Cobalt-containing silicotungstate sandwich dimer [{Co3(B-beta-SiW9O33(OH))(B-beta-SiW8O29(OH)2)}2]22-

The 6-cobalt-substituted [{Co3(B-beta-SiW9O33(OH))(B-beta-SiW8O29(OH)2)}2]22- has been characterized by IR and UV-vis spectroscopy, elemental analysis, magnetic studies, electrochemistry, and gel filtration chromatography. A single-crystal X-ray analysis was carried out on K10Na12[{Co3(B-beta-SiW9O33(OH))(B-beta-SiW8O29(OH)2)}2].49H2O (KNa-1), which crystallizes in the monoclinic system, space group P2(1)/n, with a=19.9466(8) A, b=24.6607(10) A, c=34.0978(13) A, beta=102.175(1) degrees, and Z=2. Polyanion 1 represents a novel class of asymmetric sandwich-type polyanions. It contains three cobalt ions, which are encapsulated between an unprecedented (B-beta-SiW9O34) fragment and a (B-beta-SiW8O31) unit. Polyanion 1 is composed of two sandwich species via two Co-O-W bridges in the solid state and almost certainly in solution as well based on gel filtration chromatography. UV-visible spectroscopy and cyclic voltammetry also confirmed its stability. Two well-separated groups of waves appeared in the voltammetric pattern: the wave observed in the negative potential range versus a saturated calomel electrode features the redox processes of WVI centers; the two reversible redox couples observed in the positive potential domain are attributed to the redox processes of Co2+ centers and indicated that the two types of Co2+ centers in the structure are oxidized in separate waves. Such reversibility of Co2+ centers within multi-Co-substituted polyoxometalates is uncommon. The magnetic properties of KNa-1 are also discussed. The ferromagnetic ground state has been studied by magnetic susceptibility and magnetization measurements and fitted according to an anisotropic exchange model.     

On the electrochemical behavior of selanyl azulenes

Journal of Solid State Electrochemistry - The electrochemical behavior of substituted 1-phenylselanyl azulenes has been established by cyclic, differential pulse, and rotating disk electrode...     

Adjoint Sensitivity Analysis of a Fluid-Structure Interaction Problem

A fluid-structure mathematical model usually includes parameters whose actual values are known only approximately or can vary around some reference values. The objective of the sensitivity analysis is to determine quantitatively the behavior of the responses of a fluid-structure system locally around a chosen point of the trajectory in the phase-space of parameters and dependent variables. In this work, the response considered is the total mechanical energy of the structure. The sensitivities with respect to all the parameters the fluid-structure system depends on are useful in many situations as well as for optimization purposes. We present the theoretical developments necessary for the application of the adjoint sensitivity analysis methods (ASAM) for the fully coupled governing equations of an aeroelastic system. The algorithm is general and can be applied for any kind of fluid-structure interaction problems. Illustrative numerical examples are presented for the case of typical section with two degrees of freedom. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Intermediate moduli spaces of stable maps

We describe the Chow ring with rational coefficients of as the subring of invariants of a ring , relative to the action of the group of symmetries S_d. We compute by following a sequence of intermediate spaces for .     

Quasilinearity of some composite functionals associated to Schwarz’s inequality for inner products

The quasilinearity of certain composite functionals associated to Schwarz’s celebrated inequality for inner products is investigated. Applications for operators in Hilbert spaces are given as well.     

Quantum-chemical simulation and experimental study of some magnetic nanoparticles stabilized in fluid suspensions by using organic coating

Abstract

The biomedical applications of magnetic nanoparticles require the surface modification with organic, hydrophilic molecules, able to ensure the stability of the resulted colloidal suspensions. We present the quantum mechanical approach of two molecules developing stable interfaces with magnetic Co_0.5Fe_2.5O₄ nanoparticles. Sodium oleate, and citric acid, ensuring steric and respectively electrostatic stabilization are comparatively analyzed. The roles of dipole moment and frontier orbitals energies were emphasized to better understanding of some interface phenomena for the optimization of magnetic nanoparticle suspension preparation. Further, practical yielding of colloidal Co_0.5Fe_2.5O₄ nanoparticles by coating with sodium oleate and respectively with citric acid is discussed.     

Mica surfaces stabilize pentavalent uranium

High-resolution X-ray photoelectron spectroscopy was used to demonstrate that reduction of aqueous U6+ at ferrous mica surfaces at 25 degrees C preserves U5+ as the dominant sorbed species over a broad range of solution compositions. Polymerization of sorbed U5+ with sorbed U6+ and U4+ is identified as a possible mechanism for how mineral surfaces circumvent the rapid disproportionation of aqueous U5+. The general nature of this mechanism suggests that U5+ could play an important, but previously unidentified, role in the low-temperature chemistry of uranium in reducing, heterogeneous aqueous systems.     

The influence of titanium dioxide phase composition on dyes photocatalysis

A comparative study of TiO₂ powders prepared by sol–gel methods is presented. Titanium tetraisopropoxide was used as the precursor for the sol–gel processes. The effects of the annealing treatment on phase, crystallite size, porosity and photodegradation of dyes (methyl orange and methylene blue) were studied. The phase structure, microstructure and surface properties of the films were characterized by using X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). The X-ray diffraction was used for crystal phase identification, for the accurate estimation of the anatase–rutile ratio and for the crystallite size evaluation of each polymorph in the samples. It was found that the only TiO₂ anatase phase of the synthesized TiO₂ develops below 500 °C, between 600 and 800 °C the anatase coexist with rutile and above 800 °C only the rutile phase was found in the samples. Attention has been paid not only to crystal structures, but also to the porosity, the particle size and the photocatalytic properties. However, the annealing temperature was found to have significant influence on the photocatalytic properties. Different TiO₂ doctor blade thin films were obtained mixing the sol gel powder (100% anatase) and TiO₂ Aldrich with TiO₂ Degussa P25. The surfactant (Triton X100 or sodium dodecyl sulfate) affects the packing density of the particles during deposition and the photocatalytic degradation efficiency of the dyes. The photocatalytic degradation kinetics of methyl orange and methylene blue using TiO₂ thin film were investigated.     

Hypervalent Organoselenium(II) Compounds with Organophosphorus Ligands. Crystal and Molecular Structure of [2‐(iPr2NCH2)C6H4]Se[S2PR′2] (R′ = Ph,OiPr)

Redistribution reactions between diorganodiselenides of type [2‐(R₂NCH₂)C₆H₄]₂Se₂ [R = Et, iPr] and bis(diorganophosphinothioyl disulfanes of type [R′₂P(S)S]₂ (R = Ph, OiPr) resulted in the hypervalent [2‐(R₂NCH₂)C₆H₄]SeSP(S)R′₂ [R = Et, R′ = Ph ( 1 ), OiPr ( 2 ); R = iPr, R′ = Ph ( 3 ), OiPr ( 4 )] species. All new compounds were characterized by solution multinuclear NMR spectroscopy (¹H, ¹³C, ³¹P, ⁷⁷Se) and the solid compounds 1 , 3 , and 4 also by FT‐IR spectroscopy. The crystal and molecular structures of 3 and 4 were determined by single‐crystal X‐ray diffraction. In both compounds the N(1) atom is intramolecularly coordinated to the selenium atom, resulting in T‐shaped coordination arrangements of type (C,N)SeS. The dithio organophosphorus ligands act monodentate in both complexes, which can be described as essentially monomeric species. Weak intermolecular S ··· H contacts could be considered in the crystal of 3 , thus resulting in polymeric zig‐zag chains of R and S isomers, respectively.     

Interference-free biosensor based on screen-printing technology and sol-gel immobilization for determination of acetaldehyde in wine

A monoenzymatic amperometric biosensor was developed for the detection of acetaldehyde. The sensor is based on the association of screen-printed carbon electrodes and aldehyde dehydrogenase immobilized by a sol-gel entrapment method. Modification of screen-printed carbon electrodes with Reinecke salt of Meldola's Blue (MBRS) resulted in highly sensitive and interference-free nicotinamide-adenine dinucleotide (NADH) detectors. Based on MBRS-mediated oxidation of NADH at -150 mV versus pseudo Ag/AgCl, acetaldehyde was determined in the range 10-260 microM, compatible with wine quality monitoring. The method of immobilization based on sol-gel entrapment was optimized to obtain the best compromise between sensitivity and operational stability. The sensor response was stable for 40 consecutive assays with methyltrimethoxysilane used as alkoxide precursor, thus allowing a possible calibration of the sensor before each measurement. The biosensors were used to analyze French wines. The method was validated with a commercially available enzymatic kit based on a standard spectrophotometric method.