Interfacial concentrations of chloride and bromide in zwitterionic micelles with opposite dipoles: Experimental determination by chemical trapping and a theoretical description

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

WC-CoCr coatings sprayed by high velocity oxygen-fuel (HVOF) flame on AA7050 aluminum alloy: electrochemical behavior in 3.5% NaCl solution

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

Evaluation of the photoelectrocatalytic method for oxidizing chloride and simultaneous removal of microcystin toxins in surface waters

The production of chlorine was investigated in the photoelectrocatalytic oxidation of a chloride-containing solution using a TiO(2) thin-film electrode biased at current density from 5 to 50 mA cm(-2) and illuminated by UV light. Such parameters as chloride concentrations from 0.001 to 0.10 mol L(-1), pH 2-12, and interfering salts were varied in this study in order to determine their effect on this oxidation process. At an optimum condition this photoelectrocatalytic method can produce active chlorine at levels compatible to water disinfections processes using a chloride concentration higher than 0.010 mol L(-1) at a pH of 4 and a current density of 30 mA cm(-2). The method was successfully applied to treat surface water collected from a Brazilian river. After 150 min of photoelectrocatalytic oxidation, we obtained a 90% reduction in total organic carbon removal, a 100% removal of turbidity, a 93% decrease in colour and a chemical oxygen demand (COD) removal of around 96% (N=3). The proposed technology based on photoelectrocatalytic oxidation was also tested in treating 250 mL of a solution containing 0.05 mol L(-1) NaCl and 50 mu g L(-1) of Microcystin aeruginosa. The bacteria is completely removed after 5 min of photoelectrocatalysis following an initial rate constant removal of -0.260 min(-1), suggesting that the present method could be considered as a promising alternative to chlorine-based disinfections. (C) 2008 Elsevier Ltd. All rights reserved.

Electrochemical behavior of metallic chromium in chloride media

The electrochemical behavior of metallic chromium in aqueous solutions containing chloride ions at different pH was studied by means of open-circuit potential vs. time measurements, cyclic voltammetry and electrochemical impedance spectroscopy. The composition of the surface oxides was analyzed by XPS. For solutions with pH<3 the formation of a passive layer occurs via a dissolution/precipitation process while for pH>3 the mechanism changes. XPS analysis revealed that Cr2O3 basically constitutes the passive layer.

Morphological analysis of pits formed on Al 2024-T3 in chloride aqueous solution

It has been used a new image analysis method, based on segmentation by shape parameters, for pits morphology examination from Al 2024 aluminum-copper alloy in chloride aqueous solution. Corrosion behavior of this alloys in naturally aerated 3.5% NaCl solution has been investigated through open circuit potential measurements. Afterwards, pits have been characterized by image analysis taking density and size measurements right from corroded surfaces. Morphological investigation has been conducted for profiles, cut orthogonally from mean surface planes, and observed through light microscopy. Image analysis data could demonstrate that pits are wider than deep, evoluting for conical, quasi-conical or irregular shapes. Most pits have presented a quasi-conical morphology, but the wider ones have evoluted to an irregular shape influenced by sub-surface microstructure. Image analysis based on shape segmentation could enhance the differences on morphological behavior. (C) 2004 Elsevier B.V. All rights reserved.

Aggregation behaviour of hydrophobically modified poly(allylammonium) chloride

The behaviour of hydrophobically modified poly(allylammonium) chloride having octyl, decyl, dodecyl and hexadecyl side chains has been studied in aqueous solution using fluorescence emission techniques. Micropolarity studies using the I-1/I-3 ratio of the vibronic bands of pyrene show that the formation of hydrophobic microdomains depends on both the length of the side chain and the polymer concentration. The I-1/I-3 ratio of the polymers with low hydrophobe content (less than 5% mel) changes substantially when reaching a certain concentration. These changes are assigned to aggregation originating from interchain interactions. This behaviour is also confirmed by the behaviour of the monomer/excimer emission intensities of pyrene- dodecanoic acid used as a probe. For polymers having dodecyl side chains and hydrophobe contents higher than 10%, aggregates are formed independently of the polymer concentration. Anisotropy measurements show that microdomains resulting from the inter- and/or intramolecular interactions are similar to those observed for cationic surfactants. Viscosity measurements show that the coil dimensions are substantially decreased for the polymers having high hydrophobe contents, indicating intramolecular associations.

Solid-state and solution structural study of acetylacetone-modified tin(IV) chloride used as a precursor of SnO2 nanoparticles prepared by a sol-gel route

The effect of addition of different amounts of acetylacetone (acacH) on the species formed at room temperature and after thermohydrolysis at 70 degreesC for 30 and 120 min of ethanolic SnCl4.5H(2)O solutions is followed by EXAFS spectroscopy at the Sn K-edge. We show that thermohydrolyzed solutions are a mixture of SnO2 nanoparticles and soluble tin polynuclear species. The complexation of the tin molecular precursors by acetylacetonate ligands is evidenced by H-1, C-13, and Sn-119 NMR spectroscopy and EXAFS for a acacH/Sn ratio higher than 2. Single crystals are isolated from solution and the structure, determined by X-ray diffraction, is built up from monomeric Cl-3(H2O)Sn(acac)-H2O units bridged together by hydrogen bonding. The acacH/Sn ratio in solution controls the polycondensation of the hydrolyzed species but not the crystallite size of the SnO2 nanoparticles (similar to2 nm). Because of the major presence of chelated tin mono- and dimeric complexes in solution for acacH/Sn > 2, the condensation is almost inhibited, meanwhile the decrease of amount of chelated complexes for the acacH/Sn < 2 gives rise to an increase of the number of nanoparticles.

Synthesis and structural characterization of dichlorobis (1-phenyl-3-methylpyrazole) palladium(II) and diazidobis (1-phenyl-3-methylpyrazole) palladiium(II)

Mononuclear pyrazolyl Pd(II) complexes of the type [PdX2(phmPz)(2)] (X = Cl-, N-3(-)) have been prepared. The 1-phenyl-3-methylpyrazole displaces acetonitrile from [PdCl2(CH3CN)(2)] to form [PdCl2(PhMPz)(2)] (phmPz = 1-phenyl-3-methylpyrazole) (1). [Pd(N-3)(2)(PhmPz)(2)] (2) could be obtained by metathesis from [PdCl2(CH3CN)(2)] or by substitution of the chloride in (1) by the azide ion. Both complexes were characterized by elemental analysis, infrared spectroscopy, H-1 and C-13 NMR and by single crystal X-ray diffraction. The coordination geometry around Pd(II) in these complexes is nearly square-planar, with the ligands in a trans configuration.

Factors which affect the catalytic activity of iron(III) meso tetrakis(2,6-dichlorophenyl)porphyrin chloride in homogeneous system

An optimization study of the reaction conditions of Fe(TDCPP)Cl when it is used as catalyst in the hydroxylation of cyclohexane by iodosylbenzene (PhIO) has been carried out, It was found that Fe(TDCPP)Cl follows the classical PhIO mechanism described for Fe(TPP)Cl, which involves the monomeric active species Fe-IV(O)P-+. (I). In the optimized condition ([Fe(TDCPP) = 3.0 X 10(-4) mol l(-1) in 1,2-dichloroethane (DCE); ultrasound stirring at 0 degrees C; PhIO/FeP molar ratio = 100), this FeP led to a yield of cyclohexanol (C-ol) of 96% and a turnover number of 96, Therefore, Fe(TDCPP)Cl may be considered a good biomimetic model and a very stable, resistant and selective catalyst, which yields C-ol as the sole product. DCE showed to be a better solvent than dichloromethane (DCM), 1 DCE:1 MeOH mixture or acetonitrile (ACN). Since the Fe-IV(O)P-+. is capable of abstracting hydrogen atom from DCM, MeOH or ACN, the solvent competes with the substrate. Presence of O-2 lowers the yield of C-ol, as it can further oxidize this alcohol to carboxylic acid in the presence of radicals, Presence of H2O also causes a decrease in the yield, since it converts the active species I into Fe-IV(OH)P, which cannot oxidize cyclohexane. Addition of excess imidazole or OH- to the system results in a decrease in the yield of C-ol, due to the formation of the hexacoordinated complexes Fe(TDCPP)Im(2)(+) (low-spin, beta(2) = 2.5 X 10(8) mol(-2) l(2)) and Fe(TDCPP)(OH)(2)(-) (high-spin, beta(2) = 6.3 X 10(7) mol(-2) l(2)), the formation of both Fe(TDCPP)Im(2)(+) and Fe(TDCPP)(OH)(2)(-) complexes were confirmed by EPR studies. The catalytic activities of Fe(TDCPP)C and Fe(TFPP)Cl were compared, the unusually high yields of C-ol with Fe(TFPP)Cl obtained when ultrasound, DCM and O-2 atmosphere were used, suggest that a parallel mechanism involving the mu-oxo dimer form, O-2 and radicals may also be occurring with this FeP, besides the PhIO mechanism.

Indirect determination of chloride and sulfate ions in alcohol fuel by capillary electrophoresis

A capillary zone electrophoresis method using indirect UV detection for the analysis of chloride and sulfate in alcohol fuel samples was developed. The anions were analyzed in less than 3 min using an electrolyte containing 10 mmol 1(-1) chromate and 0.75 mmol 1(-1) hexamethonium bromide (HMB) as electroosmotic flow modifier. Coefficients of variation were better than 0.6% for migration time (n = 10) and between 2.05 and 2.82% for peak area repeatabilities. Analytical curves of peak area versus concentration in the range of 0.065-0.65 mg kg(-1) for chloride and 0.25-4.0 mg kg(-1) for sulfate were linear with coefficients of correlation higher than 0.9996. The limits of detection for sulfate and chloride were 0.033 and 0.041 mg kg(-1), respectively. Recovery values ranged from 85 to 103%. The method was successfully applied for the quantification of sulfate and chloride in five alcohol fuel samples. The concentration of sulfate varied from 0.45 to 3.12 mg kg(-1). Chloride concentrations were below the method's LOD.

Rheological study of the thermoreversible sol-gel transition of sulfate modified zirconyl chloride aqueous sol

The sols prepared by mixing a ZrOCl2 acidified solution to a hot H2SO4 aqueous solutions were studied in order to clarify the mechanism of thermoreversible sol-gel transition observed in this system. The viscoelastic properties of these suspensions were analyzed during the sol-gel transition by dynamic rheological measurements and quasi-elastic light scattering. The rheological properties were correlated to mass fractal and nearly linear growth models, and percolation theory. The results evidence that the thermoreversible sol-gel transition in this system is due to the formation of a network of physically linked aggregates having fractal structure. The decrease of the SO42- contents in the initial solution leads to the decrease of the fractal dimensionality from 2.3 to 1.8, indicating a change of the kinetic mechanism of aggregate growth. Near the gel point these samples have the typical scaling expected from percolation theory. (C) 2004 Elsevier B.V. All rights reserved.

2,3-Dihydrobenzofuran neolignans from Aristolochia pubescens

From a hexane extract of stems and roots of Aristolochia pubescens, the new neolignans (2S,3S,1'R,2'R)- and (2S,3S, 1'S,2'R)-2,3-dihydro-5-(1',2'-dihydroxypropyl)-2-(4-hydroxy-3-methylbenzofuran) and (2S,3S,1'R,2'R)- and (2S,3S,1'S,2'R)-2,3-dihydro-5-(1',2'-dihydroxypropyl)-2-(3,4-dimethoxyphenyl)-7-methoxy-3-methyl-benzofuran were isolated, together with the known neolignan licarin A, and its bisnor-neolignan aldehyde and acid derivatives. In addition, sitosterol, 8R,9R-oxide-beta-caryophyllene, kobusone, ent-kauran-16 alpha, 17-diol, vanillin, vanillic acid, (+)-sesamin, (+)eudesmin, and (-)-cubebin were isolated. The structures of the new compounds have been elucidated by spectroscopic methods and by chemical transformation using Mosher's acid chloride. (C) 1999 Elsevier B.V. Ltd. All rights reserved.

Effects of the magnesium and chloride ions and shikimate on the structure of shikimate kinase from Mycobacterium tuberculosis

Bacteria, fungi and plants can convert carbohydrate and phosphoenolpyruvate into chorismate, which is the precursor of various aromatic compounds. The seven enzymes of the shikimate pathway are responsible for this conversion. Shikimate kinase (SK) is the fifth enzyme in this pathway and converts shikimate to shikimate-3-phosphate. In this work, the conformational changes that occur on binding of shikimate, magnesium and chloride ions to SK from Mycobacterium tuberculosis (MtSK) are described. It was observed that both ions and shikimate influence the conformation of residues of the active site of MtSK. Magnesium influences the conformation of the shikimate hydroxyl groups and the position of the side chains of some of the residues of the active site. Chloride seems to influence the affinity of ADP and its position in the active site and the opening length of the LID domain. Shikimate binding causes a closing of the LID domain and also seems to influence the crystallographic packing of SK. The results shown here could be useful for understanding the catalytic mechanism of SK and the role of ions in the activity of this protein.

Electrochemical Behavior of Cu-9% Al-5% Ni-2% Mn Alloy in Chloride Media

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)