Scielo RSS <![CDATA[Química Nova]]> http://www.scielo.br/rss.php?pid=0100-404220030001&lang=en vol. 26 num. 1 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=S0100-40422003000100001&lng=en&nrm=iso&tlng=en</link> <description/> </item> <item> <title><![CDATA[<B>Caracterization and classification of solid waste "pó do balão", produced by merchant pig iron industry which use charcoal as energy source in Brasil</B>: <B>case study of Sete Lagoas region, State of Minas Gerais</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100002&lng=en&nrm=iso&tlng=en This research was developed by considering that the solid waste produced in the process of pig iron production represents the loss of raw materials and the increase in environmental problem. The charcoal based mini blast-furnace off gases dust named CHARCOK was collected from SIDERPA <FONT FACE=Symbol>&frac34;</FONT> Siderúrgica Paulino Ltda, located in Sete Lagoas, Minas Gerais. The Charcok was characterized and classified according to ABNT (Associação Brasileira de Normas Técnicas) standard. The results showed that the Charcok should be classified as Class I Wastes <FONT FACE=Symbol>&frac34;</FONT> "Hazard Wastes" because of its high concentration of phenols (54.5mg C6H5OH/kg). The Charcok had high concentration of iron and charcoal which can be used as energy source. <![CDATA[<B>Determination of <FONT FACE=Symbol>a</FONT>-Tocopherol (vitamin E) in irradiated garlic by high performance liquid chromatography (HPLC)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100003&lng=en&nrm=iso&tlng=en The effects of 60Co ionizing radiations in doses of 0, 75, 100, 150, 200 and 250Gy on garlic, upon the alpha-tocopherol concentration were studied. The alpha-tocopherol contents were established by high performance liquid chromatography (HPLC), after direct hexane extraction from the garlic samples. The alpha-tocopherol was determined through normal-phase column, and mobile phase was composed by hexane: iso-propyl alcohol (99:01 v/v), with 2mL/min flow rate and fluorescence detector. It is statistically shown that an irradiation dose of up to 150 Gy does not affect the garlic alpha-tocopherol content. <![CDATA[<B>Mineral influence on chemical composition of drinking water supply from Mogi-Guaçu and Pardo rivers</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100004&lng=en&nrm=iso&tlng=en This work studied bottom sediment from catchment area of 13 stations of water treatment of Mogi-Guaçu and Pardo river basins, through identification of mineralogical matrix and its correlation with potential bioavailable metal concentrations. The main clay minerals present were kaolinite and illite. The values of iron and manganese grades were derived from reddish-purple soil, which is rich of such elements. They had higher values on areas with weak vegetation cover compared with other areas linked with more vegetation density. Higher values of calcium at Campestrinho station (IG 69) were associated to occurrence by weathering of calcium feldspars markedly present on regional porphiritic acid rocks. The concentrations of phosphorous are characteristically high on areas near urbanized regions. <![CDATA[<B>Construction and application of UNS S31254 stainless steel as indicator electrode in conductimetric tritations</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100005&lng=en&nrm=iso&tlng=en UNS S31254 SS electrodes have been built to substitute platinum in conductimetric titrations. The electrodes were tested in both acid-basic titration (chloridric acid and sodium hydroxide) and precipitation titration (sodium chloride and argentum nitrate as titrant). The practical application was exemplified from conductimetric tritations of HF <FONT FACE=Symbol>&frac34;</FONT> HNO3 mixtures used in metalurgical industry to passivate stainless steels. The results were compared with those obtained using commercial platinum electrodes. The equivalent volumes obtained were comparable within 3% experimental error. Its application depends on the nature of electrolyte. These results have shown that stainless steel, less expensive than platinum (about three order of magnitude), can substitute platinum electrodes in routine analyses and didactic laboratories. <![CDATA[<B>Evaluation of the air pollution by particulate lead</B>: <B>geochemical approach</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100006&lng=en&nrm=iso&tlng=en High lead concentrations up to 5478 mg kg-1 were detected in dry atmospheric precipitations in Rio Grande city and adjacent area. Lead anomalies cover up to 30% of the study area. Lead concentration measurement in dry atmospheric precipitation and suspended particulate matter provides a possibility to detect concentrations above lead threshold in the air. The most impacted areas are fishermen's villages. The most possible source of lead in the air is uncontrolled sub industrial activity of local population <![CDATA[<B>Thermal behavior of hydrated kaolinite</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100007&lng=en&nrm=iso&tlng=en Well-ordered kaolinite from the Brazilian Amazon Region (State of Pará) was initially reacted at 60 &deg;C with a water dimethylsulfoxide mixture. After washing and characterisation, the resulting material was washed several times with methanol and in the final step with water. The water molecules displace the previously dimethylsulfoxide intercalated molecules and two different hydrated kaolinites were obtained. An unstable phase characterized by an interplanar basal distance of 0,996 nm that after drying collapse to the stable 0,844 nm hydrated kaolinite. The dehydration of the sample to disordered kaolinite was accompanied by Powder X-ray Diffractometry, thermal analysis (simultaneous TG and DSC) and FTIR spectroscopy. <![CDATA[<B>Constituents of the bark of <I>Tapirira guianensis</I> (Anacardiaceae)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100008&lng=en&nrm=iso&tlng=en From the hexane extract of barks of Tapirira guianensis were isolated and identified beta-sitosterol, 3beta-O-beta-D-glucopyranosyl-sitosterol, sitostenone and stigmast-4-en-6beta-ol-3-one. Besides these compounds six alkyl ferulates were obtained including a new one with an unusual odd alkyl chain, nonadecyl coumarate. All structures were determined by spectral data. <![CDATA[<B>Determination of paracetamol in pharmaceutical products using a carbon paste biosensor modified with crude extract of zucchini (<I>Cucurbita pepo</I>)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100009&lng=en&nrm=iso&tlng=en Crude extracts of several vegetables such as peach (Prunus persica), yam (Alocasia macrorhiza), manioc (Manihot utilissima), artichoke (Cynara scolymus L), sweet potato (Ipomoea batatas (L.) Lam.), turnip (Brassica campestre ssp. rapifera), horseradish (Armoracia rusticana) and zucchini (Cucurbita pepo) were investigated as the source of peroxidase (POD: EC 1.11.1.7). Among those, zucchini (Cucurbita pepo) crude extract was found to be the best one. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of paracetamol to N-acetyl-p-benzoquinoneimine which the electrochemical reduction back to paracetamol was obtained at a peak potential of <FONT FACE=Symbol>&frac34;</FONT>0.10V. A cyclic voltammetric study was performed by scanning the potential from + 0.5 to <FONT FACE=Symbol>&frac34;</FONT> 0.5 V. The recovery of paracetamol from two samples ranged from 97.3 to 106% and a rectilinear calibration curve for paracetamol concentration from 1.2x10-4 to 2.5x10-3 mol L-1 (r=0.9965) were obtained. The detection limit was 6.9x10-5 mol L-1 and the relative standard deviation was less than 1.1% for a solution containing 2.5x10-3 mol L-1 paracetamol and 2.0x10-3 mol L-1 hydrogen peroxide (n=12). The results obtained for paracetamol in pharmaceutical products using the proposed biosensor and Pharmacopoeial procedures are in agreement at the 95% confidence level. <![CDATA[<B>Evaluating trace element contamination in mariculture activities</B>: <B>partial results of a case study carried out in the coastal region of Santa Catarina, Brazil</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100010&lng=en&nrm=iso&tlng=en Adopting the perspective of human health risk assessment, an interdisciplinary research group has been investigating since 1998 the quality of mussels and oysters cultivated in coastal zones of Santa Catarina State. Evaluation of physico-chemical parameters considered relevant in measuring the degree of eutrophication showed values compatible with the dynamics of well balanced environmental systems. Concentrations of metallic and semi-metallic elements in seawater and bivalves were found to be similar to or lower than those found in Chile, Greenland and the USA. Further investigations focusing upon sediments will provide new and useful data for the management of sustainable mariculture strategies in Brazil. <![CDATA[<B>Bis insertion reaction of 1,2-diphenylacetilene into Pd-C bond of cyclometallated species</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100011&lng=en&nrm=iso&tlng=en The present paper deals with the bis-insertion reactions of 1,2-diphenylacetylene into Pd-C bond of the cyclopalladated complexes [Pd(dmba)(&micro;-NCO)]2 (1) and [Pd(dmba)(MeCN)2](NO3) (2) (dmba = N,N-dimethylbenzylamine, MeCN = acetonitrile). Two new complexes [Pd{PhC=CPh-CPh=CPhC6H4CH2N(CH 3)2}(NCO)] (3) and [Pd{PhC=CPh-CPh=CPhC6H4CH2N(CH 3)2}(NO3 )] (4) were obtained and characterized by IR and NMR spectroscopy and elemental analysis. <![CDATA[<B>Electrochemical detection in capillary electrophoresis</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100012&lng=en&nrm=iso&tlng=en This review focuses the development of electrochemical detection systems coupled to capillary electrophoresis. Conductometric, amperometric, voltametric, and potentiometric modes of detection are reviewed. The positioning of the electrodes, interferences of high electric field, and the materials employed in the fabrication and modification of the electrodes are discussed. The advantages of the use of electrochemical detection with capillary electrophoresis, regarding to the sensitivity and selectivity, is exemplified with a large number of applications. Also, the use of electrochemical detection systems in microchip technology is addressed. <![CDATA[<B>Capillary electrophoresis coupled to plasma spectrometry</B>: <B>an efficient tool for speciation</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100013&lng=en&nrm=iso&tlng=en The most important features of the CE-ICP hyphenation, as well as its advantages and drawbacks as a tool for speciation are discussed. The fundamental principles of capillary electrophoresis and inductively coupled plasma mass spectrometry are also presented. Some applications involving different designs proposed in the literature to couple CE and ICP system for elemental speciation are reviewed. <![CDATA[<B>Application of microbial lipases to concentrate polyunsaturated fatty acids</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100014&lng=en&nrm=iso&tlng=en Several polyunsaturated fatty acids (PUFA) belonging to the ômega 6 series, such as cis-6,9,12 gamma-linolenic acid, as well as those of the ômega 3 series, such as cis-5,8,11,14,17-eicosapentaenoic acid and cis-4,7,10,13,16,19-docosahexaenoic acid are of considerable interest due to their nutritional and therapeutic properties. Methods used for the concentration of PUFA from natural sources include urea adduct formation, solvent winterization, supercritical fluid extraction and lipase-catalyzed reaction. Lipases are known to have little reactivity on PUFA and these acids can be enriched by selective hydrolysis, direct esterification of glycerol with PUFA and interesterification. Since lipase reactions are advantageous with respect to fatty acid, positional specificities and mild incubation condition, these enzymes are considered to be suitable for the production of PUFA concentrates for medical purposes. <![CDATA[<B>Square wave voltammetry. Part I</B>: <B>theoretical aspects</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100015&lng=en&nrm=iso&tlng=en The theoretical aspects of square wave voltammetry were discussed. Reversible, irreversible and quase-reversible electrode reactions were analyzed and the correlations between parameters like frequency, period, square wave potential and amplitude were showed. In this way, diagnostic relationships allow to characterize the electrode process. The analytical applications were discussed in base of the increment in the analytical response (current) due to the characteristics of the developed equations and the unique mode of collecting the electrode response, i.e., the direct and reverse signals. Finally, recent advances in the basic theory, as the applications to the hydrodynamic electrode and the ultramicroelectrode were also analyzed, and the multiple pulses square wave voltammetry was also introduced. <![CDATA[<B>Volatile compounds in floral honeys</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100016&lng=en&nrm=iso&tlng=en A review about origin, composition and importance of volatile compounds in floral honeys is presented. Hydrocarbons, aromatic components, acids, diacids, terpenoids, ketones, aldehydes, esters and alcohols have been found in honey aroma of different botanical origin. Cis-rose oxide has been proposed as an indicator for Tilia cordata honey. Citrus honeys are known to contain methyl anthranilate, a compound which other honeys virtually lack. Linalool, phenylethylalcohol, phenylacetaldehyde, p-anisaldehyde and benzaldehyde are important contributors for the aroma of different unifloral honeys. Both isovaleric acid, gama-decalactone and benzoic acid appears to be important odourants for Anarcadium occidentale and Croton sp. honeys from Brazil. The furfurylmercaptan, benzyl alcohol, delta-octalactone, eugenol, phenylethylalcohol and guaiacol appear to be only relevant compounds for Anarcadium occidentale. The vanillin was considered an important odourant only for Croton sp.. <![CDATA[<B>SPR</B>: <B>New tool for biosensors</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100017&lng=en&nrm=iso&tlng=en This paper reviewed the development and theoretical aspects of surface plasmon ressonance (SPR) technique and discusses this powerful sensor technology in the development of biosensors, as well as for the investigation of biological interactions and clinical assays. The SPR has been proven to be a valuable tool to investigate dynamic processes, such as adsorption, degradation, determination of dieletric properties, association/dissociation kinetics, affinity constants of specific ligand-ligate interactions, allowing real-time analysis at almost any surface. The SPR as a complementary technique alongside electrochemical methods is also presented. <![CDATA[<B>The phosphoinositide cascate</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100018&lng=en&nrm=iso&tlng=en Inositol is a polyalcohol required for the proper formation of cell membranes. In the body, its plays an important role in the transmission of nerve impulses, its also helps in the transporting of fats within the body. In mammals, inositol exists as phosphorylated derivatives, various phosphoinositides, and in its free form. Agonist stimulated hydrolysis of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] is the first step in the transmembrane signalling mechanism when cells respond to external stimuli. Under control of activated phospholipase C (PLC) via G-protein, two second messengers D-myo-inositol 1,4,5-triphosphate [Ins(1,4,5)P3] and diacylglycerol are released into the cell. From Ins(1,4,5)P3, enzymatic process under phosphatases or kinases control affords subsequent inositol phosphate metabolites. During the last decade the synthesis of modified inositol phosphate derivatives has been strongly investigated. This paper reviews principal aspects about synthesis and biological functions of these biomolecules. <![CDATA[<B>Chiral alcohols</B>: <B>chemical and catalytic methods of preparation by asymmetric reduction</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100019&lng=en&nrm=iso&tlng=en The importance of chiral alcohols as starting materials for the production of fine chemicals and as useful chirons for the building of several interesting molecules or natural products is reported. The useful and common methods of asymmetric reduction such as the chemical (with organoboron or organoaluminum reagents) and the catalytic ones (with ruthenium or rhodium complexes) for preparation of chiral alcohols are described; even the newer and much more rare electrocatalytic methods are reported. <![CDATA[<B>Green chemistry</B>: <B>the 12 principles of green chemistry and it insertion in the teach and research activities</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100020&lng=en&nrm=iso&tlng=en Green chemistry <FONT FACE=Symbol>&frac34;</FONT> defined as the design, development, and application of chemical processes and products to reduce or eliminate the use and generation of substances hazardous to human health and the environment. This article summarizes the 12 principles of green chemistry, describing how they have been applied to the academic, industrial and research activities around the world. <![CDATA[<B>A low cost thermal bath (room temperature to 0 ºC)</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100021&lng=en&nrm=iso&tlng=en Thermal baths to decrease ambient temperature are an indispensable tool for most research and teaching laboratories, especially those in tropical or equatorial regions. A simple and inexpensive thermal bath has been developed based on a scratched compressor. It has three possible setups for cooling: sample immersed into the bath, sample flowing through the bath, and cooling liquid flowing in a jacket around the sample. It has been tested for 40 months. The temperature ranges from room temperature to 0 &deg;C, when using water. The repeatability is better than 3% and the precision varies from 0.5% to 2%. <![CDATA[<B>Proposition of a photocatalytic reactor to inactivate airborne microorganisms</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100022&lng=en&nrm=iso&tlng=en The TiO2/UV photocatalytic reactor was investigated as an alternative system to inactivate airborne microorganisms. The experiments performed in the absence of the catalyst showed that direct photolysis was not efficient to destruct microorganisms, with only 30% of inactivation. Similar inactivation percentage was obtained using TiO2 in absence of UV radiation. The destruction of microorganisms present in a contaminated indoor atmosphere, using the combination of TiO2/UV was very efficient, reaching more than 98% of destruction. <![CDATA[<B>Caffeine extraction from stimulating beverages</B>: <B>a new approach for a classic organic chemistry experiment</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100023&lng=en&nrm=iso&tlng=en Caffeine extraction procedures from water soluble and water insoluble materials for preparing stimulating beverages are described. Water soluble materials used were instant tea and coffee and water insoluble materials were, among others, guaraná powder and maté leaves. The extraction of caffeine from water soluble materials, especially instant tea, is more suitable for an organic chemistry teaching laboratory than the classic experiment using tea leaves, due to the economy of time and a larger amount of extracted caffeine. The procedure is time-saving and requires only a four-hour period. The experiments illustrate the extraction process as used in undergraduate organic chemistry laboratories. <![CDATA[<B>A proposal of synthesis for the integrated teaching of organic and inorganic experimental chemistry in the undergraduate courses</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100024&lng=en&nrm=iso&tlng=en The synthesis of the layered compound VO(PO4)(H2O)2 and its use to oxidize 2-butanol to the ketone 2-butanone, is proposed as an experiment to integrate the organic and inorganic experimental undergraduate chemistry courses, in an atempt to overcome the observed disrupture between organic and inorganic chemistry. <![CDATA[<B>Early developments of the helmontian concept of gas</B>: <B>part II</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100025&lng=en&nrm=iso&tlng=en This paper focuses on the early interpretations of the concept of gas, originally created by J. B. Van Helmont (1579 <FONT FACE=Symbol>&frac34;</FONT> 1644). Our main interest is on the ideas of English physicians and chemical philosophers of the seventeenth century. Gas was usually associated with the material cause of diseases, with the vital spirit, or with a volatile spirit produced in some kinds of material transformations. As a general trend, however, the authors who did not want to embrace the details of the medico-chemical system proposed by Van Helmont preferred to use more well-known words (such as vapours, exhalations, effluvia, odours, spirits), avoiding the use of the neologism. <![CDATA[<B>Comentário sobre a revisão "DDT: toxicidade e contaminação"</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422003000100026&lng=en&nrm=iso&tlng=en This paper focuses on the early interpretations of the concept of gas, originally created by J. B. Van Helmont (1579 <FONT FACE=Symbol>&frac34;</FONT> 1644). Our main interest is on the ideas of English physicians and chemical philosophers of the seventeenth century. Gas was usually associated with the material cause of diseases, with the vital spirit, or with a volatile spirit produced in some kinds of material transformations. As a general trend, however, the authors who did not want to embrace the details of the medico-chemical system proposed by Van Helmont preferred to use more well-known words (such as vapours, exhalations, effluvia, odours, spirits), avoiding the use of the neologism.