Dosage De L′antimoine Dans Le Zinc Electrolytique Et Le Sulfate De Zinc

Abstract

Anmodic-stripping voltammetry at a haning-drop mercury electrode has been applied to the precise and accurate trace analysis of antominy in metalic zinc and in solutions of zinc sulfate. A sample preparation methos is described which obviates loss of antimony by voltalization. A mixture of zinc sulfate and 6M hydrochloricacid is used as supporting electrolyte, in order to enhance the separation o the closely spaced dissolution peaks of copper and antimony.     

De novo asymmetric synthesis of (−)-nanaomycin A

The de novo asymmetric total synthesis of (?)-nanaomycin A is described. The entirely linear route required only 13 steps from commercially available starting materials (3% overall yield). Key transformations include a Claisen rearrangement, an asymmetric dihydroxylation, a regioselective tosylation, a diastereoselective intramolecular Friedel-Crafts alkylation and a nitrile hydrolysis. As the route relies on a Sharpless asymmetric dihydroxylation it is equally amenable for the synthesis of (+)-nanaomycin A.     

Internet化学资源搜索引擎Chemie.De简介

Internet已经发展成为最大的信息载体和传输工具 ,学会有效地利用网上资源是教育信息化的基本要求。本文比较系统地介绍了Internet化学资源搜索引擎Chemie .De的一般特点和所提供的主要服务 ,以期对化学教育工作者有所帮助。     

一种新的De Novo生物活性分子设计方法

由药效团进行虚拟活性结构生成与3D-QSAR模型相结合,筛选出有前途的结构多样性的化合物,并从中寻找活性先导化合物,是一种新的分子设计方法。采用这种方法对抗小麦赤霉病类含氟农药进行了研究,共生成了53个虚拟活性结构,通过3D-QSAR模型筛选出其中10个活性较高的结构,在活性最高的化合物基础上进行了结构修饰,得到了活性更高且毒性较低的理想化合物。研究结果表明这种方法能突破原模型化合物结构模式的局限,可以找到结构新颖的活性先导化合物,是一种非常有前途的分子设计方法,而且具有较高的筛选效率。     

De Novo Design and Synthesis of Four-Helix Bundle Peptides

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De‐agglomeration of Silica Nanoparticles in the Presence of Surfactants

The effect of the type of surfactant and pH on de‐agglomeration of a hydrophilic silica nano‐powder in a high shear mixer was investigated. It has been found that the presence of surfactant does not affect the general pattern of de‐agglomeration characterized by the transition of a single modal aggregates size distribution with the median of 10 µm, through a bi‐modal distributions with the second median of the order of 100 nm to a single modal distribution with the median of the order of 100 nm. None of the investigated surfactants enabled de‐agglomeration of the nano‐powder into a primary nanoparticle.

At pH=4, breakage of large secondary aggregates was enhanced by the addition of PEG and PVP, whereas the addition of SDS slowed down de‐agglomeration. The final aggregates were larger in all suspensions containing surfactant than in surfactant free suspensions. At pH=9 all surfactants drastically reduced de‐agglomeration rate without affecting the size of the primary aggregates. PEG induced bridge flocculation of the primary aggregates leading to a drastic change of the rheology of suspension.     

Modelisation Des Nappes De Solubilite Du Diagramme De Phases Mg(NO3)2–Al(NO3)3–H2O

A program has been written to describe solubility surfaces of the polythermal ternary phase diagram Mg(NO₃)₂–Al(NO₃)₃–H₂O, using the model proposed by Cohen-Adad et al. [2]. In this work we present the calculation of the solubility surface of Mg(NO₃)₂×6H₂O and Al(NO₃)₃×9H₂O in the phase diagram. The calculated isothermal sections are in a good agreement with experimental determinations. Coefficients of the fitting equation that describes the solubility field allow drawing any isothermal section. The monovariant line was also calculated. The chosen model is well adapted to calculations of these solubility surfaces and gives very good results. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthèse Et Cyclisation De Carboxylsulfamides Dérivés D'amines Et D'α-Hydroxyesters. Éavaluation De L'Activité Bactéeriostatique

Abstract

Les carboxylsulfamides sont obtenus à partir de l'isocyanate de chlorosulfonyle, d'amines primaires et d'α-hydroxyesters. Après réduction alcaline, ces carboxylsulfamides sont cyclisés dans les conditions de la réaction de Mitsunobu pour conduire aux N-sulfamoyloxazolidinones chides avec des rendements élevés.

The synthesis of carboxylsulfamides was carried out starting from chlorosulfonyl isocyanate, primary amines and α-hydroxyesters. After reduction, the carboxylsulfamides were cyclised under Mitsunobu conditions giving N-sulfamoyloxazolidinones in good yields.     

Enantioselective De Novo Synthesis of α,α-Diaryl Ketones from Alkynes

Chiral α,α-diaryl ketones are structural motifs commonly present in bioactive molecules, and they are also valuable building blocks in synthetic organic chemistry. However, catalytic asymmetric synthesis of α,α-diaryl ketones bearing a tertiary stereogenic center remains largely unsolved. Herein, we report a catalytic de novo enantioselective synthesis of α,α-diaryl ketones from simple alkynes via chiral phosphoric acid (CPA) catalysis. A broad range of enolizable α,α-diaryl ketones are prepared in good yields and with excellent enantioselectivities. The described protocol also serves as an efficient deuteration method for the preparation of enantiomerically enriched deuterated α,α-diaryl ketones. Using the methodology reported, bioactive molecules, including one of the best-selling anti-breast cancer drugs, tamoxifen, are readily synthesized.     

Automated De Novo Drug Design: Are We Nearly There Yet?

Medicinal chemistry and, in particular, drug design have often been perceived as more of an art than a science. The many unknowns of human disease and the sheer complexity of chemical space render decision making in medicinal chemistry exceptionally demanding. Computational models can assist the medicinal chemist in this endeavour. Provided here is an overview of recent examples of automated de novo molecular design, a discussion of the concepts and computational approaches involved, and the daring prediction of some of the possibilities and limitations of drug design using machine intelligence.     

Dissolution De L'hydroxyapatite et Du Phosphate Tricalcique β Dans Les Solutions D'acide Nitrique

Using an isoperibol calorimeter for rapid reactions and a Calsol type microcalorimeter for slow processes, are applied to determine the enthalpies of solution of two synthetic phosphate products in nitric acid. Namely, β tricalcium phosphate Ca₃(PO₄)₂ and the calcium hydroxyapatite Ca₁₀ (PO₄)₆ (OH)₂ are measured by varying pH value of the solvent. Some dissolution mechanisms are proposed for various pH values. They are ensured by complementary reactions of solution of Ca(NO₃)₂, Ca(H₂ PO₄)₂ and H₃ PO₄ in the same solvents. An extrapolation of solution enthalpies to pH=7 leads to the enthalpy of solution of these products in the pure water. These values are Δ_sol H °=–138.3 kJ mol^–1 for Ca₃ (PO₄)₂ and –393.6 kJ mol^–1 for Ca₁₀ (PO₄)₆ (OH)₂ . This revised version was published online in August 2006 with corrections to the Cover Date.     

Variation De L'énergie Superficielle D'une Bentonite Par Traitement Chimique Et Thermique

Variation of surface energy of a bentonite by chemical and thermal treatments. The effect of an attack by hydrochloric acid and of thermal treatments on the dispersive surface energy, γ^d_s, and on the morphology index of a bentonite has been studied by inverse gas chromatography at infinite dilution. The results show that γ^d_s is very sensitive to two parameters: one is the atomic scale morphology of the clay material, the other one is the mineral impurity contents, mainly composed of alkaline and alkaline-earth oxides. The large increase of γ^d_s after a moderate treatment [t < 10 h, HC1 < 2N and thermal treatment temperature (TTT)≤300°C] is attributed to the bentonite purification and to the lateral surface appearence. However, a more severe treatment (t>10h, HC1 >3N et TTT > 500°C) destroys the lamellar structure of the montmorillonite and in this case the measured γ^d_s is attributed to the basal surface.     

Amélioration De L'aptitude Au Décochage Et Au Débourrage: Des Sables Liés Au selicate De Soude Et Durcis: Par Le Gaz Carbonique

Improvement In the aptitude to discharge and to unstop of sands binded with sodium silicate and hardened by carbon dioxide. Chemically hardened sands offer a large choice of moulding and coring processes by the use of organic and mineral compounds. The use of these binders requires a knowledge of associated risks, to obtain a reduced residual resistance (in order to facilitate the discharging and the unstopping of the parts) and for the success of the products.The aim of this study was to rationalise the utilisation conditions of sodium silicate moulded sands, with additives, hardened by carbon dioxide. This should minimize the eventual defects in the cast parts. Sand resistance is very important right after the casting; it makes more difficult the tasks of discharging and unstopping. The need to incorporate organic matter to the sands becomes a necessity. The role of the organic matter is to reduce the sand resistance. The use of silicate binder requires the identification of the mechanism of the mixture hardening by carbon dioxide. It also calls for a knowledge of the gel structure formation, and of the influence of certain parameters on the properties.The experimental part is concerned with a comparative study of the behaviour of these sands in the foundry.The factors influencing this behaviour are: grain size, carbon dioxide blowing-in time, binder rates, adjuvant ratios and mixing time, etc…A thermographie study was carried out in order to perform the experimental work in real conditions.The obtained results have led to the determination of the optimal values of the above-mentionned parameters. This allows to obtain the smallest residual resistance, hence to improve the discharging and unstopping processes.This approach is clearly exhaustive and shows all possible interactions of the adjuvants with sodium silicate and the considered sands.     

Study on Mg／Fe Mixed Oxides Derived from Hydrotalite as De—SOx Catalyst

A novel class of desulfurization agent derived from hydrotalcite has been developed and its activity for SOx uptake have been investigated. The results showed that the Mg/Fe mixed oxide having high SOx uptake ability at a broad reaction temperature (e.g.673K-973K). The Mg/Fe ratio of the mixed oxide strongly affect the desulfurization role of the material and it can be used repeatly without much loss of SOx uptake ability.     

Partial De Novo Sequencing and Unusual CID Fragmentation of a 7 kDa,Disulfide-Bridged Toxin

A 7 kDa toxin isolated from the venom of the Texas coral snake (Micrurus tener tener) was subjected to collision-induced dissociation (CID) and electron-transfer dissociation (ETD) analyses both before and after reduction at low pH. Manual and automated approaches to de novo sequencing are compared in detail. Manual de novo sequencing utilizing the combination of high accuracy CID and ETD data and an acid-related cleavage yielded the N-terminal half of the sequence from the reduced species. The intact polypeptide, containing 3 disulfide bridges produced a series of unusual fragments in ion trap CID experiments: abundant internal amino acid losses were detected, and also one of the disulfide-linkage positions could be determined from fragments formed by the cleavage of two bonds. In addition, internal and c-type fragments were also observed.     

La Méthylfluorone,réactif spécifique De L'antimoine

The purity of the methyl fluorone was controlled by the melting point of its acctyl derivative. Methyl fluorone is stable in the solid state, but not in ethyl alcohol solution. The solubility of the pure methyl fluorone which we prepared is 0.095% in ethyl alcohol, only a fifth of the solubility of the product used by P. Wenger, R. Duckert and Cl. Blancpain.We prefer the filter paper technique to that of a spotting plate or micro test tube. We were led to reject the use of tartaric solutions pH 4. recommended by the abovementioned authors, and prefer solutions in 1 N HCl.In employing the filter paper impregnated with a drop of the saturated alcoholic solution of methyl fluorone, antimony and molybdenum produce a colour change from yellow to red. germanium and tin a slight change from yellow to orange.If the filter paper is impregnated with a drop of acid solution (I N HCl) of methyl fluorone in alcohol, the sharpness of the reaction of antimony and molybdenum is appreciably increased, whilst the colouration due to germanium and tin do not interfere.By treating the spot with a few drops of H₂O₂ + HCl, the colouration due to molybdenum disappears and the reaction for antimony, which was selective, now becomes specific for this element.