Scielo RSS <![CDATA[Química Nova]]> http://www.scielo.br/rss.php?pid=0100-404220020002&lang=en vol. 25 num. 2 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <link>http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200001&lng=en&nrm=iso&tlng=en</link> <description/> </item> <item> <title><![CDATA[<B>The effect of temperature on the catalytic performance of iron oxide with copper and aluminum</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200002&lng=en&nrm=iso&tlng=en Aluminum and copper doped hematite was evaluated in the high temperature shift (HTS) reaction at several temperatures in order to find catalysts that can work in different operational conditions. It was found that the catalysts work in kinetic regime in the range of 300-400 ºC. Both copper and aluminum increases the activity and selectivity. Aluminum acts as textural promoter whereas copper acts as structural one. The most promising catalyst is that with both copper and aluminum which showed higher activity and selectivity than a commercial sample. This catalyst has the advantages of being non toxic and can work at low temperatures. <![CDATA[<B>Chemical durability of the Li<SUB>2</SUB>O-ZrO<SUB>2</SUB>-BaO-SiO<SUB>2 </SUB>glass-ceramic treated with acidic and basic solution</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200003&lng=en&nrm=iso&tlng=en The chemical durability of the Li2O-ZrO2-BaO-SiO2 system was examined by determination of the Vickers hardness. The dependence of hardness and of the chemical resistance with BaO addition was investigated. The experimental results indicate that the hardness increases with the BaO content. The samples surface's morphology submitted to the chemical treatment in acidic (H2SO4) and basic (KOH) solution was accompanied by scanning electron microscopy. The chemical durability of the materials with BaO showed better than the glass ceramic without this content. These materials treated with H2SO4 solution showed a preferential attack to the silica rich sites. <![CDATA[<B>Propagation of airborne fluorine contamination on groundwater and soil near fertilizer factories in Rio Grande (RS)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200004&lng=en&nrm=iso&tlng=en Fluoride concentration was determined in rainwater, ground water and soil in the zone of fertilizer industry in the city of Rio Grande. In contaminated rainwater fluorine concentration was registered up to the value of 4,4 mg.L-1. Fluorine concentration in the shallow ground water in general reflects its distribution in the atmosphere, but cannot be used as marker of atmosphere contamination in the urban area due to dissolving influence of residential effluents. The 0,01% HCl extracts from the set of surface soil samples demonstrates fluoride distribution in the zone of influence of industrial emissions, which coincides to the numerical simulation of fluorides dispersion in the air. <![CDATA[<B>Analysis of residue pesticide in tomatoes by thin layer chromatography</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200005&lng=en&nrm=iso&tlng=en Pesticide residues are determined by thin layer chromatography (TLC) using the Hill reaction as a detection method. Tomatoes samples without pesticide were fortified with atrazine, diuron, chloroxuron and metribuzin, and were applyed in silica gel plates with the help of a microsyringe. The pesticides were elued with ethyl acetate. There was no need of cleaning up because no interference was noticed. After the revelation of the plates, the diameters of the spots were measure by using a rule. The range of the determined concentration for all the pesticides was from 0.1 to1.0 ng/muL. The results obtained through TLC can be used for semi-quantitative analysis.The results obtained were compared to gas and liquid chromatography, showing good agreement between both techniques. <![CDATA[<B>Synthesis and phytotoxic activity evaluation of lactone derivatives of 2,4-dimethyl-8-oxabicyclo[3.2.1]-oct-6-en-3-one</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200006&lng=en&nrm=iso&tlng=en The alkene 2,4-dimethyl-8-oxabicyclo[3.2.1]-oct-6-en-3-one (3) was converted to 1,3,10-trimethyl-8-oxabicyclo[5.3.0]-dec-3-ene-2,9-dione (7) and 1,3-dimethyl-8-oxabicyclo[5.3.0]-dec-3-ene-2,9-dione (8) with a 55% overall yield in both cases. Lactones (7) and (8) were converted in two steps to 1,3,4-trimethyl-13-methylene-6-oxatricyclo[8.3.0.0(3,7)]-trideca-2,5,12-trione (12) (63%) and 1,3-dimethyl-13-methylene-6-oxatricycle[8.3.0.0(3,7)]-trideca-2,5,12-trione (13) (45% from 8). The effect of lactones (7), (8), (12), (13) and the intermediates (5) and (6), at the concentration of 250 mug mL-1, on the growth of Cucumis sativus L. and Sorghum bicolor L. was evaluated. The best results were observed for lactone (13) that caused 100% inhibition on the root growth of C. sativus and lactone (12) that inhibited 90% of the root growth for S. bicolor. <![CDATA[<B>Textural and structural characterization of V<SUB>2</SUB>O<SUB>5</SUB>/TiO<SUB>2</SUB> catalysts obtained by the sol-gel method</B>: <B>comparison between conventional and supercritical drying</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200007&lng=en&nrm=iso&tlng=en This work describes a modified sol-gel method for the preparation of V2O5/TiO2 catalysts. The samples have been characterized by N2 adsorption at 77K, x-ray diffractometry (XRD) and Fourier Transform Infrared (FT-IR). The surface area increases with the vanadia loading from 24 m² g-1, for pure TiO2, to 87 m² g-1 for 9wt.% of V2O5. The rutile form is predominant for pure TiO2 but became enriched with anatase phase when vanadia loading is increased. No crystalline V2O5 phase was observed in the catalysts diffractograms. Two species of surface vanadium observed by FT-IR spectroscopy a monomeric vanadyl and polymeric vanadates, the vanadyl/vanadate ratio remains practically constant. <![CDATA[<B>Supercritical fluid extraction for some carbamate insecticides in potatoes samples, with HPLC/fluorescence determination and HPLC/mass spectrometry confirmation</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200008&lng=en&nrm=iso&tlng=en Six supercritical fluid extraction (SFE) methods were tested, by varying the following operational parameters: CO2 pressure, time and temperature of extraction, type and proportion of static modifier, and Hydromatrix®/sample rate into cell. Firstly, insecticide carbamates were extracted from spiked potatoes samples (fortification level of 0,5 mg.Kg-1) by using SPE procedures, and then final extracts were analyzed HPLC/fluorescence. Good performance was observed with SFE methods that operated with values of temperature and CO2 pressure of 50 ºC and 350 bar, respectively. Best efficiency was obtained when it was used acetonitrile as a modifier (3% on the cell volume), and Hydromatrix®/sample rate of 2:1. Static time was of 1 min; total extraction time was of 35 min; dynamic extraction was performed with 15 mL of CO2, and it was used methanol (2 mL) for the dissolution of the final residue. In such conditions, pesticide recoveries varied from 72 to 94%, depending on the analyzed compound. In higher extraction temperatures, a rapid degradation was observed for some compounds, such as aldicarb and carbaryl; presence of their metabolites was further confirmed by HPLC-APCI/MS in positive mode. Detection limits for chromatographic analysis varied from 0,2 to 1,3 ng. <![CDATA[<B>Effect of ferric acetylacetonate catalyst concentration on the cure of polyurethane based on hydroxy terminated polybutadiene and isophorone diisocyanate</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200009&lng=en&nrm=iso&tlng=en The reaction between hydroxy-terminated polybutadiene and isophorone diisocyanate constitutes the base of the curing process of the most composite solid propellant used in the propulsion of solid rocket propellant. In this work, differential scanning calorimetry and viscosity measurements were used to evaluate the effect of the ferric acetylacetonate catalyst concentration on the reaction between HTBR and IPDI. These analyses show one exotherm, which shifts to lower temperatures as the catalyst concentration increases. The viscosity analyses show that the increase of temperature causes, at first, a reduction in the mixture viscosity, reaching a minimum range called gelification region (increasing the crosslinking density). <![CDATA[<B>Study of some oxoacidbasic reactions in molten NaCl in the temperature range of 1100K to 1200 K</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200010&lng=en&nrm=iso&tlng=en Equilibrium constants (K) of some oxoacidbasic reactions in molten NaCl in the temperature range of 1100K to 1200K, have been measured potentiometrically with a calcia stabilized zirconia oxide ion (O2-) indicator electrode. In molten NaCl at 1100K the pKs values (in molality scale) for HCl/H2O and HO-/H2O are respectively 11.0 ± 0.3; 1.6 ± 0.3 and the pKs for CaO is 4.3 ± 0.3. The results have been compared with those determined previously by Combes for the molten equimolar NaCl-KCl mixture and are in good agreement with literature data and gives some qualitative explanation of the comparison of oxoacidbasic properties between molten NaCl and NaCl-KCl. <![CDATA[<B>Comparative QSAR of antimicrobial hydrazides</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200011&lng=en&nrm=iso&tlng=en The comparative QSAR is a tool for validating any statistical model that seems to be reasonable in describing an interaction between a bioactive new chemical entity, BIONCE, and the biological system. In order to deeper the understanding of the relationships and the meaning of parameters within the model it is necessary some kind of lateral validation. This validation can be accomplished by chemical procedures using physicochemical organic reactions and by means of biological systems. In this paper we review some of such comparisons and also present a lateral validation between the same set of antimicrobial hydrazides acting against Saccharomyces cerevisiae yeast and Escherichia coli bacterium cells. QSARs are presented to shed light in this important way of stating that the QSAR model is not the endpoint, but the beginning. <![CDATA[<b>Chemical constituents from <i>simira glaziovii</i> (K. schum) steyerm. and <sup>1</sup>H and <sup>13</sup>C NMR assignments of ophiorine and its derivatives</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200012&lng=en&nrm=iso&tlng=en Chromatographic fractionation of bark extracts from Simira glaziovii (Rubiaceae) afforded the steroids beta-sitostenone, stigmastenone, beta-sitosterol and stigmasterol, methyl trans-4-hidroxy-3-methoxycinamate (1), the alkaloids harmane (2) and the new stereoisomer of ophiorine B (3). The structures were established by ¹H and 13C NMR, including 2D techniques and mass spectral analysis, of the natural products and pentaacetyllyalosidic acid (4a) and beta-carboline monoterpene tetraacetylglucoside (5, 1,22-lactamlyaloside) derivatives obtained by chemical transformations. <![CDATA[<B>Employment of factorial design for optimization of pirolisys and atomization temperatures for Al, Cd, Mo and Pb determination by ETAAS</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200013&lng=en&nrm=iso&tlng=en This work describes a factorial design for the optimization of pyrolysis and atomization temperatures in ETAAS. As examples, Cd and Pb were determined using lower pyrolysis and atomization temperatures and Al and Mo with higher pyrolysis and atomization temperatures. Good results were obtained for Cd employing Rh (m o = 1.4 pg) as a permanent modifier with pyrolysis and atomization temperatures of 640 and 1500 °C, respectively. For Zr, W or Zr+W, the Cd pyrolysis and atomization temperatures were 500 and 1500 °C, respectively, with m o = 1.4 pg using Zr or W and 1.5 pg using Zr+W. The best results for Pb were those using Rh, Zr, W and Zr+Rh, obtaining characteristic masses of 42, 37, 34 and 36 pg, respectively. Pyrolysis and atomization temperatures of 910 and 1850 °C, respectively, were achieved for this metal. For Al, the best results were obtained when Zr or Zr+W were used. Mo was also tested as a possible permanent modifier for Al, but the results were not satisfactory. The results obtained for Mo without modifier were similar to those with conventional modifiers (Mg or Pd+Mg) and the results obtained using permanent chemical modifiers were not satisfactory. In all situations, the experiments were performed faster than those using the univariate procedure. <![CDATA[<B>Use of reagent in suspension in flow injection analysis</B>: <B>spectrophotometric determination of sulphate in natural water</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200014&lng=en&nrm=iso&tlng=en This paper presents an automatic procedure employing a reagent in the form of a slurry in a flow-injection system. The feasibility of the proposal is demonstrated by sulphate determination in water using the Barium Chloranilate method, which is based on the precipitation of barium sulphate. The release of a stoichiometric amount of highly colored chloranilic ions is monitored at 528 nm. The reaction is carried out in alcoholic medium in order to reduce the solubility of the reagent. A considerable improvement in the sensitivity is attained by adding ferric ions to the released chloranilic ions. An on-line filtration step to separate the excess reagent from the released chloranilic ions was necessary. In addition, a column containing a cation exchange resin was included in the manifold to remove potentially interfering ions. The proposed procedure is suitable for 30 determinations per hour and the relative standard deviation is less than 2%. The analytical curve is linear between 0.0 and 40 mg L-1 and the determination limit is about 2.0 mg L-1SO4(2-). Accuracy was confirmed by running several samples already analysed by a standard turbidimetric procedure. <![CDATA[<B>Atmospheric chemistry of sulfur (IV)</B>: <B>emissions, aqueous phase reactions and environmental effects</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200015&lng=en&nrm=iso&tlng=en The oxidation process of sulfur(IV) species by oxygen, ozone and nitrogen oxides, catalysed by trace metal ions, can play an important role in atmospheric chemistry processes like acid rain, visibility degradation and health hazard. An overview of the more relevant investigations on emissions sources, aqueous phase conversion process and environmental impact is presented. <![CDATA[<B>The <I>Copaifera</I> L. genus</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200016&lng=en&nrm=iso&tlng=en This review details the history, chemistry and pharmacology of the Copaifera L. genus (Leguminosae - Caesalpinoideae), including copaiba oils. <![CDATA[<B>Materials for cathodes of secondary lithium batteries</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200017&lng=en&nrm=iso&tlng=en In this work, cathodes employed in secondary lithium batteries are reviewed. These cathodes have great technologic and scientific importance, specifically, materials for cathodes as electronic conductor polymers (ECP), transition metal oxides (TMO) and nanocomposites of ECP/TMO. The use of a specific cathodic material is based in some intrinsic characteristics that improve the performance of the battery. Thus, some vantages and disvantages of these insertion compounds are discussed, as lithium insertion capacity, energy density, and the ciclability of these materials. <![CDATA[<B>Reduction of amides by boranes</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200018&lng=en&nrm=iso&tlng=en Despite the fact that boranes are frequently used in amide reductions, the reaction mechanisms of the involved are note well known. This work presents the results of a bibliographic search on probable amide reduction mechanisms and an analysis of the existing literature. Steric and electronic effects were considered in light of reactivity since it could be concluded that the formation of intermediates and products depends mainly on the substitution patterns of both the boron and nitrogen atoms. Otherwise, results described in the literature for the reactions of boranes, sodium borohydride, lithium aluminum hydride, alkylboranes or haloboranes with others functional groups such as carboxylic acids, esters, ketones and alkenes were analysed with the aim to obtain something about the N-substituted amide reactions employing boranes. <![CDATA[<B>Recycling of copper from an automated analyzer of carbon and nitrogen</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200019&lng=en&nrm=iso&tlng=en Isotopic and elemental analysis of N, C and S in liquid and solid samples has been simplified with the advent of automated systems. The simplest method of automation for this kind of analysis involves an elemental analyzer interfaced directly to the ion source of an IRMS (Isotope Ratio Mass Spectrometry). In the analyzer reduction system, an expressive amount of oxidized copper is generated as solid residue. This material is normally imported and the price is very high. A methodology was proposed for the recovery of metallic copper in order to recycle this reagent in the reduction system of a GC-IRMS, using the hydrogen gas in the vacuum line. Results show that it is possible to obtain a recycle of about 95 % of the initial metallic copper used in the reduction system. <![CDATA[<B>Amperometric immunosensor</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200020&lng=en&nrm=iso&tlng=en The reaction between antigen and antibody has been widely used in many strategies for the development of analytical methodology, due to its high specificity. The immuno-reaction has been successfully employed for the biosensor development. A focus on biosensor based on immunoassay coupled to amperometric transducer is presented. <![CDATA[<B>Propolis</B>: <B>100 years of research and future perspectives</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200021&lng=en&nrm=iso&tlng=en Propolis is a multifunctional material used by bees in the construction and maintenance of their hives. The chemical composition and pharmacological properties have been studied for centuries. Today they represent an important raw material for many health products and constitute a new interdisciplinary area for research. Among others they show important antimicrobial and cytotoxic activities and various pharmacological properties. This paper presents an overview of the scientific literature and patents concerning propolis. <![CDATA[<B>Variables search technique applied to gas separation</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200022&lng=en&nrm=iso&tlng=en This paper describes an experimental design technique, known as variables search, developed to expose the critical variables and screen out the irrelevant ones. It is easy to learn and use and clearly dissociates the main and interactions effects from each other. An example of air separation process by pressure swing adsorption was used to demonstrate how the variables search technique works. The phases of identification of the critical variables is shown, step by step,. <![CDATA[<B>Glassy state on the undergraduate course in chemistry (physical chemistry)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200023&lng=en&nrm=iso&tlng=en We consider the relevance of the study of the glassy state properties and the glass transition as important topics of the physical chemistry for undergraduate courses of Chemistry. Two of the most important theoretical approaches for the description of the glassy state, the thermodynamic and the kinetic models, are summarized with emphasis on the physical chemistry aspects. Examples illustrating the glass transition of some materials are also presented. <![CDATA[<B>Implications, large and small, from chemical education research for the teaching of chemistry</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200024&lng=en&nrm=iso&tlng=en Research studies in chemical education pose a communication problem for chemists. Unlike the findings from other specializations in chemistry the findings in chemical education tend to be reported in education journals that are not readily accessible to most chemists or chemistry teachers. This lecture is an attempt to remedy this gap in communication. Research studies fall into three broad categories. (i) issues related to the content of chemistry itself, that is, What content to teach? And What meaning of each topic is to be conveyed? (ii) issues related to how chemical content is taught, such as, the role of lectures, practical work, particular pedagogies, etc. and (iii) issues related to its learning, that is, learning of concepts, conceptual change, motivation, etc. Findings in each of these categories of research over the last twenty years have drawn attention to opportunities for improving the quality of chemical education in each of the levels of formal education where chemistry is taught. Sometimes the research findings seem small since they, in fact, merely diagnose the actual problem in teaching and learning. At other times, the research findings are large because they provide a solution to these problems. What remains to be done is to disseminate the findings so that appropriate teaching occurs more widely, with its consequent gains in the quality of learning. Research findings, of these small and large types will be used to illustrate the potential of research to make the practice of chemical education more effective. <![CDATA[<B>Professores Athos da Silveira Ramos e Raymundo Moniz de Aragão, dois professores de carreira profícua e brilhante na UFRJ</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422002000200025&lng=en&nrm=iso&tlng=en Research studies in chemical education pose a communication problem for chemists. Unlike the findings from other specializations in chemistry the findings in chemical education tend to be reported in education journals that are not readily accessible to most chemists or chemistry teachers. This lecture is an attempt to remedy this gap in communication. Research studies fall into three broad categories. (i) issues related to the content of chemistry itself, that is, What content to teach? And What meaning of each topic is to be conveyed? (ii) issues related to how chemical content is taught, such as, the role of lectures, practical work, particular pedagogies, etc. and (iii) issues related to its learning, that is, learning of concepts, conceptual change, motivation, etc. Findings in each of these categories of research over the last twenty years have drawn attention to opportunities for improving the quality of chemical education in each of the levels of formal education where chemistry is taught. Sometimes the research findings seem small since they, in fact, merely diagnose the actual problem in teaching and learning. At other times, the research findings are large because they provide a solution to these problems. What remains to be done is to disseminate the findings so that appropriate teaching occurs more widely, with its consequent gains in the quality of learning. Research findings, of these small and large types will be used to illustrate the potential of research to make the practice of chemical education more effective.