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91.
Franco Ugozzoli Ottorino Ori Alessandro Casnati Andrea Pochini Rocco Ungaro David N. Reinhoudt 《Supramolecular chemistry》2013,25(2):179-184
Abstract The crystal and molecular structures of the 1,3-diisopropoxy-p-tertbutyl calix[4]arene crown-5 fixed in the partial cone conformation and that of its potassium picrate salt have been determined by single crystal X-ray diffraction studies. Energy calculations have been performed to gain more insight on the stabilizing cation…ligand interactions. The calculation of the total potential energy indicates that the contribution which comes from the electrostatic polarization induced by the electric field of the cation on the rotated nucleus gives a net stabilizing contribution of almost 6 kcal/mol. A comparison between the molecular geometry of some partial cone 1,3-disubstituted-p-tertbutylcalix[4]arene derivatives is reported and discussed in view of the preorganization principle. 相似文献
92.
A natural digraph analog of the graph theoretic concept of “an independent set” is that of “an acyclic set of vertices,” namely a set not spanning a directed cycle. By this token, an analog of the notion of coloring of a graph is that of decomposition of a digraph into acyclic sets. We extend some known results on independent sets and colorings in graphs to acyclic sets and acyclic colorings of digraphs. In particular, we prove bounds on the topological connectivity of the complex of acyclic sets, and using them we prove sufficient conditions for the existence of acyclic systems of representatives of a system of sets of vertices. These bounds generalize a result of Tardos and Szabó. We prove a fractional version of a strong‐acyclic‐coloring conjecture for digraphs. © 2008 Wiley Periodicals, Inc. J Graph Theory 59: 177–189, 2008 相似文献
93.
A new approach for liquid chromatography mass spectrometry (LC-MS) is described, based on achieving soft thermal vaporization followed by supersonic expansion and direct sample compound ionization, while in a supersonic molecular beam (SMB). The soft molecular vaporization step utilizes spray formation that is continued by fast thermal vaporization inside a channel supersonic nozzle, followed by ultrafast supercooling in a supersonic expansion. The short time (several microseconds) spent by the vaporized compound in the heated nozzle prior to its expansion cooling may result in incomplete vibrational equilibrium and thus reduced degree of dissociation. In addition, even if vibrational equilibrium at the nozzle temperature is obtained, the sample compounds have significantly reduced time for their dissociation, which is thus further minimized (kinetic consideration). As soon as the molecules expand and form a SMB, they are supercooled and any further dissociation is avoided. While in the SMB, the sample molecules can be ionized either by electron ionization as described in this paper or by hyperthermal surface ionization. The major goal of this method is to obtain high quality library searchable electron ionization mass spectra, for a broad range of thermally labile compounds, with higher sensitivity than that achievable by particle beam LC-MS. The soft thermal vaporization nozzle is described and mass spectral results with corticosterone are demonstrated. The potential advantageous features of this new method are discussed. 相似文献
94.
Andrea Fedorková Hans-Dieter Wiemhöfer Renáta Oriňáková Andrej Oriňák Marian Cristian Stan Martin Winter Dušan Kaniansky Ana Nacher Alejos 《Journal of Solid State Electrochemistry》2009,13(12):1867-1872
The polypyrrole–LiFePO4 composites were synthesized by simple chemical oxidative polymerization of pyrrole (Py) monomer directly on the surface of
LiFePO4 particles. Properties of resulting polypyrrole–LiFePO4 (PPy-LiFePO4) samples (especially conductivity) are strongly affected by the preparation technique, polymer additives, and conditions
during synthesis. For increasing of PPy-LiFePO4 conductivity, we used polyethylene glycol (PEG) as additive during polymerization. The electrochemical behavior of the samples
was examined by cyclic voltammetry and electrochemical impedance spectroscopy. It was found that PPy/PEG composite polymer
decreased the particle to particle contact resistance. Impedance measurements showed that the coating of PPy/PEG significantly
decreases the charge transfer resistance of LiFePO4 electrodes. 相似文献
95.
A compact, strictly all-fiber, picosecond pulse source based on ytterbium (Yb) doped fiber is described. Stable solitary mode-locking is obtained in a fiber-oscillator utilizing a carefully designed chirped fiber-Bragg-grating (C-FBG) for both dispersion control and spectral filtering. Self-starting is assured through the use of a fiber-coupled semiconductor-saturable-absorber-mirror (SESAM). The oscillator’s 50 MHz 3.8 ps pulse-train output at 1064 nm wavelength is amplified to 1.2 W average power by an Yb-doped fiber-amplifier, yielding 6.45 ps parabolic pulses. Numerical simulations of the fiber-oscillator design based on the modified nonlinear Schrödinger equation (NLSE), agree well with the experimental results. 相似文献
96.
Zuzana Nováková Renáta Oriňáková Andrej Oriňák Lenka Škantárová Jaromír Hubálek Frantisek Lofaj 《Surface and interface analysis : SIA》2014,46(5):333-339
The functionality of silver nanostructures prepared by means of electrochemical deposition of silver into the pores of anodic alumina oxide (AAO) template was examined in correlation to electrodeposition conditions. The optical activity as well as the chemical separation ability of prepared nanostructured films was studied. The surface enhanced Raman spectroscopy (SERS) performance was evaluated by the signals of rhodamine 6G, 4‐aminothiophenol and 2,7‐dichlorfluorescein. Nanostructured silver substrates showed moderate surface enhancement for Raman scattering from adsorbed molecules with the magnitude of about 26.9. Moreover, a novel separation/pre‐concentration function of the silver nanowire structures was indicated. The identification and position detection of the model compounds were realised with SERS. The separation of single chemical components from the two‐component mixture over the examined silver nanostructured films was sufficiently approved. The results obtained demonstrated the potential of the prepared substrate as a SERS detection and separation probe for further implementation to any instrumentation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
97.
Theoretical calculations of the amount of Ni that is applied electrolytically in the form of a coating on Fe powder particles
in a fluidized bed are based upon the assumption of distribution of charge between the surface of the solid cathode and the
powder particles present in the working volume of the electrolyte. The experimentally measured data show good agreement with
theory. The efficiency of the coating process is rather low because of inhibition of the process by hydroxocomplexes formed
in the course of electrolysis. The inhibition effect becomes more significant in the case of high suspension density, small
powder particles, high current density, and prolonged time of electrolysis.
Received: 5 May 1997 / Accepted: 30 June 1997 相似文献
98.
99.
Molecular dynamics simulations in the isobaric–isothermal ensemble are used to investigate the structure and dynamics of an ionic liquid confined at ambient temperature and pressure in hydroxylated amorphous silica nanopores. The use of the isobaric–isothermal ensemble allows estimating the effect of confinement and surface chemistry on the density of the confined ionic liquid. The structure of the confined ionic liquid is investigated using density profiles and structural order parameters while its dynamics is assessed by determining the mobility and ionic conductivity of the confined phase. Despite the important screening of the electrostatic interactions (owing to the small Debye length in ionic liquids), the local structure of the confined ionic liquid is found to be mostly driven by electrostatic interactions. We show that both the structure and dynamics of the confined ionic liquid can be described as the sum of a surface contribution arising from the ions in contact with the surface and a bulk-like contribution arising from the ions located in the pore centre; as a result, most properties of the confined ionic liquid are a simple function of the surface-to-volume ratio of the host porous material. In contrast, the ionic conductivity of the confined ionic liquid, which is a collective dynamical property, is found to be similar to the bulk. This study sheds light on the complex behaviour of hybrid materials made up of ionic liquid confined in inorganic porous materials. 相似文献
100.
Ori Shalev Prof. Dr. Silvio E. Biali 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(43):10214-10225
Macrocyclic compounds (calix[4]- and calix[6]arene derivatives) with aryl rings interconnected by spirocyclopropyl groups have been synthesized and structurally characterized. The compounds were prepared by the reaction of dichlorocarbene with calixarenes possessing exocyclic double bonds at the bridges, followed by reductive perdechlorination of the spirocyclopropyl groups. In all systems, pairs of geminal rings connected to the quaternary spiro carbon atoms are oriented anti, and the methylene groups of the cyclopropyl rings are located in isoclinal positions. Calix[6]rotane adopts in the crystal and in solution a 1,3,5-alternate conformation. The presence of the spirocyclopropyl groups increases the rigidity of the macrocyclic ring. 相似文献