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1.
Jovi Tze Wai Kan 《Tetrahedron letters》2004,45(33):6357-6359
Poly(ethylene glycol) (PEG) was used for the immobilization of α,α,α-trifluoroacetophenone and the utility of this supported ketone has been examined in dioxirane mediated epoxidation of alkenes. The PEG-ketone reagent was found to be an effective homogeneous catalyst for the epoxidation of a variety of alkenes in the presence of Oxone® and was readily recovered from the reaction mixtures and reused. 相似文献
2.
A Minor New Flavone from Scutellaria baicalensis Georgi 总被引:1,自引:0,他引:1
A new flavone,6,2′-dihydroxy-5,7,8,6′-tetramethoxyflavone,was isolated from the roots of Scutellaria baicalensis. Its structure was established on the basis of spectral evidences. 相似文献
3.
J. C. van Loon 《Fresenius' Journal of Analytical Chemistry》1969,246(2):122-124
Summary A procedure is given for the atomic absorption determination of platinum, palladium and gold in silver beads. Interferences by coexisting ions usually found in the parting solution could be eliminated by addition of 1% of lanthanum. The lowest working ranges in which it is possible to obtain results comparable in accuracy to those from a good spectrophotometric determination are estimated for each metal. (1 ppm Pd, 1 ppm Au, 5 ppm Pt). The results of several determinations using the proposed procedure to analyse silver assay beads are given.
Bestimmung von Platin, Palladium und Gold in dokimastischen Silberperlen durch Atomabsorptions-Spektrophotometrie
Zusammenfassung Störungen durch in der Scheidelösung vorhandene Begleitionen konnten durch Zusatz von 1% Lanthan verhindert werden. Die unteren Grenzen für eine genaue Bestimmbarkeit wurden festgelegt (1 ppm Pd, 1 ppm Au, 5 ppm Pt) und Ergebnisse mehrerer Beleganalysen mitgeteilt.相似文献
4.
The noble metals are inhomogeneously distributed in sulphide ores and their host rocks. It is therefore necessary to analyse large sample sizes to obtain representative analyses. A nickel sulphide fire assay technique has been adapted to extract the noble metals from a large sample size (50 g) into a nickel sulphide button. Subsequently the fire assay button is dissolved in hydrochloric acid and the solution is filtered. The noble metal residue retained on the filter paper is analysed quantitatively by i.n.a.a. techniques. This method is rapid, relatively inexpensive and has better sensitivities for all the noble metals than other analytical techniques. 相似文献
5.
K. G. Neoh E. T. Kang K. L. Tan 《Journal of polymer science. Part A, Polymer chemistry》1991,29(5):759-766
The changes in the structure of leucoemeraldine (LM) and emeraldine (EM) base upon doping by perchlorate anions are studied by X-ray photoelectron spectroscopy (XPS) and infrared (IR) absorption spectroscopy. In the case of LM, interactions of the amine nitrogens with the perchlorate anions result in a nitrogenonium ion structure analogous to that arising from the protonation of imine nitrogens in EM by HCl except the chloride anion in the latter has been replaced by the perchlorate anion. A small amount of partially ionic and covalent chlorine is also incorporated in the LM–perchlorate complexes. The maximum electrical conductivity that is achieved in these complexes is about 4 S/cm. In contrast, the maximum conductivity of the EM–perchlorate complexes is three orders of magnitude lower. The interactions of perchlorate anions with EM base result in the preferential disappearance of the imine units over the amine units. 相似文献
6.
Controlled grafting of well-defined epoxide polymer brushes on the hydrogen-terminated Si(100) substrates (Si-H substrates) was carried out via the surface-initiated atom-transfer radical polymerization (ATRP) at room temperature. Thus, glycidyl methacrylate (GMA) polymer brushes were prepared by ATRP from the alpha-bromoester functionalized Si-H surface. Kinetic studies revealed a linear increase in GMA polymer (PGMA) film thickness with reaction time, indicating that chain growth from the surface was a controlled "living" process. The graft polymerization proceeded more rapidly in the dimethylformamide/water (DMF/H(2)O) mixed solvent medium than in DMF, leading to much thicker PGMA growth on the silicon surface in the former medium. The chemical composition of the GMA graft-polymerized silicon (Si-g-PGMA) surfaces were characterized by X-ray photoelectron spectroscopy (XPS). The fact that the epoxide functional groups of the grafted PGMA were preserved quantitatively was revealed in the reaction with ethylenediamine. The "living" character of the PGMA chain end was further ascertained by the subsequent growth of a poly(pentafluorostyrene) (PFS) block from the Si-g-PGMA surface, using the PGMA brushes as the macroinitiators. 相似文献
7.
Hyun-Ji Lee Taek-Jun Chung Hueck-Jin Kwon Hyun-Joong Kim William Tai Yin Tze 《Cellulose (London, England)》2012,19(4):1251-1258
The fabrication and evaluation of nanocomposites based on microbial cellulose and polyaniline (PANi) are described. Microbial cellulose, so called, bacterial cellulose (BC) was introduced to interfacial polymerization of aniline. Two different phases based on water and chloroform made it easy for nanosized PANi particles to be synthesized on BC. Without any help of a surfactant or templates, BC played a critical role of supporting the growth of PANi. As a function of aniline concentration, the corresponding PANi content and volume resistivity were checked. From morphological images observed by FE-SEM, PANi nanoparticles were densely arrayed along every fiber of BC. The conjugated backbone of PANi was thought to contribute to the improvements of thermal stability of PANi/BC composites. The stiffness and brittleness of PANi were compensated by more ductile BC, suggesting BC can be a promising substrate for it. By the simple and facile interfacial polymerization, the electrical conductivity of PANi/BC composites reached up to 3.8?×?10?1?S/cm when 0.32?M of aniline was used. This PANi/BC nanocomposite can be useful in applications requiring biocompatibility and electrical conductivity such as biological and chemical sensors. 相似文献
8.
An alternative approach to an AB2 monomer, N‐[3,5‐bis(4‐hydroxybenzoyl)benzene]‐4‐fluorophthalimde, 4, for hyperbranched poly(arylene ether ketone imide)s has been developed. The key steps were a para‐position selective electrophilic aromatic substitution of fluorobenzene with 5‐nitroisophthaloyl dichloride and a subsequent clean conversion of the aryl fluorides to phenol groups using potassium hydroxide as the nucleophile. The overall yield for the synthesis of 4 was 51.6%. 相似文献
9.
10.
Abdelkrim Azzouz Vasilica-Alisa Aruş Nicoleta Platon Kamel Ghomari Ieana-Denisa Nistor Tze Chieh Shiao René Roy 《Adsorption》2013,19(5):909-918
Dendrimers bearing hydroxyl groups supported by layered double hydroxides (CO3–LDH) with Mg/Al ratio ranging from 1:1 to 5:1 showed improved properties for the reversible capture of carbon dioxide (CO2). The adsorption capacity of the starting LDH was due to the intrinsic base-like behavior, and was found to depend on the Mg/Al ratio. When contacted with polyol dendrimers in aqueous media, no intercalation took place. This was explained in terms of low exfoliation grade of LDH and hydrophobic character of the dendrimer molecules. The latter rather adsorb on the external surface of the LDH stacks for low dendrimer loadings, or aggregate into organic clusters for higher contents. Analyses through thermal programmed desorption of CO2 revealed that dendrimer incorporation advantageously attenuates the basicity strength of the starting LDH support, by lowering the desorption temperature. The OH groups of the organic moiety were found to display an amphoteric character, and act as the main adsorption sites. The weak interactions with CO2 facilitate easier release of the major part of adsorbed CO2 at temperature not exceeding 80–100 °C. On polyol organo-LDHs, the reversible CO2 retention was discussed herein in terms of acid–base interactions. This concept allows envisaging the capture of diverse pollutants and other greenhouse gases by modifying the chemical groups on the dendritic moiety. 相似文献