calix(4)arene and pyridine

Pyridyl-based triazole-linked calix[4]arene conjugates, viz. L(1) and L(2), were synthesized and characterized. These two conjugates were shown to be selective and sensitive for Zn(2+) among the 12 metal ions studied in HEPES buffer medium by fluorescence, absorption, and visual color change with the detection limit of ~31 and ~112 ppb, respectively, by L(1) and L(2). Moreover, the utility of the conjugates L(1) and L(2) in showing the zinc recognition in live cells has also been demonstrated using HeLa cells as monitored by fluorescence imaging. The zinc complexes of L(1) and L(2) were isolated, and the structure of [ZnL(1)] has been established by single-crystal XRD and that of [ZnL(2)] by DFT calculations. TDDFT calculations were performed in order to demonstrate the electronic properties of receptors and their zinc complexes. The isolated zinc complexes, viz. [ZnL(1)] and [ZnL(2)], have been used as molecular tools for the recognition of anions on the basis of their binding affinities toward Zn(2+). [ZnL(2)] was found to be sensitive and selective toward phosphate-bearing ions and molecules and in particular to pyrophosphate (PPi) and ATP among the other 18 anions studied; however, [ZnL(1)] was not sensitive toward any of the anions studied. The selectivity has been shown on the basis of the changes observed in the emission and absorption spectral studies through the removal of Zn(2+) from [ZnL(2)] by PPi. Thus, [ZnL(2)] has been shown to detect PPi up to 278 ± 10 ppb at pH 7.4 in aqueous methanolic (1/2 v/v) HEPES buffer.

Topics: Absorption; Adenosine Triphosphate; Calixarenes; Chemistry Techniques, Analytical; Diphosphates; HeLa Cells; Humans; Imines; Intracellular Space; Models, Molecular; Molecular Conformation; Organometallic Compounds; Phenols; Pyridines; Quantum Theory; Solutions; Spectrometry, Fluorescence; Zinc

The photophysical properties of the new pyridin-2'-yl-1,2,3-triazole chromophore have been investigated. Spectroscopic experiments and molecular modelling have provided evidence for a photoinduced charge transfer occurring from the triazole group to the pyridine ring. Hepta- and tetrachromophoric systems have been synthesized by covalently linking seven or four chromophores of this kind, respectively, to a beta-cyclodextrin and a calix[4]arene. They exhibit different fluorescence spectra, decays and quantum yields. Special attention has been paid to the binding of cadmium and zinc ions and to the resulting photophysical effects which are various and very different for the grafted beta-cyclodextrin and calix[4]arene systems.

Topics: Absorption; beta-Cyclodextrins; Cadmium; Calixarenes; Color; Fluorescence; Models, Molecular; Phenols; Pyridines; Spectrometry, Fluorescence; Time Factors; Triazoles

The interaction of a calix(4)arene derivative, namely 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra[2-(4-pyridyl)methoxy]calix(4)arene, 1a, and its monomeric component, p-tert-butylphenoxy-4-pyridine, 1b, with metal cations has been investigated in acetonitrile and methanol. (1)H NMR measurements carried out in CD(3)CN show the primary role played by the pyridyl nitrogens in their complexation with metal cations. Conductance measurements demonstrated that for all cations (except mercury) the composition of the metal ion complexes of 1a is 1:1 (ligand:metal cation). However, 1a hosts two mercury cations per unit of ligand. For the monomer 1b, complexes of 2:1 (ligand:metal cation) stoichiometries are formed with the exception of Pb(2+) (1:1 composition). The thermodynamics of complexation of these systems are reported in acetonitrile. Data in methanol are limited to stability constant values for mercury(II) and these ligands. This paper demonstrates for the first time that thermodynamic data for the complexation of the monomeric component of the ligand and metal cations contribute significantly to the interpretation of systems involving cation-calixarene interactions in solution.

Topics: Calixarenes; Cations; Metals, Heavy; Models, Molecular; Molecular Conformation; Phenols; Pyridines; Thermodynamics