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991.
Susanne Burri Patrick Sturm Thomas Baur Matti Barthel Alexander Knohl Nina Buchmann 《Isotopes in environmental and health studies》2014,50(4):497-513
Pulse labelling experiments provide a common tool to study short-term processes in the plant–soil system and investigate below-ground carbon allocation as well as the coupling of soil CO2 efflux to photosynthesis. During the first hours after pulse labelling, the measured isotopic signal of soil CO2 efflux is a combination of both physical tracer diffusion into and out of the soil as well as biological tracer release via root and microbial respiration. Neglecting physical back-diffusion can lead to misinterpretation regarding time lags between photosynthesis and soil CO2 efflux in grassland or any ecosystem type where the above-ground plant parts cannot be labelled in gas-tight chambers separated from the soil. We studied the effects of physical 13CO2 tracer back-diffusion in pulse labelling experiments in grassland, focusing on the isotopic signature of soil CO2 efflux. Having accounted for back-diffusion, the estimated time lag for first tracer appearance in soil CO2 efflux changed from 0 to 1.81±0.56 h (mean±SD) and the time lag for maximum tracer appearance from 2.67±0.39 to 9.63±3.32 h (mean±SD). Thus, time lags were considerably longer when physical tracer diffusion was considered. Using these time lags after accounting for physical back-diffusion, high nocturnal soil CO2 efflux rates could be related to daytime rates of gross primary productivity (R2=0.84). Moreover, pronounced diurnal patterns in the δ13C of soil CO2 efflux were found during the decline of the tracer over 3 weeks. Possible mechanisms include diurnal changes in the relative contributions of autotrophic and heterotrophic soil respiration as well as their respective δ13C values. Thus, after accounting for physical back-diffusion, we were able to quantify biological time lags in the coupling of photosynthesis and soil CO2 efflux in grassland at the diurnal time scale. 相似文献
992.
Composites of three-dimensional (3D) carbon nanostructures coated with olivine-structured lithium iron phosphates (LiFePO4) as cathode materials for lithium ion batteries have been prepared through a Pechini-assisted reversed polyol process for the first time. The coating has been successfully performed on nonfunctionalized commercially available 3D carbon used as catalysts. Thermal analysis revealed no phase transitions till crystallization occurred at 579 °C. Morphological investigation of the prepared composites showed a very good quality of the coating on the 3D carbon structures. A great enhancement of the crystallinity of the olivine structure and of the composites was revealed by the structural investigation performed on pure LiFePO4 and composites after annealing at 600 °C for 10 h under nitrogen atmosphere. The cyclic voltammetry curves of the composites show well-defined peaks and smaller value of the polarization overpotential indicating an enhancement of electrode reaction reversibility compared to the LiFePO4 phase. 相似文献
993.
Le Provost R Wille T Louise L Masurier N Müller S Reiter G Renard PY Lafont O Worek F Estour F 《Organic & biomolecular chemistry》2011,9(8):3026-3032
A new generation of organophosphate (OP) scavengers was obtained by synthesis of β-cyclodextrin-oxime derivatives 8-12. Selective monosubstitution of β-cyclodextrin was the main difficulty in order to access these compounds, because reaction onto the oligosaccharide was closely related to the nature of the incoming group. For this purpose, non-conventional activation conditions were also evaluated. Intermediates 5 and 7 were then obtained with the better yields under ultrasounds irradiation. Finally, the desired compounds 8-10 were obtained from 5-7 in high purity by desilylation using potassium fluoride. Quaternarisation of compounds 8 and 9 was carried out. OP hydrolytic activity of compounds 8-12 was evaluated against cyclosarin (GF) and VX. None of the tested compounds was active against VX, but these five cyclodextrin derivatives detoxified GF, and the most active scavengers 10 and 11 allowed an almost complete hydrolysis of GF within 10 min. Even more fascinating is the fact that compounds 9 and 10 were able to hydrolyze enantioselectively GF. 相似文献
994.
Baldermann S Mulyadi AN Yang Z Murata A Fleischmann P Winterhalter P Knight M Finn TM Watanabe N 《Journal of separation science》2011,34(19):2759-2764
Centrifugal precipitation chromatography and a high-speed counter-current chromatography system equipped with a spiral tubing support rotor (spHSCCC) were successfully applied for the identification and isolation of carotenoid cleavage-like enzymes from Enteromorpha compressa (L.) Nees. This is the first study separating active enzymes from a complex natural matrix by spHSCCC. The target enzymes were identified after fractionation of the proteins in an acetone Tris-buffer gradient by centrifugal precipitation chromatography. Also, an aqueous two-phase solvent system consisting of PEG 1000 and mono- and dibasic potassium phosphate was used for the isolation of the enzymes by spHSCCC. The purified fractions contained two proteins of 65 and 72 kDa, respectively. The enzymes could cleave β-carotene and β-apo-8'-carotenal to produce β-ionone. 相似文献
995.
Susanne Lühn Simone Schiemann Susanne Alban 《Analytical and bioanalytical chemistry》2011,399(2):673-680
In 2008, heparin contaminated with oversulfated chondroitin sulfate (OSCS) penetrated the worldwide market and was associated
with severe adverse effects. Feasible and reliable methods to test heparin for adulteration are needed. The objective was
to develop a simple approach based on a microplate assay for quantification of heparin and sulfated glycans using the fluorescent
heparin sensor polymer-H (polymer-H assay). However, both heparin and OSCS concentration-dependently increase the fluorescence
intensity (FI) of polymer-H, so that OSCS in heparin cannot be detected. The idea was a two-step procedure including, first,
separation of heparin by degradation with heparinase I, and then measurement of the remaining OSCS. To achieve complete heparin
(unfractionated heparin (UFH), enoxaparin) degradation, several conditions (e.g. incubation time and heparinase I concentration)
were optimized by using the aXa assay for monitoring. Defined UFH/OSCS mixtures incubated in this way showed a concentration-dependent
FI increase in the polymer-H assay (λ
(em) 330 nm, λ
(ex) 510 nm). The sensitivity was unexpectedly high with an LOD/LOQ of 0.5%/0.6% OSCS content in heparin. Further experiments
testing UFH/OSCS mixtures in the aXa assay confirmed our hypothesis: OSCS inhibits heparinase I resulting in incomplete heparin
degradation and thus an additional FI increase of polymer-H by intact heparin. This two-step microplate fluorescence assay
is a sensitive, rapid, and simple method for quantification of OSCS in heparin. In contrast with 1H NMR and CE, neither expensive equipment nor much experience are required. It could be applied not only in the quality control
of heparin, but also in clinical practice, to check the applied heparin preparation when a patient suffers any adverse effect. 相似文献
996.
Hecht E Usmani SM Albrecht S Wittekindt OH Dietl P Mizaikoff B Kranz C 《Analytical and bioanalytical chemistry》2011,399(7):2369-2378
Scanning probe techniques enable direct imaging of morphology changes associated with cellular processes at life specimen.
Here, glutaraldehyde-fixed and living alveolar type II (ATII) cells were investigated by atomic force microscopy (AFM), and
the obtained topographical data were correlated with results obtained by scanning electron microscopy (SEM) and confocal microscopy
(CM). We show that low-force contact mode AFM at glutaraldehyde-fixed cells provides complementary results to SEM and CM.
Both AFM and SEM images reveal fine structures at the surface of fixed cells, which indicate microvilli protrusions. If ATII
cells were treated with Ca2+ channel modulators known to induce massive endocytosis, changes of the cell surface topography became evident by the depletion
of microvilli. Low force contact mode AFM imaging at fixed ATII cells revealed a significant reduction of the surface roughness
for capsazepine and 2-aminoethoxydiphenyl-borate (CPZ/2-APB)-treated cells compared to untreated control cells (Rc of 99.7 ± 6.8 nm
vs. Rc of 71.9 ± 4.6 nm for N = 22), which was confirmed via SEM studies. CM of microvilli marker protein Ezrin revealed a cytoplasmic localization of
Ezrin in CPZ/2-APB-treated cells, whereas a submembranous Ezrin localization was observed in control cells. Furthermore, in
situ AFM investigations at living ATII cells using low force contact mode imaging revealed an apparent decrease in cell height
of 17% during stimulation experiments. We conclude that a dynamic reorganization of the microvillous cell surface occurs in
ATII cells at conditions of stimulated endocytosis. 相似文献
997.
Rösken Liz M. Körsten Susanne Fischer Christian B. Schönleber Andreas van Smaalen Sander Geimer Stefan Wehner Stefan 《Journal of nanoparticle research》2014,16(4):1-14
In the experiments, multifunctional nanocomposites with fluorescence, superparamagnetism, and bioactivity were synthesized to isolate and detect bacteria. Fluorescent-magnetic nanocomposites (FMNPs) (Fe3O4@SiO2@FITC–SiO2, core/shell) were first synthesized. Then, FMNPs were conjugated with N-hydroxysuccinimide-activated 4-oxo-4-(prop-2-ynyloxy) butanoic acid (NHS-activated ester) by the linker of 3-aminopropyltriethoxysilane, and alkyne-functionalized fluorescent-magnetic nanocomposites (FMNPs-alkyne) were produced. After 3′-azidopropyl-O-α-d-manno-pyranoside was grafted on the surface of FMNPs-alkyne by click chemistry, the final product—mannose derivatives-grafted fluorescent-magnetic nanocomposites (FMNPs-mannose) were obtained. Common techniques (Nuclear magnetic resonance, ESI mass spectra, etc.) indicated the successful synthesis of the target products. The results of scanning electron microscopy, transmission electron microscopy, and dynamic light scattering showed that FMNPs with one or more magnetic cores have regular structure with a diameter around 100 nm. Fluorescence spectra and fluorescence microscopy indicated that those nanocomposites exhibited strong and stable fluorescence property. FMNPs-mannose have a saturation magnization of 6.88 emu/g at room temperature. FMNPs-mannose were applied to adhere to Escherichia coli ATCC25722 and Staphylococcus aureus ATCC6538. The results showed that FMNPs-mannose were able to specifically adhere to E. coli ATCC25722. However, it had no effect with S. aureus ATCC6538. The obtained FMNPs-mannose will find its application in bacteria detection and separation. 相似文献
998.
Susanne Olsson Dr. Anders Lennartson Prof. Mikael Håkansson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12415-12423
We report the absolute asymmetric synthesis (AAS) of indenylzinc reagents by using total spontaneous resolution followed by enantiospecific conversion into 1‐chloroindene. The chiral complex [Zn(dcp)(ind)(tmeda)] (dcp=2,6‐dichlorophenoxy and tmeda=N,N,N′,N′‐tetramethylethylenediamine) ( 3 ) was prepared from the achiral starting materials indene, potassium, zinc chloride, TMEDA, and 2,6‐dichlorophenol. The reagent resolved spontaneously on crystallization, and single crystals of 3 react with N‐chlorosuccinimide in the presence of benzoquinone in 2‐propanol to give 1‐chloroindene in >98 % enantiomeric excess. It was found that (R)‐ 3 gave (R)‐1‐chloroindene upon reaction, indicating an SE2′‐mechanism. Since bulk samples of 3 gave optically active product upon chlorination, total spontaneous resolution must have occurred. This demonstrates that enantiopure products can be obtained through the absolute asymmetric synthesis of organometallic reagents starting from achiral materials. The general absolute asymmetric synthesis (AAS) method offers easy access to both enantiomers and an almost limitless variation in the design of the product. 相似文献
999.
Andrey P. Antonchick Sara López-Tosco Juan Parga Sonja Sievers Markus Schürmann Hans Preut Susanne Höing Hans R. Schöler Jared Sterneckert Daniel Rauh Herbert Waldmann 《Chemistry & biology》2013,20(4):500-509
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1000.
Wiedmer SK D'Orazio G Smått JH Bourdin D Baños-Pérez C Sakeye M Kivilompolo M Kopperi M Ruiz-Jiménez J Fanali S Riekkola ML 《Journal of chromatography. A》2011,1218(30):5020-5029
The need for novel packing materials in both capillary electrochromatography (CEC) and capillary liquid chromatography (CLC) is apparent and the development towards more selective, application-oriented chromatographic phases is under progress world-wide. In this study we have synthesized new polyethyleneimine (PEI) functionalized Mn(2)O(3), SiO(2), SnO(2), and ZrO(2) particles for the fabrication of packed capillary columns for CEC and CLC. The nanocasting approach was successful for the preparation of functionalized metal oxide materials with a controlled porosity and morphology. PEI functionalization was done using ethyleneimine monomers to create particles which are positively charged in aqueous solution below pH 9. This functionalization allowed the possibility to have both hydrophobic (due to its alkyl chain) and ionic interactions (due to positively charged amino groups) with selected compounds. For comparison aminopropyl-functionalized silica was also synthesized and tested. Both slurry pressure and electrokinetic packing procedures used gave similar results, but fast sedimentation of the material caused some problems during the packing. The high stability and wide pH range of PEI-functionalized SiO(2) material, with potential for hydrophobic and electrostatic interactions, proved to be useful for the CEC and CLC separation of some model acidic and neutral compounds. 相似文献