Resumo em Inglês:Sediment contamination is evaluated by determining organic micropollutants (organochlorine compounds - OCs and polycyclic aromatic hydrocarbons - PAHs) in two important Brazilian water reservoirs. Trace levels of OCs were observed in the Santana reservoir (44.8 ng g-1 d.w. of p,p'-DDT), while in the Funil reservoir the levels were below detection level. Forty-eight percent of the found sigmaocs were polychlorinated biphenyls, 29% dichlorodiphenyltrichloroethane (DDT), 18% Drins, and 5% other pesticides (HCB, Heptachlor, Heptachlor-epoxide, gamma-HCH and a-Endosulfan). We observed lower levels of sigmaPAH in the Funil reservoir (1 to 275 ng g-1d.w.) than in the Santana reservoir (2.2 to 26.7 µg g-1 d.w.).
Resumo em Inglês:The aim of this study is to determine the influence of frying time on the alterations of sunflower, corn and soybean oils during deep fat frying of potato chips. The analytical methods used to evaluate the oil alterations are: free fatty acids, peroxide value, refractive index and total polar compounds. An increase of free fatty acids, refractive index and total polar compounds with frying time were observed. The different behaviors observed for the three vegetables oils can be explained by the differences in the initial composition and quality of them.
Resumo em Inglês:Methane, the main constituent of natural gas (> 85%), is employed in large scale as an energy source (thermoelectric power plants, automobiles, etc). However, significant quantities of this gas contribute to the greenhouse effect. The catalytic combustion of methane can minimize these emissions. Palladium is one of the metals that shows the highest activity, depending on the different active forms of the metal. In this article, we focus on the influence of particle size and pretreatment on the catalytic performance of palladium in the methane combustion reaction.
Resumo em Inglês:Nitrogen content in natural gas was studied in experimental and computational investigations to identify its influence on the emission level of exhaust gases from combustion facilities. Changes in natural gas composition with different N2 concentrations may result from introducing a new source gas into the system. An industrial burner fired at 75 kW, housed in a laboratory-scale furnace, was employed for runs where the natural gas/N2 proportion was varied. The exhaust and in-furnace measurements of temperature and gas concentrations were performed for different combustion scenarios, varying N2 content from 1-10 %v. Results have shown that the contamination of natural gas with nitrogen reduced the peak flame temperature, the concentration of unstable species, the NO X emission level and the heat transfer rate to the furnace walls, resulting from the recombination reactions.
Resumo em Inglês:In this work we describe the processing of poly(styrene sulphonate) films (PSS) doped with neodymium (Nd). Optical density measurements in the UV-Vis-NIR region show the typical bands observed for neodymium chloride (NdCl3) in solution. In the case of films, the intensity ratio between the peaks at 800 nm (4I9/2 -> 4F5/2 + ²H7/2) and 580 nm (4I9/2 -> 4G5/2 + ²G7/2) is equal to 0.83. Infrared spectra present an enhancement in the absorption region of aromatic rings. Site selective luminescence spectroscopy shows that the incorporation of Nd introduces a hipsochromic shift and a line shape definition in UV luminescence compared to PSS film, decreasing the interaction between aromatic groups. In addition, the film exhibits an intense radiative transition at 1061 nm (4F3/2->4I11/2), comparable to the one present in crystalline materials doped with Nd.
Resumo em Inglês:Gaseous mercury sampling conditions were optimized and a dynamic flux chamber was used to measure the air/surface exchange of mercury in some areas of the Negro river basin with different vegetal coverings. At the two forest sites (flooding and non-flooding), low mercury fluxes were observed: maximum of 3 pmol m-2 h-1 - day and minimum of -1 pmol m-2 h-1 - night. At the deforested site, the mercury fluxes were higher and always positive: maximum of 26 pmol m-2 h-1 - day and 17 pmol m-2 h-1 - night. Our results showed that deforestation could be responsible for significantly increasing soil Hg emissions, mainly because of the high soil temperatures reached at deforested sites.
Resumo em Inglês:The state of São Paulo is the main Brazilian consumer of pesticides. Sugar cane, which uses a great amount of these products, is extensivelly cultivated in this state, such as in the Corumbataí river basin, an important source of water for the region. In order to implement an efficient and low-cost monitoring program, the temporal characterization of the use of pesticides on sugar cane in this basin was performed. After knowing the seasonal trends of consumption, a better choice of sampling time, became possible. The combination of data from this survey with partitioning indices, average doses and toxicological classifications showed to be important for defining the pesticides to be included in the monitoring program.
Resumo em Inglês:Droplet counter-current chromatography, rotation locular counter-current chromatography and high-speed counter-current chromatography were applied to the preparative separation of the alkaloid ricinine from the dichloromethane extracts of Ricinus communis leaves. The solvent system used was composed of dichloromethane-methanol-water (93:35:72 v/v/v) and all techniques led to the isolation of large amounts of the alkaloid. The best result was obtained through HSCCC, since the ricinine yield was respectively 50% and 30% higher than when using RLCCC or DCCC.
Resumo em Inglês:Pilocarpus riedelianus was studied in order to obtain compounds with activity against fungi and bacteria. The dichloromethane extract, the most active one, was chromatographed yielding hexane and dichloromethane fractions. Six known sesquiterpenes, alpha-calacorene, beta-calacorene, gamma-calacorene, cadalene, sesquichamaenol and 1-hydroxy-1,3,5-bisabolatrien-10-one were identified in the hexane fractions. The identification of these compound was done by NMR and GC/MS analyses. The hexane fraction from the dichloromethane extract showed activity against several fungi and bacteria.
Resumo em Inglês:Five compounds, 2-hexyl-3-methyl-butanodioic acid (1), cytochalasin D (2), 7-dechlorogriseofulvin (3), cytochalasin B (4) and griseofulvin (5), have been isolated from the endophytic fungus Xylaria sp., and their structures were elucidated on the basis of spectroscopic data. In the bioautography assay against Cladosporium cladosporioides and Cladosporium sphaerospermum, compounds 1 and 2 were found to be active while compounds 3, 4 and 5 did not show antifungal activity.
Resumo em Inglês:Eleven oleanane, ursane and lupane-type triterpenes were isolated from the leaves of Terminalia brasiliensis Camb, daturadiol (3<FONT FACE=Symbol>b</font>,6beta-dihydroxy-olean-12-ene), 3beta-hydroxy-30-norlupan-20-one, lupenone, beta-amyrenone, alpha-amyrenone, lupeol, beta-amyrin, alpha-amyrin, betulin, erythrodiol and uvaol, in addition to squalene, sitosterol and alpha-tocopherol. The structures of these compounds were identified by ¹H and 13C NMR spectral analysis and comparison with literature data.
Resumo em Inglês:A boron-doped diamond electrode is used for determination of Mn(II) in atmospheric particulate matter by square wave cathodic stripping voltammetry. The analytical curve was linear for Mn(II) concentrations between 5.0 and 37.5 µg L-1, with quantification limit of 3.6 µg L-1. The precision was evaluated by the relative standard deviation, with values between 5.1% and 9.3%. The electrode is free of adsorption, minimizing memory effects. Samples collected in the workplace atmosphere of a foundry had Mn(II) concentrations between 0.4 and 4 µg m-3. No significant differences were observed between the proposed method and inductively coupled plasma optical emission spectroscopy.
Resumo em Inglês:In this work, preliminary results of the use of hydrophobic thin films obtained by plasma deposition to protect grains and seeds are presented: grains coated by the films did not present biological degradation when stored in a saturated water vapor environment, but had their germination accelerated in the presence of water. A model that explains the difference of behavior of the films when exposed to water in vapor form or in liquid form, based on the formation of microchannels within the film that lead to water uptake in seeds, is presented. The model was successfully tested using quartz crystal measurements, which showed that the microchannels within the films can favor the adsorption and permeation of water when the films are immersed in water.
Resumo em Inglês:In this paper, we describe a practical route for the synthesis of Biginelli compounds using In(OTf)3. To study the generality of this catalyst, several examples using aromatic aldehydes, 1,3-dicarbonyl compounds, urea, and thiourea were investigated. The present procedure provides an efficient modification of the classical Biginelli reaction, namely short reaction times and simple work-up, that not only preserves the simplicity of the original protocol but also produces excellent yields of 3,4-dihydropyridin-2(1H)-ones. Thiourea was used with similar success to provide the corresponding 3,4-dihydropyridin-2(1H)-thiones. In this case, the (+/-)-monastrol, antimitotic agent, was obtained in 92% yield and new thio analogues were synthesized.
Resumo em Inglês:The driving force of boron adsorption on some tropical soils was evaluated by means of thermodynamic parameters. The batch method was employed, and the reaction was monitored at different pH values. The Langmuir equation successfully fitted the experimental results and provided reasonable isotherm parameters. Boron adsorption increased as a function of the pH of the soil solution and the concentration of added boron. The reaction was favorable and proceeded spontaneously, being strongly exoergic, as indicated by a negative free energy (deltaG) and a separation factor (K R) < 1. The boron adsorption phenomenon and the soil-solution interface were thermodinamically described using a theoretical model.
Resumo em Inglês:Two ortho-iodoallyloxybenzoates, methyl 4-O-allyl-2,3-di-O-benzyl-6-O-(2-iodobenzoyl)- alpha-D-glucopyranoside (3) and methyl 4-O-allyl-2,3-di-O-benzyl-6-O-(2-iodobenzoyl)- alpha-D-galactopyranoside (4) were synthesized in seven conventional steps from methyl alpha-D-glucopyranoside and methyl alpha-D-galactopyranoside, respectively. Bu3SnH-mediated aryl radical cyclization of 3 provided exclusively the hydrogenolysis product 12. The reaction of 4 gave the reduced uncyclized product 13 and only traces of 4A, resulting from 11-endo aryl radical cyclization. In previous papers we described that in similar Bu3SnH-mediated radical reaction of ortho-iodoallyloxybenzamides, analogs of 3 and 4, we obtained macrolactams resulting from 11-endo cyclization. An hypothesis to explain the differences is presented. It was assumed that in the aryl radical formed from iodobenzamides there is a suitable conformation to cyclization, which is stabilized by an intramolecular hydrogen bond.
Resumo em Inglês:Thiosemicarbazones are a class of compounds known by their chemical and biological properties, such as antitumor, antibacterial, antiviral and antiprotozoal activity. Their ability to form chelates with metals has great importance in their biological activities. Their synthesis is very simple, versatile and clean, usually giving high yields. They are largely employed as intermediates, in the synthesis of others compounds. This article is a survey of some of these characteristics showing their great importance to organic and medicinal chemistry.
Resumo em Inglês:We present studies involving metallic ions and the herbicide glyphosate. The metallic complexes of Cu(II), Zn(II), Mn(II), Ni(II), Cd(II), Pb(II), Cr(III), Fe(III), Co(III), ammonium, sodium, Ag(I), alkaline earth metals and of some lanthanides ions are described. The complexes are discussed in terms of their synthesis, identification, stability and structural properties, based on data from the current literature.
Resumo em Inglês:Nitric oxide (•NO) is a substance that acts as a second-messenger and is associated with a number of important physiological functions such as regulation of the vascular tonus, immune modulation and neurotransmission. As a physiological mediator, alteration of its concentration level may cause pathophysiological disfunctions such as hypertension, septic shock and impotence. Possible therapeutic approaches are being developed to control NO levels in vivo. We review herein the main physical and chemical properties of •NO, its biological functions and available chemical interventions to reduce and increment its physiological concentration levels. Recent developments in the field are also highlighted.
Resumo em Inglês:Currently, the accumulation of rice husk is a serious environmental problem. The burning of rice husk generates a considerable volume of ash, that falls to the ground and gets into the air and the rivers, causing a disequilibrium in the ecosystem. This motived research into solutions that aim to exploit the husks for energy generation and the ashes for developing diverse technological products. This work presents the possibilities of using rice husks and their ashes after burning.
Resumo em Inglês:This review reports the determination of absolute configuration of primary and secondary alcohols by ¹H NMR spectroscopy, using the Mosher method. This method consists in the derivatization of an alcohol possessig unknown absolute configuration with one or both enantiomers of an auxiliary reagent. The resulting diastereoisomer spectra are registered and compared, and the chemical shift differences (<FONT FACE=Symbol>Dd</FONT>R,S = deltaR - deltaS) are measured. The determination of the absolute configuration of the alcohol molecule is based on the correlation between its chiral center and the auxiliary reagent's chiral center. Therefore, the determination of the absolute configuration depends on aromatic ring shielding effects on the substituents of the alcohol as evidenced by the ¹H NMR spectrum.
Resumo em Inglês:This article deals with electrocatalysis and electrocatalysts for low temperature fuel cells and also with established means and methods in electrocatalyst research, development and characterization. The intention is to inform about the fundamentals, state of the art, research and development of noble metal electrocatalysts for fuel cells operating at low temperatures.
Resumo em Inglês:MIPs are synthetic polymers that are used as biomimetic materials simulating the mechanism verified in natural entities such as antibodies and enzymes. Although MIPs have been successfully used as an outstanding tool for enhancing the selectivity or different analytical approaches, such as separation science and electrochemical and optical sensors, several parameters must be optimized during their synthesis. Therefore, the state-of-the-art of MIP production as well as the different polymerization methods are discussed. The potential selectivity of MIPs in the extraction and separation techniques focusing mainly on environmental, clinical and pharmaceutical samples as applications for analytical purposes is presented.
Resumo em Inglês:The aim of this paper is the description of the strategies and advances in the use of MIP in the development of chemical sensors. MIP has been considered an emerging technology, which allows the synthesis of materials that can mimic some highly specific natural receptors such as antibodies and enzymes. In recent years a great number of publications have demonstrated a growth in their use as sensing phases in the construction of sensors . Thus, the MIP technology became very attractive as a promising analytical tool for the development of sensors.
Resumo em Inglês:A microcontrolled, portable and inexpensive photometer is described. It uses six light-emitting diodes (LEDs) as radiation sources and a phototransistor as detector, as well as a microcontroller (PIC - Programmable Controller of Interruption). This device provided total autonomy to the proposed photometer, which was successfully applied to determination of Fe2+ in ferrous syrups and of seven clinical biochemical parameters. As the components are cheap (~U$30.00) and easy to find, the proposed photometer is an economical alternative for routine chemical analyses in small laboratories, for research and teaching. Being portable and microcontrolled, it allows doing field chemical analyses.
Resumo em Inglês:A new construction of a capillary electrophoresis instrument with a universal conductivity detector (oscillometric detector) is described. The performance of the electrophoresis equipment was evaluated through the separation and detection of inorganic anions and cations in aqueous solutions. The results reproduced those found in the literature for the investigated probe ions, showing an efficient separation and good repeatability.
Resumo em Inglês:The present contribution describes three different modern experiments for possible adoption in undergraduate organic chemistry laboratories. These are: 1. electrocatalytic hydrogenation of benzaldehyde to benzyl alcohol; 2. identification of three volatile components, obtained from pineapple fruit, by mass spectrometry and 3. microwave mediated fast synthesis of N-(p-chlorophenyl)phthalamic acid from phthalic anhydride and p-chloroaniline under solvent-free conditions. The experiments can be executed in a short period of time, putting the undergraduate student in contact with a variety of topics in organic chemistry and several techniques of analysis, showing multidisciplinarity in organic chemistry.
Resumo em Inglês:This work illustrates the modeling procedure for a solvent mixture using the simplex- centroid approach. The selected experiment was the optimization of the peak current observed in the direct determination of nickel by anodic stripping voltammetry (ASV) in a solvent mixture composed of N,N-dimethylformamide, ethanol and water. The text is presented in a tutorial way, showing in detail the several steps which must be followed in such a process. Since not all possible mixtures lead to a measurable instrumental response, pseudocomponents had to be used to rescale the experimental design. This also allows to show how to apply this tool, usually troublesome for non-specialists in mixture modeling procedures.
Resumo em Inglês:This paper focuses on the teaching development practice in the field of chemistry covering such disciplines as chemistry teaching practice, chemistry teaching instrumentation and chemistry teaching methodology and/or didactics, thereby describing and analysing the logics of the development practice and the role of teachers as well as the epistemological identity configurations (knowledges which are proper to said identity) within this discipline field.