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71.
Dr. Antoine Demont Dr. Carmelo Prestipino Dr. Olivier Hernandez Dr. Erik Elkaïm Serge Paofai Prof. Nikolaï Naumov Dr. Bruno Fontaine Prof. Régis Gautier Dr. Stéphane Cordier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(38):12711-12719
The crystal structure of Cs2BaTa6Br15O3 has been elucidated by using synchrotron X‐ray powder diffraction and absorption experiments. It is built from edge‐bridged octahedral [(Ta6${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]4? cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta6 clusters is similar to that of Cs2LaTa6Br15O3 exhibiting 14‐MEs per [(Ta6${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]5? motif. The poorer electron‐count cluster presents longer metal–metal distances as foreseen according to the electronic structure of edge‐bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13‐ and 14‐ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid‐state compounds is related to those of the discrete octahedral units. Oxygen–barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron‐poor Ta6 cluster in the solid state. 相似文献
72.
Poul Erik Hansen Fadhil S. Kamounah Diana Zhiryakova Yana Manolova Liudmil Antonov 《Tetrahedron letters》2014
It has recently been suggested that 1,1′,1′′-(2,4,6-trihydroxybenzene-1,3,5-triyl)triethanone may be tautomeric. Using 13C NMR chemical shifts and deuterium isotope effects on 13C chemical shifts, it is demonstrated that this is not the case. This compound occurs as a strongly hydrogen bonded benzene structure with hydrogen bonds between OH groups and the acetyl groups in both non-polar and hydrogen donating solvents. Quantum-chemical calculations using MP2 and M06-2X methods show substantial preference for the phenol structure in both the gas phase, and in cyclohexane and methanol. In addition, conventional UV–vis spectroscopy data suggest not tautomeric, but aggregation behaviour of the molecule in methanol and acetonitrile. 相似文献
73.
Jingbo Chang Guihua Zhou Erik R. Christensen Robert Heideman Junhong Chen 《Analytical and bioanalytical chemistry》2014,406(16):3957-3975
Graphene (G) is attracting significant attention because of its unique physical and electronic properties. The production of graphene through the reduction of graphene oxide (GO) is a low-cost method. The reduction of GO can further lead to electrically conductive reduced GO. These graphene-based nanomaterials are attractive for high-performance water sensors due to their unique properties, such as high specific surface areas, high electron mobilities, and exceptionally low electronic noise. Because of potential risks to the environment and human health arising from heavy-metal pollution in water, G-/GO-based water sensors are being developed for rapid and sensitive detection of heavy-metal ions. In this review, a general introduction to graphene and GO properties, as well as their syntheses, is provided. Recent advances in optical, electrochemical, and electrical detection of heavy-metal ions using graphene or GO are then highlighted. Finally, challenges facing G/GO-based water sensor development and outlook for future research are discussed. 相似文献
74.
Pierre Gras Nicolas Ratel‐Ramond Sbastien Teychn Christian Rey Erik Elkaim Batrice Biscans Stphanie Sarda Christle Combes 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(9):862-866
Calcium pyrophosphate hydrate (CPP, Ca2P2O7·nH2O) and calcium orthophosphate compounds (including apatite, octacalcium phosphate etc.) are among the most prevalent pathological calcifications in joints. Even though only two dihydrated forms of CPP (CPPD) have been detected in vivo (monoclinic and triclinic CPPD), investigations of other hydrated forms such as tetrahydrated or amorphous CPP are relevant to a further understanding of the physicochemistry of those phases of biological interest. The synthesis of single crystals of calcium pyrophosphate monohydrate (CPPM; Ca2P2O7·H2O) by diffusion in silica gel at ambient temperature and the structural analysis of this phase are reported in this paper. Complementarily, data from synchrotron X‐ray diffraction on a CPPM powder sample have been fitted to the crystal parameters. Finally, the relationship between the resolved structure for the CPPM phase and the structure of the tetrahydrated calcium pyrophosphate β phase (CPPT‐β) is discussed. 相似文献
75.
Intramolecular NH…O,S,N interactions in non-tautomeric systems are reviewed in a broad range of compounds covering a variety of NH donors and hydrogen bond acceptors. 1H chemical shifts of NH donors are good tools to study intramolecular hydrogen bonding. However in some cases they have to be corrected for ring current effects. Deuterium isotope effects on 13C and 15N chemical shifts and primary isotope effects are usually used to judge the strength of hydrogen bonds. Primary isotope effects are investigated in a new range of magnitudes. Isotope ratios of NH stretching frequencies, νNH/ND, are revisited. Hydrogen bond energies are reviewed and two-bond deuterium isotope effects on 13C chemical shifts are investigated as a possible means of estimating hydrogen bond energies. 相似文献
76.
Bialczak RC McDermott R Ansmann M Hofheinz M Katz N Lucero E Neeley M O'Connell AD Wang H Cleland AN Martinis JM 《Physical review letters》2007,99(18):187006
We present a new method to measure 1/f noise in Josephson quantum bits (qubits) that yields low-frequency spectra below 1 Hz. A comparison of the noise taken at positive and negative bias of a phase qubit shows the dominant noise source to be flux noise and not junction critical-current noise, with a magnitude similar to that measured previously in other systems. Theoretical calculations show that the level of flux noise is not compatible with the standard model of noise from two-level state defects in the surface oxides of the films. 相似文献
77.
The effect of the simultaneous presence of monovalent and divalent cations on the thermodynamics of polyelectrolyte solutions is an incompletely solved problem. In physiological conditions, combinations of these ions affect structure formation in biopolymer systems. Dynamic light scattering measurements of the collective diffusion coefficient D and the osmotic compressibility of semidilute hyaluronan solutions containing different ratios of sodium and calcium ions are compared with simple polyelectrolyte models. Scaling relationships are proposed in terms of polymer concentration and ionic strength J of the added salt. Differences in the effects of sodium and calcium ions are found to be expressed only through J. 相似文献
78.
We implement time propagation of the nonequilibrium Green function for atoms and molecules by solving the Kadanoff-Baym equations within a conserving self-energy approximation. We here demonstrate the usefulness of time propagation for calculating spectral functions and for describing the correlated electron dynamics in a nonperturbative electric field. We also demonstrate the use of time propagation as a method for calculating charge-neutral excitation energies, equivalent to highly advanced solutions of the Bethe-Salpeter equation. 相似文献
79.
Karlsson Erik Neuhausen Jörg Eichler Robert Danilov Ivan I. Vögele Alexander Türler Andreas 《Journal of Radioanalytical and Nuclear Chemistry》2021,328(2):707-715
Journal of Radioanalytical and Nuclear Chemistry - The usage of silver as a filtering material for removal of iodine from the gas phase of a lead–bismuth eutectic based nuclear reactor was... 相似文献
80.
Determination of conditional stability constants for some divalent transition metal ion‐EDTA complexes by electrospray ionization mass spectrometry 下载免费PDF全文
Susanne Boija Ann Almesåker Erik Hedenström Dan Bylund Håkan Edlund Magnus Norgren 《Journal of mass spectrometry : JMS》2014,49(7):550-556
Conditional stability constants of coordination complexes comprising divalent transition metals, Cu2+, Ni2+, Zn2+, Co2+, and ethylenediaminetetraacetic acid (EDTA) were determined utilizing electrospray ionization mass spectrometry. The deviation of signal response of a reference complex was monitored at addition of a second metal ion. The conditional stability constant for the competing metal was then determined through solution equilibria equations. The method showed to be applicable to a system where Co2+ and Zn2+ competed for EDTA at pH 5. When Cu2+ and Ni2+ competed for EDTA, the equilibrium changed over time. This change was shown to be affected in rate and size by the type of organic solvent added. In this work, 30% of either methanol or acetonitrile was used. It was found that if calibration curves are prepared for both metal complexes in solution and the measurements are repeated with sufficient time space, any change in equilibrium of sample solutions will be discovered. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献