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Denis Damiron Nidhal Okhay Samer Al Akhrass Philippe Cassagnau Eric Drockenmuller 《Journal of polymer science. Part A, Polymer chemistry》2012,50(1):98-107
The crosslinking of poly(dimethylsiloxane) elastomers and coatings by the thermal curing of poly(dimethylsiloxane‐co‐methylvinylsiloxane) and 1,12‐diazido‐dodecane was studied. This crosslinking pathway relies on the cycloaddition of azides and alkenes as well as the thermal generation of nitrene transient radicals, which react with alkenes, yielding respectively 1,2,3‐triazoline and aziridine crosslinking knots. The influence of temperature and the ratio of azide and vinyl functionalities has been investigated by rheological, swelling, and insoluble fraction measurements for materials crosslinked in bulk and by comparison of the thickness before and after extraction of the soluble materials by soxhlet extraction for the crosslinked coatings. The preparation of highly crosslinked PDMS‐based elastomers and coatings has been demonstrated, even if the fraction of elastically effective crosslinks in bulk remained below 160 mol/m3. Advantageously, this system does not require additional initiator or catalyst, is not sensitive to moisture or oxygen, and can be extended to a wide range of unsaturated polymers as well as different organic or inorganic solid substrates. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
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Equations of state that are based on the lattice-statistics approach use Guggenheim's quasi-chemical approximation to describe the non-randomness in the mixture due to the energetic interactions between the molecules. For ternary and higher-component systems the non-randomness expression is complex and requires an iterative calculation procedure. We have shown that the non-randomness parameters play a negligible role in the application of the GCLF-EoS model (based on the Panayiotou–Vera EoS) for predicting vapor–liquid equilibria. Omission of the non-randomness parameters from such calculations can significantly improve the computation efficiency. Binary, ternary, and quaternary vapor–liquid equilibria predictions were made including polystyrene, polyvinyl acetate, polyethylene, and polypropylene in polar and non-polar solvents to test the theory. 相似文献
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Raed Ghanem Hutaf Baker Mobeen Abu Seif Raed A. Al-Qawasmeh Abdl-Azizi Mataneh Samer Ibrahim Al-Gharabli 《Journal of solution chemistry》2010,39(4):441-456
Spectroscopic methods and theoretical calculations were used to study the photophysical properties of colchicine (1). The characteristic bands of colchicine (1) transitions occurring at ∼245 nm and 350 nm arise from n–π
* and π–π
* transitions, and were found to be blue shifted with increasing polarity index of the solvent and red shifted (bathocrhomic)
with increasing acidity of the media. Solvent type and polarity were found to affect both the rate constant and photo conversion
yield. Excitation of colchicine (1) at 366 nm populates the S1 orbital, from which the photoreaction of colchicine (1) initially produces lumicolchicine directly in its ground state by a concerted disrotatory electrocyclization (i.e., 4π electrocyclization involving the tropolone ring). The acidity of the media affects both rate constants and conversion yield;
both of these were inversely proportional to the acid concentration. The presence of acid decreases the photo conversion yield
of colchicine (1) from 90% to 40%. The ionic strength affects both the rate constants and the photo conversion yield; rate constants are inversely
related to the ionic strength. The photochemistry of colchicine (1) is explained on the basis of the initial formation of a solvation complex in the ground state. 相似文献
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"Molecular chameleons". Design and synthesis of a second series of flexible nucleosides 总被引:1,自引:0,他引:1
The second series of flexible shape-modified nucleosides is introduced. The "fleximers" feature the purine ring systems split into their individual imidazole and pyrimidine components. This structural modification serves to introduce flexibility to the nucleoside while still retaining the elements essential for recognition. As a consequence, these structurally innovative nucleosides can more readily adapt to their environment and should find use as bioprobes for investigating enzyme-coenzyme binding sites as well as nucleic acid and protein interactions. Their design and synthesis is described. 相似文献
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Samer Hassan Tatyana P. Lyubimova Dmitry V. Lyubimov Masahiro Kawaji 《International Journal of Multiphase Flow》2006
The effects of small vibrations on a particle oscillating near a solid wall in a fluid cell, relevant to material processing such as crystal growth in space, have been investigated experimentally and theoretically. Assuming the boundary layer around the particle to be thin compared to the particle radius at high vibration frequencies, an inviscid fluid model was developed to predict the motion of a spherical particle placed near a wall of a rectangular liquid-filled cell subjected to a sinusoidal vibration. Under these conditions, a non-uniform pressure distribution around the particle results in an average pressure that gives rise to an attraction force. Theoretical expressions for the attraction force are derived for the particle vibrating normal to and parallel with the nearest cell wall. The magnitude of this attractive force has been verified experimentally by measuring the motion of a steel particle suspended in the fluid cell by a thin wire. Experiments performed at high frequencies showed that the mean particle position, when the particle is brought near a cell wall, shifts towards the same wall, and is dependent on the cell amplitude and frequency, particle and fluid densities. 相似文献
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Samer Aouad Amal Aoun Mira Skaf Madonna Labaki John El Nakat Bilal El Khoury Pierre Obeid Edmond Abi-Aad Antoine Aboukaïs 《Comptes Rendus Chimie》2013,16(10):868-871
The effects of CoxMgyAl2Oz mixed oxides composition and ruthenium addition on the oxidation of propylene and carbon black (CB) were investigated. Different reactive cobalt and ruthenium oxide species were formed following calcination at 600 °C. The addition of ruthenium was beneficial for the CB oxidation under “loose contact” conditions and for propylene oxidation when the cobalt content was intermediate to low. The calculated activation energy for CB oxidation was decreased from 151 kJ mol−1 for the uncatalyzed reaction to 111 kJ mol−1 over the best catalyst. 相似文献
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Dr. Samer Gozem Dr. Ekaterina Mirzakulova Dr. Igor Schapiro Dr. Federico Melaccio Prof. Dr. Ksenija D. Glusac Prof. Dr. Massimo Olivucci 《Angewandte Chemie (International ed. in English)》2014,53(37):9870-9875
The photophysics of flavins is highly dependent on their environment. For example, 4a‐hydroxy flavins display weak fluorescence in solution, but exhibit strong fluorescence when bound to a protein. To understand this behavior, we performed temperature‐dependent fluorescent studies on an N(5)‐alkylated 4a‐hydroxy flavin: the putative bacterial luciferase fluorophore. We find an increase in fluorescence quantum yield upon reaching the glass transition temperature of the solvent. We then employ multiconfigurational quantum chemical methods to map the excited‐state deactivation path of the system. The result reveals a shallow but barrierless excited state deactivation path that leads to a conical intersection displaying an orthogonal out‐of‐plane distortion of the terminal pyrimidine ring. The intersection structure readily explains the observed spectroscopic behavior in terms of an excited‐state barrier imposed by the rigid glass cavity. 相似文献
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Samer Al-Ashhab 《Journal of Pure and Applied Algebra》2007,208(2):647-653
Given a complex that is a differential graded vector space, it is known that a single mapping defined on a space of it where the homology is non-trivial extends to a strongly homotopy Lie algebra (on the graded space) when that mapping satisfies two conditions. This strongly homotopy Lie algebra is non-trivial (it is not a Lie algebra); however we show that one can obtain an sh-Lie algebra where the only non-zero mappings defining it are the lower order mappings. This structure applies to a significant class of examples. Moreover in this case the graded space can be replaced by another graded space, with only three non-zero terms, on which the same sh-Lie structure exists. 相似文献
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Misfolded proteins in Alzheimer's disease and type II diabetes 总被引:1,自引:0,他引:1