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91.
92.
In the present article we concentrate our study on the growth problem for the weighing matrix W(12,11) and show that the unique W(12,11) has three pivot structures. An improved algorithm for extending a k?×?k (0,+,-) matrix to a W(n,n-1), if possible, has been developed to simplify the proof. For the implementation of the algorithm special emphasis is given to the notions of data structures and parallel processing. 相似文献
93.
Sanchez-Prado L Barro R Garcia-Jares C Llompart M Lores M Petrakis C Kalogerakis N Mantzavinos D Psillakis E 《Ultrasonics sonochemistry》2008,15(5):689-694
The sonochemical degradation of 5 μg l−1 triclosan, a priority micro-pollutant, in various environmental samples (seawater, urban runoff and influent domestic wastewater) as well as in model solutions (pure and saline water) was investigated. Experiments were conducted with a horn-type sonicator operating at 80 kHz frequency and a nominal applied power of 135 W, while solid-phase microextraction coupled with gas chromatography–electron capture detector (SPME/GC–ECD) was employed to monitor triclosan degradation. The latter followed pseudo-first order kinetics with the rate constant being (min−1): 0.2284 for seawater > 0.1051 for 3.5% NaCl in deionised water > 0.0597 for centrifuged urban runoff 0.0523 for untreated urban runoff > 0.0272 for deionised water > 0.0063 for wastewater influent. SPME/GC–ECD and SPME coupled with gas chromatography–mass spectrometry (SPME/GC–MS) were also used to check for the formation of chlorinated and other toxic by-products; at the conditions in question, the presence of such compounds was not confirmed. 相似文献
94.
Christoph Spahn Florian Hurter Mathilda Glaesmann Christos Karathanasis Marko Lampe Mike Heilemann 《Angewandte Chemie (International ed. in English)》2019,58(52):18835-18838
Photobleaching is a major challenge in fluorescence microscopy, in particular if high excitation light intensities are used. Signal‐to‐noise and spatial resolution may be compromised, which limits the amount of information that can be extracted from an image. Photobleaching can be bypassed by using exchangeable labels, which transiently bind to and dissociate from a target, thereby replenishing the destroyed labels with intact ones from a reservoir. Here, we demonstrate confocal and STED microscopy with short, fluorophore‐labeled oligonucleotides that transiently bind to complementary oligonucleotides attached to protein‐specific antibodies. The constant exchange of fluorophore labels in DNA‐based STED imaging bypasses photobleaching that occurs with covalent labels. We show that this concept is suitable for targeted, two‐color STED imaging of whole cells. 相似文献
95.
Sara Trujillo Estela Pérez‐Román Apostolos Kyritsis José Luis Gómez Ribelles Christos Pandis 《Journal of Polymer Science.Polymer Physics》2015,53(19):1391-1400
Novel biomaterials are needed for bone tissue repair with improved mechanical performance compared to classical bioceramics. The objective of this work was to characterize a hybrid filler material, which is capable to coat as a thin film porous scaffolds improving their mechanical properties for bone tissue engineering. The hybrid filler material is a blend of chitosan and silica network formed through in situ sol–gel using tetraethylortosilicate and 3‐glycidoxypropyltrimethoxysilane (GPTMS) as silica precursors. The hypothesis was that the epoxy ring of GPTMS could react with the amino groups of chitosan in acidic media while it is also reacting the siloxane groups of hydrolyzed silica precursors. The formation of the hybrid organic–inorganic network was assessed by different physical techniques revealing changes in molecular mobility and hydrophilicity upon chemical reaction. Finally, the cytotoxicity of the samples was also evaluated by MTT assay. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1391–1400 相似文献
96.
Insights into the Cascade Reaction of CO and Heteroallenes Mediated by Dinitrogen Hafnocene Complexes: The Indirect Effect of Nitride's Nucleophilicity 下载免费PDF全文
Dr. Christos E. Kefalidis Prof. Dr. Laurent Maron 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4743-4747
A DFT mechanistic exploration of the reactivity of the dinitrogen hafnocene complex, [{(η5‐C5H2‐1,2,4‐Me3)2Hf}2(μ2‐N2)], towards mixtures of CO/CO2 and CO/OCNtBu is reported. The crucial role of the nitride intermediate is highlighted, as well as the importance of the bridging mode of the cyanate ligand between the two Hf metal atoms throughout the process. Interestingly, the CO2 addition to the nitride intermediate occurs through an outer‐sphere transition state, whereas the addition of the heteroallene is governed by the steric congestion imposed by cyclopentadienyl ligands. 相似文献
97.
Christos Economou Justin P. Romaire Tony Z. Scott Brendan T. Parr Seth B. Herzon 《Tetrahedron》2018,74(26):3188-3197
We recently reported a convergent strategy to access the polycyclic guanidinium alkaloid (+)-batzelladine B via an aldol addition–retro-aldol–aza-Michael addition cascade. Here we describe the application of this approach toward the total syntheses of (+)-batzelladine E, (?)-dehydrobatzelladine C, and (+)-batzelladine K. The identification of suitable methods to functionalize a common tropane core by electrophilic alkynylation and nucleophilic 1,2-addition were essential to generalizing this approach. We provide evidence for the intermediacy of an acylallene species in the cascade reaction. 相似文献
98.
Christos Fytas 《Tetrahedron》2008,64(28):6749-6754
Adamantane and cyclooctane lipophilic 2,6-diketopiperazines (2,6-DKPs) have been prepared by a simple and effective method, including the synthesis of the corresponding iminodiacetic amido-ester derivatives and their intramolecular cyclization. In this method, the key step of the imide formation was accomplished by a novel base-induced cyclization protocol, which involved the treatment of amido-ester 2,6-DKP precursors with potassium bis(trimethylsilyl)amide. Moreover, the cyclization methodology used allowed the synthesis of the respective 1-functionalized 2,6-DKPs in one pot and in excellent yields when the same primary amido-esters were treated with the previous base and the intermediate potassium imidate salts were then reacted with the electrophile benzyl bromoacetate. Hydrogenolysis of the benzyl 2,6-diketopiperazine acetates afforded the respective carboxylic acids, which constitute versatile intermediates in the synthesis of peptidomimetics and other bioactive molecules concerning our pharmacological studies. 相似文献
99.
Dr. Samuel F. Haysom Jonathan Machin Dr. James M. Whitehouse Dr. Jim E. Horne Dr. Katherine Fenn Dr. Yue Ma Dr. Hassane El Mkami Dr. Nils Böhringer Prof. Dr. Till F. Schäberle Prof. Dr. Neil A. Ranson Prof. Dr. Sheena E. Radford Prof. Dr. Christos Pliotas 《Angewandte Chemie (International ed. in English)》2023,62(34):e202218783
The β-barrel assembly machinery (BAM complex) is essential for outer membrane protein (OMP) folding in Gram-negative bacteria, and represents a promising antimicrobial target. Several conformational states of BAM have been reported, but all have been obtained under conditions which lack the unique features and complexity of the outer membrane (OM). Here, we use Pulsed Electron-Electron Double Resonance (PELDOR, or DEER) spectroscopy distance measurements to interrogate the conformational ensemble of the BAM complex in E. coli cells. We show that BAM adopts a broad ensemble of conformations in the OM, while in the presence of the antibiotic darobactin B (DAR-B), BAM′s conformational equilibrium shifts to a restricted ensemble consistent with the lateral closed state. Our in-cell PELDOR findings are supported by new cryoEM structures of BAM in the presence and absence of DAR-B. This work demonstrates the utility of PELDOR to map conformational changes in BAM within its native cellular environment. 相似文献
100.
Irene Zacharaki Christos Kontoyannis Alexis Lycourghiotis Christos Kordulis 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,324(1-3):208-216
Mesoporous anatase was prepared following sol–gel and using urea as template. The influence of calcination temperature on the phase stability, nanocrystal/aggregate size, pore size distribution and specific surface area as well as on the acid–base behavior in aqueous solutions was studied using X-ray diffraction, laser-Raman and diffuse reflectance spectroscopies, scanning electron microscopy and laser scattering as well as N2 adsorption–desorption isotherms and potentiometric mass titrations.The crystal structure was kept constant upon calcination over the whole temperature range, 200–500 °C. In this range anatase is constituted from primary nanocrystals. These are assembled into larger, rather spherical, clusters of about 30–40 nm and then into aggregates of various sizes (0.2–0.3 μm and 2–100 μm) with a distribution centered at about 12 μm. Increase of the calcination temperature caused an increase in the size of the primary nanocrystals from 8.1 nm at 200 °C to 17.1 nm at 500 °C, whereas calcination does not influence the morphology at micro-scale. Moreover, increase of the calcination temperature from 200 °C to 500 °C brings about a shift in the mean pore diameter from 47 nm to 91 nm accompanied by a decrease in the specific surface area and pore volume. The above effects were related with the aforementioned increase in the size of the primary nanocrystals. The value of pzc and the values of surface charge determined at various pH do not practically depend on the calcination temperature. The absence of pore space confinement effects was explained in terms of the structure and size of the interface development between the anatase surface and the electrolytic solution. 相似文献