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51.
Barton B Rhinow D Walter A Schröder R Benner G Majorovits E Matijevic M Niebel H Müller H Haider M Lacher M Schmitz S Holik P Kühlbrandt W 《Ultramicroscopy》2011,111(12):1696-1705
We report the implementation of an electrostatic Einzel lens (Boersch) phase plate in a prototype transmission electron microscope dedicated to aberration-corrected cryo-EM. The combination of phase plate, Cs corrector and Diffraction Magnification Unit (DMU) as a new electron-optical element ensures minimal information loss due to obstruction by the phase plate and enables in-focus phase contrast imaging of large macromolecular assemblies. As no defocussing is necessary and the spherical aberration is corrected, maximal, non-oscillating phase contrast transfer can be achieved up to the information limit of the instrument. A microchip produced by a scalable micro-fabrication process has 10 phase plates, which are positioned in a conjugate, magnified diffraction plane generated by the DMU. Phase plates remained fully functional for weeks or months. The large distance between phase plate and the cryo sample permits the use of an effective anti-contaminator, resulting in ice contamination rates of <0.6 nm/h at the specimen. Maximal in-focus phase contrast was obtained by applying voltages between 80 and 700 mV to the phase plate electrode. The phase plate allows for in-focus imaging of biological objects with a signal-to-noise of 5-10 at a resolution of 2-3 nm, as demonstrated for frozen-hydrated virus particles and purple membrane at liquid-nitrogen temperature. 相似文献
52.
Marco A. Loza-Mejía Rafael Castillo Alfonso Lira-Rocha 《Journal of molecular graphics & modelling》2009,27(8):55
Although 9-anilinoacridines are among the best studied antitumoral intercalators, there are few studies about the effect of isosteric substitution of a benzene moiety for a heterocycle ring in the acridine framework. According to these studies, this approach may lead to effective cytotoxic agents, but good cytotoxic activity depends on structural requirements in the aniline ring which differ from those in 9-anilinoacridines. The present paper deals with molecular modeling studies of some 9-anilino substituted tricyclic compounds and their intercalation complexes (in various DNA sequences) resulting from docking the compounds into various DNA sequences. As expected, the isosteric substitution in 9-anilinoacridines influences the LUMO energy values and orbital distribution, the dipole moment, electrostatic charges and the conformation of the anilino ring. Other important differences are observed during the docking studies, for example, changes in the spatial arrangement of the tricyclic nucleus and the anilino ring at the intercalation site. Semiempirical calculations of the intercalation complexes show that the isosteric replacement of a benzene ring in the acridine nucleus affects not only DNA affinity but also base pair selectivity. These findings explain, at least partially, the different structural requirements observed in several 9-anilino substituted tricyclic compounds for cytotoxic activity. Thus, the data presented here may guide the rational design of new agents with different DNA binding properties and/or a cytotoxic profile by isosteric substitution of known intercalators. 相似文献
53.
Kasem K. Kasem Franklin A. Schultz 《Journal of Inorganic and Organometallic Polymers》1994,4(4):377-390
Multiply charged electroactive anions [IrCl
6
2–
, Fe(CN)
6
3–
, and W(CN)
8
4–
] are electrostatically incorporated in polymeric films of tris(4-vinyl-4-methyl-2,2-bipyridine) ruthenium(II) [poly-Ru(vbpy)
3
2+
] from aqueous trifluoroacetate solution. Values of apparent diffusion coefficients (D
ct) and heterogenous electron transfer rates (k
et) are measured for these anions as a function of their relative concentration (
M/
Ru) in the film.D
ct andk
et decrease systematically as
M/
Ru increases in a manner that is independent of charge and chemical identity of the ion. This result suggests that a nonchemical process, presumably electrostatic cross-linking, limits diffusional motion and is responsible for the decrease inD
ct andk
et with increasing anion content. Protonated polyvinyl-pyridine films exhibit similar ranges and variations inD
ct andk
et, which suggest similar structures and mechanisms of charge transport for these films and poly-Ru(vbpy)
3
2+
. 相似文献
54.
Hydrogenation of aromatics under mild conditions on transition metal complexes in zeolites. A cooperative effect of molecular sieves 总被引:1,自引:0,他引:1
The hydrogenation of aromatics, i.e. benzene, toluene, -methylstyrene, anisole, and ethyl benzoate, can be carried out under a very low (1/12000) catalyst to substrate ratio, and mild reaction conditions (80°C, 6 atm of H2O), on Rh and Ni organometallic complexes anchored on USY zeolites. A strong cooperative effect between the faujasite surface and the transition metal surface complex is thought to be responsible for the simultaneous enhancement of concentrations of arene and H2 in the neighborhood of the catalytic centers, and for the observed electronic effects. 相似文献
55.
Circularly polarized luminescence (CPL) materials have received increasing attention in recent years. Amongst various CPL materials, circularly polarized phosphorescence (CPP) materials featuring long life-time represent a novel research frontier and exhibit promising applications in various fields. Herein, the state-of-the-art advances of CPP materials are systematically summarized, as classified into transition metal complexes, organic small molecules, polymers, and organic/inorganic hybrid materials. Besides, the recent applications of CPP materials in organic light-emitting diodes and encryption display are also summarized. Furthermore, the current challenges and future perspectives are put forward. It is expected that this review will offer more inspirations for the future rational design of advanced CPP materials, thus further promoting their future practical applications. 相似文献
56.
Thanh Hai Nguyen Phan Khanh Linh Tran Van An Dinh Duy Thanh Tran Nam Hoon Kim Joong Hee Lee 《Advanced functional materials》2023,33(7):2210101
Development of multifunctional electrocatalysts with high efficiency and stability is of great interest in recent energy conversion technologies. Herein, a novel heteroelectrocatalyst of molecular iron complex (FeMC)-carbide MXene (Mo2TiC2Tx) uniformly embedded in a 3D graphene-based hierarchical network (GrH) is rationally designed. The coexistence of FeMC and MXene with their unique interactions triggers optimum electronic properties, rich multiple active sites, and favorite free adsorption energy for excellent trifunctional catalytic activities. Meanwhile, the highly porous GrH effectively promotes a multichannel architecture for charge transfer and gas/ion diffusion to improve stability. Therefore, the FeMC–MXene/GrH results in superb performances towards oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in alkaline medium. The practical tests indicate that Zn/Al–air batteries derived from FeMC–MXene/GrH cathodic electrodes produce high power densities of 165.6 and 172.7 mW cm−2, respectively. Impressively, the liquid-state Zn–air battery delivers excellent cycling stability of over 1100 h. In addition, the alkaline water electrolyzer induces a low cell voltage of 1.55 V at 10 mA cm−2 and 1.86 V at 0.4 A cm−2 in 30 wt.% KOH at 80 °C, surpassing recent reports. The achievements suggest an exciting multifunctional electrocatalyst for electrochemical energy applications. 相似文献
57.
Y. Li G. C. L. Wong E. Caine E. L. Hu C. R. Safinya 《International Journal of Thermophysics》1998,19(4):1165-1174
We have used lithographically patterned microchannel arrays with channel widths ranging from 1 to 20 m, fabricated using electron beam lithography and reactive ion etching, in structural studies of DNA–cationic lipid complexes in confinement. Various techniques have been developed for loading these DNA–membrane complexes into the microchannels or to form the complexes in situ by sequentially depositing DNA and lipid solutions into the microchannels. Optical microscopy studies indicate that such complex formation is strongly influenced by the periodic channel structure even at channel widths much larger than the persistent length of the DNA molecules. Preliminary x-ray diffraction experiments conducted at Stanford Synchrotron Radiation Laboratory (SSRL) yielded only a weak signal from the lipid bilayers in the complexes. The use of a microfocused x-ray beam produced by the newly developed Bragg–Fresnel optics at a third-generation synchrotron facility may dramatically increase the signal-to-noise ratio and allow observation of orientational as well as positional ordering of DNA molecules induced by the microchannels. Structural control of the DNA–membrane complexes has a broad range of potential applications in gene probe technology and as mesoscopic biomolecular composites. 相似文献
58.
Attempts to carry out the hydroformylation of allyldiethylamine homogeneously catalyzed by rhodium complexes led to unexpected formation of N,N,N,N-tetraethyl-1,4-diaminobutane and 4-(diethylamino)-1-butanole as final products. The role of the catalyst on the product formation and the reaction mechanism are briefly discussed. 相似文献
59.
Carlos Moreno-Castilla 《Carbon》2004,42(1):83-94
Adsorption of organic molecules from dilute aqueous solutions on carbon materials is a complex interplay between non-electrostatic and electrostatic interactions. Non-electrostatic interactions are essentially due to dispersion and hydrophobic interactions, whereas the electrostatic or coulombic interactions appear with electrolytes when they are ionized at the experimental conditions used. Both interactions depend on the characteristics of the adsorbent and the adsorptive and the solution chemistry. Among them the carbon surface chemistry has a great influence on both electrostatic and non-electrostatic interactions, and can be considered one of the main factors in the adsorption mechanism from dilute aqueous solutions. In this paper the current knowledge about the fundamental factors that control the adsorption process from aqueous phase will be presented. 相似文献
60.