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51.
52.
Alves L Ballesteros B Boronat M Cabrero-Antonino JR Concepción P Corma A Correa-Duarte MA Mendoza E 《Journal of the American Chemical Society》2011,133(26):10251-10261
Small gold nanoclusters in a very narrow size distribution (1.1 ± 0.5 nm) have been stabilized onto multiwalled carbon nanotubes (MWCNT). Theoretical studies supported by XPS and (16)O(2)/(18)O(2) isotopic exchange experiments have shown that, on small gold nanoparticles (0.9-1.5 nm), dissociation of molecular O(2) and formation of a surface oxide-like layer is energetically favorable and occurs at room temperature, while O(2) recombination and desorption involves a larger activation barrier. CO titration experiments and theoretical studies demonstrate that the reactivity of the oxidized particles toward CO does not only depend on particle size but also on oxygen coverage. The oxidation-reduction process described is reversible, and the oxidized nanoparticles are active in the epoxidation of styrene with air. 相似文献
53.
Rivera A Farías T de Ménorval LC Autié-Castro G Yee-Madeira H Contreras JL Autié-Pérez M 《Journal of colloid and interface science》2011,360(1):220-226
The employment of an acid natural clinoptilolite (AZH-1) in the adsorption and separation of n-paraffins has been evaluated. Natural clinoptilolite, NZ, was the raw material used to prepare the sodium-exchanged clinoptilolite (AZ) starting from which the AZH-1 sample was obtained by acid treatment. The structural stability of the samples after the applied treatments was demonstrated. The nitrogen adsorption experiments indicated that the acid sample has a homogeneous porous distribution and a considerable increase in the micropore volume with respect to NZ and AZ. The employment of the inverse gas chromatography at infinite dilution (IGCID) allowed studying the adsorption and separation of n-paraffin mixtures on AZH-1. It was also confirmed that the diffusion on AZH-1 took place in an unblocked structure through the A channel of ten members with minimal interactions. The IGCID results demonstrated the capacities of the acid Cuban natural zeolite in the adsorption and separation of n-paraffin mixtures. 相似文献
54.
Perez-Peralta N Contreras M Tiznado W Stewart J Donald KJ Merino G 《Physical chemistry chemical physics : PCCP》2011,13(28):12975-12980
We have explored in silico the potential energy surfaces of the C(5)Li(n)(n-6) (n = 5, 6, and 7) clusters using the Gradient Embedded Genetic Algorithm (GEGA) and other computational strategies. The most stable forms of C(5)Li(5)(-) and C(5)Li(6) are two carbon chains linked by two lithium atoms in a persistent seven membered ring capped by two Li atoms. The other Li atoms are arrayed on the edge of the seven membered ring. In contrast, the global minimum structure for C(5)Li(7)(+) is a bicapped star of D(5h) symmetry. The molecular orbital analysis and computed magnetic field data suggest that electron delocalization, as well as the saturation of the apical positions of the five-membered carbon ring with lithium atoms in C(5)Li(7)(+) plays a key role in the stabilization of the carbon-lithium star. In fact, the planar star sub-structure for the carbon ring are unstable without the apical caps. This is also what has been found for the Si analogues. The split of the B(ind)(z) in its σ- and π-contribution indicates that C(5)Li(7)(+) is a π-aromatic and σ-nonaromatic system. 相似文献
55.
Leonor Y. Vargas Méndez Vladimir V. Kouznetsov 《Central European Journal of Chemistry》2011,9(5):877-885
We report an efficient and useful synthesis of new attractive spiropiperdine scaffolds 4 based on an intramolecular acyl transfer process in 1′-acyl-1-benzyl-3′,4′-dihydro-1′H-spiro[piperidine-4,2′-quinolines]
3 using simple and mild debenzylation reaction conditions (HCOONH4/Pd/C). The compounds 3 were prepared by acylating 1-benzyl-4′-methyl-3′,4′-dihydro-1′H-spiro[piperidine-4,2′-quinolines] 2 that are easily available from 1-benzyl-4-piperidone 1. The intramolecular character of this process was proven primarily through a crossover experiment technique. Through an examination
of all spectroscopic information (1H, 13C NMR, VT-1H NMR, and 2D NMR) it was possible to correctly predict amide configurations and piperidine ring conformations of starting and final spiropiperidine
compounds.
相似文献
56.
María Leonor S. Varas 《Advances in Computational Mathematics》1996,5(1):31-49
We present a method for signal reconstruction based upon the location of its singularities which are identified by a wavelet transform technique. The reconstructed signal is an infconvolution spline approximant. The data for the interpolation problem which we solve comes from a compact signal coding procedure. Error bounds and convergence results for the calculated signal are given. 相似文献
57.
Inner projections of the polarization propagator were used to study the indirect through-space transmission of the Fermi contact term of CF couplings via a CX (X = F, H) intermediate bond. When X = H a large capability for transmitting this component is observed. But for X = F a notable inhibition of this transmission mechanism is observed. The role of the fluorine lone pairs in this behaviour is discussed. 相似文献
58.
N.M. Peruchenaa L. Sosa G.A. Aucar R.H. Contreras 《Journal of Molecular Structure》1995,330(1-3):211-216
Vicinal J(SnCCSn) and J(SnCCC) spin-spin coupling constants are calculated within the RPA MNDO method for different dihedral angles, θ, determined by the intervening bonds, in model compounds. For both types of couplings, calculated values closely follow Karplus-like dependences. Results are discussed in terms of experimental values, and the effects of substituents attached to the coupled atoms are briefly analyzed for the θ = 0 ° and θ = 180 ° conformations. These last values were also calculated using the RPA AM1 method. Results indicate that the RPA MNDO and RPA AM1 approaches show interesting potential for studying the structural dependences of 3J(SnSn) and 3J(SnC) couplings in tin-containing compounds. 相似文献
59.
Implantation of P in B bulk doped Si (hole concentration = 2.1×1020 cm?3) followed by multiple pulse laser annealing with a XeCl laser has produced the incorporation of P in substitutional sites of the matrix and also charge carrier compensation. We report in this paper light scattering studies of these samples, in which a decrease of the hole-induced softening of the Si-Raman line is observed. This softening depends on the type and concentration of free carriers and thus, in our case, on the degree of compensation. This softening is discussed in terms of the interaction of the continuum of free carrier excitations with the Raman phonon. We also report the observation of the vibrations of 11B-31 P pairs. 相似文献
60.