Conductance Study of Binding of Some Rb+ and Cs+ Ions by Macrocyclic Polyethers in Acetonitrile Solution

A conductance study of the interaction between Rb+ and Cs+ ions and18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6),dibenzo-24-crown-8 (DB24C8), and dibenzo-30-crown-10 (DB30C10) inacetonitrile solution has been carried out at various temperatures. The formationconstants of the resulting 1:1 complexes were determined from the molarconductance-mole ratio data and found to vary in the orderDC18C6 > 18C6 > DB30C10 > DB18C6 DB24C8for Rb+ ion andDC18C6 > 18C6 > DB30C10 DB24C8 > DB18C6for Cs+ ion. The enthalpy and entropy of complexation were determined fromthe temperature dependence of the formation constants. The complexes with the18-crowns are both enthalpy and entropy stabilized while, in the case of largecrown ethers, the corresponding complexes are enthalpy stabilized but entropydestabilized.     

Combination of the Hybrid Steepest-Descent Method and the Viscosity Approximation

In the context of a general q-uniformly smooth Banach space, we will prove the convergence of a scheme which covers Yamada’s hybrid steepest-descent method and Moudafi’s viscosity approximation in their complete forms. Moreover, we present an application to the minimization over a set of fixed points.     

Synthesis and characterization of a Ni nanoparticle stabilized on Ionic liquid‐functionalized magnetic Silica nanoparticles for tandem oxidative reaction of primary alcohols

In this research, preparation of the magnetic nanoparticle, coating by a silica shell using (3‐aminopropyl) triethoxysilane and synthesis of a novel sulfonic acid‐substituted imidazolium‐based ionic liquid onto the surface of these particles via a multi‐component reaction, is described. The functionalized nanoparticles was loaded by Ni nanoparticles and characterized by means of techniques such as XRD, FTIR, SEM, EDX, TEM, TGA and ICP‐OES. The nanostructures have spherical shapes that ranged in size from 80 to 100 nm. The catalytic activity of these nanoparticles was tested in aerobic oxidation of primary alcohols that showed good performance in the wide range of primary alcohols in water at mild reaction conditions. As a second step of this work, the tandem oxidative synthesis of alkylacrylonitriles and bisindolylmethanes were investigated using primary alcohols under oxidation conditions. This catalyst system can be recovered using external magnet and reused for five consecutive cycles without significantly less of its activity.     

Electropolymerized coatings of poly(o‐anisidine) and poly(o‐anisidine)‐TiO2 nanocomposite on aluminum alloy 3004 by using the galvanostatic method and their corrosion protection performance

Poly(o‐anisidine) (POA) and poly(o‐anisidine)‐TiO₂ (POA‐TiO₂) nanocomposite coatings on aluminum alloy 3004 (AA3004) have been investigated by using the galvanostatic method. The electrosynthesized coatings were characterized by FT ‐ IR spectroscopy, XRD, SEM ‐ EDX and SEM. The corrosion protection performance of POA and POA‐TiO₂ nanocomposite coatings was investigated in the 3.5% NaCl solution by using potentiodynamic polarization technique and electrochemical impedance spectroscopy. The results show that the corrosion rate of the nanocomposite coatings is about 900 times lower than the bare AA3004 under optimal conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Structural characterization of new Cd(2+) fluorescent sensor based on lumazine ligand: AM1 and ab initio studies

6-Thienyllumazine (TLM) is synthesized as a new fluorescent sensor that is capable of indicating selectively the presence of Cd(2+) ion via a fluorescence signal. Experiment has been performed in the presence of Ni(2+), Co(2+), Cu(2+), Ag(+), Mn(2+), Hg(2+), Zn(2+), Pb(2+), and Mg(2+) metal ions in aqueous solutions. The product was characterized by elemental analysis, mass, and NMR spectra. The spectral characteristics (maxima, quantum yields, Stokes shift, and lifetimes) of TLM in organic and aqueous solvents have been studied with the help of absorption and fluorescence spectroscopy, as well as, using time dependent spectrofluorimetry (single photon counting technique). The fluorescence dependence of TLM on the pH has also been investigated. The experimental results indicate that TLM exists in two ionic forms: neutral (acid) and anion (base). Electronic structure calculations of TLM were carried out using Semiempirical Austin Model 1 (AM1) and ab initio Hartree-Fock (HF) with 6-31G* basis set and using Gaussian 03 program. Absorption energies for TLM have been calculated using ZINDO method. The theoretical results confirm the presence of the thiophene and pteridine rings in two conformations: twisted at angle of about 35 degrees in the excited state and coplanar in the ground state.     

Zwitterionic Salts from the Reaction of Symmetrical and Unsymmetrical (thio)Barbituric Acids with 2‐Pyridinecarbaldehyde under Solvent‐free Condition

A simple and efficient synthesis for the preparation of unusual charge‐separated pyridinium (thio)barbiturate zwitterion derivatives was achieved via a one‐pot reaction of (thio)barbituric acid derivatives and 2‐pyridinecarbaldehyde under solvent‐free condition and also in methanol under refluxing. The structure of the compounds was confirmed by ¹H NMR, ¹³C NMR, FT‐IR, mass and X‐ray analysis. The mechanism of the formation is discussed. Instead, no related pyridinium zwitterion was afforded from the reaction between dimedone and 2‐pyridinecarbaldehyde under the same conditions and its xanthene derivative was obtained.