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Química Nova, Volume: 25, Número: 1, Publicado: 2002
  • Exame de um sonho Editorial

    Torresi, Susana I. de Córdoba de; Pardini, Vera L.; Ferreira, Vitor F.
  • Interação de compostos organossulfurados derivados do alho com o citocromo-c: um estudo eletroquímico Artigo

    Reina, Luisa del Carmen Barrett; Montanari, Carlos Alberto; Donnici, Claudio Luis; Diógenes, Izaura Cirino Nogueira; Moreira, Ícaro de Sousa

    Resumo em Inglês:

    Organosulfur compounds present in garlic and onion have been evaluated as inhibitors of chemical carcinogenesis. Among them diallylsulfide was mainly investigated and studies demonstrated its metabolization to the corresponding sulfoxide and sulfone. In this work, we report the investigation of the interaction between the diallylsulfide and its oxidized derivatives, through cyclic voltammetry, with horse heart cytocrome-c (on a modified electrode with 4-mercaptopyridine). Our results suggest that there is a reversible interaction between cytocrome-c and diallylsulfide and diallylsulfone and an irreversible interaction with the diallylsulfoxide.
  • Estudo do biomaterial Ti-6Al-4V empregando-se técnicas eletroquímicas e XPS Artigo

    Ramires, Ivan; Guastaldi, Antonio Carlos

    Resumo em Inglês:

    The Ti-6Al-4V alloy used as biomaterial has been used over the last years. The literature shows controversies concerning the kind and the chemical composition of the film naturally and elctrochemically formed on the surface of the titanium alloy. The presente work studies the film composition before and after the electrochemical polarization tests using the x Ray photoelectron spectroscopy (XPS) technique. The results showed that the film naturally formed on the metallic surface is constituted of a variety of oxides which do not cover the whole surface of the metallic alloy and therefore, metallic Ti, Al and V can be found on the uncovered areas. The tests of XPS made after the polarization up to 4V (SCE) showed that the electrochemically formed film is constituted only of TiO2 and that the peak current observed around 1,5 V (SCE) is due to the oxidation of any kind of titanium oxide or the growth of the film.
  • CGAR E CGAR-EM na análise dos constituintes químicos isolados do extrato hexanico de Sebastiania argutidens (Euphorbiaceae) Artigo

    Branco, Alexsandro; Pizzolatti, Moacir G.

    Resumo em Inglês:

    The fractionation column with SiO2 of the hexane extract of Sebastiania argutidens (Euphorbiaceae) yielded fractions containing hydrocarbons, carboxylic acids, sterols and pentacyclic triterpenes. Besides, one fraction showed the presence of several methyl esters, including four uncommon long chain palmitate esthers as minor components. The characterization of these chemical constituents have been done by High Resolution Gas Chromatography (HRGC) and HRGC coupled to Mass Spectrometry (GC/MS). Campesterol, stigmasterol, b-sitosterol, glutin-5-en-3-ol were identified by HRGC co-injection with standards.
  • Aplicação de técnicas eletroquímicas no estudo da dissolução oxidativa da covelita (CuS) por Thiobacillus ferrooxidans Artigo

    Teixeira, Christiane Medina; Ramires, Ivan; Garcia Júnior, Oswaldo; Guastaldi, Antonio Carlos

    Resumo em Inglês:

    Among the copper sulphides, chalcopyrite (CuFeS2), covellite (CuS) and chalcocite (Cu2S) are the most important source of minerals for copper mining industry. The acknowledge of behaviour of these sulphides related with bacterial leaching process are essential for optimization procedures. Despite of its importance, covellite has not deserved much interest of researchers regarding this matter. In this work it was studied the oxidation of covellite by the chemolithotrophic bacterium Thiobacillus ferrooxidans by using electrochemical techniques, such as open circuit potentials with the time and cyclic voltammetry. The experiments were carried out in acid medium (pH 1.8), containing or not Fe2+ as additional energy source, and in different periods of incubation; chemical controls were run in parallel. The results showed that a sulphur layer is formed spontaneously due the acid attack, covering the sulphide in the initial phase of incubation, blocking the sulphide oxidation. However, the bacterium was capable to oxidize this sulphur layer. In the presence of Fe2+ as supplemental energy source, the corrosion process was facilitated, because ocurred an indirect oxidation of covellite by Fe3+, which was produced by T. ferrooxidans oxidation of the Fe2+ added in the medium.
  • Influência da catálise ácida e básica na preparação da sílica funcionalizada pelo método sol-gel Artigo

    Nassar, Eduardo José; Messaddeq, Younès; Ribeiro, Sidney José Lima

    Resumo em Inglês:

    Some aspects of the chemistry involved in the preparation and characterization of functionalized silicon oxide by sol-gel method are considered in this work. The synthesis was performed with different silicon alcoxide precursors and the influence of the acid and basic catalyst was investigated. Characterization was performed by infrared absorption spectroscopy, elemental analysis and 29Si NMR. Infrared data show Si-C and -CH2- vibrational modes at 1250 to 1280 and 2920 to 2940 cm-1, respectively. The elemental analysis confirmed the presence of organic groups in the inorganic silica network. 29Si NMR results show different hydrolisys depending on the acid or base catalysis.
  • Aspectos práticos relacionados ao uso do Rincoforol, o feromônio de agregação da Broca-do-olho-do-coqueiro Rhynchophorus palmarum L. (Coleopterate: Curculionidae) no controle de pragas do coqueiro: análise de sua eficiência em campo Artigo

    Navarro, Daniela Maria do Amaral Ferraz; Murta, Maria Márcia; Duarte, Adriana Guimarães; Lima, Ivanildo Soares de; Nascimento, Ruth Rufino do; Sant'Ana, Antônio Euzébio Goulart

    Resumo em Inglês:

    Rhynchophorol (6-Methyl-2-hepten-4-ol) is the major constituent of the aggregation pheromone of Rhynchophorus palmarum L. (Coleoptera: Curculionidae), which is released by males of this species. The racemic mixture has been produced in one step-simplified preparation. The pheromone is placed into ampoules and furnished to coconut farmers. In the field, traps baited with Rhynchophorol and pieces of sugarcane attract both males and females, reducing the population of R. palmarum. The best conditions for field application are showed.
  • Intervalos de referência para elementos menores e traço em cabelo humano para a população da cidade do Rio de Janeiro <FONT FACE=Symbol>-</FONT> Brasil Artigo

    Carneiro, Maria Tereza W.D.; Silveira, Carmem L. Porto da; Miekeley, Norbert; Fortes, Lúcia M. de Carvalho

    Resumo em Inglês:

    Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of twenty minor and trace elements in hair samples from an urban population group (N = 1775), aiming at the establishment of reliable hair reference intervals. Statistical evaluation of the data with respect to age, sex and anatomic region was performed by multivariant analysis and according to recommendations of the International Federation of Clinical Chemistry (IFCC). The results show that mainly age and anatomic region (scalp or pubis) influence significantly the concentration of several elements. Comparison of the here calculated reference intervals with those previously published and used by clinical laboratories for this population showed larger discrepancies and the need for an urgent revision of these data.
  • Aplicação de algoritmos genéticos na seleção de variáveis em espectroscopia no infravermelho médio: determinação simultânea de glicose, maltose e frutose Artigo

    Costa Filho, Paulo A. da; Poppi, Ronei J.

    Resumo em Inglês:

    Genetic algorithm was used for variable selection in simultaneous determination of mixtures of glucose, maltose and fructose by mid infrared spectroscopy. Different models, using partial least squares (PLS) and multiple linear regression (MLR) with and without data pre-processing, were used. Based on the results obtained, it was verified that a simpler model (multiple linear regression with variable selection by genetic algorithm) produces results comparable to more complex methods (partial least squares). The relative errors obtained for the best model was around 3% for the sugar determination, which is acceptable for this kind of determination.
  • Influência do meio reacional no comportamento fotoquímico do inseticida paration etílico Artigo

    Santos, Francismário Ferreira; Rezende, Maria Olímpia Oliveira

    Resumo em Inglês:

    The photodegradation of parathion in natural and dezionised waters was studied under irradiation at two different wavelengths: 280 nm and 313 nm. The influence of humic acids was evaluated. The results demonstrated that the degradation occurred only due to photochemical processes. The chemical hydrolysis and biological processes can be neglected in this case. The addition of humic acids did not increase the photodegradation rate in either water samples (natural or dezionised). In alkaline solutions the photodegradation rate was higher in dezionised water when compared to natural waters. The kinetic degradation in all experiments obeyed a first order reaction pattern.
  • Síntese de nanotubos de carbono de parede simples por sublimação de grafite em atmosfera de hélio Artigo

    Romero, José Gino Venegas; Luengo, Carlos Alberto; Huber, John G; Rosolen, José Maurício

    Resumo em Inglês:

    Macroscopic samples of fullerene nanostructures are obtained in a modified arc furnace using the electric arc method with a Helium atmosphere at low pressures. High purity graphite rods are used as electrodes but, when drilled and the orifices filled with powders of transition metals (Fe, Co, Ni) acting as catalysts, the resulting particles are carbon nanostructures of the fullerene family, known as Single Wall Nanotubes (SWNTs). They have typical diameters of 1.4 nm, lengths up to tenths of microns and they are arranged together in bundles containing several SWNTs. Those samples are observed and analyzed using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques.
  • Fotoquímica de chalconas fluoradas no estado sólido Artigo

    Cesarin-Sobrinho, Dari; Netto-Ferreira, José Carlos

    Resumo em Inglês:

    Chalcone and its fluorinated derivatives were synthesized and photolyzed in the solid state. UV irradiation of chalcone and its monosubstituted fluorine derivatives (3- and 4-fluorchalcone) resulted in a mixture of anti-head-head (gamma-truxinic), sin-head-tail (alpha-truxilic) and anti-head-tail (epsilon-truxilic) dimers. On the other hand, upon irradiation of 3,4- and 3,5-difluorchalcone a stereoselective formation of the alpha-truxilic photodimer was observed, whereas for 2-substituted chalcones (2,3difluorchalcone, 2,5-difluorchalcone, 2,6-difluorchalcone and 2,3,4-trifluorchalcone) the beta-truxilic dimer was stereoselectively obtained. 2',3',4',5',6'-pentafluorchalcone was the less reactive of all chalcones studied and at least one of the possible photodimers, i.e the anti-head-head isomer, was identified. Irradiation of polyfluorinated chalcones such as 2,3,5,6-tetrafluor-, 2,3,4,5,6-pentafluor-, and 2,2',3,3',4,4',5,5',6,6'-decafluorchalcone led only to polymerization and/or decomposition products.
  • Decomposição de precursores metalorgânicos: uma técnica química de obtenção de filmes finos Revisão

    Alves, Oswaldo Luiz; Ronconi, Célia Machado; Galembeck, André

    Resumo em Inglês:

    This review focus the more relevant foundations and applications of the Metallo-Organic Decomposition (MOD) technique, mainly within the last decade. The technique has grown significantly, mainly due to the good results concerning the preparation of multicomponent oxide systems with composition, structural and morphologic control, in a relatively simple way. This opened new opportunities to obtain materials with well-defined electrical and optical properties.
  • Novas tendências no tratamento de efluentes têxteis Revisão

    Kunz, Airton; Peralta-Zamora, Patricio; Moraes, Sandra Gomes de; Durán, Nelson

    Resumo em Inglês:

    Textile effluents, when not correctly treated, cause a high impact to the environment. The main recalcitrant compounds present in textile effluent are represented by the synthetic dyes, used during the fibber dying process. Among others, the azo dyes are considered the most harmful due to its mutagenic and carcinogenic character. In the present work we reported a revision study on the new tendencies for remediation of textile effluents, mainly to degrade the recalcitrant compounds. For this purpose, chemical, physical, photochemical, biological and combined processes were investigated.
  • Dissulfeto de molibdênio, um material multifuncional e surpreendente Revisão

    Wypych, Fernando

    Resumo em Inglês:

    The aim of this work is to review the chemical and physical properties of layered molybdenum disulfide. The three polymorphic/polytypic modifications of the compound were found, the polytypes 2H (molybdenite) and 3R are semiconductors while the polymorph 1T is an electronic conductor. 2H-MoS2 has several important industrial applications as hydrotreatment catalysts, energy storage devices, solar cells, solid lubricants, among others. When intercalated, the 2H phase changes to a distorted 1T phase, producing unstable intercalation compounds that can be exfoliated in solution, producing single layers and consequently nanocomposites. The direct synthesis of the 1T phase produces stable intercalation compounds. Recently molybdenum disulfide was prepared as nanotubes and fulerene-like structures that bring new insights in the investigation of this important material.
  • Reações de ortometalacão em piridinas Revisão

    Souza, Marcus .V. N. de; Almeida, Mauro V. de

    Resumo em Inglês:

    In this paper we describe a powerful methodology for the regiospecific construction of polysubstituted aromatic and heteroaromatic compounds. The DoM reaction (direct ortho-metalation) comprises the deprotonation in position ortho of a aromatic or heteroaromatic containing DMG (directed metalation group) by strong bases, normally an alkyllithium reagent, leading to an ortho-lithiated species. These species, upon treatment with electrophilic reagents, gives 1,2 disubstituted products.
  • Aspectos relacionados à utilização da equação logística quadrática em processos eletroquímicos Divulgação

    Varela, Hamilton; Torresi, Roberto M.; Gonzalez, Ernesto R.

    Resumo em Inglês:

    The concepts of dissipation and feedback are contained in the behavior of many natural dynamical systems. They have been used to predict the evolution of populations leading to the formulation of the quadratic logistic equation (QLE). More recently, the QLE has been used to provide a better understanding of physicochemical systems with promising results. Many physical, chemical and biological dynamic phenomena can be understood on the basis of the QLE and this work describes the main aspects of this equation and some recent applications, with emphasis on electrochemical systems. Also, it is illustrated the concept of potential energy as a convenient way of describing the stability of the fixed points of the QLE.
  • Propelente sólido compósito polibutadiênico: I- influência do agente de ligação Divulgação

    Sciamareli, Jairo; Takahashi, Marta Ferreira Koyama; Teixeira, José Maria; Iha, Koshun

    Resumo em Inglês:

    In the Brazilian Complete Spacial Mission, the research of Vehicle Satellite Launcher is important. The solid propellant composite used in this vehicle is made with ammonium perchlorate, aluminiun powder and hydroxy terminated polibutadiene resin. In the propellant the bonding agent has a function to promote the interaction between solids and polimeric matrix, improving mechanical properties as stress, strain, aging characteristics and moisture embrittlement. Due its importance in propellant, bonding agent is consider as industrial secret and the literature about it is generic, without greater informations.
  • O conceito de incerteza aplicado aos processos de medição associados à preparação de uma solução de referência para calibração Divulgação

    Buchmann, José Henrique; Sarkis, Jorge Eduardo de Souza

    Resumo em Inglês:

    The implementation of a quality assurance program in chemical analytical laboratories, that can aid in demonstrate the quality of their results, is an issue of great concern. As a consequence, it is mandatory to give an estimate of the confidence that can be placed on the obtained results. An useful measure of this confidence is the measurement uncertainty and, nowadays, a result without the corresponding uncertainty statement cannot be considered reliable. This paper presents a summary of the most important mechanisms for the evaluation and reporting of the measurement uncertainty. In implementing these principles, it is described the measurement uncertainty estimation associated with the preparation of a uranium elemental reference solution at 2.4 mg.kg-1 from the corresponding certified reference material (in this example at 1003 mg.kg-1).
  • Técnicas para análise de desempenho de computadores Divulgação

    Vazquez, Pedro A. M.

    Resumo em Inglês:

    A series of open source benchmarks for computer performance analysis of personal computers with a focus on computational chemistry calculations is presented. The results returned by these tests are discussed and used to correlate with the actual performance of a set of computers available for research on two computing intensive fields of chemistry, quantum chemical and molecular simulation calculations.
  • Enzymeless biosensors: uma nova área para o desenvolvimento de sensores amperométricos Divulgação

    Sotomayor, Maria Del Pilar Taboada; Kubota, Lauro Tatsuo

    Resumo em Inglês:

    The aim of this work is to describe the recent area that it has been developed for the construction of amperometric sensors, with the purpose to make possible a more effective electron transfer between enzyme and electrode. The advances reported in the literature will be described, such as enzymatic configurations that can be mimic using the chemistry of the artificial enzymes.
  • A química medicinal de N-acilidrazonas: novos compostos-protótipos de fármacos analgésicos, antiinflamatórios e anti-trombóticos Divulgação

    Barreiro, Eliezer J.; Fraga, Carlos A. M.; Miranda, Ana L. P.; Rodrigues, Carlos R.

    Resumo em Inglês:

    In this article are described new bioactive N-acylhydrazone (NAH) derivatives, structurally designed as optimization of aryl hydrazones precursors planned by molecular hybridization of two 5-lipoxigenase inhibitors, e.g. CBS-1108 and BW-755c. The analgesic, antiedematogenic and anti-platelet aggregating profile of several isosteric compounds was investigated by using classic pharmacological assays in vivo and ex-vivo, allowing to identify new potent peripheric analgesic lead, a new anti-inflammatory and an antithrombotic agent. During this study was discovered dozen of active NAH compounds clarifying the structure-activity relationship for this series of NAH derivatives, indicating the pharmacophore character of the N-acylhydrazone functionality.
  • Determinação em fluxo do carbonatoresidual do solo empregando pervaporação Nota Técnica

    Grassi, Viviane; Miyazawa, Mario; Pavan, Marcos A.; Kamogawa, Marcos Y.

    Resumo em Inglês:

    The objective of this study was to develop a method for the direct determination of residual CO3(2-) in acid soil using a flow system coupled with pervaporation. The gas released from the acidified sample was separated though a hydrophobic membrane and detected by conductivimetry. The detection limit was 0.054 mmol c kg-1 for CO2/CO3(2-) with relative error of 3.1%. The analytical frequency was 20 samples per hour. The method is recommended for studying the reactions and kinetics of lime applied in acid soils.
  • Construindo o estágio de docência da pós-graduação em química Educação

    Feitosa, Judith P. A.

    Resumo em Inglês:

    The teaching apprenticeship established by CAPES for post-graduation scholarship beholders has been discussed and the criterion adopted for the implementation in the post-graduation in Inorganic Chemistry Program presented. A teaching plan for the new subject is proposed, based on the experience gained through a first group. An instrument for evaluation of the student's performance has been developed and analyzed. Aspects like knowledge, clearness, enthusiasm, confidence, good manage on the audio-visual resources, class length are mentioned by degree of importance and the major difficulties faced and pointed out by the students.
  • Quatro alternativas para resolver a equação de Schrödinger para o átomo de hidrogênio Educação

    Custodio, Rogério; Politi, José Roberto dos Santos; Segala, Maximiliano; Haiduke, Roberto Luiz Andrade; Cyrillo, Márcio

    Resumo em Inglês:

    Quantum chemistry describes the hydrogen atom as one of the few systems that permits an exact solution of the Schrödinger equation. Students tend to consider that little can be learned from the hydrogen atom and forget that it can be used as a standard to test numerical procedures used to calculate properties of multielectronic systems. In this paper, four different numerical procedures are described in order to solve the Schrödinger equation for the hydrogen atom. The basic motivation is to identify new insights and methods that can be obtained from the application of powerful numerical techniques in a well-known system.
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