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排序方式: 共有141条查询结果,搜索用时 15 毫秒
1.
M. Carmen Galan 《Tetrahedron letters》2006,47(10):1563-1565
Secologanin, a complex iridoid terpene natural product, was derivatized at the vinyl and ester functional groups using cross-metathesis and transesterification methodology, respectively. 相似文献
2.
Summary A new technique is described for the identification of the chloride ion through the formation of chromyl chloride, based on the extraction of the latter with carbon tetrachloride. The identification limit is 2g of chloride. It is possible to carry out the test in the presence of many other anions, including fluoride, which cannot be present when the traditional distillation technique is employed.
Zusammenfassung Vorgeschlagen wird eine neue Technik zum Chloridnachweis durch Bildung von Chromylchlorid. Dieser Nachweis beruht auf der Extraktion des Chromylchlorids mit Tetrachlorkohlenstoff. Die Nachweisgrenze liegt bei 2g Chlorid, wobei die Möglichkeit besteht, den Test auch in Gegenwart von Fluorid durchzuführen, das bei Anwendung der üblichen Destillationsmethoden nicht anwesend sein darf.相似文献
3.
An improved spectrophotometric method is proposed for the determination with iodide of trace amounts of bismuth in copper and cartridge brass. The sample is dissolved in nitric acid and the bismuth is separated from the copper by an ammoniacal precipitation in the presence of iron(III) hydroxide as a gathering agent. The hydroxide precipitate is dissolved in hydrochloric acid, sulfuric acid is added, the solution is evaporated to a few ml, hydrobromic acid is added to volatilize the antimony and tin, and the solution is evaporated to fumes of sulfuric acid. The bismuth iodide color is then developed with a composite potassium iodide—sodium hypophosphite reagent. Factors affecting the bismuth iodide color are investigated. 相似文献
4.
Galan MC Venot AP Glushka J Imberty A Boons GJ 《Journal of the American Chemical Society》2002,124(21):5964-5973
It is demonstrated that conformationally restricted oligosaccharides can act as acceptors for glycosyltransferases. Correlation of the conformational properties of N-acetyl lactosamine (Galbeta(1-4)GlcNAc, LacNAc) and several preorganized derivatives with the corresponding apparent kinetic parameters of rat liver alpha-(2,6)-sialyltransferase-catalyzed sialylations revealed that this enzyme recognizes LacNAc in a low energy conformation. Furthermore, small variations in the conformational properties of the acceptors resulted in large differences in catalytic efficiency. Collectively, our data suggest that preorganization of acceptors in conformations that are favorable for recognition by a transferase may improve catalytic efficiencies. 相似文献
5.
Summary After a brief introduction of the subject, the paper focusses on the first step in any optimization procedure: the delineation
of the parameter space, wherein the global optimum is to be found. For organic modifier optimization in reversed-phase liquid
chromatography it is shown that the necessary information can be derived from a single water-methanol gradient. It first yields
an estimate of the total number of solutes in the sample, which is vital to define the peak capacity needed to achieve separation
at a certain confidence level. Next, the gradient allows the prediction of suitable isocratic methanol binary solvents, and
transfer rules formulate the iso-eluotropic composition of the common binary solvents (tetrahydrofuran and acetonitrile).
Because all predictions are based on a statistical analysis of a limited data base, attention is given to the practical situation
where an actual sample deviates from the average solute behaviour. Such deviations are revealed in the first isocratic run
and can be used to arrive at a better estimate of solute retention. 相似文献
6.
L. De Galan C. Erkelens C. Jongerius W. Maertens C. I. Mooring 《Fresenius' Journal of Analytical Chemistry》1973,264(2):173-176
Summary Detection limits for the determination of a number of elements in solid sodium chloride by differential pulse polarography, flame absorption and emission spectrometry were established. These methods were used for a quantitative investigation on the distribution of ppm quantities of Cu, Pb, Cd, Zn, Mn, Mg, Sr and Ba between the crystallizate and the mother solution obtained in a partial crystallization of sodium chloride from its saturated solution. Recoveries of the crystallization process, calculated from the results of the analysis, vary from 86% for Pb to 115% for Sr.
Bestimmung von Spurenverunreinigungen in reinstem Natriumchlorid durch Differential-Pulspolarographie und Flammenspektrometrie
Zusammenfassung Die Nachweisgrenzen für die Bestimmung einer Zahl von Elementen im festen Natriumchlorid wurden mit Differential-Pulspolarographie, Absorptions- und Emissions-Flammenspektrometrie bestimmt. Diese Methoden wurden benutzt zur quantitativen Untersuchung der Verteilung von ppm-Mengen Cu, Pb, Cd, Zn, Mn, Mg, Sr und Ba zwischen kristallisiertem Salz und Mutterlösung bei teilweiser Kristallisation vom Natriumchlorid aus seiner gesättigten Lösung. Die Ausbeuten des Kristallisationsprozesses, berechnet aus den Analysenergebnissen, schwanken von 86% für Pb bis 115% für Sr.
Lecture presented at Euroanalysis I Conference, 28. 8.–1. 9. 1972 in Heidelberg, Germany. 相似文献
7.
Aresta M Tommasi I Quaranta E Fragale C Mascetti J Tranquille M Galan F Fouassier M 《Inorganic chemistry》1996,35(14):4254-4260
Extended labeling experiments have shown that formation of rhodium peroxocarbonate from CO(2) and [RhCl(eta(2)-O(2))(P)(3)] (P is PEt(2)Ph or PEtPh(2)) proceeds through O-O bond cleavage and CO(2) insertion. O-transfer to ancillary phosphine ligand to give R(3)P=O selectively (>85%) involves the Rh-linked O atom of the peroxo group of RhCl(CO(4))(P)(3). 相似文献
8.
Dr. David Benito‐Alifonso Shirley Tremel Bo Hou Harriet Lockyear Dr. Judith Mantell Prof. David J. Fermin Dr. Paul Verkade Dr. Monica Berry Dr. M. Carmen Galan 《Angewandte Chemie (International ed. in English)》2014,53(3):810-814
A series of glycan‐coated quantum dots were prepared to probe the effect of glycan presentation in intracellular localization in HeLa and SV40 epithelial cells. We show that glycan density mostly impacts on cell toxicity, whereas glycan type affects the cell uptake and intracellular localization. Moreover, we show that lactose can act as a “Trojan horse” on bi‐functionalized QDs to help intracellular delivery of other non‐internalizable glycan moieties and largely avoid the endosomal/lysosomal degradative pathway. 相似文献
9.
M.T.C. de Loos-Vollebregt L. de Galan 《Spectrochimica Acta Part B: Atomic Spectroscopy》1982,37(8):659-672
Analytical results are presented obtained with Zeeman atomic absorption (ZAA) using a modified sine wave magnetic field. The measurement at zero field strength is lengthened to 0.5 ms for a 50 Hz magnetic field of 10 kG.The a.c. Zeeman system is extended with an additional intensity measurement performed at an intermediate field strength. The three field Zeeman system (3FZAA) permits simultaneous correction for background absorption and stray radiation at the expense of halved analytical sensitivity. The background correction capabilities of ZAA and 3FZAA are the same. However, the 3FZAA signals show increased noise in comparison to ZAA.In the three field system the roll-over problem, inherent in existing Zeeman systems, is shifted to higher concentration and to higher absorbance. The height and the position of the maximum in ZAA and 3FZAA analytical curves do not depend on the amount of background absorption.A method for the extension of analytical curves in AA is presented. Utilizing an a.c. modulated magnetic field any sensitivity between zero and ordinary AA sensitivity can be obtained. 相似文献
10.
J.W.M. van Uffelen M.T.C. de Loos-Vollebregt L. de Galan 《Spectrochimica Acta Part B: Atomic Spectroscopy》1982,37(6):527-531
This note describes a simple power supply for a magnet to be used in a.c. ZAA spectrometry. The modified sine wave shape of the 50 Hz 10 kG magnetic field allows a 0.5 ms period at zero field to perform the zero field intensity measurement. At lower maximum field strength, the zero field period can be extended. 相似文献