Scielo RSS <![CDATA[Química Nova]]> vol. 39 num. 8 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[AVALIAÇÃO DOS TEORES DE Pb, Cd, Sn, Co, Hg, Mo E As EM SOLOS DA PENÍNSULA FILDES - ANTÁRTICA]]> Antarctic Continent is one of the few places that has not been explored at all, but studies show that this place is suffering interference by human activities. Therefore, monitoring of this region becomes very important. After optimization and verification of the methodology, the concentrations of Pb, Cd, Sn, Co, Hg, Mo and As in soil samples collected in the Fildes Peninsula, King George Island, Antarctica, were determined by ICP-MS. The ranges found (µg kg-1) were: for Pb 525.2-2314.1, for Cd 54.8-193.8, for Sn 54.8-193.8, for Co 2095.0-11094.1, for Hg &lt; 2.4-54.6, for Mo 5.3-38.7 and for As 120.3-1297.1. In general, the presence of these elements can be attributed to different factors, such as natural composition of soil, melting process and transport of chemical elements caused by physical phenomena as sea and air currents, besides anthropic contamination. Using enrichment factor was possible suggest contribution by anthropic activities mainly for Co and As. Thus, it is important monitoring the elements levels constantly assisting in environmental protection. <![CDATA[ANALYSIS OF A COMMERCIAL PORTABLE LITHIUM-ION BATTERY UNDER LOW CURRENT CHARGE-DISCHARGE CYCLES]]> The dependence between the transferred charge and the corresponding transference time to charge and discharge a portable cell phone Li-ion battery (LiCoO2/C) under cycles of low intensity currents was studied in detail. The voltage curve profile between 3.0 and 4.2 V and the charging and discharging time are strongly influenced by the applied current intensity. A linear dependence between the stored and extracted charges, into and from the battery, with the intensity of applied current was also observed. Allometric equations were found to describe the correlation between the charge transference time and the applied current intensity to charge and discharge the battery. <![CDATA[APPLICATION OF THERMAL PLASMA FOR INERTIZATION OF SLUDGE PRODUCED DURING TREATMENT OF LANDFILL LEACHATE]]> One of the outstanding issues of concern by governments and society in general relates to the final destination of solid waste, which can bring severe impacts on social, political, economic and environmental dimensions. The sustainable development of enterprises and industries goes for the care of the planet, thus ensuring the quality of life for future generations and the planet. The disposal of municipal waste in landfills is the technique most commonly employed for the remediation of solid residues. The residues undergo decomposition beneath the soil and in the presence of water this generates leachate, which percolates down to the bottom of the landfill through drainage. This drained liquid is collected from the landfill installations and subjected to treatment, which involves physico-chemical and biological processes. Landfill leachate commonly contains heavy metals due to the incorrect disposal of products such as fluorescent bulbs and batteries. In this context, a method for the treatment of sludge originating from the physicochemical remediation of leachate using thermal plasma is proposed in this paper. The efficiency of the method was verified by monitoring the total organic carbon content, water content and density of the sludge. The quantity of metals present in the samples was determined before and after pyrolysis by thermal plasma using flame atomic absorption spectroscopy (FAAS), scanning electron microscopy (SEM) and X-ray fluorescence (XRF) spectrometry techniques. The results show that the leachate treatment method used was efficient, presenting the best results for the samples of iron and zinc. <![CDATA[INTERACTION OF CHALCONES WITH CT-DNA BY SPECTROPHOTOMETRIC ANALYSIS AND THEORETICALSIMULATIONS]]> Chalcones are open chain molecules precursors of flavonoids and isoflavonoids, found spread in edible plants. Because they are easily accessible trough Claisen Shmidt condensation, a great variety of derivatives are available. They have also shown potential in pharmacological and biological applications. It is known that chalcone derivatives display a role in the treatment of complex diseases such as cancer, among others, where the DNA is considered as the target for the action of these kinds of compounds. This action is commonly explained as the inhibition of the DNA replications and transcriptions through interactions. However, not conclusive associations between these DNA-Drug interactions and toxicity have been found. This research focuses on the capacity of a chalcone`s family to interact with DNA. Therefore, the binding constants for each compounds with Calf Thymus DNA [CT-DNA] were determined by spectrophotometric titration at room temperature. In addition, the effect of increasing the chalcone`s concentration over the relative viscosity of CT-DNA at room temperature was assessed. On the other hand, with the aim to find the optimal DNA-chalcone configurations, as well as consistently predict their binding, a computational work was undertaken. To accomplish these goals within a reasonable time framework, an empirical scoring function (AScore) and a docking engine (ShapeDock) were performed using the ArgusLab package. The results of viscosity and docking measurement provided structural insights which suggest that chalcones bind with DNA via interaction as well as intercalation. The presence of interactions is also evidenced by the spectrophotometric study which showed luminescence quenching of the chalcones upon interaction with CT-DNA. <![CDATA[ANÁLISE DA CONCENTRAÇÃO E COMPOSIÇÃO DE AEROSSÓIS DE QUEIMADAS NO PANTANAL MATO-GROSSO]]> The Earth's atmosphere has a large number of small solid and liquid particles which differ in size, shape and composition. One of the most obvious characteristics of the phenomena of air pollution is linked to the occurrence of atmospheric aerosol. The research was conducted in a protected nature reserve, Private Natural Heritage Reserve (RPPN) Social Service of Commerce (SESC) Pantanal , at 111 m of altitude (16º39' S, 56º47' W) and is referred to here as SESC - Advanced Research Center of Wetland , located about 160 km from Cuiabá - MT. The sampling device consists of samplers fine and coarse particles, separating the fine fraction of the aerosol (dp &lt;2.5 µm) from the coarse fraction (2.5 &lt;dp &lt;10 µm). In August 2012, concentrations of fine particles were up to nine times higher (up to 18 µg m-3) than that recorded in the rainy months of 2012 and 2013 (amounts around 2 µg m-3). The concentrations of coarse particles were up to three times higher in the dry season, compared to the rainy season. <![CDATA[MICROEXTRAÇÃO LÍQUIDO-LÍQUIDO DISPERSIVA ASSISTIDA POR VORTEX E ULTRASSOM APLICADA À DETERMINAÇÃO DE AGROTÓXICOS TRIAZINAS, TRIAZINONAS E O TRIAZOL FLUTRIAFOL EM ÁGUA]]> This study aimed at developing and validating a method for the simultaneous determination of triazines (ametryne, atrazine, prometryne and terbuthylazine), triazinones (metribuzin and hexazinone) and a triazole (flutriafol) in water by ultrasound vortex assisted dispersive liquid-liquid microextraction (USVADLLME) and GC-MS. The experimental conditions that provided the best results were: 5.00 mL of sample, 100 mL of extractor solvent (toluene), vortex agitation for 30 s and sonication for 1 min. at 240 W and 40 ºC. The USVADLLME provided recoveries ranging from 77.2% to 109%, with a repetitivity and intermediate precision varying from 1.4 to 9.0% and 2.9 to 15%, respectively. The method detection limits ranged between 0.10 and 2.71 µg L-1. The method was applied to different surface water samples and a matrix effect was not observed. Once validated, the proposed method was applied to ten water samples of an important agricultural region of Mato Grosso State/Brazil, but none of the studied analytes were detected. The USVADLLME is proposed as an efficient, fast, simple and non-expensive alternative technique for the simultaneous determination of multiclass pesticides in water. <![CDATA[ELECTROCHEMICAL OXIDATION OF ETHYLENE AT PANI/Pt AND Ag/PANI/Pt MODIFIED ELECTRODES]]> The electrochemical behavior of ethylene on PANI/Pt and Ag/PANI/Pt modified electrodes was investigated in different media. Morphology of the deposits of PANI were observed by SEM analysis, complemented by the EDX techniques to obtain the Ag composition that shows that Ag is deposited in the polymeric matrix which covered the whole platinum surface. The electrodic system comprising Ag/PANI/ Pt electrode exhibited a more important electrocatalytic response for ethylene oxidation in neutral solutions than the PAN/Pt and Pt electrodes at 20 ºC.The results suggest that the oxidation of ethylene on Ag/PANI/Pt electrode is limited by adsorption-controlled reaction while the oxidation at PANI/Pt is mass transport-limited. <![CDATA[DETERMINAÇÃO DE METAIS POR TÉCNICAS DE ESPECTROMETRIA ATÔMICA EM AMOSTRAS DE CARVÃO MINERAL E CINZAS UTILIZANDO METODOLOGIA DE SUPERFÍCIE DE RESPOSTA]]> This paper describes the method optimization using response surface methodology for Cu, Fe, Zn and Na determinations in coal and ash samples by spectrometry techniques. The sample preparation was performed using a recirculation system adapted in the digestion tubes. This system allowed increase of temperature in the digester block above the boiling point of the reaction medium, avoiding acid evaporation during the heating. The digestions were realized with HNO3 and H2O2 for 1 h in a digester block at 145 °C. The limits of detection for determination of Cu, Fe, Zn and Na in both samples were satisfactory. The RSD for the analytes were lower than 6.0%. Statistical tests showed that results for all analytes do not vary significantly with official method (ASTM), considering a confidence limit of 95%. Besides, the accuracy was verified by recovery tests, whose values ranged from 92.7 to 104.7% in coal, and 98.7 to 115.3% in ash. <![CDATA[MECHANISTIC ASPECTS OF PHOTOCATALYTIC ACTIVITY OF METALLOPORPHYRIN-TITANIUM MIXTURES IN MICROEMULSIONS]]> Photocatalytic activity of titanium citrate and its water-in-oil microemulsions mix with zinc (II) tetraphenylporphyrin have been studied by means of adding 4-chlorophenol and following its degradation using artificial ultraviolet and visible light. 4-Chlorophenol is degraded in 71 and 86%, respectively, in 30 min with the generation of various intermediaries, whose possible formation mechanisms have been proposed based in the results of this research. The generation of benzene derivatives, different to those usually reported for this type of treatment, suggests the possibility of controlling the generation of intermediaries by simply changing the type of surfactant. In the case discussed here, we have derived a simple method for isomer generation of trimethylbenzene using a model organohalogenated compound as water contaminant and cetyltrimethylammonium bromide as surfactant. <![CDATA[<em>IN VITRO</em> Cr(VI) SPECIATION IN SYNTHETIC SALIVA AFTER RELEASING FROM ORTHODONTIC BRACKETS USING SILICA-APTES SEPARATION AND GF AAS DETERMINATION]]> A method for Cr(VI) speciation in synthetic saliva after releasing from orthodontic brackets, using silica nanoparticles organofunctionalized with (3-aminopropyl)triethoxysilane (APTES) for Cr(III)/Cr(VI) separation and GF AAS determination is proposed. Under the optimized conditions, Cr(VI) speciation was performed using 150 mg of silica organofunctionalized with 2.0% (v v-1) of APTES at pH 8. It was observed different sensitivity when calibrations of GF AAS were performed using Cr(III) or Cr(VI) as standard solutions. Consequently, calibrations using stoichiometric mixtures (Cr(III) + Cr(VI)) were used for total Cr determination and calibration using Cr(VI) was used only for the determination of this specie. The reliability of the proposed silica-APTES separation procedure and GF AAS determination was checked by addition of both species in synthetic saliva. Recoveries ranging from 97 to 110% were obtained. The repeatability, based on the relative standard deviation (RSD) inter days was less than 6%. A corrosion test was carried out on 20 orthodontic brackets from two different models, after immersion in synthetic saliva (pH=6.0) at 37 °C with agitation (125 rpm) for 24 h. It was observed that about 40% of the total chromium released from the analyzed orthodontic brackets was Cr(VI). <![CDATA[Cr/S/TiO<sub>2</sub>-LOADED HOLLOW GLASS MICROSPHERES AS AN EFFICIENT AND RECYCLABLE CATALYST FOR THE PHOTOCATALYTIC DEGRADATION OF INDIGO CARMINE UNDER VISIBLE LIGHT]]> Chromium and sulfur co-doped nanometer TiO2 hollow glass microspheres (Cr/S/TiO2-HGM) were synthesized by a sol-gel method. Characterization used X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), N2 adsorption-desorption (Brunauer-Emmett-Teller (BET) measurements) and UV-Vis diffuse reflectance spectroscopy. The photocatalytic activity was evaluated by photodegradation of indigo carmine in an aqueous solution under visible light irradiation. The results indicated that the Cr/S/TiO2 containing 0.60% (atomic ratio) chromium and 1.2% (atomic ratio) sulfur calcined at 500 ºC for 2 h had high catalytic efficiency under visible light irradiation. The floating Cr/S/TiO2-HGM catalyst had greater photocatalytic activity than Cr/S/TiO2 powder. Therefore, Cr/S/TiO2-HGM is a promising, high-performing, visible-light-driven, and more reusable photocatalyst. <![CDATA[SULFONIC ACID-FUNCTIONALIZED LUS-1: AN EFFICIENT CATALYST FOR ONE-POT SYNTHESIS OF 2,4-DIAMINO PYRIMIDINE-5-CARBONITRILE DERIVATIVES]]> An efficient acidic functionalization of mesoporous silica LUS-1 (Laval University Silica) and its application as a recyclable heterogeneous catalyst in the synthesis of 2,4-diamino pyrimidine-5-carbonitriles via condensation reaction of aromatic aldehydes, malononitrile and guanidine carbonate in solvent-free condition has been reported. This green method offers a number of advantages such as short reaction time, good yields, simple work-up procedure, recyclable catalyst and environmentally friendly conditions. <![CDATA[PRECIPITATION REACTION OF CLAVULANIC ACID: THERMODYNAMIC AND ELECTRONIC STUDY]]> In the present article the theoretical calculation of thermodynamic parameters for the two main precipitation agents, potassium 2-ethylhexanoate and t-octylamine, employed by the pharmaceutical industry to obtain potassium clavulanate for clinical use, is described. The results obtained using the standard thermochemistry calculation in the Gaussian package and by calculation of the reactivity indexes of the reagents and products are compared. The calculated thermodynamic parameters indicate that the reactivity indexes present a better correlation with the experimentally obtained percentage yield. In addition, a series of additional precipitation agents that are also used in industrial procedures to obtain potassium clavulanate for clinical use, were compared. This was done to verify if any present, a priori, better properties than potassium 2-ethylhexanoate or t-octylamine. The consistency of the reactivity indexes calculated clearly suggests that the methodology employed can be used to screen future precipitation agents for possible use in the production of potassium clavulanate. <![CDATA[THE PHENOLIC COMPOSITION OF THE HEPATOPROTECTIVE AND ANTIOXIDANT FRACTIONS OF <em>Albizia lebbeck</em> L.]]> An investigation of the hepatoprotective and antioxidant activities of the chloroform, ethyl acetate and n-butanol fractions of the leaves of Albizia lebbeck L. was performed. The first two fractions expressed the best results regarding the suppression of the increased levels of plasma amino-transferases and alkaline phosphatase in liver-damaged mice (after intoxication with CCl4) compared with silymarin and the significantly increased GSH content of alloxan- induced diabetic rats compared with vitamin E (tests and reference drugs were orally administered). The bioactive fractions of Albizia lebbeck L. were subjected to chromatographic analysis to investigate their phenolic contents using a HPLC-PDA-ESI-MS/MS technique in the negative ion mode. The results constitute the first report of the presence of seven compounds in the genus Albizia, three of which were identified as 3-O-caffeoylquinic acid, cafeic acid, myricetin; four other flavonoids (in mg 100 g-1 dry powder ± SD), myricetin 3-O-rhamnoside (0.129 ± 0.0052), quercetin 3-O-dideoxypentoside (0.011 ± 0.001), kaempferol 3-O-glucoside (0.015 ± 0.002), quercetin 3-O-dihexoside (0.138 ± 0.002); quercetin 3-O-rutinoside at a level of 0.135 ± 0.004; and the aglycones quercetin, luteolin and kaempferol. Method validation was performed, providing an analytical technique that can be used to detect trace amounts of the identified compounds in Albizia extracts with rapid sample preparation. <![CDATA[COMPLEXOS DE INCLUSÃO BINÁRIOS, TERNÁRIOS E QUATERNÁRIOS CONTENDO ÓLEO ESSENCIAL DE <em>Lippia sidoides</em>]]> The aim of this work was the production and characterization of binary, ternary and quaternary complexes based on β-cyclodextrin (β-CD) and Lippia sidoides essential oil (EO). OE:β-CD formulations at proportions of 1:10 to 2:10 (binary); added with surfactant or polymer (ternary) or with both (quaternary) were prepared and submitted to spray drying at optimized operating conditions (inlet gas temperature: 160 °C, drying gas flow rate: 60 m3/h; feed flow rate: 4 g/min; pressure and flow rate of the atomizing air: 2.5 kgf/cm2 and 17 lpm). The responses evaluated were the encapsulation efficiency (EE), powder properties, product morphology, and process efficiency (REC). The results showed that the addition of polymer and surfactant to β-CD, generating ternary and quaternary complexes improved the encapsulation efficiency, drying yield, and modify the particles morphology. Samples with lower EO: β-CD ratio (1:10) showed high encapsulation efficiency. <![CDATA[CLINICAL ASPECTS OF THE POISONING BY THE PESTICIDE ENDOSULFAN]]> Endosulfan is an organochlorine insecticide, widely used in insect control. Unfortunately, it is also an acute neurotoxic compound to both insects and mammals, including humans, and has been responsible for many severe poisonings and several fatal cases. Endosulfan also imitates or enhances the effect of the female hormone estrogen, having the capability of causing reproductive and developmental damage in both, animals and humans, and its exposure has been linked to liver tissue injury. This persistent lipophilic compound is one of the most abundant organochlorine pesticides in the environment, capable of undergoing long range transport to remote locations such as the Arctic. It is practically water-insoluble, but readily adheres to clay particles and persists in soil and water for several years. Its indiscriminate and injudicious use in the control of insects on a wide range of agricultural products and in the extermination of house-hold pests, has considerably increased the hazard risk for human health. Also, this compound has a high fatality rate in humans when ingested accidentally, from food or water contaminated, or in suicidal cases. The aim of this article is to review and summarize chemical, biochemical, environmental, and toxicological data of endosulfan and draw attention to its toxicological potential risk to human health. <![CDATA[ESTRATÉGIAS DE SÍNTESE NA DESCOBERTA DE FÁRMACOS: O EMPREGO DA SÍNTESE ORIENTADA PELA DIVERSIDADE ESTRUTURAL]]> Drug discovery often involves screening synthetic small molecules for their ability to bind to a macromolecular target. Target-Oriented Synthesis of a specific compound or a focused library can be planned combining retrosynthetic analysis and rational drug design. Biologically active molecules also can be identified through the unfocused screening of compound libraries. Diversity-Oriented Synthesis (DOS) emerges as an excellent strategy that leads to a library of structurally complex and diverse small molecules, covering a larger chemical space and increasing the probability of identifying modulators. <![CDATA[VALIDAÇÃO DE UM MÉTODO ANALÍTICO PARA DETERMINAÇÃO DE MARCADORES ORGÂNICOS GEOQUÍMICOS EM AMOSTRAS DE SEDIMENTOS MARINHOS]]> This paper describes the validation of an alternative method for determination of n-alkanes, sterols (OLs) and n-alkanols (ALCs) in marine sediments, through adaptation of clean up. The method reduced the material consumption, the discards produced and working time. The recovery percentages were 60-129% for n-alkanes, 52-67% for OLs and 43-141% for ALCs, acceptable values compared to other studies. The application in Antarctic marine sediments presented satisfactory results indicating contribution of planktonic organisms, higher animals and a little contribution from vegetation. <![CDATA[NANOPARTÍCULAS DE Au EM LÍQUIDO IÔNICO SUPORTADAS EM FILMES BIOPOLIMÉRICOS: UMA AULA PRÁTICA PARA INVESTIGAÇÃO DA ATIVIDADE ANTIMICROBIANA]]> The synthesis of Au nanoparticles (NPs) in ionic liquid (IL) supported on biopolymers films applied in the investigation of antimicrobial activity was introduced as a new experimental practice for undergraduates in the nanotechnology discipline at the Department of chemistry, at University Federal of Rio Grande- FURG. The Au NPs were synthesized by reduction of tetrachloroauric acid complex trihydrate (HAuCl4.3H2O) in IL 1-n-butyl-3-methyl-imidazolium hexafluorophosphate (BMI.PF6) using sodium borohydride at room temperature. Subsequently, the Au NPs were supported in the biopolymers films using a solution of cellulose acetate dissolved in acetone. The biopolymers films containing supported Au NPs were applied in the investigation of antimicrobial activity against bacteria Escherichia coli e Staphylococcus aureus. <![CDATA[PREPARAÇÃO DE 1,2,4-OXADIAZOL: SEQUÊNCIA DIDÁTICA APLICADA EM DISCIPLINA DE SÍNTESE ORGÂNICA NA GRADUAÇÃO]]> 1,2,4-oxadiazoles are used in a wide range of applications, including medicinal chemistry and chemistry of materials. However, this kind of oxadiazoles is not usually prepared in an undergraduate organic teaching laboratory. This work describes a didactic sequence for the preparation of 1,2,4-oxadiazols, mediated by microwave irradiation, employing home-use microwave oven. For the development of this practice, one lecture and one laboratory session were used. At the end of this session, a questionnaire was applied to evaluate the didactic sequence. The conclusion was that this approach can be used for the preparation of 1,2,4-oxadiazoles as a pedagogical practice to make the process of teaching easier and enjoyable.