Scielo RSS <![CDATA[Química Nova]]> vol. 27 num. 2 lang. en <![CDATA[SciELO Logo]]> <link></link> <description/> </item> <item> <title><![CDATA[<B>Luminescent thin films obtained from ytrium hydroxycarbonates activated by terbium or europium</B>]]> These films were obtained by dip coating. Parameters like dislocation velocity; number of deposits, suspension concentration, and number of deposits followed or not by heat treatment between each deposit and calcination temperature were evaluated for establishing the best homogeneity. The obtained films were characterized in terms of their morphology, optical quality and photoluminescence by scanning electron microscopy (SEM), UV-vis absorption spectrophotometry and luminescence spectroscopy, respectively. The morphologic and luminescent characteristics showed dip coating as good laboratory technique for development of thin films for optical applications. <![CDATA[<B>Lignans of <I>Strychnos guianensis</I> (Aublet) Mart.</B>]]> The present communication reports the isolation and identification of three lignans from metanolic root extracts of Strychnos guianensis (Aublet) Mart.: olivil (1), cycloolivil (2) and the unknown derivative cycloolivil carbonate (3). From hexane extracts was identified a long chain fatty acid mixture and the triterpene lupeol. The analyses were based on chromatographic and spectroscopy techniques (IR, MS, GC/MS, ¹H-NMR and 13C-NMR, 1D (BB, DEPT 135) and 2D (¹H, ¹ H-COSY, ¹H, 13C-COSY, ¹H, 13C-COSY-LR, HMQC, HMBC and NOESY) and comparison with literature data. <![CDATA[<B>Quantitative analysis of phenol and alkylphenols in Brazilian coal tar</B>]]> The main purpose of this work is the identification and quantification of phenolic compounds in coal tar samples from a ceramics factory in Cocal (SC), Brazil. The samples were subjected to preparative scale liquid chromatography, using Amberlyst A-27TM ion-exchange resin as stationary phase. The fractions obtained were classified as "acids" and "BN" (bases and neutrals). The identification and quantification of phenols, in the acid fraction, was made by gas chromatography coupled to mass spectrometry (GC/MS). Nearly twenty-five phenols were identified in the samples and nine of them were also quantified. The results showed that coal tar has large quantities of phenolic compounds of industrial interest. <![CDATA[<B>DNA-damaging activity of a cinnamate derivative and further compounds from <I>Cinnamomum australe</I> (Lauraceae)</B>]]> The bioactive compound trans-3'-methylsulphonylallyl trans-cinnamate (1) along with the inactives iryelliptin (2) and (7R,8S,1'S)-delta8'-3',5'-dimethoxy-1',4'-dihydro-4'-oxo-7.0.2',8.1'-neolignan (3) were isolated from the leaves of Cinnamomum australe. The structures of these compounds were assigned by analysis of 1D and 2D NMR data and comparison with data registered in the literature for these compounds. The DNA-damaging activity of 1 is being described for the first time. <![CDATA[<B>Effects of <FONT FACE=Symbol>b</FONT>-polynitration on the catalytic efficiency of rutheniumporphyrins in cyclohexane oxidation</B>]]> Rutheniumporphyrins, especially with several nitro groups in b-positions, were used in the cyclohexane oxidation in the presence of iodosylbenzene, hydrogen peroxide and sodium hypochlorite as oxygen donors, under mild conditions. The beta-polynitrated complexes were able to promote the catalytic cyclohexane oxidation. They show an exceptionally high catalytic efficiency and resistance to attack by strong oxidizing agents. The cyclohexane oxidation was monitored by gas chromatography and the results showed that the beta-polynitrated rutheniumporphyrins are better catalysts when compared to other complexes not beta-polynitrated. In all cases, the 2-phenylsubstituted complexes were more efficient than 4-phenylsubstituted complexes. The importance of the ortho effect to oxidation was shown. <![CDATA[<B>The use of pseudopotentials and HF/MP2/DFT models for the prediction of vibrational frequencies of metal complexes</B>]]> Four different pseudopotentials and three methodologies were employed in the calculation of the geometry and the frequencies of metal complexes like [M(NH3)2X2] [X=halogen, M=Zn, Cd], and [Hg(NH3)2]Cl2. The vibrational assignments were carefully checked and compared to the theoretically calculated ones. Graphical procedures were employed to estimate family errors and their average behavior. The calculated results show the SBK-X basis set with the best results for the geometries and calculated frequencies, for individual species and statistical results. Its use is recommend, mainly if the neighborhood atoms are described with similar pseudopotentials. Excellent results were also obtained with the Hay and Wadt pseudopotential. <![CDATA[<B>Ultra-trace monitoring of copper in environmental and biological samples by inductively coupled plasma atomic emission spectrometry after separation and preconcentration by using octadecyl silica membrane disks modified by a new schiff's base</B>]]> Ultra-trace amounts of Cu(II) were separated and preconcentrated by solid phase extraction on octadecyl-bonded silica membrane disks modified with a new Schiff,s base (Bis- (2-Hydroxyacetophenone) -2,2-dimethyl-1,3-propanediimine) (SBTD) followed by elution and inductively coupled plasma atomic emission spectrometric detection. The method was applied as a separation and detection method for copper(II) in environmental and biological samples. Extraction efficiency and the influence of sample matrix, flow rate, pH, and type and minimum amount of stripping acid were investigated. The concentration factor and detection limit of the proposed method are 500 and 12.5 pg mL-1, respectively. <![CDATA[<B>The choice of the spectral region in the use of spectroscopic and chemometric methods</B>]]> A method is presented for the choice of spectral regions when absorption measurements are coupled to chemometric tools to perform quantitative analyses. The method is based on the spectral distribution of the relative standard deviation of concentration (s c/c). It has been applied to the development of PLS-FTNIR calibration models for the determination of density and MON of gasoline, and ethanol content and density of ethanol fuel. The new method was also compared with the correlation (R²) method and has proved to generate PLS calibration models that present better accuracy and precision than those based on R². <![CDATA[<B>Nitric oxide decomposition on copper supported on zeolites</B>]]> Direct decomposition of NO on copper supported on zeolite catalysts such as MCM-22 and Beta was compared with that on the thoroughly studied Cu-ZSM-5. The catalysts were prepared by ion-exchange in basic media. They were characterized by atomic absorption, surface area, nitrogen adsorption at 77K, X-ray diffraction and temperature programmed reduction. The products of the reaction were analyzed by Fourier transform infrared spectroscopy using a gas cell. Catalytic activity tests indicated that zeolite catalysts, like Beta and MCM-22, lead to NO conversion values comparable to ZSM-5. <![CDATA[<B>Study of the bioavailability of metals in the sediments of Lagoa da Pampulha (Pampulha Lake)</B>]]> The presence of metals in the sediments of Pampulha Lake was investigated in order to determine the bioavailability of metals in these sediments for the cultivation of vegetables such as lettuce. The chemical analyses of metals and As were accomplished by the k0 neutron activation technique. The plans for recovering this lake foresee the removal of the deposited sediments and transport of the discarded material to a specific area after the dam. The present study suggests that this strategy of discarding sediments doesn't imply any risk for the local population, in relation to the bioavailability of metals in these sediments. <![CDATA[<B>Quantitative chemical analysis for the standardization of copaiba oil by high resolution gas chromatograpy</B>]]> Quantitative GC-FID was evaluated for analysis of methylated copaiba oils, using trans-(-)-caryophyllene or methyl copalate as external standards. Analytical curves showed good linearity and reproducibility in terms of correlation coefficients (0.9992 and 0.996, respectively) and relative standard deviation (< 3%). Quantification of sesquiterpenes and diterpenic acids were performed with each standard, separately. When compared with the integrator response normalization, the standardization was statistically similar for the case of methyl copalate, but the response of trans-(-)-caryophyllene was statistically (P < 0.05) different. This method showed to be suitable for classification and quality control of commercial samples of the oils. <![CDATA[<B>Synthesis of new derivatives from 1,2<FONT FACE=Symbol>a</FONT>,4<FONT FACE=Symbol>a</FONT>,5-tetramethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one</B>]]> In this paper we report the synthesis of biologically active compounds through a [3+4] cycloaddition reaction to produce the main frame structure, followed by several conventional transformations. The 1,2alpha,4alpha,5-tetramethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one (11) obtained from a [3+4] cycloaddition reaction was converted into 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8 -oxabicyclo[3.2.1]octan-3-one (13) in 46% yield. This was further converted into the alcohols 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (14), 1,2alpha,4alpha,5-tetramethyl-6,7-exo-isopropylidenedioxi-8 -oxabicyclo[3.2.1]octan-3beta-ol (15), 1,2alpha,4alpha,5-tetramethyl-3-butyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (17), 1,2alpha,4alpha,5-tetramethyl-3-hexyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (18) and 1,2alpha,4alpha,5-tetramethyl-3-decyl-6,7-exo-isopropylidenedioxi-8-oxabicyclo[3.2.1]octan-3 alpha-ol (19). Dehydration of 17, 18 and 19 with thionyl chloride in pyridine resulted in the alkenes 20, 21 and 22 in ca. 82% - 89% yields from starting alcohols. The herbicidal activity of the compounds synthesized was evaluated at a concentration of 100 &micro;g g-1. The most active compound was 21 causing 42,7% inhibition against Cucumis sativus L. <![CDATA[<B>The promoter action of zinc on catalyts for styrene synthesis</B>]]> Ethylbenzene dehydrogenation in the presence of steam is the main commercial route to produce styrene. The industrial catalyst is chromium and potassium-doped hematite, which easily deactivates with time due to potassium loss. In order to find non-toxic and potassium free catalysts, the promoter action of zinc on hematite was studied in this work. It was found that zinc acts as structural promoter by stabilizing the Fe3+ species (active phase) as maghemite. Although it decreases the specific surface area, it increases four times the catalytic activity as compared to hematite. <![CDATA[<b>The significance of lead speciation analysis in blood plasma for health risk assessment</b>]]> Lead absorption is influenced by the species that are formed and the physicochemical characteristics of lead, among others. Lead plasma concentration is < 5% of total blood lead and represents the biologically active fraction able to cross the cell membranes. Health risks mainly depend on a specific metal and its species. Speciation analysis is the analytical activity of identifying and determining different metal species. Chromatographic methods are very useful in the identification of species and the techniques most used to determine metals in biological fluids are ICP OES/MS and AAS. Lead speciation analysis in blood plasma is fundamental for understanding and evaluating the interaction mechanisms between that analyte and its biological targets. <![CDATA[<B>Speciation analysis of arsenic compounds by voltammetric and polarographic methods</B>: <B>a comparative review of their main advantages and applications</B>]]> This paper provides a review on voltammetric and polarographic methods for the speciation analysis of inorganic and organic arsenic compounds in different matrices. A discussion on the main advantages of electroanalytical methods in comparison with other analytical methods employed for arsenic speciation is presented. The mechanistic aspects of the most relevant techniques employing cathodic and anodic stripping voltammetry as well as polarographic methods published in the last twenty five years are summarized and discussed. The bibliographic references cited in this work were selected from the Web of Science (published by the ISI) and the main journals of analytical chemistry. <![CDATA[<B>New stationary phases based on silica for high performance liquid chromatography</B>]]> The present work reviews recent advances in the preparation of new reversed phase packing materials such as sterically protected, bidentate, hybrid organic-inorganic and monolithic phases and phases containing embedded polar groups. The bonding chemistry involved in the preparation of these phases as well as their advantages over conventional C8 and C18 reversed phases are discussed. Understanding the reasons behind the development of these newer column packings helps analysts select the best stationary phase for a given application. <![CDATA[<b><i>Cis</i></b><b>-1,4 polymerization of butadiene with Ziegler-Natta catalyst systems based on neodymium</b>]]> Nowadays the catalyst systems based on neodymium are the ones most used in the high cis polybutadiene production. These systems contain a neodymium compound (catalyst), an alkylaluminium compound (cocatalyst) and a halogen compound (halogenating agent). The microstructure, molecular weight characteristics and the reaction activity are influenced by the nature and concentration of catalyst system components. Those characteristics are also affected by the polymerization conditions. This paper presents a brief review on 1,4-cis-butadiene polymerization on neodymium catalysts. <![CDATA[<B>The use of TEMPO (2,2,6,6-tetramethylpiperidine-<I>N</I>-oxyl) for the oxidation of primary and secondary alcohols</B>]]> The oxidation of alcohols to obtain ketones, aldehydes or carboxylic acids is a fundamental transformation in organic synthesis and many reagents are known for these conversions. However, there is still a demand for mild and selective reagents for the oxidation of alcohols in the presence of other functional groups. As an alternative, the nitroxyl radical TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) has been demonstrated to be a useful reagent for the transformation of alcohols. The oxidation of alcohols using TEMPO is often efficient, fast, selective, made in mild conditions and can tolerate sensitive functional groups. In this article we report different methodologies using TEMPO in the oxidation of alcohols. <![CDATA[<B>Cheese</B>: <B>chemical, biochemical and microbiological aspects</B>]]> This article presents a brief historical outline of cheese manufacture. Chemical, biochemical and microbiological aspects are presented: the main constituents of curd, the reactions involved in the development of flavour, and the role of micro-organisms and enzymes in the fermentation and maturation processes. A brief description of the characteristics of some cheeses is also given. <![CDATA[<B>Hydrogenation of organic compounds by an electrochemical method for <I>in situ</I> hydrogen generation</B>: <B>electrocatalytic hydrogenation</B>]]> Electrocatalytic hydrogenation (HEC) may be compared to catalytic hydrogenation (HC). The difference between these methods is the hydrogen source: HC needs a hydrogen gas supply; HEC needs a source of protons (solvent) to be reduced at a cathode surface. HEC has presented interesting advances in the last decades due to investigation of the influence of the supporting electrolyte, co-solvent, surfactant, presence of inert gas and the composition of the electrode on the reaction. Several classes of organic compounds have been hydrogenated through HEC: olefins, ketones, aldehydes, aromatics, polyaromatics and nitro-compounds. This paper shows some details about the HEC which may be regarded as a promising technique for the hydrogenation of organic compounds both in industrial processes and in laboratories. <![CDATA[<B>New natural products able to act on the stabilization of microtubules, an important target against cancer</B>]]> Microtubules are involved in many aspects of cellular biology and represent an important target of anticancer chemotherapeutics. In the past five years, novel natural products such as epothilones, discodermolide, sarcodictyin, eleutherobin, and laulimalide, all of which have biological activities similar to those of paclitaxel (Taxol<FONT FACE=Symbol>â</FONT>), have been discovered. Taxol<FONT FACE=Symbol>â</FONT> is an important antitumor drug approved by the FDA for the treatment of ovarian, breast and non-small-cell lung carcinomas and became the first natural product described that stabilized microtubules avoiding the cellular replication. The present article reports new natural products that are able to act on the stabilization of microtubules. <![CDATA[<b>A low cost multimeter for data acquisition</b>]]> A digital multimeter (~U$ 240.00 on the national market) connected to a microcomputer by a RS-232 serial interface is proposed for data acquisition in equipment with analog output. Data are measured at the rate of 2 points per second and stored in text files by the software that accompanies the device, running in a Windows environment. The performance of the multimeter was verified by monitoring the transient signals generated in flow injection systems associated with fluorimetric, spectrophotometric and flame photometric detection. In addition, the performance of the proposed device was similar to that attained by employing an interface card with a 12-bit analog-to-digital converter for acquisition of the signals generated by a capillary electrophoresis equipment with oscillometric detection. <![CDATA[<B>Chemical recycling of spent commercial zeolites</B>]]> Pyro and hydrometallurgical processes were applied to the treatment of spent commercial zeolites (a molecular sieve and a ZSM-5 sample). Both catalysts were employed in pilot plant units. They were kept in their original shape, they were not regenerated and were not subjected neither to mechanical stress nor to overheating zones during their time on-stream. Two recycling processes were tested: (i) direct solubilization of samples in mixtures of HF + H2O2 (60 ºC, 1 h). Although silicon was solubilized, insoluble matter was found in both samples, particularly in the molecular sieve, due to its high amounts of alkaline and alkaline-earth metals; (ii) fusion with KHSO4 (5 h, 600 ºC) with KHSO4/zeolite mass ratio 6:1. After fusion the solid was solubilized in water (100 ºC), leaving silicon as SiO2 residue. In both processes, solubilized metals were isolated by conventional selective precipitation techniques. Analysis of final products by common analytical methods shows that metals present in the original catalysts were recovered with very high yields except when the molecular sieve was treated with HF + H2O2. This reactant mixture proved to be suitable for processing zeolites with a low alkaline and alkaline-earth metal content whereas fusion with KHSO4 appeared to be adequate for all types of zeolites. <![CDATA[<B>Bromine recovery from waste aqueous solutions</B>]]> A laboratory procedure was devised to recover bromine from waste alkaline aqueous solutions used in the isotopic determination of N-15. The laboratory apparatus comprises two round bottom flasks (1 and 2 L), a dropping funnel, a gas bubbler, a gas regulator and glass fittings. The waste solution is acidified with sulfuric acid forming molecular bromine that is stripped out by a flow of nitrogen gas bubbled through the solution. This gas is then bubbled through a solution of lithium hydroxide generating lithium bromide and lithium hypobromite. The efficiency of bromine recovery was estimated to be 82&plusmn;2%. This resulting solution was successfully reused in the isotopic determination of N-15. The procedure can recycle most of the bromine used in the laboratory saving resources and preserving the environment. The procedure can be adapted to recover bromine of other laboratory waste streams. <![CDATA[<B>Radiocarbon dating of sambaqui archaeological sites using a CO<SUB>2</SUB> absorption technique</B>: <B>an alternative to the benzene synthesis</B>]]> The sambaquis are archaeological sites with remains of pre-historical Brazilian civilizations. They look like small hills containing different kinds of shells, animal and fish bones, small artifacts and even human skeletons. Since the sambaqui sites in the Rio de Janeiro state are younger than 6000 years, the applicability of CO2 absorption on Carbo-Sorb® and 14C determination by counting on a low background liquid scintillation counter was tested. The International Atomic Energy Agency standard reference material IAEA-C2 was used in order to standardize the method. Nine sambaqui samples from five different archaeological sites found in the Rio de Janeiro state were analyzed and 14C ages between 2100 and 3600 years BP were observed. The same samples were sent to the 14C Laboratory of the Centro de Energia Nuclear na Agricultura (CENA/USP) where similar results were obtained. <![CDATA[<B>The pedagogical nature of experimental activities: research in a teaching credentials course in chemistry</B>]]> In this paper we discuss the characteristics of experimental activities described by teachers and students in a teaching credentials course in Chemistry. The research pointed out a set of characteristics that seem to favor the learning process: the bringing up of the student's knowledge; the mediation by peers; the dialogue to set out the student's knowledge; the debate; the validation of arguments; the discussion about the context. The authors argument that, because of the empirical view of Science present in Chemistry courses, the discussion about the nature of Science is important. <![CDATA[<B>Environmental education at university level</B>: <B>proposed ways</B>]]> Environmental education is a big challenge in this century and the University has an important role to play in it. This paper presents a practical experience of environmental education in the university teaching at the University of Bahia. That experience involves the creation of an interdisciplinary group that has been developing research and teaching activities with interdisciplinary perspectives. The paper also discusses a methodology proposed by this group aiming to include environmental education in science teaching using social and cultural approaches. <![CDATA[<B>A flow analysis experiment involving enzymatic reactions and chemiluminescence</B>]]> An experiment is proposed to introduce some fundamentals of flow analysis, chemiluminescence and kinetic monitoring of enzymatic reactions in undergraduate courses. Chemiluminescence detection is performed with a simple spectrophotometer equipped with a lab-made spiral flow cell constructed from a polyethylene tube. The hydrogen peroxide produced by the glucose oxidation in the presence of glucose oxidase is continuously monitored by the reaction with luminol in alkaline media in a flow injection system. The exercise allows also the discussion of important analytical features and the comparison with different optical methods of analysis. <![CDATA[<B>"Laboratório químico-prático do Rio de Janeiro"</B>: <B>the first attempt at establishing the science of Chemistry in Brazil (1812- 1819)</B>]]> Until the present date, historians of science have described inaccurately the first laboratory created in Brazil for establishing and divulging Chemistry, namely the "Laboratório Químico-Prático do Rio de Janeiro". During recent research carried out in the Arquivo do Museu Imperial (Petrópolis, RJ), I localized a document entitled "Ensaio histórico analítico das operações do Laboratório Químico-Prático do Rio de Janeiro", which allowed me to gain the relevant information to correct some of the observations made in the first chronicles. <![CDATA[<B>Chemistry in Princess Isabel's education</B>]]> The private archive of the Brazilian Imperial Family holds a wealth of little known documents about the education of the daughters of Emperor D. Pedro II, especially of the eldest, Isabel, Princess Imperial. Science, particularly chemistry, for which her father had a particular fondness, occupied an important place in the girl's education. The study of these documents sheds a new light on the contrast between female education in the country in general, during most of the 19th century, and the careful upbringing envisaged by the Emperor for his future successor. <![CDATA[<B>Linus Pauling</B>: <B>why Vitamin C?</B>]]> The overwhelming interest shown by Pauling in the last twenty years of his life on the use of daily megadoses of Vitamin C for the maintenance of good-health is explained by a psyco-analytic approach, on the basis of documented stages of his life, from early boyhood to senior citizen. <![CDATA[<B>The Chemist's education</B>]]> Training of highly qualified personnel is the most transversal axis among those identified in the document "Mobilizing Axes in Chemistry", published by SBQ, in 2002, which demands to deep the discussions, initiated in the symposium "The Chemist's Education", whose main objective was to discuss the repercussions of that training in the teaching and in the industrial section. After the publication of an initial paper, a couple of meetings and workshops held in Rio de Janeiro, in December 2003, involving the national chemist community, discussed the "The role of the graduate degrees in the Chemist's Education" and "The Chemist's Education", and confirmed the need to invest in the formation of qualified human resources in profusion and in all levels. Actions to be taken were delineated. Presently, the graduate programs in Chemistry are showing expressive results. However, although these professionals are mostly absorbed by the academy (the absorption of the industry is less significant), only a few programs give special attention to the didactical and pedagogical training. The regional decentralization is actually a tendency in most programs, but the interaction academy-economic activities is still a challenge. It is necessary to establish with the industrial section, the highly qualified professional's profile in Chemistry that the industry can absorb. The undergraduation is growing in number and quality, however still excessively concentrated in the Southeast area. The national "Curricula Guidelines" for Chemistry Courses, through its flexible approach, propitiate the integral, interdisciplinary (non compartmentalized) and critical-reflexive training of the professionals as citizens and as entrepreneurs. However, deficiencies are still recognized. The evaluation system of undergraduate courses has been able to identify the most fragile modalities of courses and other indicators. It was also verified that Brazilian chemistry industry absorbs minimally the highly qualified professionals, which is attributed to the fact that the Federal Council of Chemistry is vertically organized and does not recognize the graduate degrees as professional qualification. In the conclusion, it stands out, among other aspects, the importance of the effective implantation of the national curricula guidelines, bringing out courses whose didactical and pedagogical projects may offer a solid formation in Chemistry, but comprehensive and general enough to enable the Chemistry professionals to develop varied skills.