Podzolization as a deferralitization process: dynamics and chemistry of ground and surface waters in an Acrisol-Podzol sequence of the upper Amazon Basin

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Ferroelectric and dielectric behaviour of Bi0.92La0.08FeO3 multiferroic thin films prepared by soft chemistry route

Bi0.92La0.08FeO3 (BLFO) thin films were grown on platine substrates by the soft chemical route. Ferroelectric and dielectric behaviors of BLFO films deposited by spin-coating technique and annealed at 773 K for 2 h in air atmosphere were explained. BLFO thin films obtained presents a rhombohedral structure. The BLFO films present dielectric and ferroelectric behaviors with dielectric permittivity and dielectric loss of approximately 81 and 0.0144 at 1 kHz. The Au/BLFO/Pt capacitor shows a hysteresis loop with remnant polarization of 20.6 mu C/cm(2) and coercive field of 53.88 kV/cm. The polarization switching and the fatigue behavior of the BLFO films were significantly enhanced.

Natural products from Brazilian biodiversity as a source of new models for medicinal chemistry

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Tropical biodiversity: has it been a potential source of secondary metabolites useful for medicinal chemistry?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hydroxymethylnitrofurazone:Dimethyl-beta-cyclodextrin Inclusion Complex: A Physical-Chemistry Characterization

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Sol phase and sol-gel transition in SnO2 colloidal suspensions

The effect of concentration on the structure of SnO2 colloids in aqueous suspension, on their spatial correlation and on the gelation process was studied by small angle x-ray scattering (SAXS). The shape of the experimental SAXS curves varies with suspension concentration. For diluted suspensions ([SnO2] less than or equal to 0.13 mol L-1), SAXS results indicate the presence of colloidal fractal aggregates with an internal correlation length xi congruent to 20 Angstrom, without any noticeable spatial correlation between them. This suggests that the aggregates are spatially arranged without any significant interaction like in ideal gas structures. For higher concentrations ([SnO2] = 0.16, 0.32, and 0.64 mol L-1), the colloidal aggregates are larger (xi = 24 Angstrom) and exhibit a certain degree of spatial correlation between them. The pair correlation function corresponding to the sol with the highest concentration (0.92 mol L-1) reveals a rather strong short range order between aggregates, characteristic of a fluid-like structure, with an average nearest-neighbor distance between aggregates d(1) = 125 Angstrom and an average second-neighbor distance d(2) = 283 Angstrom. The pair distribution function remains essentially invariant during the sol-gel transition, suggesting that gelation involves the formation of a few points of connection between the aggregates resulting in a gel network constituted by essentially linear chains of clusters..

Growth kinetics of tin oxide nanocrystals in colloidal suspensions under hydrothermal conditions

Colloidal suspensions of tin oxide nanocrystals were synthesized at room temperature by the hydrolysis reaction of tin chloride (II), in an ethanolic solution. The coarsening kinetics of such nanocrystals was studied by submitting the as-prepared suspensions to hydrothermal treatments at temperatures of 100, 150 and 200 degrees C for periods between 60 and 12,000 min. Transmission electron microscopy (TEM) was used to characterize the samples (i.e. distribution of nanocrystal size, average particle radius and morphology). The results show that the usual Ostwald ripening coarsening mechanism does not fit well the experimental data, which is an indicative that this process is not significant for SnO2 nanocrystals, in the studied experimental conditions. The morphology evolution of the nanocrystals upon hydrothermal treatment indicates that growth by oriented attachment (OA) should be significant. A kinetic model that describes OA growth is successfully applied to fit the data. (c) 2006 Elsevier B.V. All rights reserved.

Nonlinear properties and stability of SnO2 varistors prepared by evaporation and decomposition of suspensions

SnO2 varistors doped with CoO, Cr2O3 and Nb2O5 were prepared by evaporation and decomposition of suspensions. The composition of the varistors was optimized to improve electrical properties, such as nonlinearity, leakage current and electrical stability. The best results were achieved with the following composition: 99.15% SnO2 +0.75% CoO+0.05% Cr2O3 +0.05% Nb2O5. Samples showed high density, reaching 99.5% of the theoretical density, as well as an homogeneous microstructure. The nonlinear coefficient was higher than 30 in the current range from 10(-7) to 10(-2) A/cm(2). The leakage current was 0.86 mu A/cm(2). These samples showed high stability of electrical parameters when they were exposed to high current of 27 mA/cm(2) for different time periods up to 30 min. (c) 2005 Elsevier Ltd. All rights reserved.

Study of synthesis variables in the nanocrystal growth behavior of tin oxide processed by controlled hydrolysis

Tin dioxide nanoparticle suspensions were synthesized at room temperature by the hydrolysis reaction of tin chloride (II) dissolved in ethanol. The effect of the initial tin (II) ion concentration, in the ethanolic solution, on the mean particle size of the nanoparticles was studied. The Sn2+ concentration was varied from 0.0025 to 0.1 M, and all other synthesis parameters were kept fixed. Moreover, an investigation of the effect of agglomeration on the nanoparticle characteristics (i.e., size and morphology) was also done by modifying the pH of the SnO2 suspensions. The different samples were characterized by transmission electron microscopy, optical absorption spectroscopy in the ultraviolet range, and photoluminescence measurements. The results show that higher initial ion concentrations and agglomeration lead to larger nanoparticles. The concentration effect is explained by enhanced growth due to a higher supersaturation of the liquid medium. However, it was observed that the agglomeration of the nanoparticles in suspension induce coarsening by the oriented-attachment mechanism.

SAXS study of the kinetics of formation of ZnO colloidal suspensions

We have investigated, by in situ small-angle X-ray scattering (SAXS), the kinetics of formation of zinc oxide colloidal suspensions obtained after refluxing alcoholic solution of zinc acetate and catalysed by lithium hydroxide. The experimental results demonstrate that the suspensions are composed of colloidal spheroidal particles with a multimodal size distribution. The average radius of the main mode, approximately 2 nm, is invariant but the number of these basic particles continuously increases for increasing hydrolysis reaction time. The other two modes correspond to particles with average radii close to 6 and 10 nm, respectively. The larger particles are formed by coagulation of the smaller ones. (C) 1999 Elsevier B.V. B.V. All rights reserved.

APPLICATIONS OF ARTIFICIAL-INTELLIGENCE IN ORGANIC-CHEMISTRY .17. NEW PROGRAMS IN THE SISTEMAT PROJECT

This work describes the new improvements of the SISTEMAT project, one system for structural elucidation mainly in the field of Natural Products Chemistry. Some examples of the resolution of problems using C-13 Nuclear Magnetic Resonance and Mass Spectroscopy are given. Programs to discover new heuristic rules for structure generation are discussed. The data base contains about 10000 C-13 NMR spectra.

The chemistry of enaminones, diazocarbonyls and small rings: our contribution

After thirty two years in Brazil and retired from Universidade Estadual de Campinas the author wishes to present this account, a summary of a large part of the research in synthetic methodology developed by the research groups of Albert J. Kascheres and the author at Universidade Estadual de Campinas Chemistry Institute. Contributions have been made to the area of enaminones, diazocarbonyls, cyclopropenones and azirines.