Pd催化的配体导向C—H键乙酰化反应的理论研究

Pd催化的配体导向C-H键官能化反应已经成为有机化学中一种重要的合成手段. 我们用B3PW91密度泛函方法研究了Pd催化的配体导向C-H键乙酰化反应中催化剂和底物配合步骤以及C-H键活化步骤中的热力学性质. 研究发现, 具有不同导向基团的反应物之间竞争反应的选择性取决于导向基团与Pd(OAc)₂的配合步骤, 配合反应稳定常数大的较容易生成乙酰化的产物. 另一方面, 反应的选择性与C-H键的活化步骤无关, 并且与导向基团的配位原子的气相碱性、原子上的电荷密度以及最高占据轨道能量都没有相关性.     

Influence of containing moisture on hydrothermal stability of modified collagen thermal characteristics analysis by DSC

The thermal stability of sheepskin collagen cross-linked with chrome sulfate and mimosa (MI)–oxazolidine (OZ), respectively, had been researched in this experiment. All samples’ shrinkage temperatures (T _s) are determined by a special T _s-testing-apparatus and denaturation temperatures (T _d) are determined by the differential scanning calorimetry. The relations between the modified collagens containing moisture and their hydrothermal stability, T _s or T _d, were studied. The results show that the cross linking agents can enhance the thermal stability of modified collagen whose T _s are 109.8 and 110.6 °C for collagen treated with chrome and MI–OZ, respectively. When the samples contain 25–71.9% moisture for chrome leather and 20–71.1% for leather treated with MI–OZ, the hydrothermal stability will decrease with the increase of moisture. It was found that the difference between T _s and T _d of collagen modified by chrome is more obvious than that of collagen modified with MI–OZ. And when the moisture of chrome leather exceeds 55%, T _d cannot express thermal stability of modified collagen as a substitute for T _s, and the moisture is 40% for leather tanned with MI–OZ.     

汞离子氧化碘离子实验的设计与研究

通过分析硝酸汞与碘化钾混合溶液不发生氧化还原反应的原因,成功地设计了Hg2+氧化I-的实验方法。结果表明,沉淀反应的存在阻止了氧化还原反应的发生,可能是沉淀反应速率快于氧化还原反应速率所致。该方法仪器简单、操作方便,现象明显易观察,成功率高、效果好。     

Synthesis and fluorescent properties of europium complexes with amide-type podand ligands of methyl salicylate

Amide-type podands derived from N,N′-(ethane-1,2-diyl)bis(2-hydroxybenzamide) and 2-chloro-N-phenylacetamide (substituted with methyl, methoxy, chlorine, nitrogen) were synthesized. Solid complexes of europium nitrate with podands were also synthesized and characterized by elemental analysis, ethylenediaminetetraacetic acid (EDTA) titrimetric analysis, thermal analysis, molar conductivity analysis, and infrared (IR) and ultraviolet–visible (UV–Vis) spectra analysis. The fluorescent properties of the europium(III) [Eu(III)] complexes in a solid state were also investigated. Under excitation of UV light, target Eu(III) complexes exhibited characteristic europium ion emissions. The influence of the substituent on the fluorescence intensity was discussed. Electrochemical properties were also investigated and discussed.     

Silver-based coordination complexes of carboxylate ligands: crystal structures,luminescence and photocatalytic properties

The complexes [Ag₄(dpe)₄]·(btec) (1) and [Ag₄(bpy)₄]·(btec)·12H₂O (2) (dpe = 1,2-di(4-pyridyl)ethylene, bpy = 4,4′-bipyridine, H₄btec = 1,2,4,5-benzenetetracarboxylic acid) have been synthesized in aqueous alcohol/ammonia by slow evaporation at room temperature and characterized by elemental analysis, single-crystal X-ray diffraction, FTIR, UV–Vis and luminescence spectroscopies. Both complexes are composed of 1D infinite cationic [Ag/dpe(bpy)] _n ⁿ⁺ chains and discrete btec^4? anions. Their three-dimensional supramolecular structures are built up of cationic sheets formed from [Ag/dpe(bpy)] _n ⁿ⁺ units via weak Ag…Ag and Ag…N interactions, plus anionic btec^4? sheets featuring electrostatic, π–π and hydrogen bonding interactions. Both complexes exhibited photocatalytic activity for the decomposition of methyl orange under UV light irradiation.     

Enhanced production of poly-3-hydroxybutyrate by recombinant Escherichia coli containing NAD kinase and phbCAB operon

With the help of Tn5 transposon technique, gene yfjB encoding NAD kinase in Escherichia coli (E. coli) was inserted into chromosome of recombinant E. coli polyhydroxybutyrate (PHB) containing PHB synthesis operon integrated in the host genome. After successful transposition of an extra yfjB gene copy into genome, the selected recombinant named E. coli PHBTY4 showed stronger NAD kinase activity than that of E. coli PHB. Shake flask studies suggested that both cell dry weight and PHB accumulation were significantly increased in E. coli PHBTY4 compared with that of the control. E. coli PHBTY4 produced approximately 23 g/L PHB compared with its control which synthesized only 10 g/L PHB when grown under the same conditions in a 6 L fermentor after 32 h of cultivation. In addition, E. coli PHBTY4 maintained high genetic stability during the cultivation processes. These results revealed a practical method to construct genetically stable strains harboring extra NAD kinase gene to enhance NADP(H)-dependent bio-reactions.     

Synthesis and characterization of a novel binuclear iron phthalocyanine/reduced graphene oxide nanocomposite for non-precious electrocatalyst for oxygen reduction

Binuclear iron phthalocyanine/reduced graphene oxide(bi-Fe Pc/RGO) nanocomposite with good electrocatalytic activity for ORR in alkaline medium was prepared in one step. High angle annular dark field image scanning transmission electron microscopy(HAADF-STEM) and energy dispersive X-ray spectroscopy element mapping results show bi-Fe Pc was uniformly distributed on RGO. An obvious cathodic peak located at about-0.23 V(vs. SCE) in CV and an onset potential of-0.004 V(vs. SCE) in LSV indicate the as-prepared bi-Fe Pc/RGO nanocomposite possesses high activity which is closed to Pt/C for ORR. The ORR on bi-Fe Pc/RGO nanocomposite follows four-electron transfer pathway in alkaline medium. Compared with Pt/C, there is only a slight decrease(about 0.02 V vs. SCE) for bi-Fe Pc/RGO nanocomposite when the methanol exists. The excellent activity and methanol tolerance in alkaline solutions proves that bi-Fe Pc/RGO nanocomposite could be considered as a promising cathode catalyst for alkaline fuel cells.     

Open‐Pore Two‐Dimensional MFI Zeolite Nanosheets for the Fabrication of Hydrocarbon‐Isomer‐Selective Membranes on Porous Polymer Supports

Two‐dimensional zeolite nanosheets that do not contain any organic structure‐directing agents were prepared from a multilamellar MFI (ML‐MFI) zeolite. ML‐MFI was first exfoliated by melt compounding and then detemplated by treatment with a mixture of H₂SO₄ and H₂O₂ (piranha solution). The obtained OSDA‐free MFI nanosheets disperse well in water and can be used for coating applications. Deposits made on porous polybenzimidazole (PBI) supports by simple filtration of these suspensions exhibit an n‐butane/isobutane selectivity of 5.4, with an n‐butane permeance of 3.5×10^?7 mol m^?2 s^?1 Pa^?1 (ca. 1000 GPU).     

Ordered PdCu‐Based Nanoparticles as Bifunctional Oxygen‐Reduction and Ethanol‐Oxidation Electrocatalysts

The development of superior non‐platinum electrocatalysts for enhancing the electrocatalytic activity and stability for the oxygen‐reduction reaction (ORR) and liquid fuel oxidation reaction is very important for the commercialization of fuel cells, but still a great challenge. Herein, we demonstrate a new colloidal chemistry technique for making structurally ordered PdCu‐based nanoparticles (NPs) with composition control from PdCu to PdCuNi and PtCuCo. Under the dual tuning on the composition and intermetallic phase, the ordered PdCuCo NPs exhibit better activity and much enhanced stability for ORR and ethanol‐oxidation reaction (EOR) than those of disordered PdCuM NPs, the commercial Pt/C and Pd/C catalysts. The density functional theory (DFT) calculations reveal that the improved ORR activity on the PdCuM NPs stems from the catalytically active hollow sites arising from the ligand effect and the compressive strain on the Pd surface owing to the smaller atomic size of Cu, Co, and Ni.     

Rapid Identification of the Receptor‐Binding Specificity of Influenza A Viruses by Fluorogenic Glycofoldamers

The re‐emergence of influenza raises a global concern that viral pandemics can unpredictably occur. However, effective approaches that can probe the infection risk of influenza viruses for humans are rare. In this work, we develop a glycofoldamer that can rapidly identify the glycan‐receptor specificity of influenza viruses in a high‐throughput manner. The coupling of glycan receptors that can be recognized by hemagglutinin (a surface protein on the virion capsid of influenza) to a fluorogenic‐dye foldamer produces the glycofoldamers with minimal fluorescence in aqueous solution. After interaction with human‐infecting virus strains for only five minutes, the fluorescence intensity of the glycofoldamer is remarkably enhanced with a blue‐shifted emission peak. The probes have also proven effective for the rapid identification of 1) the human‐ or bird‐infecting properties of influenza viruses in a high‐throughput manner and 2) the receptor‐specificity switch of a virus strain by mutations.