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231.
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
232.
Cover Picture: An Unexpected Fluctuating Reactivity for Odd and Even Carbon Numbers in the TiO2‐Based Photocatalytic Decarboxylation of C2‐C6 Dicarboxylic Acids (Chem. Eur. J. 7/2014)
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233.
A new and general synthesis of the linearly fused [1,2,4]triazolo[1,5-b]isoquinoline ring system starting from 2,3-diaminoisoquinolinium salts has been elaborated. Starting compounds bearing an alkyl group in position 4 easily reacted with aldehydes to yield the cyclized products. In the case of a lack of electron donating group in position 4 (e.g., unsubstituted or 4-cyano substituted diamino derivatives) a Dimroth rearrangement took place under the same reaction conditions to yield 3-isoquinolylhydrazones. The mechanism of this unexpected transformation has been verified by isotope labelling experiments. Clarification of the reaction mechanism allowed finding proper reaction conditions to eliminate the rearrangement route, and thus, to perfect successful ring closure to the fused triazoles. 相似文献
234.
Gurcel C Vercoutter-Edouart AS Fonbonne C Mortuaire M Salvador A Michalski JC Lemoine J 《Analytical and bioanalytical chemistry》2008,390(8):2089-2097
The O-linked β-N-acetylglucosamine (O-GlcNAc) modification is an abundant post-translational modification in eukaryotic cells. This dynamic glycosylation plays
a fundamental role in the activity of many nuclear and cytoplasmic proteins and is associated with pathologies like type II
diabetes, Alzheimer’s disease or some cancers. However the exact link between O-GlcNAc-modified proteins and their function in cells is largely undefined for most cases. Here we report a strategy based
on the 1,3-dipolar cycloaddition, called click chemistry, between unnatural N-acetylglucosamine (GlcNAc) analogues (substituted with an azido or alkyne group) and the corresponding biotinylated probe
to specifically detect, enrich and identify O-GlcNAc-modified proteins. This bio-orthogonal conjugation confirms that only azido analogue of GlcNAc is metabolized by the
cell. Thanks to the biotin probe, affinity purification on streptavidin beads allowed us to identify 32 O-GlcNAc-azido-tagged proteins by LC-MS/MS analysis in an MCF-7 cellular model, 14 of which were previously unreported. This
work illustrates the use of the click-chemistry-based strategy combined with a proteomic approach to get further insight into
the pattern of O-GlcNAc-modified proteins and the biological significance of this post-translational modification.
Figure Detection of biotinylated O-GlcNAz proteins in MCF-7 cells
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Caroline Gurcel and Anne-Sophie Vercoutter-Edouart contributed equally to this work. 相似文献
235.
《Analytical letters》2012,45(12):837-849
Abstract A quantitative method has been developed for the determination of the tricyclic antidepressant drug nortriptyline in plasma, utilizing a combined technique of gas chromatography - mass spectrometry called mass fragmentography. A metabolite, desmethylnortriptyline, may be analyzed in the same run. The compounds are first converted to their heptafluorobutyranide derivatives. A complete chromatogram takes less than five minutes. Quantitive determinations under the present conditions are possible down to a few nanograms of nortriptyline per milliliter. There is a good correlation between the new method and that previously used which was based upon in vitro 3 11-acetylation labelling. 相似文献
236.
《Journal of Coordination Chemistry》2012,65(3):297-306
Abstract The infrared spectra of the complexes M(aq)2(H2O)2X2 (M = Fe, Co, Ni, Cu; aq = 8-aminoquinoline; X =Cl, Br) have been determined over the range 4000-50 cm?1. Absence of vM-X bands indicates that the halide is not coordinated to the metal ion and the complexes are correctly formulated [M(aq)2-(H2O)2]X2. Deuteration of the amino group and the effects of metal ion substitution enable assignment of the vM-NH2, vM-N and vM-OH2 modes as well as the amino group vibrations. 18 O-Labelling assists in identifying the vO-H, vO-H……X and δO-H bands. The spectra are consistent with trans-octahedral coordination and axial bonding of the water molecules. The far infrared spectra of the mono(aminoquinoline) complexes [M(aq)X2]n (M = Cu, Zn; X = Cl, Br) are consistent with the proposed structure of polymeric octahedral coordination involving both bridging and terminal M-X bonds. The vM-NH2, vM-N, vM-X(terminal) and vM-X(bridging) bands are assigned by studying the effects of amino group deuteration, metal ion substitution and halide substitution. 相似文献
237.
Suppose G is a graph, k is a non‐negative integer. We say G is k‐antimagic if there is an injection f: E→{1, 2, …, |E| + k} such that for any two distinct vertices u and v, . We say G is weighted‐k‐antimagic if for any vertex weight function w: V→?, there is an injection f: E→{1, 2, …, |E| + k} such that for any two distinct vertices u and v, . A well‐known conjecture asserts that every connected graph G≠K2 is 0‐antimagic. On the other hand, there are connected graphs G≠K2 which are not weighted‐1‐antimagic. It is unknown whether every connected graph G≠K2 is weighted‐2‐antimagic. In this paper, we prove that if G has a universal vertex, then G is weighted‐2‐antimagic. If G has a prime number of vertices and has a Hamiltonian path, then G is weighted‐1‐antimagic. We also prove that every connected graph G≠K2 on n vertices is weighted‐ ?3n/2?‐antimagic. Copyright © 2011 Wiley Periodicals, Inc. J Graph Theory 相似文献
238.
S. Consoli K. Darby-Dowman N. Mladenović J.A. Moreno Pérez 《European Journal of Operational Research》2009
This paper studies heuristics for the minimum labelling spanning tree (MLST) problem. The purpose is to find a spanning tree using edges that are as similar as possible. Given an undirected labelled connected graph, the minimum labelling spanning tree problem seeks a spanning tree whose edges have the smallest number of distinct labels. This problem has been shown to be NP-hard. A Greedy Randomized Adaptive Search Procedure (GRASP) and a Variable Neighbourhood Search (VNS) are proposed in this paper. They are compared with other algorithms recommended in the literature: the Modified Genetic Algorithm and the Pilot Method. Nonparametric statistical tests show that the heuristics based on GRASP and VNS outperform the other algorithms tested. Furthermore, a comparison with the results provided by an exact approach shows that we may quickly obtain optimal or near-optimal solutions with the proposed heuristics. 相似文献