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11.
An indirect method of arsenic determination in the submicrogram range via the determination of molybdenum is presented here. High sensitivity is achieved by combination of the chemical amplification during formation of dodecamolybdoarsenic acid (arsenic: molybdenum ratio 1 12) with multiplication due to the formation of ion-association complexes during flotation-spectrophotometric molybdenum determination with crystal violet (molar ratio 1 2). Thus, the amplification factor relating to arsenic is 24.Dodecamolybdoarsenic acid is formed in a weakly acidic medium and is quantitatively extracted byn-butanol. Back extraction of the heteropoly acid to the aqueous phase and its simultaneous destruction provides the basis for the reaction of released molybdate ions with thiocyanate ions. The molybdenum-thiocyanate complex forms a sparingly soluble ion-association complex with crystal violet which can be floated with toluene on the phase boundary (film flotation). After separation of the aqueous phase the floated molybdenum compound is dissolved in acetone and the resulting free crystal violet ions are subjected to photometric determination at 590 nm as equivalent of the concentration of arsenic. The molar absorptivity of crystal violet is 3.2 · 1051 · mol–1 · cm–1. Beer's law is obeyed in a concentration range from 0.01 to 1 g Mo · ml–1 (0.001–0.1 g As · ml–1). The resulting detection limit for arsenic is 1 ng · ml–1. 相似文献
12.
Peter G. Jones Steffi Friedrichs 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(12):m623-m627
Bis(1,3‐thiazolidine‐2‐thione‐κS2)gold(I) bis(4‐chlorobenzenesulfonyl)amide, [Au(C3H5NS2)2](C12H8Cl2NS2O4), has no imposed symmetry. Classical N—H⋯N and N—H⋯O hydrogen bonds link the residues to form chains parallel to the b axis. Weaker interactions involve C—H⋯O, C—H⋯Au and a number of X⋯Cl contacts (X = Cl, S or Au) clustered in the region y ≃ . In bis(1‐methylimidazolidine‐2‐thione‐κS2)gold(I) bis(4‐iodobenzenesulfonyl)amide, [Au(C4H8N2S)2](C12H8I2NS2O4), the Au atom of the cation and the N atom of the anion lie on the twofold axis (0, y, ) in the space group C2/c. The formula unit forms a self‐contained ring with two symmetry‐equivalent N—H⋯O hydrogen bonds, and weak C—H⋯X (X = O, I or S), Au⋯I and I⋯I contacts are observed. In both compounds, the anions display extended conformations. 相似文献
13.
Andreas Marx Peter Erdmann Martin Senn Steffi Krner Tobias Jungo Mario Petretta Petra Imwinkelried Adrian Dussy Klaus J. Kulicke Ludwig Macko Margareta Zehnder Bernd Giese 《Helvetica chimica acta》1996,79(7):1980-1994
Two synthetic pathways towards 4′-C-acylthymidines are presented. These modified mononucleosides are precursors of the 2′-deoxyribonucleotide 4′-C-radical. They were converted into their corresponding 3′-O-[(2-cyanoethyl) N,N-diisopropylphosphoramidites] 3a–c and incorporated in oligonucleotides by solid-phase synthesis. The structure of some modified nucleosides was revealed by X-ray crystal-structure analysis. 相似文献
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15.
Rosario Rodil Steffi Schrader Monika Moeder 《Rapid communications in mass spectrometry : RCM》2009,23(5):580-588
A comparison was made between the electrospray ionization (ESI) and atmospheric pressure photoionization (APPI) tandem mass spectrometric (MS/MS) responses of eleven ultraviolet (UV) filters. Four of the target compounds were favourably ionized in negative ion mode, and the other seven compounds in positive ion mode. For nine of the compounds APPI generated a similar response to that of ESI, but the APPI signal‐to‐noise (S/N) ratios were 1.3–60 times higher. The two most polar of the UV filter compounds (PBSA and BP‐4) were more efficiently ionized by ESI, offering higher signal intensities and lower detection limits. APPI was, however, less susceptible to ion suppression than ESI when real samples were injected. In order to optimize the APPI conditions different dopant solvents were examined to enhance the efficiency of the photoionization process. Among the evaluated dopants, toluene was selected as the best compromise. At a toluene flow rate of 10% of the solvent flow rates the ionization response increased by a factor of 40–50 over the use of no dopant for the compounds in positive ion mode and by more than 300 for the compounds in negative ion mode. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
16.
Thomas Loewenstein Dr. Melanie Rudolph Markus Mingebach Kerstin Strauch Yvonne Zimmermann Dr. Andreas Neudeck Dr. habil. Steffi Sensfuss Dr. Derck Schlettwein Prof. Dr. 《Chemphyschem》2010,11(4):783-788
A strategy is presented to realize textile‐based photovoltaic cells motivated by developments of textile‐based electronics and their demand of grid‐independent energy supply. Beyond this, a development of textile‐based photovoltaics also represents an attractive pathway towards very flexible and rugged solar cells. The need for compatibility of an appropriate photovoltaic technology with the physical limitations of textiles is stressed. Electrodeposition from aqueous solutions is presented as a successful strategy to realize semiconductor structures on textiles and detailed control and influence of the deposition conditions is discussed. The role of microelectrode effects, options of forced convection, deposition under pulsed potential, alternative deposition baths and different substrate metals are emphasized. An active electrode material is presented which reaches a conversion efficiency close to the 1 % limit under AM 1.5 illumination conditions and thereby opens the door for a further optimization towards devices of technical interest. 相似文献
17.
Monika Moeder Steffi Schrader Ursula Winkler Rosario Rodil 《Journal of chromatography. A》2010,1217(17):2925-2932
An at-line analysis protocol is presented that allows the determination of four UV filters, two polycyclic musk compounds and caffeine in water at concentration level of ng L−1. The fully automated method includes analytes enrichment by Microextraction by packed sorbent (MEPS) coupled directly to large volume injection-gas chromatography–mass spectrometry. Two common SPE phases, C8 and C18, were examined for their suitability to extract the target substances by MEPS. The analytes were extracted from small sample volumes of 800 μL with recoveries ranging from 46 to 114% for the C8-sorbent and 65–109% for the C18-sorbent. Limits of detection between 34 and 96 ng L−1 enable the determination of the analytes at common environmental concentration levels. Both sorbents showed linear calibration curves for most of the analytes up to a concentration level of 20 ng mL−1. Carryover was minimized by washing the sorbents 10 times with 100 μL methanol. After this thorough cleaning, the MEPS are re-used and up to 70 analyses can be performed with the same sorbent. The fully automated microextraction GC–MS protocol was evaluated for the influence of matrix substances typical for wastewater. Dilution of samples prior to MEPS is recommended when the polar caffeine is present at high concentration. Real water samples were analyzed by the MEPS-GC–MS method and compared to standard SPE. 相似文献
18.
Franziska Emmerling Werner Kraus Bernhard Noll Steffi Noll Hans‐Jürgen Pietzsch 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(12):m579-m582
The molecular structures of the two mononuclear title complexes, namely (4‐methoxybenzenethiolato‐κS)oxido[2,2′‐(3‐phenylpropylimino)bis(ethanethiolato)‐κ3S,N,S′]technetium(V), [Tc(C14H21NS2)(C7H7OS)O], (I), and (4‐methoxybenzenethiolato‐κS)oxido[2,2′‐(propylimino)bis(ethanethiolato)‐κ3S,N,S′]technetium(V), [Tc(C7H15NS2)(C7H7OS)O], (II), exhibit the same coordination environment for the central Tc atoms. The atoms are five‐coordinated (TcNOS3) with a square‐pyramidal geometry comprising a tridentate 2,2′‐(3‐phenylpropylimino)bis(ethanethiolate) or 2,2′‐(propylimino)bis(ethanethiolate) ligand, a 4‐methoxybenzenethiolate ligand and an additional oxide O atom. Intermolecular C—H...O and C—H...S hydrogen bonds between the monomeric units result in two‐dimensional layers with a parallel arrangement. 相似文献
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20.
Bourderioux A Lefoix M Gueyrard D Tatibouét A Cottaz S Arzt S Burmeister WP Rollin P 《Organic & biomolecular chemistry》2005,3(10):1872-1879
Myrosinase, a thioglucoside glucohydrolase, is the only enzyme able to hydrolyse glucosinolates, a unique family of molecules bearing an anomeric O-sulfated thiohydroximate function. Non-hydrolysable myrosinase inhibitors have been devised and studied for their biological interaction. Diverse modifications of the O-sulfate moiety did not result in a significant inhibitory effect, whereas replacing the D-glucopyrano residue by its carba-analogue allowed inhibition to take place. X-Ray experiments carried out after soaking allowed for the first time inclusion of a non-hydrolysable inhibitor inside the enzymatic pocket. Structural tuning of the aglycon part in its pocket is being used as a guide for the development of simplified and more potent inhibitors. 相似文献