Absolute configurations and circular dichroism of sesquiterpene-coumarin ethers

The absolute stereochemistry of 14 naturally occurring sesquiterpenecoumarin ethers is discussed. In 13 cases the coumarin moiety is isofraxidin (7-hydroxy-6,8-dimethoxycoumarin), in one case scopoletin (7-hydroxy-6-methoxycoumarin). The sesquiterpene moieties belong either to the bicyclic drimenole series or to its consecutive products (methyl migration, ring opening). The CD spectra of all compounds are given. The assignments of the absolute configurations are based on the method ofHoreau, chemical correlation by degradation reactions, extensive comparison of CD data, and biogenetic considerations.

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Absolute Konfigurationen und Circulardichroismus von Sesquiterpen-Cumarin-Ethern

Zusammenfassung Es wird die absolute Stereochemie von 14 natürlich vorkommenden Sesquiterpen-Cumarin-Ethern diskutiert. In 13 Fällen wird die Cumarineinheit von Isofraxidin (7-Hydroxy-6,8-dimethoxycumarin) repräsentiert, in einem Fall von Scopoletin (7-Hydroxy-6-methoxycumarin). Der Sesquiterpenteil ist entweder von Drimenol oder Folgeprodukten (Methylgruppenwanderung, Ringöffnung) abgeleitet. Die CD-Spektren aller Verbindungen sind angegeben. Die Zuordnung der absoluten Konfigurationen basiert auf der Methode vonHoreau, chemischer Korrelation über Abbaureaktionen, Vergleich der CD-Spektren und biogenetischen Überlegungen.

     

土壤中铅的含量及其化学形态分析

对广州市黄埔港区所取土壤中铅的化学形态分析进行了研究。采用含不同组分提取剂的连续提取程序对1 g土壤进行提取,使之分成8种形态的铅,并用火焰原子吸收光谱法(FAAS)对每种提取所得的形态中的铅进行了测定。另在一份试样中直接测定其总铅量,对提取剂的组成及其溶液的浓度及提取操作条件进行了研究和优化,对FAAS测定方法的仪器工作条件作了说明。试验结果表明,所取试样中大部分铅以稳定的结合形态存在,以可交换态和碳酸盐结合态存在的铅仅达6%,总铅量随土壤深度的增加而减少。FAAS测定方法的灵敏度和检出限依次为0.007 mg.L-1及0.01 mg.L-1,分析和测定了4个试样中8种形态的铅量,其加和量为147.9 mg.kg-1,与直接测得的总铅量(159.9 mg.kg-1)之间的偏差小于10%。     

Copper ring-disk microelectrodes: fabrication, characterization, and application as an amperometric detector for capillary columns

A novel approach to the fabrication of metal ring-disk (RD) microelectrodes is presented that employs flexible chemical vapor deposition (CVD) and electrode modification techniques. Specifically, the development of a copper ring-disk microelectrode is described utilizing a combination of CVD coating, electroetching, and electroplating. Initially, a 25 μm diameter tungsten wire is concentrically coated by CVD with an insulating layer of silica, a layer of tungsten metal, and finally, a second outer layer of silica. The copper surface was prepared by first creating micrometer cavities by electrochemical etching the tungsten in hydroxide solutions followed by electrodeposition of copper from aqueous solutions of Cu(II). Each step of the process was characterized by scanning electron microscopy, optical microscopy, and cyclic voltammetry, demonstrating the preparation of a viable metal-based dual ring-disk microelectrode system. For the purpose of demonstrating the concept of introducing specific selectivity into the device, amperometric detection of galactose in 0.1 M NaOH was performed at +0.60 V in bulk solution and after flow injection analysis in a capillary column.     

高温超导体的Cu-O键型和氧上的部分电荷

多数钙钛矿型化合物是离子型绝缘体，而高温超导化合物则有金属电性，它们是以什么键型为主？对此等人[1]认为用共价或金属成键图像描述高温超导体在化学上更合理，Nepela等人[2]指出超导体临界温度（Tc）随阴离子平均电负性与阳离子平均电负性之差增大而升高．这意味着离子性较强的超导体有较高的人．杨频等问运用晶型键参数方法估算结果表明高温超导体属干部分离子性与部分共价性键．以上不同的结果都是基丁理论处理或估算得到的·本文试图在实验上通过比较不同成键特征的铜化合物的x光电子能潜（＊P8）来估计对高温超导性起重要作用的C…     

瓯柑石油醚提取物的GC-MS分析

为了研究瓯柑的挥发性成分和脂溶性成分, 采用GC-MS分析法进行分离鉴定, 并用面积归一法确定各成分的质量分数. 从瓯柑果肉石油醚提取物中分离鉴定出11种成分, 占总提取物的97.43%, 其主要成分为(Z, Z)-9, 12-十八碳二烯酸(37.46%)、γ-谷甾醇(22.91%);从瓯柑皮石油醚提取物中分离鉴定出10种成分, 占总提取物的99.79%, 其主要成分为柠檬烯(86.39%).     

Chemical fixation of CO2 with highly efficient ZnCl2/[BMIm]Br catalyst system

The chemical fixation of CO₂ with mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under the ZnCl₂/[BMIm]Br catalyst system without using additional organic solvents was achieved in excellent selectivity (>98%) and TOF (5410 h⁻¹) and the catalyst could be used six times almost without losing its catalytic activity and selectivity. Besides, the pure cis-cyclic carbonate of cyclohexene oxide was obtained in this catalyst system.     

Rh/Al2O3上CO和NO的吸附性能及相互作用

利用ＴＰ－ＩＲ动态方法研究了ＣＯ和ＮＯ在Ｒｈ／Ａｌ２Ｏ３上吸附性能和相互作用的动态行为，结果表明，Ｒｈ／Ａｌ２Ｏ３的孪生中心对ＣＯ的吸附强于对ＮＯ的吸会，线式和桥式中心则对ＮＯ的吸附强于对ＣＯ的吸附，ＣＯ和ＮＯ共吸附－ＴＰ（ＣＯ和ＮＯ中）－ＩＲ动态过程结果揭示出２２２４ｃｍ＾－１谱带的出现和强度的增加与孪生ＣＯ谱带以及吸附的ＮＯ谱带的强度减弱同时发生，表明是由吸附的ＮＯ和孪生ＣＯ形成Ｒｈ－ＮＣＯ。     

Cyclic Conjugation Energy Effects in Polycyclic π-Electron Systems

Summary. The fact that cyclic arrangements of double bonds have a dramatic effect on the behavior of conjugated organic molecules is known since the 19th century. The fact that in monocyclic conjugated systems the size of the cycle and the number of -electrons involved is decisive for their stability (aromaticity) or lack of stability (antiaromaticity) is known since the 1930s. In polycyclic -electron systems several cyclic effects are present simultaneously and their separation became possible only recently. A molecular orbital method has been elaborated, by means of which the energy effects of individual cycles in polycyclic -electron systems can be estimated. This method is briefly outlined and illustrated by pertinent examples. An exhaustive bibliography of the topic considered is given.     

径向基-偏最小二乘-贝叶斯方法及其在化学模式分类中的应用

提出一种用于模式分类的RBF-PLS—Bayes方法。它集成地应用径向基(RBF)变换与偏最小二乘(PLS)方法，从原有模式中提取出分类能力甚强的成分，然后进行贝叶斯(Bayes)判别。这种集成方法尤其适用于复杂化学信息的模式分类，本文将其应用于两种类型的化学模式分类问题，均取得了令人满意的效果。与经典的判别分析方法和单纯的神经网络方法相比，具有明显的优越性。