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PubMed2001

Protein-calixarene interactions: complexation of Bovine Serum Albumin by sulfonatocalix[n]arenes.

The complexation of Bovine Serum Albumin with sulfonatocalix[n]arenes has been demonstrated by means of electrospray mass spectrometry, dynamic light scattering and atomic force microscopy; with sulfonatocalix[4]arene one strong and two weaker binding sites are detected; the effects on the structure of thin films formed by surface deposition of BSA show that the sulfonatocalix[n]arenes act to reticulate the films and produce essentially planar systems.

Animals↗
PubMed2006

Sterically crowded azulene-based dication salts as novel guests: synthesis and complexation studies with crown ethers and calixarenes in solution and in the gas phase.

The 1,4-bis(3-guaiazulenylmethylium)benzene and 1,4-bis[1-(4,6,8-trimethylazulenylmethylium)]benzene dication salts were synthesized via an acid-catalyzed condensation/dehydration protocol with guaiazulene-terephthalaldehyde (2 : 1 ratio), and 4,6,8-trimethylazulene-terephthalaldehyde (2 : 1 ratio) respectively in one-pot processes. A similar condensation reaction with the parent azulene led to an insoluble oligomer that was shown by MALDI-TOF-MS to contain 1,4-bis[(diazulenyl)methylium]benzene as a repeating unit. Dication salts and were fully characterized by 2D NMR and NOE techniques and by electrospray-MS (ES-MS) and MALDI-TOF-MS. NMR studies confirm that the dications are best represented as bis-tropylium species. A delicate balance of electronic (inductive stabilization) and steric influence of the alkyl groups on the seven-membered ring seems to influence the chemo-/regioselectivity of the co-condensation process. NMR titration and T(1) measurements established that, despite its highly crowded structure, dication forms host-guest HG complexes with dibenzo-30-crown-10 (DB30C10) and dibenzo-24-crown-8 (DB24C8) in solution, but fails to complex with the smaller dibenzo-18-crown-6 (DB18C6). The corresponding HG cation-molecule cluster ions were also detected in the gas phase by ES-MS, showing the formation of both dication-crown 1 : 1 and 1 : 2 complexes. Similar complexation of dication salt with DB30C10 was observed via NMR titration and T(1) measurements in solution and by ES-MS in the gas phase. Although solution complexation studies (NMR titration) did not indicate stable complex formation between and p-tert-butyl-methoxycalix[8]arene, their [HG](2+) and [H(2)G](2+) clusters were detectable by ES-MS. Solution decomplexation experiments (HG(2+) --> H + G(2+)) were performed on -crown complex by addition of DMSO, acetone, silver tosylate, and tropylium cation salt. Complexation of with DB30C10 was also studied by microcalorimetric titration.

Calixarenes↗
PubMed2005

Potassium-selective membrane electrodes based on macrocyclic metacyclophanes analogous to calixarenes.

The tetrabutyl ester derived from 9,16,25,32-tetrahydroxy[3.1.3.1]metacyclophane was an excellent ionophore for constructing a K+-selective membrane electrode. This ionophore exhibited a much higher selectivity toward K+ than the structurally similar potassium ionophore IV commercially available from Fluka. In particular, the interference from organic ammonium ions decreased remarkably. Potassium ionophore IV possessed oxygen atoms in the ring structure, while the present ionophore changed the oxygen atoms to carbon atoms. Thus, the removal of oxygen atoms in ring constituents of the metacyclophane acted to reduce the interaction with the NH3+ group of organic ammonium ions. The size of the cavity of the present ionophore was between those of calix[4]arene and calix[6]arene derivatives, which act as Na+ and Cs+ ionophores, respectively, demonstrating that the ability to recognize alkali metal cations was strongly cavity size-dependent. The present K+-selective electrode had less interference from Rb+ and Cs+ than an electrode constructed using valinomycin, but suffered greater interference from Na+.

Calixarenes↗
PubMed2000

Rigidified calixarenes bearing four carbamoylmethylphosphineoxide or carbamoylmethylphosphoryl functions at the wide rim

Conformationally rigidified tetraCMPO derivatives have been prepared from calix[4]arene bis(crown ether) 4a in which adjacent oxygens are bridged at the narrow rim by two diethylene glycol links. Acylation of the tetraamine 4c with the CMPO-active ester 5b gave the tetraphosphine oxide 6a, while the tetraphosphinate 6b and the tetraphosphonate 6c were obtained by Arbuzov reaction of tetrabromoacetamido derivative 7 with PhP(OEt)2 or P(OEt)3. The extraction ability of these CMPO derivatives was checked for selected lanthanides and actinides and compared with the analogous compounds 1b, 10b and 10d derived from calix[4]arene tetrapentyl ether. All rigidified bis(crown ether) ligands are more effective extractants than their pentyl ether counterparts and require only 1/10 of the concentration (cL= 10 4M) to obtain the same distribution coefficients, while with CMPO itself a 2,000-fold concentration is necessary. This could be a consequence of a better preorganisation of the ligating functions owing to the rigidity which on the other hand did not change the observed selectivity for americium (DAm/DEu=9-19) and for light lanthanides over heavy ones. NMR relaxivity titration curves show that the complex of Gd3+ with ligand 6a is highly oligomerised in anhydrous acetonitrile over a large range of ligand:metal concentration ratios. Nuclear magnetic relaxation dispersion (NMRD) profiles also showed that large oligomers were formed, and their mean tumbling times were deduced from the Solomon-Bloembergen-Morgan equations. The NMR spectra of dia- and paramagnetic lanthanide complexes with 6a agreed with the presence of two conformers with an elongated calix[4]arene skeleton in which the distances between opposite methylene groups are different. Contrary to what was observed with ligand 2a, the addition of nitrate ions does not labilize the metal complexes, presumably because of the rigidification effect of the ether bridges. Single-crystal X-ray structures were obtained for the active ester 5b and for diphenylphosphorylacetic acid 5a.

Journal Article↗
PubMed2001

Calixarene--poly(dithiophene)-based chemically modified electrodes.

The stepwise synthesis of cone and partial cone 1,3-bridged n-propoxy-calix[4]crown ethers ("monomers" 2 and 3) with an electropolymerizable 2,2'-dithiophene-3-yl-hexylene functionality at the lower rim, is described. The potential of 2 and 3 as sensing agents for alkali metal ions was investigated by 1H NMR titration experiments with NaSCN and KSCN. The results obtained have confirmed that the presence of the heterocyclic subunit does not affect the well-known size-selectivity observed with calix[4]crowns. Monomers 2 and 3 were electropolymerized (Pt as a working electrode, CH2Cl2/CH3CN, Bu4NPF6) to produce the title chemically modified electrodes (CMEs). After coating with a PVC membrane containing a lipophylic cation exchanger, CMEs based on calix[4]-crown-5 2b (cone) and 3b (partial cone) were tested for the potentiometric recognition of alkali metal ions in aqueous solution. In agreement with NMR titration studies, a satisfactory potentiometric response in terms of K+/Na+ selectivity was obtained only with CME 2b (pK(K/Na) 1.51). The amperometric responses of PVC-uncoated CMEs were studied by cyclic voltammetry (CV) experiments in CH3CN solution. High Na- selectivity was found with the CME based on partial cone calix[4]crown-4 3a, and frequency response analysis (FRA) measurements support this finding.

Journal Article↗
PubMed2003

Synthesis and structural analysis of the polymetallated alkali calixarenes [M4(p-tert-butylcalix[4]arene-4H)(thf)x]2.n THF (M=Li, K; n=6 or 1; x=4 or 5) and [Li2(p-tert-butylcalix[4]arene-2H)(H2O)(mu-H2O)(thf)].3 THF.

To study the structures and reactivities of alkali metallated intermediates of calix[4]arenes, three compounds were isolated: [Li(4)(p-tert-butylcalix[4]arene-4H)(thf)(4)](2).6 THF (1), [Li(2)(p-tert-butylcalix[4]arene-2H)(H(2)O)(mu-H(2)O)(thf)].3 THF (2), and [K(4)(p-tert-butylcalix[4]arene-4H)(thf)(5)](2).THF (3). The structure of 1 is shown to be dependent on the coordinating solvent. Partial hydrolysis of 1 leads to the formation of 2. The potassium compound 3 features a different structure to that of 1, due to a higher coordination number as well as stronger cation-pi-bonding interactions.

Journal Article↗
PubMed2006

Calixarenes as hosts for ammonium cations: a quantum chemical study and mass-spectrometric investigations.

Host-guest complexes of tetramethylcavitand with different ammonium cations were investigated by using a quantum chemical method at the density functional level (BP86, B3 LYP). The NH4+ cation is strongly bound to the host. Increasing methyl substitution at the cation decreases its inclination towards the complex formation. The calculated data are in line with results from electrospray ionization mass spectrometry (ESI-MS) experiments. They reveal stable aggregates only for the NH4+ cation and for the primary alkylammonium cations.

Journal Article↗
PubMed2004

Solvent extraction and stripping of silver ions in room-temperature ionic liquids containing calixarenes.

We found that a calix[4]arene-bearing pyridine is soluble in a typical room-temperature ionic liquid (RTIL), 1-alkyl-3-methylimidazolium hexafluorophosphate. Pyridinocalix[4]arene showed a high extraction ability and selectivity for silver ions. The extraction performance of the calix[4]arene was greatly enhanced by dissolution in RTILs compared to in chloroform. In a competitive extraction test using five different metal ions (Ag+, Cu2+, Zn2+, Co2+, Ni2+), only silver ions were transferred by the calix[4]arene from the aqueous feed phase into the RTILs, through a cation-exchange mechanism. The pyridinocalix[4]arene was found to form a stable 1:1 complex with silver ions, both by slope analysis and by Job's method. Since it is easy to strip silver ions from RTILs by controlling the aqueous-phase pH, the extraction performance of calix[4]arene in RTILs was maintained after five repeated uses.

Journal Article↗
PubMed2006

Mono- and dinuclear oxovanadium(V)calixarene complexes and their activity as oxidation catalysts.

The background of the investigation is constituted by reactive moieties and intermediates playing relevant roles on the surfaces of vanadiumoxide-based catalysts during the oxygenation/dehydrogenation of organic substrates. With the aim of modeling such species, a series of mono- and dinuclear charged and uncharged vanadium oxo complexes containing p-tert-butylated calix[4]arene and calix[8]arene ligands (denoted H4B and H8B' ', respectively, in the protonated forms) has been synthesized and characterized: PPh4[O=VB] ((PPh41), O=VB(OAc) (2), PPh4[O2V2HB' '] (3), and [mu-O(O=V(OMe))2B(Me2)] (4), where superscripts OAc and Me2 indicate that one or two protons of H4B are substituted by these residues, respectively. These compounds were analyzed both in solution and by means of single-crystal X-ray crystallography; it turned out that the crystal structures are retained on dissolution (2 changed only from the paco to the cone structure). In the case of 4, it could be shown that the bulk product consists of a mixture of two isomers (4t and 4c) differing in the relative positions of the vanadium-bound methoxy groups. Subsequently, all compounds were tested as catalysts for the oxidation of alcohols with O2. It turned out that the two dinuclear complexes efficiently catalyze the oxidation of 1-phenyl-1-propargyl alcohol and fluorenol; in addition, they even show some activity with respect to the oxidation of dihydroanthracene. This may hint to a higher activity of dinuclear sites on the surfaces of heterogeneous catalysts as well.

Journal Article↗
PubMed1998

Calixarenes Derivatized with Sulfur-Containing Functionalities as Selective Extractants for Heavy and Precious Metal Ions.

The calix[4]arenes 5,11,17,23-tert-butyl-25,26,27,28-(2-methylthioethoxy)calix[4]arene, 25,26,27,28-(2-methylthioethoxy)calix[4]arene, and 5,11,17,23-tert-butyl-25,26,27,28-(2-(2-thiophenecarboxy)ethoxy)calix[4]arene have been prepared. The structure of 25,26,27,28-(2-methylthioethoxy)calix[4]arene has been verified by X-ray crystallography. The crystals with the empirical formula C(40)H(48)O(4)S(4) are monoclinic C2/c with a = 20.428(2) Å, b = 10.581(1) Å, c = 20.445(2) Å, beta = 118.461(5) degrees, Z = 4. These calix[4]arenes are effective extractants for transferring heavy metal ions from aqueous solution into chloroform. The extraction of Sn(II), Hg(II), Ag(I), Pd(II), Au(III), MeHg(II), Pb(II) and Cd(II) into chloroform with these calix[4]arenes is compared with that performed with 5,11,17,23-tert-butyl-25,26,27,28-(2-N,N-dimethyldithiocarbamoylethoxy)calix[4]arene, 25,26,27,28-(2,N,N-dimethyldithiocarbamoylethoxy)calix[4]arene, and 5,11,17,23-tert-butyl-25,26,27,28-(2-mercaptoethoxy)calix[4]arene.

Journal Article↗