Microstructural evolution of AZ31 magnesium alloy subjected to sliding friction treatment

Microstructural evolution and grain refinement mechanism in AZ31 magnesium alloy subjected to sliding friction treatment were investigated by means of transmission electron microscopy. The process of grain refinement was found to involve the following stages: (I) coarse grains were divided into fine twin plates through mechanical twinning; then the twin plates were transformed to lamellae with the accumulation of residual dislocations at the twin boundaries; (II) the lamellae were separated into subgrains with increasing grain boundary misorientation and evolution of high angle boundaries into random boundaries by continuous dynamic recrystallisation (cDRX); (III) the formation of nanograins. The mechanisms for the final stage, the formation of nanograins, can be classified into three types: (i) cDRX; (ii) discontinuous dynamic recrystallisation (dDRX); (iii) a combined mechanism of prior shear-band and subsequent dDRX. Stored strain energy plays an important role in determining deformation mechanisms during plastic deformation.     

Enantioselective phospha-Michael reaction of diethyl phosphonate with exocyclic α,β-unsaturated benzocyclic ketones catalyzed by a dinuclear zinc−AzePhenol catalyst

The dinuclear zinc complexes as high performance catalysts were used to catalyze phospha-Michael reaction of exocyclic α,β-unsaturated benzocyclic ketones under mild conditions, and the desired products possessing 1-indanones or 1-tetralones skeleton were obtained with excellent enantioselectivities of up to 99%/99% ee and yields of up to 99%. The absolute stereochemistry of the major products catalyzed by (R,R)-L1 was determined to be the (R,R)-configuration by X-ray crystallographic analysis of 3d. A positive nonlinear effect was observed and the possible mechanism was proposed.     

Large‐Scale Synthesis of Enantiopure Molecular Cages: Chiroptical and Recognition Properties

A convenient and efficient gram‐scale synthesis for enantiopure hemicryptophane–tren (tren=tris(2‐aminoethyl)amine) derivatives has been developed. The four‐step synthesis is based on the optical resolution of a key intermediate, cyclotriveratrylene, for which the energy barrier for racemization has been measured to ensure that no racemization occurs during the two last steps of the synthetic pathway. The assignments of the absolute configurations have been performed by electronic circular dichroism and the enantiopurity was determined by NMR spectroscopy in the presence of enantiopure camphor sulfonic acid. To highlight the interest of such compounds, the recognition of norephedrine neurotransmitter was investigated and showed a remarkable enantioselectivity towards the C₃ symmetrical hosts. Finally, this highly modular synthetic pathway was used to provide eight enantiopure hemicryptophanes with different sizes, shapes, and functionalities. These results underline the high potential of this approach, which could lead to many applications in chiral recognition or asymmetric supramolecular catalysis.     

Crystal structure,thermal expansion and magnetic properties of Nd2Cu0.8Ge3 compound

A new ternary intermetallic compound, Nd₂Cu_0.8Ge₃, was synthesized and its crystal structure was determined by Rietveld refinement of X-ray powder diffraction data. The Nd₂Cu_0.8Ge₃ compound crystallizes in space group I4₁/amd (No. 141), with a tetragonal a-ThSi₂ structure type, and a=0.41783(2) nm, c=1.43689(9) nm, Z=2 and D_calc=7.466 g/cm³. Using the high temperature powder X-ray diffraction (HTXRD) technique, the lattice thermal expansion behavior of the compound was investigated in the temperature range of 298–648 K, and the result shows that its unit-cell parameters increased anisotropically when temperature increased. The magnetic susceptibility measured in the temperature range of 5–300 K indicated antiferromagnetic order of Nd₂Cu_0.8Ge₃ at low temperatures, and the magnetic susceptibility can be well described over the range of 50–300 K using Curie–Weiss law. The calculated effective magnetic moment (μ_eff) is 3.53 μ_B and dominated by the contribution of the Nd³⁺ ions.     

Optimization and validation of organochlorine compounds in adipose tissue by SPE‐gas chromatography

Scientific evidence has shown an association between organochlorine compounds (OCC) exposure and human health hazards. Concerning this, OCC detection in human adipose samples has to be considered a public health priority. This study evaluated the efficacy of various solid‐phase extraction (SPE) and cleanup methods for OCC determination in human adipose tissue. Octadecylsilyl endcapped (C₁₈‐E), benzenesulfonic acid modified silica cation exchanger (SA), poly(styrene‐divinylbenzene (EN) and EN/RP₁₈ SPE sorbents were evaluated. The relative sample cleanup provided by these SPE columns was evaluated using gas chromatography with electron capture detection (GC–ECD). The C₁₈‐E columns with strong homogenization were found to provide the most effective cleanup, removing the greatest amount of interfering substance, and simultaneously ensuring good analyte recoveries higher than 70%. Recoveries > 70% with standard deviations (SD) < 15% were obtained for all compounds under the selected conditions. Method detection limits were in the 0.003–0.009 mg/kg range. The positive samples were confirmed by gas chromatography coupled with tandem mass spectrometry (GC‐MS/MS). The highest percentage found of the OCC in real samples corresponded to HCB, o,p′‐DDT and methoxychlor, which were detected in 80 and 95% of samples analyzed respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Intrinsic Crosslinking and Gel-Breaking Rheokinetics of CMHEC/CTAB Systems

The intrinsic rheokinetics of carboxymethyl hydroxyethyl cellulose and cetyltrimethyl ammonium bromide (CMHEC/CTAB) synergistic fracturing fluid in static crosslinking and gel-breaking processes were studied in this work. Microrheological properties including solid–liquid balance (SLB) and elasticity index (EI) during the static crosslinking and gel-breaking processes were obtained. The effects of temperature on the crosslinking process, concentration of gel-breaker (ammonium persulfate), and temperature on the gel-breaking process were investigated. The novel intrinsic crosslinking and gel-breaking rheokinetics equations were established, respectively. The results show that the crosslinking process can be divided into two stages, and the intrinsic crosslinking rheokinetics equation can well describe EI curves during the static crosslinking process at different temperatures. The EI curves during the gel-breaking process can be well described by the intrinsic gel-breaking rheokinetics equation. The parameters for these two rheokinetics equations are well-defined and reasonable.     

Synthesis,structure and property of diorganotin N‐[(3‐methoxy‐2‐oxyphenyl)methylene]tyrosinates

Five new diorganotin N‐[(3‐methoxy‐2‐oxyphenyl)methylene] tyrosinates, R₂Sn[2‐O‐3‐MeOC₆H₃CH=NCH (CH₂C₆H₄OH‐4)COO] (R = Me, 1 ; Et, 2 ; Bu, 3 ; Cy, 4 ; Ph, 5 ), have been synthesized and characterized by elemental analysis, IR, NMR (¹H, ¹³C and ¹¹⁹Sn) spectra, and the X‐ray single crystal diffraction. In non‐coordinated solvent, complexes 1 – 5 have penta‐coordinated tin atom. In the solid state, 1 – 3 are centrosymmetric dimmers in which each tin atom is seven‐coordinated in a distorted pentagonal bipyramid, and 4 displays discrete molecular structure with distorted trigonal bipyramidal geometry, and the tin atom of 5 is hexa‐coordinated and possess the distorted octahedral geometry with a coordinational methanol molecule. The intermolecular O‐H???O hydrogen bonds in 1 – 4 link molecules into the different one‐dimensional supramolecular chain with R₂² (30) or R₂² (20) macrocycles, and the molecules of 5 are joined into a two‐dimensional supramolecular network containing R₄⁴ (24) and R₄⁴ (28) two macrocycles. Bioassay results against human tumour cell HeLa indicated that 3 ‐ 5 belonged to the efficient cytostatic agents and the activity decreased in the order 4 > 3 > 5 > 2 > 1. The fluorescence determinations show the complexes may be explored for potential luminescent materials.