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781.
Depletion of high field strength elements (HFSE: Nb, Ta, Zr, Hf ) relative to other lithophile trace elements in arc magmas
and variations of Nb/Ta and Zr/Hf ratios in mantle-derived rocks can be addressed through studies of minerals, which concentrate
and fractionate these elements. The presence of rutile, a common accessory Ti-oxide phase in various mantle rocks, has often
been invoked to explain the Nb and Ta depletion in arc lavas because it has the highest HFSE abundances among the known mantle
minerals. In this study, we measure the concentrations of Nb, Ta, Zr and Hf (at > 200 ppm) in rutile of two metasomatized
mantle lherzolites using a Cameca SX-100 electron microprobe and obtain Nb/Ta ratios with an accuracy of about ± 5%. Mass
balance calculations indicate that ≤ 1−5% of Nb and Ta in the rocks reside in major minerals and that the balance is hosted
by accessory Ti-oxides. The Nb/Ta ratios vary significantly in nearby rutile grains in both peridotites (17–33, average 23;
12–37, average 21). Therefore, individual rutile grains may not be representative of the total grain population. However,
Nb/Ta ratios measured in the bulk rock lherzolites by solution ICP-MS (21 ± 0.3) are within the analytical error of the average
Nb/Ta values calculated for 5–7 rutile grains in both samples. These results emphasise that a representative grain selection
must be analysed in order to determine trace elements contents of bulk rocks from data on accessory phases. 相似文献
782.
Wassim Hadj Ali Delphine Derrien Florent Alix Céline Pérollier Olivier Lépine Sami Bayoudh Florence Chapuis-Hugon Valérie Pichon 《Journal of chromatography. A》2010,1217(43):6668-6673
The aim of this work was to develop a method for the clean-up of a mycotoxin, i.e. Ochratoxin A (OTA), from cereal extracts employing a new molecularly imprinted polymer (MIP) as selective sorbent for solid-phase extraction (SPE) and to compare with an immunoaffinity column. A first series of experiments was carried out in pure solvents to estimate the potential of the imprinted sorbent in terms of selectivity studying the retention of OTA on the MIP and on a non-imprinted polymer using conventional crushed monolith. The selectivity of the MIP was also checked by its application to wheat extracts. Then, after this feasibility study, two different formats of MIP: crushed monolith and micro-beads were evaluated and compared. Therefore an optimization procedure was applied to the selective extraction from wheat using the MIP beads. The whole procedure was validated by applying it to wheat extract spiked by OTA at different concentration levels and then to a certified contaminated wheat sample. Recoveries close to 100% were obtained. The high selectivity brought by the MIP was compared to the selectivity by an immunoaffinity cartridge for the clean-up of the same wheat sample. The study of capacity of both showed a significant higher capacity of the MIP. 相似文献
783.
Stability of [Ru(II)(tpy)(bpy)(OH(2))](2+)-modified graphite electrodes during indirect electrolyses
The stability of a graphite felt electrode modified by covalent attachment of [Ru(II)(tpy)(bpy)(OH(2))](2+) is investigated during the indirect electrolyses of alcohols in a flow cell. The continuous increase of the local potential of the electrode during the electrolyses attests to its degradation. Cyclic voltammetry analyses of the modified electrode after electrolyses show a total decrease of 80-90% of the wave corresponding to the Ru(III/II) couple. The concentration of remaining alcohol measured at the outlet of the cell is almost constant during all the electrolyses but increase when the potential exceeds 0.95 V(SCE). At low potentials, the electrode can be regenerated by reaction with Ru(II)Cl(2)(DMSO)(tpy) and then CF(3)SO(3)H, followed by hydrolysis, showing that the bipyridine ligand remains covalently attached to the electrode. At high potentials, the graphite is oxidized and the catalyst is partly lost in the reaction medium. XPS analyses of Ru core levels reveal that the ruthenium disappeared after electrolysis, showing that the degradation of the modified electrode is due to the demetalation of the oxidized complex. 相似文献
784.
785.
Trefzer C Škovierová H Buroni S Bobovská A Nenci S Molteni E Pojer F Pasca MR Makarov V Cole ST Riccardi G Mikušová K Johnsson K 《Journal of the American Chemical Society》2012,134(2):912-915
Benzothiazinones (BTZs) are antituberculosis drug candidates with nanomolar bactericidal activity against tubercle bacilli. Here we demonstrate that BTZs are suicide substrates of the FAD-dependent decaprenylphosphoryl-β-D-ribofuranose 2'-oxidase DprE1, an enzyme involved in cell-wall biogenesis. BTZs are reduced by DprE1 to an electrophile, which then reacts in a near-quantitative manner with an active-site cysteine of DprE1, thus providing a rationale for the extraordinary potency of BTZs. Mutant DprE1 enzymes from BTZ-resistant strains reduce BTZs to inert metabolites while avoiding covalent inactivation. Our results explain the basis for drug sensitivity and resistance to an exceptionally potent class of antituberculosis agents. 相似文献
786.
787.
Dr. Amanda J Welford Dr. John J. Caldwell Dr. Manjuan Liu Meirion Richards Dr. Nathan Brown Dr. Cara Lomas Dr. Graham J. Tizzard Dr. Mateusz B. Pitak Dr. Simon J. Coles Prof. Suzanne A. Eccles Dr. Florence I. Raynaud Prof. Ian Collins 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(16):5657-5664
The 2,11‐cembranoid family of natural products has been used as inspiration for the synthesis of a structurally simplified, functionally diverse library of octahydroisobenzofuran‐based compounds designed to augment a typical medicinal chemistry library screen. Ring‐closing metathesis, lactonisation and SmI2‐mediated methods were exemplified and applied to the installation of a third ring to mimic the nine‐membered ring of the 2,11‐cembranoids. The library was assessed for aqueous solubility and permeability, with a chemical‐space analysis performed for comparison to the family of cembranoid natural products and a sample set of a screening library. Preliminary investigations in cancer cells showed that the simpler scaffolds could recapitulate the reported anti‐migratory activity of the natural products. 相似文献
788.
Sébastien Benzekry Guillemette Chapuisat Joseph Ciccolini Alice Erlinger Florence Hubert 《Comptes Rendus Mathematique》2012,350(1-2):23-28
We present in this Note a new mathematical model designed to optimize and to rationalize the association between cytotoxic and antiangiogenic drugs in the treatment of a primary tumor. This model takes into account the non-linear interlinkings between both drugs. In particular, this original model integrates the influence of the vasculature state on the delivery of the drugs to the tumor. In the future, this model could be used in clinical oncology to optimize antiangiogenic-based combinational regimen so as to ensure a maximum efficacy. 相似文献
789.
Jumanova Raigul Rakhymbay Gulmira Abildina Ainaz Avchukir Khaisa Bakhytzhan Yeldana Vacandio Florence Argimbayeva Akmaral 《Journal of Solid State Electrochemistry》2023,27(1):223-233
Journal of Solid State Electrochemistry - The nanotubular structure of titanium dioxide (TiO2) is most suitable for creating high-performance energy storage and conversion devices. This paper... 相似文献
790.