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排序方式: 共有180条查询结果,搜索用时 31 毫秒
71.
Modification of capillary electrophoresis (CE) capillaries by poly(hydroxyethyl methacrylate) (poly(HEMA), poly(diethylene glycol monomethacrylate) (poly(DEGMA) and poly(triethylene glycol monomethacrylate) (poly(TEGMA), was studied. Methods based on physical adsorption of the modifier and on its chemical binding were compared on the basis of the electroosmotic flow (EOF) reproducibility, the EOF dependence on the pH, the symmetry of the peak of positively charged tyramine, the stability of the coating and the separation of standard and milk proteins in the modified capillaries. Reproducible coatings were obtained by chemical binding of the polymers to the capillary walls and by coating with a solution of a polymer, as also demonstrated by the atomic force microscopy. 相似文献
72.
Calculations performed using both density functional theory (DFT) and the modified coupled-pair functional (MCPF) approach show that FeC5H6+ is more stable than HFeC5H5+ by about 10 kcal/mol. The ground state of FeC5H6+ is a quartet state derived from the 3d7 occupation of Fe+. For HFeC5H5+, the MCPF approach yields a sextet ground state while DFT yields a quartet; however, these two states are close in energy at both levels of theory. 相似文献
73.
Bardají GG Cantó M Alibés R Bayón P Busqué F de March P Figueredo M Font J 《The Journal of organic chemistry》2008,73(19):7657-7662
A new and versatile synthetic route to Securinega alkaloids is reported. The first synthesis of allosecurinine has been accomplished in seven steps and 40% yield, starting from (+)-menisdaurilide, using a vinylogous Mannich reaction as the key transformation. Similarly, viroallosecurinine has been synthesized from (-)-menisdaurilide. 相似文献
74.
V. V. Saraev P. B. Kraikivskii D. A. Matveev A. S. Kuzakov A. I. Vil’ms A. A. Fedonina 《Russian Journal of Coordination Chemistry》2008,34(6):438-442
The interaction of Ni(II) bis-tetrafluoroborate complexes [Ni(Dppe)2](BF4)2 and [Ni(CH3CN)6](BF4)2 (where Dppe = 1,2-bis(diphenylphosphino)ethane)) with Ni(0) phosphine complexes Ni(Dppe)2 and Ni(PPh3)4 in 1 : 1 mixture of toluene-acetonitrile was studied by the EPR method. The counter-disproportionation was shown to occur in a solution between the cationic Ni(II) complexes and the Ni(0) complexes to give Ni(I) complexes almost in quantitative amounts. The structures of the cationic Ni(I) complexes obtained were found to depend on both the solvent nature and the presence of a free phosphine in a solution. 相似文献
75.
Rimola A Constantino E Rodríguez-Santiago L Sodupe M 《The journal of physical chemistry. A》2008,112(15):3444-3453
The structure, relative energies, and binding energies of the complexes formed by the interaction of Cu+ (d10,1S) and Cu2+ (d9,2D) cations with the (glycyl)n glycine (n = 1-3) oligomers have been theoretically determined by means of density functional methods. The most stable structures of the Cu+ systems present linear dicoordination geometries, in agreement with a recent X-ray absorption spectroscopic study of Cu(I) interacting with model dipeptides. This is attributed to an efficient reduction of metal-ligand repulsion through sd sigma hybridization in dicoordinated linear structures. In contrast, for Cu2+ systems the lowest energy structures are tricoordinated (n = 1), tetracoordinated (n = 2), and pentacoordinated (n = 3). For both copper cations, binding energy values show that the interaction energies increase when the peptide chain is elongated. Differences on the coordination properties of the ligands are discussed according to their length as well as to the electronic configuration of the metal cations, which are compared to the Cu+/2+-glycine systems. 相似文献
76.
77.
In this paper, we provide an overview of some of the results obtained in the mathematical theory of intermediate quantifiers that is part of fuzzy natural logic (FNL). We briefly introduce the mathematical formal system used, the general definition of intermediate quantifiers and define three specific ones, namely, “Almost all”, “Most” and “Many”. Using tools developed in FNL, we present a list of valid intermediate syllogisms and analyze a generalized 5-square of opposition. 相似文献
78.
MnO and Mn2O3 nanoparticles were prepared in air and argon atmosphere by thermal decomposition of nanocrystalline manganese carbonate synthesized by reaction of manganese(II) nitrate with glycerol. Samples were characterized using transmission electron microscopy, simultaneous thermal analysis and X-ray diffraction analysis. Average sizes of prepared nanoparticles were calculated from XRD patterns using Scherrer equation. Also, the conditions for decomposition of manganese carbonate were optimized to obtain optimal nanoparticle sizes. Due to suitable sizes of prepared nanoparticles and the initial material, this method can be used in a wide range of industrial applications. 相似文献
79.
80.
Dr. Francisco Núñez‐Zarur Dr. Xavier Solans‐Monfort Prof. Roser Pleixats Dr. Luis Rodríguez‐Santiago Prof. Mariona Sodupe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(43):14553-14565
DFT (B3LYP‐D) calculations have been used to better understand the origin of the recovered Hoveyda–Grubbs derivative catalysts after ring‐closing diene or enyne metathesis reactions. For that, we have considered the activation process of five different Hoveyda–Grubbs precursors in the reaction with models of usual diene and enyne reactants as well as the potential precursor regeneration through the release/return mechanism. The results show that, regardless of the nature of the initial precursor, the activation process needs to overcome relatively high energy barriers, which is in agreement with a relatively slow process. The precursor regeneration process is in all cases exergonic and it presents low energy barriers, particularly when compared to those of the activation process. This indicates that the precursor regeneration should always be feasible, unlike the moderate recoveries sometimes observed experimentally, which suggests that other competitive processes that hinder recovery should take place. Indeed, calculations presented in this work show that the reactions between the more abundant olefinic products and the active carbenes usually require lower energy barriers than those that regenerate the initial precatalyst, which could prevent precursor regeneration. On the other hand, varying the precursor concentration with time obtained from the computed energy barriers shows that, under the reaction conditions, the precursor activation is incomplete, thereby suggesting that the origin of the recovered catalyst probably arises from incomplete precursor activation. 相似文献