Studies on the catalytic hydrogenation of Baylis Hillman derivatives of substituted isoxazolecarbaldehydes

Results of the catalytic hydrogenation of Baylis-Hillman adducts obtained from substituted 3-, 4- and 5-isoxazolecarbox-aldehydes and their corresponding acetates in the presence of Raney-Ni and Pd-C are presented. The hydrogenation of Baylis-Hillman adducts of substituted 5-isoxazolecarbaldehydes and 3-isoxazolecarbaldehydes in the presence of Raney-Ni furnishes diastereoselectively syn enaminones over anti and in the presence of boric acid as an additive further enhancement of diastereoselectivity in favor of syn isomer is observed. The Pd-C-promoted hydrogenation of these substrates is also diastereoselective in favor of syn isomer but occurs without the hydrogenolysis of isoxazole-ring. The presence of boric acid as additive in this hydrogenation exhibits no pronounced effect on diastereoselectivity. The Raney-Ni-mediated hydrogenation of Baylis-Hillman adducts of substituted 4-isoxazolecarbaldehydes yield pyridone derivatives and Pd-C-promoted hydrogenation of the same substrate is diastereoselective to afford the anti isomer of the resulting products. The enaminones derived from Baylis-Hillman adducts of 3- and 5-isoxazolecarbaldehydes serve as versatile precursors for '-hydroxy-1, 3-diketones, which undergo acid-catalyzed ring-closure reaction to afford the furanone derivatives in excellent yields

Synthesis of liquid menthol by hydrogenation of dementholized peppermint oil over Ni catalysts

Hydrogenation of (-)-menthone and (+)-isomenthone was studied at 2.7 MPa and 100 ºC. The objective was to produce a liquid menthol mixture rich in (-)-menthol from dementholized peppermint oil. Ni-based catalysts were tested and compared for this reaction: a) 6 and 12% Ni dispersed into a nonstoichiometric magnesium aluminate (Ni-Mg-Al) with spinel structure; b) Ni-Raney catalyst. Both types of catalysts were active for (-)-menthone and (+)-isomenthone hydrogenation. Lower conversion but higher selectivity to (-)-menthol was obtained with Ni-Mg-Al catalysts. However, they rapidly lost their activity. Instead Ni-Raney catalysts kept its original activity even after several hydrogenation runs.

Emulation of chiral hydrogenation catalysts by adsorbtion of small molecules onto Ni surfaces

Adsorption of small molecules on the Ni{111} and NiO{111} surfaces is investigated under UHV and elevated pressures (~10-1 mbar) of hydrogen and water. The molecules considered are chosen for their relevance to understanding the mechanism of enantioselective hydrogenation on Raney Nickel modified by chiral molecules. Adsorption of water onto, and its subsequent reaction with, oxygen-covered Ni{111} is dependent on the initial atomic oxygen coverage. An OH species (O1s binding energy 531.5eV), oriented perpendicular to the surface, forms at atomic oxygen coverages <0.25ML. The reaction does not consume all the adsorbed oxygen for coverages ≥0.12ML. The p(2×2) atomic oxygen uperstructure is unreactive, while an OH species is formed on the p(√3×√3) superstructure at binding energy 530.9eV. L-alanine is adsorbed on Ni{111} as a model chiral modifier molecule. At low coverages, alanine forms a presumed tridentate alaninate species for coverages ≥0.11ML at 250K. A minority, bidentate zwitterionic species forms at coverages >0.11ML, but was not observed at 300K. Saturation occurs at 0.25ML. At high alanine coverages (≥0.19ML) and H2 pressure (≥1×10-2 mbar), the tridentate L-alaninate converts to bidentate zwitterionic L-alanine at 300K. Thermal evolution of L-alanine on Ni{111} under varying hydrogen pressures is examined. Adsorption of L-alanine onto hydroxylated NiO{111} at 300K in UHV, mimicking a catalyst surface under aqueous conditions, yields the tridentate alaninate which is immune to the effects of elevated hydrogen pressure. Exposing the L-alanine/Ni{111} adsorption system to water (≤10-1 mbar) oxidises the surface and recreates the L-alanine/hydroxylated NiO{111} system. Pyruvic acid on Ni{111} is examined as a model for hydrogenation substrate adsorption. Behaviour is coverage dependent and several conformations are possible at low coverages (≤0.1ML). Annealing at coverages <0.2ML causes a condensation reaction, releasing water onto the surface. High coverages do not condense and a saturation coverage of ~0.35ML is found.

Propriedades elétricas e magnéticas de novos compostos com o ânion condutor [Ni(dmit)2]- e radicais magnéticos nitronil nitróxido

Three compounds have been synthesized with formulae [3-MeRad][Ni(dmit)2] (1), [4-MeRad][Ni(dmit)2] (2) and [4-PrRad][Ni(dmit)2] (3) where [Ni(dmit)2]- is an anionic pi-radical (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) and [3-MeRad]+ is 3-N-methylpyridinium alpha-nitronyl nitroxide, [4-MeRad]+ is 4-N-methylpyridinium alpha-nitronyl nitroxide and [4-PrRad]+ is 4-N-propylpyridinium alpha-nitronyl nitroxide. The temperature-dependent magnetic susceptibility of 1 revealed that an antiferromagnetic interaction operates between the 3-MeRad+ radical cations with exchange coupling constants of J1 = - 1.72 cm-1 and antiferromagnetism assigned to the spin ladder chains of the Ni(dmit)2 radical anions. Compound 1 exhibits semiconducting behavior and 3 presents capacitor behavior in the temperature range studied (4 - 300 K).

Effect of casting atmosphere on the shear bond strength of a ceramic to Ni-Cr and Ni-Cr-Be alloys

The success of metal-ceramic restorations depends on an optimal bond between metal and ceramic. This study evaluated the effect of 3 casting atmospheres on the metal-ceramic bond strength (MCBS) of 2 Ni-Cr alloys, with beryllium (Fit Cast V) and without beryllium (Fit Cast SB). Sixty acrylic resin patterns (8 mm long and 5 mm diameter) were obtained using a fluorocarbon resin matrix. Wax was used to refine the surface of acrylic resin patterns that were invested and cast in an induction casting machine under normal, vacuum, and argon atmospheres at a temperature of 1340ºC. The castings were divested manually and airborne-particle abraded with 100-µm aluminum-oxide. Ten castings were obtained for each group. The IPS Classic V ceramic was applied (2 mm high and 5 mm diameter). The shear bond strength was tested in a mechanical testing machine with a crosshead speed of 2.0 mm/min. The MCBS data (MPa) were subjected to 2-way analysis of variance (α=0.05). There was no statistically significant difference (p>0.05) between the alloys or among the casting atmospheres. Within the limitations of this study, it may be concluded that the presence of beryllium and the casting atmosphere did not interfere in the MCBS of the evaluated metal-ceramic combinations

Preparação de membranas de acetato de celulose organomodificadas para adsorção dos íons Cu(II), Cd(II), Mn(II) e Ni(II)

Cellulose acetate polymeric membranes had been prepared by a procedure of two steps, combining the method of phase inversion and the technique of hydrolysis-deposition. The first step was the preparation of the membrane, and together was organomodified with tetraethylortosilicate and 3-aminopropyltrietoxysilane. Parameters that exert influence in the complexation of the metallic ion, as pH, time of complexation, metal concentration, had been studied in laboratory using tests of metal removal. The membranes had presented resistance mechanics and reactivity to cations, being able to be an alternative for the removal, daily pay-concentration or in the study of the lability of metals complexed.

Estudo da eletrocristalização de Ni e Ni-P sobre ultramicroeletrodo de platina

This work describes a comparative study of the electrocrystallization of Ni and Ni-P on Pt ultramicroelectrodes using chronoamperometric measurements. It was possible to confirm that in all cases a progressive nucleation was the predominant mechanism. Moreover, the application of the Atomistic Theory to the experimental rate of nuclei formation showed that the number of atoms in the critical nucleus was zero, except for Ni-P on Pt at low overpotentials were a value of one was observed. Furthermore, the physical characterisation of the different deposits on Pt by atomic force microscopy allowed observing the coalescence of the hemispherical nuclei of Ni and Ni-P at t max thus confirming the results obtained from the current-time analysis.

Prediction of good glass formers in the Al-Ni-La and Al-Ni-Gd systems using topological instability and electronegativity

A new criterion has been recently proposed combining the topological instability (lambda criterion) and the average electronegativity difference (Delta e) among the elements of an alloy to predict and select new glass-forming compositions. In the present work, this criterion (lambda.Delta e) is applied to the Al-Ni-La and Al-Ni-Gd ternary systems and its predictability is validated using literature data for both systems and additionally, using own experimental data for the Al-La-Ni system. The compositions with a high lambda.Delta e value found in each ternary system exhibit a very good correlation with the glass-forming ability of different alloys as indicated by their supercooled liquid regions (Delta T(x)) and their critical casting thicknesses. In the case of the Al-La-Ni system, the alloy with the largest lambda.Delta e value, La(56)Al(26.5)Ni(17.5), exhibits the highest glass-forming ability verified for this system. Therefore, the combined lambda.Delta e criterion is a simple and efficient tool to select new glass-forming compositions in Al-Ni-RE systems. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3563099]

Effect of weak dipolar interaction on the magnetic properties of Ni nanoparticles assembly analyzed with different protocols

The effect of weak dipolar interactions (DIs) between Ni nanoparticles (NPs) in samples with different Ni concentrations was investigated by performing a detailed characterization of their structural and magnetic properties. From the determination of several physical parameters of Ni NP assemblies, it was found that the ac and dc magnetic susceptibility measurements are valuable for identifying the DIs between NPs while hysteresis loops measurements showed to be very insensitive, provided that the strength of the DI field is much smaller than the maximum coercive field. Therefore, the sensitivity of the observed static and dynamical magnetic properties to the effect of weak DI depends on the measurement protocols used. (C) 2011 American Institute of Physics. [doi:10.1063/1.3556767]

Increase in the magnitude of the energy barrier distribution in Ni nanoparticles due to dipolar interactions

The energy barrier distribution E(b) of five samples with different concentrations x of Ni nanoparticles using scaling plots from ac magnetic susceptibility data has been determined. The scaling of the imaginary part of the susceptibility chi""(v, T) versus T ln (iota t/tau(0)) remains valid for all samples, which display Ni nanoparticles with similar shape and size. The mean value < E(b)> increases appreciably with increasing x, or more appropriately with increasing dipolar interactions between Ni nanoparticles. We argue that such an increase in < E(b)> constitutes a powerful tool for quality control in magnetic recording media technology where the dipolar interaction plays an important role. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3533911]

Role of dipolar interactions in a system of Ni nanoparticles studied by magnetic susceptibility measurements

The role of dipolar interactions among Ni nanoparticles (NPs) embedded in an amorphous SiO(2)/C matrix with different concentrations has been studied performing ac magnetic susceptibility chi(ac) measurements. For very diluted samples, with Ni concentrations < 4 wt % Ni or very weak dipolar interactions, the data are well described by the Neacuteel-Arrhenius law. Increasing Ni concentration to values up to 12.8 wt % Ni results in changes in the Neacuteel-Arrhenius behavior, the dipolar interactions become important, and need to be considered to describe the magnetic response of the NPs system. We have found no evidence of a spin-glasslike behavior in our Ni NP systems even when dipolar interactions are clearly present.

Electronic, structural, and transport properties of Ni-doped graphene nanoribbons

We have investigated the electronic and transport properties of zigzag Ni-adsorbed graphene nanoribbons (Ni/GNRs) using ab initio calculations. We find that the Ni adatoms lying along the edge of zigzag GNRs represent the energetically most stable configuration, with an energy difference of approximately 0.3 eV when compared to the adsorption in the middle of the ribbon. The carbon atoms at the ribbon edges still present nonzero magnetic moments as in the pristine GNR even though there is a quenching by a factor of almost five in the value of the local magnetic moments at the C atoms bonded to the Ni. This quenching decays relatively fast and at approximately 9 A from the Ni adsorption site the magnetic moments have already values close to the pristine ribbon. At the opposite edge and at the central carbon atoms the changes in the magnetic moments are negligible. The energetic preference for the antiparallel alignment between the magnetization at the opposite edges of the ribbon is still maintained upon Ni adsorption. We find many Ni d-related states within an energy window of 1 eV above and below the Fermi energy, which gives rise to a spin-dependent charge transport. These results suggest the possibility of manufacturing spin devices based on GNRs doped with Ni atoms.

Near-Barrier Fusion of the (8)B+(58)Ni Proton-Halo System

Fusion cross sections were measured for the exotic proton-halo nucleus (8)B incident on a (58)Ni target at several energies near the Coulomb barrier. This is the first experiment to report on the fusion of a protonhalo nucleus. The resulting excitation function shows a striking enhancement with respect to expectations for normal projectiles. Evidence is presented that the sum of the fusion and breakup yields saturates the total reaction cross section.

Reaction cross sections for (8)B, (7)Be, and (6)Li+(58)Ni near the Coulomb barrier: Proton-halo effects

Elastic scattering of (8)B, (7)Be, and (6)Li on a (58)Ni target has been measured at energies near the Coulomb barrier. Optical-model fits were made to the experimental angular distributions, and total reaction cross sections were deduced. A comparison with other systems provides striking evidence for proton-halo effects on (8)B reactions. As opposed to the situation for the neutron-halo nucleus (6)He, for which particle transfer dominates, the ""extra"" cross section observed for (8)B appears to result entirely from projectile breakup.

Partial magnetic ordering and crystal structure of the ludwigites Co(2)FeO(2)BO(3) and Ni(2)FeO(2)BO(3)

We present an extensive study of the structural, magnetic, and thermodynamic properties of the two heterometallic oxyborates: Co(2)FeO(2)BO(3) and Ni(2)FeO(2)BO(3). This has been carried out through x-ray diffraction at room temperature (RT) and 150 K, dc and ac magnetic susceptibilities, and specific-heat experiments in single crystals above 2 K. The magnetic properties of these iron ludwigites are discussed in comparison with those of the other two known homometallic ludwigites: Fe(3)O(2)BO(3) and Co(3)O(2)BO(3). In both ludwigites now studied we have found that the magnetic ordering of the Fe(3+) ions occurs at temperatures very near to which they order in Fe(3)O(2)BO(3). A freezing of the divalent ions (Co and Ni) is observed at lower temperatures. Our x-ray diffraction study of both ludwigites at RT and 150 K showed very small ionic disorder in apparent contrast with the freezing of the divalent ion spins. The structural transition that occurs in homometallic Fe(3)O(2)BO(3) has not been found in the present mixed ludwigites in the temperature range investigated.