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91.
Astrid Kaunzinger Frank Podebrad RÜDiger Liske Birgit Maas Armin Dietrich Armin Mosandl 《Journal of separation science》1995,18(1):49-53
The direct enantioselective analysis of 3-, 4-, and 5-hydroxy fatty acids from biological material has been achieved by enantioselective multidimensional gas chromatography (enantio-MDGC) with heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)- or (2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as chiral stationary phase. All the bacteria investigated produced polyesters of enatiomerically pure (R) configured compounds. 相似文献
92.
Multiresidue method using SPME for the determination of various pesticides with different volatility in confined atmospheres 总被引:1,自引:0,他引:1
An analytical method is described for assessing the vapour concentration of 11 pesticides (bioallethrin, chlorpyriphos methyl, folpet, malathion, procymidone, quintozene, chlorothalonil, fonofos, penconazole and trimethacarb) in confined atmospheres (e.g. a greenhouse after pesticide application). This study is a successful extension of a method previously developed by the authors for dichlorvos to much less volatile pesticides. Sampling was performed by using polydimethylsiloxane–solid phase micro-extraction (PDMS–SPME) fibres immersed in a 250-mL sampling flask through which air samples were dynamically pumped from the analysed atmosphere. After a 40-min sampling duration, samples were analysed by GC/MS.Calibration was performed from a vapour-saturated air sample. The linearity of the observed signal versus pesticide concentration in the vapour phase was proved from spiked liquid samples whose headspace concentrations were measured by using the proposed method. This procedure gave calibration curves with regression coefficients (R2) greater than 0.98, and the repeatability of these measurements was found with RSDs of 1.9–7.6%. As a field application test, this analysis procedure was used for the determination of gaseous procymidone concentrations as a function of time in the atmosphere of an experimental 8-m2 and 20-m3 greenhouse. The pesticide was sprayed according to real cultivation conditions, and measurements were made for 80 h after application (8 measurements). The observed concentrations found ranged from 200 to 500 µg m–3, thus indicating the level of contamination of the air breathed by people in such working conditions.Abbreviations GC/MS
gas chromatography/mass spectrometry
- SIM
selective ion monitoring
- FC43
perfluorotributylamine
- RSD
relative standard deviation
- LOD
limit of detection
- LOQ
limit of quantification 相似文献
93.
Mario Wurglics Astrid Michelitsch Gotthard Wurm 《Monatshefte für Chemie / Chemical Monthly》2002,133(9):1225-1230
Summary. Comparative studies of redox behaviour and antioxidative activity (AOA) were carried out with two series of arylnaphthoquinone
derivatives. For the electrochemical investigations, a voltammetric procedure combined with a glassy carbon electrode was
applied. The AOA was examined using the photo-chemiluminometric method with the Photochem? measuring device according to Popov et al. and the chemical procedure with the radical quencher DPPH (diphenylpicrylhydrazyl). Both the redox potential and the antioxidative activity of the investigated compounds are influenced
by their substituents. Compounds with the OH-group at position 3 are easiest to oxidize (E
p = 0.18 V; pH 7.4). The lag phases (AOA) of these compounds are five to ten times greater than those of the strong antioxidants ascorbic
acid and Trolox?. As suggested for other natural compounds, we also found a good correlation between the oxidation potential and the AOA.
Therefore, it seems that a good antioxidative activity requires a low redox potential.
Corresponding authors. E-mail: wurglics@pharmchem.uni-frankfurt.de
Received March 1, 2002; accepted March 28, 2002 相似文献
94.
This paper discusses the behaviour of angiotensin 1 and neurotensin together with their metabolites in a three-phase liquid phase microextraction under acidic conditions. Variations in donor phase, organic phase, and acceptor phase are studied with extraction recovery as response variable. It is proved that for all peptides the transport across the organic phase is mediated by heptane-1-sulphonic acid. n-Octanol gave overall best results as organic phase. A donor phase volume of 1.0 mL was chosen as a compromise between optimal recovery and robustness of the LPME device. The optimal pH of the donor phase (using acceptor phase of pH 2) was found to be different for the peptides, which opens opportunities for selective sample preparation. Decreasing the acceptor phase pH to 1.0 resulted in increased extraction recoveries. On using 1.0 mL of donor phase containing 50 mM heptane-1-sulphonic acid pH 3, n-octanol as organic phase immobilized in the pores of the fibre, and 20 microL of acceptor phase containing 0.1 mol/L HCl, extraction recoveries up to 82% (enrichment factor = 41) were achieved. To our knowledge this is the first report on liquid phase microextraction of angiotensins and neurotensins. 相似文献
95.
Jensen HH Lyngbye L Jensen A Bols M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(5):1218-1226
From the pK(a) values of the conjugate acids of a large series of hydroxylated piperidines and hexahydropyridazines, a consistent difference in basicity was found between stereoisomers having an axial or equatorial hydroxyl (OH) group either beta or gamma to the amine. Compounds with an equatorial OH group in the 3-position were 0.8 pH units more acidic than otherwise identical compounds with an axial OH group, whilst compounds with an equatorial OH group in the 4-position relative to the amine were 0.4 pH units more acidic than the corresponding compound with an axial OH. A similar effect was observed for the COOMe substituent. The difference in electron-withdrawing power of axial and equatorial substituents was explained by a difference in charge-dipole interactions in the two systems. Since this stereoelectronic substituent effect causes differences in basicity in different conformers, certain piperidines and hexahydropyridazines were found to change conformation upon protonation. A method for predicting the pK(a) of piperidines which takes stereochemistry into account is described. 相似文献
96.
Influence of the particle size of the MgCl2 support on the performance of Ziegler catalysts in the polymerization of ethylene to ultra‐high molecular weight polyethylene and the resulting polymer properties 下载免费PDF全文
An Philippaerts Richard Ensinck Nicolas Baulu Astrid Cordier Kersten Woike Romain Berthoud Gert De Cremer John R. Severn 《Journal of polymer science. Part A, Polymer chemistry》2017,55(16):2679-2690
A highly systematic size series of Ziegler catalysts with similar porosities and surface textures are synthesized by varying the stirring speed during the MgCl2 support synthesis. Besides the mean particle size, the only substantial difference observed between the various catalysts is the size and number of nodules per particle. Varying the mean diameter of the catalyst particles between 1.5 and 11.9 µm, leads to a pronounced impact on the activity in ultra‐high molecular weight polyethylene (UHMWPE) polymerization, while the Mw capabilities are only affected to a limited extend. In addition, it is observed that both the Mws as the polymer bulk density (BD) increases during the course of the polymerization. This particularity allows to optimize the Mw and/or BD at a set polymer size, by tuning the catalyst particle size. This is particularly interesting in UHMWPE production, as control of the morphological and structural properties of the UHMWPE reactor powders are critical for efficient processing as well as the performance of the final product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2679–2690 相似文献
97.
Astrid K. Torres Arellano Gregory B. McKenna 《Journal of Polymer Science.Polymer Physics》2015,53(18):1261-1272
We use calorimetry and rheology to investigate reports of extremely fragile polymers and the speculation that d,l ‐lactic acid should be extremely fragile. The dynamic fragilities of lactic acid, polysulfone, bisphenol‐A polycarbonate, and poly(vinyl chloride) were studied. The polymers were used as received and after a wash‐precipitation treatment. The current dynamic fragility findings are not in agreement with those reported by C. Evans, H. Deng, W. Jager, J. Torkelson, Macromolecules 2013 , 46 (15), 6091–6103 of extremely high fragilities for the mentioned polymers. We also found no sample preparation history effect on the dynamic fragility values. The calorimetric and rheological results for the d,l ‐lactic acid show dynamic fragility values that are consistent with each other and are not extremely fragile. Calorimetric measurements that use a broad range of cooling rates gave smaller dynamic fragility values than those obtained from a limited range at higher cooling rates. The importance of the results is discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1261–1272 相似文献
98.
Jing Zhang Dr. Astrid Schaly Dr. Jean-Claude Chambron Dr. Bruno Vincent Nathalie Zorn Dr. Emmanuelle Leize-Wagner Marion Jean Dr. Nicolas Vanthuyne 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(7):e202103759
Chiral gold(I) acetylide trinuclear complexes 1 – 3 based on the cyclotribenzylene platform and terminal PR3 ligands (R=Ph, Et, and Cy, respectively), were characterized and their light emission studied. They exhibited long-lived blue phosphorescence in CHCl3 and a weak fluorescence in the UV. In MeOH/CHCl3 mixtures of >1:1 volume ratio, 1 and 2 exhibited a new emission band at ca. 540 nm that developed at the expense of the UV emission. DLS studies demonstrated the presence of molecular aggregates of Ø 30–80 nm. The green emission observed in MeOH-rich solvent mixtures was therefore induced by aggregation, and could originate from Au⋅⋅⋅Au interactions. The AIE spectrum of 3 was observed only in solutions containing 99 % of MeOH, and correlated with its solid state emission. The AIE profiles of the enantiomers of 1 differed from that of rac- 1 , suggesting that the latter is a true racemate. 相似文献
99.
100.
Bering Eivind Torstensen Jonathan . Lervik Anders de Wijn Astrid S. 《Cellulose (London, England)》2022,29(3):1365-1380
Cellulose - We investigate the dissolution mechanism of cellulose using molecular dynamics simulations in both water and a mixture solvent consisting of water with Na $$^+$$ , OH $$^-$$... 相似文献