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741.
742.
743.
Agáta Dujavová Michaela Valeriánová Vladimír Štrbík Zuzana Matkovičová Gustav Plesch Ivan Kostič 《Central European Journal of Physics》2007,5(2):229-235
Rhenium avoids air degradation of the target as well as of precursor thin films during the preparation of high temperature
Tl-based superconductors. Addition of Re has been used during synthesis of oriented Tl(Re)-Ba-Ca-Cu-O films. High temperature
superconducting Tl-based thin films were prepared by a two step method combining RF magnetron sputtering and ex-situ thallination. Precursors with a composition of Re0.1Ba2Ca2Cu3Ox were deposited on a CeO2 buffered R-plane sapphire substrate. The sputtered films were prepared at room temperature in an Ar atmosphere. The thallination
of the precursor films was performed in a one zone configuration, where both the pellet and precursor film were kept at the
same temperature. The thallination temperature varied in the range of 850–880°C and samples were held for 30, 45 and 60 min
at this temperature in a flowing oxygen atmosphere. Besides Tl-2212, X-ray diffraction reveals the possibility of also preparing
the Tl-2223 phase, which was until now not reported in a Re doped form.
Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia 相似文献
744.
Marianna Teplova Christoph Falschlunger Olga Krasheninina Michaela Egger Aiming Ren Dinshaw J. Patel Ronald Micura 《Angewandte Chemie (International ed. in English)》2020,59(7):2837-2843
Pistol ribozymes constitute a new class of small self‐cleaving RNAs. Crystal structures have been solved, providing three‐dimensional snapshots along the reaction coordinate of pistol phosphodiester cleavage, corresponding to the pre‐catalytic state, a vanadate mimic of the transition state, and the product. The results led to the proposed underlying chemical mechanism. Importantly, a hydrated Mg2+ ion remains innersphere‐coordinated to N7 of G33 in all three states, and is consistent with its likely role as acid in general acid base catalysis (δ and β catalysis). Strikingly, the new structures shed light on a second hydrated Mg2+ ion that approaches the scissile phosphate from its binding site in the pre‐cleavage state to reach out for water‐mediated hydrogen bonding in the cyclophosphate product. The major role of the second Mg2+ ion appears to be the stabilization of product conformation. This study delivers a mechanistic understanding of ribozyme‐catalyzed backbone cleavage. 相似文献
745.
Dvoráková H Lang J Vlach J Sýkora J Cajan M Himl M Pojarová M Stibor I Lhoták P 《The Journal of organic chemistry》2007,72(19):7157-7166
NMR spectroscopy, X-ray diffraction analysis, and quantum chemical calculations were used for conformational behavior study of partially alkylated thiacalix[4]arenes bearing methyl (1), ethyl (2), or propyl (3) groups at the lower rim. The conformational properties are governed by two basic effects: (i) stabilization by intramolecular hydrogen bonds, and (ii) sterical requirements of the alkoxy groups at the lower rim. While the monosubstituted derivatives 1a and 3a adopt the cone conformation in solution, distally disubstituted compounds 1b, 1'b, 2b, 2'b, 3b, and 3'b exhibit several interesting conformational features. They prefer pinched cone conformation in solution, and, except for 3'b, they form also 1,2-alternate conformation, which is flexible and undergoes rather fast transition between two identical structures. The crystal structures of the compounds 1b, 2b, 2'b, and 3b revealed yet quite rare 1,2-alternate conformation forming molecular channels held together by pi-pi interactions. Different channels-with hexagonal symmetry, 0.26 nm wide-are formed in the crystal structure of the pinched cone conformation of 3b. An uncommon hydrogen bonding pattern was found in dimethoxy and dipropoxy derivatives 1'b and 3'b that adopt distorted cone conformations in crystal. Trialkoxy-substituted compounds 1c and 3c adopt the partial cone conformation in solution. A higher mobility of methyl derivative 1c enables also existence of the cone conformer. 相似文献
746.
Patrick Achenbach Carlos Ayerbe Gayoso Ralph Böhm Olga Borodina Damir Bosnar Vakkas Bozkurt Luka Debenjak Michael O. Distler Anselm Esser Ivica Friščić Yuu Fujii Toshiyuki Gogami Mar Gómez Rodríguez Osamu Hashimoto Satoshi Hirose Hiroki Kanda Masashi Kaneta Eunhee Kim Junichiro Kusaka Amur Margaryan Harald Merkel Ulrich Müller Sho Nagao Satoshi N. Nakamura Josef Pochodzalla Christophe Rappold Joerg Reinhold Takehiko R. Saito Alicia Sanchez Lorente Salvador Sánchez Majos B. Sören Schlimme Matthias Schoth Florian Schulz Concettina Sfienti Simon Širca Liguang Tang Michaela Thiel Kyo Tsukada 《Few-Body Systems》2014,55(8-10):887-892
At the Mainz Microtron MAMI exploratory experiments on the spectroscopy of mesonic weak decays (MWD) of electroproduced Λ-hypernuclei were performed. A unique setup was realized to use the broad momentum-band kaon spectrometer Kaos at zero degree angle with respect to the high-intensity electron beam direction to tag strangeness producing processes. A sample of order 103 MWD from a beryllium target was collected by the coincidence technique with the high-resolution multi-spectrometer facility of the A1 Collaboration. It is conjectured that this sample contains monochromatic two-body decays from stopped hyperfragment decays as well as a wide momentum distribution of quasi-free produced Λ- and Σ-hyperon decays and three-body decays from hyperfragments. Stopped hyperfragments will be identified as monochromatic peaks in the π ? momentum spectrum from which their masses can be extracted with a precision of 50 keV/c 2. 相似文献
747.
Aufderheide M Scheffler S Möhle N Halter B Hochrainer D 《Analytical and bioanalytical chemistry》2011,401(10):3213-3220
In the field of inhalation toxicology, progress in the development of in vitro methods and efficient exposure strategies now offers the implementation of cellular-based systems. These can be used to analyze the hazardous potency of airborne substances like gases, particles, and complex mixtures (combustion products). In addition, the regulatory authorities require the integration of such approaches to reduce or replace animal experiments. Although the animal experiment currently still has to provide the last proof of the toxicological potency and classification of a certain compound, in vitro testing is gaining more and more importance in toxicological considerations. This paper gives a brief characterization of the CULTEX® Radial Flow System exposure device, which allows the exposure of cultivated cells as well as bacteria under reproducible and stable conditions for studying cellular and genotoxic effects after the exposure at the air–liquid or air–agar interface, respectively. A commercial bronchial epithelial cell line (16HBE14o-) as well as Salmonella typhimurium tester strains were exposed to smoke of different research and commercial available cigarettes. A dose-dependent reduction of cell viability was found in the case of 16HBE14o- cells; S. typhimurium responded with a dose-dependent induction of revertants. The promising results recommend the integration of cellular studies in the field of inhalation toxicology and their regulatory acceptance by advancing appropriate validation studies. 相似文献
748.
In this study, we give the proof of concept for a method to determine binding constants of compounds in solution. By implementing
a technique based on magnetic beads with a microfluidic device for segmented flow generation, we demonstrate, for individual
droplets, fast, robust and complete separation of the magnetic beads. The beads are used as a carrier for one binding partner
and hence, any bound molecule is separated likewise, while the segmentation into small microdroplets ensures fast mixing,
and opens future prospects for droplet-wise analysis of drug candidate libraries. We employ the method for characterization
of drug–protein binding, here warfarin to human serum albumin. The approach lays the basis for a microfluidic droplet-based
screening device aimed at investigating the interactions of drugs with specific targets including enzymes and cells. Furthermore,
the continuous method could be employed for various applications, such as binding assays, kinetic studies, and single cell
analysis, in which rapid removal of a reactive component is required. 相似文献
749.
Schöbel H Leidlmair C Bartl P Aleem A Hager M Echt O Märk TD Scheier P 《Physical chemistry chemical physics : PCCP》2011,13(3):1092-1098
Helium nanodroplets are co-doped with C(60) and ammonia. Mass spectra obtained by electron ionization reveal cations containing ammonia clusters complexed with up to four C(60) units. The high mass resolution of Δm/m≈ 1/6000 makes it possible to separate the contributions of protonated, unprotonated and dehydrogenated ammonia. C(60) aggregates suppress the proton-transfer reaction which usually favors the appearance of protonated ammonia cluster ions. Unprotonated C(x)(NH(3))(n)(+) ions (x = 60, 120, 180) exceed the abundance of the corresponding protonated ions if n < 5; for larger values of n the abundances of C(60)(NH(3))(n)(+) and C(60)(NH)(n-1)NH(4)(+) become about equal. Dehydrogenated C(60)NH(2)(+) ions are relatively abundant; their formation is attributed to a transient doubly charged C(60)-ammonia complex which forms either by an Auger process or by Penning ionization following charge transfer between the primary He(+) ion and C(60). The abundance of C(x)NH(3)(+) and C(x)NH(4)(+) ions (x = 120 or 180) is one to two orders of magnitude weaker than the abundance of ions containing one or two additional ammonia molecules. However, a model involving evaporation of NH(3) or NH(4) from the presumably weakly bound C(x)NH(3)(+) and C(x)NH(4)(+) ions is at odds with the lack of enhancement in the abundance of C(120)(+) and C(180)(+). Mass spectra of C(60) dimers complexed with water complement a previous study of C(60)(H(2)O)(n)(+) recorded at much lower mass resolution. 相似文献
750.
Schaffhauser DF Andrini O Ghezzi C Forster IC Franco-Obregón A Egli M Dittrich PS 《Lab on a chip》2011,11(20):3471-3478
Voltage clamp measurements reveal important insights into the activity of membrane ion channels. While conventional voltage clamp systems are available for laboratory studies, these instruments are generally unsuitable for more rugged operating environments. In this study, we present a non-invasive microfluidic voltage clamp system developed for the use under varying gravity levels. The core component is a multilayer microfluidic device that provides an immobilisation site for Xenopus laevis oocytes on an intermediate layer, and fluid and electrical connections from either side of the cell. The configuration that we term the asymmetrical transoocyte voltage clamp (ATOVC) also permits electrical access to the cytosol of the oocyte without physical introduction of electrodes by permeabilisation of a large region of the oocyte membrane so that a defined membrane patch can be voltage clamped. The constant low level air pressure applied to the oocyte ensures stable immobilisation, which is essential for keeping the leak resistance constant even under varying gravitational forces. The ease of oocyte mounting and immobilisation combined with the robustness and complete enclosure of the fluidics system allow the use of the ATOVC under extreme environmental conditions, without the need for intervention by a human operator. Results for oocytes over-expressing the epithelial sodium channel (ENaC) obtained under laboratory conditions as well as under conditions of micro- and hypergravity demonstrate the high reproducibility and stability of the ATOVC system under distinct mechanical scenarios. 相似文献