Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> http://www.scielo.br/rss.php?pid=0103-505320150008&lang=pt vol. 26 num. 8 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Synthesis of 4-Arylselanylpyrazoles Through Cyclocondensation Reaction Using Glycerol as Solvent]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801533&lng=pt&nrm=iso&tlng=pt <p>We describe here a simple method to synthesize 4-arylselanylpyrazoles by reaction of α-arylselanyl-1,3-diketones with arylhydrazines using glycerol as solvent at 60 °C under N2 atmosphere. This is a direct cyclocondensation reaction performed with α-arylselanyl-1,3-diketones and arylhydrazines bearing electron-withdrawing and electron-donating groups affording the corresponding 4-arylselanylpyrazoles in moderate to good yields.</p> <![CDATA[Metal-Modified Mesoporous Silicate (MCM-41) Material: Preparation, Characterization and Applications as an Adsorbent]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801542&lng=pt&nrm=iso&tlng=pt <p>Mesoporous silicate (MCM-41) materials, modified with Cu<sup>II</sup>, Fe<sup>III</sup> or Al<sup>III</sup> were prepared by a hydrothermal method and were characterized by nitrogen adsorption at 77 K, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR), adsorption of pyridine as monitored by Fourier transform infrared spectroscopy (FTIR) and <italic>n</italic>-butylamine titration. The degree of ordering of the mesoporous material was decreased by the presence of Cu, Fe, or Al. The added Fe or Cu gave rise to new acidic and oxidation-reduction sites, while Al resulted in new acidic sites. The hydrothermal stabilities of selected samples were studied as a function of temperature and pH. All the samples were stable in acidic and neutral media at temperatures from 303 to 363 K. Adsorption of phenol on MCM-41 at 303 K was strongly influenced by the pH and by the modification with Cu, Fe, or Al. Phenol adsorption was particularly strong at the Al-modified material at pH 3, apparently due to the acidic character of phenol.</p> <![CDATA[Selective Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bimetallic Cu-Ni Catalysts Supported on γ-Al2O3]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801551&lng=pt&nrm=iso&tlng=pt <p>A series of Cu or Ni monometallic and Cu-Ni bimetallic catalysts supported on γ-Al<sub>2</sub>O<sub>3</sub> were synthesized by incipient wetness impregnation method. X-ray diffraction results exhibited the formation of bimetallic Cu-Ni phase in the reduced Cu-Ni(1:1)/γ-Al<sub>2</sub>O<sub>3</sub> catalyst. Among the catalyst examined for hydrogenolysis of glycerol, bimetallic catalysts exhibited higher catalytic activity than monometallic catalysts due to synergetic effect of Cu-Ni bimetal. Cu-Ni(1:1)/γ-Al<sub>2</sub>O<sub>3</sub> catalyst displayed a maximum glycerol conversion of 71.6% with 92.8% selectivity to 1,2-propanediol at 210 °C and 4.5 MPa hydrogen pressure. The superior performance of Cu-Ni(1:1)/γ-Al<sub>2</sub>O<sub>3</sub> catalyst was attributed to the formation of bimetallic Cu-Ni phase, high active metal surface area, small Cu-Ni particle size, and high acidic strength of the catalyst. Stability and reusability of Cu-Ni(1:1)/γ-Al<sub>2</sub>O<sub>3</sub> catalyst was performed and detailed characterization results of fresh and used catalysts suggested that bimetallic Cu-Ni phase remained stable after reuses.</p> <![CDATA[New Terpenoids from Croton limae (Euphorbiaceae)]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801565&lng=pt&nrm=iso&tlng=pt <p>An asymmetrical dimer of kaurane diterpene and monoterpene and four novel diterpenes were isolated from the roots of <italic>Croton limae</italic>, along with kaempferol-3-<italic>O</italic>-glucoside, ombuin- 3-O-rutinoside and acetyl aleuritolic acid. The cytotoxic activity of the kaurane diterpene was evaluated against colorectal adenocarcinoma (HCT-116), ovarian carcinoma (OVCAR-8) and glioma (SF-295) cell lines, exhibiting IC<sub>50</sub> values of 7.14, 8.19 and &gt; 10 µg mL<sup>−1</sup>, respectively.</p> <![CDATA[A Fast Chromatographic Method for Determination of Daidzein and Genistein in Spiked Water River Samples Using Multivariate Curve Resolution]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801573&lng=pt&nrm=iso&tlng=pt <p>This work reports the development of a fast chromatographic methodology for quantitation of two phytoestrogens: daidzein (DAI), and genistein (GEN), in river water samples. The proposed method is based on high performance liquid chromatography-diode array detection (HPLC-DAD) data, and multivariate curve resolution-alternative least square (MCR-ALS) second-order calibration. Initially, the method was evaluated analyzing a synthetic validation set; prepared based on a Taguchi design. Subsequently, the method was applied to predict the concentration of the phytoestrogens in spiked river water samples, previously pre-processed by solid phase extraction (SPE). By implementation of the present chromatographic methodology, a 50% reduction in operation time was achieved (from 7.00 to 3.25 min) when compared with previous work in the literature. Precision was achieved even in the presence of non-modeled constituents and strong background. Thus, the proposed method is a rapid and robust alternative for the quantitation of studied phytoestrogens.</p> <![CDATA[Maleic Anhydride as a Compatibilizer and Plasticizer in TPS/PLA Blends]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801583&lng=pt&nrm=iso&tlng=pt <p>In recent decades, starch has been studied as a raw material due to low production costs. The limitations associated with starch being highly permeable to water vapor and its mechanical properties being dependent on the relative humidity have been investigated. The proprieties of thermoplastic starch/poly(lactic acid) (TPS/PLA) blends have been studied by researchers, as well as the incorporation of compatibilizers to improve the interfacial interaction between the blend components. The purpose of this study was to evaluate the effect of maleic anhydride (MA) as a compatibilizer and a plasticizer. The blends were prepared in a torque rheometer through different mixture processes. Blends prepared with grafted MA showed interfacial adhesion and small domains of PLA in the TPS matrix, due to the use of MA as a compatibilizer. The presence of free MA in the TPS/PLA blends affected the mechanical and thermal properties, suggesting a plasticizer effect.</p> <![CDATA[Palladium Nanoparticles Supported on Poly(<italic>N</italic>-vinylpyrrolidone)-Grafted Silica as an Efficient Catalyst for Copper-Free Sonogashira and Suzuki Cross-Coupling Reactions]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801591&lng=pt&nrm=iso&tlng=pt <p>Palladium catalyst based on polyvinylpyrrolidone-silica hybrid support was prepared and exhibited excellent activity and stability in copper, amine and phosphine-free Sonogashira-Hagihara and Suzuki-Miyaura cross-coupling reactions. The polymeric catalyst was applied efficiently in the coupling reactions of chloro (as well as iodo) and bromoarenes. Elemental analysis of Pd by inductively coupled plasma (ICP) and hot filtration test revealed low leaching of the metal into solution from the supported system. The catalyst could be reused many times in repeated cycles without significant decline in its activity.</p> <![CDATA[Urinary Excretion Profile of Luteinizing Hormone in Brazilian Athletes]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801599&lng=pt&nrm=iso&tlng=pt <p>Luteinizing hormone (LH) can be used by athletes as an alternative way to take illicit advantage of androgenic effects, since it stimulates the secretion of testosterone by the Leydig cells. As consequence, LH use is illegal for male athletes and the hormone is included in the World Anti-Doping Agency (WADA) prohibited list. Since LH is an endogenous substance, the strategy used to allow the detection of LH abuse was the establishment of a reference value. All analyses were developed by IMMULITE<sup>®</sup>, which was submitted to a complete validation performance with urine. The hormone showed to be stable at 4 °C and -20 °C for at least 40 days and for 10 days at room temperature and unstable after the second cycle of freezing and thawing. The reference population of male Brazilian athletes showed a cut-off value of 37.4 mIU mL-1. The results indicate the assay is suitable for application in doping control analysis.</p> <![CDATA[Surface Modification and Spectroscopic Characterization of TiO<sub>2</sub> Nanoparticles with 2-Aminoethyl Dihydrogen Phosphate]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801608&lng=pt&nrm=iso&tlng=pt <p>A common strategy for the surface modification of nano TiO<sub>2</sub> and other metal oxide nanoparticles is based on anchor groups using chelating ligands that can carry additional functionalities. This would allow the exploration of further applications of these materials. In the present work, we report the modification of TiO<sub>2</sub> nanoparticles from nano TiO<sub>2</sub> (Degussa P-25) dispersion in distilled water in the presence of 2-aminoethyl dihydrogen phosphate, followed by removing the excess of the capping agent through washing with water. The surface functionalization and the kind of surface interaction were analyzed applying different characterization methods like CHN elemental analysis, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), attenuated total reflectance (ATR-FTIR), X-ray powder diffraction (XRD) and <sup>1</sup>H, <sup>13</sup>C, <sup>31</sup>P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), confirming the presence of modifying agent on the surface. In the study of modified nano TiO<sub>2</sub> by MAS NMR spectroscopy, a distinct downfield shift for <sup>31</sup>P signal has been seen comparing to the pure cappping agent due to P-O-Ti bond formation. The phosphate groups interact with the surface via quite strong covalent interaction, while according the analyses results, the surface amine groups remained uncoordinated.</p> <![CDATA[Chromatographic and Calculation Methods for Analysis of the Lipophilicity of Newly Synthesized Thiosemicarbazides and their Cyclic Analogues 1,2,4-Triazol-3-thiones]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801617&lng=pt&nrm=iso&tlng=pt <p>This paper describes the evaluation of the lipophilicity of newly synthesized thiosemicarbazides and their cyclic analogues 1,2,4-triazol-3-thiones obtained using experimental and calculated methods. Previous studies have shown these compounds have antibacterial activity. The chromatographic behavior of analyzed compounds was studied by reversed phase high performance liquid chromatography (RP-HPLC) and reversed phase thin layer chromatography (RP-TLC). The aqueous mobile phases containing methanol were used in order to determine retention parameter (R<sub>M</sub>) and capacity factors (log k) of analyzed compounds. The lipophilicity parameters were obtained by linear extrapolation and they were compared with the calculated log P obtained using several software packages. The results indicate that both experimental chromatographic methods yielded similar results, and these methods are appropriate for determining the lipophilicity of analyzed compounds. High values of correlation coefficients between the log P values calculated using known algorithms (milogP, ALOGPs, AClogP, AlogP, MLOGP, KOWWIN, XLOGP2, XLOGP3) and the experimental data were obtained. Eight standard solutes with known log P<sub>OW</sub> were analyzed under the same conditions as the tested substances in order to determine the log P<sub>HPLC</sub> and log P<sub>TLC</sub>parameters. A good correlation was obtained between log k<sub>w</sub> (or R<sub>MW</sub>) and the slope. All tested compounds were in agreement with the rule of five claims by Lipiński. The calculated log P values were experimentally confirmed (log P<sub>HPLC</sub> and log P<sub>TLC</sub>).</p> <![CDATA[Synthesis of Triacetin and Evaluation on Motor]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801625&lng=pt&nrm=iso&tlng=pt <p>Triacetin (or glycerol triacetate) was obtained by acetylating the glycerol by-product of biodiesel production process. This procedure is an interesting alternative that follows the principles of green chemistry. In this work, triacetin was synthesized using reactions between glycerol and acetic acid, as well as glycerol and acetic anhydride, using homogeneous and heterogeneous acid catalysis. The goal is to use this product as an additive for biodiesel produced from palm oil, which is a fuel with physical properties that require improvement. The products were characterized by Fourier transform infrared spectroscopy (FTIR), <sup>13</sup>C nuclear magnetic resonance (NMR) and gas chromatography (GC). The reaction between glycerol and acetic anhydride was the most effective for obtaining the desired product, with an approximate selectivity of 98% for triacetin. The triacetin was added to diesel fuel oil and biodiesel in proportions from 5 to 10% v/v, and the mixtures were tested in an electrical generator. In the test, the engine showed no problems during operation, and incorporating the mixtures did not result in significant consumption. Small reductions were detected in CO, O<sub>2</sub> and opacity, but no changes were observed in the emissions of NO<sub>x</sub> and CO<sub>2</sub>.</p> <![CDATA[Non-Enzymatic Amperometric Determination of Glucose by CuO Nanobelt Graphene Composite Modified Glassy Carbon Electrode]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801632&lng=pt&nrm=iso&tlng=pt <p>We have successfully developed for the first time an electrochemical sensor for glucose by using a simple and effective design of growing CuO nanobelts graphene composites (CuO@G). The as prepared composites were characterized by X-ray diffraction studies (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The prepared composite material exhibits higher electrocatalytic activity for the oxidation of glucose compared to chemically reduced graphene (C rGO) and bare CuO nanobelts. The optimized protocol has linearity with current response for glucose concentration in the range 0.5-6.5 μmol L<sup>−1</sup> and detection limits were found to be 0.05 μmol L<sup>−1</sup> (3σ). The method exhibits good reproducibility and selectivity towards glucose in the presence of other electro active compounds that are normally present in blood serum like dopamine, ascorbic acid, uric acid and sodium chloride. The protocol has been successfully applied for glucose determination in clinic human blood serum samples.</p> <![CDATA[Separation and Preconcentration of Trace Amounts of Lead from Water Samples Using Solvent-Assisted Dispersive Solid Phase Extraction]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801642&lng=pt&nrm=iso&tlng=pt <p>This paper describes a new approach for the preconcentration of lead (Pb<sup>2+</sup>) by solventassisted dispersive solid phase extraction (SADSPE) prior to analyzing by flame atomic absorption spectrometry (FAAS). In this method, the dispersion of the sorbent was achieved by injecting a solution of the sorbent into the aqueous sample. Thereby, a cloudy solution formed. The cloudy state resulted from the dispersion of the fine particles of the sorbent in the bulk aqueous sample. Pb ions reacted with 1-(2-pyridylazo)-2-naphthole (PAN) as chelating agent to form a hydrophobic complex. After extraction, phase separation was performed by centrifugation and as a result, the enriched analyte in this demented phase could be determined by FAAS. Some parameters that influenced solvent-assisted dispersive solid phase extraction and subsequent determination were evaluated in detail. Under optimized conditions (pH 9, PAN concentration: 1.0 × 10<sup>-3</sup> mol L<sup>-1</sup>, sorbent: 0.1% m/v 1,4-dichlorobenzene, disperser solvent: 0.5 mL ethanol), a preconcentration factor of 50 could be obtained, and the limit of detection (LOD) for lead was 1.3 μg L<sup>-1</sup>. Relative standard deviation for ten replicate determinations of the standard solution containing 20 μg L<sup>-1</sup> lead was 5.0%. The proposed method was successfully applied for the determination of lead in water samples with satisfactory results.</p> <![CDATA[Spurious Phosphorus Pyramidalization Induced by Some DFT Functionals]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801648&lng=pt&nrm=iso&tlng=pt <p>The molecular geometries of boraphosphabenzene (BP-benzene) and boron phosphorus coronene (BP-coronene) can be misinterpreted when they are obtained from density functional theory (DFT) calculations. In this study, we found that some exchange-correlation (XC) functionals yielded a distorted geometry of the above molecules when P atoms are present in their resonance structures. This phosphorus pyramidalization may be due to spurious errors caused by using these functionals. To verify this behavior, the electronic structures of BP-benzene and BP-coronene were studied using sixteen functionals (B3LYP, B97D, BHLYP, BP96, PBE, PBE0, PWLDA, Slater-Dirac-exchange, TPSS, M05, M06, M062X, M08HX, M11, wB97 and wB97X-D) with the SVP or TZVPP basis sets. The calculations were carried out using the TURBOMOLE and GAMESS programs. The geometry optimization calculations were carried out for each functional using both of the basis sets. Two different initial geometries, plane (D<sub>3h</sub> symmetry) and distorted (C1 symmetry) were considered. The optimized geometries of the BP-systems obtained at the MP2/TZVPP and CC2/TZVPP levels of theory exhibited D<sub>3h</sub> symmetry. These calculations were used as a reference and compared with those obtained from DFT. The optimized geometries obtained from DFT were found to exhibit C<sub>1</sub> symmetry for the majority of the XC functionals.</p> <![CDATA[The Inhibition of Sodium Oleate for Pitting Corrosion of Aluminum Alloy 2024 in 0.1 mol L<sup>-1</sup> NaCl Solution]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801656&lng=pt&nrm=iso&tlng=pt <p>The inhibition mechanism of sodium oleate (C<sub>17</sub>H<sub>33</sub>COONa) for pitting corrosion of aluminum alloy (AA) 2024 in 0.1 mol L<sup>-1</sup> NaCl solution was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy with energy dispersive spectrometer (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). C<sub>17</sub>H<sub>33</sub>COONa showed good inhibition effect on uniform corrosion of AA2024 in 0.1 mol L<sup>-1</sup> NaCl solution by promoting surface passivity of aluminum alloy. But in NaCl solution with high concentration (3.5 wt.% NaCl), C<sub>17</sub>H<sub>33</sub>COONa could not promote passivity of aluminum alloy. C<sub>17</sub>H<sub>33</sub>COONa also suppressed the tendency of pitting initiation and reduced the pitting corrosion sensitivity of aluminum alloy. The addition of 0.1 g L<sup>-1</sup> C<sub>17</sub>H<sub>33</sub>COONa showed good inhibition performance but further concentration increase had little effect on the inhibition efficiency. The C<sub>17</sub>H<sub>33</sub>COO− groups adsorbed on the surface of aluminum alloy by chemical adsorption effect, which promoted oxidation of the aluminum alloy surface.</p> <![CDATA[Characterization and Distribution of Pyrogenic Carbon in a Fraction of Archaeological Black Earth from Caxiuanã]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801664&lng=pt&nrm=iso&tlng=pt <p>This study aims to determine the atomic ratio of O/C in an archaeological black earth (ABE) profile of the Ilha de Terra site, a region of Caxiuanã in the Pará State, Brazil, to determine the types of pyrogenic carbon (PyC) particles and to infer the source of biomass and burning temperature necessary to produce the PyC. The O/C ratios were monitored using scanning electron microscopy combined with energy dispersive spectroscopy (SEM/EDS). The results indicated atomic ratios for clay, silt and fine sand fractions that were between those registered for the PyC particles types: condensed combustion (CC) (0.09, 0.1, 0.13), charcoal (0.32, 0.31, 0.34) and char (0.43, 0.45, 0.52). CC is the predominant type of particle found because of the high firing temperature (&gt; 350 °C), which is consistent with the probable biomass sources of wood, cellulose and lignin.</p> <![CDATA[Simultaneous Determination of Environmental Contaminants with Different Volatilities in Tap Water Samples Using a New Approach to Single-Drop Microextraction Procedure]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801674&lng=pt&nrm=iso&tlng=pt <p>A new single-drop microextraction approach is proposed for the extraction of compounds with a wide range of volatilities from tap water samples with separation/detection by gas chromatographymass spectrometry. This new microextraction mode is called direct immersion-headspace-single drop microextraction (DI-HS-SDME). Trihalomethanes (THMs), hydrocarbons with low molecular weight (benzene, ethyl benzene and xylenes) and polycyclic aromatic hydrocarbons (PAHs) were the model compounds. Ten milliliters of tap water samples and drop volume of 1.5 µL of 1-octanol were used. The optimal condition for DI-HS-SDME mode was 80 min of total extraction time (48 min at 40 °C in DI-SDME mode and 32 min at 12 °C in HS-SDME mode) and the addition of 1.2 g of NaCl. The analytical figures of merit were evaluated, the limits of detection ranged from 0.03 µg L<sup>-1</sup> for o-xylene and ethyl benzene to 6 µg L<sup>-1</sup> for THMs. The proposed method represents a promising alternative for the analysis of aqueous matrices which contain compounds with very different ranges of volatility.</p> <![CDATA[Simultaneous Determination of Catecholamines and Metanephrines in Urine by Liquid Chromatography Electrospray Ionization Tandem Mass Spectrometry: Successful Clinical Application]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801684&lng=pt&nrm=iso&tlng=pt <p>Determination of urinary catecholamines and metanephrines is important for diagnosis of pheochromocytoma. Liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed for the determination of catecholamines and metanephrines in human urine using deuterated internal standards (IS). In this method, 1000 µL of urine samples were treated by liquid-liquid extraction using ethyl acetate and subjected to LC-MS/MS analysis using positive electrospray ionization (ESI+). A BDS HYPERSILTM C18 column (125 mm × 3 mm, 3 µm) was used and mobile phase was water:methanol (98:2, v/v) with 0.25% of formic acid at 200 µ L min<sup>−1</sup>. The method has a chromatographic running time of approximately 10 min. The average of recovery was 92.9-106.1% for epinephrine, 94.6-107.7% for norepinephrine, 98.0-108.8% the dopamine, 94.2-105.1% the metanephrine, 97.0-106.0% for normetanephrine. The precision was lower than 7.0% for all analytes. Furthermore, this method has been implemented successfully in routine laboratory due to its easy execution and excellent precision.</p> <![CDATA[Bulk Atmospheric Deposition of Major Ions and Dissolved Organic Nitrogen in the Lower Course of a Tropical River Basin, Southern Bahia, Brazil]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801692&lng=pt&nrm=iso&tlng=pt <p>Major ionic constituents (Cl<sup>–</sup>, Na<sup>+</sup>, K<sup>+</sup>, Mg<sup>2+</sup>, Ca<sup>2+</sup>, NH<sub>4</sub><sup>+</sup>, NO<sub>3</sub><sup>–</sup>, SO<sub>4</sub><sup>2–</sup>) and dissolved organic nitrogen were determined, from September 2009 to January 2010, in bulk atmospheric deposition in the lower course of Cachoeira River, southern Bahia, Brazil, where studies on this theme are still absent. The high fluxes of Na+, Mg2+ and Cl– observed in the innermost sampling site evidence the continuity of marine influence in the atmosphere of the city of Itabuna. Concentrations of H<sup>+</sup>, Ca<sup>2+</sup>, SO<sub>4</sub><sup>2–</sup> and NO<sub>3</sub><sup>–</sup> denoted non-marine anthropogenic sources. The contributions of dissolved organic and inorganic nitrogen were different between the evaluated sites. This region is still subject to little impact by anthropogenic emissions compared to other urban areas in Brazil, according to estimates of atmospheric fluxes of SO<sub>4</sub><sup>2–</sup>, NO<sub>3</sub><sup>–</sup> and NH<sub>4</sub><sup>+</sup>.</p> <![CDATA[A Computational Protein Structure Refinement of the Yeast Acetohydroxyacid Synthase]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801702&lng=pt&nrm=iso&tlng=pt <p>A combined molecular modeling and molecular dynamics simulation was carried out to obtain an improved description of the yeast acetohydroxyacid synthase (AHAS) in aqueous solution. After a thorough homology modeling, the AHAS catalytic dimer was subjected to a molecular dynamics (MD) simulation to analyze its behavior and optimize its geometry. The AHAS 3D molecular structure was analyzed according to the number of salt bridges and hydrogen bonds formed. During 20 ns of MD simulation, an average fluctuation of 3.9 Å was obtained. The cofactor thiamine diphosphate makes a relevant contribution to the system stability; this hypothesis was confirmed by the decrease in the average fluctuation of 0.3 Å. Moreover, the Ramachandran plot revealed no denaturation framework during the time of the simulation.</p> <![CDATA[CuO Nanofibers Immobilized on Paraffin-Impregnated Graphite Electrode and its Application in the Amperometric Detection of Glucose]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801710&lng=pt&nrm=iso&tlng=pt <p>1-D nanostructures are promising materials for development of electrochemical devices offering benefits such as fast electron transfer rates and large surface areas. Copper oxide nanofibers (CuO-NFs) synthesized by electrospinning technique and subsequent thermal treatment, were used to modify paraffin-impregnated graphite electrode (PIGE) for a sensitive non-enzymatic glucose detection. The structure and morphology of CuO-NFs were characterized by scanning electron microscopy and transmission electron microscopy. The electrocatalytic activity towards glucose oxidation was evaluated by cyclic voltammetry and chronoamperometry. The results reveal a wide linear response to glucose ranging from 1.0 × 10<sup>-6</sup> to 1.93 × 10<sup>-3</sup>mol L<sup>-1</sup> (R<sup>2</sup> = 0.9927). The limit of detection was 0.39 × 10<sup>-6</sup> mol L<sup>-1</sup> (LOD = 3σ/s). The high aspect ratio of the nanofibers arranged in a three-dimensional network structure significantly enhances the electron transfer process. The electrode preparation is simple and rapid execution, and more importantly the graphite rod is relative low-cost and easy to achieve surface renewal for reusability.</p> <![CDATA[Influence of the Lipid Phase Removal on the Quantification of Cu, Fe and Zn Bound to Proteins from Golden Flaxseed (<italic>Linum usitatissimum L</italic>.)]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801718&lng=pt&nrm=iso&tlng=pt <p>The analysis of metals bound to proteins requires careful sample preparation. Experimental procedures involved in this area should be developed aiming to retain the metal species bound to the protein structure. Some pre-fractionation steps are commonly used and in many cases it is necessary to disrupt the lipid-protein interaction by performing lipid removal before protein extraction. This paper presents a systematic investigation on the influence of using hexane, chloroform and methanol neat or in sequence to remove the lipid fraction in golden flaxseed (<italic>Linum usitatissimum L.</italic>), before extracting the protein phase using Tris-HCl buffer solution for analysis of Cu, Fe and Zn bound to proteins. The results showed that the organic solvent used has a strong influence on the determination of these metals. With hexane, the total protein content and Cu, Fe and Zn concentrations in Tris-HCl phase were higher than those found using methanol:chloroform (1:2 v/v).</p> <![CDATA[Dinor Casearin X, a New Cytotoxic Clerodane Diterpene from <italic>Casearia sylvestris</italic>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801725&lng=pt&nrm=iso&tlng=pt <p>A new clerodane-type diterpene, named dinor casearin X, and four known casearins (A, B, G and J) were isolated from leaves of <italic>Casearia sylvestris</italic>(Salicaceae). These compounds were evaluated for cytotoxic activity against five human cancer cell lines (A2058, HL-60, HCT, MCF-7 and HeLa) as well as against a murine melanoma cell line (B16F10-Nex2). Among these compounds, dinor casearin X exhibited the highest cytotoxic activity against HL-60 cells with IC<sub>50</sub> of 0.51 ± 0.11 µg mL<sup>-1</sup>, whereas casearin A exhibited the highest cytotoxic activity against HCT cells (IC<sub>50</sub> 1.84 ± 0.14 µg mL<sup>-1</sup>).</p> <![CDATA[Multivariate Analysis of Perfumes by Ultraviolet Spectrophotometry]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801730&lng=pt&nrm=iso&tlng=pt <p>An efficient, fast and cost-effective method for detecting adulteration in perfumes by UV spectroscopy and multivariate analysis is proposed. Classification of perfumes, either as original or fake, was accomplished with the spectroscopic data using chemometric techniques such as principal component analysis (PCA), soft independent modeling of class analogy (SIMCA) and linear discriminant analysis (LDA).</p> <![CDATA[Prediction of Phase Separation Using a Modified Regular Solution Theory and the SMD Continuum Solvation Model]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000801737&lng=pt&nrm=iso&tlng=pt <p>It is proposed a new expression for the β parameter in the regular solution theory, using the solvation free energy concept instead of the solubility parameter. This modified regular solution theory can be applied for any liquid mixture combined with any method for solvation free energy calculation. The new approach was tested in fifteen liquid mixtures using the solvation model density (SMD) continuum solvation model and has successfully predicted the phase behavior, with exception of water-acetonitrile mixture. This flaw can be attributed to the microheterogeneity of this system. The main advantage of the present approach is a fast prediction of phase separation.</p>