Sol–gel preparation of aminopropyl-silica-magnesia hybrid materials

A series of aminopropyl-silica-magnesia hybrid materials has been prepared by the sol–gel method from tetraethoxysilane (TEOS), magnesium chloride (MgCl₂) and aminopropyltriethoxysilane (APTES) under acid conditions. The APTES:TEOS ratio was varied between 0:1 and 1:0. The aminopropyl coverage concentrations for APTES-silica-Mg samples were in the range of 0.3–2.3 mmol g⁻¹. The hybrid materials were characterized by numerous techniques, including X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Fourier transform Raman spectroscopy (FT-Raman), solid-state ¹³C and ²⁹Si nuclear magnetic resonance (¹³C- and ²⁹Si-NMR), thermogravimetry (TGA), N₂ adsorption–desorption, small-angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). The increase of APTES content in the silica network resulted in the increase of six-membered siloxane rings. The hybrid systems were shown to be formed from fully-condensed, trifunctional APTES species. The porosity and morphology of the hybrid materials were influenced by the initial TEOS/APTES ratio. The radius of gyration of the primary particles, determined by SAXS, was between 1.1 and 2.9 nm.     

Chemical constituents and allelopathic activity of Machaerium eriocarpum Benth.

Abstract

The analysis by HPLC-PDA of the hydroalcoholic extract of the leaves of M. eriocarpum together with the injection of the fractions containing the already identified metabolites allowed the detection of at least 5 flavonoids, of which two are derived from apigenin and three from luteolin. After isolating larger amounts of isovitexin (I), assays were performed to evaluate the allelopathic activity together with the crude extract. The results show that the initial inhibition indexes were very similar to those observed in the treatments with F17 (Fraction enriched in isovitexin) and F18 (isovitexin), mainly in the concentrations of 500 and 1000?mg L^?1. The index of the number of lateral roots, an increase of the inhibitory effect is observed with the increase of the concentration of M. eriocarpum extract.     

Synthesis and characterization of all‐conjugated copolymers of 3‐hexyl‐thiophene and EDOT by grignard metathesis polymerization

Random regioregular copolymers of 3‐hexylthiophene and 3,4‐ethylenedioxythiophene were synthesized by grignard metathesis polymerization. Soluble copolymers were obtained with a high degree of regioregularity and with a monomer ratio close to the feed ratio. A comparison between the optical properties and the thin film morphologies of these copolymers and poly(3‐hexylthiophene) is also presented. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chiral Calcium–BINOL Phosphate Catalyzed Diastereo‐ and Enantioselective Synthesis of syn‐1,2‐Disubstituted 1,2‐Diamines: Scope and Mechanistic Studies

A highly enantioselective, chiral, Lewis acid calcium–bis(phosphate) complex, Ca[ 3 a ]_n, which catalyzes the electrophilic amination of enamides with azodicarboxylate derivatives 2 to provide versatile chiral 1,2‐hydrazinoimines 4 is disclosed. The reaction gives an easy entry to optically active syn‐1,2‐disubstituted 1,2‐diamines 6 in high yields with excellent enantioselectivities, after a one‐pot reduction of the intermediate 1,2‐hydrazinoimines 4 . The geometry and nature of the N‐substituent of the enamide affect dramatically both the reactivity and the enantioselectivity. Although the calcium–bis(phosphate) complex was a uniquely effective catalyst, the exact nature of the active catalytic species remains unclear. NMR spectroscopy and MS analysis of the various calcium complexes Ca[ 3 ]_n reveals that the catalysts exist in various oligomer forms. The present mechanistic study, which includes nonlinear effects and kinetic measurements, constitutes a first step in understanding these calcium–bis(phosphate) complex catalysts. DFT calculations were carried out to explore the mechanism and the origin of the enantioselectivity with the Ca[ 3 ]_n catalysts.     

An Experimental and Theoretical Investigation on Pentacoordinated Cobalt(III) Complexes with an Intermediate S=1 Spin State: How Halide Ligands Affect their Magnetic Anisotropy

Understanding the factors that control the magnitude and symmetry of magnetic anisotropy should facilitate the rational design of mononuclear metal complexes in the quest for single‐molecule magnets (SMMs), based on a single metal ion, with high blocking temperatures and large energy barriers. The best strategy is to define magnetostructural correlations through the investigation of a series of metal complexes. It has been demonstrated that the main contribution to the magnetic anisotropy arises from the spin‐orbit coupling (SOC) effect in metal‐ion‐based systems, so current studies focus particularly on the use of both ligands and metal ions possessing a large SOC. In this context, we report a unique series of halide Co^III complexes, [CoL(X)], with X=Cl, Br, I ( CoX ) and L=2,2′‐(2,2′‐bipyridine‐6,6′‐diyl)bis(1,1‐diphenylethanethiolate), which possess a rare intermediate S=1 spin ground state. The S=1 Co^III complexes are attractive species because they possess a remarkably large axial zero‐field splitting (defined by D from the following Hamiltonian: H =DS_z²), as well as the halide ligands inducing large SOC constants. The single‐crystal X‐ray structures reveal that the CoBr and CoI complexes are isostructural with the previously described CoCl complex. Their coordination sphere displays a distorted pentacoordinated square pyramidal geometry, with the halide located in the Co^III axial position. Large positive D values of 35, 26, and 18 cm^?1 are found for CoCl , CoBr , and CoI , respectively, through analysis of the magnetic susceptibility data as a function of temperature. To rationalize this trend, theoretical calculations based on both density functional theory (DFT) and complete active space self‐consistent field (CASSCF) methods are performed successfully. Both the sign and magnitude of D are predicted remarkably well by these theoretical approaches. The DFT calculations also show that the resulting D values originate from a balance of several contributions, and that many factors, including differences in their structural properties and in the contribution of the halide, should be taken into account to explain the trend of D in this series of complexes.     

Enantiopure Sulfinyl Aniline as a Removable and Recyclable Chiral Auxiliary for Asymmetric C(sp3)−H Bond Activation

An original and recyclable chiral bidentate aniline‐sulfoxide‐based directing group has been developed. This auxiliary allows challenging stereoselective Pd‐catalyzed direct functionalization of small cycloalkanes through C–aryl and C–alkyl bond formation. Although moderate diastereoselectivities are observed, both optically pure enantiomers of the highly functionalized products can be obtained separately by simple silica gel chromatography and cleavage of the chiral auxiliary. This strategy was further applied to the preparation of enantiomerically pure 1,2,3‐trisubstituted cyclopropane carboxylic acid derivatives, with three stereogenic centers and bearing both alkyl and aromatic substituents. These molecular scaffolds are not yet reported in the literature. The synthetic utility of this approach is validated by the chiral auxiliary being readily cleaved and recovered posteriori to the C?H activation step, without deterioration of its optical purity. Finally, an unprecedented palladacycle intermediate generated through C?H activation of the cyclopropane moiety has been isolated and fully characterized. Initial DFT calculations shed additional light on the reactivity of this original intermediate.     

Bicriteria path problem minimizing the cost and minimizing the number of labels

We address a bicriterion path problem where each arc is assigned with a cost value and a label (such as a color). The first criterion intends to minimize the total cost of the path (the summation of its arc costs), while the second intends to get the solution with a minimal number of different labels. Since these criteria, in general, are conflicting criteria we develop an algorithm to generate the set of non-dominated paths. Computational experiments are presented and results are discussed.     

A new TEM method for the characterization of the tertiary γ′ nano-precipitates in a PM disk superalloy: influence of ageing

An original method for characterizing the γ′-phase tertiary precipitates in a Ni-based superalloy manufactured by powder metallurgy is described. This investigation is made using post mortem transmission electron microscopy (TEM). It is based on the analysis of sheared areas within crept specimens, which allows the precipitates revealed by the dislocations in their glide plane to be observed. The characteristics of these nano-precipitates, i.e. their size, their volume fraction and the channel width between them, are determined for two different heat treatments (HTs). The results show a wide distribution of the microstructural parameters for a given HT, but only slight differences between the microstructures produced by the two different HTs. This microstructural information allows a better understanding of the wide variety of the deformation micromechanisms observed during creep at high temperature.