Journal of the Brazilian Chemical Society

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List of Papers (Total 1,297)

Synthesis, characterization and molecular structures of the pyridinium trans-Bis(pyridine)tetrachlororuthenate(III) and pyridinium trans-(carbonyl)(pyridine)tetrachlororuthenate(III)

The pyHtrans-RuCl4(py)2(1) and pyHtrans-RuCl4(CO)(py)(2) complexes were synthesized and found to crystallize in space group P21/n, Z = 4 with a = 8.080(7), b = 22.503(7), c = 10.125(6) Å, b = 93.19(6)° for (1) and a = 7.821(1), b = 10.337(3), c = 19.763(3) Å, b = 93.07(1)° for (2). The structures were solved by Patterson and difference Fourier techniques and refined to R = 0.062...

The effect of annulation upon the solvatochromic behaviour of related merocyanines

The effect of annulation of the donor and/or the acceptor ring fragments of related merocyanines is discussed with the aid of a theoretical model based on semiempirical calculations performed with the AM1 method. The theoretical expectations are validated with examples of eight solvatochromic dyes described in the literature.

Determination of iron in alkaline salts by ICP-AES using 1-(2-Thiazolylazo)-p-cresol (TAC) for preconcentration and separation

The present paper describes the use of 1-(2-thiazolylazo)-p-cresol (TAC) for separation, preconcentration and determination of iron traces (ng g-1) in alkaline salts by the ICP-AES technique. The proposed method is based on the liquid-liquid extraction of the complex formed between iron(III) and 1-(2-thiazolylazo)-p-cresol (TAC). Parameters such as: TAC amount, pH effect...

A HF/CI-SD study of the low-lying states of nitroprusside ion

Since the discovering of two photoexcited metastable states of crystalline sodium nitroprusside, Na2Fe(CN)5NO.2H2O (SNP), showing rather long lifetimes at temperatures below 160 K, much effort has been devoted toward the study of its electronic structure. Despite this tremendous effort the nature of the frontier orbitals and the related low energy excitations remains...

Equilibrium studies of ternary complexes formed by bromide, sulfate, selenite and selenate ions with Zn2+, Mg2+ and 1, 4, 7, 13, 16, 19-hexaaza- 10, 22- dioxacyclotetracosane (obisdien)

Bromide, sulfate, selenite and selenate were found to form bridges in the cavity of mononuclear and binuclear Obisdien:Zn(II) and Obisdien:Mg(II) complexes in aqueous solution at 25.0 °C and m = 0.100 M (KCl). Potentiometric equilibrium measurements were used to determine the formation constants of the species formed in these systems in the pH range 2-12. For the Obisdien: Zn2...

On the Nb(V) electrochemistry in "dry

The Nb(V) reduction in acetonitrile, containing up to 10 mM residual water, was investigated as a function of chloride and Nb(V) concentrations. The effect caused by hydrogen chloride and a proton donor was also examined. Before any electron transfer occurs NbCl5 initially hydrolyzes resulting in HCl and hydroxy-species, all being in equilibrium. Nb(IV) formed after a...

Synthesis of acyclic insect pheromones from cycloalkanones via acetylenic lactones

Figure 1 describes a general method for the preparation of insect pheromones. Several members of the title compounds, along with their geometric and/or positional isomers, have been prepared from Z-lactones 2a-d, which are easily available from the corresponding acetylenic lactones 1a-d, prepared earlier from cycloalkanones. The Z to E isomerization of alkenyl acetates 6a-d to 8a...

Deposition of colloidal hematite onto mercury from water-ethanol mixtures

The adherence of hematite (aFe2O3) particles onto mercury electrodes in water-ethanol mixtures has been studied by counting using optical microscope images. The number of attached particles, when the ethanol content is small, decreases as the ethanol concentration increases. At a mole fraction of ethanol near to 0.2, the number of particles goes through a minimum and then it...

Voltammetric response of hydrogen adsorbates on platinum in acid solutions: a possible H-adatom subsurface state

Combined potential routines involving voltammetric sweeps and potential holdings covering the H-adatom potential range were applied to Pt electrodes in different aqueous acid solutions to produce an enhancement of the "third" H-atom electrodesorption current peak at ca. 0.22 V vs. RHE. This peak can be observed for Pt electrodes of different topographies. Seemingly, the...

Synchronous-scan fluorescence and the complexation of copper (II) ions by humic substances

Two fluorescence bands were detected using synchronous-scan fluorescence on samples of terrestrially derived humic substances (lex/lem 380/398, 440/458 nm) without the addition of copper. A third band (lex/lem 502/520 nm) was detected after severe quenching of the second band (lex/lem 440/458 nm) caused by additions of copper. A more energetic band (lex/lem 333/351 nm) is present...

A comparative study of the polarographic behavior of cobalt(II), nickel(II), manganese(II), and zinc(II) in azide solutions

The electrochemical behavior of cobalt(II), nickel(II), manganese(II), and zinc(II) was studied by polarography at several azide concentrations. The reduction waves of cobalt(II) and nickel(II) exhibit a shift of the potential towards more positive values, with the increasing ligand concentration in solution. The maximum anticipation observed is 300 mV for cobalt(II) and 370 mV...

Models of the electroreduction of passive layers on cobalt

Potentiostatic current transient techniques were employed to study the electroreduction process of surface layers formed on polycrystalline cobalt in carbonate-bicarbonate ion-containing solutions. The dynamic system analysis performed using parametric identification procedures and non-linear fit routines demonstrated that data obtained under a wide variety of experimental...

An interdisciplinary approach to the electrochemistry at solid electrodes

An interdisciplinary approach to the electrochemistry at solid electrodes is presented here taking into account new basic interpretations for either phase growth or phase disruption under conditions far from equilibrium. For this purpose imaging data derived from scanning tunneling microscopy (STM) and atomic force microscopy (AFM) at different scale lengths are extremely useful...

Fine tuning of the properties of organically modified heteropolymetalates

Keggin-type" organically modified oxopolymetalates of formula [R]4[SiW11O40(SiR')2], (R=Bu4N+, R' = -C2H5, -C10H21, -CH=CH2, -CH2CH=CH2, -OH, -C6H5, -C10H7, -C6H4NH2 (o, p), -C6H4NMe2 (p), -C6H4CH=CH2, -C6H4CF3, -C6H4CH=CHC6H5) were synthesized. The oxide core presented reversible redox properties which were tuned by the choice of the organic modifier. Parallel variations of the...

On-line microwave-assisted sample decomposition for lead determination in fish slurry samples by electrothermal atomic absorption spectrometry

An on-line microwave-assisted decomposition procedure for the determination of lead in fish is proposed. 300 µL slurry and 400 µL of a 6 mol L-1 HNO3 solution were simultaneously injected, and the mixture was positioned inside a microwave oven. The decomposed sample inside the flushing solution was collected in the autosampler cup of a graphite furnace. The proposed procedure...

Essential oil in the taxonomy of Ocimum selloi benth

Chemical composition analysis of the essential oil from the leaves and flowers of two accessions of Ocimum selloi Benth, cultivated at the Federal University of Viçosa was carried out. For accession A the major component was identified as estragole and represented 94,95% and 92,54% of the oil from the leaves and flowers respectively. For accession B, the oil from the leaves and...

New Heptacoordinated Organotin(IV) Complexes Derivatives of 2,6-diacetylpyridinebis(2-furanoylhydrazone), H2dapf, and 2,6-diacetylpyridinebis(2-thenoylhydrazone), H2dapt: Crystal and Molecular Structure of [Me2Sn(Hdapt]Br.H2O

The reaction of the ligands H2dapf and H2dapt, with R4-mSnXm (m = 2, 3; R = Me, Ph and X = Cl, Br) led to the formation of eight new heptacoordinated organotin(IV) complexes, which were studied by microanalysis, IR, NMR and Mössbauer spectroscopy to investigate their structural properties. The methyl derivative [Me2Sn(Hdapt)]Br.H2O was also studied by single crystal X-ray...

The Cathodic Cleavage of the Nitrobenzoyl Group from Protected Aliphatic Amines in N,N-Dimethylformamide

The electrochemical reduction of aliphatic amines protected by the 4- and 3- nitrobenzoyl group in N,N-dimethylformamide was reported. The compounds are reduced in two cathodic steps. The first one at about -1 V vs. SCE occurs with the formation of the rather stable anion radicals, involving one electron transfer . The reduction to dianion occurs at potentials between -1.5 and -2...

Flavanones from Vernonia diffusa

From the methanolic extract of the wood of Vernonia diffusa two flavanones were isolated and identified: hesperidin and a new flavanone, 3'-methylhesperetin (homoesperetin) and sucrose, which was identified as its acetyl derivative. The homoesperetin was identified as the aglicone obtained in the hydrolysis of the new natural flavanone glycoside, homoesperetin-7-O-rutinoside...

Extraction Kinetics and Molecular Size Fractionation of Humic Substances From Two Brazilian Soils

In the present study, the extraction behaviour of humic substances (HS) from an Oxisol and a Mollisol from South Brazil, by using 0.1 and 0.5 mol L-1 NaOH and 0.15 mol L-1 neutral pyrophosphate solutions, respectively, was systematically studied. The kinetics and efficiency of HS extraction were evaluated by means of UV/Vis spectroscopy. The isolated humic acids (HA) and fulvic...

Voltammetric Behaviour of Metronidazole at Mercury Electrodes

Metronidazole is the most important drug of the group of 5-nitroimidazoles and possesses toxicity to anaerobic micro-organisms DNA being the main target for their biological action. The mechanism of biological action of metronidazole is dependent upon the nitro group reduction process. The reduction of metronidazole is pH dependent in acid medium and four electrons are involved...

Determination of Gaseous Analytes in Flow Systems: A Review

Efforts to develop flow systems for the determination of gaseous analytes in gaseous samples are critically reviewed. Although flow systems present a suitable alternative to management and processing of gaseous samples, relatively few papers dealing with this subject are found in the literature. The increased demand for determination of gaseous analytes, the advent of automated...

Xanthones and coumarins from Kielmeyera lathrophyton

Three xanthones and six coumarins were isolated from the hexane extract of the stems of Kielmeyera lathrophyton, among them two new prenylated xanthones 1,5-dihydroxy -6'-methyl -6' -(4-methyl -3-pentenyl) -pyrano(2',3':3,2) -xanthone, 1,7 -dihydroxy -6' -methyl -6' -(4 -methyl -3 -pentenyl) -pyrano(2',3':3,2) -xanthone, and two new 4 -s -butylcoumarins 7 -hydroxy -8 -(3-methyl...

A modulated differential scanning calorimetry and small-angle x-ray scattering study of the interfacial region in structured latices

The interfacial structure of poly(styrene) (PS)-poly(methyl acrylate) (PMA) structured latices has been investigated by means of modulated-temperature differential scanning calorimetry (M-TDSC) and small-angle x-ray scattering (SAXS). The differential of heat capacity, dCp/dT, signal from M-TDSC was used to quantify the weight fraction of interface in these latices. For PS-PMA...

Spectrophotometric determination of phosphorus in iron alloys employing a flow injection system

A flow-injection procedure for spectrophotometric determination of phosphorus in electrolytic iron and iron alloys is proposed. The method is based on the ammonium molybdate reaction followed by stannous chloride reduction in acidic medium. In order to circumvent the severe interference caused by the major constituents such as Fe(III) and Cr(III), a mini-column packed with AG50W...