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221.
Marc Verloo Mia Eeckhout 《International journal of environmental analytical chemistry》2013,93(2):179-181
Abstract The determination of metal species in solutions is important to evaluate their biological activity in natural ecosystems. The practical possibilities of different analytical techniques to determine and speciate metals in soil systems are discussed. Separative techniques such as ion exchange chromatography and gelpermeation chromatography allow a species estimation based on charge characteristics or molecular size of water soluble metal compounds. Electrochemical techniques such as potentiometry with ion-selective electrodes and polarography provide more detailed information about complex formation and stability. 相似文献
222.
223.
Johannes Schranck Mia Burhardt Christoph Bornschein Dr. Helfried Neumann Prof. Dr. Troels Skrydstrup Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9534-9538
A carbonylative α‐arylation process employing unactivated nitriles for the first time is described. The reaction tolerates a range of (hetero)aryl iodides and several nitrile coupling partners. No prefunctionalization of the nitriles is necessary and the resulting β‐ketonitriles are obtained in good to excellent yields. The methodology also allows for a convenient 13C‐labelling of the generated carbonyl moiety. 相似文献
224.
Köhler V Mazet C Toussaint A Kulicke K Häussinger D Neuburger M Schaffner S Kaiser S Pfaltz A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(28):8530-8539
Anionic boron-bridged bisoxazolines (borabox ligands) have been synthesized and characterized in their protonated forms. The ligands are tuneable over a wide range, allowing either alkyl or aryl substituents at the oxazoline rings and the central bridging boron atom. The structural parameters of this new ligand type have been investigated by X-ray analyses of palladium and copper complexes. Electronic properties have been studied by (13)C NMR spectroscopy and by DFT calculations on palladium allyl complexes and compared to those of analogous bisoxazoline (box) complexes. Borabox complexes are more electron-rich at the metal center than their neutral box congeners, and as a consequence of the longer bonds between the bridging atom and the oxazoline rings, their bite angles are larger. Palladium(II) complexes bearing an unsubstituted allyl ligand and homoleptic copper(II) complexes each possess an almost flat chelate ring. NMR analysis of a (1,3-diphenylallyl)(borabox)palladium complex showed a 92:8 mixture of (syn,syn) and (anti,syn) allyl isomers, in contrast with a previously reported box analogue that existed exclusively in the (syn,syn) form. Comparison of the corresponding crystal structures revealed that the distance between the bisoxazoline and the allyl ligand in the borabox complex is shorter. In the copper-catalyzed allylic oxidation of cyclohexene and cyclopentene with tert-butyl perbenzoate, borabox ligands gave results similar-and in some cases superior-to those obtained with analogous box ligands. 相似文献
225.
Lozano O Mejia J Tabarrant T Masereel B Dogné JM Toussaint O Lucas S 《Analytical and bioanalytical chemistry》2012,403(10):2835-2841
Nanoparticles (NPs) of SiO(2) (15 nm) or Ag (20 - 40 nm) were dispersed in water, coffee and milk at several aqueous dilutions. The NPs dispersions concentrations were quantified with an ion beam technique: Particle-Induced X-ray Emission. Additional measurements in relation to the state of the NPs dispersions were done: particle size distribution by centrifuge liquid sedimentation and the extreme surface composition by X-ray photoelectron spectroscopy. The particle size distribution of SiO(2) and Ag NPs dispersions in water and Ag NPs in coffee remained mostly as primary particles with hydrodynamic diameters close to the reported pristine NPs diameter. SiO(2) NPs agglomerated in coffee. In milk, both NPs presented an adsorption with milk lipids. Extreme surface composition corroborated adsorption in milk and showed that SiO(2) agglomerates adsorb some coffee components. A linear tendency in the measurement of the concentration dilutions of all dispersions was measured, and a lack of media influence in the slope of each curve was found. Limits of detection with the current setup were estimated at 0.5 and 0.3 mg/ml for SiO(2) and Ag NPs, respectively. 相似文献
226.
Marc Toussaint 《General Relativity and Gravitation》2000,32(9):1689-1709
A special case of metric-affine gauge theory of gravity (MAG) is equivalent to general relativity with Proca matter as source. We study in detail a corresponding numeric solution of the Reissner-Nordström type. It is static, spherically symmetric, and of electric type. In particular, this solution has no horizon, so it has a naked singularity at its origin. 相似文献