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81.
A potassium-selective liquid-membrane microelectrode based on valinomycin is described. Tip diameters of about 2 μm as well as high discrimination against Na+, H3O+, acetylcholine and some other quaternary ammonium ions, allow the intracellular measurement of potassium ion activity changes. The inherently high membrane resistance of the neutral carrier-based microelectrodes is reduced by adding a lipophilic charge carrier to the valinomycin. Results are compared with those of classical microelectrodes. 相似文献
82.
Markus Lerchi Elmar Reitter Wilhelm Simon 《Analytical and bioanalytical chemistry》1994,349(4):272-276
A pulsed molecular beam Fourier transform microwave spectrometer especially designed for the quantitative analysis of polar pollutants in air is presented. This very fast method has a sensitivity in the ppm range and can be applied to a wide variety of substances. Details of the apparatus and the results of some performance tests are given. 相似文献
83.
Jürg K. Schneider Peter Hofstetter Ern Pretsch Daniel Ammann Wilhelm Simon 《Helvetica chimica acta》1980,63(1):217-224
N,N,N′,N′-Tetrabutyl-3,6-dioxaoctane-dithioamide, an Ionophore with Selectivity for Cd2+ The dioxa-dithioamide 3 behaves as a highly selective ionophore for Cd2+ in solvent polymeric membranes. It induces cation-permselectivity in these membranes with a transference number of 1 for Cd(NO3)2- and of 2 for CdCl2-solutions. In the presence of a proton carrier, 3 may be used to selectively pump Cd2+ through membranes by coupling with a pH gradient. 相似文献
84.
A kinetic study of the aqueous persulphate initiated polymerisation of methacrylamide has shown that the rate of polymerisation is represented by the equation where the overall rate constant, . Chain transfer with monomer, where CM = 5.4 × 10?3 at 60°, is shown to be the dominant transfer step. Comparison with kinetic studies of the analogous acrylamide polymerisation shed doubt on the ‘cage effect’ interpretation of complex orders with respect to monomer. An alternative explanation is proposed. 相似文献
85.
Nicholas J Lawrence John Liddle Simon M Bushell David A Jackson 《The Journal of organic chemistry》2002,67(2):457-464
The intermediate anion derived from the vicarious nucleophilic substitution (VNS) of hydrogen reacts with a series of alkyl halides to generate the corresponding alpha-alkylated conventional VNS product in a one-pot process. This one-pot VNS-alkylation reaction offers a convenient route to a range alpha-substituted nitrobenzyl phosphine oxides, sulfones, and esters via a three-component coupling reaction. Reactions of alpha-chloroethyl phenyl sulfone (14) and ethyl 2-chloropropionate (16) with nitrobenzene followed by subsequent addition of an alkylating agent give a series of sulfones and esters bearing an alpha-aryl quaternary center. The VNS-alkylation protocol has been applied to the synthesis of derivatives of Indoprofen from nitrobenzene using readily available inexpensive starting materials. Indoprofen itself was prepared using the conventional VNS reaction in four steps and 24% overall yield from nitrobenzene. 相似文献
86.
Báthori M Pongrácz Z Tóth G Simon A Kandra L Kele Z Ohmacht R 《Journal of chromatographic science》2002,40(7):409-415
A new ecdysteroid glycoside, 2-deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside, is isolated from the herb Silene italica ssp. nemoralis (Waldst. and Kit.) Nyman. The compound is purified with multistep chromatography, such as classical column chromatography on alumina and droplet countercurrent distribution. Also, it is expanded using twice low-pressure reversed-phase liquid column chromatography. Chromatography in four steps results in the purified 2-deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside. Two other ecdysteroids have also been separated, including the formerly identified integristerone A and 24(28)-dehydromakisterone A. 相似文献
87.
Four compounds in the system (Li, Na)VO3 were synthesized and their structures refined in the space group . Site population analysis showed that their compositions are (Na0.5Li0.5)VO3, (Na0.62Li0.38)VO3, (Na0.71Li0.29)VO3 and (Na0.84Li0.16)VO3. All have the structure of LiVO3 and α-NaVO3 which are related to the silicate pyroxenes. Structural data of eight compounds in the system (K, Na, Li)VO3 were compiled, and correlations were established by multiple regression analyses between the effective ionic radii rM1 and rM2 of the alkali metal ions and various structural parameters. The size of the M2 site and the relative displacement of the (VO3)∞ chains are found to depend primarily on rM2 only. The size of the M1 site and the amount of chain rotation are affected by both rM1 and rM2. Changes in lattice parameters are related to the chain movements. The anomalous chain configuration of LiVO3 is also discussed. 相似文献
88.
Smith BM Lappi SE Brewer SH Dembowy S Belyea J Franzen S 《Langmuir : the ACS journal of surfaces and colloids》2004,20(4):1184-1188
The surface of a germanium internal reflectance element (IRE) was modified to bind 6X-histidine (his)-tagged biomolecules. The step-by-step surface modification was monitored via single-pass attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FT-IR). Initially an adlayer of 7-octenyltrimethoxysilane (7-OTMS) was formed on the Ge crystal through the surface hydroxyl groups, which were produced via ozonolysis of the Ge surface. The vinyl moiety of 7-OTMS was oxidized to a carboxylic acid, which was activated by 1,1'-carbonydiimidazole (CDI) to produce a labile imidazole. The labile imidazole that resulted from the CDI coupling was then displaced by the primary amine of nitrilotriacetic acid (NTA). Nickel sulfate was added to the system, and it coordinated with the three carbonyl groups and the nitrogen on NTA, thus leaving the ability of Ni to coordinate with two adjacent histidine residues. Binding of his-tagged biotin to nickel nitrilotriacetic acid (Ni-NTA) was observed by ATR-FT-IR spectroscopy. The surface modification method presented in this paper had minimal nonspecific binding, the Ni-NTA surface was reusable if stored properly, and complete removal of the organic surface was achievable. 相似文献
89.
Poon KW Liu W Chan PK Yang Q Chan TW Mak TC Ng DK 《The Journal of organic chemistry》2001,66(5):1553-1559
Up to eight redox-active ferrocenyl units have been incorporated, through the unsaturated ethynyl linkers, on the periphery of a series of cyclic tetrapyrrole derivatives including zinc(II) phthalocyanine and 2,3-naphthalocyanine, and nickel(II) meso-diphenylporphyrin. The synthesis of the former two macrocycles 4 and 7 involves the Sonogashira coupling reaction of ferrocenylethyne with 4,5-dichlorophthalonitrile (1) or 6,7-dibromonaphthalonitrile (5), respectively, followed by a base-promoted cyclization. The meso-bis(ferrocenylethynyl)porphyrin 11 has been prepared from the dibromo analogue 10 also by a palladium-catalyzed coupling reaction. These novel macrocyclic compounds have been spectroscopically and electrochemically characterized. As revealed by cyclic voltammetry, the ferrocenyl moieties appear to be electrochemically independent in these complexes and there is no significant electronic coupling among the iron(II) centers. 相似文献
90.
Nitrogen bridgehead compounds part 21. Preparation of new quaternary 2,3a,6a-triazaphenalenium salts
István Bitter Béla Pete István Hermecz Gábor Tóth Kálmán Simon Mátyás Czugler Zoltán Mészáros 《Tetrahedron letters》1982,23(28):2891-2894
The first representatives of a new ring system, the 2,3a,6a-triazaphenalenium quaternary salts are prepared by the cycloaddition of tetrahydro-4H-pyrido[1,2-a] pyrimidin-4-ones containing an α-chloroenamine moiety with azomethines. 相似文献