129 research outputs found
Cation-π Interaction in Complex Formation Between Tl+ Ion and Calix[4]crown-6 and Some Calix[4]biscrown-6 Derivatives: Thallium-203 NMR, Proton NMR and X-Ray Evidences
No full textMetallocapped complexation of the thallium(I) ion with calix[4]crown-6 (1) and three different calix[4]biscrown-6
derivatives (2-4) has been investigated by a combination of 203Tl and 1H NMR in a CD3CN/CDCl3 (4:1 v/v) solution.
The results clearly revealed the formation in solution of mono- and dithallium(I) complexes in which the metal cations
are held in the ligands’ cavities close to the calix[4]arene ring. In addition, a solid state mononuclear complex between
1,3-calix[4]bis-o-benzo-crown-6 (3) and TlClO4 was prepared, and its X-ray crystal structure was determined. The
results of the structural data in solution and the solid state suggested that the calix[4]crown-6 derivatives considered
provide π cavities as active sites for the complexation of thallium(I) ions
Selective Extraction of Cesium at Tracer Level Concentration From a Sodium Nitrate Solution with Calix Crowns: Molecular Modeling Study of the Cs+/Na+ Selectivity
No full textCalix[4]arene mono- and bis-crown6 in the 1,3 alternate conformation are highly selective extractants for cesium towards sodium in an acidic liquid waste. Extraction and selectivity are related to complexation properties which can be studied by Molecular Dynamics techniques. In this paper, we describe the results of Molecular Dynamics simulations in an explicit water phase for four complexes of 1,3-alternate mono- and bis-crown-calix[4]arenes. The structural features obtained are interpreted on the basis of cation/ligand complementarity and can explain the relative performances in Na+ and Cs+ extraction for the compounds simulated
Lanthanide Complexes of Encapsulating Ligands: Luminescent Device at the Molecular Level
No full textLanthanide complexes of encapsulating ligands are studied as luminescent devices at the molecular level. The photophysical properties of the complexes which, up till now, showed the most intense luminescence are reported. The luminescence intensity of these complexes is discussed considering the efficiency of incident light-emitted light conversion, defined as the product of the absorption efficiency and the luminescence quantum yield. It is illustrated how the metal luminescence intensity can be enhanced by adapting the ligands on basis of previously obtained experimental results. The possible application of these complexes in fluoroimmunoassays is examined
A tangled web of lies: reflections on ethnographic fieldwork with Syrian Turkmen women on the side of a road in Beirut
No full textIn this essay, the author reflects upon the performances of kizb (lying) she and Syrian Turkmen women acted out on a street in Beirut. The women worked informally selling tissues as well as potentially other services that were deemed as too immoral to be explicitly and publicly spoken as the truth, at least in front of an ethnographer. Meanwhile, the author had her own morally problematic behaviour to conceal. Over time, plot-holes in each of their narratives inevitably started to surface. Yet none of them were willing to call out the other’s performance of kizb. This essay considers some of the reasons behind this kizb reciprocity between the women and the author. In doing so, the author also explores briefly some of the complexities that arise in the relationship between the ethnographer and her interlocutors. © 2017, © 2017 Council for British Research in the Levant
Nuclear Wastes Treatment by Means of Supported Liquid Membranes Containing Calixcrown Compounds
No full textPermeability variation with repeated caesium transport experiments has been chosen to measure the leaching of the supported liquid membrane by the contacting aqueous solutions. This allowed us to characterize the SLM stability. Whereas classical crown ethers such as the widely used 21C7 derivatives were revealed to be poorly efficient and poorly stable in SLMs, crown-6-calix[4]arene compounds in the so-called 1,3-alternate configuration led to very stable (over 50 days), highly selective (concentration factor > 100) and efficient (decontamination factor = 20) SLMs, for the removal of caesium from high salinity and acidity media. These results were achieved by using proper organic diluents and introducing hydrophobic substituents in the frame of the calixarenes
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