Attempted synthesis of a meta-metalated calixarene.
ABSTRACT: An evidence for the formation of a rare meta-metalated inherently chiral calixarene is described. Our strategy involved using a mesoionic carbene to direct C-H activation, but proved to form an unexpectedly unstable intermediate that was identified through high-resolution mass spectrometry. On route to our target, a new optimized method to mononitrocalixarenes was developed, including optimized and high yielding transformations to azide and 1,2,3-triazole derivatives which may have application in other areas of research.
Project description:Lithiation and subsequent reaction with CO(2) was applied to calixarenes with different, equal or mixed, ether functions at the lower-rim site as well as tert-butylated or non-tert-butylated upper-rim positions. Whereas this reaction fails for symmetric calixarene ethers with alkoxy residues greater than methoxy, the carboxylation of mixed methoxy-propoxy calixarene ethers is possible. In connection with this, several new monobridge-substituted calixarenes were characterized with respect to their conformational behaviour in solution and the X-ray crystal structure of one key intermediate is taken into consideration.
Project description:Calixarenes constrained to 1,3-alternate conformation and functionalized at the upper rim with four and two nitronyl nitroxides have been synthesized, and characterized by X-ray crystallography, magnetic resonance (EPR and (1)H NMR) spectroscopy, and magnetic studies. Such calixarene tetraradicals and diradicals provide scaffolds for through-bond and through-space intramolecular exchange couplings.
Project description:In order to understand the still-poorly understood interplay between calixarene conformations and cation and anion recognition in multicomponent systems, the ion pair receptors 1 and 2 were synthesized. In solution and in the solid state, the calixarene subunit of receptor 1 adopts a cone conformation, while that of 2 interconverts between the cone and the partial cone conformation. These geometric features differ from previous systems where the calixarene moiety was locked in the 1,3-alternate conformation. A combination of 1H NMR spectroscopic analyses and single crystal X-ray diffraction studies reveal that receptor 1 binds the fluoride and the chloride anion via significantly different binding modes, displaying, for instance, 1?:?1 and 2?:?3 binding stoichiometries with CsF and CsCl, respectively. In the case of 2, the conformation of the calixarene constituent of 2 is highly dependent on the size and quantity of anions present. For example, upon treatment of 2 with the fluoride anion (as both the TBA+ and Cs+ salts), the calixarene unit coexists as cone and partial cone conformers that are inter-convertible. In the presence of excess CsF, the aromatic rings of the calixarene subunit becomes locked in the pinched cone conformation with the result that an ion pair-mediated coordination polymer is formed. In the presence of excess CsCl, the calixarene unit of 2 adopts only the partial cone conformation stabilized by aryl CH-anion hydrogen bonding interactions. The present systems constitute a rare set of related receptors wherein the effects of conformational changes are so tightly coupled with ion recognition.
Project description:The synthesis of the triple-calixarene derivative 6 in which three calixarene macrocycles are linked to a central 1,3,5-trimethylbenzene moiety is reported. Derivative 6 is able to give multiple-threading processes in the presence of dialkylammonium axles. The formation of pseudorotaxane, pseudorotaxane, and pseudorotaxane by threading one, two, and three, respectively, calix-wheels of 6 has been studied by 1D and 2D NMR, DOSY, and ESI-FT-ICR MS/MS experiments. The use of a directional alkylbenzylammonium axle led to the stereoselective formation of endo-alkyl pseudo[n]rotaxane stereoisomers.
Project description:Here, we present an electrochemical sensor based on gold electrodes modified with calixarene functionalized with carboxypiperidino groups at the upper rim. It has been demonstrated that these groups are involved in a complex formation with dopamine (DA) on the surface of gold electrodes. The supramolecular complex calixarene-DA created on the gold electrode surface has been characterized electrochemically and the measuring conditions have been optimized. The presented sensor displayed a detection limit in the pM range. The DA determination was performed successfully in the presence of ascorbic acid, uric acid and selected neurotransmitters.
Project description:Inhibition of H3N2 influenza PA endonuclease activity by a panel of anionic calix[n]arenes and ?-cyclodextrin sulfate has been studied. The joint experimental and theoretical results reveal that the larger, more flexible and highly water-soluble sulfonato-calix[n]arenes have high inhibitory activity, with para-sulfonato-calixarene, SC8, having an IC50 value of 6.4 ?M. Molecular docking calculations show the SC8 can interact at both the polyanion binding site and also the catalytic site of H3N2 influenza PA endonuclease.
Project description:Several lower-rim perfluoroalkylated (fluorous) calixarenes have been synthesized by O-alkylation of the parent calixarene. The compounds are formed in the cone conformation. They are soluble in several fluorous solvents and show promise for use in sensing, selective extractions and other applications.
Project description:In the title compound, C(56)H(44)Br(4)O(4), the calixarene unit displays the 1,2-alternate conformation with crystallograpically imposed inversion symmetry. The four phen-oxy rings of the calixarene unit are twisted about the mean plane defined by the four methyl-ene C atoms bridging the benzene rings, with dihedral angles of 46.73?(6) and 66.11?(5)°. The dihedral angle between adjacent phen-oxy rings is 74.75?(7)°. The two pendant bromo-phenyl rings on the same side of the calixarene unit are nearly perpendicular to each other, with a dihedral angle of 72.85?(10)° due to an intra-molecular C-H?? inter-action. In the crystal, a Br?Br contact of 3.6350?(5)?Å, an inter-molecular C-H?Br hydrogen bond and an inter-molecular C-H?? inter-action are observed.
Project description:Self-aggregating calixarenes carrying four DOTA ligands on the upper rim for stable complexation of paramagnetic GdIII-ions have already been proposed as MRI probes. In this work, we investigate the luminescence properties of TbIII-DOTA-calixarene-4OPr containing four propyl-groups and compare them with those of the analog substituted with a phthalimide chromophore (TbIII-DOTA-calixarene-3OPr-OPhth). We show that, given its four aromatic rings, the calixarene core acts as an effective sensitizer of Tb-centered luminescence. Substituents on the lower rim can modulate the aggregation behavior, which in turn determines the luminescence properties of the compounds. In solid state, the quantum yield of the phthalimide derivative is almost three times as high as that of the propyl-functionalized analog demonstrating a beneficial role of the chromophore on Tb-luminescence. In solution, however, the effect of the phthalimide group vanishes, which we attribute to the large distance between the chromophore and the lanthanide, situated on the opposite rims of the calixarene. Both quantum yields and luminescence lifetimes show clear concentration dependence in solution, related to the strong impact of aggregation on the luminescence behavior. We also evidence the variability in the values of the critical micelle concentration depending on the experimental technique. Such luminescent calixarene platforms accommodating stable lanthanide complexes can be considered valuable building blocks for the design of dual MR/optical imaging probes.
Project description:In the title compound, C(90)H(120)O(18)·2CH(3)CN, the calixarene has a 1,2,3-alternate conformation and possesses inversion symmetry. It crystallizes as an acetonitrile disolvate, with a half-mol-ecule of calixarene and one mol-ecule of solvent in the asymmetric unit. In the crystal, the two solvent mol-ecules are enclosed in voids between the calixarene mol-ecules. They form weak C-H?O hydrogen bonds involving an O atom of the lower rim substituent. The cavity of the calixarene itself is enclosed by two opposite phenol rings, which are turned into the cavity due to the presence of a C-H?? inter-action. The calixarene mol-ecule exhibits disorder of one substituent on its lower rim [occupancy ratio 0.897?(3):0.103?(3)].