spheres of aquated europium(iii) ions.

Journal Article↗
PubMed2006

Synthesis, crystal structure and reactivity of uranium(IV) complexes with p-tert-butylcalix[4]arene ligands.

Reactions of UCl4 with 25,27-dimethoxy-5,11,17,23-tetra-tert-butylcalix[4]arene (H2Me2calix) in THF or pyridine at 80 degrees C gave [UCl2(Me2calix)L2] [L = THF (1) or pyridine (2)]. Similar treatment of U(acac)(4) (acac = MeCOCHCOMe) with H2Me2calix in THF or pyridine afforded [U(acac)2(Me2calix)] (3). The bis-calixarene compound [U(Me2calix)(H2calix)] (4) was obtained by reaction of U(OTf)4 or U(OTf)3 with H2Me2calix in pyridine at 110 degrees C. Treatment of UCl4 with H2Me2calix in pyridine at 110 degrees C gave [Mepy][UCl2(Hcalix)(py)2] (5) resulting from demethylation and acid cleavage of the methoxy groups of the calixarene ligand of 2. Adventitious traces of air were responsible for the formation of [Hpy][Mepy]4[{UCl(calix)}3(mu3-O)][UCl6] (6) during the reaction of UCl4 and H2Me2calix, and of [{U(Me2calix)(mu3-O)LiCl(THF)}2] (7) during the reaction of 2 with tBuLi. The X-ray crystal structures of 1.2THF, 2.2py, 3.0.25L (L = THF and py), 4.2py, 5, 6.3py and 7.THF have been determined.

Journal Article↗
PubMed2006

Phosphorus-phosphorus coupling in a diphosphine with a ten bond P...P separation.

The large, unsymmetrical diphosphine 5,11,17,23-tetra-tert-butyl-25,26-bis(diphenylphosphinomethoxy)-27(or 28)-benzoyloxy-28(or 27)-hydroxycalix[4]arene, in which the phosphorus atoms are separated by ten bonds, was prepared by monobenzoylation of 5,11,17,23-tetra-tert-butyl-25,26-bis(diphenylphosphinoylmethoxy)-27,28-bis(hydroxy)calix[4]arene, followed by reduction with phenyl silane. Its molecular structure has been determined by X-ray crystallography. In the solid state, the phosphorus atoms are separated by 5.333(1) A. NMR investigations reveal an unexpected "through-space"J(PP') coupling constant of 8.0 Hz and also show that, in solution, the calixarene is conformationally mobile, the phenoxy ring flipping rapidly through the calixarene annulus. The spatial proximity of the two phosphorus atoms was further demonstrated by the ease of obtaining the cis-chelate complex [Pd(eta3-C3H4Me)(THF)2]BF4 (THF = tetrahydrofuran).

Journal Article↗
PubMed2006

Pyrene-p-tert-butylcalixarenes inclusion complexes formation: a surface photochemistry study.

Diffuse reflectance and luminescence techniques were used to study the photophysics and photochemistry of pyrene within p-tert-butylcalix[n]arenes with n = 4, 6, and 8, and to study their ability to form inclusion complexes in heterogeneous media. Evidences for inclusion complex formation were found for the three hosts under study. Ground state diffuse reflectance results have shown the formation of ground state dimers of pyrene inside the cavity of calix[6]arene and calix[8]arene, with this feature much more evident for calix[6]arene. For calix[4]arene, only a monomer fits inside the cavity and the presence of pyrene microcrystals outside the cavity was detected. A luminescence lifetime distribution analysis was performed, revealing the presence of prompt emissions from the pyrene microcrystals outside the cavity in the case of calix[4]arene and from the constrained dimers inside the cavities of calix[6]arene and calix[8]arene. Transient absorption results have shown the presence of pyrene radical cation and also of trapped electrons for the three hosts under study. The formation of the phenoxyl radical of the calixarene following the laser pulsed excitation of pyrene at 355 nm is increased for calix[6]arene and calix[8]arene. This feature is particularly relevant for calix[6]arene, suggesting a very favourable situation for the hydrogen atom abstraction to occur. The analysis of the degradation products revealed the presence of hydroxypyrene as a major photodegradation product for the three hosts. Dihydro-hydroxypyrene was also formed in the case of calix[6]arene and calix[8]arene. The formation of the calixarene's phenoxyl radical and subsequent hydrogen abstraction is consistent with the formation of dihydro-dihydroxypyrene.

Journal Article↗
PubMed2006

Calculation of the absolute thermodynamic properties of association of host-guest systems from the intermolecular potential of mean force.

The authors report calculations of the intermolecular potential of mean force (PMF) in the case of the host-guest interaction. The host-guest system is defined by a water soluble calixarene and a cation. With an organic cation such as the tetramethylammonium cation, the calixarene forms an insertion complex, whereas with the Lanthane cation, the supramolecular assembly is an outer-sphere complex. The authors apply a modified free energy perturbation method and the force constraint technique to establish the PMF profiles as a function of the separation distance between the host and guest. They use the PMF profile for the calculation of the absolute thermodynamic properties of association that they compare to the experimental values previously determined. They finish by giving some structural features of the insertion and outer-sphere complexes at the Gibbs free energy minimum.

Computer Simulation↗
PubMedDate not supplied

Synthesis and characterization of new chiral calix[4]arenes.

The unique chiral calixarenes were successfully synthesized by the following two methods: the Williamson ether synthesis and a stepwise ether cleavage with a mild Lewis acid. The high regioselectivity is recognized by the latter stepwise method. The ionophores having oligoethylene glycol unit efficiently extracted larger alkali metal ions like K+, Rb+, and Cs+ than smaller ones like Li+ and Na+. Their ion selectivity apparently changed by the chain length of crown ether. All racemates obtained could be resolved to each enantiomer by HPLC using a chiral column. The calixarenes with planar chirality recognized the chirality of guest molecules. Thus, the (-)-receptor resolved strongly forms 1:1 complex with (R)-(+)-alpha-phenylethylammonium picrate.

Journal Article↗
PubMed2003

Investigation of host-guest stability constants of calix[n]arenes complexes with aromatic molecules by RP-HPLC method.

Under reversed-phase high-performance liquid chromatographic conditions [Spherisorb ODS 1 stationary phase, UV detection at 254 nm, and acetonitrile-dichloromethane-acetic acid-methyl-tert-butylether (84.6/4.5/0.9/10, v/v/v/v) as the mobile phase], adding p-tert-butylcalix[8] (10(-5)-3.10(-5))-[12]arenes (10(-5)-4.10(-5) mol/L) to the mobile phase leads to decreased sorption of aromatic solutes on the surface of the sorbent because of the formation of host-guest inclusion complexes between the calixarenes and the aromatic molecules. Stability constants of the complexes (781-9338M(-1)) are determined from the relationship between the solute capacity factors and the calixarene concentration in the mobile phase.

Journal Article↗
PubMed2001

A 1:1:1 chloroform/tetrahydrofuran solvate of p-tert-butyltetrahomodioxacalix[4]arene.

The title compound, 7,13,21,27-tetra-tert-butyl-3,17-dioxapentacyclo[23.3.1.1(5,9).1(11,15).1(9,23)]ditriaconta-1(29),5,7,9(30),11(31),12,14,19(32),20,22,25,27-dodecaene-29,30,31,32-tetraol, crystallizes as a solvate with one molecule of chloroform and one molecule of tetrahydrofuran, C46H60O6.CHCl3).C4H8O. The calixarene assumes a cone-like conformation stabilized by intramolecular hydrogen bonds involving both phenolic and ether O atoms. The two solvent molecules are located in each of the two half-cone cavities of the calixarene.

Journal Article↗
PubMed1998

Protein surface recognition by synthetic agents: design and structural requirements of a family of artificial receptors that bind to cytochrome c.

The design, synthesis, and evaluation of a novel series of receptors for protein surface recognition are described. The design of these agents is based around the attachment of four constrained peptide loops onto a central calix[4]arene scaffold. This arrangement mimics the role of the hypervariable loops in antibody combining regions and defines a large surface area for binding to a complementary region of the exterior of a target protein. Using affinity and gel filtration chromatographies we show that one particular receptor binds strongly to the surface of cytochrome c. The site of binding is presumably close to the heme edge region, which contains several charged lysine residues. This is supported by the observation that the receptor inhibits the reduction of Fe(III) cytochrome c to its Fe(II) form. We also show that binding is strongly dependent on the nature of the substituents on the lower rim of the calixarene. The nmr and computational studies suggest that this effect may be due to conformational differences among the differently substituted receptors.

Animals↗
PubMed2006

Noncovalent synthesis in aqueous solution and spectroscopic characterization of multi-porphyrin complexes.

The interactions of the tetracationic meso-tetrakis(N-methyl-4-pyridyl)porphyrin (H(2)TMPyP) and its metallo derivatives (MTMPyP) (where M=copper(II), zinc(II), and gold(III) with the octa-anionic form (at neutral pH) of 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)calix[4]arene (C(4)TsTc) lead to a series of complex species whose stoichiometry and porphyrin sequence can be easily tuned. Crystallographic, spectroscopic, and diffusion NMR studies converge towards a common picture in which a central 1:4 porphyrin/calixarene unit serves as a template for the formation of more complex species. These species arise by successive, stepwise addition of single porphyrin molecules above and below the plane of the 1:4 central core to ultimately give a 7:4 complex. Noticeably, the stoichiometry of the various complex species corresponds to the actual concentration ratio of porphyrins and calixarenes in solution allowing the stoichiometry of these species to be easily tuned. This behavior and the remarkable stability of these species allow homo-porphyrin and hetero-(metallo)porphyrin species to be formed with control of not only the stoichiometry but also the sequence of the porphyrin array. The flexibility and ease of this approach permit, in principle, the design and synthesis of porphyrin arrays for predetermined purposes. For example, we have shown that it is very easy to design and obtain mixed porphyrin species in which a foreseen photoinduced electron-transfer is indeed observed.

Calixarenes↗
PubMed2003

Novel cinchona carbamate selectors with complementary enantioseparation characteristics for N-acylated amino acids.

The synthesis and chromatographic evaluation of the enantiomer separation capabilities of covalently immobilized calix[4]arene-cinchona carbamate hybrid type receptors derived from quinine (QN) and its corresponding C9-epimer (eQN) in different solvents are reported. The receptors display complementary enantiomer separation profiles in terms of elution order, chiral substrate specificity, and mobile phase characteristics, indicating the existence of two distinct chiral recognition mechanisms. The QN-derived receptor binds the (S)-enantiomers of N-acylated amino acids more strongly, shows preferential recognition of open-chained amino acids, and superior enantioselectivity in polar media such as methanol/acetic acid. In contrast, the eQN congener preferentially recognizes the corresponding (R)-enantiomers, displays good enantioselectivity (alpha up to 1.74) for cyclic amino acids, and enhanced stereodiscriminating properties in apolar mobile phases, e.g., chloroform/acetic acid. A comparison of the enantiomer separation profiles with those of the corresponding QN and eQN tert-butyl carbamate congeners indicates no significant level of cooperativity between the calix[4]arene module and the cinchona units in terms of overall chiral recognition, most probably as a consequence of residual conformational flexibility of the calixarene module and the carbamate linkage.

Amino Acids↗
PubMed2005

Band intensity in the IR spectra and conformations of calix[4]arene and thiacalix[4]arene.

The experimental IR and Far IR spectra of the calix[4]arene, p-tert-butylcalix[4]arene, thialcalix[4]arene and p-tert-butylthiacalix[4]arene were examined at different temperatures and interpreted. The band frequencies and intensities in the IR spectra of the calix[4]arene and thialcalix[4]arene were calculated. The absorption curves of the four possible calix[4]arene conformations: cone, partial cone, 1,2- and 1,3-alternate were computed. The bands characteristic for each conformation are defined and assigned. The obtained spectra-structure correlation can be used for the characteristic of calixarenes conformation.

Calixarenes↗
PubMed2005

The hydrogen bonding and conformations of p-tert-butylcalix[4]arene as studied by IR spectroscopy and by DFT calculations.

IR and far IR spectra of p-tert-butylcalix[4]arene were recorded at various temperatures between 16 and 180 degrees C and spectra of solutions and crystalline solids were obtained. Ab initio density functional calculations gave vibrational frequencies and infrared intensities for four conformers: cone, partial cone, 1,2- and 1,3-alternate. Complete assignments were made for experimental IR spectra of the cone conformer. The bands characteristic for each conformation were defined. It was revealed that O--H stretching low-frequency shift Deltanu in the cone conformation exceeds Deltanu shifts for other conformers. The effect was stipulated by a cooperative interaction of cyclic hydrogen bonds. The obtained spectra-structure correlation can be used for characteristic of calixarenes conformation.

Calixarenes↗
PubMed2002

Study on the molecular recognitions of calix[n]arenes to 2,3-diaminonaphthalene by using fluorometric technique.

The molecular recognition properties of calixarenes to 2,3-diaminonaphthalene (DAN) were investigated. We found that the fluorescence emission of DAN has a blue shift after p-sulfonic sodium calix[4]arece (SSCA) was added to DAN. The proposed mechanism of the molecular recognition between SSCA and DAN indicates that DAN goes into the cavity of SSCA with the help of the hydrogen bonding between the amino group of DAN and sulphonyl group of SSCA. The inclusion ratios and inclusion constants of the host-guest complexes are determined by using the deduced equations.

2-Naphthylamine↗
PubMed2003

Selective complex formation of some chromogenic calix[4]arene derivatives detected by Fourier transform infrared spectroscopy 1. Solution experiments.

A calix[4]arene derivative containing ethoxycarbonylmethoxy groups in the coordination sphere and an iminopyridinium indicator group was studied by FT-IR spectroscopy in acetonitrile solution. The characteristic changes of v(C=O) stretching vibration offered an opportunity for the improvement on selectivity of the ion recognition process of this ligand. The shift of the carbonyl stretching vibration band depended on complex formation as well as on the equilibrium constants of complex formation. In the case of sodium complex, a well-defined isobestic point was detected in the v(C=O) region while altering the sodium concentration. The affinity of thallium(III) to form complex with calixarene 1 was found comparable with those of lithium, sodium or calcium. The complex was found to be an M2L type supramolecule, whereas one molecule of triethylamine was necessary for the formation of each complex.

Acetonitriles↗
PubMed2003

Peptido- and glycocalixarenes: playing with hydrogen bonds around hydrophobic cavities.

This Account reviews the synthesis, conformations, and supramolecular properties of calixarenes endowed with alpha-amino acids or peptides (Peptidocalixarenes) and carbohydrate units (Glycocalixarenes), with a major emphasis on calix[4]arenes functionalized on the aromatic nuclei (upper or wide rim). Most properties of N-linked peptidocalix[4]arenes are found to be quite different from those of the corresponding C-linked derivatives. An interesting example is the tendency of C-linked peptidocalix[4]arenes to form self-assembled nanotubes in the solid state. In several cases the hydrogen bonding donor and acceptor groups of the amino acid residues and the cavity of cone calix[4]arenes act cooperatively in guest binding in nonpolar solvents but not in water, where hydrophobic interactions dominate. Upper-rim bridged peptidocalix[4]arenes act as vancomycin mimics being able to bind d-alanyl-d-alanine (d-Ala-d-Ala) residues. Glycocalix[4]arenes show the phenomenon of multivalency in their binding to specific lectins, and those bearing thiourea spacers between the calix[4]arene scaffold and the sugar units are able to bind aromatic carboxylates and phosphates, making them attractive as novel site specific drug delivery systems.

Alanine↗
PubMedDate not supplied

Synthesis and characterization of immunogens based on calix[4]arene-crown-6 for the generation of antibodies directed towards cesium ions.

With the aim of generating antibodies directed towards cesium, a calix[4]arene-crown-6 in the 1,3-alternate conformation bearing an N-hydroxysuccinimide function was synthesized. The calixarene was coupled to bovine serum albumin using different calixarene/protein ratios, and cesium was loaded. Conjugates were characterized using trinitrobenzenesulfonic acid derivatization, matrix assisted laser desorption ionisation-mass spectrometry (MALDI-TOF-MS), and inductively coupled plasma-mass spectrometry (ICP-MS). Targeted lysines were determined after enzymatic cleavage followed by MALDI-TOF-MS, and a progressive targeting related to lysines accessibility was observed.

Animals↗
PubMedDate not supplied

Conjugation, immunoreactivity, and immunogenicity of calix[4]arenes; model study to potential calix[4]arene-based Ac3+ chelators.

For the development of calix[4]arene-based radiotherapeutic agents, the conjugation to biomolecules and immunogenicity in mice of potential 225Ac3+-chelating calix[4]arenes were studied. A calix[4]arene triethyl ester isothiocyanate and a bis(calix[4]arene) hexacarboxylic acid, containing a masked thiol functionality, were used in conjugation experiments to a mouse monoclonal antibody and serum albumins. All characterization techniques indicate that only the calix[4]arene carboxylic acid is successfully conjugated to the biomolecules. The immunoreactivity of the conjugates is not impaired when up to 6 equiv of calixarene are bound to the monoclonal antibody. Animal tests indicated that the immunogenicity toward the calix[4]arene is strongly influenced by the nature of the carrier, the dosage, and the injection method. No immune response occurred when a homologous carrier was used or when a heterologous carrier was applied at a dosage of 10 microg per immunization via intravenous injection. Under all other conditions, the presence of antibodies directed against the calix[4]arene was demonstrated. Thus, for the application in radioimmunotherapy, the conjugation of a calix[4]arene to a humanized antibody will probably not lead to an immune response, and the immunoreactivity will not be disturbed.

Actinium↗