Scielo RSS <![CDATA[Química Nova]]> http://www.scielo.br/rss.php?pid=0100-404220080003&lang=en vol. 31 num. 3 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <link>http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300001&lng=en&nrm=iso&tlng=en</link> <description/> </item> <item> <title><![CDATA[<b>Isolation of compounds attractive to the leaf-cutting ant <i>Atta sexdens rubropilosa </i>forel (hymenoptera: Formicidae) from <i>Mabea fistulifera</i> elaiosome</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300002&lng=en&nrm=iso&tlng=en Mabea fistulifera (Euphorbiaceae)is a pioneer plant species with seeds dispersed by the ant Atta sexdens rubropilosa. Since the ants are attracted to the seeds to use its elaiosome as a source of energy, we investigated its composition. The elaiosomes from 13,000 seeds were extracted with a methanol:chloroform mixture (2:1 v/v) and yielded 22% of a residue. This residue was fractionated by column chromatography and its composition determined by infrared spectroscopy and chromatography/mass spectrometry (GC-MS). The elaiosome lipids are constituted mainly by free fatty acids, triacylglycerols and minor quantities of monoacylglycerols or diacylglycerols. <![CDATA[<b>The volatile constituents of propolis from Piaui</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300003&lng=en&nrm=iso&tlng=en The essential oils of five samples obtained in different regions of the state of Piaui were analyzed by GC-MS. Ninety-one volatile constituents were tentatively identified and eight were positively identified. The principal components obtained from each sample were: 1,8-cineole, exo-fenchol, terpin-4-ol and fenchone (Teresina), a-pinene, caryophyllene oxide, b-pinene and a-copaene (Pio IX), (E)-caryophyllene, a-copaene, a-pinene, caryophyllene oxide and d-cadinene (Campo Maior), (E)-caryophyllene, a-gurjunene and b-selinene (Pedro II) and (E)-caryophyllene, a-gurjunene, d-cadinene and a-copaene (Lagoa de Sao Francisco). The five samples presented differences in the chemical composition of volatile fractions. The studies pointed out the need of characterizing propolis from Piaui by geographic regions and by seasons (drought and rainy periods). <![CDATA[<b>Evaluation of gels obtained from acetylation of chitosan in heterogeneous medium</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300004&lng=en&nrm=iso&tlng=en Chitosan was acetylated during 2, 5 and 10h and physical gels were obtained at different polymer concentrations in N,N-dimethylacetamide containing 5% of LiCl. Acetylation was confirmed by infrared spectroscopy and 13C NMR, and degrees of acetylation in the range of 0.82-0.91 were determined by NMR. The O-acetylation degree (0.12-0.15) was exclusively determined by a volumetric method. Rheological studies showed that the storage modulus values were smaller for the more acetylated samples and increased with the temperature and the polymer concentration. All the gels presented storage modulus superior to loss modulus, evidencing more elastic than viscous characteristics. The results obtained in this work suggest a gelation process based on a balance between O and N-acetylation and intermolecular bonds. <![CDATA[<b>Allelopathic potential of catechins of the <i>Tachigali myrmecophyla </i>(Leguminosae)</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300005&lng=en&nrm=iso&tlng=en Two compounds, (+)-catechin and epicatechin, were isolated from leaves of T. myrmecophyla, using chromatographic techniques. The structural identification was carried out on the basis of ¹H and 13C NMR spectral data and comparison with literature data. The compounds (+)-catechin and epicatechin were submitted to germination inhibition and radicle and hypocotyl growth assays. Results showed some significant activities confirming the initial hypothesis about allelopathic properties of that plant. <![CDATA[<b>Validation of hplc methods for analysis of vitamins B<sub>1</sub>, B<sub>2</sub>, B<sub>6</sub> and niacin naturally present in cereal flours</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300006&lng=en&nrm=iso&tlng=en Complex B vitamins are present in some cereal foods and the ingestion of enriched products contributes to the recommended dietary intake of these micronutrients. To adapt the label of some products, it is necessary to develop and validate the analytical methods. These methods must be reliable and with enough sensitivity to analyze complex B vitamins naturally present in food at low concentration. The purpose of this work is to evaluate, with validated methods, the content of vitamins B1, B2, B6 and niacin in five cereal flours used in food industry (oat, rice, barley, corn and wheat). <![CDATA[<b>Essential oils from leaves of <i>cryptocarya </i>spp from the atlantic rain forest</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300007&lng=en&nrm=iso&tlng=en The essential oils from leaves of four Cryptocarya spp endemic in the Brazilian Atlantic rain forest were obtained by hydrodistillation and shown by GC-MS analysis to contain mono and sesquiterpenes. The major components of the oil of Cryptocarya moschata were linalool (34.3%), a-terpinene (17.0%), g-terpinene (10.4%), 1,8-cineole (5.8%) and trans-ocimene (4.8%), whilst those of C. botelhensis were a-pinene (22.7%), b-pinene (9.2%), trans-verbenol (8.4%), trans-pinocarveol (5.5%) and myrtenal (5.4%). The principal compounds of C. mandioccana oil were b-caryophyllene (13.8%), spathulenol (10.2%), caryophyllene oxide (7.8%), d-cadinene (6.9%) and bicyclogermacrene (6.4%), whilst those of C. saligna were germacrene D (15.5%), bicyclogermacrene (13.8%), spathulenol (11.8%) and germacrene B (5.7%). <![CDATA[<b>Laboratory scale assessment of an electrolytic process for water treatment</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300008&lng=en&nrm=iso&tlng=en Water treatment uses chlorine for disinfection causing formation of trihalomethanes. In this work, an electrolytic water pre-treatment was studied and applied to the water from a fountainhead. The action against microorganisms was evaluated using cast-iron and aluminum electrodes. Assays were made in laboratory using the electrolytic treatment. After 5 min of electrolysis the heterotrophic bacteria count was below 500 cfu/mL and complete elimination of total and fecal coliforms was observed. Using electrolytic treatment as a pretreatment of conventional tap water treatment is proposed. <![CDATA[<b>Determination of aflatoxin B<sub>1</sub> (<i>Piper nigrum</i> L.) and oregano (<i>Origanum vulgare</i> L.) by thin-layer chromatography and densitometry</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300009&lng=en&nrm=iso&tlng=en An analytical study based on extraction with methanol-water, immunoaffinity cleanup and separation, identification and quantification of aflatoxin B1 by thin-layer chromatography,in ground black and white pepper and oregano was carried out. Validation of the applied methodology was done through accuracy and precision studies. Recoveries of aflatoxin B1 and relative standard deviations, from spice samples spiked at levels from 4.86 to 97.70 µg/kg, were, respectively, higher than 72% and lower than 20%. Application to spice samples available in Minas Gerais state, purchased at popular markets, showed no contamination with aflatoxin B1. <![CDATA[<b>Magnetic niobia as adsorbent of organic contaminants in aqueous medium</b>: <b>effect of temperature and pH</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300010&lng=en&nrm=iso&tlng=en This work describes novel materials based on pure iron oxide and iron oxide/niobia composite to produce a magnetic adsorbent. These materials were prepared with synthetic iron oxide and characterized by powder XRD, SEM, FTIR, TPR and Mössbauer spectroscopy. Results showed that the main iron oxides formed were goethite (aFeOOH) and maghemite (gFe2O3) with small particle size. The iron oxide and iron oxide/niobia composite showed high adsorption ability for organic compounds. The positive enthalpy indicated an endothermic adsorption process suggesting physical adsorption. <![CDATA[<b>The influence of drying temperature on the yield and the chemical composition of the essential oil from <i>Tanaecium nocturnum</i> (Barb. Rodr.) Bur. & K. Shum</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300011&lng=en&nrm=iso&tlng=en The yields and chemical compositions of the essential oils obtained by steam distillation of the fresh and dried (30 and 40 ºC) leaves, stems and roots of Tanaecium nocturnum are reported. The identification and quantification of the volatile constituents were accomplished by GC/MS and GC/FID, respectively. The essential oils obtained from the various parts of the plant were constituted mainly of benzaldehyde. Large losses and variations in the quantities of the components during the drying process were observed. The presence of mandelonitrile in higher concentration in the stem and roots indicates that this species produces cyanogenic glycosides. <![CDATA[<b>Thermoanalysis of soybean oil extracted by two methods</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300012&lng=en&nrm=iso&tlng=en The thermal stability of vegetable oils is an important factor that affects their quality. In this study, we investigated the thermal stability of oil and lecithin extracted from soybeans by two distinct processes: mechanical extraction (pressing) and physical extraction (solvent). Thermal analysis was used to obtain information about different methodologies of extraction. The physically extracted products proved more stable than those extracted mechanically. Raman and UV-Vis techniques were applied to underpin the discussion of process differences. <![CDATA[<b>Folates in conventional and organic broccoli and losses during cooking</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300013&lng=en&nrm=iso&tlng=en Broccoli is a vegetable consumed in many countries and a possible source of folates, which are water-soluble vitamins active during DNA synthesis. The folates found in the samples analyzed were 5-methyltetrahydrofolate and 5-formyltetrahydrofolate. The vitamin content varied between 413.7 and 742.2 µg/100 g for 5-methyltetrahydrofolate and from 4.8 to 12.8 µg/100 g for 5-formyltetrahydrofolate. In organic broccoli the amount of 5-methyltetrahydrofolate was significantly higher than in the same vegetable cultivated by traditional methods, for the commercial samples analyzed. The losses of these folates after cooking in water were of approximately 68%, most of it (53%) found in the cooking water. <![CDATA[<b>An easy and direct method for the synthesis of 1,2,4-triazole derivatives through carboxylic acids and hydrazinophthalazine</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300014&lng=en&nrm=iso&tlng=en We have developed an easy method for the synthesis of thirteen compounds derived from 1,2,4-triazoles through a carboxylic acid and hydrazinophthalazine reaction, with a 75-85% yield mediated by the use of agents such as 1-ethyl-3-(3'-dimethylaminopropyl)-carbodiimide hydrochloride and 1-hydroxybenzotriazole. The operational simplicity of this method and the good yield of products make it valuable for the synthesis of new compounds with pharmacological activity. <![CDATA[<b>Analysis of BTEX in the emissions from an internal combustion engine burning diesel oil and diesel-biodiesel mixture (B10) by gas chromatography</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300015&lng=en&nrm=iso&tlng=en This paper describes the procedures for analysing pollutant gases emitted by engines, such as volatile organic compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) by using high resolution gas chromatography (HRGC). For IC engine burning, in a broad sense, the use of the B10 mixture reduces drastically the emissions of aromatic compounds. Especially for benzene the reduction of concentrations occurs at the level of about 24.5%. Although a concentration value below 1 µg mL-1 has been obtained, this reduction is extremely significant since benzene is a carcinogenic compound. <![CDATA[<b>Simultaneous determination of B-Group vitamins in enriched cookies</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300016&lng=en&nrm=iso&tlng=en The objective of this research was to determine the levels of enrichment of vitamins B1, B2, B6 and B3 in different types and brands of enriched cookies. The chromatographic separation was performed in a C18 column with gradient elution and UV detection at 254 and 287 nm. The results show that only 5 of the 24 brands evaluated are in accordance with the Brazilian legislation with respect to the vitamin content declared on the labels. However, consumption of approximately 100-150 g of most of the brands supplies the recommended dietary intake for children and adults of the vitamins evaluated. <![CDATA[<b>Effect of sulfur and nitrogen dioxides on the performance of a proton exchange membrane fuel cell</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300017&lng=en&nrm=iso&tlng=en There is presently much interest in the clean and efficient generation of energy by proton exchange membrane fuel cells (PEMFC), using hydrogen as fuel. The generation of hydrogen by the reforming of other fuels, anaerobic fermentation of residual waters and other methods, often produce contaminants that affect the performance of the cell. In this work, the effect of gaseous SO2 and NO2 on the performance of a H2/O2 single PEMFC is studied. The results show that SO2 decreases irreversibly the performance of the cell under operating conditions, while NO2 has a milder effect that allows the recovery of the system. <![CDATA[<b>Influence of digestion method and sample mass on the recovery of nutrients in organic residues</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300018&lng=en&nrm=iso&tlng=en The influence of nitric-perchloric, aqua regia, dry ashing and microwave digestion methods, in combination with 100 and 200 mg of sample, on the characterization and recovery of nutrients in samples of sludge sewage, poultry, swine, quail and bovine manures, organic compost, organic substrate and humic material were studied. Nitric-perchloric digestion with 200 mg samples recovered the higher nutrient contents. The nitric-perchloric method recovered also low levels of K. Dry ashing caused S volatilization and microwave digestion produced dark color extracts and this impaired S determination. Aqua regia recovered the lowest contents of nutrients in the organic residues evaluated. <![CDATA[<b>The effect of microwave irradiation on the crystalline structure and catalytic activity of clays</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300019&lng=en&nrm=iso&tlng=en The effect of microwave (MW) irradiation on the crystalline structure of two natural clays and one commercial clay, Montmorillonite K10, was analyzed comparing the X-ray diffraction, N2 isotherms, NMR-MAS of 27Al and 29Si spectra of the clays before and after MW irradiation. The preparation of dioxolane ketals of isatin was used to analyze the MW effect on the catalyst activation. The yields achieved using catalysts activated by MW irradiation were lower (2 to 5%) than the yields achieved using catalysts activated by heat in a conventional oven. <![CDATA[<b>Safe shelf life of single-base propellants</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300020&lng=en&nrm=iso&tlng=en The purpose of this work was to determine the safe shelf life of single-base propellants. The kinetic parameters relative to the consumption of the stabilizer diphenylamine (DPA) added to the propellant were determined as a function of the storage and ageing time. High Performance Liquid Chromatography (HPLC) with spectrophotometric detection was used to determine the DPA percentage before and after the artificial ageing at 60, 70 and 80 ºC. The experimental data were very well adjusted to a pseudo-first order kinetic model and the respective kinetic constants are 8.0-10-3 day-1 (60 ºC); 1.9-10-2 day-1 (70 ºC); 1.2-10-1 day-1 (80 ºC). The activation energy was calculated as 130 kJ mol-1 and the half-time for depletion of the DPA at the hypothetical temperature of 40 ºC of storage was estimated as being 6 years. <![CDATA[<b>Determination of etoricoxib in human plasma using automated on-line solid-phase extraction coupled with LC-APCI/MS/MS</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300021&lng=en&nrm=iso&tlng=en A liquid chromatography-tandem mass spectrometry method with atmospheric pressure chemical ionization (LC-APCI/MS/MS) was validated for the determination of etoricoxib in human plasma using antipyrin as internal standard, followed by on-line solid-phase extraction. The method was performed on a Luna C18 column and the mobile phase consisted of acetonitrile:water (95:5, v/v)/ammonium acetate (pH 4.0; 10 mM), run at a flow rate of 0.6 mL/min. The method was linear in the range of 1-5000 ng/mL (r²>0.99). The lower limit of quantitation was 1 ng/mL. The recoveries were within 93.72-96.18%. Moreover, method validation demonstrated acceptable results for the precision, accuracy and stability studies. <![CDATA[<b>Study of lead behaviour in Brazillian latosoils treated with phosphates</b>: <b>contributions to the remediation of contaminated sites</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300022&lng=en&nrm=iso&tlng=en Phosphates have been used for lead immobilization in soils but the influence of soil type is not fully understood. In this work, lead chemical behaviour in two Brazilian latosoils (LA and LV) was studied via treatment with phosphates. The Pb concentration in Toxicity Characteristic Leaching Procedure (TCLP) solutions was decreased in all treatments. After treatment with H3PO4 the Pb concentration in the LA remained within the regulatory limit established by EPA. The ecotoxicological results with Daphnia pulex showed that this treatment reduced the lead bioavailability. Sequential extraction analyses showed that the lead was transferred from the most available to the residual fraction. Relevant decrease of soluble lead was observed in all phosphate treatments. <![CDATA[<b>The antagonic effect of iron and zinc in formulations of feeding diets studied by response surface methodology for mixtures</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300023&lng=en&nrm=iso&tlng=en Nutritional therapy with enteral diets became substantially specialized over the last years. This work's aim was to study the effect of the components of a formulation: fiber, calcium and medium-chain triglycerides for dialysability of minerals. Analysis of multiple variables was carried out using response surface methodology. The level curve showed an antagonic effect of interaction between iron and zinc. TCM was the variable responsible for characterizing competition between the two minerals in the formulation. More studies on foods are needed for knowing the effecs of minerals in formulations. <![CDATA[<b>Amphotericin B associated with triglyceride-rich nanoemulsion</b>: <b>stability studies and <i>in vitro</i> antifungal activity</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300024&lng=en&nrm=iso&tlng=en Amphotericin B (AB) is the standard drug for invasive fungal infection therapy. It has a broad spectrum of activity and it is the best antifungal available against most yeasts and molds. Its therapeutic use, however, is limited by significant side effects, leading to a low therapeutic index when it is used as the traditional formulation (Fungizone®). Due to self-association, AB can form pores in cholesterol-containing membranes. We propose a triglyceride-rich nanoemulsion as a delivery system for AB in low levels of aggregation to reduce the toxicity against host cells. <![CDATA[<b>Evaluation of the chemical compostion of wine produced from jabuticaba (<i>Myrciaria jabuticaba</i>)</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300025&lng=en&nrm=iso&tlng=en This work aimed to characterize the chemical composition of samples of alcoholic beverages fermented from jabuticaba produced in five successive crops. Up to 2005 most of the results didn't meet the current legal standards for wines and there was a negative correlation between parameters such as pH and volatile acidity, pH and total acidity, volatile acidity and alcohol content (p<0.01). The implementation of Good Manufacturing Practices and must sulfitation during the 2006 harvest lowered volatile acidity and more than 60% of the samples were in accordance with legislation. Also, a significant improvement in alcohol content was found (p<0.05) <![CDATA[<b>Casbane diterpenes and acetophenones of <i>Croton nepetaefolius</i> (Euphorbiaceae)</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300026&lng=en&nrm=iso&tlng=en Croton nepetaefolius is an aromatic plant native to the northeast of Brazil where it is extensively used in folk medicine as a sedative, orexigen and antispasmodic agent. The present work deals with the chromatographic analysis of the ethanolic extract of Croton nepetaefolius stalk. It allowed the isolation and characterization of two diterpenoids named 1,4-dihydroxy-2E,6E,12E-trien-5-one-casbane and 4-hydroxy-2E,6E,12E-5-one-casbane, two acetophenones named 2-hydroxy-4,6-dimethoxyacetophenone and 2-hydroxy-3,4,6-trimethoxyacetophenone and the steroids 3-O-b-D-glucopiranosylsitosterol and a mixture of b-sitosterol and stigmasterol. Structural elucidation was done on the basis of spectral data, mainly high field NMR and EIMS. <![CDATA[<b>Volatile constituents of the oils from <i>Povedadaphne Quadriporata</i> (lauraceae) from "Alberto M. Brenes" biological preserve, Costa Rica</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300027&lng=en&nrm=iso&tlng=en The composition of the leaf, bark and wood oils of Povedadaphne quadriporata W. Burger from Costa Rica were analyzed by capillary GC/FID and GC/MS. One hundred and sixty-three compounds were identified. The major components from the leaf oil were a-pinene (21.2%), germacrene D (18.1%), b-pinene (14.8%), a-phellandrene (7.8%), a-copaene (6.6%), b-caryophyllene (6.1%) and d-cadinene (3.5%). From bark oil, the main constituents were a-pinene (27.7%), p-cymene (7.8%), b-pinene (7.4%), camphene (3.6%), a-copaene (3.5%) and limonene (3.3%). From wood oil, 1,10-di-epi-cubenol (8.0%), a-eudesmol (3.4%), cadalene (3.4%) and d-cadinene (3.0%) were the major compounds identified. This paper describes for the first time the composition of essential oils in this unique species and genus. <![CDATA[<b>Analytical study of oxygenated species in the ozonized theobroma oil</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300028&lng=en&nrm=iso&tlng=en Ozonization of theobroma oil at different applied ozone dosages was carried out with measurement of peroxide index values, oxygen percentage content and fatty acids composition. The comparison of peroxide values with percentage content of oxygen at different applied ozone dosages showed good correlation (r=0.9923). Unsaturated fatty acids and triacylglycerols decrease with ozone applied dosage due to ozone reaction with double bonds. Small amounts of oleic acid were consumed with applied ozone dosage at 35 mg/g, which demonstrated that peroxide values and oxygen content were not principally increased by the ozone attack on the double bonds, but other mechanisms could be involved in the reaction system. <![CDATA[<b>Structure, reactivity, and biological properties of hidantoines</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300029&lng=en&nrm=iso&tlng=en Hydantoin (imidazolidine-2,4-dione) is a 2,4-diketotetrahydroimidazole discovered by Baeyer in 1861. Thiohydantoins and derivatives were prepared, having chemical properties similar to the corresponding carbonyl compounds. Some biological activities (antimicrobial, anticonvulsant, schistosomicidal) are attributed to the chemical reactivity and consequent affinity of hydantoinic rings towards biomacromolecules. Therefore, knowledge about the chemistry of hydantoins has increased enormously. In this review, we present important aspects such as reactivity of hydantoins, acidity of hydantoins, spectroscopy and cristallographic properties, and biological activities of hydantoin and its derivatives. <![CDATA[<b>The state of the art of chromatography associated with the tandem mass spectrometry for toxic compound analyses in food</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300030&lng=en&nrm=iso&tlng=en Chromatography combined with several different detection systems is one of the more used and better performing analytical tools. Chromatography with tandem mass spectrometric detection gives highly selective and sensitive analyses and permits obtaining structural information about the analites and about their molar masses. Due to these characteristics, this analytical technique is very efficient when used to detect substances at trace levels in complex matrices. In this paper we review instrumental and technical aspects of chromatography-tandem mass spectrometry and the state of the art of the technique as it is applied to analysis of toxic substances in food. <![CDATA[<b>Liquid-phase microextraction (LPME)</b>: <b>fundamentals and applications to the analysis of drugs in biological samples</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300031&lng=en&nrm=iso&tlng=en The analysis of drugs and metabolites in biological fluids usually requires extraction procedures to achieve sample clean-up and analyte preconcentration. Commonly, extraction procedures are performed using liquid-liquid extraction or solid-phase extraction. Nevertheless, these extraction techniques are considered to be time-consuming and require a large amount of organic solvents. On this basis, microextraction techniques have been developed. Among them, liquid-phase microextraction has been standing out. This review describes the liquid-phase microextraction technique based on hollow fibers as a novel and promising alternative in sample preparation prior to chromatographic or electrophoretic analysis. The basic concepts related to this technique and its applicability in extraction of drugs are discussed. <![CDATA[<b>The urban solid waste integrated management environmental and economic-energetic perspective</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300032&lng=en&nrm=iso&tlng=en The importance of urban solid waste integrated systems is characterized by the several components of these systems, which are, basically, formed by physical, chemical and biological methods. This article, characterizes these methods and, which is also important, identifies the several and potential environmental impacts of those techniques. It's also extremely important to make a study of the economic rentability of those infrastructures and, also, characterize the quantitative energetic contributions of some components of these systems. This study was analysed and their results are presented in this article. <![CDATA[<b>Ring-closing olefin metathesis</b>: <b>a powerful tool for the synthesis of natural macrocycles</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300033&lng=en&nrm=iso&tlng=en For a quarter of a century, metathesis has become indispensable for the synthesis of natural and non-natural products, particularly of biologically active compounds. This review illustrates through a maximum of appropriate examples the power and the versatility of the metathesis ring-closure (RCM) reaction as a key ring-closure methodology for the synthesis of natural macrocycles. Its high functional group compatibility as well as the possibility of further transformations makes this reaction a powerful tool in the cases where the structural framework and function requirements are difficult to meet. <![CDATA[<b>Peptide sequencing using mass spectrometry</b>: <b>a practical guide</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300034&lng=en&nrm=iso&tlng=en This paper introduces the basics of peptide mass spectra interpretation applied to proteomics and is directed to chemists, biochemists and biologists. The manuscript presents a well detailed protocol aiming to serve as a first choice guide for understanding peptide sequencing. The tutorial was elaborated based on both a thorough bibliographic revision and the author's experience. In order to prove the applicability of the proposed guide, spectra obtained on different instruments have been successfully interpreted by applying the presented rational. <![CDATA[<b>Evaluation of chemical precipitation and encapsulation techniques in the treatment and joint disposal of liquid wastes containing chromium and laboratory glassware</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300035&lng=en&nrm=iso&tlng=en In this paper, we present procedures for the treatment and final disposal of residual solutions containing chromium, in order to evaluate the effectiveness of chemical precipitation of the metal and the potential of the glass encapsulation technique, using broken laboratory glassware. The results demonstrated that pH-values convenient for chemical precipitation are between 10 - 11. With regard to Cr(OH)3 encapsulation, the leaching and solubilization tests allowed to classify the waste as non-dangerous and non-inert. Finally, it is pointed out that the adoption of waste management practices in universities should be encouraged, helping to train professionals skilled in good laboratory practices. <![CDATA[<b>Hydrometallurgical route to recover molybdenum, nickel, cobalt and aluminum from spent hydrotreating catalysts in acid medium</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300036&lng=en&nrm=iso&tlng=en This work describes a hydrometallurgical route for processing spent commercial catalysts (CoMo and NiMo/Al2O3). Samples were preoxidized (500 ºC, 5 h) in order to eliminate coke and other volatile species present. The calcined solid was dissolved in concentrated H2SO4 and water (1:1 vol/vol) at 90 ºC; the insoluble matter was separated from the solution. Molybdenum was recovered by solvent extraction using tertiary amines at pH around 1.8. Cobalt (or nickel) was separated by addition of aqueous ammonium oxalate at the above pH. Phosphorus was removed by passing the liquid through a strong anion exchange column. Aluminum was recovered by neutralizing the solution with NaOH. The route presented in this work generates less final aqueous wastes because it is not necessary to use alkaline medium during the metal recovery steps. <![CDATA[<b>Environmental education in secondary schools in the region of Ribeirão Preto (SP, Brazil)</b>: <b>how teachers' views of the environment determine their teaching and some reflections on chemistry teachers' higher education</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300037&lng=en&nrm=iso&tlng=en During short courses, 95 secondary school teachers from 49 state schools and 421 students from the Ribeirão Preto region (in Sao Paulo state, Brazil, with a population of 530,000) were asked to fill in different questionnaires. The points raised in the teacher's questionnaire were used as a guide to establish a continuous dialogue during the short courses. Most of the schools claimed to have some kind of environmental education (EE). Based on the questionnaires and dialogues we analyzed how the teachers' perceptions on EE reflect on the views secondary students hold about their own responsibility for preserving the environment. The role of universities in the preparation of chemistry teachers capable of effectively approaching EE is also discussed. <![CDATA[<b>The place of teaching practice and internship in the chemistry courses leading to teaching credentials at the state universities of São Paulo</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300038&lng=en&nrm=iso&tlng=en The literature presents a new understanding of the teaching practice and the supervised internship.Mutual interaction between them is expected one providing subsidies to the other.The present article shows the conceptions prevailing at the São Paulo state universities regarding these activities.Students,when interviewed, report difficulties in dealing with classroom situations. It is possible to observe that chemists wish to prepare new chemists deviating from the objectives of a Chemistry course leading to teaching credentials . <![CDATA[<b>Non-destructive determination of total nitrogen in plants by diffuse reflectance near infrared spectroscopy</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300039&lng=en&nrm=iso&tlng=en Diffuse reflectance near-infrared (DR-NIR) spectroscopy associated with partial least squares (PLS) multivariate calibration is proposed for a direct, non-destructive, determination of total nitrogen in wheat leaves. The procedure was developed for an Analytical Instrumental Analysis course, carried out at the Institute of Chemistry of the State University of Campinas. The DR-NIR results are in good agreement with those obtained by the Kjeldhal standard procedure, with a relative error of less than ± 3% and the method may be used for teaching purposes as well as for routine analysis. <![CDATA[<b>Demonstrating the fundamentals, potentialities and limitations of sequential injection analysis</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300040&lng=en&nrm=iso&tlng=en The sensitivity and accuracy of sequential injection methods are dependent on efficient overlapping of reagent and sample zones as they are propelled toward the detector cell. The formation of the reduced phosphomolybdic acid is used to demonstrate that the overlapping efficiency in a fixed reaction coil relies on a suitable choice of reagent to sample volume ratio. Additionally, under poor mixing conditions or highly concentrated samples, the reaction extension is strongly dependent on the reagent concentration. The zone-sampling concept is exploited to determine phosphate in cola-based soft drinks after in-line dilution in an auxiliary coil. <![CDATA[<b>Teaching chemistry at the Higher School of Agriculture "São Bento", Olinda - São Lourenço da Mata - Pernambuco (1912-1936)</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422008000300041&lng=en&nrm=iso&tlng=en The present work proposes the investigation of the role of chemistry in the curriculum of the Higher School of Agriculture "São Bento" (1912-1936) and its function in the education of agronomic engineers. The circumstances under which the Higher Schools of Agriculture and Veterinary Medicine in Olinda were founded at the beginning of the XXth century are discussed. The article further treats the influence of the principles of Justus von Liebig, which were seen at that time as essential for a rational agriculture.