Enantioselective Diels–Alder reactions with left-handed G-quadruplex DNA-based catalysts

Since the discovery of left-handed G-quadruplex (L-G4) structure formed by natural DNA, there has been a growing interest in its potential functions. This study utilised it to catalyse enantioselective Diels-Alder reactions, considering its different optical rotation compared to an ordinary G4. It was determined that when L-G4 was used with a combination of copper(II) ions, there was a good enantioselectivity (?52% ee) without further addition of ligands. When further consideration was given by adding G4 ligands, G4 was further stabilised, even obtaining a better enantioselectivity (up to ?80% ee). Moreover, when using ligands that have regulatory effects on G4, the ee value can be adjusted. In this work, a minimal left-handed G4 was reported. A follow-up study was also conducted, which recovers that the minimal left-handed G4 remains its catalytic effect and enantioselectivity, but is not so effective as the former case. This indicates that a complete G4 structure is relatively conducive to chiral catalysis.     

Analysis of secondary electron emission using the fractal method

Based on the rough surface topography with fractal parameters and the Monte–Carlo simulation method for secondary electron emission properties, we analyze the secondary electron yield(SEY) of a metal with rough surface topography. The results show that when the characteristic length scale of the surface, G, is larger than 1 × 10^-7, the surface roughness increases with the increasing fractal dimension D. When the surface roughness becomes larger, it is difficult for entered electrons to escape surface. As a result, more electrons are collected and then SEY decreases. When G is less than 1 × 10^-7,the effect of the surface topography can be ignored, and the SEY almost has no change as the dimension D increases. Then,the multipactor thresholds of a C-band rectangular impedance transfer and an ultrahigh-frequency-band coaxial impedance transfer are predicted by the relationship between the SEY and the fractal parameters. It is verified that for practical microwave devices, the larger the parameter G is, the higher the multipactor threshold is. Also, the larger the value of D,the higher the multipactor threshold.     

Hydrogen production via catalytic decomposition of NH3 using promoted MgO-supported ruthenium catalysts

Catalytic decomposition of NH_3 to high purity hydrogen offers a promising strategy for fuel cells, but presents challenges for high hydrogen yields at comparatively low temperatures due to the lack of efficient catalysts. Here, we report the facile preparation of ultra-fine ruthenium(Ru) species dispersed on Mg O, which show excellent activity and high temperature stability for NH_3 decomposition reaction. The hydrogen yield of the prepared Ru/Mg O catalysts reaches ca. 2,092 mmol H_2 g~(–1) Ru min~(–1) at450 °C, far exceeding that of the previously reported most reactive Ru-based catalysts and the same chemical composition samples prepared by other approaches. Various characterization techniques containing X-ray absorption fine structure(XAFS),in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRTFTS) and temperature-programmed reduction/desorption(TPR/TPD) were carried out to explore the structure-function relation of the prepared Ru/Mg O catalysts. We found that the Ru species interact strongly with the Mg O support, which can efficiently protect the Ru species and Mg O support from agglomerating during NH_3 decomposition test, maintaining the stability of the catalysts.     

我国高等学校分析化学教材建设研究

从教材出版工作者的角度,对我国高等学校分析化学课程改革,特别是分析化学教材建设的发展进行了初步研究。从时间上看,分析化学教材的发展经历了雏形期、发展期和成熟期3个时期。文中重点阐述了不同时期典型分析化学教材的外在表现形式和具体教学内容的特点和变化,并对分析化学教材的建设趋势进行了初步探讨。     

电感耦合等离子体原子发射光谱法测定人造金刚石中铁、钴、锰、镍

1引言近年来,我国人造金刚石的产量和应用有了很大的发展。以现有的人造金刚石合成技术,通常以Fe,Ni,Co,Mn等元素组成的合金作为触媒,这使人造金刚石中极易残留这些金属组成的包裹体。诸多研究表明,包裹体含量和分布情况对人造金刚石的性能有着重要影响[1]。经查阅文献,已有使用X射线荧光光谱法对人造金刚石中杂质元素含量进行半定量分析的报道[2]。电感耦合等离子体发射光谱法(ICP-AES)被广泛应用于岩矿、土壤样品中多元素分析[3]。本实验以在大气气氛中高温灰化和混合酸对样品进行前处理,采用ICP-AES测定人造金刚石中Fe,Co,Ni和Mn。本方法操作简便,处理效果良好。     

弯纵复合超声直线马达的研究

本文研究了一种利用一阶纵振动和二阶弯曲振动的弯纵直线超声马达，采用加粗两端金属块的方法达到频率简并。实验测量得出一阶纵振动为36．6kHz，二阶弯曲振动频率为37．3kHz。利用该马达设计研制了一套驱动装置，经实验测得，当马达的预压力14．3N时，该装置无承载且无负载速度大于6cm／s；该装置承载196N的重物且负载l-2kgf时，仍能正常运行。     

超短超强激光脉冲辐照超薄碳膜电离状态研究

为了进一步理解极端条件下物质的电离特性, 特别是超短超强激光脉冲辐照超薄靶时等离子体的形成与分布, 本文以超薄碳膜为例, 细致研究了超短超强激光脉冲辐照下原子的离化过程. 分析和比较了强激光场直接作用电离和靶内静电场电离等两种场致电离形式, 在碰撞电离可以忽略的情况下, 发现更多的电离份额是来自靶内静电场的电离方式. 研究了激光脉冲强度对电离的影响, 发现激光脉冲强度越强, 电离速度越快, 产生的高价态离子所占比例也越高.当激光强度为1×10²⁰ W/cm²时, 尽管该强度高于电离生成C⁺⁶所需要的激光强度阈值, 但该激光脉冲并不能将整个靶电离成C⁺⁶离子, 对此本文进行了详细的分析. 在研究激光脉冲宽度的影响时, 发现激光脉宽越小, 电离速度越快, 但越小的激光脉冲电离获得的高价态离子越少.     

Chiral amine-thioureas bearing multiple hydrogen bonding donors: highly efficient organocatalysts for asymmetric Michael addition of acetylacetone to nitroolefins

New bifunctional organocatalysts amine-thioureas bearing multiple hydrogen bonding donors were synthesized and applied in catalytic asymmetric Michael addition of acetylacetone to aryl and alkyl nitroolefins. Multiple hydrogen bonding donors play a significant role in accelerating reactions, improving yields and enantioselectivities.     

CaCu3Ti4O12 陶瓷介电模量响应特性的研究

由于CaCu₃Ti₄O₁₂巨介电常数陶瓷的低频区直流电导较大, 本文采用模量 M"-f频谱表征与分析了低频和高频的两个松弛极化过程. 研究认为, 这两个特征峰属于晶界区Schottky 势垒耗尽层边缘深陷阱的电子松弛过程, 其中高频松弛峰起源于晶粒本征缺陷的电子松弛过程, 而低频松弛峰则为与氧空位有关的松弛极化过程. 对于CaCu₃Ti₄O₁₂这类低频下具有高直流电导的陶瓷材料, 采用模量频谱能更有效地分析研究其损耗极化机理. 关键词： 3Ti₄O₁₂陶瓷')" href="#">CaCu₃Ti₄O₁₂陶瓷 模量 松弛过程 电导     

Asymmetric construction of 3-vinylidene-pyrrolidine derivatives containing allene moiety via Ag(I)/TF-BiphamPhos-catalyzed 1,3-dipolar cycloaddition of azomethine ylides with diethyl 2-(3,3-diphenylpropa-1,2-dienylidene) malonate

Catalytic asymmetric 1,3-dipolar cycloaddition of various azomethine ylides with diethyl 2-(3,3-diphenylpropa-1,2-dienylidene)malonate has been developed successfully with good to excellent enantioselectivity for the effcient construction of 3-vinylidene-pyrrolidine derivatives containing a unique allene moiety.