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991.
G. Ruano J.C. Moreno-López M.C.G. Passeggi R.A. Vidal J. Ferrón M.Á. Niño R. Miranda J.J. de Miguel 《Surface science》2012,606(5-6):573-579
The growth of ultrathin epitaxial layers of aluminum fluoride on Cu(100) has been studied by a combination of surface science techniques. Deposition at room temperature results in step decoration followed by the formation of dendritic two-dimensional islands that coalesce to form porous films. Ultrathin layers (up to 2 monolayers in thickness) are morphologically unstable upon annealing; de-wetting takes place around 430 K with the formation of three-dimensional islands and leaving a large fraction of the Cu surface uncovered. Films several nanometers thick, on the contrary, are stable up to ca. 730 K where desorption in molecular form sets on. The effect of electron irradiation on the AlF3 has also been characterized by different spectroscopic techniques; we find that even small quantities of stray electrons from rear electron beam heating can provoke significant decomposition of the aluminum fluoride, resulting in the release of molecular fluorine and the formation of deposits of metallic aluminum. These features make AlF3 an interesting material for spintronic applications. 相似文献
992.
Balsells JM Jurado-Navas A Paris JF Castillo-Vázquez M Puerta-Notario A 《Optics letters》2012,37(4):719-721
In this paper, the performance of the variable weight multiple pulse-position modulation (MPPM) coding technique in an atmospheric optical communication environment under gamma-gamma optical scintillation is analyzed, proposing a closed-form expression for the average bit error rate (BER). This study is based on a hyperexponential fitting of the conditional BER in absence of turbulence fluctuations, leading to closed-form expressions that characterize the behavior of this nonlinear coding scheme. Finally, conditional and average BER expressions proposed here are corroborated with Monte Carlo simulations results. 相似文献
993.
Maria A. Alvarez Edgardo J. Saavedra Mónica S. Olivella Fernando D. Suvire Miguel A. Zamora Ricardo D. Enriz 《Central European Journal of Chemistry》2012,10(1):248-255
The multidimensional Conformational Potential Energy Hypersurface (PEHS) of cyclotrisarcosyl was comprehensively investigated
at the DFT (B3LYP/6-31G(d), B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p)), levels of theory. The equilibrium structures, their
relative stability, and the Transition State (TS) structures involved in the conformational interconversion pathways were
analyzed. Aug-cc-pVTZ//B3LYP/6-311++G(d,p) and MP2/6-31G(d)//B3LYP/6-311++G(d,p) single point calculations predict a symmetric
cis-cis-cis crown conformation as the energetically preferred form for this compound, which is in agreement with the experimental data.
The conformational interconversion between the global minimum and the twist form requires 20.88 kcal mol-1 at the MP2/6-31G(d)//B3LYP/6-311++G(d,p)
level of theory. Our results allow us to form a concise idea about the internal intricacies of the PEHSs of this cyclic tripeptide,
describing the conformations as well as the conformational interconversion processes in this hypersurface. In addition, a
comparative analysis between the conformational behaviors of cyclotrisarcosyl with that previously reported for cyclotriglycine
was carried out 相似文献
994.
995.
Ryding MJ Ruusuvuori K Andersson PU Zatula AS McGrath MJ Kurtén T Ortega IK Vehkamäki H Uggerud E 《The journal of physical chemistry. A》2012,116(20):4902-4908
Molecular cluster ions H(+)(H(2)O)(n), H(+)(pyridine)(H(2)O)(n), H(+)(pyridine)(2)(H(2)O)(n), and H(+)(NH(3))(pyridine)(H(2)O)(n) (n = 16-27) and their reactions with ammonia have been studied experimentally using a quadrupole-time-of-flight mass spectrometer. Abundance spectra, evaporation spectra, and reaction branching ratios display magic numbers for H(+)(NH(3))(pyridine)(H(2)O)(n) and H(+)(NH(3))(pyridine)(2)(H(2)O)(n) at n = 18, 20, and 27. The reactions between H(+)(pyridine)(m)(H(2)O)(n) and ammonia all seem to involve intracluster proton transfer to ammonia, thus giving clusters of high stability as evident from the loss of several water molecules from the reacting cluster. The pattern of the observed magic numbers suggest that H(+)(NH(3))(pyridine)(H(2)O)(n) have structures consisting of a NH(4)(+)(H(2)O)(n) core with the pyridine molecule hydrogen-bonded to the surface of the core. This is consistent with the results of high-level ab initio calculations of small protonated pyridine/ammonia/water clusters. 相似文献
996.
Indium-mediated allylation of N-tert-butanesulfinyl ketimines afforded in high yields and diastereoselectivities homoallylic amine derivatives with the nitrogen atom bonded to a quaternary stereocenter. 相似文献
997.
A Mayoral C Magen M Jose-Yacaman 《Chemical communications (Cambridge, England)》2012,48(69):8667-8669
The optical response of multibranched gold nanoparticles is studied by means of electron energy-loss spectroscopy (EELS) in aberration corrected STEM mode. In every case the plasmon response is constant and variations in the maxima positions were found to be dependent on the branches aspect ratio. The good spatial resolution combined with the high energy resolution (0.18 eV) of the monochromated electron beam allows mapping the different plasmonic modes along the entire nanoparticles ranging from 0.7 eV up to 2.25 eV. 相似文献
998.
Ceron MA Guzman-Lucero DJ Palomeque JF Martínez-Palou R 《Combinatorial chemistry & high throughput screening》2012,15(5):427-432
Fifty-six ionic liquids were efficiently synthesized in parallel format under one-pot, solvent-free microwave-assisted synthesis. These compounds were evaluated as extracting agents of nitrogen-containing compounds from a real Diesel feed before being submitted to the hydrodesulfurization process to obtain ultralow sulfur Diesel. Our results showed that halogenated ionic liquids are an excellent alternative due to these ionic liquids are relatively inexpensive, presenting a high selectivity for the extraction of nitrogen-containing compounds and can be regenerated and recycled. 相似文献
999.
Numerous members of the Anthemideae tribe are important as cut flowers and ornamental crops, as well as being medicinal and aromatic plants, many of which produce essential oils used in folk and modern medicine and in the cosmetics and pharmaceutical industry. Essential oils generally have a broad spectrum of bioactivity, owing to the presence of several active ingredients that work through various modes of action. Due to their mode of extraction, mostly by distillation from aromatic plants, they contain a variety of volatile molecules such as terpenes, phenol-derived aromatic and aliphatic components. The large genus Artemisia L., from the tribe Anthemideae, comprises important medicinal plants which are currently the subject of phytochemical attention due to their biological and chemical diversity. Artemisia species, widespread throughout the world, are one of the most popular plants in Chinese traditional preparations and are frequently used for the treatment of diseases such as malaria, hepatitis, cancer, inflammation and infections by fungi, bacteria and viruses. Extensive studies of the chemical components of Artemisia have led to the identification of many compounds as well as essentials oils. This review summarizes some of the main reports on the chemistry and anti-infective activities of Artemisia. Li. essential oils from the data in the recent literature (2000-2011). 相似文献
1000.
Dr. Francisco Rodríguez‐Llansola Dr. Daniel Hermida‐Merino Belén Nieto‐Ortega Dr. Francisco J. Ramírez Prof. Juan T. López Navarrete Prof. Juan Casado Prof. Ian W. Hamley Dr. Beatriu Escuder Dr. Wayne Hayes Dr. Juan F. Miravet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(46):14725-14731
A chiral bisurea‐based superhydrogelator that is capable of forming supramolecular hydrogels at concentrations as low as 0.2 mM is reported. This soft material has been characterized by thermal studies, rheology, X‐ray diffraction analysis, transmission electron microscopy (TEM), and by various spectroscopic techniques (electronic and vibrational circular dichroism and by FTIR and Raman spectroscopy). The expression of chirality on the molecular and supramolecular levels has been studied and a clear amplification of its chirality into the achiral analogue has been observed. Furthermore, thermal analysis showed that the hydrogelation of compound 1 has a high response to temperature, which corresponds to an enthalpy‐driven self‐assembly process. These particular thermal characteristics make these materials easy to handle for soft‐application technologies. 相似文献