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Wavelet-Based determination of Cu and Pb in water samples using potentiometric stripping analysis with a Lab-Made potentiostatEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This paper demonstrates the possibility of simultaneously determining lead and copper in mineral, river and tap water by potentiometric stripping analysis using a low-cost lab-made potentiostat and a wavelet-based signal processing method. Pb(II) and Cu(II) concentrations were found to be in the range 3-7 µg L-1. Relative standard deviations were on average smaller than 3%, which is satisfactory in view of the trace concentration. For comparison, the determination was also carried out by using a high-end commercial equipment (μAutolab Type II, Eco Chemie). The average and standard deviation of the results were similar to...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

In vitro effect of silver nanoparticles on creatine kinase activityEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
One of the most prominent nanoproducts is the silver nanoparticle (AgN), since silver ions exhibit remarkably unusual physical, chemical and biological properties. Creatine kinase (CK) plays a central role in metabolism of high-energy consuming tissues such as brain, skeletal muscle and heart, where it functions as an effective buffering system of cellular ATP levels. A decrease of CK activity may impair energy homeostasis, contributing to cell death. In the present work we studied the in vitro effect of AgN on the activity of CK from rat brain, heart and skeletal muscle. Our results demonstrated that AgN (10, 25 and 50 mg...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Photochemical Dissolved Gaseous Mercury (DGM) formation/consumption in the Negro River Basin, brazilian AmazonEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Dissolved gaseous mercury (DGM) formation/consumption was measured during several scientific excursions in the Negro River basin, Amazon, Brazil. Measurements were carried out following diel patterns in both white and black water bodies. In white waters, with pH values around 7 and low dissolved organic carbon (DOC) concentration, mercury saturation prevails during the sunlit period, similar to behavior observed elsewhere. This was attributed to DGM generated by a photoinduced mechanism of Hg2+ reduction. On the other hand, in black waters, with pH around 5 and high DOC values (up to 20 mg L-1), DGM concentration stays bel...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

DIADORIM: a Monte Carlo Program for liquid simulations including quantum mechanics and molecular mechanics (QM/MM) facilities: applications to liquid ethanolEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This paper presents a Metropolis Monte Carlo (MMC) computer program developed to simulate liquids and solutions including QM/MM facilities: the energy from intermolecular interactions is calculated with classical force field functions and the internal molecular energies are calculated using Quantum Chemistry methods. The following facilities were implemented: (i) the semiempirical MOPAC 6 quantum chemistry package was included as a subroutine of the main MMC simulation program; (ii) alternatively, an interface with an external data bank was developed to allow the use of energies previously obtained; (iii) calculation in Np...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Micelle-mediated extraction and determination of tin in soft drink and water samplesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A micelle-mediated phase preconcentration of trace quantities of Sn(IV) as a prior step to its determination by spectrophotometry has been developed, based on cloud point extraction (CPE) of the complex of Sn(IV) with pyrocatechol violet complex in surfactant media. Pyrocatechol violet (PCV) and cetyltrimethylammonium bromide (CTAB) were used as chelating agent and cationic surfactant, respectively. The optimal extraction and reaction conditions (e.g. surfactant concentration, reagent concentration and the effects of pH and time) were studied and the analytical characteristics of the method (e.g., limit of detection, linea...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Electrosynthesis and catalytic activity of polymer-nickel particles composite electrode materialsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Nickel-polymer composite electrode materials have been synthesized using various strategies, all comprising the electrochemical reduction of nickel(II) cations or complexes, incorporated by either ion-exchange or complexation into various poly(pyrrole-carboxylate) thin films coated by oxidative electropolymerization onto carbon electrodes. The electrocatalytic activity and the stability of the different composites have been then evaluated in the course of the electrocatalytic hydrogenation of ketones and enones in aqueous electrolytes. The best results were obtained using nickel-polymer composites synthesized by electrored...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Equilibrium, thermoanalytical and spectroscopic studies to characterize phytic acid complexes with Mn(II) and Co(II)Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Potentiometric studies were carried out to determine the binding degree of phytic acid with Co(II) and Mn(II) ions, in the absence of dioxygen. Equilibrium constants for all major complexes formed are reported, and the results are presented in the form of distribution diagrams showing the concentrations of individual complexes as a function of pH. The formation constants of the complexes show higher values for the species in which the ligand was more deprotonated. Potentiometric data indicates that the species [MH4L]6-, was totally formed at pH 7.0 and the complexes were synthesized from this data. A solid state complex of...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Tri-n-butyltin Hydride-Mediated radical reactions of ortho-and meta-Iodobenzamides to synthesize benzomacrolactams: surprising formation of biphenyl compounds from meta-regioisomersEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Reactions of methyl 4-O-allyl-2,3-di-O-benzyl-6-deoxy-6-(3-iodobenzoylamino)-α-D-galactopyranoside, its gluco epimer, methyl 2,3-di-O-benzyl-6-deoxy-6-(3-iodobenzoylamino)-4-O-(1-pentenyl)-α-D-glucopyranoside and its ortho-regioisomer with tri-n-butyltin hydride were performed in different conditions. Depending on reaction conditions the three meta-iodo isomers gave a surprising amount of biphenyl compounds. The 2-iodo isomer led only to the undesired but expected hydrogenolysis product. No cyclized products were isolated in all the reactions. The structures of the new biphenyl products were elucidated by ¹H and 13C NMR...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Electrical and magnetic properties of quaternary rare earth thiophosphate: K4Sm2[PS4]2[P2S6]Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The quaternary alkali metal, rare earth thiophosphate phase K4Sm2[PS4]2[P2S6] was synthesized by ceramic method and characterized by powder X-ray diffraction (XRD), SEM-EDX scanning electron microscope-microprobe analyses, electrochemical impedance and magnetic measurements. The crystal structure consists of layers of ²∞Sm2[PS4]2[P2S6]4- separated by K+ cations. The electrical conductivity measurements indicate that the compound is a semiconductor with a resistivity of 1.0 x10(11) Ω cm. The magnetic moment, evaluated from χ-1 versus T at low temperature is 0.57 µB.O tiofosfato quaternário de metal alcalino e terra r...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Extractive Resolution of racemic mandelic acid through a bulk liquid membrane containing binary chiral carrierEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A method of bulk liquid membrane (BLM) using complex of di(2-ethylhexyl) phosphoric acid (D2EHPA) and O,O'-dibenzoyl-(2R, 3R)-tartaric acid (L-(-)-DBTA) was developed for the extractive resolution of racemic mandelic acid (rac MA). The effects of resolution time, concentration of D2EHPA in the organic phase, concentration of rac MA in the feed phase, stirring speed and temperature on extractive resolution were studied. The experimental results have shown that the greatest separation factor (α) 2.74 and the enantiomeric excess value (ee, %) 46.47% were obtained when the resolution time was about 4 h, the molar concentratio...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Antioxidant properties of plant extracts: an EPR and DFT comparative study of the reaction with DPPH, TEMPOL and spin trap DMPOEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This work presents a comparative study of the antioxidant activity of extracts from nine plant species belonging to the Brazilian flora - Swartzia langsdorffii, Machaerium villosum, Pterogyne nitens, Pera glabrata, Aegiphyla sellowiana, Copaifera langsdorffii, Chrysophyllum inornatum, Iryanthera juruensis, Didymopanax venosum - acting on the free-radicals DPPH (2,2-diphenyl-1-picrylhydrazyl) and TEMPOL (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy-1-oxyl) by electron paramagnetic resonance (EPR), and acting on the hydroxyl radical (OH) by the spin-trapping technique generated by a Fenton reaction. Results showed that t...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Synthesis of α- and β-lapachone derivatives from hetero diels-alder trapping of alkyl and aryl o-quinone methidesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Methylene and aryl o-quinone methides (o-QMs) generated by Knoevenagel condensation of 2-hydroxy-1,4-naphthoquinone with formaldehyde and arylaldehydes, undergo facile hetero Diels-Alder reaction with some substituted styrenes (as dienophiles) in aqueous ethanol media providing derivatives of α- and β-lapachone.Foram sintetizados, em um único pote reacional, alguns derivados da α- e β-lapachonas a partir de reação de hetero Diels-Alder, em etanol aquoso, entre estirenos substituídos (como dienófilos) e o-quinonas metídeos (o-QMs) metilênicas e arílicas geradas por condensação de Knoevenagel da 2-hidróxi-1,4-...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Chemo-enzymatic epoxidation of sunflower oil methyl estersEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The chemo-enzymatic epoxidation of the methyl esters of sunflower oil with lipase from Candida antarctica B and aqueous H2O2 in the presence and absence of an acyl donor was investigated. The biphasic system (CH2Cl2/H2O) comprised Candida antarctica B lipase (CALB, 1000 u g-1) and 30% (v/v) aqueous hydrogen peroxide. In some cases the conversion was higher than 99%. The best results were obtained for the biphasic system after 16 h of reaction, at 30 ºC, using 10 mmol of octanoic acid in relation to 1 g of the oil, 6 mL of dichlomethane and 5 mL of water.Foi realizada a epoxidação quimio-enzimática de ésteres metílico...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

The UV/H2O2 - photodegradation of poly(ethyleneglycol) and model compoundsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The general mechanism for the photodegradation of polyethyleneglycol (PEG) by H2O2/UV was determined studying the photooxidation of small model molecules, like low molecular weight ethyleneglycols (tetra-, tri-, di-, and ethyleneglycol). After 30 min of irradiation the average molar mass (Mw) of the degradated PEG, analysed by GPC, fall to half of its initial value, with a concomitant increase in polydispersitivity and number of average chain scission (S), characterizing a random chain scission process yielding oligomers and smaller size ethyleneglycols. HPLC analysis of the photodegradation of the model ethyleneglycols pr...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Cadmium and lead cloud point preconcentration and determination in tobacco samples by thermospray flame furnace atomic absorption spectrometryEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A thermospray flame furnace atomic absorption spectrometer (TS-FF-AAS) was employed to determine Cd and Pb in different Brazilian tobacco samples. Sample pretreatment consisted of acid decomposition and cloud point (CP) preconcentration optimized by Doehlert design. To promote phase separation in the cloud point procedure, polyoxyethylene(8) isooctylphenyl ether (Triton® X-114) and 2-(bromo-2-pyridylazo)-5-diethyl-amino-phenol (Br-PADAP) were used as a nonionic surfactant and a complexing agent, respectively. The variables of the cloud point preconcentration procedure optimized by Doehlert design were: complexing agent vo...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Cytotoxic lipidic α-amino acids from the zoanthid Protopalythoa variabilis from the Northeastern coast of BrazilEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Two lipidic α-amino acids 1a and 1b were isolated from the zoanthid Protopalythoa variabilis using a bioguided fractionation for cytotoxic activity. The structures of the metabolites were determined by spectroscopic methods, including NMR (nuclear magnetic resonance) ¹H e 13C, IR (infrared) and high resolution mass spectrometry (positive mode). The cytotoxic activity of the crude extract, as well as of the mixture of 1a and 1b were measured in vitro using the MTT assay for four human tumor cell lines. This finding has important biological and chemical implications for this type of compound. This is the first report of li...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Lewis acid promoted Friedländer condensation reactions between anthranilonitrile and ketones for the synthesis of tacrine and its analoguesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The scope of Lewis acid-promoted cyclodehydratation reactions between anthranilonitrile and several ketones, to afford tacrine and its derivatives, was expanded to include the use of various metal chloride salts not reported in the literature. The ability of the Lewis acids to effectively promote the cyclodehydratation between anthranilonitrile and cyclohexanone as the ketone was found to be the following order: InCl3 > AlCl3 ~ BF3.Et2O > FeCl3 > BiCl3 ~ SbCl3 ~ SnCl2.2H2O. The reactions were performed under both solvent and solvent-free conditions in good to excellent yields. Other Lewis acids screened, such as RuCl3, CeC...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Different coordination modes for disulfoxides towards diorganotin(IV) dichlorides. X-ray crystal structures of 1,2-cis-bis-(phenylsulfinyl)ethene (rac-,cis-cbpse) and adducts [{Ph2SnCl2(meso-bpse)}n] and [{n-Bu2SnCl2(pdtd)}2]Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The reactions of meso-1,2-bis(phenylsulfinyl)ethane (meso-bpse) with Ph2SnCl2, 2-phenyl-1,3-dithiane trans-1-trans-3-dioxide (pdtd) with n-Bu2SnCl2 and 1,2-cis-bis-(phenylsulfinyl)ethene (rac-,cis-cbpse) with Ph2SnCl2, in 1:1 molar ratio, yielded [{Ph2SnCl2(meso-bpse)}n], [{n-Bu2SnCl2(pdtd)}2] and [{Ph2SnCl2(rac,cis-cbpse)}x] (x = 2 or n), respectively. All adducts were studied by IR, Mössbauer and 119Sn NMR spectroscopic methods, elemental analysis and single crystal X-ray diffractometry. The X-ray crystal structure of [{Ph2SnCl2(meso-bpse)}n] revealed the occurrence of infinite chains in which the tin(IV) atoms appear i...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

The asymmetric total synthesis of (+)- and (-)-trypargine via Noyori asymmetric transfer hydrogenationEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A concise and efficient total synhesis of (+)- and (-)-trypargine (6 steps and 38% overall yield), a 1-substituted β-carboline guanidine alkaloid isolated from the skin of the African frog K. senegalensis, was developed based on the construction of the β-carboline moiety via Bischler-Napieralski reaction and the enantioselective reduction of the dihydro-β-carboline intermediate via an asymmetric transfer hydrogenation reaction using Noyori's protocol.Uma síntese total e eficiente da (+) e (-)-tripargina, alcalóide β-carbolínico isolado da pele da rã africana K. Senegalensis, foi realizada em 6 etapas e 38% de rendi...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Synthesis, structural and spectral studies of five- and six-coordinate adducts of organotin(IV) halides containing dibenzylsulfoxide (dbso) as ligand. The crystal structures of fac-[MeSnCl3(dbso)2] and trans-[Ph2SnCl2(dbso)2]Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The reaction of the ambidentate ligand dibenzylsulfoxide (dbso) with Me2SnCl2 in 1:1 molar ratio leads to the formation of the five-coordinate adduct [Me2SnCl2(dbso)], whereas the same reaction conditions with Ph2SnCl2 provide the six-coordinate adduct trans-[Ph2SnCl2(dbso)2]. On the other hand, the reaction with nBu2SnCl2 forms the dimeric adduct [{nBu2SnCl2(dbso)}2], which probably possesses octahedral tin(IV) nuclei and bridging chlorides. The adducts [MeSnCl3(dbso)2] and [Ph3SnCl(dbso)] were also prepared and included in the study. All complexes were studied by microanalysis and IR, NMR (¹H, 13C and 119Sn) and Mössba...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Synthesis and structural characterization of block and random low molecular weight copolymers composed of L-lactic acid and isosorbide succinate moietiesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Isosorbide succinate moieties were incorporated into poly(L-lactide) (PLLA) backbone in order to obtain a new class of biodegradable polymer with enhanced properties. This paper describes the synthesis and characterization of four types of low molecular weight copolymers. Copolymer I was obtained from monomer mixtures of L-lactide, isosorbide, and succinic anhydride; II from oligo(L-lactide) (PLLA), isosorbide, and succinic anhydride; III from oligo(isosorbide succinate) (PIS) and L-lactide; and IV from transesterification reactions between PLLA and PIS. MALDI-TOFMS and 13C-NMR analyses gave evidence that co-oligomerizatio...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Reference concentrations for trace elements in urine for the Brazilian population based on q-ICP-MS with a simple dilute-and-shoot procedureEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Biomonitoring of trace elements is of critical importance in human health assessment. However, trace element concentrations in biological fluids are affected by environmental and physiological parameters, and therefore considerable variations can occur between specific population subgroups. Brazil is a large country with large environmental diversity and with a limited knowledge of the reference values (baseline data) for trace elements in biological fluids. Atomic absorption spectrometry (AAS) and inductively coupled plasma emission spectrometry (ICP-OES) are still the dominant analytical techniques used for biomonitoring...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Study on the interaction between doxorubicin and Deoxyribonucleic acid with the use of methylene blue as a probeEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this work, the interaction of doxorubicin with calf thymus double strand Deoxyribonucleic acid (ds-DNA) has been investigated with the use of Methylene Blue (MB) dye as a probe by the application of UV-Vis spectrophotometry, voltammetry and spectrofluorometry. The voltammetric behavior of doxorubicin has been investigated at glassy carbon electrode using differential pulse voltammetry. Doxorubicin is reduced, yielding one reduction peak. Both UV-Vis spectrophotometry and differential pulse voltammetry studies confirm the intercalation reaction. The results showed that both doxorubicin and the MB molecule could intercala...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

State-of-the-art in immobilized polymer stationary phases for high-performance liquid chromatographyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Increasing stability and reducing the high activity of residual groups from stationary phases have been the main focuses of research on the preparation of reversed-phase high-performance liquid chromatography (RP-HPLC) phases over the last four decades. New and more efficient strategies for modifying the silica surface as well as the introduction of new chromatographic supports have minimized these effects and have enabled the increasing popularization of RP-HPLC. In this paper, an overview will be given of the state-of-the-art in stationary phases for RP-HPLC based on immobilization of pre-synthesized organic polymers on ...
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Indexation, internationalization and professionalizationEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
(Source: Journal of the Brazilian Chemical Society)
Source: Journal of the Brazilian Chemical Society - November 6, 2009 Category: Chemistry Source Type: journals

Volatile constituents of five Baccharis Species from Northeastern ArgentinaEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Essential oils obtained by hydrodistillation from the aerial parts of Baccharis gaudichaudiana, B. microcephala, B. penningtonii, B. phyteumoides and B. spicata collected from different locations in Argentina were analyzed. Qualitative and quantitative analysis were performed using a GC/FID/MS system with a special configuration. Essential oil yields ranged from 0.1 to 0.2% (m/v of dry material). Different chemical patterns were observed in the essential oils composition of the species studied: spathulenol and β-pinene were the main constituents in B.gaudichaudiana, whereas caryophyllene oxide and spathulenol were the maj...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Preparation of novel trifluoroacetylketene O,N-acetals and trifluoromethyl-containing S,S-sulfoximido N-substituted heterocyclesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Two new trifluoroacetylketene O,N-acetals [CF3C(O)CH=C(OEt)(NS(O)R2), where R = CH3, Ph] derived from the reaction of 4,4-diethoxy-1,1,1-trifluorobut-3-en-2-one [CF3C(O)CH=C(OEt)2] with S,S-dimethyl- and S-methyl-S-phenyl-sulfoximide [HN=S(O)R2], in the presence of triethylamine, have been obtained, in 60-72% yields, and applied in the synthesis of S,S-dimethylsulfoximido-substituted pyrazoles, isoxazoles and pyrimidines, in 55-89% yields, from the reactions of 4-ethoxy-4-(S,S-dimethylsulfoximido)-1,1,1-trifluorobut-3-en-2-one with hydrazines, hydroxylamine hydrochloride and acetylguanidine.Este trabalho descreve a síntes...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

An easy synthesis of 3,5-disubstituted 1,2,4-oxadiazoles from carboxylic acids and arylamidoximes mediated by ethyl chloroformateEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An efficient, clean and easy high-yielding synthesis of 3,5-disubstituted 1,2,4-oxadiazoles starting from mixed anhydrides (generated from carboxylic acids and ethyl chloroformate) and arylamidoximes is described.Uma síntese limpa, fácil e eficiente de vários 1,2,4-oxadiazóis 3,5-dissubstituídos partindo de um anidrido misto (gerado a partir de um ácido carboxílico e cloroformiato de etila) e amidoxima é descrita. (Source: Journal of the Brazilian Chemical Society)
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Spark ignition vehicle contributions to atmospheric fine elemental carbon concentrations in coastal, rural and urban communities using polycyclic aromatic hydrocarbon tracers in the CMB model modified for reactivityEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We apportioned the elemental carbon (EC) component of ambient PM2.5 attributable to emissions from spark ignition (SI) vehicles in samples collected over a three-year period in twelve Southern California communities, including coastal, rural, and urban areas using the chemical mass balance model (CMB8) modified for polycyclic aromatic hydrocarbon (PAH) reactivity. Selected PAH/EC ratios, measured in samples collected in the Caldecott tunnel were evaluated for use as fingerprints. PAH reactivity which occurs during atmospheric transport and affects the source contribution estimates during the summer/fall/spring months was a...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Preparation of silver-montmorillonite nanocomposites by reduction with formaldehyde and borohydrideEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Na-rich montmorillonite (MMT) was intercalated with silver cations, which were subsequently reduced with formaldehyde or sodium borohydride. The silver-montmorillonite nanocomposites were studied by UV-visible spectrometry, transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The influence of different reducing agents on the dispersity and size of silver particles deposited on montmorillonite surface was investigated. The reduction with borohydride gives rise to uniformly dispersed silver particles with a narrow particle size distribution from 3 nm to 13 nm. Formaldehyde reduction forms unevenly dispersed...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Concentration of airbone trace metals in a bus station with a high heavy-duty diesel fractionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Total particulate matter (TSP) and PM10 samples were collected in a bus station, in the period of August 2006 to February 2007. Buses are the only significant emission sources in this area once light duty vehicles represent about 1-2% of total flux and no other activities are developed in the location. Concentrations of metals in the samples were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). Ca, Mg, Fe and Al were the most abundant elements and accounted for about 50.1%, 24.2%, 6.5% and 18.7% of the total metal content. Co, Ni, Cd, Cr and Pb were under detection limits except for a few s...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Regional geochemical baselines and controlling factors for trace metals in sediments from the Poxim River, Northeast BrazilEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The Poxim river hydrographic sub-basin comprises four freshwater rivers, Poxim-Açu, Poxim-Mirim, Poxim and Pitanga, and is located in the East of Sergipe State, Northeast of Brazil. The present work investigates the distribution, the factors controlling concentrations, and toxicity risks of the metals Co, Cr, Cu, Li, Mn, Ni, Pb, Zn, Al and Fe, in surface sediments of the four rivers. Toxicity was evaluated using the Consensus-based Sediment Quality Guidelines for freshwater ecosystems. Spearman correlation analysis did not indicate any association of the metals with organic matter, however strong, moderate and weak correl...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

A new polyacetylene from Vernonia scorpioides (Lam.) Pers. (Asteraceae) and its in vitro antitumoral activityEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The dichloromethane fraction obtained from hydroalcoholic crude extract of leaves and flowers of Vernonia scorpioides (Asteraceae) was investigated, resulting in the isolation and structure elucidation of a new polyacetylene namely 5-octa-2,4,6-triynyl-furan-2(5H)-one. The structure of the isolated compound was determined based on IR, NMR (1D and 2D) and MS spectrometric data. The antitumor potential, including cytotoxicity to tumor cells and genotoxicity, was investigated. The results suggest that apoptotic cell death may have occurred, at least in part, via a caspase-dependent mechanism.A fração diclorometano obtida pe...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

K10-montmorillonite as support for a cationic manganese(III)-salen complexEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A commercial K10-montmorillonite was used as support for the immobilization of a cationic manganese(III)-salen complex. The catalytic behavior of the resulting material was tested in the enantioselective epoxidation of three different alkenes, viz.: styrene, α-methylstyrene and 6-cyano-2,2-dimethylchromene, at 0 ºC, using three different oxidant systems: m-chloroperoxybenzoic acid (m-CPBA) and N-methylmorpholine (NMO) as co-oxidant, iodosylbenzene (PhIO) and sodium hypochlorite. All samples, before and after the catalytic studies, were characterised by nitrogen adsorption at -196 ºC, DRX, FTIR and chemical analysis, in ...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Synthesis, characterization and thermal behaviour of solid 2-methoxycinnamylidenepyruvate of light trivalent lanthanidesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Solid state Ln-2-MeO-CP compounds, where Ln stands for light trivalent lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd) and 2-MeO-CP is 2-methoxycinnamylidenepyruvate, were synthesized in this work. Simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, experimental and theoretical infrared spectroscopy and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results led to information regarding the composition and stability of the isolated complexes.Compostos Ln-2-MeO-CP no estado sólido, em que ...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Oxidative DNA damage induced by S(IV) in the presence of Cu(II) and Cu(I) complexesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The DNA damage induced by S(IV) in the presence of some Cu(II) complexes in air saturated solution was investigated. The addition of S(IV) to an air saturated solution containing CuII GGA (GGA = glycylglycyl-L-alanine), CuII G3 (G3 = triglycine) or CuII G4 (G4 = tetraglycine) and Ni(II) traces, causes rapid formation of the respective Cu(III) complex, with simultaneous O2 uptake and S(IV) oxidation. SO3- and HO were detected by EPR-spin trapping experiments. The DNA strand breaks were attributed to the oxysulfur radicals formed. In the reduction of Cu(II)/BCA (BCA = 4,4' dicarboxy-2-2'-biquinoline) by S(IV), with CuI B...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Preparation and characterization of PVA/PASA-PVA/PDDAB bipolar membraneEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Bipolar membranes (BMP) were prepared by bonding together separate anion and cation exchange membrane. For the preparation of the cation selective layer, aqueous solution of PVA [poly(vinyl alcohol)], and PASA [poly(anetholesulfonic acid sodium salt)], where the ratio of PVA/PASA was changed for the control of the membrane charge density, were cast for negatively charged membranes. These membranes were annealed at 100 ºC for 45 min and cross-linked in an aqueous solution containing 10% Na2SO4, 1.5% H2SO4, and 0.5% glutaraldehyde in order to control water content of the gel membranes. The anion selective layers were prepar...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Seasonal variability of essential oils of Eugenia uniflora leavesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Seasonal influence on the chemical composition of essential oils of Eugenia uniflora leaves with red-orange fruit colour biotype has indicated the presence of two oil clusters in the two seasons of the Brazilian Cerrado. Cluster I included samples collected during dry months (April-September) which were characterized by the highest percentages of spathulenol (10%) and caryophyllene oxide (4.1%). In cluster II, whose samples were collected during wet months (October-March), the major constituent was selina-1,3,7(11)-trien-8-one epoxide (29%). The canonical correlation indicated that spathulenol and caryophyllene oxide revea...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Synthesis, chemical reactivity and fungicidal activity of pyrido[1,2-b][1,2,4]triazine derivativesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The synthesis of some new pyrido[1,2-b][1,2,4]triazines (2-12) was achieved by cyclocondensation of 4-aryl-1,6-diamino-2-oxo-1,2-dihydropyridine-3,5-dicarbonitriles (1a, b) with α,β-bifunctional compounds. Pyrido[1,2:2´,3´]triazino[5´,6´-f]triazines (13-14) were also prepared. The behavior of 1a, b toward interactions with indole-2,3-dione and its N-acetyl analogue have been studied under different reaction conditions. The structures of the new products have been deduced from elemental analysis and spectral data (UV, IR, ¹H NMR, 13C NMR and mass spectra). The new synthesized compounds were screened for their antifun...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

CD-MEKC method to analyze triterpene acids in traditional chinese medicinesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A cyclodextrin-modified micellar electrokinetic chromatographic (CD-MEKC) method was developed to separate and determine betulinic acid (BA), oleanolic acid (OA) and ursolic acid (UA) in traditional Chinese medicines (TCMs). Three pentacyclic triterpene acids were baseline seperated in the buffer (pH 9.0) of 6% (v/v) methanol containing 10 mmol L-1 disodium tetraborate, 10 mmol L-1 sodium dihydrogen phosphate, 50 mmol L-1 sodium dodecylsulfate, 15 mmol L-1 2-hydroxypropyl-β-cyclodextrin within 15 min. The good linear relationships between the peak area and concentration were obtained in the ranges of 16.5-330 µg mL-1, 18...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Catalyst, Co-ion and the media effect on the oscillatory behavior of resorcinol in the BZ reactionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The study pertains to the oscillatory behavior of resorcinol as organic substrate in Belousov-Zhabotinsky (BZ) reaction in presence of different metal ions as catalysts in aqueous acid media. It is found that Mn2+ ion as catalyst is most reactive in comparison to ferroin (Fe2+). On varying the aqueous acid media, it is observed that protonated species with respect to organic substrate (resorcinol) is more easily formed in aqueous sulfuric acid, owing to which maximum number of oscillations are observed in this medium. Moreover, the effect of different anions like acetate, carbonate and sulfate associated with the same meta...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Oxidation of chalcogenides using the peroxo complex of molybdenum [MoO(O2)2(H2O)(hmpa)], hmpa = hexamethylphosphoramideEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This work reports the oxidation of a variety of selenides, sulfides, tellurides, selenoxides, sulfoxides and telluroxides with [MoO(O2)2(H2O)(hmpa)] [hmpa = (Me2N)3PO] in tetrahydrofuran at 65-70 ºC to produce the corresponding selenones, sulfones and tellurones in high yields.A oxidação de diversos selenetos, sulfetos, teluretos, selenóxidos, sulfóxidos e teluróxidos com o complexo [MoO(O2)2(H2O)(hmpa)] [hmpa = (Me2N)3PO] em tetraidrofurano a 65-70 ºC, para produzir as correspondentes selenonas, sulfonas e teluronas em altos rendimentos, é relatada neste trabalho. (Source: Journal of the Brazilian Chemical Society)
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Simple flow injection amperometric system for simultaneous determination of dipyrone and paracetamol in pharmaceutical formulationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this work a simple flow injection methodology with pulsed amperometric detection for simultaneous determination of dipyrone (DI) and paracetamol (PCT) in pharmaceutical formulations is described. The compounds are detected by applying four sequential potential pulses as function of the time. Dipyrone is directly detected at +0.40 V and paracetamol indirectly at 0.00 V through the reduction of the oxidation product (N-acetyl-p-benzoquinoneimine) electrochemically generated at +0.65 V. The fourth potential pulse (-0.05 V) is applied for the cleaning of the electrode surface (glassy carbon). The linear response range was o...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Multi-pumping mechanised determination of selenium in natural waters by light emitting diode (LED) spectrometryEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
It has been developed a fully mechanised procedure for the determination of selenium in waters employing a LED based spectrometer and solenoid multi-pumps as solution propelling devices. The proposed method is based on the reaction of selenium with potassium iodide in an acidic medium to liberate iodine, which oxidizes Variamine Blue to form a violet-colour species which absorb at 530 nm. The system was mechanised using the multicommutation process and a stopped flow strategy in the final step reaction. The analytical curve was linear between 0.010 and 0.500 mg L-1, with an equation ΔA = 0.501 (± 0.004) C and r = 0.999. ...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Three electrode electrochemical microfluidic cell: construction and characterizationEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This work describes the construction and characterization of an electrochemical flow-through microcell with the three electrodes (working, pseudo-reference, and auxiliary) inserted in microchannels with thickness smaller than 20 µm. These microchannels were constructed between two stacked polycarbonate slides using one or more overlapped toner masks as spacer. This strategy allows the construction of microcells with a variable internal volume on the working electrode (0.6 to 2.4 µL). Three different materials were optimized as electrodes: gold film or graphite-epoxy composite as working electrode, silver-epoxy composite ...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Dissociation of molecular aggregates under high hydrostatic pressure: the influence of water structure on Benzene cluster solubilityEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In some critical conditions water can solvate hydrophobic molecules, becoming a powerful solvent for nonpolar agents. To discuss the pressure effect on hydrated benzene clusters we carried out six consecutive 5000 ps (pico seconds) molecular dynamics simulations of benzene molecules in water cubic boxes at different pressure conditions, ranging from 1 bar to 5 kbar. Radius of gyration, diffusion coefficient, radial atomic pair distribution functions, number of hydrogen bonds between water molecules and the solvent accessible surface were monitored. Results showed that above 3 kbar the second hydration layer structure vanis...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Rapid and accurate simultaneous determination of abamectin and ivermectin in bovine milk by high performance liquid chromatography with fluorescence detectionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An analytical method using high performance liquid chromatography with fluorescence detection for the simultaneous determination of abamectin and ivermectin in bovine milk was developed and validated. The best recovery results were achieved by using acetonitrile for extraction of the compounds followed by solid phase extraction in cartridges containing C18 for the purification of the extract. Pre-column derivatization was accomplished with N-methylimidazole and trifluoroacetic anhydride. The method limit of detection (LOD) values for abamectin and ivermectin were 0.10 and 0.14 µg L-1 and the limit of quantification (LOQ) ...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Insect pheromone research in South AmericaEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Insect pheromone research has a long and rich history built up primarily by studies conducted in the Northern hemisphere. Not surprisingly, these studies have largely targeted species relevant to these regions of the world, for the most part agricultural and forest pests. Pheromone research in South American countries came a few decades behind, albeit their strong dependence in agriculture and therefore in pest management. In the last 20 years, a combination of economic, environmental and technical factors have come together to generate a small but rising number of chemical ecologists working in pheromone chemistry and bio...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Density-functional based tight-binding: an approximate DFT methodEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The DFTB method, as well as its self-consistent charge corrected variant SCC-DFTB, has widened the range of applications of fundamentally well established theoretical tools. As an approximate density-functional method, DFTB holds nearly the same accuracy, but at much lower computational costs, allowing investigation of the electronic structure of large systems which can not be exploited with conventional ab initio methods. In the present paper the fundaments of DFTB and SCC-DFTB and inclusion of London dispersion forces are reviewed. In order to show an example of the DFTB applicability, the zwitterionic equilibrium of gly...
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals

Editorial: the Centrality of ChemistryEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
(Source: Journal of the Brazilian Chemical Society)
Source: Journal of the Brazilian Chemical Society - September 5, 2009 Category: Chemistry Source Type: journals