排序方式: 共有64条查询结果,搜索用时 15 毫秒
41.
Salima Lakehal Nadia Ouddai Douniazed Hannachi Mohmed Bououdina 《International journal of quantum chemistry》2013,113(10):1447-1452
Theoretical studies on ytterbium trichelates, Yb(L)3(L = trifluoromethanesulfonate (OTF), perchlorate (ClO4), p‐toluenesulfonic (TOS), nitrobenzenesulfonic (NBSA), and dodecylsulfate (DOS), are carried out using density functional theory method at the PW91/TZP level, for the first time. All ligands are bidentate and the compounds exhibit a distorted trigonal prismatic structure, with a maximum twist angle obtained for ytterbium p‐toluenesulfonic compound Yb(TOS)3. The quantum theory of atoms in molecules (AIM) and energy decomposition analysis reveal the dominant ionic character in ytterbium–oxygen bonding with a little covalent character. According to the Pearson terminology, the Yb(NBSA)3complex reveals the higher acidity. © 2012 Wiley Periodicals, Inc. 相似文献
42.
Sofiane Mekki Valrie Rolland Salima Bellahouel Arie van der Lee Marc Rolland 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(8):o301-o305
Two concomitant polymorphs, (I) and (II), of a β‐benzyl‐β‐hydroxyaspartate analogue [systematic name: dibenzyl 2‐benzyl‐2‐hydroxy‐3‐(4‐methylphenylsulfonamido)succinate], C32H31NO7S, crystallize from a mixture of ethyl acetate and cyclohexane at ambient temperature. The structure of (I) has triclinic (P) symmetry and that of (II) monoclinic (P21/c) symmetry. Both crystal structures are made up of a stacking of homochiral racemic dimers (2S,3S and 2R,3R) which are internally connected by a similar R22(9) hydrogen‐bonding pattern consisting of intermolecular N—H...O and O—H...O hydrogen bonds. The centroid of the racemic dimer lies on an inversion centre. The main structural difference between the two polymorphs is the conformational orientation of two of the four aromatic rings present in the molecule. Polymorph (II) is found to be twinned by reticular merohedry with twin index 3 and twin fractions 0.854 (1) and 0.146 (1). 相似文献
43.
Salima Atlas Mustapha Raihane Gregory B. Kharas Emi Hanawa Benjamin L. Hill Jessica D. Davis 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):491-495
Novel copolymers of trisubstituted ethylene monomers, fluorine ring-substituted 2-phenyl-1,1-dicyanoethenes, RC6H4CH[dbnd]C(CN)2 (where R is 2-F, 3-F, and 4-F) and 4-fluorostyrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C-NMR. High T g of the copolymers, in comparison with that of poly(4-fluorostyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. The gravimetric analysis indicated that the copolymers decomposed in two stages in the range 210–600°C. 相似文献
44.
This paper describes algorithms to compute Voronoi diagrams, shortest path maps, the Hausdorff distance, and the Fréchet distance in the plane with polygonal obstacles. The underlying distance measures for these algorithms are either shortest path distances or link distances. The link distance between a pair of points is the minimum number of edges needed to connect the two points with a polygonal path that avoids a set of obstacles. The motivation for minimizing the number of edges on a path comes from robotic motions and wireless communications because turns are more difficult in these settings than straight movements.Link-based Voronoi diagrams are different from traditional Voronoi diagrams because a query point in the interior of a Voronoi face can have multiple nearest sites. Our site-based Voronoi diagram ensures that all points in a face have the same set of nearest sites. Our distance-based Voronoi diagram ensures that all points in a face have the same distance to a nearest site.The shortest path maps in this paper support queries from any source point on a fixed line segment. This is a middle-ground approach because traditional shortest path maps typically support queries from either a fixed point or from all possible points in the plane.The Hausdorff distance and Fréchet distance are fundamental similarity metrics for shape matching. This paper shows how to compute new variations of these metrics using shortest paths or link-based paths that avoid polygonal obstacles in the plane. 相似文献
45.
Stabilization of a Diphosphagermylene through pπ–pπ Interactions with a Trigonal‐Planar Phosphorus Center
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Dr. Keith Izod Daniel G. Rayner Dr. Salima M. El‐Hamruni Dr. Ross W. Harrington Dr. Ulrich Baisch 《Angewandte Chemie (International ed. in English)》2014,53(14):3636-3640
N‐Heterocyclic carbenes and their heavier homologues are, in part, stabilized by delocalization of the N lone pairs into the vacant p‐orbital at carbon (or a heavier Group 14 element center). These interactions are usually absent in the corresponding P‐substituted species, owing to the large barrier to planarization of phosphorus. However, judicious selection of the substituents at phosphorus has enabled the synthesis of a diphosphagermylene, [(Dipp)2P]2Ge, in which one of the P centers is planar (Dipp=2,6‐diisopropylphenyl). The planar nature of this P center and the correspondingly short P? Ge distance suggest a significant degree of P? Ge multiple bond character that is due to delocalization of the phosphorus lone pair into the vacant p‐orbital at germanium. DFT calculations support this proposition and NBO and AIM analyses are consistent with a Ge? P bond order greater than unity. 相似文献
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47.
Salima Boughdiri Bahoueddine Tangour Monique Rivière-Baudet 《Journal of organometallic chemistry》2004,689(21):3279-3286
Theoretical studies of germanazene rings [(GeII-NR)2,3; R = H, Me, CN, Ph] have been performed at the DFT/B3LYP level. The fully optimized geometrical structures display four or six-membered planar rings of alternating germanium and nitrogen, in good agreement with the available X-ray experimental data. The hypothetical molecule (GeN-H)2 presents only a small distortion from planarity. Although the planar conformation could indicate some degree of delocalization, the stabilization energy - estimated using the concept of homodesmotic reactions - indicates very little or no aromatic character in these molecules. The easy experimental formation of these germanazenes can be explained by di- (or tri-)merisation of the transient monomeric germylene-imine GeNR in its triplet state. When R = CN, in conformity with the experimental results, the most stable species is the isomeric carbodiimide form (GeNCN)n, a result which is easily explained by the maximum spin density on the terminal nitrogen in the calculated monomer. 相似文献
48.
Synthesis and characterization of copolymers based on styrene and partially fluorinated acrylates 总被引:2,自引:0,他引:2
Copolymers of styrene and fluorinated acrylate monomers with F-octylalkyl, F(CF2)8(CH2)n′ side groups were prepared by free radical polymerization. Thermal behaviour of the resulting polymers was investigated by DSC and TGA. Even if at the macroscopic scale the polymers surfaces are homogeneous and clear, the analysis indicates that all samples exhibit two glass transitions temperatures. This discontinuity may be regarded as an indication for microphase separation of fluorine-rich and polystyrene-rich microphases. Water and hexadecane contact angles measurements show that these polymers are quite surface active in the solid state. Surface and bulk organizations were investigated by XPS analysis. A strong correlation between bulk organization and surface properties of the polymers could be established. Preferential adsorption of fluorinated segments at the material surface were more pronounced than expected in the bulk. 相似文献
49.
The empirical valence bond (EVB) method [J. Chem. Phys. 52, 1262 (1970)] has always embodied charge transfer processes. The mechanism of that behavior is examined here and recast for use as a new empirical potential energy surface for large-scale simulations. A two-state model is explored. The main features of the model are: (1) explicit decomposition of the total system electron density is invoked; (2) the charge is defined through the density decomposition into constituent contributions; (3) the charge transfer behavior is controlled through the resonance energy matrix elements which cannot be ignored; and (4) a reference-state approach, similar in spirit to the EVB method, is used to define the resonance state energy contributions in terms of "knowable" quantities. With equal validity, the new potential energy can be expressed as a nonthermal ensemble average with a nonlinear but analytical charge dependence in the occupation number. Dissociation to neutral species for a gas-phase process is preserved. A variant of constrained search density functional theory is advocated as the preferred way to define an energy for a given charge. 相似文献
50.
Mohamed Bouhrim Hayat Ouassou Salima Boutahiri Nour Elhouda Daoudi Hamza Mechchate Bernard Gressier Bruno Eto Hamada Imtara Amal A. Alotaibi Mohammed Al-zharani Abderrahim Ziyyat Hassane Mekhfi Abdelkhaleq Legssyer Mohammed Aziz Mohamed Bnouham 《Molecules (Basel, Switzerland)》2021,26(6)
Opuntia dillenii Ker Gawl. is one of the medicinal plants used for the prevention and treatment of diabetes mellitus (DM) in Morocco. This study aims to investigate the antihyperglycemic effect of Opuntia dillenii seed oil (ODSO), its mechanism of action, and any hypoglycemic risk and toxic effects. The antihyperglycemic effect was assessed using the OGTT test in normal and streptozotocin (STZ)-diabetic rats. The mechanisms of action were explored by studying the effect of ODSO on the intestinal absorption of d-glucose using the intestinal in situ single-pass perfusion technique. An Ussing chamber was used to explore the effects of ODSO on intestinal sodium-glucose cotransporter 1 (SGLT1). Additionally, ODSO’s effect on carbohydrate degrading enzymes, pancreatic α-amylase, and intestinal α-glucosidase was evaluated in vitro and in vivo using STZ-diabetic rats. The acute toxicity test on mice was performed, along with a single-dose hypoglycemic effect test. The results showed that ODSO significantly attenuated the postprandial hyperglycemia in normal and STZ-diabetic rats. Indeed, ODSO significantly decreased the intestinal d-glucose absorption in situ. The ex vivo test (Ussing chamber) showed that the ODSO significantly blocks the SGLT1 (IC50 = 60.24 µg/mL). Moreover, ODSO indu\ced a significant inhibition of intestinal α-glucosidase (IC50 = 278 ± 0.01 µg/mL) and pancreatic α-amylase (IC50 = 0.81 ± 0.09 mg/mL) in vitro. A significant decrease of postprandial hyperglycemia was observed in sucrose/starch-loaded normal and STZ-diabetic ODSO-treated rats. On the other hand, ODSO had no risk of hypoglycemia on the basal glucose levels in normal rats. Therefore, no toxic effect was observed in ODSO-treated mice up to 7 mL/kg. The results of this study suggest that ODSO could be suitable as an antidiabetic functional food. 相似文献