Photo-Fenton degradation of the herbicide tebuthiuron under solar irradiation: Iron complexation and initial intermediates

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

Effect of iron on inhibition of acid demineralisation of bovine dental enamel in vitro

Objectives: Iron ions (Fe2+) have been shown to be cariostatic in many studies particularly by their ability to reduce bacterial metabolism. Nevertheless, the role of iron ions on dissolution of enamel is unexplored. The aim of the present study was therefore to investigate the protective effect of increasing concentrations (0-120 mmol/L) of Fe2+ on the dissolution of enamel.Design: Enamel powder was subjected to acetic acid made with increasing concentrations with respect to FeSO4 center dot 7H(2)O. In order to determine the amount of enamel dissolved, the phosphate released in the medium was analysed spectrophotometrically using the Fiske-Subarrow method. Data were tested using Kruskall-Wall and Dunn's tests (p < 0.05). The degree of protection was found to approach maximum at about 15 mmol/L Fe2+. Higher concentrations of Fe2+ did not have an extra effect on inhibition of dissolution of enamel powder. In the next step, the protective effect of 15 mmol/L Fe2+ against mineral dissolution of the bovine enamel was evaluated using a simple abiotic model system. Enamel blocks were exposed to a sequence of seven plastic vials, each containing 1 mL of 10 mmol/L acetic acid. The acid in vial 4 was made 15 mmol/L with respect to FeSO4 center dot 7H(2)O. The mineral dissolved during each challenge was thus determined by phosphate released as described above. Data were tested using two-way ANOVA (p < 0.05). Results: Lower demineralisation (around 45%) was found in vial 4 (with Fe) that continued stable until vial 7.Conclusions: Thus, our data suggest that Fe2+, can be effective on inhibition of dissolution of enamel and that this effect may be durable. (c) 2006 Elsevier Ltd. All rights reserved.

Novel SrTi1-xFexO3 nanocubes synthesized by microwave-assisted hydrothermal method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Estudo da preparação de nanocompósitos magneto-luminescentes unidimensionais baseados em telúrio

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Síntese e caracterização de ferritas de manganês e zinco visando aplicação como agente de contraste em diagnóstico médico

This work aims to synthesize the manganese and zinc ferrite, by the polymeric precursor method, in order to obtain materials with appropriate characteristics for the application in medical diagnosis techniques. The manganese and zinc ferrite powders with the composition of Mn(1-x)ZnxFe2O4, where x=0,23, were prepared and calcined in air at different times and temperatures. The X-ray diffraction (XRD) data show that the sample calcined at 400°C crystallize as ferrite (monophase), but in an inverted spinel structure (high content of iron occupying manganese tetrahedral site and manganese occupying the iron octahedral site). The samples calcined at temperatures between 600°C and 900°C shows the secondary phase of hematite and the sample calcined at 1100oC shows to be monophase in ferrite with normal spinel structure. The monophase powders of ferrite showed a reduction in the surface area and an increasing in the pore size for higher calcination temperatures. The magnetic analysis show that the sample calcined at 400°C presents satisfactory magnetization at room temperature, however, it behaves as diamagnetic material at low temperatures (10K). The powder containing hematite, without the partial substitution of iron ions by manganese, showed to have low transition temperature, and consequently low magnetization at room temperature. The hematite, when partially substituted, provides materials with irregular magnetization at the saturation region. The powder calcined at 1100°C shows high magnetization either at room temperature or low temperature (10K)

Exploiting Distinct Molecular Architectures of Ultrathin Films Made with Iron Phthalocyanine for Sensing

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

Preconcentration and determination of metal ions in commercial ethanol used as fuel for automotive engines

The present investigation reports the synthesis, characterization, and adsorption properties of a new nanomaterial based on organomodified silsesquioxane nanocages. The adsorption isotherms for CuCl,, CoCl2, ZnCl2, NiCl2, and FeCl3 from ethanol solutions were performed by using the batchwise method. The equilibrium condition is reached very quickly (3 min), indicating that the adsorption sites are well exposed. The results obtained in the flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 2 g of the nanomaterial, using 5 mL of 1.0 mol L-1 HCl solution as eluent. The sorption-desorption of the metal ions made possible the development of a method for preconcentration and determination of metal ions at trace level in commercial ethanol, used as fuel for car engines. The values determined by recommended method for plants 1, 2, and 3 indicated an amount of copper of 51, 60, and 78 mu g L-1, and of iron of 2, 15, and 13 mu g L-1, respectively. These values are very close to those determined by conventional analytical methods. Thus, these similar values demonstrated the accuracy of the determination by recommended method.

Determination of copper, iron, nickel and zinc in gasoline by FAAS after sorption and preconcentration on silica modified with 2-aminotiazole groups

Silica gel chemically modified with 2-aminotiazole groups (SiAT), was used for preconcentration of cupper, zinc, nickel and iron from gasoline, normally used as a engine fuel. Surface characteristics and surface area of the silica gel were obtained before and after chemical modification using FT-IR, Kjeldhal and surface area analysis (B.E.T.). The retention and recovery of the analyte elements were studied by applying batch and column techniques. The experimental parameters, such as shaking time in batch technique, flow rate and concentration of the eluent (HCl-0.25-2.00 mol 1(-1)) and the amount of silica, on retention and elution, have been investigated. Detection limits of the method for cupper, iron, nickel and zinc are 0.8, 3, 2 and 0.1 mug 1(-1), respectively. The sorption-desorption of the studied metal ions made possible the development of a preconcentration method for metal ions at trace level in gasoline using flame AAS for their quantification. (C) 2004 Published by Elsevier Ltd.

Synthesis, characterization and thermal behaviour on solid tartrates of some bivalent metal ions

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

Determination of Copper, Iron, Nickel and Zinc in fuel kerosene by FAAS after adsorption and pre-concentration on 2-aminothiazole-modified silica gel

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

The effects of copper ions on the synthesis of periplasmic and membrane proteins in Acidithiobaeillus ferrooxidans as analyzed by SDS-PAGE and 2D-PAGE

The effects of 200 mM copper ions on the synthesis of membrane and periplasmic proteins were investigated in iron-grown cells of Acidithiobacillus ferrooxidans (At. ferrooxidans). Total membrane protein profiles of cells grown in the absence of copper ions (unadapted cells) and in the presence of copper ions (copper-adapted cells) were compared by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Crude preparations of outer membrane and periplasmic proteins were analyzed by SDS-PAGE. The synthesis of proteins was diminished or increased in the presence of copper ions. Low molecular weight proteins (< 14 kDa) were significantly repressed by copper. These proteins are probably acidic proteins located in the outer membrane. An over-expression of a periplasmic protein of about 17 kDa was detected in the copper-adapted cells and was assumed to be rusticyanin, a 16.5-kDa periplasmic copper protein present in At. ferrooxidans cells and involved in the electron-transport chain of the iron oxidation pathway. To our knowledge, this is the first report of a possible involvement of the rusticyanin and outer membrane proteins in the mechanism of copper resistance in At. ferrooxidans. (C) 2003 Elsevier B.V. All rights reserved.

Small-angle X-ray scattering and X-ray absorption near-edge structure study of iron-doped siloxane-polyoxyethylene nanocomposites

The local and medium-range structures of siloxane-POE hybrids doped with Fe(III) ions and prepared by the sol-gel process were investigated by X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) and small-angle X-ray scattering (SAXS), respectively. The experimental results show that the structure of these composites depends on the doping level. EXAFS data reveal that, for low doping levels ([O]/[Fe] > 40, oxygens being of the ether-type of the POE chains), Fe(III) ions are surrounded essentially by a shell of chlorine atoms, suggesting the formation of FeCl4- anions. At high doping levels ([O]/[Fe] < 20), Fe(III) ions interacts mainly with oxygen atoms and form FeOx species. The relative proportion of FeOx species increases with iron concentration, this result being consistent with the results of SAXS measurements showing that increasing iron doping induces the formation of iron-rich nanodomains embedded in the polymer matrix.

Characterization of iron(III)porphyrin-hydroxo complexes in organic media through UV-Vis and EPR spectroscopies

The interaction of OH- with Fe(TPP)(+), Fe(TDCPP)(+), Fe(TMP)(+) and Fe(TFPP)(+) in 1,2-dichloroethane was studied by titrating FeP solutions with aliquots of a solution of tetrabutylammonium hydroxide in acetonitrile. The number of OH- ions (n) coordinated to the FeP and the stability constants (beta(n)) for the FeP-OH- complexes were calculated from UV-Vis absorbance data and iron spin states were determined through EPR spectroscopy, Fe(TMP) (+) forms a high-spin mono-hydroxo complex, while Fe(TPP)I and Fe(TDCPP)(+) form high-spin bis-hydroxo complexes. To our knowledge, this is the first time that the formation of bis-hydroxo complexes from Fe(TPP) (+) has been reported, and this was possible because the studies were carried out in basic organic media, In this same medium, Fe-III-Fe-II reduction upon OH- addition to Fe(TFPP) (+) was observed, without concomitant formation of the mu-oxo dimeric species [Fe(TFPP)](2)O. (C) 1999 Elsevier B.V., All rights reserved.

Effect of presence of an acid catalyst on structure and properties of iron-doped siloxane-polyoxyethylene nanocomposites prepared by sol-gel

In this work we investigate the effect of hydrochloric acid (HC) addition on the structure and thermal and magnetic properties of iron-doped siloxane-polyoxyethylene (POE) hybrids prepared by the sol-gel route. X-ray powder diffraction (XRD) and X-ray absorption near edge structure (XANES) results reveal the dominance of ferrihydrite nanoparticles and a mixture of this phase with FeCl4- species in the hybrid prepared without and with HCl, respectively. Thermal analysis reveals the existence of two crystalline polymeric phases in the hybrid prepared with HCl whereas hybrids prepared without HCl are amorphous. The 105 and 60 Angstrom sized ferrihydrite nanoparticles were detected by SAXS analysis of the composite prepared without and with HCl, respectively. The magnetic results suggest that in both samples antiferromagnetic nanoparticles coexist with small clusters/isolated ions. In the sample without HCl addition, larger particles dominate the magnetic behavior, while the opposite occurs for the sample prepared using HCl catalyst. (C) 2004 Elsevier B.V. All rights reserved.

Thermal investigation of solid 2-methoxycinnamylidenepyruvate of some bivalent transition metal ions

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