Rapid Fabrication of Hollow SiO2 Spheres with Novel Morphology

The hydrolysis of tetraethoxysilane (TEOS) occurred on the surface of poly(methyl methacrylate) (PMMA) microshperes immediately after these microshperes were prepared in TEOS. Micron-sized hollow SiO2 spheres were obtained by calcination of the coated PMMA microshperes. It was found that the final hollow spheres were constituted by small SiO2 particles.     

Headspace Solid-phase Microextraction–Gas Chromatographic–Mass Spectrometric Analysis of the Essential Oils of Two Traditional Chinese Medicines, Angelica pubescens and Angelica sinensis

Angelica pubescens and Angelica sinensis belong to the Umbelliferae family and both are used as traditional Chinese medicines. In the present study, headspace solid-phase microextraction (HS-SPME) with gas chromatography-mass spectrometry (GC-MS) was used for the analysis of the volatile constituents present in their roots. Eighty-seven compounds in Angelica pubescens and thirty-six compounds in Angelica sinensis were identified by GC-MS. Their relative contents were calculated by the peak area ratio. HS-SPME was compared to steam distillation (SD) by analyzing the volatile constituents of Angelica sinensis root. A good agreement between results obtained with both techniques was found. As a conclusion, HS-SPME is a powerful tool for determining the volatile constituents present in the TCMs.     

Amine-templated metal squarates

Two layered amine-templated cobalt squarates, [C₆N₂H₁₄]₂[Co₂(C₄O₄)₃(H₂O)₄], I, and [C₃N₂H₅]₂[Co₂(C₄O₄)₃(H₂O)₄], II, have been prepared under hydrothermal conditions. Both I and II contain chains formed by dimers comprising two cobalt atoms bound to the squarate units, the chains being connected through hydrogen bond interactions. An amine-templated cobalt squarate of the formula [C₄N₂H₁₂][Co(C₄O₄)₂(H₂O)₄][H₂O]₂, III, as well as its Ni, Zn and Cd analogues have been prepared by room temperature reactions. III has a layered architecture wherein the cobalt-squarate monomers are linked by the amine molecules. Co and Zn analogues of [Ni(C₄O₄)(H₂O)₂(C₃N₂H₄)] with ligating imidazole units have also been prepared and characterized.     

从头计算方法比较TiSi_2的C54相和C49相

采用平面波超软赝势描述多电子体系,利用密度泛函理论和广义梯度近似,计算出C54相和C49相TiSi2的晶格常数、体弹性模量、形成能、电子态密度(DOS)和Mulliken电荷布居等性质.通过比较这两种物质的性质,发现尽管两者形成能很相近,但C49相结构对称性差、体弹性模量小、熔点低,Ti原子d轨道的反键强、离子性弱.这些性质上的差异和C49相TiSi2在固相反应中优先形成有关.     

Synthesis and photoluminescence properties of 8-hydroxyquinoline derivatives and their metallic complexes

Three new 8-hydroxyquinoline derivatives, i.e. 5-[(4-styryl-benzylidene)-amino]-quinolin-8-ol (1), 5-[(4-bromo-2-fluoro-benzylidene)-amino]-quinoline-8-ol (2) and 2-[2-(9-ethyl-9H-carbazol-2yl)-vinyl]-quinolin-8-ol (3), and their metallic complexes were synthesized and identified by ultraviolet-visible (UV-Vis), ¹H nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectrometer (FTIR), mass spectrometry (MS) spectra and elemental analyses. Their fluorescence properties were studied by photoluminescence, which indicated that the luminescence wavelength of 5-and 2-substitued-8-hydroxyquinoline derivatives shifted to red in comparison with that of 8-hydroxyquinoline. Meanwhile, the fluorescence lifetime of 2-[2-(9-ethyl-9H-carbazol-2yl)-vinyl]-quinolin-8-ol and its zinc complex showed long lifetime in benzene solution. __________ Translated from Chinese Journal of Organic Chemistry, 2007, 27(3): 402–408 [译自: 有机化学]     

Needlelike and spherical polyelectrolyte complex nanoparticles of poly(l-lysine) and copolymers of maleic acid

We report on the bulk and surface properties of dispersions consisting of nonstoichiometric polyelectrolyte complex (PEC) nanoparticles. PEC nanoparticles were prepared by mixing poly(l-lysine) (PLL) or poly(diallyldimethylammonium chloride) (PDADMAC) with poly(maleic acid-co-alpha-methylstyrene) (PMA-MS) or poly(maleic acid-co-propylene) (PMA-P). The monomolar mixing ratio was n-/n+ = 0.6, and the concentration ranged from 1 to 6 mmol/L. Subsequent centrifugation enabled the separation of the excess polycation, resulting in a stable coacervate phase further used in the experiments. The bulk phase parameters turbidity and hydrodynamic radius (R(h)) of the PEC nanoparticles showed a linear dependence on the total polymer content independently of the mixed polyelectrolytes. This can be interpreted by the increased collision probability of the polyelectrolyte chains when the overlap concentration is approached or exceeded. Different morphologies of the cationic PEC nanoparticles, which were solution-cast onto Si supports, were obtained by atomic force microscopy (AFM). The combinations of PLL/PMA-MS and PDADMAC/PMA-MS revealed more or less hemispherical particle shapes, whereas that of PLL/PMA-P revealed an elongated needlelike particle shape. Circular dichroism and attenuated total reflection Fourier transform infrared (ATR-FTIR) measurements proved the alpha-helical conformation for the PEC PLL/PMA-P and the random coil conformation for the PEC PLL/PMA-MS. We conclude that stiff alpha-helical PLL induces anisotropic elongated PEC nanoparticles, whereas randomly coiled PLL forms isotropic spherical PEC nanoparticles.     

Improved hygrothermal durability of flax/polypropylene composites after chemical treatments through a hybrid approach

There are growing research interests in flax fibers due to their renewable ‘green’ origin and high strength. However, these natural fibers easily absorb moisture and have poor adhesion with polymer matrix leading to low interfacial strength for the composites. A hybrid chemical treatment technique combining alkali (sodium hydroxide) and silane treatments is adopted in the current study to modify flax fibers for improved performances of flax/polypropylene composites. Changes in chemical composition, microstructure, wettability, surface morphology, crystallinity and tensile properties of single flax fiber before and after chemical treatments were comprehensively characterized using techniques including SEM, FTIR, AFM, XRD, micro-fiber tester, etc. It was found that hemicellulose and lignin at the fiber surface were removed due to alkali treatment, which helped to reduce moisture absorption of the composites. Alkali-treated flax fibers were later subjected to silane treatment, which helped to improve the compatibility between flax fiber and polypropylene matrix. After alkali-silane hybrid chemical treatment, moisture absorption of the composites was further decreased. At the same time, the interfacial bonding strength between flax and polypropylene is significantly enhanced. All these results validate the great advantage of the hybrid chemical treatment approach for flax/polypropylene composites, which has the potential to promote the application of chemical treatment techniques in the plant fiber composite industry.

Graphic abstract

     

烯丙基碘和锡与醛的选择加成反应

含活性基团的醛可与烯丙碘和锡粉直接进行亲核加成反应，得到高烯丙基的醇，水的存在不利于此反应的进行，与烯丙基溴相比，烯丙基碘反应活性更强，可在短时间内得较高的产率。     

1,4-Addition of benzene to a dihydrocyclopent[a]indene diradical: synthesis and DFT study

Photochemical cyclization of compound 1, a homoenediyne (-CCC=CCH2CC-) bearing two ethynylanthracene chromophores, yields two isomeric dihydrocyclopent[a]indene ring systems, spiro-fused to the 9-position of a 9,10-dihydroanthracene moiety. Evidence of a photochemically initiated diradical cyclization pathway is proposed on the basis of (i) hydrogen abstraction from reaction with 1,4-cyclohexadiene (1,4-CHD) and (ii) the observation of 1,4-addition of benzene (solvent). The reaction was further analyzed by a complete density functional theory (DFT) study, using an unrestricted approach (UBLYP) with a 6-31G* basis set for the open-shell triplet states of the reactants, products, and diradical intermediates to model the photochemical nature of observed transformation. A mechanism detailing the observed cyclization/addition reaction is proposed.