修饰型多相手性催化剂在不对称合成中的应用

本文评述了修饰型多相手性催化剂在不对称合成中的应用。按照不同的制备方法及催化反应对一些多相催化体系进行了归类总结, 包括过渡金属手性配合物的固相化、修饰型手性固体催化剂、手性分子筛及嵌入型粘土手性催化剂。对酒石酸及金鸡纳碱修饰型金属催化剂的反应机理也进行了探讨。     

Acid and redox properties of mixed oxides prepared by calcination of chromate-containing layered double hydroxides

Layered double hydroxides (LDHs) with Mg and Al in the layers and carbonate, nitrate or chloride in the interlayer, or with Zn and Al in the layers and chloride in the interlayer, have been prepared by coprecipitation, and have been used as precursors to prepare chromate-containing LDHs. All these systems, as well as those obtained upon their calcination up to 800 °C, have been characterised by powder X-ray diffraction, FT-IR and vis-UV spectroscopies, temperature-programmed reduction (TPR), nitrogen adsorption at −196 °C for surface texture and porosity assessment, and FT-IR monitoring of pyridine adsorption for surface acidity determination. The results obtained show that the crystallinity of the chromate-containing LDH depends on the precursor used. The layered structure of the Mg, Al systems is stabilised up to 400 °C upon incorporation of chromate; however, the Zn,Al-chromate samples collapse between 200 and 300 °C, with simultaneous formation of ZnO. Calcination of the samples above 400 °C gives rise to a reduction of Cr(VI) to Cr(III), as concluded from vis-UV spectroscopic studies. The TPR profiles show that chromate in ZnAl hydrotalcite is more easily reduced than that incorporated in the magnesium ones. Moderately strong surface Lewis acid sites exist in all samples calcined below 500 °C.     

UV-vis辐照下H2Fe2Ti3O10/TiO2插层材料光催化活性的研究

在高压汞灯辐照下,通过插入反应将H2Fe2Ti3O10与n-C3H7NH2/C2H5OH和TiO2溶胶制备出H2Fe2Ti3O10/TiO2插层复合物.插入TiO2的层状钙钛矿化合物H2Fe2Ti3O10在UV-vis辐照下表现出高活性.实验结果表明H2Fe2Ti3O10/TiO2作为光催化剂在可见光(λ＞420nm)下辐照24h,降解甲基橙的速率为59.0;.与相同条件下降解率只有24;的商用光催化剂TiO2(Degussa P-25)相比,H2Fe2Ti3O10/TiO2表现出了更高的光催化活性.     

Synthesis and studies of some cholest-5-en-3-ol-(3β)[4-phenylpyridylazo]carbonate-containing supramolecular hydrogen-bonded mesogens

Mesogenic materials containing cholest-5-en-3-ol-(3β)[4-phenylpyridylazo]carbonate (CPPC) and 4-n-alkyloxybenzoic acids have been synthesized using hydrogen bonding as a mechanism for self-assembly. Phase diagrams of the binary mixtures of the hydrogen bond donor and acceptor were established using polarizing optical microscopy. The maximum isotropization point was observed for the 50 mol % composition confirming the formation of stable 1 : 1 complexes due to intermolecular hydrogen bonding. All the supramolecular assemblies built from 1 : 1 molar ratios of the hydrogen bond donor and acceptor moieties exhibit well defined smectic A (SmA) liquid crystal phases on heating and cooling cycles. The SmA phases exhibited by the complexes are not observed for the individual components. The azobenzene moiety of CPPC undergoes trans-cis-photoisomerization with a quantum yield of 0.1 and the activation energy for the thermal cis-trans-isomerization was estimated as 92 kJ mol-¹.     

Why do non-symmetric dimers intercalate? The synthesis and characterisation of the α-(4-benzylidene-substituted-aniline-4′-oxy)-ω-(2-methylbutyl-4′-(4″-phenyl)benzoateoxy)alkanes

Ten new non-symmetric liquid crystal dimers belonging to the family of compounds α-(4-benzylidene-substituted-aniline-4′-oxy)-ω-(2-methylbutyl-4′-(4″-phenyl)benzoateoxy)-alkanes have been synthesised and their transitional properties characterised. The dimers contain either a hexamethylene or octamethylene spacer, while the terminal substituents on the 4-benzylideneaniline fragment are H, CH₃, F, Cl and Br. The unsubstituted dimers are not liquid crystalline, while the remaining compounds exhibit enantiotropic nematic behaviour. The trends in the clearing temperatures, according to the chemical nature of the terminal substituent, are largely consistent with those established for conventional low molar mass liquid crystals. Three of the dimers also exhibit an intercalated smectic A phase, specifically the two bromo-substituted dimers and the chloro-substituted dimer containing a hexamethylene spacer. The driving force for the formation of this phase is considered to be, at least in part, the specific anisotropic interaction between the unlike mesogenic units. The absence of smectic behaviour for the isosteric methyl-substituted dimers reveals that steric factors alone cannot stabilise the intercalated smectic A phase.     

Controllable Modulation of Defects for Layered Double Hydroxide Nanosheets by Altering Intercalation Anions for Efficient Electrooxidation Catalysis

Hydrazine (N₂H₄) is considered as one of the most potential energy storage materials in liquid fuel cells, as it contains high energy and power density, and the high-efficiency oxidation of N₂H₄ in fuel cells has drawn great attention. However, the most used catalysts are expensive noble metal catalysts, thus the development of highly efficient non-noble metal catalysts is crucial to reduce the cost of hydrazine oxidation in practical industry. Herein, we synthesized a series of CoFe-layered double hydroxides (CoFe-LDHs) intercalated with different anions via a simple one-step co-precipitation method for the electrooxidation of hydrazine. Through altering the intercalated anions of CoFe-LDHs, the defects and the electronic structure can be well controlled, and the catalytic performance for the electrooxidation of hydrazine were well promoted by using NO₃⁻ intercalated into CoFe-LDH compared with other anions (like Cl⁻, BO₃³⁻, CO₃²⁻). This work developed a series of hydrazine electrooxidation catalysts and established the relationship between the intercalated anions, the fine structure of the catalyst and the electrocatalytic performance.     

Optimal charge inhomogeneity for the d+id-wave superconductivity in the intercalated graphite CaC6

The coexistence of superconductivity and charge inhomogeneity was observed in many cuprate superconductors. The relationship between those two is still controversial. Similarly, in the graphene sheets of the intercalated graphitic superconductor CaC₆, the charge inhomogeneity was also observed. We simulate such a system by constructing the Hubbard model on the honeycomb lattice with charge inhomogeneity imposed by force. Utilizing the finite-temperature determinant quantum Monte Carlo algorithm, we examine the relationship between the superconducting pairing and the charge inhomogeneity. An optimal charge inhomogeneity for the d+id-wave pairing is found. While for other artificial charge inhomogeneities, the d+id-wave pairing is monotonically suppressed. The possible π-phase shift induced by charge inhomogeneity is also examined.     

以功能为导向的插层结构功能材料结构设计及应用

插层结构功能材料是近年来迅速发展的一类新型功能材料。北京化工大学化工资源有效利用国家重点实验室多年来以插层结构功能材料的研究为基础,针对＂以功能为导向的结构设计＂等关键科学问题展开了大量基础和应用研究,实现了对材料微观主客体的设计和介观、宏观结构的调控,制备了多种新型插层结构功能材料,广泛应用于催化、环保、医药、纺织、...     

夹层化合物四氯合镉(Ⅱ)酸4-硝基苯铵的合成与结构

The title compound was prepared by the solid state reaction of stoichiometric amounts of CdCl₂·H₂O and 4-nitroaniline . The crystal used for X-ray analysis was obtained by slow evaporation of an ethanol-aqueous solution of the solid state reaction at room temperature. The structure of compound was characterized by X-ray diffraction analysis. The crystal belongs to orthorhombic, space group Pbca, a=0.77864(7)nm,b=0.72547(6)nm,c=3.3126(2)nm,Z=4,V=1.8712(3)nm³,D_c=1.890g·cm^-3,μ=1.763mm^-1, F(000)=1048,R=0.0300,wR=0.0697. The title compound is a typical two-dimensional organic intercalated compound. The inorganic layers of the compound are formed by CdCl₆ octahedra sharing corner Cl atoms (i.e. catena-poly[dihlorocadmium-di-μ-chloro]). The organic ammonium cations are intercalated between every two metal-halogen layers and formed the organic layers of the compound through hydrogen bonding.     

Yb-C_(60)插入化合物的拉曼光谱研究

本文主要对 Ybx C6 0 插入化合物在室温下的拉曼散射的实验结果进行了分析和讨论。名义组分为 Yb3C6 0 的化合物是超导相 ,可观测到由电 -声子相互作用引起的拉曼谱线展宽。高Yb组分的 Ybx- C6 0 ( x≥ 4)的拉曼谱线的展宽则更为严重 ,这表明 C6 0 分子已发生了严重的畸变。当 Ybx C6 0 样品暴露于空气中时 ,虽然该样品已变成了非晶态 ,但 C6 0 分子的畸变已大大的减小了。