Enantioselective chromenone benzoxazole receptor for glutamic acid and its derivatives

Combination of a binaphthyl unit with chromenone benzoxazole fragments provided a chiral receptor that is enantioselective for glutamic acid and its derivatives. The receptor racemic mixture was resolved by TLCs impregnated with (R,R)-thiodilactic acid. High association constants were measured for dansylglutamic acid, using a fluorescent method. This receptor can be used for the resolution of the tosylglutamic acid racemic mixture.     

Structural and spectroscopic investigations of blue, vanadium-doped ZrSiO4 pigments prepared by a sol-gel route

A sol-gel reaction starting from silicon and zirconium alkoxides, in water-ethanol mixtures, was employed to obtain vanadium-doped zirconium silicate powders (zircon). The reactions were performed by modulating both (a) the amount of the vanadium salt in the starting mixture and also (b) the amount of mineralizer (NaF). The products of the sol-gel reaction were calcined at 600, 800, 1000, and 1200 degrees C. The samples were characterized by X-ray powder diffraction (XRPD), electron paramagnetic resonance spectroscopy (EPR), scanning electron microscopy (SEM), X-ray absorption near-edge spectroscopy (XANES), and diffuse UV-vis-near-IR reflectance spectroscopy. Results from the structural, morphological, and optical characterization are examined and cross-compared to produce a consistent picture of the key factors leading to the formation, growth, and optical properties of the reaction products.     

Determination of simazine, terbuthylazine, and their dealkylated chlorotriazine metabolites in soil using sonication microextraction and gas chromatography

A rapid analytical method is proposed for the determination of simazine, terbuthylazine, and their chloro dealkylated metabolites (simazine-desethyl, simazine-bisdesethyl, and terbuthylazine-desethyl) in soil. A sonication micromethod is presented for the extraction of -triazine herbicides and their metabolites. Final determination is by gas chromatography (GC) with nitrogen-phosphorus detection. The identity of all compounds was confirmed by GC with mass selective detection in the selected-ion monitoring mode. All chromatograms were very clean, without interfering peaks, and no cleanup was needed. The limits of detection were 1 pg for simazine-bisdesethyl; 5 pg for simazine, terbuthylazine, and terbuthylazine-desethyl; and 10 pg for simazine-desethyl. The limits of quantitation were 1, 5, and 10 ppb, respectively. Mean recoveries from fortified soils ranged from 76% for simazine-bisdesethyl to 102% for simazine-desethyl, with relative standard deviations of 3-6%.     

A Monte Carlo simulation of free energy relationships for the electron transfer reaction between Fe+ and Fe2+ in water

A free energy barrier ΔF^≠ = 174.2 kJ/mol for the self-exchange electron transfer reaction model Fe⁺/Fe²⁺ in water has been calculated by combining Monte Carlo simulations and the statistical perturbation theory. We have shown that, even for those electron transfer reactions that present a very high free energy barrier of activation, the free energy curve behaves parabolically versus the reaction coordinate, which justifies the quadratic expression for the activation free energy done by Marcus.     

Aluminium alkyl complexes supported by [OSSO] type bisphenolato ligands: synthesis, characterization and living polymerization of rac-lactide

Aluminium alkyl complexes [(OSSO)AlR](1-3: R = Me, Et) were isolated in good yields from the protonolysis reaction of AlR3 with the corresponding tetradentate 1,omega-dithiaalkanediyl-bridged bisphenols (1,4-dithiabutanediyl-bis(6-tert-butyl-4-methylphenol), etbmpH2; ortho-xylylenedithio-bis(6-tert-butyl-4-methylphenol), xytbmpH2). The monomeric structures of all three complexes were confirmed by X-ray diffraction studies. Complexes 1 and 2 have an isotypic packing arrangement. The aluminium center is coordinated by the etbmp ligand and one alkyl group with distorted trigonal bipyramidal geometry. Complex 3 shows Cs symmetry with square pyramidal geometry around the metal center. Substitution reaction of complex 1 with trityl alcohol gave the monomeric alkoxide complex [(etbmp)Al(OCPh3)] 4, which has a similar trigonal bipyramidal geometry around the aluminium atom as complex 1. In the presence of isopropanol, complexes 1-3 initiated the living ring-opening polymerization of rac-lactide (PDI = 1.03-1.06, Mw/Mn). The ligand structure influenced the tacticity of the obtained polymer, with complex 3 giving heterotactic-enriched polylactides.     

Flow-injection potentiometric determination of triiodide by plasticized poly(vinyl chloride) membrane electrodes and its application to the determination of chlorine-containing disinfectants

Plasticized poly(vinyl chloride) (PVC) membranes of different compositions were tested for use in the construction of potentiometric flow detectors for triiodide. A membrane with a 2:1 (w/w) 2-nitrophenyl octyl ether to PVC ratio was selected. The influence of thiosulphate in the carrier solution composition and of the flow-injection variables on the determination of triiodide was studied. In the selected conditions, a linear relationship between peak height and log[I₃⁻] was obtained between 5 × 10⁻⁶ and 1 × 10⁻⁴ mol l⁻¹ triiodide. Peak height relative standard deviations for 2 × 10⁻⁵ and 1 × 10⁻⁴ mol l⁻¹ triiodide were ±0.4 and ±1.8%, respectively, and sampling frequency was 80 samples per hour. The method proposed was applied satisfactorily to the iodometric determination of different chlorine-containing disinfectants, among them trichloroisocyanuric acid and dichloroisocyanurate in several types of commercial sample.     

Characterisation of cement pastes by inverse gas chromatography

Two cement pastes, commonly used in concrete formulations, were characterised by IGC at 35-80 degrees C before and after coating with an epoxy resin and a hardener. The cements are mixtures of hydrates in various proportions, such as calcium silicate hydrate (CaO-SiO2-H2O) and calcium hydroxide Ca(OH)2. Apolar and polar probes were used to determine the dispersive and acid-base characteristics of the cement pastes. These materials have high surface energy as judged from the dispersive contribution to the surface free energy (gamma(s)d) values lying in the 50-70 mJ/m2 range at 60-80 degrees C. Examination of the specific interactions permitted to show that the cement pastes are strongly amphoteric species with a substantial predominant Lewis basicity that is in line with the basic pH of their aqueous suspensions. Following coating with an epoxy resin (DGEBA) and a hardener (triethylene tetramine), the surface energy of the cements decreases substantially with the mass loading of the organic material. The surface thermodynamic properties were also correlated with the surface chemical composition as determined by X-ray photoelectron spectroscopy.     

Non convex control problems in Banach spaces

We consider a general control problem which includes, as particular cases, Bolza, Lagrange and Mayer problems. We show that it can be reduced to a free problem and we give sufficient conditions for the existence of a minimum over all absolutely continuous arcs with values in a reflexive, separable Banach space. A regularization result is also proved and an application to explicit control problems is considered.This work was supported by the Laboratorio per la Matematica Applicata del C. N. R.-Istituto di Matematica della Università di Genova.     

Synthesis and characterization of palladium–tin bicolloids prepared by chemical liquid deposition

Palladium–tin bicolloids have been prepared by chemical liquid deposition. The metals were cocondensed at 77 K with ethanol, 2-propanol, 2-methoxyethanol, 2-butanone and acetone. The distribution of particle sizes was determined by transmission electron microscopy of the stables dispersions. The sizes ranged from 3.8 nm for 2-methoxyethanol to 8.3 nm for acetone colloids. Electrophoretic measurements such as colloid charge and zeta potential were achieved. lt was found that the colloids possess electrical charge; therefore, it is postulated that their stability is by simple solvatation. The colloids showed stability over 1 week at room temperature. The zeta-potential values are in agreement with the stability and electrophoretic mobility. The highest zeta potential was obtained for PdSn–2-methoxyethanol colloids with 379 mV and the lowest for 2-butanone with 114 mV. The colloids exhibit absorption bands in the UV region. In the visible region no plasma absorption was found. Active solids obtained by evaporation of the solvent contain a certain amount of the solvent incorporated, and owing to their reactivity they produce a mixture of tin oxide with palladium and tin. The presence of solvents can be observed by Fourier transform IR incorporation in the finely divided solids. Characteristic bands for each solvent were measured. By means of thermogravimetric analysis and differential scanning calorimetry the thermal stability of the solids and the transition heat give us the carbonaceous residues in the films. The elemental analysis of the powders was carried out.