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排序方式: 共有211条查询结果,搜索用时 31 毫秒
111.
Bleken F Skistad W Barbera K Kustova M Bordiga S Beato P Lillerud KP Svelle S Olsbye U 《Physical chemistry chemical physics : PCCP》2011,13(7):2539-2549
Four 3D 10-ring zeolites, IM-5, TNU-9, ZSM-11 and ZSM-5, with Si/Al = 14-24 and crystal sizes below 2 microns, were tested as catalysts for the methanol to hydrocarbons reaction (MTH) at atmospheric pressure, 350 °C and WHSV = 9 h(-1). All catalysts gave initially full methanol conversion, and showed strikingly similar effluent product selectivities. However, their life-time duration differed significantly, and decreased in the order: ZSM-11 > ZSM-5 ? TNU-9 > IM-5. A main difference between the two groups of stability behaviour was the size of cavities formed by channel intersections; larger cavities in TNU-9 and IM-5 leading to polyaromatics formation and a more rapid deactivation compared to ZSM-5 and ZSM-11. Effluent yield-conversion plots suggested that polymethylated benzene intermediates were more important in IM-5 and TNU-9 than in ZSM-5 and ZSM-11, where alkene methylation and cracking reactions seemed to dominate product formation. However, this difference had only minor influence on effluent selectivity. 相似文献
112.
Katia NN Lecointre A Regueiro-Figueroa M Platas-Iglesias C Charbonnière LJ 《Inorganic chemistry》2011,50(5):1689-1697
The synthesis of ligand L(P)H(8), based on a 2,6-bispyrazolyl-pyridine scaffold functionalized by iminobismethylenephosphonate functions, is described and its pK values were determined by a combination of pH-spectrophotometric titrations and potentiometry. The interaction of L(P) with Tb(3+) was investigated in water (0.01 M TRIS/HCl pH = 7.0) by means of UV-vis and fluorescence titration experiments and evidenced the formation of at least three species with 1:1; 1:2, and 2:1 M-L ratios, the 1:1 complex appearing as particularly stable under these conditions (log K(cond) > 8). Na(4)[LnL(P)H] complexes (Ln = Eu and Tb) were prepared and characterized by elemental analysis, IR spectroscopy, and electrospray mass spectrometry. Their photophysical properties were investigated in aqueous solutions, revealing an excellent shielding of the Ln cations from the solvent environment (no water molecules in the first coordination sphere), very long luminescence lifetimes (τ(H(2)(O)) = 1.50 and 3.28 ms, respectively, for Eu and Tb) and reasonable luminescent quantum yields (?(H(2)(O)) = 2.4 and 37%, respectively, for Eu and Tb). Using fetal bovine serum as a model for biological media showed the Tb complex to remain luminescent in these conditions. The structure of the europium complex was studied by means of density functional theory (DFT) modeling, confirming the wrapping of the ligand around the cation, and the very good shielding of the coordinated Ln cation. The conditional stability constant for the formation of the Tb complex with L(P) was determined by competition experiments with EDTA and monitored by fluorescence spectroscopy (log K(TbL(P)cond) = 14.1 ± 0.3, 0.01 M TRIS/HCl, pH = 7.4) and was used to determine the thermodynamic constant (log K(TbL(P)) = 20.4 ± 0.4). A systematic comparison with ligand L(C), in which phosphonate functions are replaced by carboxylate ones, is made throughout the study, highlighting the large interest of the introduction of phosphonate moieties to obtain biologically stable luminescent lanthanide complexes. 相似文献
113.
This work presents a methodology for including the Elastohydrodynamic (EHD) film effects to a lateral vibration model of a deep groove ball bearing by using a novel approximation for the EHD contacts by a set of equivalent nonlinear spring and viscous damper. The fitting of the equivalent contact model used the results of a transient multi-level finite difference EHD algorithm to adjust the dynamic parameters. The comparison between the approximated model and the finite difference simulated results showed a suitable representation of the stationary and dynamic contact behaviors. The linear damping hypothesis could be shown as a rough representation of the actual hysteretic behavior of the EHD contact. Nevertheless, the overall accuracy of the model was not impaired by the use of such approximation. Further on, the inclusion of the equivalent EHD contact model is equated for both the restoring and the dissipative components of the bearing?s lateral dynamics. The derived model was used to investigate the effects of the rolling element bearing lubrication on the vibration response of a rotor?s lumped parameter model. The fluid film stiffening effect, previously only observable by experimentation, could be quantified using the proposed model, as well as the portion of the bearing damping provided by the EHD fluid film. Results from a laboratory rotor–bearing test rig were used to indirectly validate the proposed contact approximation. A finite element model of the rotor accounting for the lubricated bearing formulation adequately portrayed the frequency content of the bearing orbits observed on the test rig. 相似文献
114.
La-Torre-Riveros Lyda Doménech-Carbó Antonio Cabrera Carlos R. Doménech-Carbó María Teresa Huahuasoncco-Condori Wilber Quispe Guzmán Dino Gutiérrez-Castillo María del Carmen Carmona-Ochoa Katia Pérez-Trujillo Amelia 《Journal of Solid State Electrochemistry》2019,23(5):1541-1552
Journal of Solid State Electrochemistry - A series of sherds from the archeological site of Qotakalli in the area of Cusco (Perú), corresponding to four different Inka periods, were studied by... 相似文献
115.
Katia Buonasera Giovanni D’Orazio Salvatore Fanali Paola Dugo Luigi Mondello 《Journal of chromatography. A》2009,1216(18):3970-3976
In the present research, the separation of a series of organophosphorus pesticides (fensulfothion, fenamiphos, profenofos, fonofos, isofenphos, dialifos, sulprofos and prothiofos), by using nano-liquid chromatography (nano-LC) with UV detection is described. Three 100 μm ID capillary columns, packed with different silica-based stationary phases (CN, C18, and phenyl), were investigated. Among these, the phenyl column offered the best results in terms of chromatographic performance, and was selected for pesticide analyses. Parameters, such as sample dilution solvent, injection volume, mobile phase composition and flow rate, were optimized in order to define the ideal experimental conditions. With the aim of improving sensitivity, on-column focusing of large injection volumes was applied: a sensitivity increase of circa 100-fold was attained, with limits of detection (LODs) and quantification (LOQs) within the 4.4–37.5 and 14.5–125.0 ng/mL ranges, respectively. The method was validated, with satisfactory results, through the measurement of the following parameters: limits of detection and quantification, precision, linearity and recovery. Finally, five different baby foods, previously fortified with a solution of the eight aforementioned pesticides, and then subjected to liquid–liquid extraction and solid-phase extraction clean-up, were analyzed. 相似文献
116.
Walter Baratta Prof. Cinzia Barbato Dr. Santo Magnolia Dr. Katia Siega Dr. Pierluigi Rigo Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(10):3201-3206
The osmium complexes trans‐[OsCl2(dppf)(diamine)] (dppf: 1,1′‐bis(diphenylphosphino)ferrocene; diamine: ethylenediamine in 3 , propylenediamine in 4 ) were prepared by the reaction of [OsCl2(PPh3)3] ( 1 ) with the ferrocenyl diphosphane, dppf and the corresponding diamine in dichloromethane. The reaction of derivative 3 with NaOCH2CF3 in toluene afforded the alkoxide cis‐[Os(OCH2CF3)2(dppf)(ethylenediamine)] ( 5 ). The novel precursor [Os2Cl4(P(m‐tolyl)3)5] ( 2 ) allows the synthesis of the chiral complexes trans‐[OsCl2(diphosphane)(1,2‐diamine)] ( 6 – 9 ; diphosphane: (R)‐[6,6′‐dimethoxy(1,1′‐biphenyl)‐2,2′‐diyl]bis[1,1‐bis(3,5‐dimethylphenyl)phosphane] (xylMeObiphep) or (R)‐(1,1′‐binaphthalene)‐2,2′‐diylbis[1,1‐bis(3,5‐dimethylphenyl)phosphane] (xylbinap); diamine=(R,R)‐1,2‐diphenylethylenediamine (dpen) or (R,R)‐1,2‐diaminocyclohexane (dach)), obtained by the treatment of 2 with the diphosphane and the 1,2‐diamine in toluene at reflux temperature. Compounds 3 – 5 in ethanol and in the presence of NaOEt catalyze the reduction of methyl aryl, dialkyl, and diaryl ketones and aldehydes with H2 at low pressure (5 atm), with substrate/catalyst (S/C) ratios of 10 000–200 000 and achieving turnover frequencies (TOFs) of up to 3.0×105 h?1 at 70 °C. By employment of the chiral compounds 6 – 9 , different ketones, including alkyl aryl, bulky tert‐butyl, and cyclic ketones, have successfully been hydrogenated with enantioselectivities up to 99 % and with S/C ratios of 5000–100 000 and TOFs of up to 4.1×104 h?1 at 60 °C. 相似文献
117.
Giovanni De Filpo Katia Armentano Elvira Pantuso Alexander I. Mashin Giuseppe Chidichimo Fiore P. Nicoletta 《Liquid crystals》2019,46(6):986-993
Polymer Dispersed Liquid Crystals (PDLCs) are liquid crystal dispersions in a polymer matrix, which look like opaque in their OFF state, when no electric field is applied, and transparent in their ON state. They are generally obtained by a phase separation process, such as Thermal, Solvent- and Polymerization-Induced Phase Separation (TIPS, SIPS and PIPS, respectively), between two transparent conductive glass substrates. In this paper, a new electro-optical device, formed by a porous polymer membrane imbibed with liquid crystal by capillary suction, is presented (Polymer Membranes Dispersed Liquid Crystals, PMDLC). Polymer membrane surfaces were made conductive before liquid crystal loading by magnetron sputtering of a thin layer of conductive indium tin oxide. The morphology and the electro-optical response of these devices were investigated and the observed transmittances and relaxation times were found to be similar to those of conventional PDLCs. In addition, PMDLCs showed interesting flexibility as no solid conductive substrate is required and economic convenience as there is no loss of liquid crystal in the polymer matrix. 相似文献
118.
Maria De Bernardi Giovanni Vidari Paola Vita-Finzi Katia Gluchoff Fiasson 《Tetrahedron letters》1982,23(44):4623-4624
Some sesquiterpene furans with lactarane and seco-lactarane skeletons which previously have isolated from many and species, were chemically derived from stearyl belutinal via a tansformation similar to the biosynthetic pathway. 相似文献
119.
Fadoua Asraoui Ayoub Kounnoun Francesco Cacciola Fouad El Mansouri Imad Kabach Yassine Oulad El Majdoub Filippo Alibrando Katia Arena Emanuela Trovato Luigi Mondello Adnane Louajri 《Molecules (Basel, Switzerland)》2021,26(11)
Medicinal plants offer imperative sources of innovative chemical substances with important potential therapeutic effects. Among them, the members of the genus Inula have been widely used in traditional medicine for the treatment of several diseases. The present study investigated the antioxidant (DPPH, ABTS and FRAP assays) and the in vitro anti-hyperglycemic potential of aerial parts of Inula viscosa (L.) Aiton (I. viscosa) extracts through the inhibition of digestive enzymes (α-amylase and α-glucosidase), responsible of the digestion of poly and oligosaccharides. The polyphenolic profile of the Inula viscosa (L.) Aiton EtOAc extract was also investigated using HPLC-DAD/ESI-MS analysis, whereas the volatile composition was elucidated by GC-MS. The chemical analysis resulted in the detection of twenty-one polyphenolic compounds, whereas the volatile profile highlighted the occurrence of forty-eight different compounds. Inula viscosa (L.) Aiton presented values as high as 87.2 ± 0.50 mg GAE/g and 78.6 ± 0.55mg CE/g, for gallic acid and catechin, respectively. The EtOAc extract exhibited the higher antioxidant activity compared to methanol and chloroform extracts in different tests with (IC50 = 0.6 ± 0.03 µg/mL; IC50 = 8.6 ± 0.08 µg/mL; 634.8 mg ± 1.45 AAE/g extract) in DPPH, ABTS and FRAP tests. Moreover, Inula viscosa (L.) Aiton leaves did show an important inhibitory effect against α-amylase and α-glucosidase. On the basis of the results achieved, such a species represents a promising traditional medicine, thanks to its remarkable content of functional bioactive compounds, thus opening new prospects for research and innovative phytopharmaceuticals developments. 相似文献
120.