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71.
Square-wave voltammetry with the hanging drop mercury electrode as the working electrode was used for the determination of
ultratraces of explosives in aqueous solution. It was shown that the strong pressure dependence of the pneumatically controlled
multimode electrode system of a conventional Metrohm apparatus could be compensated by an additional pressure regulation,
through which the pressure variations could be decreased when switching from deaeration to the static measurements. By using
square-wave voltammetry with this electrode system after this modification the limits of detection for 2,4,6-trinitrotoluene
(TNT) and other TNT-metabolites could be decreased down to 0.2 μg L−1 when using a measurement time of 6 min. Also a simultaneous determination of TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine
(RDX) was shown to be possible over a wide linear range and the detection limits then were 2.2 μg L−1 for TNT and 25 μg L−1 for RDX. By applying the highly stable and adjustable pressure as mentioned before, the calibrations could be kept stable
over a period of up to 1 week. 相似文献
72.
Colourless single crystals of [Hg(OH)](NO3)(H2O) were obtained by slow evaporation of an aqueous solution of Hg(NO3)2 and Bi(NO3)3. The crystal structure (orthorhombic, Pbca, Z = 8, a = 943.2(2), b = 697.6(1), c = 1349.0(2) pm, R1(all) = 0.0780) contains [Hg(OH)] = …OH–Hg–OH–Hg… zig zag chains (O–Hg–O angle: 168°, Hg–O–Hg angle: 112°, Hg–OH distance: 212 pm) to which one water molecule is attached loosely. The [Hg(OH)](H2O) chains are connected via bis‐monodentate‐bridging nitrate ions to corrugated layers that are stacked in the [001] direction. Hg2+ has an effective 2+2+2(+1) coordination. 相似文献
73.
The major flavonoids present in the leaves and flowers of the cannabinoid-free cannabis (Cannabis sativa subsp. sativa L.) cultivars Felina and Futura are orientin (1), vitexin (2), luteolin-7-O-beta-D-glucuronide (3), and apigenin-7-O-beta-D-glucuronide (4), while prenylated flavonoids, to which the potent estrogenicity of hops (Humilus lupulus L.) is associated, are absent. The different composition of flavonoids has chemotaxonomic value. 相似文献
74.
Paulette A. Greenidge Alfred Merz Gerd Folkers 《Journal of computer-aided molecular design》1995,9(6):473-478
Summary A representative range of pyrimidine nucleoside analogues that are known to inhibit herpes simplex virus (HSV) replication have been used to construct receptor binding site models for the varicella-zoster virus (VZV), thymidine kinase (TK) and human TK1. Given a set of interacting ligands, superimposed in such a manner as to define a pharmacophore, the pseudoreceptor modelling technique Yak provides a means of building binding site models of macromolecules for which no three-dimensional experimental structures are available. Once the models have been evaluated by their ability to reproduce experimental binding data [Vedani et al., J. Am. Chem. Soc., 117 (1995) 4987], they can be used for predictive purposes. Calculated and experimental values of relative binding affinity are compared. Our models suggest that the substitution of one residue may be sufficient to determine ligand subtype affinity. 相似文献
75.
Herbert W. Zimmermann 《Angewandte Chemie (International ed. in English)》1986,25(2):115-130
Ethidium and acridine dyes are classical model substances for studying the binding of small, pharmacologically active molecules to DNA. Intercalation between the DNA base pairs is nearly always proposed as the most important type of binding. According to our investigations, however, there is a second type of binding, which also occurs when the concentration of the bound molecules is low and will be referred to here as external or preintercalative binding. The experimental binding isotherms show that the binding constant for intercalation KS1 is considerably smaller than that for external binding KS2 (KS1 > KS2). This surprising result is not due to the binding enthalpy (ΔH ≈ ΔH) but to the binding entropy (ΔS > ΔS). Electrostatic interactions between the dye and the DNA represent the most important contribution to both types of binding; they are supplemented by hydrogen bonds and hydrophobic interactions. The behavior of a substance in living cells, however, cannot be reliably predicted from its in vitro binding to DNA. Very few substances are bound to the DNA of the nuclear chromatin in cell culture; for example, dyes often accumulate instead in the lysosomes. In some cases the dye binds specifically and very efficiently to the mitochondria of the living cell, especially to the mitochondrial membranes, the sites of oxidative phosphorylation. 相似文献
76.
Absolute small angle X-ray studies of concentration fluctuations were performed in order to determine thermodynamic properties of a model blend, consisting ofn-hexane and perfluoro-n-hexane. The quantities which we determined were the second derivate of the Gibbs free energy of mixing with respect to the concentration of the components, the location of the spinodal, interaction and solubility parameters, the energy gradient density coefficient as well as the correlation length of the fluctuations at various compositions and temperatures, particularly in the neighbourhood of the spinodal and the critical point. The data obtained were compared with those obtainable from the well known location of the binodal, to test the reliability of the scattering method. 相似文献
77.
Parac-Vogt TN Pacco A Nockemann P Laurent S Muller RN Wickleder M Meyer G Vander Elst L Binnemans K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):204-210
Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded between 0.24 mT and 1.4 T for lanthanum(III)- and gadolinium(III)-containing [15]metallacrown-5 complexes derived from alpha-aminohydroxamic acids and with copper(II) as the ring metal. The influence of the different R-groups on the proton relaxivity was investigated, and a linear relationship between the relaxivity and the molecular mass of the metallacrown complex was found. The selectivity of the metallacrown complexes was tested by transmetalation experiments with zinc(II) ions. The crystal structure of the copper [15]metallacrown-5 gadolinium complex with glycine hydroximate ligands is reported. 相似文献
78.
Hofmann C Boll R Heitmann B Hauser G Dürr C Frerich A Weitnauer G Glaser SJ Bechthold A 《Chemistry & biology》2005,12(10):1137-1143
The oligosaccharide antibiotic avilamycin A is composed of a polyketide-derived dichloroisoeverninic acid moiety attached to a heptasaccharide chain consisting of six hexoses and one unusual pentose moiety. We describe the generation of mutant strains of the avilamycin producer defective in different sugar biosynthetic genes. Inactivation of two genes (aviD and aviE2) resulted in the breakdown of the avilamycin biosynthesis. In contrast, avilamycin production was not influenced in an aviP mutant. Inactivation of aviGT4 resulted in a mutant that accumulated a novel avilamycin derivative lacking the terminal eurekanate residue. Finally, AviE2 was expressed in Escherichia coli and the gene product was characterized biochemically. AviE2 was shown to convert UDP-D-glucuronic acid to UDP-D-xylose, indicating that the pentose residue of avilamycin A is derived from D-glucose and not from D-ribose. Here we report a UDP-D-glucuronic acid decarboxylase in actinomycetes. 相似文献
79.
Dieter Seebach Thomas Weller Gerd Protschuk Albert K. Beck Marvin S. Hoekstra 《Helvetica chimica acta》1981,64(3):716-735
Preparation of 1,3-Diketones and of Nitro-diketones by (1:1)-Acylation of Lithium Enolates with Acyl Chlorides Slow addition of precooled solutions of lithium enolates in THF (Fig. 1) to solutions of equimolar amounts of acyl chlorides in the same solvent at temperatures between ? 80 and ? 100° furnishes 1, 3-diketones in acceptable to good yields (Tables 1?3). Even 3-nitropropionyl and 4-nitrobutyryl chloride can be employed for the (1:1)-acylation of enolates to give the synthetically useful 5- and 6-nitro-1, 3-diketones 13 and 25 , respectively. The scope and the limitations of this method of preparing 1, 3-diketones are given and are compared with alternative methods. 相似文献
80.
Ernst Bayer Gerd Wahl und Heinz Günther Witsch 《Fresenius' Journal of Analytical Chemistry》1961,181(1):384-390
Zusammenfassung Es werden zwei neue, sehr selektive Trennflüssigkeiten, Äthylenglykol-bis(propionitril)-äther und Glycerin-tri(propionitril)-äther, angegeben. Die Trennflüssigkeiten sind so selektiv wie ,-Bis(propionitril)-äther, erlauben aber höhere Arbeitstemperaturen von 140° bzw. 170°C. An Säulen kleinen Querschnittes wird die präparative Trennung größerer Mengen unter Ausnutzung der Selektivität dieser Trennflüssigkeiten aufgezeigt.Die Trennwirksamkeit und die Belastbarkeit von Säulen verschiedenen Durchmessers zwischen 1–10 cm wird angegeben. Die Trennwirksamkeit liegt in der gleichen Größenordnung wie die der analytischen Säulen. Die Belastbarkeit steigt proportional dem Querschnitt an.I. Mitteilung: E. Bayer u. H. G. Witsch, diese Z. 170, 278 (1959). 相似文献