Two‐Coordinate Fe0 and Co0 Complexes Supported by Cyclic (alkyl)(amino)carbenes

The CAAC [CAAC=cyclic (alkyl)(amino)carbene] family of carbene ligands have shown promise in stabilizing unusually low‐coordination number transition‐metal complexes in low formal oxidation states. Here we extend this narrative by demonstrating their utility in affording access to the first examples of two‐coordinate formal Fe⁰ and Co⁰ [(CAAC)₂M] complexes, prepared by reduction of their corresponding two‐coordinate cationic Fe^I and Co^I precursors. The stability of these species arises from the strong σ‐donating and π‐accepting properties of the supporting CAAC ligands, in addition to steric protection.     

氮化铝纳米锥的低温生长与场发射性能(英文)

考察了在600℃以下通过反应AlCl3+NH3→AlN+3HCl制备AlN纳米锥的规律,结果表明在500℃时仍可获得AlN纳米锥,当温度为480℃时则无氮化物生成。场发射测试显示在500~600℃温区内制得的AlN纳米锥的开启电场处于14.2~20 V·μm-1范围,且随制备温度升高而减小。结果表明AlN纳米锥可在低温条件下获得,且具有较好的场发射性能。     

Low‐Temperature Synthesis of Crystalline Inorganic/Metallic Nanocrystal‐Halloysite Composite Nanotubes

We have demonstrated a facile approach for the low‐temperature synthesis of crystalline inorganic/metallic nanocrystal‐halloysite composite nanotubes by employing the bulk controlled synthesis of inorganic/metallic nanocrystals on halloysite nanotubes. The halloysite clay nanotubes can adsorb the target precursor and induce inorganic/metallic nanocrystals to grow in situ. The crystalline phase and morphology of the composite clay nanotubes is tunable. By simply tuning the acidity of the titania sol, the crystalline titania‐clay nanotubes with tunable crystalline phases of anatase, a mixture of anatase and rutile or rutile are achieved. The approach is general and has been extended to synthesize the representative perovskite oxide (barium and strontium titanate)‐halloysite composite nanotubes. Metallic nickel nanocrystal can also be grown on the surface of halloysite nanotubes at low temperature. The traditional thermal treatment for crystallite transformation is not required, thus intact contour of halloysite nanotubes and the crystallinity structure of halloysite nanotubes can be guaranteed. The combined properties from inorganic/metallic nanocrystal (high refractive index, high dielectric constant and catalytic ability) and the halloysite clay nanotubes are promising for applications such as photonic crystals, high‐k‐gate dielectrics, photocatalysis and purification.     

Direct Electrochemistry of Horseradish Peroxidase Immobilized in a Low Molecular Weight Gel

The ternary system of dodecylpyridinium bromide (DDPB)/acetone/H₂O with appropriate composition can form a gel spontaneously and the gel is stable in hydrophobic ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim]PF₆). Based on the gelation phenomenon we observed, the low molecular weight gelator (LMWG) was first tried to immobilize horseradish peroxidase (HRP) on glassy carbon electrode (GCE). The scanning electron microscope (SEM) images, the UV‐Vis spectra and the bioactivity measurement indicate that the gel is suitable for the immobilization of HRP. The direct electrochemistry of the HRP‐gel modified GCE (HRP‐gel/GCE) in [Bmim]PF₆ shows a pair of well‐defined and quasi‐reversible redox peaks with the heterogeneous electron transfer rate constant (k_s) being 14.4 s^?1, indicating that the direct electron transfer between HRP and GCE is fast. The HRP‐gel/GCE is stable and reproducible. Also the electrode exhibits good electrocatalytic effect on the reduction of trichloroacetic acid (TCA), showing good promise in bioelectrocatalysis.     

Chemical‐Looping Reforming of Methane Using Iron Based Oxygen Carrier Modified with Low Content Nickel

Fe₂O₃/Al₂O₃ and Fe₂O₃/Al₂O₃ modified by low content of Ni (below 2% in weight) oxygen carriers were prepared by mechanical mixing and impregnation method. The synthesized oxygen carriers were characterized by means of X‐ray diffraction (XRD), X‐ray fluorescence (XRF), scanning electron microscopy (SEM), BET‐surface area and temperature programmed reduction (TPR). Besides, redox cyclic reactivity and the performance of chemical looping reforming of methane of the oxygen carriers were studied in a thermal gravimetrical analysis (TGA) and fixed bed at 850°C. It was observed that the redox reactivity of the oxygen carriers is improved by Ni addition because synergic effect may occur between NiO and Fe₂O₃/Al₂O₃ to form NiFe₂O₄ and NiAl₂O₄ spinel phases. However, the improvement was not apparent as Ni addition reached 1 wt% or more because more nickel loaded resulted in methane decomposition into H₂ and carbon leading to carbon deposition. The SEM and BET analysis showed that NiFe₂O₄ and NiAl₂O₄ particles dispersed into the pores of the Fe₂O₃/Al₂O₃ particles in the course of preparation. In addition, the resistance to sintering of the modified samples increased with the Ni addition increasing. The results of successive redox cycles showed that the Ni modified Fe₂O₃/Al₂O₃ oxygen carriers have good regenerability. With integration of reactivity and carbon deposition, the content 1.04 wt% of nickel doping was an optimal amount in the three modified samples.     

低温富集/GC-MS分析南丰蜜桔果肉成分的方法研究

建立了低温富集/气相色谱-质谱测定南丰蜜桔果肉成分的方法。对样品前处理中的溶剂种类、冷冻温度以及冷冻时间进行了优化,最终确定低温富集的前处理条件：正己烷为萃取溶剂;冷冻温度为-40 ℃;冷冻时间选择1 h。结果表明,采用低温富集/GC-MS结合保留指数定性对南丰蜜桔果肉进行成分分析,共鉴别出64种主要成分,主要包括酯类、萜烯类、醇类以及烷烃类。将低温富集所得结果分别与常温液液萃取结果及文献结果进行比较,所建立的方法可选择性富集一些极性大、热稳定性较差、难挥发性的物质。     

The effects of σC—Se–π hyperconjugation in 1‐methoxy‐ and 1‐nitro‐4‐[(phenylselanyl)methyl]benzene

The structures of 1‐methoxy‐4‐[(phenylselanyl)methyl]benzene, C₁₄H₁₄OSe, (1), and 1‐nitro‐4‐[(phenylselanyl)methyl]benzene, C₁₃H₁₁NO₂Se, (2), were determined at 130 K. The two structures, which differ in that (1) contains an electron‐rich aromatic ring and (2) contains an electron‐deficient aromatic ring, both adopt conformations which allow for σ_C—Se–π hyperconjugation. However, although there are significant differences in the ⁷⁷Se chemical shifts for these two compounds, they do not display significantly different H₂C—Se or H₂C—C_ar bond lengths, suggesting that the effects of σ_C—Se–π hyperconjugation in (1) and (2) are not strong enough to be manifested in measurable differences in the structural parameters.     

The low‐temperature form of calcium gold stannide,CaAuSn

The EuAuGe‐type CaAuSn phase has been synthesized and single‐crystal X‐ray diffraction analysis reveals that it has an orthorhombic symmetry (space group Imm2), with a = 4.5261 (7) Å, b = 7.1356 (11) Å and c = 7.8147 (11) Å. The structure features puckered layers that are connected by homoatomic Au—Au and Sn—Sn interlayer bonds. This structure is one of the two parent structures of its high‐temperature polymorph (ca 873 K), which is an intergrowth structure of the EuAuGe‐ and SrMgSi‐type structures in a 2:3 ratio.     

Asymptotic profile of solutions for strongly damped Klein‐Gordon equations

We consider the Cauchy problem in R ⁿ for strongly damped Klein‐Gordon equations. We derive asymptotic profiles of solutions with weighted L^1,1( R ⁿ) initial data by a simple method introduced by the second author. Furthermore, from the obtained asymptotic profile, we get the optimal decay order of the L²‐norm of solutions. The obtained results show that the wave effect will be relatively weak because of the mass term, especially in the low‐dimensional case (n = 1,2) as compared with the strongly damped wave equations without mass term (m = 0), so the most interesting topic in this paper is the n = 1,2 cases to compare the difference.     

A computational method for large‐scale differential symmetric Stein equation

We propose a numerical method for solving large‐scale differential symmetric Stein equations having low‐rank right constant term. Our approach is based on projection the given problem onto a Krylov subspace then solving the low dimensional matrix problem by using an integration method, and the original problem solution is built by using obtained low‐rank approximate solution. Using the extended block Arnoldi process and backward differentiation formula (BDF), we give statements of the approximate solution and corresponding residual. Some numerical results are given to show the efficiency of the proposed method.