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排序方式: 共有450条查询结果,搜索用时 390 毫秒
151.
Deshpande MD Scheicher RH Ahuja R Pandey R 《The journal of physical chemistry. B》2008,112(30):8985-8989
The interaction strength of sodium ions (Na(+)) with cellulose is investigated from first principles for varying degrees of water content. We find that the interaction of water molecules and Na(+) can be studied independently at the various OH groups in cellulose which we categorize as two different types. In the absence of water, Na(+) forms strong ionic bonds with the OH groups of cellulose. When water molecules are anchored to the OH groups via hydrogen bonds, Na(+) can eventually no longer bind to the OH groups, but will instead interact with the oxygen atoms of the water molecules. Due to the rather weak attachment of the latter to the OH groups, Na(+) becomes effectively more mobile in the fully hydrated cellulose framework. The present study thus represents a significant step toward a first-principles understanding of the experimentally observed dependence of ionic conductivity on the level of hydration in cellulose network. 相似文献
152.
A one-pot, two-step synthesis of the title compounds employs a multicomponent Ugi condensation reaction, microwave irradiation, and Fe(0) as a reductant. Two pathways are accessible; both routes utilize bifunctional, o-nitro-substituted arenes leading to either C2, N4, C5 substitution (A) or C2, N4 substitution (B). 相似文献
153.
Fast analysis of decabrominated diphenyl ether using low-pressure gas chromatography-electron-capture negative ionization mass spectrometry 总被引:1,自引:0,他引:1
Dirtu AC Ravindra K Roosens L van Grieken R Neels H Blust R Covaci A 《Journal of chromatography. A》2008,1186(1-2):295-301
This paper reports the applicability of low-pressure gas chromatography-mass spectrometry operated in electron-capture negative ionization mode (LP-GC-ECNI-MS) for the analysis of decabrominated diphenyl ether (BDE-209). Particular attention was paid to find optimal injector and oven conditions for minimal thermal degradation of BDE-209. The analytical characteristics were compared for LP-GC columns (10 m x 0.53 mm) with different film thicknesses (d(f) 0.15 microm versus 0.25microm) and for a conventional GC column (15 m x 0.25 mm, 0.10 microm d(f)). Short residence times (6.5 and 9.8 min) of BDE-209 were found for the LP-GC systems with 0.15 and 0.25microm d(f), respectively, resulting in a low elution temperature and minimal degradation. Additionally, baseline separation of 22 polybrominated diphenyl ether (PBDE) congeners (major components of PBDE technical mixtures) was possible in less than 12 min using the LP-GC-ECNI-MS system with 0.15microm d(f). The optimized method was applied for the determination of PBDEs in Belgian indoor dust samples. The obtained concentrations of BDE-209 (range 8-292 ng/g dry weight) were in the same range or lower than concentrations in dust from other European countries. 相似文献
154.
A novel homologous series of thermotropic mesomorphs has been synthesized and studied with a view to understanding and establishing the effect of molecular structure on mesomorphic properties with reference to rigidity and flexibility of the homologues series: RO-C6H4-CH?CH-CO-C6H4-OC18H37(n). The novel homologous series comprises 13 novel homologues (C1 to C18), from which 11 homologues are enantiotropically mesogenic (C3 to C18). Smectogenic mesophase commences from C7 homologue, and nematogenic mesophase is exhibited by C3 to C18 homologues in enantiotropic manner. Thus, C7 to C18 homologues are enantiotropically smectogenic plus nematogenic. Textures of smectic phase are of the type A or C, and that of nematic phase are threaded or Schlieren as confirmed through an optical polarizing microscope equipped with a heating stage. Transition curve of a phase diagram behaved in a normal manner except N-I transition curve, which shows minor deviating trend (C12 to C18) from expected normal behavior. An odd-even effect is exhibited by N-I and Sm-N transition curves. Analytical, spectral, and thermal data confirm the molecular structures of novel homologues. Thermal stabilities for smectic and nematic are 52.7°C and 66.6°C, respectively, whose total mesophase lengths range from 12.0°C to 28.0°C. Thus, novel series of chalcones is a low melting series whose mesogenic transition temperatures vary between 38.0 and 86.0°C. 相似文献
155.
Sonawane RP Mück-Lichtenfeld C Fröhlich R Bergander K Hoppe D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(22):6419-6429
Highly diastereoselective lithiation-substitution reactions of an (S)-proline derived S-alkyl thiocarbamate was accomplished. The configuration of the predominant alkyllithium species and the stereochemical course of the electrophilic substitution reactions are deduced by a combination of X-ray crystal structure analysis, NMR spectroscopic studies, deuteration/dedeuteration experiments, and quantum chemical calculations. The lithium intermediate (S,S)-9 was found to be kinetically and thermodynamically favoured, whereas (S,R)-9 rapidly epimerizes. 相似文献
156.
Kim S Ohulchanskyy TY Pudavar HE Pandey RK Prasad PN 《Journal of the American Chemical Society》2007,129(9):2669-2675
We report energy-transferring organically modified silica nanoparticles for two-photon photodynamic therapy. These nanoparticles co-encapsulate two-photon fluorescent dye nanoaggregates as an energy up-converting donor and a photosensitizing PDT drug as an acceptor. They combine two features: (i) aggregation-enhanced two-photon absorption and emission properties of a novel two-photon dye and (ii) nanoscopic fluorescence resonance energy transfer between this nanoaggregate and a photosensitizer, 2-devinyl-2-(1-hexyloxyethyl)pyropheophorbide. Stable aqueous dispersions of the co-encapsulating nanoparticles (diameter < or = 30 nm) have been prepared in the nonpolar interior of micelles by coprecipitating an organically modified silica sol with the photosensitizer and an excess amount of the two-photon dye which forms fluorescent aggregates by phase separation from the particle matrix. Using a multidisciplinary nanophotonic approach, we show: (i) indirect excitation of the photosensitizer through efficient two-photon excited intraparticle energy transfer from the dye aggregates in the intracellular environment of tumor cells and (ii) generation of singlet oxygen and in vitro cytotoxic effect in tumor cells by photosensitization under two-photon irradiation. 相似文献
157.
Thiquynhxuan Le Wang Tian Ravindra A. V. Xuxiang Yuquan Ju Shaohua Zhang Libo 《Kinetics and Catalysis》2021,62(3):436-444
Kinetics and Catalysis - Submicron zeolite has become the focus of research because of its high thermal stability, high catalytic activity, and uniform size. A rapid method for synthesizing... 相似文献
158.
The objective of the study is to find the tolerance on vane pitch dimensions of a Vertical Turbine (VT) pump impeller. For this purpose, the study is divided into two parts viz. to find the critical hydraulic eccentricity of a VT pump impeller by way of numerical simulations and design of experiments to find the vane pitch tolerance using critical hydraulic eccentricity. The effect of impeller vane pitch deviations on hydraulic unbalance is examined for a vertical turbine pump using Design of Experiments (DOE). A suitable orthogonal matrix has been selected with vane pitch at different axial locations of an impeller as the control factors. Hydraulic eccentricity, which is the output of the DOE experiments is analyzed using S/N ratio, ANOM and regression analysis to find the significant control factor effecting the hydraulic unbalance and hence vibrations. The vane pitch deviation at outlet and inlet of impeller shroud geometry are found to be the most critical factor affecting the pump vibrations. 相似文献
159.
Choi DS Kim JH Shin US Deshmukh RR Song CE 《Chemical communications (Cambridge, England)》2007,(33):3482-3484
By employing superacidic fluoroantimonate ionic liquid (IL), [bmim][Sb(2)F(11)], as catalyst, not only thermodynamically-controlled but also kinetically-controlled Friedel-Crafts alkenylations of arenes with alkynes have been realized for the first time. 相似文献
160.
Combination of Cyanine Behaviour and Giant Hyperpolarisability in Novel Merocyanine Dyes: Beyond the Bond Length Alternation (BLA) Paradigm
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Dr. Venkatakrishnan Parthasarathy Dr. Ravindra Pandey Dr. Matthias Stolte Dr. Sampa Ghosh Dr. Frédéric Castet Prof. Dr. Frank Würthner Prof. Dr. Puspendu Kumar Das Dr. Mireille Blanchard‐Desce 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):14211-14217
Merocyanine dyes that exhibit antithetic cyanine‐like behaviour and giant first‐order hyperpolarisability (β) values have been designed. These cyanine‐type dyes open up an intriguing route towards molecular‐based electro‐optic materials as well as new second‐harmonic generation dyes for imaging. 相似文献