calixarenes and cesium-chloride

Theoretical studies of a new ion-pair receptor, meso-octamethylcalix[4]pyrrole (OMCP), and its interactions with the halide anions F(-), Cl(-), and Br(-) and the cesium halides CsF, CsCl, and CsBr have been performed. Geometries, binding energies, and binding enthalpies were evaluated with the restricted hybrid Becke three-parameter exchange functional (B3LYP) method using the 6-31+G(d) basis set and relativistic effective core potentials. The optimized geometric structures were used to perform natural bond orbital (NBO) analysis. The two typical types of hydrogen bonds, N-H…X(-) and C-H…X(-), were investigated. The results indicate that hydrogen bonding interactions are dominant, and that the halide anions (F(-), Cl(-), and Br(-)) offer lone pair electrons to the σ*(N-H) or σ*(C-H) antibonding orbitals of OMCP. In addition, electrostatic interactions between the lone pair electrons of the halide anion and the LP* orbitals of Cs(+) as well as cation-π interactions between the metal ion and π-orbitals of the pyrrole rings have important roles to play in the Cs(+)•OMCP•X(-) complexes. The current study further demonstrates that this easy-to-make OMCP host compound functions as not only an anion receptor but also an ion-pair receptor.

Topics: Algorithms; Bromides; Calixarenes; Cesium; Chlorides; Computer Simulation; Coordination Complexes; Fluorides; Hydrogen Bonding; Models, Molecular; Molecular Conformation; Porphyrins; Quantum Theory; Thermodynamics

The complexation reactions between the macrocyclic ionophore, p-isopropylcalix[6]arene and Cs+ cation were studied in dimethylsulfoxide-acetonitrile (DMSO-AN) binary non-aqueous solvents at different temperatures using a conductometry method. The conductance data show that the stoichiometry of the (p-isopropylcalix[6]-arene·Cs)+ complex in all binary mixed solvents is 1:1. The stability of the complexes is affected by the composition of the binary solvent media and a non-linear behavior was observed for changes of log K(f) of the complex versus the composition of the binary mixed solvents. The thermodynamic parameters (DH°(c) and DS°(c)) for formation of (p-isopropyl-calix[6]arene·Cs)+ complex were obtained from temperature dependence of the stability constant and the obtained results show that the (p-isopropylcalix[6]arene·Cs)+ complex is enthalpy destabilized, but entropy stabilized, and the values of the mentioned parameters are affected strongly by the nature and composition of the binary mixed solvents.

Topics: Acetonitriles; Calixarenes; Cations; Cesium; Chelating Agents; Chlorides; Conductometry; Coordination Complexes; Dimethyl Sulfoxide; Solvents; Thermodynamics

A polyvinylchloride (PVC) based liquid membrane ion selective electrode (ISE) for cesium was fabricated with 5-(4'-nitrophenylazo)25,27-bis(2-propyloxy)26,28-dihydroxycalix[4]arene as ionophore. Different membrane constituents were investigated to realise optimum performance of the ISE developed. Of the four plasticizers and two ion additives studied, the best response was observed with membrane having 2-nitro phenyl octyl ether (oNPOE) as plasticizer and potassium tetrakis (perchloro phenyl) borate (KTpClPB) as ion additive. Linear response over concentration range of 10(-5)-10(-1)M CsCl was obtained. The Nernstian slope of the response was 56 mV per decade for Cs with a response time less than 20s. Matched potential method has been applied to find out the selectivity for Cs over several ions like Rb(+), K(+), Na(+), NH(4)(+), Sr(2+), Ba(2+), Ca(2+), Mg(2+), Cu(2+), Pb(2+), Zn(2+), Ni(2+) and Ce(3+). The response of ISE for Cs(+) was fairly constant over the pH range of 3-11. The lifetime of the electrode is 9 months which is the longest life for any membrane-based Cs-ISE so far developed. The concentration of cesium in two simulated high level active waste streams was determined and results agreed well with those obtained independently employing atomic absorption spectrometry.

Topics: Calixarenes; Cesium; Chlorides; Electrochemistry; Hydrogen-Ion Concentration; Ion-Selective Electrodes; Ions; Membranes, Artificial; Phenols; Plasticizers; Polyvinyl Chloride; Potentiometry; Radioactive Waste; Rivers; Spectrophotometry, Atomic; Water Pollutants, Chemical

Solvent-extraction studies provide confirming evidence that meso-octamethylcalix[4]pyrrole acts as an ion-pair receptor for cesium chloride and cesium bromide in nitrobenzene solution. The stoichiometry of the interaction under extraction conditions from water to nitrobenzene was determined from plots of the cesium distribution ratios vs cesium salt and receptor concentration, indicating the formation of an ion-paired 1:1:1 cesium:calix[4]pyrrole:halide complex. The extraction results were modeled to evaluate the equilibria inherent to the solvent-extraction system, with either chloride or bromide. The binding energy between the halide anion and the calix[4]pyrrole was found to be about 7 kJ/mol larger for cesium chloride than for the cesium bromide. The ion-pairing free energies between the calix[4]pyrrole-halide complex and the cesium cation are nearly the same within experimental uncertainty for either halide, consistent with a structural model in which the Cs+ cation resides in the calix bowl. These results are unexpected since nitrobenzene is a polar solvent that generally leads to dissociated complexes in the organic phase when used as a diluent in extraction studies of univalent ions. Control studies involving nitrate revealed no evidence of ion pairing for CsNO3 under conditions identical to those where it is observed for CsCl and CsBr.

Topics: Bromides; Calixarenes; Cesium; Chlorides; Ions; Molecular Structure; Nitrobenzenes; Porphyrins; Solutions; Solvents; Water