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Química Nova, Volume: 26, Número: 5, Publicado: 2003

  • Pardini, Vera L.; Pinto, Angelo C.; Andrade, Jailson B. de

  • Determinação de compostos de massa molecular alta em folhas de plantas da Amazônia Artigo

    Siqueira, Denilson Soares de; Pereira, Alberto dos Santos; Aquino Neto, Francisco Radler de; Cabral, José Augusto; Ferreira, Carlos Alberto Cid; Simoneit, Bernd R. T.; Elias, Vladimir O.

    Resumo em Inglês:

    The fractIons of dichloromethane extracts of leaves from andiroba (Carapa guianensis - Meliaceae), caapi (Banisteriopsis caapi - Malpighiaceae), cocoa (Theobroma cacao - Sterculiaceae), Brazil nut (Bertholletia excelsa - Lecytidaceae), cupuaçu (Theobroma grandiflorum - Sterculiaceae), marupá (Simaruba amara - Simaroubaceae) and rubber tree (Hevea brasiliensis - Euphorbiaceae), were analyzed by HT-HRGC and HT-HRGC-MS. Esters of homologous series of fatty acids and long chain alcohols, phytol, amyrines and tocopherols were characterized. The characterization of the compounds was based mainly in mass spectra data and in addition by usual spectrometric data (¹H and 13C NMR, IR).

  • Constituintes químicos de Arrabidaea samydoides (Bignoniaceae) Artigo

    Pauletti, Patrícia Mendonça; Bolzani, Vanderlan da Silva; Young, Maria Claudia Marx

    Resumo em Inglês:

    Chemical investigation of Arrabidaea samydoides resulted in the isolation of the flavone chrysin; five triterpenes: lupeol, ursolic acid, 3b,16a-dihydroxy-urs-12-ene, uvaol, and erythrodiol; and two sterols: sitosterol and stigmasterol. The structures of these compounds were established by spectroscopic analysis. This paper deal with the first phytochemical study of Arrabidaea samydoides.

  • Estudo eletroanalítico do herbicida paraquat em soluções aquosas por voltametria de onda quadrada utilizando ultramicroeletrodos Artigo

    Souza, Djenaine de; Machado, Sergio A. S.

    Resumo em Inglês:

    The electrochemical behavior of paraquat on Pt, Au and carbon fiber ultramicroelectrodes were studied in laboratory samples by square wave voltammetry at high frequencies. The results showed two reversible peaks for paraquat reduction, in agreement to the literature data. The first peak was associated to the reduction of paraquat molecule in solution, with the further adsorption of the intermediate on the electrode surface. This adsorbed species undergoes to electroreduction in a reaction associated to the second voltammetric peak. The variation in pH and square wave parameters showed the best conditions to reduce paraquat as pH 5.0, frequency as high as 1000 s-1, scan increment of 2 mV and square wave amplitude of 50 mV. At such conditions, a variation of paraquat concentrations from 4.3 x 10-6 to 1.66 x 10-4 mol L-1 presented values for the detection limit equal to 3.9, 6.2 and 20.3 ppb on Pt, Au and carbon, respectively, at 1000 s-1. These values are quite below17 the allowed limit of paraquat in drinking water.

  • Estudo microestrutural do catalisador Ni/gama-Al2O3: efeito da adição de CeO2 na reforma do metano com dióxido de carbono Artigo

    Valentini, Antoninho; Probst, Luiz Fernando Dias; Carreño, Neftalí L. V.; Leite, Edson R.; Pontes, Fenelon M.; Longo, Elson; Schreiner, Wido H.; Lisboa-Filho, Paulo N.

    Resumo em Inglês:

    The carbon dioxide reforming of methane was carried out over nickel catalysts supported on the gamma-Al2O3/CeO2 system prepared by wet impregnation. With the increase of the CeO2 weight in the catalyst, a higher stability was observed in the catalytic activity, together with an excellent resistance to carbon deposition and a better Ni dispersion. The catalysts were characterized by means of surface area measurements, TPR, H2 chemisorption, XRD, SEM, EDX, XPS and TEM. An interaction between Ni and CeO2 was observed to the Ni/CeO2 sample after activation in a H2 atmosphere above 300 ºC. Such behavior has a significantly influence on the catalytic activity.

  • Síntese e avaliação da atividade fitotóxica de novos análogos oxigenados do ácido helmintospórico Artigo

    Barbosa, Luiz Cláudio de Almeida; Demuner, Antônio Jacinto; Maltha, Célia Regina Álvares; Silva, Patrícia Silvana da; Silva, Antônio Alberto da

    Resumo em Inglês:

    Several compounds related to helminthosporic acid (3) were synthesized via the [3+4] cycloaddition. The reaction of 3-hydroxymethyl-2-methylfuran (12) with 1,1,3,3-tetrabromo-4-methylpentan-2-one (13) resulted in 7-hydroxymethyl-4alpha-isopropyl-1alpha-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one (8) (37%) and 7-hydroxymethyl-2alpha-isopropyl-1alpha-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one (14) (12%), which were converted into 7-formyl-4alpha-isopropyl-1alpha-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one (16) (32% from 8) and 7-formyl-2alpha-isopropyl-1alpha-methyl-8-oxabicyclo[3.2.1]oct-6-en-3-one (18) (40% from 14), respectively. Reduction of (8) resulted in 7-hydroxymethyl-4alpha-isopropyl-1alpha-methyl-8-oxabicyclo[3.2.1]oct-6 -en-3alpha-ol (11) (63% from 8) and 7-hydroxymethyl-4alpha-isopropyl-1alpha-methyl-8-oxabicyclo[3.2.1]oct-6-en-3 beta-ol (15) (30% from 8). The 4alpha-isopropyl-1alpha-methyl-3-oxo-8-oxabicyclo[3.2.1]oct-6-en-7-oic acid (19) was obtained by oxidation of (16) (78%). The results of biological tests are described in details. The best result was observed for compound (15) that caused 76% inhibition on the root growth of D. tortuosum.

  • Determinação de As em amostras orgânicas de interesse ambiental por espectrometria de absorção atômica com atomização eletrotérmica após combustão em bomba de O2 Artigo

    Dias, Vera Maria da Costa; Satte, Maria Salete Selaimen

    Resumo em Inglês:

    The toxicity of the major As species present in the environment justifies the effort for quantifying the element in environmental organic samples, which can vary from animal and vegetal tissues to coal and industrial residues. This paper comments about the applicability of the O2 bomb digestion, as a general procedure for all environmental organic materials. A rapid and straightforward method is suggested, which consists in burning the sample in the bomb at high O2 pressure, dissolving the vapours in diluted HNO3 and determining As in the resulting solution by atomic absorption spectrometry with electrothermal atomization. The method was applied to certified materials and plant samples.

  • Novos materiais à base de nanofibras de carbono como suporte de catalisador na decomposição da hidrazina Artigo

    Vieira, Ricardo; Pham-Huu, Cuong; Keller, Nicolas; Ledoux, Marc J.

    Resumo em Inglês:

    Today satellites propulsion is based on the use of monopropellant and/or bipropellant chemical systems. The maneuvering of satellite is based on the hydrazine decomposition micropropulsors catalyzed by metallic iridium supported on g-alumina. This reaction is a surface reaction and is strongly exothermic and implies that the operation of the micropropulsor is controlled by the mass and heat diffusions. For this reason and for the fact that the propulsor operation is frequently in pulsed regime, the catalyst should support high pressure and temperature variations within a short time period. The performance and the durability of the commercial catalyst are jeopardized by the low thermal conductivity of the alumina. The low thermal conductivity of the alumina support restricts the heat diffusion and leads to the formation of hot spots on the catalyst surface causing the metal sintering and/or fractures of the support, resulting in loss of the activity and catalyst destruction. This work presents the synthesis and characterization of new carbon composite support for the active element iridium, in substitution of the commercial catalysts alumina based support. These supports are constituted of carbon nanofibers (30 to 40 nm diameter) supported on a macroscopic carbon felt. These materials present high thermal conductivity and mechanical resistance, as well as the easiness to be shaped with different macroscopic shapes. The mechanical stability and the performance of the iridium supported on the carbon composite support, evaluated in a laboratory scale test in hydrazine decomposition reaction, are superior compared to the commercial catalyst.

  • Aplicação da CLAE para determinação do ácido 10-Hidróxi-2-decenóico (10-HDA) em geléia real pura e adicionada a mel brasileiro Artigo

    Koshio, Shinnosuke; Almeida-Muradian, Ligia Bicudo de

    Resumo em Inglês:

    The aim of this paper was to determine the 10-HDA in pure royal jelly and products containing royal jelly, using HPLC methodology. 10-HDA is the natural indicator of the presence of royal jelly in products and also gives the authenticity of pure royal jelly. The chromatographic conditions used were: isocratic system, C18-H column, auto sampler, diode array UV-VIS detector (225 nm), mobile phase with methanol/water (45:55), pH= 2.5 and a-naphtol as internal standard. The results obtained using laboratory samples for pure royal jelly were 2.37%, varying from 0.15% for honey with 10% of royal jelly to 2.10% for honey with 90% of royal jelly respectivelly. For commercial products, the 10-HDA content varied from no detectable to 0.026%. The recovery test presented a minumum of 100.44% The detection limit was 45.92 ng/mL and the quantification limit was 76.53 ng/mL.

  • Filmes de titânio-silício preparados por "spin" e "dip-coating" Artigo

    Nassar, Eduardo J.; Ciuffi, Katia J.; Gonçalves, Rogéria R.; Messaddeq, Younes; Ribeiro, Sidney J. L.

    Resumo em Inglês:

    The conditions for the preparation of luminescent materials, consisting of Eu3+ ions entrapped in a titanium matrix, in the forma of a thin film, using the sol-gel process, are described. The films were obtained from sols prepared with TEOS and TEOT, in the presence of acetylacetone as the hidrolysis-retarding agent, using the dip-coating and spin-coating techniques. The influence of these techniques on the films based on titanium and silicon are presented. The Eu3+ was used as a luminescent probe. The films have been characterized by luminescence, reflection and transmittance. The thickness of the films could be related to the preparation procedure. Transparent thin films have been prepared by dip-coating technique.

  • Distribuição de compostos organoclorados nas águas e sedimentos da bacia do rio Piracicaba/SP - Brasil Artigo

    Del Grande, Marcelo; Rezende, Maria Olímpia Oliveira; Rocha, Odete

    Resumo em Inglês:

    The great utilization of synthetic and persistent xenobiotic cumulative compounds is the main causes of the deterioration of aquatic ecosystems. The one of objective of this work was the determination of the organochlorine levels in the Piracicaba river basin, situated at the center of São Paulo state. Four PCBs congeners, PCP and HCB were determined by GC-ECD in two different matrices: water and sediments. The pattern of the compound distribution indicated a dominance of PCP, HCB and PCB-200. The results indicated contamination in the sampling points located in Campinas, Piracicaba, Santa Bárbara d'Oeste and Sumaré cities.

  • Fluidos supercríticos em química analítica. II. Cromatografia com fluido supercrítico: instrumentação Revisão

    Carrilho, Emanuel; Tavares, Maria Cecília H.; Lanças, Fernando M.

    Resumo em Inglês:

    The first paper in this series discussed the basic theory involved in supercritical fluid chromatography (SFC) and how the technique progressed from gas and liquid chromatography. The first SFC instruments were simple adaptations of the commercially available liquid chromatographs with packed columns followed by modifications in gas chromatographs using open tubular capillary columns. In this paper, the most important aspects regarding instrumentation are covered, including practical, simple, and the most important, inexpensive solutions to build a home-made SFC system.

  • Métodos de preparação e atividade biológica do ácido quinolínico e derivados Revisão

    Souza, Marcus Vinícius Nora de; Almeida, Mauro Vieira de; Le Hyaric, Mireille; Cardoso, Sílvia Helena; Amarante, Giovanni Wilson

    Resumo em Inglês:

    In 1981 2,3-pyridine dicarboxylic acid (quinolinic acid) was discovery to be a selective agonist for the N-methyl -D-aspartic acid (NMDA) receptor. As a consequence it possesses neurotoxic activity resulting from overstimulation of the receptor. Quinolinic acid is implicated as an etiological factor in a range of neurodegenerative disease including AIDS related dementia, Huntington´s disease and Lyme disease. In the design of novel therapies to treat these diseases, some molecules have been identified as an important target. In this paper we described different methods to prepare quinolinic acid and derivatives.

  • Híbridos inorgânico-orgânicos derivados da reação de filossicatos com organossilanos Revisão

    Fonseca, Maria Gardênnia da; Airoldi, Claudio

    Resumo em Inglês:

    Silylation reactions involving hydroxylated surfaces are an important route for synthesis of new materials that could present selected properties, for application in different areas such as catalysis, chromatography, adsorption and electrochemistry. An overview of many synthetic routes, comprising organosilanes to yield phyllosilicates is now presented.

  • Contaminação ambiental por compostos organoestânicos Revisão

    Godoi, Ana Flavia Locateli; Favoreto, Rodrigo; Santiago-Silva, Mary

    Resumo em Inglês:

    The occurrence and the effects of organotin compounds (OTs) have been studied since a long time, due to their widespread use and deleterious effects. Some OTs are used as pesticides in crops, or as biocides in antifouling paints, applied in the ship hulls to avoid attachment and growth of tube worms, mussels and barnacles. However, "nontarget" organisms may be exposed, resulting in the poisoning of biological system, originating mutations and sentencing species to extinction. In this work we reported a revision study on the history of OTs and the techniques developed for its assessment and control.

  • Aspectos regio- e estereoquímicos da adição de Michael assimétrica via iminas quirais com centros estereogênicos pré-existentes Revisão

    Schenato, Rossana A.; Santos, Éverton M. dos; Tenius, Beatriz S. M.; Oliveira, Eduardo R. de

    Resumo em Inglês:

    The asymmetric Michael addition reactions using chiral imines, under neutral conditions (deracemizing alkylation process), constitute one of the main methods for the stereocontrolled elaboration of quaternary carbon centers. This protocol is based on the conjugate addition of secondary chiral enamines to electron-deficient alkenes. The focus of this report deals with the discussion of regio- and stereochemical aspects of the deracemizing alkylation process concerning enamines bearing a resident chiral center.

  • Caracterização e estabilidade físico-química de sistemas poliméricos nanoparticulados para administração de fármacos Revisão

    Schaffazick, Scheila Rezende; Guterres, Sílvia Stanisçuaski; Freitas, Liane de Lucca; Pohlmann, Adriana Raffin

    Resumo em Inglês:

    Polymeric nanoparticle systems such as nanocapsules and nanospheres present potential applications for the administration of therapeutic molecules. The physico-chemical characteristics of nanoparticle suspensions are important pre-requisites of the success of any dosage form development. The purpose of this review is to present the state of the art regarding the physico-chemical characterization of these drug carriers, in terms of the particle size distribution, the morphology, the polymer molecular weight, the surface charge, the drug content and the in vitro drug release profiles. Part of the review is devoted to the description of the techniques to improve the stability of colloidal systems.

  • Química verde, os desafios da química do novo milênio Divulgação

    Prado, Alexandre G. S.

    Resumo em Inglês:

    The fundamental concepts of the green chemistry are highlighted in order to present the enormous number of challenges to develop a new chemistry in research, industry and education. The practice of an environmental friendly chemistry are presented to improve the economics of chemical manufacturing and to enhance the much-tarnished image of chemistry and to present the opportunities to discover and apply this new chemistry. The challenges and opportunities of green chemistry in the world and Brazil are introduced and discussed in this report.

  • A química dos ésteres de fosfato Divulgação

    Domingos, Josiel B.; Longhinotti, Elisane; Machado, Vanderlei Gageiro; Nome, Faruk

    Resumo em Inglês:

    This work summarizes important aspects of the chemistry of phosphate esters, with special emphasis on: i) advances in the design of enzymatic models for phosphatases; and ii) nerve agents and currently used strategies for detoxification. The physical organic chemical aspects that are responsible by the reactivity of phosphate esters are also discussed.

  • Construção de uma fonte de corrente e de uma sonda para medida de condutividade pelo método da sonda de quatro pontas Nota Técnica

    Araújo, Olacir Alves; Botter Júnior, Wilson; Carvalho, Jesiel Freitas; Verde, Ediron Lima

    Resumo em Inglês:

    This paper describes the construction of an eletrical current source and of a probe to be used in the measurement of eletrical conductivity through a four-point probe method. These pieces of equipments can be obtained at the low price of US$ 50.00 and are adequate for eletrical conductivity measurements in the semiconductor range, that is from 10-1 to 10-6 S cm-1.

  • Desenvolvimento de um dispositivo para obtenção de monocristais de ligas à base de cobre Nota Técnica

    Blanco, Matildes; Barelli, Nilso; Benedetti, Assis Vicente; Flor, Samuel Waldemar Andrade

    Resumo em Inglês:

    This paper describes the drawing, construction and optimization of a device, which can be used to obtain single crystals of different metallic materials with melting point from 550 to 1050 ºC. Components of ease obtaining and of low cost were used. The device was based on the modified Bridgman technique and it was used to obtain single crystals of copper-based alloys. The temperature axial profiles and a difference less then 1% in the temperature between the wall and the center of the ceramic tube in the critical region for obtaining single crystals of good quality indicated that the oven presents a good thermal stability. Single crystals of CuZnAl and CuAlAg alloys of good quality were growth and characterized using optical microscopy and Laüe X-ray back reflection.

  • Determinação de tanino em pedúnculo de caju: método da vanilina versus método do butanol ácido Nota Técnica

    Agostini-Costa, Tânia da Silveira; Lima, Andréa; Lima, Marcelo Victor

    Resumo em Inglês:

    To improve tannin assay in cashew apple, several parameters were examined, including (1) extraction solvents, (2) effects of water and boiling time on butanol acid reaction and (3) correlation between vanillin and butanol acid assay of tannin in cashew apples. The 50-70% acetone extracted the greatest amount of tannin from cashew apples. Concentrations of water in butanol reagents were adjusted and boiling time of butanol reaction was reduced at 15 min. Tannin of unripe cashew apples was purified on Sephadex LH-20, aiming to obtain tannin standard for butanol assay. The vanillin assay presented high correlation with the butanol acid assay.

  • Métodos Ultravioleta Selectivo y de reducción con Hidracina en la determinación del ión nitrato an aguas subterraneas

    Belgrano, Roberto F.; Colasurdo, Viviana; Díaz, Oscar A.

    Resumo em Inglês:

    In this study, a comparison of two methods, the Selective UV Spectrophotometrical Method and Reduction with Hidrazine Method, for the determination of Nitrate ion in groundwater, was carried out. For this purpose, the results from all the drinking water collectings of the city of Olavarría, Argentina, were employed. Both methods present significant different means, but they don´t present significant differences in their variances.

  • O método das trajectórias clássicas: colisões coplanares do tipo A+BC Educação

    Marques, Jorge M. C.; Riganelli, Antonio; Varandas, António J. C.

    Resumo em Inglês:

    The general methodology of classical trajectories as applied to elementary chemical reactions of the A+BC type is presented. The goal is to elucidate students about the main theoretical features and potentialities in applying this versatile method to calculate the dynamical properties of reactive systems. Only the methodology for two-dimensional (2D) case is described, from which the general theory for 3D follows straightforwardly. The adopted point of view is, as much as possible, that of allowing a direct translation of the concepts into a working program. An application to the reaction O(¹D)+H2->O+OH with relevance in atmospheric chemistry is also presented. The FORTRAN codes used are available through the web page <a href="http://www.qqesc.qui.uc.pt">www.qqesc.qui.uc.pt</a>.

  • Inserção do conceito de economia atômica no programa de uma disciplina de química orgânica experimental Educação

    Merat, Leila Maria Oliveira Coelho; San Gil, Rosane Aguiar da Silva

    Resumo em Inglês:

    In this paper, the atom economy concepts are applied in a series of experiments during an experimental organic chemistry class, to implement "green chemistry" in an undergraduate course.

  • Prof. Celso Augusto Fessel Graner In Memoriam

    Rocha, Julio C.

  • Reações aldólicas assimétricas catalíticas Errata

    Corrêa Jr., Ivan R.; Pilli, Ronaldo A.
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