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排序方式: 共有168条查询结果,搜索用时 15 毫秒
51.
Markus Wiedemair Christoph Kieninger Klaus Wurst Maren Podewitz Evelyne Deery Michael D. Paxhia Martin J. Warren Bernhard Kräutler 《Helvetica chimica acta》2023,106(2):e202200158
The natural vitamin B12-derivatives are intriguing complexes of cobalt that entrap the metal within the strikingly skewed and ring-contracted corrin ligand. Here, we describe the synthesis of the Rh(III)-corrin acetylrhodibalamin ( AcRhbl ) from biotechnologically produced metal-free hydrogenobyric acid and analyze the effect of the replacement of the cobalt-center of the organometallic vitamin B12-derivative acetylcobalamin ( AcCbl ) with its group-IX homologue rhodium, to give AcRhbl . The structures of AcCbl and AcRhbl were thoroughly analyzed in aqueous solution, in crystals and by in silico methods, in order to gain detailed insights into the structural adaptations to the two homologous metals. Indeed, the common, nucleotide-appended corrin-ligand in these two metal corrins features extensive structural similarity. Thus, the rhodium-corrin AcRhbl joins the small group of B12-mimics classified as ‘antivitamins B12’, isostructural metal analogues of the natural cobalt-corrins that hold significant potential in biological and biomedical applications as selective inhibitors of key cellular processes. 相似文献
52.
Barker Evelyne Alcalde Gilles Bassot Sylvain 《Journal of Radioanalytical and Nuclear Chemistry》2017,314(1):353-358
A protocol is proposed for the measurement of 226Ra on 150 mg of solid sample without radiochemistry. To evaluate the performance of this method, standard samples were used and the results were in good agreement with reference values. The detection limit obtained is about 130 Bq kg−1 (dry weight) without mineralised solution concentration by evaporation. A concentration of the solution by 4 and/or an increase of sample mass by 4 in the case of microwave digestion system, allows achieving a detection limit of 30 Bq kg−1 (dry weight) and thus measuring 226Ra in most soils. This method could also be used for NORM sites on soil and sediment samples.
相似文献53.
We investigate the occurrence of collisions in the evolution of vortex filaments through a system introduced by Klein, Majda, and Damodaran and Zakharov . We first establish rigorously the existence of a pair of almost parallel vortex filaments, with opposite circulation, colliding at some point in finite time. The collision mechanism is based on one of the self‐similar solutions of the model, described by the authors in an earlier work. In the second part of this paper we extend this construction to the case of an arbitrary number of filaments, with polygonal symmetry, that are perturbations of a configuration of parallel vortex filaments forming a polygon, with or without its center, rotating with constant angular velocity.© 2016 Wiley Periodicals, Inc. 相似文献
54.
Oxygen-induced concurrent ultrasonic degradation of volatile and non-volatile aromatic compounds 总被引:6,自引:0,他引:6
Acoustic cavitation, induced by ultrasound, can be used to eliminate organic pollutants from water. This type of ultrasonic treatment of polluted water can be grouped with those generally referred to as advanced oxidative processes since it involves hydroxyl radicals. In this case these highly active species are generated from the dissociation of water and oxygen dissociation caused by cavitation bubble collapse. The cavitation induced degradation rates of organic compounds in water are mainly linked to their vapor pressure and solubility and here we will further explore these links by examining the degradation of a mixture of two materials with different physical properties, chlorobenzene and 4-chlorophenol. The results obtained when a dilute solution of a mixture of these compounds saturated with argon is subjected to sonication at 300 kHz, parallels previous observations achieved in an aerated aqueous medium at 500 kHz. The two compounds exhibit sequential degradation with the more volatile chlorobenzene entering the cavitation bubble and being destroyed first. The 4-chlorophenol degradation occurs subsequently only when the chlorobenzene has been completely destroyed. The two compounds exhibit different behavior when sonicated in water saturated with oxygen. Under these conditions the two compounds are degraded simultaneously, a remarkable result for which two explanations can be proposed, both of which are based on the formation of additional OH radical species: The ability to produce conditions for the simultaneous elimination of two organic compounds by the use of oxygen is of great importance in the developing field of ultrasonic water treatment. 相似文献
55.
Fischer F Zufferey E Bourgeois JM Héritier J Micaux F 《Journal of photochemistry and photobiology. B, Biology》2011,103(1):8-15
Pure luteolin is a remarkably heat (200°C/6 days) and UV stable UV-A screen, however, native luteolin enriched to 37% in an edelweiss extract lost its UV-A screen properties upon UV irradiation (~4MJm(-2)). This contrasting behavior led to the examination of a series of purified luteolin derivatives as UV screen candidates. 3',4',5,7-Tetralipoyloxyflavones were synthesized from luteolin (3',4',5,7-tetrahydroxyflavone) and fatty acid chlorides. These acylated semi-biomolecules show a hypsochromic shift in UV-Vis spectra of about Δλ(A→B)=58nm and absorbed in the centre of the harmful UV-B band (λ(max)=295nm). Luteolin was also hydroxyethylated with Br(CH(2))(2)OH. This substitution has no effect on the λ(max)=330nm absorption of luteolin (UV-A band). Finally the natural 4'-O-β-glucosyl-3',5,7-trihydroxyflavone was extracted from edelweiss and used as a purified natural benchmark. Glycosylated and hydroxyethylated luteolin are both UV stable. Fully acylated luteolin derivatives degrade upon UV exposure to a stable UV-C screen with a hypsochroic shift Δλ(B→C)=35nm. All in all, three molecular structures based on luteolin with sunscreen properties were found, distinguishable in: UV-A, UV-B, and UV-C filters. The natural product based UV-absorbers show promise as alternatives to synthetic molecules and nanoparticles in sunscreen products. 相似文献
56.
da Rocha DR de Souza AC Resende JA Santos WC dos Santos EA Pessoa C de Moraes MO Costa-Lotufo LV Montenegro RC Ferreira VF 《Organic & biomolecular chemistry》2011,9(11):4315-4322
A synthetic method to obtain α- and β-pyran naphthoquinones 10 and 11 with a hydroxyl substituent on the aromatic ring was developed. Two series of α- and β-pyran naphthoquinones were obtained from the 8-hydroxy-lawsone, and their anticancer properties were evaluated against four tumor cell lines. In general, the new compounds displayed good activity, possibly indicating that these compounds have increased pro-oxidant capacity. The 9-hydroxy-α-lapachone and 7-hydroxy-β-lapachone analogues of the natural products α-lapachone and β-lapachone were successfully produced by this methodology. 相似文献
57.
Julien SimonThi Thuan Nguyen Evelyne ChelainNathalie Lensen Julien PytkowiczGrégory Chaume Thierry Brigaud 《Tetrahedron: Asymmetry》2011,22(3):309-314
A concise synthesis of enantiopure (S)- and (R)-α-Tfm-aspartic acid and α-Tfm-serine is reported. The key step involves a Strecker-type reaction on chiral CF3-oxazolidines (Fox) derived from ethyl 4,4,4-trifluoroacetoacetate (ETFAA) or ethyl trifluoropyruvate. 相似文献
58.
The organolithium species addition to 2-hydroxymethyl fluorinated oxazolidines (Fox) provides a highly diastereoselective and straightforward route for the synthesis of enantiopure trifluoromethyl β-amino alcohols quaternarized at the β-position. 相似文献
59.
Johan T. Padding Evelyne van Ruymbeke Dimitris Vlassopoulos Wim J. Briels 《Rheologica Acta》2010,49(5):473-484
We use particle-based computer simulations to study the rheology of suspensions of high-functionality star polymers with long
entangled arms. Such particles have properties which are intermediate between those of soft colloidal particles and entangled
polymer chains. In the simulations, each star polymer is coarse-grained to a single particle. In order to faithfully reproduce
dynamical properties, it is very important to not only include time-averaged interactions (potentials of mean force) but to
also account for transient interactions induced by entanglements between the arms of different star polymers. Using a model
which has all these features, it is found that, for sufficiently high shear rates, the start-up shear stress displays an overshoot.
With increasing concentration, the core interactions increasingly dominate the initial stress response, leading to a maximum
in the stress overshoot at relatively low strain values (0.1 to 0.5). Transient forces start to dominate after this initial
stage. In a simulated experiment in which the shear rate is suddenly stepped-down from a high to a lower value, the stress
shows a clear undershoot, with the minimum stress again at a relatively low strain value (based on the new shear rate). Finally,
it is shown that a stress plateau develops in the flow curve. This plateau is absent when the transient forces between the
polymer stars are not taken into account. 相似文献
60.