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951.
Tomáš Šmejkal Denis Gribkov Jens Geier Manfred Keller Bernhard Breit 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(8):2470-2478
A library of monodentate phosphane ligands, each bearing a guanidine receptor unit for carboxylates, was designed. Screening of the library gave some excellent catalysts for regioselective hydroformylation of β,γ‐unsaturated carboxylic acids. A terminal alkene, but‐3‐enoic acid, was hydroformylated with a linear/branched (l/b) regioselectivity up to 41. An internal alkene, pent‐3‐enoic acid was hydroformylated with regioselectivity up to 18:1. Further substrate selectivity (e.g., acid vs. methyl ester) and reaction site selectivity (monofunctionalization of 2‐vinylhept‐2‐enoic acid) were also achieved. Exploration of the structure–activity relationship and a practical and theoretical mechanistic study gave us an insight into the nature of the supramolecular guanidinium–carboxylate interaction within the catalytic system. This allowed us to identify a selective transition‐state stabilization by a secondary substrate–ligand interaction as the basis for catalyst activity and selectivity. 相似文献
952.
Janko Drnovšek Igor Pušnik Jovan Bojkovski Gaber Begeš 《Accreditation and quality assurance》2010,15(2):125-131
The article describes the project of regional cooperation in proficiency testing within CARDS 2006 (assistance programme to
the Western Balkans), which was coordinated by European Committee for Standardization, European Commission and European Free
Trade Association and conducted by the University of Ljubljana, Faculty of Electrical Engineering, Laboratory of Metrology
and Quality. The later is the holder of the national standard for thermodynamic temperature as well as an accredited proficiency
testing provider and also accredited as a calibration, testing and inspection laboratory. It is also responsible for graduate
study programme Quality Engineering. Proficiency testing was considered as a core activity of the entire project, but additionally
as a very appropriate platform for knowledge transfer of EU technical legislation in selected sectors, metrology, testing
and quality assurance in general. The project had a high added value for participating laboratories in countries of Western
Balkans, because it required an active role of all participating laboratories, assured participation of staff from national
metrology institutions, all national accreditation bodies, and was supported by national quality infrastructures, such as
standardization, governmental institutions etc. in the entire Western Balkans region. The activities stimulated progress in
the area of conformity assessment, added knowledge to the implementation of technical directives and development of the technical
part of national legislation and therefore facilitated the process toward the accession to the European Union. The main objective
was therefore to organize proficiency testing in those sectors (construction, consumer protection and environment) that were
vital in the pre-accession process of countries seeking full implementation of EU technical legislation. 相似文献
953.
Wojtowicz P Zrostlíková J Kovalczuk T Schůrek J Adam T 《Journal of chromatography. A》2010,1217(51):8054-8061
Organic acidurias are a large group of inherited metabolic disorders (IMDs), commonly diagnosed by GC-MS analysis of organic acids in urine after acidic extraction and trimethylsilylation. In this study, a GC×GC-ToF-MS method has been optimized for the analysis of pathological metabolites in urine. An automated data processing strategy based on the use of mass spectra and GC retention times for the target search and quantification of pathological metabolites has been developed. Using this procedure, each unknown sample is automatically examined for the presence of markers of several diseases at the same time. The method has been applied for the analysis of 6 challenging proficiency testing samples from patients with IMDs (thymidine phosphorylase deficiency, mevalonic aciduria, hawkinsinuria, aromatic l-amino acid decarboxylase deficiency, propionic acidemia and medium-chain acyl-CoA dehydrogenase deficiency). Using the GC×GC-ToF-MS method, we were able to determine complete sets of markers for all the IMDs. The quality of the mass spectral matches for the pathological markers was higher than 800 (out of 1000). 相似文献
954.
We propose a criterion giving a sufficient condition for quantum states of a harmonic oscillator not to be expressible as a convex mixture of Gaussian states. This nontrivial property is inherent to, e.g., a single-photon state and the criterion thus allows one to reveal a signature of the state even in quantum states with a positive Wigner function. The criterion relies on directly measurable photon number probabilities and enables detection of this manifestation of a single-photon state in quantum states produced by solid-state single-photon sources in a weak coupling regime. 相似文献
955.
The mechanism of the decomposition of acryloylcarbamates 7a–b yielding highly reactive isocyanates 3a–b was proposed based on NMR measurements and quantum chemical calculations. A good agreement between the experimental kinetic data and DFT calculations allowed us to demonstrate that the stability of 7a–d depends on the presence of methyl in the acryloyl moiety and the position of the nitro group in the nitrophenolic part of the molecule. Furthermore, the reactivity of 7a–d with weakly nucleophilic and sterically hindered 2,4,6‐tri‐tert‐butylaniline was explored by 1H NMR demonstrating the usefulness of reagents 7a–d offering access to a variety of 1‐N‐substituted uracils and thymines with potentially interesting biological properties. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
956.
Rožič B Tzitzios V Karatairi E Tkalec U Nounesis G Kutnjak Z Cordoyiannis G Rosso R Virga EG Muševič I Kralj S 《The European physical journal. E, Soft matter》2011,34(2):1-11
We have studied theoretically and experimentally the effects of various types of nanoparticles (NPs) on the temperature stability range [Formula: see text] T (BP) of liquid-crystalline (LC) blue phases. Using a mesoscopic Landau-de Gennes type approach we obtain that the defect core replacement (DCR) mechanism yields in the diluted regime [Formula: see text] T (BP)(x) [Formula: see text] 1/(1 - xb) , where x stands for the concentration of NPs and b is a constant. Our calculations suggest that the DCR mechanism is efficient if a local NP environment resembles the core structure of disclinations, which represent the characteristic property of BP structures. These predictions are in line with high-resolution ac calorimetry and optical polarising microscopy experiments using the CE8 LC and CdSe or aerosil NPs. In mixtures with CdSe NPs of 3.5nm diameter and hydrophobic coating the BPIII stability range has been extended up to 20K. On the contrary, the effect of aerosil silica nanoparticles of 7.0nm diameter and hydrophilic coating is very weak. 相似文献
957.
Pavel Řezanka Klára Navrátilová Pavel Žvátora David Sýkora Pavel Matějka Ivan Mikšík Václav Kašička Vladimír Král 《Journal of nanoparticle research》2011,13(11):5947-5957
In this study, spherical gold nanoparticles (GNPs) of 14.7 nm diameter, prepared by citrate reduction of a gold(III) salt
and characterized by UV–Vis absorption spectrometry and transmission electron microscopy, were modified by a covalent attachment
of 6I-O-(3-mercaptopropyl)β-cyclodextrin (β-CD-SH) or per-6-deoxy-per-6-mercapto-β-cyclodextrin (β-CD-SH7). Subsequently, via three
alternative approaches, β-CD-modified GNPs were immobilized onto the inner wall of the fused-silica (FS) capillaries and applied
as special stationary phases for open-tubular capillary electrochromatography (OT-CEC). The first immobilization procedure
was based on pre-derivatization of a FS capillary with (3-mercaptopropyl)trimethoxysilane (MPTMS) followed by subsequent reactions
with GNPs and β-CD-SH or β-CD-SH7. The other two preparation protocols took advantage of sol–gel approach gaining a significant
increase in the interaction surface for solutes. In both instances, the sol–gel created 3D structure was further covalently
modified with GNPs. Serving that purpose, either β-CD-SH7 modified GNPs were used for the immobilization into the sol–gel
matrix (“one-step sol–gel technique”) or native GNPs were immobilized first into the sol–gel matrix and subsequently modified
with β-CD-SH7 (“two-step sol–gel technique”). The separation performance of CD-GNPs modified FS capillaries was tested by
OT-CEC in reversed-phase mode applied to separation of a model mixture of five polyaromatic hydrocarbons. The highest separation
efficiencies were obtained with the capillaries prepared by two-step sol–gel technique. However, with respect to the relatively
low reproducibility of this method, the first of the above preparation procedures, i.e., a simple pre-derivatization of the
FS capillary with MPTMS ensued with β-CD-SH7-GNPs immobilization seems to be more feasible approach providing decent separation
efficiency. 相似文献
958.
The 3D profile surface parameter H
q
and fractal dimension D were tested as indicators of mechanical properties inferred from fracture surfaces of porous solids. High porous hydrated
cement pastes were used as prototypes of porous materials. Both the profile parameter H
q
and the fractal dimension D showed capability to assess compressive strength from the fracture surfaces of hydrated pastes. From a practical point of
view the 3D profile parameter H
q
seems to be more convenient as an indicator of mechanical properties, as its values suffer much less from statistical scatter
than those of fractal dimensions. 相似文献
959.
Juraj Racko Miroslav Mikolá?ek Ralf Granzner Juraj Breza Daniel Donoval Alena Grmanová Ladislav Harmatha Frank Schwierz Karol Fr?hlich 《Central European Journal of Physics》2011,9(1):230-241
A new model is presented of current transport in Metal Insulator Metal (MIM) structures by quantum mechanical tunnelling.
In addition to direct tunnelling through an insulating layer, tunnelling via defects present in the insulating layer plays
an important role. Examples of the influence of the material and thickness of the insulating layer, energy distribution of
traps, and metal work functions are also provided. 相似文献
960.
Zdeněk Janů Zdeněk Švindrych Otakar Truněček Peter Kúš Andrej Pleceník 《Physica C: Superconductivity and its Applications》2011,471(23-24):1647-1650
Thin films of type I superconductors of a thickness comparable or less than a flux penetration length behave like type II superconductors in a mixed state. With decreasing film thickness normal domains carrying a magnetic flux get smaller with smaller number of flux quanta per domain and finally transform into single quantum flux lines, i.e. quantum vortices similar to those found in type II superconductors. We give an evidence of this behavior from the measurements of the nonlinear response of a total magnetic moment to an applied AC magnetic field, directly from the temperature dependence of an AC susceptibility. 相似文献