Scielo RSS <![CDATA[Química Nova]]> http://www.scielo.br/rss.php?pid=0100-404220060006&lang=pt vol. 29 num. 6 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<B>O biodiesel e a política de C & T brasileira</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600001&lng=pt&nrm=iso&tlng=pt <![CDATA[<B>Determinação de lamivudina, estavudina e nevirapina, em comprimidos, por cromatografia líquida de alta eficiência</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600002&lng=pt&nrm=iso&tlng=pt A high performance liquid chromatography method was developed to quantify lamivudine, stavudine and nevirapine combined in tablets. The separation was carried out in less than 10 min using a phosphate buffer of pH 3.0 and acetonitrile (75:25, v/v) as mobile phase, a LiChrospher ODS column and UV detection at 266 nm. The method was linear over the range of 15-135 µg/mL (lamivudine), 4-36 µg/mL (stavudine) and 20-180 µg/mL (nevirapine). The accuracy ranged from 98.56 to 102.04% and intra-day and inter-day precision was less than 1% for the three drugs. The method showed robustness, remaining unaffected by deliberate variations in relevant parameters. <![CDATA[<B>Metodologia para análise simultânea de ácido nicotínico, trigonelina, ácido clorogênico e cafeína em café torrado por cromatografia líquida de alta eficiência</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600003&lng=pt&nrm=iso&tlng=pt A reverse phase liquid chromatography method was developed for simultaneous determination of trigonelline, caffeine, nicotinic and chlorogenic (5-CQA) acids in roasted coffee. A gradient of acetic acid/acetonitrile was used as mobile phase and detection was carried out in the UV. The samples were extracted with acetonitrile/water (5:95 v/v) at 80 ºC/10 min. Good recovery (89 to 104%), repeatability and linearity were obtained. Detection limits of 0.01, 0.15, 0.04 and 0.04 mg mL-1 were observed for nicotinic acid, trigonelline, 5-CQA and caffeine. The method, applied to arabica and robusta coffees with different degrees of roasting, was efficient and fast (~35 min) and also allowed identification of cinnamic acids. <![CDATA[<B>Um novo método para quantificar mercúrio orgânico (Hg<SUB> orgânico</SUB>) empregando a espectrometria de fluorescência atômica do vapor frio</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600004&lng=pt&nrm=iso&tlng=pt In this work a simple and sensitive procedure to extract organic mercury from water and sediment samples, using methylene chloride in acidic media followed by CVAFS quantification has been developed. The method was evaluated for possible interferents, using different inorganic mercury species and humic acid, no effects being observed. The detection limit for organic mercury was 160 pg and 396 pg for water and sediment samples respectively. The accuracy of the method was evaluated using a certified reference material of methylmercury (BCR-580, estuarine sediment). Recovery tests using methylmercury as surrogate spiked with 1.0 up to 30.0 ng L-1 ranged from 90 up to 109% for water samples, whereas for sediments, recoveries ranged from 57 up to 97%. <![CDATA[<B>Estudo comparativo entre sílica obtida por lixívia ácida da casca de arroz e sílica obtida por tratamento térmico da cinza de casca de arroz</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600005&lng=pt&nrm=iso&tlng=pt A comparison between silica by acid leaching of rice husk (RH) and silica obtained from thermal treatment of rice husk ash (RHA) is presented. The best leaching results were obtained using 10% hydrochloric acid followed by washing with water. The alternative method, calcination of RHA at 700 ºC for 6 h followed by grinding for 80 min, was more effective. Silica obtained from RH was about 97% amorphous, had a 17.37 µm mean particle size, and a specific surface area of 296 m²/g. On the other hand, for silica obtained from RHA the values were about 95% amorphous material 0.68 µm, and 81 m²/g. <![CDATA[<B>Polimerização de estireno utilizando compostos organolantanídeos ativados por MAO</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600006&lng=pt&nrm=iso&tlng=pt In an attempt to improve the performance of organolanthanide catalysts we investigated the use of the industrially important cocatalyst methylaluminoxane (MAO) to activate organolanthanide compounds in olefin polymerization. The catalytic systems LnBrCp2(THF)2/MAO (Cp=cyclopentadienyl) and LnBrCp*2THF/MAO (Cp*= pentamethylcyclopentadienyl), Ln=Pr and Yb, were active in styrene polymerization but inactive in ethylene and propylene polymerization. These systems produced atactic polystyrene with conversions of up to 8.2% (PrBrCp*2THF, Al/Ln=200, T=80ºC, t=4 h) in toluene. In the absence of solvent, the conversion is 26.0% (1.5 h) and the molar mass of the atactic polystyrene is almost ten times higher (43 kg/mol). <![CDATA[<B>Constituintes fenólicos e terpenóides isolados das raízes de <I>Andira fraxinifolia</I> (Fabaceae)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600007&lng=pt&nrm=iso&tlng=pt Sitosterol, stigmasterol, betulinic acid, lupeol, 3-O-beta-D-glucopiranosylsitosterol, 3-O-alpha-L-rhamnopiranosylchromone, 5,7-dihydroxy-4'-methoxyisoflavone, 3',5,7-trihydroxy-4'-methoxyisoflavone and a mixture of two rel-2R,3S-3-O-alpha-L-rhamnopiranosilflavanonols were isolated from the roots of Andira fraxinifolia. Their structures were established by spectral data analysis. <![CDATA[<B>Efeitos de substituintes na ligação de hidrogênio do 3-hidroxipropenal</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600008&lng=pt&nrm=iso&tlng=pt The effect of substituents on the energies and geometries of 3-hydroxypropenal was studied using the B3LYP/6-311++G(d,p) model. The hydrogen bond energies indicate that the strongest donors and the weakest acceptors present the highest and the weakest hydrogen bonds, respectively, indicating the validity of the Madsen RAHB model. Geometric parameters indicate that the intensity of the hydrogen bond is proportional to the resonance, as suggested by the RHAB model. The effect of substituents diverges from the model proposed by Gilli et al. Sometimes the results indicate that the donor or acceptor effect is more important than the point of substitution. <![CDATA[<B>Determinação de contaminantes em óleos lubrificantes usados e em esgotos contaminados por esses lubrificantes</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600009&lng=pt&nrm=iso&tlng=pt A simple and reliable ashing procedure is proposed for the preparation of used lubricating oil samples for the determination of Zn, Fe, Pb, Ni and Cu by the flame atomic absorption spectrometry technique. Sulphanilic acid was added to oil samples, the mixture coked and the coke ashed at 550 ºC. The solutions of the ash were analysed by flame AAS for these metals. The quantification limits were 38.250 µg g-1 for Zn, 4.550 µg g-1 for Fe, 1.562 µg g-1 for Pb, 1.450 µg g-1 for Ni, and 0.439 µg g-1 for Cu. The determinations, in lubricating oil, showed good precision and accuracy with recoveries between 90 and 110 %, indicating a negligible matrix effect in the experiments using addition of analyte, with relative standard deviation lower than 5%. The results for analysis of wastewater contamined by theses lubricants showed a very high relative standard deviation. <![CDATA[<B>Caracterização química de extratos de <I>Ocimum basilicum</I> L. obtidos através de extração com CO<SUB>2</SUB> a altas pressões</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600010&lng=pt&nrm=iso&tlng=pt This work reports extraction yield and chemical characterization of the extracts obtained by high-pressure CO2 extraction of a cultivar of Ocimum basilicum L. The experiments were performed in the temperature range of 20 to 50 °C, from 100 to 250 atm of pressure. Chemical analyses were carried out by gas chromatography coupled to mass spectrometry, permitting to identify 23 compounds that were grouped into five chemical classes. Results showed that temperature and solvent density influenced positively the extraction yield. At 20 °C and 0.41 g cm-3 occurred a rise in the concentration of monoterpenes, oxygenated monoterpenes, sesquiterpenes and oxygenated sesquiterpenes. <![CDATA[<B>Variação química do óleo essencial de <I>Hyptis suaveolens </I>(L.) Poit., sob condições de cultivo</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600011&lng=pt&nrm=iso&tlng=pt This study was performed to establish the correlation between the growth conditions and essential oil composition of Hyptis suaveolens from Alfenas (MG), Brazil. The plants were grown in a greenhouse, four treatments were used and they were harvested at two different periods of time (60 and 135-day-old plants). The essential oil composition was determined by GC-MS analysis. The terpenes spathulenol, globulol, dehydroabietol, a-cadinol and beta-phellandrene were the major constituents found in the essential oil. Oxygenated sesquiterpenes represented the main group of constituents in most of the treatments. The major changes in the essential oil composition were found in 135-day-old plants grown under NPK deficiency. We also identified three groups of volatile components that have not been previously described in H suaveolens. <![CDATA[<B>Digestão de óleo lubrificante encapsulado em forno de microondas com radiação focalizada por adição de amostra ao reagente pré-aquecido</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600012&lng=pt&nrm=iso&tlng=pt The applicability of the recently proposed procedure based on gradual sample addition to microwave-assisted pre-heated concentrated acid is limited by the sample viscosity. In this work, lubricating oil samples with high viscosity were encapsulated and manually added to the microwave-assisted pre-heated concentrated digestion mixture. The procedure was applied for determination of Al, Ca, Cr, Cu, Fe, Mg, Ni, P, Pb, Si, Sn, Sr, V, W, and Zn in lubricating oil by inductively coupled plasma optical emission spectrometry (ICP OES). Determined and certified values for Ca, Mg, P, and Zn in lubricating oil were in agreement at a 95% confidence level. <![CDATA[<B>Aspectos estruturais relacionados ao processo de troca iônica no niobato lamelar K<SUB>4</SUB>Nb<SUB>6</SUB>O<SUB>17</B></SUB>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600013&lng=pt&nrm=iso&tlng=pt The niobate with formula K4Nb6O17 has a layered structure formed by stacked negative sheets and exchangeable cations in the interlayer region. In this study we discuss some structural aspects related to the ion exchange in layered hexaniobate based on X-ray diffractometry and vibrational Raman spectroscopy data. Hexaniobate has two distinct interlayer regions and the potassium ions of one interlayer in particular are preferably exchanged by other cations, leading to an interstratified material. <![CDATA[<B>Influência da temperatura do ar de secagem sobre o teor e a composição química do óleo essencial de <I>Lippia alba</I> (Mill) N. E. Brown</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600014&lng=pt&nrm=iso&tlng=pt Leaves of Lippia alba were submitted to six different drying treatments, using air at ambient temperature and heated up to 80 °C. The essential oil was extracted by steam distillation and analyzed by GC-MS. For the dried leaves, the oil content was reduced by 12 to 17% when compared with the fresh plant (0.66%). The major oil component was citral, representing 76% for the fresh plant, and varying from 82 to 84% for the dried material. These results showed that L. alba can be submitted to a drying process of up to 80 ºC without degradation and/or loss of the major, [LC1] active component. <![CDATA[<B>Adsorção de fenol sobre carvão ativado em meio alcalino</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600015&lng=pt&nrm=iso&tlng=pt The present study describes phenol adsorption on commercial active carbon (CAF) under alkaline conditions in the concentration range of 0.01 to 2.08 mmol L-1. Surface characterization has been performed by means of surface area measurements, IR spectroscopy and Boehm titration. The effect of temperature on the adsorption equilibrium isotherm was investigated at 23, 30, 40, 50 and 60 °C. The results showed that adsorption capacity decreased with increasing temperature. The adsorption kinetics and the role of surface characteristics on the adsorption of phenol also discussed. <![CDATA[<B>Variação anual de metilxantinas totais em amostras de <I>Ilex paraguariensis </I>A<I>.</I> St. - Hil. (erva-mate) em Ijuí e Santa Maria, Estado do Rio Grande do Sul</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600016&lng=pt&nrm=iso&tlng=pt Ilex paraguariensis is a native plant in Southern Brazil, whose leaves are utilized in beverages such as chimarrão and tererê. This study investigated variations of total methylxanthines in leaves from two Ilex populations collected at one-month intervals over the course of one year. The levels varied from 1.92 to 10.37 mg/g (Ijuí) and 1.77 to 9.17 mg/g (Santa Maria). Statistical analysis indicated a significative variation in the contents of all samples analysed, confirming seasonal fluctuations. These results show that the period of harvest might decisively influence the organoleptic characteristics of raw material used in industry and therefore in commercial products. <![CDATA[<B>Determinação turbidimétrica de metilbrometo de homatropina em formulações farmacêuticas empregando um sistema de análise por injeção em fluxo</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600017&lng=pt&nrm=iso&tlng=pt A flow injection turbidimetric procedure exploiting merging zones is proposed for determining homatropine methylbromide (HMB) in pharmaceutical preparations. The determination is based on the precipitation reaction of homatropine methylbromide with AgNO3 solution to form a precipitate, which was measured at 410 nm. The analytical curve was linear in the HMB concentration range from 8.0x10-4 to 1.7x10-3 mol L-1, with a detection limit of 9.5x10-5 mol L-1. The recoveries ranged from 94.9 to 104 %, the sampling frequency was 75 h-1 and relative standard deviations were smaller than 2.0 % for solutions containing 1.2x10-3 and 1.5x10-3 mol L-1 HMB (n=10). The results obtained for commercial formulations using the FIA procedure were in good agreement with those obtained by using a comparative method (r= 0.9983). <![CDATA[<B>Constituintes químicos da casca do caule de <I>Amburana cearensis</I> A.C. Smith</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600018&lng=pt&nrm=iso&tlng=pt The phytochemical analysis of the ethanol extract trunk bark of Amburana cearensis allowed the isolation and identification of twelve constituents: coumarin, sucrose, two phenol acids (vanillic acid and protocatechuic acid), five flavonoids (afrormosin, isokaempferide, kaempferol, quercetin and 4'-methoxy-fisetin), a phenol glucoside (amburoside A) and a mixture of glucosilated b-sitosterol and stigmasterol. Their structures were elucidated by spectroscopic methods such as IR, MS, ¹H and 13C NMR, including uni and bidimensional techniques, in addition to comparison with literature data. <![CDATA[<B>Estudo termogravimétrico do efeito da temperatura e da atmosfera na absorção de dióxido de enxofre por calcário</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600019&lng=pt&nrm=iso&tlng=pt Thermogravimetry was applied to investigate the effects of temperature and atmosphere on conversion of sulfur dioxide (SO2) absorbed by limestone. Ranges of temperature and particle size were studied, typical of fluidized-bed coal combustion. Isothermal experiments were performed at different temperatures (between 750 and 950 ºC) under local atmospheric pressure (~ 697 mmHg) in dynamic atmospheres of air and nitrogen. The maximum conversion was 29% higher in nitrogen atmosphere than in air atmosphere. The optimum conversion temperature was found at 831 ºC in air atmosphere and at 894 ºC in nitrogen atmosphere. <![CDATA[<B>Constituintes químicos e atividade antioxidante de S<I>ida galheirensiS</I> Ulbr. (Malvaceae)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600020&lng=pt&nrm=iso&tlng=pt The phytochemical investigation of Sida galheirensis led to the isolation of 5,4'-dihydroxy-3,7,3´-trimethoxyflavone, 17³-ethoxyphaeoforbide, a rare natural product, 6,7-dimethoxycoumarin, ortho-hydroxybenzoic acid, sitosterol-3-O-beta-D-glucopyranoside, stigmasterol-3-O-beta-D-glucopyranoside, 5,7,4'-trihydroxyflavone, 5,7,3',4'-tetrahydroxyflavone, kaempferol-3-O-beta-D-(6"-E-p-coumaroyl) glucopyranoside and luteolin 7-O-beta-D-glucopyranoside. Their structures were assigned based on spectroscopic analyses, including two-dimensional NMR techniques. Antioxidant activities of hexane, CHCl3, EtOAc, BuOH and EtOH extracts of Sida galheirensis were measured using the 1,2-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging assay. This is also the first work reporting the chemical investigation of Sida galheirensis. <![CDATA[<B>Iron oxide and pyrocatechol</B>: <B>a spectroscopy study of the reaction products</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600021&lng=pt&nrm=iso&tlng=pt The reaction of 1,2-dihydroxy-benzene (pyrocatechol) (C6H6O2) with iron oxide (Fe2O3) and sodium thiosulfate (Na2S2O3) in aqueous medium (pH 7) was investigated. Pyrocatechol suffers autoxidation and coordinates with Fe3+ in solution. The presence of S2O3(2-) in solution was fundamental to generate and stabilize the pyrocatechol oxidation products as o-semiquinones. This compound was isolated and its structure characterized using FT-IR, EPR and UV-Vis Spectroscopy as [CTA][Fe(SQ)2(Cat)]. A thermal mass loss mechanism was proposed based on Thermogravimetric Analysis (TG) to support the structural characterization. <![CDATA[<B>Uma nova síntese de <FONT FACE=Symbol>a</FONT>-bromo-acetofenonas e sua aplicação na obtenção de 2-benzoil-benzofuranas</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600022&lng=pt&nrm=iso&tlng=pt alpha-Bromoacetophenones are important in organic synthesis. They have been widely used as precursors of several natural products. Several methods of bromination aiming at their synthesis have been described, however they furnish a mixture of starting material 10, mono 8 and dibromide 11 products. We developed a novel, simple and efficient synthesis of these compounds with applications in the synthesis of benzoylbenzofurans 9, compounds with important pharmacological properties, such as the ability of dilating the coronary artery and analgesic action. Such compounds have also been used as key intermediates to obtain quinone systems. <![CDATA[<B>Vibrational contribution to dipole polarizability and first hyperpolarizability of LiH</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600023&lng=pt&nrm=iso&tlng=pt The role played by electron correlation and vibrational correction on the polarizability of the LiH molecule is demonstrated. We present results for the dipole moment, polarizability and first hyperpolarizability of the LiH molecule obtained through many-body perturbation-theory, coupled-cluster and quadratic configuration interaction methods. Our best result for the dipole polarizability, obtained using the QCISD(T) scheme, indicates that the vibrational contribution is appreciable, amounting to ca. 10% of the total polarizability. Regarding the first hyperpolarizability, the vibrational contribution is even more important and has opposite sign in comparison with the electronic contribution. <![CDATA[<B>Myoglobins</B>: <B>the link between discoloration and lipid oxidation in muscle and meat</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600024&lng=pt&nrm=iso&tlng=pt Aerobic metabolism changes rapidly to glycolysis post-mortem resulting in a pH-decrease during the transformation of muscle in to meat affecting ligand binding and redox potential of the heme iron in myoglobin, the meat pigment. The "inorganic chemistry" of meat involves (i) redox-cycling between iron(II), iron(III), and iron(IV)/protein radicals; (ii) ligand exchange processes; and (iii) spin-equilibra with a change in coordination number for the heme iron. In addition to the function of myoglobin for oxygen storage, new physiological roles of myoglobin are currently being discovered, which notably find close parallels in the processes in fresh meat and nitrite-cured meat products. Myoglobin may be characterized as a bioreactor for small molecules like O2, NO, CO, CO2, H2O, and HNO with importance in bio-regulation and in protection against oxidative stress in vivo otherwise affecting lipids in membranes. Many of these processes may be recognised as colour changes in fresh meat and cured meat products under different atmospheric conditions, and could also be instructive for teaching purposes. <![CDATA[<B>Aspectos químicos, biológicos e etnofarmacológicos do gênero <I>Cassia</B></I>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600025&lng=pt&nrm=iso&tlng=pt Species of Cassia are widely distributed in tropical and subtropical regions throughout the world, and have been extensively investigated chemically and pharmacologically.They are known to be a rich source of phenolic derivatives, most of them with important biological and pharmacological properties. Some Asian, African and Indian tribes use these species as a laxative, purgative, antimicrobial, antipyretic, antiviral and anti-inflammatory agent. Among a number of other classes of secondary metabolites, such as anthracene derivatives, antraquinones, steroids and stilbenoids, biologically active piperidine alkaloids are an especially important bioactive class of compounds that showed to be restricted to a small group of Cassia species. In this paper we present an overview of the chemical, biological and ethnopharmacological data on Cassia piblished in the literature. <![CDATA[<B>Metabólitos secundários de espécies de Anacardiaceae</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600026&lng=pt&nrm=iso&tlng=pt This review describes some aspects of the family Anacardiaceae dealing with the presence and distribution of secondary metabolites in the main genera of this family and their biological activities. It reports the occurrence of different natural compounds present in their species with special emphasis on phenolic lipids, flavonoids and triterpenes that are typical metabolites of this family. <![CDATA[<B>Principais métodos de síntese de amidinas</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600027&lng=pt&nrm=iso&tlng=pt The amidine functional group is found in a wide range of natural products and is biologically active against several pathogens. In addition, amidines have long been regarded as useful intermediates in the synthesis of heterocyclic compounds. Consequently, a great number of methods have been developed for the preparation of amidines. Pinner's method is the most commonly used. Conventional methods include: - the addition of metal amides or amines to nitriles, the addition of amines to imido esters and the condensation of amides with amines in the presence of halogenating reagents. In this report, the main methods for synthesis of amidines will be described. <![CDATA[<B>Pró-fármaco ativado por enzima, uma estratégia promissora na quimioterapia</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600028&lng=pt&nrm=iso&tlng=pt Strategies that promote selective activation of prodrugs by enzymes can be divided into two major classes: 1) deliver of a monoclonal antibody-enzyme immunoconjugate that can recognize a specific antigen and promote the prodrug to a citotoxic drug, with a high selectivity for the target cells, and 2) selective gene delivery encoding an enzyme that can promote the prodrug to a citotoxic drug for the target cells. In this article are discussed ADEPT (antibody-directed enzyme prodrug therapy), GDEPT (gene-directed enzyme prodrug therapy), VDEPT (virus-directed enzyme prodrug therapy), GPAT (genetic prodrug activation therapy) and PDEPT (polymer-directed enzyme prodrug therapy) approaches, their clinical trials, advantages, disadvantages and perspectives. <![CDATA[<B>Sensores eletroquímicos</B>: <B>considerações sobre mecanismos de funcionamento e aplicações no monitoramento de espécies químicas em ambientes microscópicos</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600029&lng=pt&nrm=iso&tlng=pt Electrochemical sensors have attracted considerable attention in recent years because they provide data about the chemical state of our surroundings and the dynamics of the chemical transformations in the form a spatially resolved image. Particular interest has been directed to measurements in restricted-volume samples as new technologies enable the fabrication of miniaturized versions of sensors with reproducible characteristics. Taking these aspects into consideration, this review focuses on the use of electrodes of micrometer dimensions to acquire chemical information in microdomains in which concentrations may not be spatially homogeneous. This is possible because microelectrodes allow fast-response measurements with micrometer resolution to be performed. On the other hand, the use of microelectrodes as amperometric sensors presents an inherent drawback owing to the insufficient specificity toward the substrate of interest. Hence, some comments on strategies to enhance the selectivity of amperometric sensors are also made. Finally, recent applications of structurally microscopic electrodes as in vivo sensors are shown, as well as a prospect of the future trend in this field. <![CDATA[<B>Polipeptídeos e proteínas com influência na qualidade da espuma da cerveja e métodos analíticos utilizados no seu estudo</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600030&lng=pt&nrm=iso&tlng=pt A review of polypeptides and proteins that influence, direct or indirectly, beer foam quality, as well as the most relevant analytical methods used in their study, are presented. Protein Z, LTP1 and hordein/glutelin fragments originated from malt have a direct influence on beer foam quality. Other proteins, like malt hordeins and albumins and wheat puroindolines, are, to some degree, also important for beer foam quality. Protein hydrophobicity is pointed out as a key parameter to enhance foam quality. Electrophoretic, chromatographic and immunological analytical methods are currently used to study polypeptides and proteins present in barley, malt, wort, beer, and foam. Best results are obtained when combinations of these methods are applied. <![CDATA[<B>Sistema aquoso bifásico</B>: <B>uma alternativa eficiente para extração de íons</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600031&lng=pt&nrm=iso&tlng=pt Solvent extraction has been successfully applied to metal ion preconcentration and often meant the use of toxic organic diluents. However, regulatory pressure is increasingly focusing on the use and disposal of organic solvents, and thus the development of nonhazardous alternatives is important. In this review, we examine the application of aqueous biphasic systems (ABS) to extraction of ions, analyzing their potential and limitations and suggest that ABSs could be an efficient substitute for oil/water biphasic systems. ABSs are formed by mixing certain inorganic salts and water-soluble polymers, or by mixing two water-soluble polymers. <![CDATA[<B>Estresse oxidativo, lesões no genoma e processos de sinalização no controle do ciclo celular</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600032&lng=pt&nrm=iso&tlng=pt The generation of reactive oxygen species (ROS) may be both beneficial to cells, performing functions in intracellular signaling and detrimental, modifying cellular biomolecules. ROS can cause DNA damage, such as base damage and strand breaks. Organisms respond to chromosome insults by activation of a complex and hierarchical DNA-damage response pathway. The extent of DNA damages determines cell fate: cell cycle arrest and DNA repair or cell death. The ATM is a central protein in the response to DNA double-strand breaks by acting as a transducer protein. Collected evidences suggest that ATM is also involved in the response to oxidative DNA damage. <![CDATA[<B>Sistemas aquosos bifásicos</B>: <B>fundamentos e aplicações para partição/purificação de proteínas</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600033&lng=pt&nrm=iso&tlng=pt By the year 2005 the world biochemical market will reach an estimated $ 100 billion and separation processes are a vital link between lab discoveries and the fulfillment of this commercialization potential. The practical application of aqueous two-phase systems (ATPS) to extraction processes has been exploited for several years for the recovery of biological products. Unfortunately, this has not resulted in an extensive presence of the technique in commercial processes. In this paper a critical overview of the fundamental thermodynamic properties related to formation of aqueous two-phase systems and their application to extraction and purification of bioparticules is presented. <![CDATA[<B>Danos oxidativos e neurodegeneração</B>: <B>o quê aprendemos com animais transgênicos e nocautes<I>?</i></B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600034&lng=pt&nrm=iso&tlng=pt Accumulated evidence indicates that oxidative stress plays a role in neurodegenerative diseases, such as Alzheimer, Parkinson and Amyotrophic Lateral Sclerosis. Here, we emphasize the results provided by the technology of genetically modified animals. Studies with transgenic and knockout mice have allowed great advances in the research of oxidative stress in general and in the central nervous system, and are pointing to potential targets for the development of new drugs and therapies to disrupt the cycle of events that lead to neuronal death. Thus, genetically modified animals are a valuable tool for the comprehension of human diseases, including neurodegenerative ones. <![CDATA[<B>Espectroscopia optogalvânica</B>: <B>alguns aspectos relevantes</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600035&lng=pt&nrm=iso&tlng=pt In this work we present the optogalvanic effect in ionized gases in an historical perspective. This effect was observed for the first time by Foote and Mohler in 1925, and explained by Penning in 1928 for mixtures (Ne-Ar) and pure gases (or vapours) in 1937. Also, we show some aspects of the contributions of Romenian authors for the development of optogalvanic spectroscopy, which was used as a new technique only after 1964. <![CDATA[<B>Aspectos toxicológicos e químicos da Anatoxina-<I>a </I>e seus análogos</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600036&lng=pt&nrm=iso&tlng=pt Anatoxin-a and its analogues are azabicyclic alkaloids that represent one of the most powerful nicotinic agonists known for the nicotinic acetylcholine receptor (nAChR). Because of this potent mechanism of action, anatoxin-a and its derivatives represent a target for the discovery of novel drugs. Their syntheses are useful for environmental monitoring and also for pharmacokinetic/pharmacodynamic and toxicological studies. Some strategies for the synthesis of anatoxin-a and analogous compounds are described herein, covering the period from 1996 to the present date. In this review, emphasis is given to the chemical and toxicological aspects of some variants of anatoxin-a, including homoanatoxin-a and anatoxin-a(s). <![CDATA[<B>Estudo de recuperação de glifosato e AMPA derivados em solo utilizando-se resinas nacionais</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600037&lng=pt&nrm=iso&tlng=pt In the present paper we studied the recoveries of glyphosate, N-(phosphonomethyl)glycine (GLY) and its major metabolite, (aminomethyl)phosphonic acid (AMPA) in soil using national (Brazilian) ion-exchange resins, derivatization by a mixture of trifluoroacetic anhydride and trifluoroethanol and analyses by GC-MS. The quantification limits were 12 ng.g-1 for both compounds and the methodology showed a range of recuperation from 85 to 94% with coefficients of variation (CV) ranging from 4.07 to 6.91% for GLY. For AMPA, the mean recoveries ranged from 87 to 102% with CVs ranging from 5.81 to 6.99%. Additional studies showed that, due to the instability of the derivatized compounds, they must be analysed keeping constant time between derivatization and analysis, preferably less than 24 h. <![CDATA[<B>Utilização de um monitor de vídeo como fonte de alta tensão para eletroforese capilar</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600038&lng=pt&nrm=iso&tlng=pt This article describes the use of a conventional CRT monitor as a high voltage power supply for capillary electrophoresis. With this monitor, a 23-kV high voltage with a ripple of 1.32% was observed. The reproducibility of the applied high voltage was evaluated by measuring the standard deviations of peak area and migration time for five consecutive injections of a test mixture containing potassium, sodium, and lithium cations at 50 mmol L-1. The errors were about 2.5% and 0.6% for peak area and migration time, respectively. The maximum current tested was about 180 mA, which covers most capillary electrophoresis applications. This system has been successfully used for several months, maintaining the desired level of performance. <![CDATA[<B>Uma proposta para o ensino da Química Analítica Qualitativa</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600039&lng=pt&nrm=iso&tlng=pt In recent years, because of the need for a more flexible curriculum established by the Curriculum Guidelines of the National Brazilian Education (law 9394/96), the pedagogical project of the Chemistry course of FFCLRP/USP has undergone alterations, amongst them the gradual reduction of the hours devoted to the discipline Qualitative Analytical Chemistry. In this context, this discipline has been carefully analyzed and reorganized in order to allow the elimination of redundancies and the introduction of activities considered important for the professional formation of both chemists and chemistry teachers. In this work, we will discuss the main strategies adopted in this reorganization with the objective of making the teaching/learning process more dynamic and efficient. <![CDATA[<B>A formação do pós-graduando em química para a docência em nível superior</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600040&lng=pt&nrm=iso&tlng=pt The article presents a brief analysis on chemistry post-graduate students' perception on teaching in higher education. This study was done based on the context of students' formation in chemistry post-graduate programs and makes suggestions on how to improve the formation process of post-graduate students in order to decrease the rupture between teaching and research in chemistry post-graduate programs. <![CDATA[<B>Do termoscópio ao termômetro digital</B>: <B>quatro séculos de termometria</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600041&lng=pt&nrm=iso&tlng=pt This work describes the evolution of temperature measurement in the last four centuries using thermometers based on the thermal expansion of liquids such as ethyl alcohol and mercury. The concept of temperature was strongly dependent on the researcher and there was no systematic temperature scale for universal use. The precursor of the common thermometer was the thermoscope, probably invented at the end of the XVIth century. In the XVIIIth century the instrument was greatly improved and several thermometric scales were proposed some of which have been in use until now. These scales were based on arbitrary points. Mercury and ethyl alcohol were the most employed thermometric fluids. In the XIXth century, the concept of absolute zero was a great advance in this field. The most important contribution during the XXth century was the establishment of international temperature scales. The design of the thermometer has been essentially the same along the last 300 years, but many models were proposed for industrial and research purposes. Its association with the densimeter was of great importance for control of industrial chemical processes and also for teaching purposes in the past. Nowadays, there is a clear tendency to replace mercury-based thermometers by electronic digital models. Thermochemistry is the natural relationship between temperature and chemistry. <![CDATA[<B>25 anos de quimiometria no Brasil</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422006000600042&lng=pt&nrm=iso&tlng=pt Chemometric activities in Brazil are described according to three phases: before the existence of microcomputers in the 1970s, through the initial stages of microcomputer use in the 1980s and during the years of extensive microcomputer applications of the ´90s and into this century. Pioneering activities in both the university and industry are emphasized. Active research areas in chemometrics are cited including experimental design, pattern recognition and classification, curve resolution for complex systems and multivariate calibration. New trends in chemometrics, especially higher order methods for treating data, are emphasized.