Electrochemical characterization of composite membranes based on crown-ethers intercalated into montmorillonite

Oxyethylene macrocyclic compounds (crown-ethers) act as ligands of intracrystalline cations of certain layered silicates as montmorillonites. Stable intercalation materials are formed which are used to prepare organic-inorganic membranes by encapsulating these intercalation compounds with a poly-butadiene thin coating. Electrochemical Impedance Spectroscopy (EIS) is used to study the resulting composite membranes in contact with aqueous electrolytes. From the impedance plots, the ionic resistance of the membranes is obtained. The thickness of the polybutadiene coating is an important factor determining the ability of ions to pass across the membrane. Marked differences in the ionic resistance are observed as a function of the nature of the interlayer macrocyclic compound. For non-intercalated montmorillonite membranes, the ionic resistance is strongly reduced, whereas for some crown-ether intercalated materials such as 18-crown-6 and dibenzo 24-crown-8, iono-selective membranes are obtained. Concerning the nature of the electrolyte, cations exhibiting greater hydration energies show higher difficulties to pass through the membrane and, consequently, the ionic resistance increases.     

Structure-property modelling of complex formation of strontium with organic ligands in water

The method of substructural molecular fragments based on representation of the molecular graph by ensembles of fragments and involving calculations of those contributions to the given property is applied to the modelling of stability constants of the complexes of strontium(II) with organic ligands in water. Reliability of predictions of developed structure-property models was examined using three different test sets of structurally diverse ligands. The obtained models have been used for generation and screening of combinatorial library of virtual ligands. Some hypothetical efficient Sr(II) binders were suggested.     

Caracterisation par analyse calorimetrique differentielle des complexes entre LiAlH4 et les ethers-couronnes 12-C-4, 15-C-5, dicyclohexano-18-C-6

The thermal behaviour of complexes [Li⁺-EC](AlH₄)^– withEC=12-C-4, 15-C-5, DC 18-C-6 (cis-anti-cis andcis-syn-cis isomers) was investigated by Differential Scanning Calorimetry (DSC). These complexes were prepared as solids from benzene solutions. Pure EC and several solvated species [Li⁺-EC](AlH₄)^–·nC₆H₆ (EC=15-C-5, DC 18-C-6syn) were also studied. DSC has revealed various phenomena. Solid-solid transitions were observed before melting for [Li⁺-EC](AlH₄)^– withEC=12-C-4 and 15-C-5. They are probably explained by small molecular modifications strongly dependent on the thermal history of the sample. A glass-transition was found for the pure crown-ether DC 18-C-6anti, the complex [Li⁺-EC](A1H₄)^– withEC=DC-18-C-6anti and the two solvates mentioned above.

     

Ion transport across membranes prepared by gel crystallization

A one-step procedure for the preparation of ion-selective membranes is described. The method employs the thermally induced gel crystallization of ultrahigh molecular weight poly(ethylene) (UHMW-PE) from a dilute xylene solution. After evaporation of the xylene, a microporous UHMW-PE film remains, which can serve as the support for liquid and polymeric ion-selective membranes. The addition of a membrane solvent and suitable receptor molecules to the xylene solution allows a one-step incorporation of these membrane components into the UHMW-PE support. The influence of the preparation conditions of the UHMW-PE support on the rates of the p-tert-butylcalix[4]arene tetraethylester-mediated transport of NaClO₄ was studied. Two concepts to improve the life-time of the membranes are introduced. In a first approach, the addition of photocrosslinkable nitril-substituted siloxane copolymers to the membrane phase has been evaluated. The enhanced viscosity of the membrane phase reduces leaching of carrier and solvent molecules from the membrane into the aqueous phases. In a second approach, the solvent is omitted and the membrane-phase merely consists of a benzo-15-crown-5 or calix[4]arene modified siloxane-copolymer, which is substituted to such a degree that ion transport no longer has to take place via diffusion of host–guest complexes but by jumping of the cations from one fixed carrier to a neighboring carrier. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 383–394, 1998     

Towards peptide versions of Cram's host-guest chemistry: the synthesis of C-disubstituted glycines with binaphthol-based crowned side-chains

Dietherification of the hydroxy groups of various α,α-disubstituted α-amino acids or their precursors, possessing either an achiral frame derived from α-hydroxymethylserine, or a 2,2′,6,6′-tetrasubstituted biphenyl frame with only an axial chirality, or a frame with α-carbon chirality derived from α-methyl-(L)-DOPA, using (R)-2,2′-bis-(5-tosyloxy-3-oxa-1-pentyloxy)-1,1′-binaphthyl as alkylating agent, gave a new series of amino acids bearing binaphthol-based crown-ethers, as building blocks for the construction of short-chain peptide helices with topologically well-localized receptors.     

Enlarging the size of calix[4]arene-crowns-6 to improve Cs/K selectivity: a theoretical and experimental study

Ab initio calculations in the gas-phase indicate that the substitution of an ethylene with a propylene moiety in the polyether bridge of 1,3-di-iso-propoxycalix[4]arene-crowns-6 could result in an enhanced Cs⁺/K⁺ selectivity which is of particular interest in nuclear waste treatment. We therefore synthesised two novel calix[4]arene-crown-6 compounds (1 and 2) having a propylene moiety in their structure and for this named calix[4]arene-propylene-crown-6. The structures of compounds 1 and 2 were elucidated by NMR in solution and for 1 also by X-ray diffraction studies in the solid state. Association constants (K_a) in CHCl₃ of the two novel calix-crowns were measured and pointed out a plateau selectivity towards alkali metal ions which was not predicted by molecular modelling calculations. These results indicate the important role played by the solvent molecules and counter-anions in binding for this class of ionophores.     

Non-Globular Organic Ionic Plastic Crystal Containing a Crown-Ether Moiety – Tuning Its Behaviour Using Sodium Salts

Organic ionic plastic crystals (OIPCs) are a class of soft materials showing positional order while still allowing orientational freedom. Due to their motional freedom in the solid state, they possess plasticity, non-flammability and high ionic conductivity. OIPC behavior is typically exhibited by ‘simple’ globular molecules allowing molecular rotation, whereas the interactions that govern the formation of OIPC phases in complex non-globular molecules are less understood. To better understand these interactions, a new family of non-globular OIPCs containing a 15-crown-5 ether moiety was synthetized and characterized. The 15C5BA molecule prepared does not exhibit the sought-after behavior because of its non-globular nature and strong intermolecular H-bonds that restrict orientational motion. However, the OIPC behavior was successfully obtained through complexation of the crown-ether moiety with sodium salts containing chaotropic anions. Those anions weaken the interactions between the molecules, allowing rotational freedom and tuning of the thermal and morphological properties of the OIPC.     

New attempts in search for superheavy elements in nature

A new procedure in search for superheavy elements (SHE) in nature is suggested. SSNTD and crown-ethers will be employed in this work.     

Arene Phosphorus-Containing Macrocyclic Crown Ethers: Last Studies

Abstract

The data on the synthesis, structures, and chemical properties of macrocyclic compounds containing endo-cyclic atoms of tri- and pentavalent phosphorus are summarized. Methods for the synthesis of the described macrocycles are reported. Peculiarities of structure, chemical properties, particularly formation of complexes, catalytic activity, and practical applications are analyzed. The bibliography includes 155 references.