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61.
N. C. Rosero-Navarro S. A. Pellice A. Durán S. Ceré M. Aparicio 《Journal of Sol-Gel Science and Technology》2009,52(1):31-40
The aim of this work is the synthesis and characterization of hybrid coatings doped with cerium salts for corrosion protection
of AA2024. The control of the inorganic and organic polymerization process allows the preparation of coatings with an open
structure and a hydrophilic character. These facts facilitate the incorporation and mobility of cerium ions through the structure,
enhancing its ability to promote a self-healing mechanism. The thermal treatment of the coatings has been limited to 120 °C
to preserve the mechanical properties of the alloy. The electrochemical behaviour of the coatings has been evaluated in 0.3
wt% NaCl solution by means of EIS technique. Electrochemical measurements evidence good barrier properties at initial immersion
time, and signals of corrosion inhibition from cerium ions at long immersion times could be assigned to the increasing of
the impedance modulus at low frequencies and the presence of cerium oxide/hydroxide precipitates. 相似文献
62.
Flavia Bonomo Guillermo Durán Frederic Maffray Javier Marenco Mario Valencia-Pabon 《Graphs and Combinatorics》2009,25(2):153-167
A b-coloring of a graph is a coloring such that every color class admits a vertex adjacent to at least one vertex receiving each of the
colors not assigned to it. The b-chromatic number of a graph G, denoted by χ
b
(G), is the maximum number t such that G admits a b-coloring with t colors. A graph G is b-continuous if it admits a b-coloring with t colors, for every . We define a graph G to be b-monotonic if χ
b
(H
1) ≥ χ
b
(H
2) for every induced subgraph H
1 of G, and every induced subgraph H
2 of H
1. In this work, we prove that P
4-sparse graphs (and, in particular, cographs) are b-continuous and b-monotonic. Besides, we describe a dynamic programming
algorithm to compute the b-chromatic number in polynomial time within these graph classes.
Flavia Bonomo: Partially supported by ANPCyT PICT-2007-00533 and PICT-2007-00518, and UBACyT Grants X069 and X606 (Argentina).
Guillermo Durán: Partially supported by FONDECyT Grant 1080286 and Millennium Science Institute “Complex Engineering Systems”
(Chile), and ANPCyT PICT-2007-00518 and UBACyT Grant X069 (Argentina).
Javier Marenco: Partially supported by ANPCyT PICT-2007-00518 and UBACyT Grant X069 (Argentina). 相似文献
63.
Reino JL Durán-Patrón RM Daoubi M Collado IG Hernández-Galán R 《The Journal of organic chemistry》2006,71(2):562-565
[reaction: see text] The biosynthetic origin of the botcinolide skeleton was investigated by means of feeding 13C- and 2H-labeled precursors to Botrytis cinerea. Three new compounds, two homobotcinolide derivatives, 3-O-acetylhomobotcinolide (5) and 8-methylhomobotcinolide (6), and a new 11-membered lactone (7), were isolated. Their structures were elucidated on the basis of spectroscopic data, including one-bond and long-range 1H-13C correlations. The relative stereochemistries were determined by combined analyses of NOE data and 1H-1H coupling constants. According to the results of feeding experiments with 13C- and 2H-labeled acetate and l-S-methylmethionine, 5 is an acetate-derived polyketide whose methyl groups originate from l-S-methylmethionine. This is a rare example of the incorporation of a methyl from methionine into a supposed C3 starter unit of the polyketide synthesis. 相似文献
64.
Eladio J. Rivera Richa Sethi Feifei Qu Ramkumar Krishnamurthy Raja Muthupillai Michael Alford Michael A. Swanson Sandra S. Eaton Gareth R. Eaton Lon J. Wilson 《Advanced functional materials》2012,22(17):3691-3698
The encapsulation of nitroxide radicals within ultrashort (ca. 50 nm) single‐walled carbon nanotubes (US‐tubes) is achieved. Tempo‐ and Iodo‐Tempo@US‐tubes are characterized by thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Electron paramagnetic resonance (EPR) spectra display characteristic signals due to the detection of the spin probes within the US‐tubes. Longitudinal proton relaxivities (r1) of both nitroxide@US‐tubes samples are 7 to 13 times greater than the free nitroxide radicals in solution, giving relaxivities comparable to the clinical contrast agent (CA) Magnevist. In addition, transverse proton relaxivities (r2) show unprecedented proton relaxation enhancement in comparison to any other reported nitroxide radical‐based system or the clinically approved T2 CA, Resovist, under the same conditions. T2‐weighted magnetic resonance imaging (MRI) phantom images show that the encapsulation of nitroxide radicals within the US‐tubes produces good contrast enhancement due to their high r2 relaxivities. The nitroxide radicals@US‐tube agents are a new promising class of spin probes for MRI and electronic paramagnetic resonance imaging (EPRI) labeling, tracking, and diagnosis. 相似文献
65.
Godoy-Caballero MP Acedo-Valenzuela MI Durán-Merás I Galeano-Díaz T 《Analytical and bioanalytical chemistry》2012,403(1):279-290
Response surface methodology has been applied to the optimization of a simple and rapid non-aqueous capillary electrophoresis
method for the separation and determination of several phenolic compounds belonging to the different families present in olive
oil. A Box–Behnken design was employed and a total of 27 experiments were performed using olive oil samples spiked with the
phenols and injected directly in the capillary after dilution 1:1 with 1-propanol. Finally, the background electrolyte (BGE)
was constituted of 25 mM boric acid and 18 mM KOH in a mixture of 74:26 (v/v) 1-propanol/methanol. The hydrophobicity of the BGE allows its miscibility with the olive oil and, as a consequence, the
possibility of characterizing and determining these kinds of compounds in this sample without any pretreatment. A hydrodynamic
injection (6 s, −30 mbar) was applied and the separation was carried out using 35 °C and +20 kV of separation temperature
and voltage, respectively. A capillary with two detection windows for serial online UV and fluorescence detection was satisfactorily
employed. The validation of the method was carried out by setting the calibration curves, and the figures of merit were finally
obtained. A lineal relationship between the corrected peak area and concentration and limits of detection in the order of
micrograms per milliliter were found. 相似文献
66.
67.
Dr. Teresa Hungría Covadonga Correas Dr. Florent Houdellier Dr. Octavio Peña Dr. Eladio Vila Prof. Dr. Alicia Castro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(29):9075-9082
In the last ten years, the study and the search for new multiferroic materials have been a major challenge due to their potential applications in electronic technology. In this way, bismuth‐containing perovskites (BiMO3), and particularly those in which the metal M position is occupied by a magnetically active cation, have been extensively investigated as possible multiferroic materials. From the point of view of synthesis, only a few of the possible bismuth‐containing perovskites can be prepared by conventional methods but at high pressures. Herein, the preparation of one of these potential multiferroic systems, the solid solution xBiMnO3‐(1?x)PbTiO3 by mechanosynthesis is reported. Note that this synthetic method allows the oxides with high x values, and more particularly the BiMnO3 phase, to be obtained as nanocrystalline phases, in a single step and at room temperature without the application of external pressure. These results confirm that, in the case of Bi perovskites, mechanosynthesis is a good alternative to high‐pressure synthesis. These materials have been studied from the point of view of their structural characteristics by precession electron diffraction and magnetic property measurements. 相似文献
68.
Teixeira Z Dreiss CA Lawrence MJ Heenan RK Machado D Justo GZ Guterres SS Durán N 《Journal of colloid and interface science》2012,382(1):36-47
Nanocapsules containing poly(d,l-lactide) shell and retinyl palmitate core have been prepared by the pre-formed polymer interfacial deposition method. Dynamic light scattering measurements yielded an average hydrodynamic diameter of ~220nm and a polydispersity index of ~0.12. Small-angle neutron scattering experiments revealed the presence of two populations of nanocapsules of core diameters ~192 and 65nm. Freeze fracture transmission electron microscopy showed a polydisperse population of nanocapsules (NC), with a poly(d,l-lactide) shell thickness between 11 and 3nm. For comparison purposes, nanoemulsions (NE, no polymer) and nanospheres (NS, polymer matrix) were also prepared. Each type of nanoparticles exhibited a different morphology (when examined by electron microscopy), in particular NC showed deformability by capillary adhesion. All three types of nanoparticles successfully encapsulated the poorly water-soluble molecules baicalein and benzophenone-3. The thermal behavior of the various nanoparticles was different to a physical mixture of its individual components. Cytotoxicity and phototoxicity assays, performed in human keratinocytes (HaCaT) and murine fibroblasts (BALB/c 3T3), showed that the NC were only cytotoxic at high concentrations. In vitro release studies of benzophenone-3, by the dialysis bag method using NC and NS, showed a sustained release; however, permeation studies using plastic surgery human abdominal skin in Franz diffusion cells showed that a higher amount of benzophenone-3 from NC penetrated into the skin, most probably due to the deformable nature of these nanoparticles. 相似文献
69.
Perdigoto ML Martins RC Rocha N Quina MJ Gando-Ferreira L Patrício R Durães L 《Journal of colloid and interface science》2012,380(1):134-140
This work is devoted to the application of hydrophobic silica based aerogels and xerogels for the removal of three toxic organic compounds from aqueous solutions. These materials were tested and characterized regarding their morphology, particle size distribution, surface area and porous structure. The equilibrium tests were carried out at different adsorbate concentrations and the experimental data were correlated by means of Langmuir and Freundlich isotherms. The equilibrium data were well described by Langmuir and Freundlich in most cases. The maximum adsorption capacity by Langmuir model was observed for the adsorption of benzene onto aerogel (192.31 mg/g), though the most promising results were obtained for toluene adsorption due to the greater adsorption energy involved. Comparing these results with other reported results, the hydrophobic silica based aerogels/xerogels were found to exhibit a remarkable performance for the removal of benzene and toluene. In addition, the regeneration of previously saturated aerogel/toluene was also investigated by using an ozonation process. The adsorption/regeneration tests with ozone oxidation showed that the aerogel might be regenerated, nevertheless the materials lost their hydrophobicity and thus different methods should be evaluated in forthcoming investigations. 相似文献
70.
Rivera EJ Barbosa C Torres R Rivera H Fachini ER Green TW Connick WB Colón JL 《Inorganic chemistry》2012,51(5):2777-2784
The direct intercalation of a pyrazolate-bridged platinum(II) bipyridyl dimer ([{Pt(dmbpy)(μ-pz)}(2)](2+); dmbpy = 4,4'-dimethyl-2,2'-bipyridine, pz(-) = pyrazolate) within a zirconium phosphate (ZrP) framework has been accomplished. The physical and spectroscopic properties of [{Pt(dmbpy)(μ-pz)}(2)](2+) intercalated in ZrP were investigated by X-ray powder diffraction and X-ray photoelectron, infrared, absorption, and luminescence spectroscopies. Zirconium phosphate layers have a special microenvironment that is capable of supporting a variety of platinum oxidation states. Diffuse reflectance spectra from powders of the blue-gray intercalated materials show the formation of a low-energy band at 600 nm that is not present in the platinum dimer salt. The nonintercalated complex is nonemissive in room-temperature fluid solution, but gives rise to intense blue-green emission in a 4:1 ethanol/methanol 77 K frozen glassy solution. Powders and colloidal suspensions of [{Pt(dmbpy)(μ-pz)}(2)](2+)-exchanged ZrP materials exhibit intense emissions at room-temperature. 相似文献