Scielo RSS <![CDATA[Química Nova]]> vol. 41 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[EXPERIMENTAL AND THEORETICAL ANALYSIS OF NA OXAZINOQUINOXALINE DERIVATIVE FOR CORROSION INHIBITION OF AISI 1018 STEEL]]> The inhibitory ability of an oxazinoquinoxaline derivative (OAQX) against the corrosion of AISI 1018 mild steel induced by aqueous 0.6 mol L-1 NaCl solution is herein evaluated. Linear polarization resistance studies showed the inhibitory efficiency of OAQX varying from 62.75% to 75.93% with OAQX concentration ranged from 0.259 x 10-4 mol L-1 to 3.243 x 10-4 mol L-1. Aiming at to investigate the Tafel curves on the OAQX electrochemical behavior at saline (0.6 mol L-1 NaCl) aqueous media the linear Tafel segments of anodic and cathodic curves were extrapolated to the intersection point which afforded corrosion potential (Ecorr) and corrosion current density (icorr) data. By applying Tafel approach the efficiency of OAQX ranges from 55.30% to 87.60%. In both analysis Langmuir isotherm lead to optimized adsorption parameter. The adsorption mechanism of OAQX is proposed from FTIR experiments and quantum calculations. The theoretical employed method is hybrid B3LYP combined with 6-311++G(d,p). Theoretical results showed OAQX as a promising inhibitor that form a stable protective metal-ligand film on metal surfaces, and differs from several heterocyclic compounds due to its solubility in small amount of DMSO (0.627 x 10-4 mol L-1) which is resistant to a saline aqueous media (0.6 mol L-1 NaCl). <![CDATA[<em>IN VITRO</em> PHYTOREMEDIATION OF PERSISTENT ORGANIC POLLUTANTS BY <em>Helianthus annuus</em> L. PLANTS]]> Plant model systems are needed to properly conduct basic laboratory studies prior to field applications of phytoremediation. In vitro plant cultures are a useful tool for such research. This study focuses on the removal and/or degradation of 24 persistent organic pollutants under in vitro conditions by Helianthus annuus L (sunflower). The main purpose of exploiting this plant for phytoremediation process is due to its strong adaptability to adverse environments conditions such as resistance to pests, disease, and others. The study of bioremediation effects of all chemical molecules under in vitro conditions showed promising results. Sixteen out of twenty-four compounds evaluated reached up to 87% for remediation. The highest accumulation of pollutants was observed in the roots, showing that these results are consistent with the current literature. Through the study, it was observed effective absorption of POPs with logKow ranging from 4.50 to 6.91. Sunflower phytoremediation process efficiently detected heptachlor, aldrin, heptachlor epoxide, trans-chlordane, chlordane, dieldrin, DDE, DDT, methoxychlor, mirex and decachlorobiphenyl. <![CDATA[FOURIER TRANSFORM INFRARED SPECTROSCOPY, THERMOGRAVIMETRIC ANALYSIS, SCANNING ELECTRON MICROSCOPY AS SUPPORTING TOOLS IN QUALITY CONTROL OF ANTIPARASITICS]]> This study shows that Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) can be used as supporting tools for the evaluation of the quality of antiparasitics. In addition, an analytical methodology was developed and validated to quantify simultaneously thiabendazole (TB), febantel (FB), toltrazuril (TZ), and fluazuron (FZ) in bulk and in their veterinary pharmaceutical formulations using reverse phase high performance liquid chromatography (RP-HPLC). In order to investigate stability, pharmaceuticals were submitted to degradation processes under different conditions, such as recommended by the International Conference on Harmonization. The chromatographic conditions were optimized and the validation parameters, such as selectivity, linearity, detection limit, quantification limit, precision, accuracy, and robustness showed results within acceptable standards. All analytes were stable in the stability assays in acid and basic media and thermal conditions, except in the oxidation process, which presented two degradation peaks. Physicochemical characterization by TGA, FTIR, and SEM of raw materials of TB, FB, TZ, and FZ provided information about the authenticity of the analytes, proving the wide applicability of the instrumental techniques. The RP-HPLC proposed method was found to be accurate, precise, and reproducible and can in addition be used for routine quality control analysis. <![CDATA[KINETIC BEHAVIOR OF SOME AZO DYES DECOLORIZATION BY VARIATION OF ZINC OXIDE AND TITANIUM DIOXIDE CONCENTRATIONS]]> The decolorization of three monoazo dyes (acid orange 7, direct orange 34, and methyl orange), one diazo dye (direct yellow 86) and one tetraazo dye (direct red 80) were mediated by n-type semiconductors as ZnO and TiO2 under pseudo-first order conditions at 30 ºC. The decolorization rate constants of these azo dyes were determined, varying the semiconductor concentration for the majority of them from 1.0 to 10.0 g L-1. In general, the highest rate constants were displayed for ZnO. This work elucidates that the decolorization capacity depends on the charge, structure, and adsorption of the azo dye on the semiconductor surface as well as the agglomeration of the photocatalyst particles. <![CDATA[INFLUENCE OF CARDANOL ENCAPSULATED ON THE PROPERTIES OF POLY(LACTIC ACID) MICROPARTICLES]]> In this study, microparticles of poly(lactic acid) (PLA) were produced to encapsulate cardanol, varying molar mass of the polymer matrix, concentration of the emulsifier (PVA) and concentration of the chemical additive (cardanol). The droplet size distribution, polydispersity index, morphology, the interaction between cardanol and PLA, cardanol encapsulation efficiency and release profile of this chemical additive were assessed. The morphological characterization showed that the microparticles containing cardanol were presented as microcapsules up to a maximum cardanol concentration limit that could be incorporated. The addition of cardanol during the production of the microparticles led to an increase in the average diameter of the microparticles obtained, both those with low and high molar mass (MPLA3 and MPLA100, respectively), with the increase depending on the quantity of cardanol incorporated. DSC results showed a shift in melting point and a change in Tg and Tm with the incorporation of cardanol, suggesting an interaction between cardanol and PLA matrix. Higher encapsulation efficiency and slower release of cardanol were achieved when using microparticles with higher molar mass (MPLA100). The microparticles of MPLA100/1PVA/50C provided the slowest additive release among the formulations tested. Therefore, the processes for encapsulation and controlled release of cardanol in the PLA matrix were efficient. <![CDATA[ENZYMATIC BIODIESEL SYNTHESIS FROM ACID OIL USING A LIPASE MIXTURE]]> The conventional biodiesel production process has some disadvantages. It is necessary to use refined vegetable oils with low free fatty acids (FFAs) content. An alternative route is to use low-cost acid oils in an enzymatic process. The use of lipases allows simultaneous esterification of FFAs and transesterification of triglycerides present in raw material forming alkyl esters. The aim of this work was to study the production of biodiesel using soybean oils with different acid contents (Acid Value of 8.5, 50, 90) and ethanol catalyzed by commercial immobilized lipases (Novozym 435, Lipozyme RM IM and Lipozyme TL IM). A significant decrease of acid value was observed mainly with Novozym 435 and Lipozyme RM IM. The use of a mixture of two immobilized lipases was also investigated to decrease catalyst cost and increase the amount of ester produced. The three commercial immobilized lipases were mixed in a dual system and tested for biodiesel synthesis from acid oil (AV of 8.5, 50 and 90). A positive synergistic effect occurred mainly for Lipozyme TL IM (1,3-specific lipase) and Novozym 435 (non-specific lipase) blend. The ester content doubled when this lipase mixture was used in ethanolysis of acid oil with AV of 90. <![CDATA[CHEMICAL CONSTITUENTS DERIVED FROM THE CANARIES MARINE SPONGE <em>Myxilla</em> sp.]]> Stigmasterols, ceramides, including ceramide-1-phosphates and pyrimidines were identified in an ethanol extract of the marine sponge Myxilla sp. The compounds were identified by MS and 1D- and 2D-NMR techniques. A simple method based on an ultra-high-performance liquid chromatography coupled with tandem mass spectrometry was developed to investigate the production of the aforementioned ceramides. This is the first report on ceramide-1-phosphates from a marine sponge. <![CDATA[PREPARATIVE SEPARATION OF ISOQUINOLINE ALKALOIDS FROM PHELLODENDRI CORTEX BY PH-ZONE-REFINING COUNTER-CURRENT CHROMATOGRAPHY]]> pH-Zone-refining counter-current chromatography (PZRCCC) was successfully used for preparative separation isoquinoline alkaloids from Phellodendri Cortex. Two target compounds of berberine and palmatine were completely resolved by a two-phase solvent system chloroform/methanol/water (4:2:2, v/v), with 10 mmol L-1 HCl in upper stationary phase and 10 mmol L-1 TEA in lower organic phase. From 2.0 g of the crude alkaloids, palmatine (448 mg, 95.1%) and berberine (159 mg, 95.4%) were obtained in one-step PZRCCC separation. The chemical structures were identified by ESI-MS and NMR data. The results indicated that PZRCCC separation is an excellent preparative separation method for isoquinoline alkaloids from Phellodendri Cortex. <![CDATA[URSOLIC ACID AND <em>CIS</em>-TILIROSIDE PRODUCED BY <em>Merremia tomentosa</em> AFFECT OVIPOSITION OF <em>Leucoptera coffeella</em> ON COFFEE PLANTS]]> To contribute to the development of new products to control the coffee leaf miner (Leucoptera coffeella), which is a major pest for coffee plants, this work aimed to select plant species able to produce substances active against this insect and to identify the active substances in the selected plant and their protein targets in the insect. Among the extracts of nineteen plant species, only that from leaves of Merremia tomentosa (Choisy) Hall. f. (Convolvulaceae) reduced the oviposition of L. coffeella on leaves of coffee plants. This extract was submitted to successive fractionation steps to achieve the isolation and identification of two active substances, ursolic acid (UA) and cis-tiliroside (CT). An in silico study showed that UA inhibits glycogen phosphorylases (GP) by binding to their allosteric site, while CT probably inhibits xanthine dehydrogenases (XT). As both GP and XT appear to be essential enzymes for insects, these results suggest that, during evolution, L. coffeella learned to identify plants producing inhibitors of these enzymes to avoid oviposition on such plants. Thus, both UA and CT have potential to be used as lead compounds in the development of new products for the control of the coffee leaf miner. <![CDATA[COMPUTATIONAL CHEMISTRY EMPLOYMENT IN VERIFICATION AND VALIDATION OF DETONATION PRESSURE OF PLASTIC EXPLOSIVE - PBX]]> Prediction of chemical explosions parameters is an important step for blast tests for civil and military applications. Applying computational chemistry and experimental results, this paper presents the decay rate of pressure in air from the epicenter of 2.70 kg of PBX-Plastic bonded explosive detonation to the distance of 2.0 meters. Pressure in the epicenter was calculated using reactive molecular dynamics simulations and the incident pressure at 1.3; 1.6 and 2.0 meters were measured with piezoelectric pressure sensors. The explosive for the full-scale test were non-confined in a cylindrical shape. Results of simulation and recorded values were consolidated and the rate of pressure decay was verified by statistic regression. Good agreement was verified between computational and experimental pressures data. This research can help designers to prepare protection devices in test areas, storages of explosives or important buildings for military proposes. <![CDATA[POLYANILINE IN THE ENVIRONMENTAL SCENARIO: AN APPROACH ON HETEROGENEOUS PHOTOCATALYSIS]]> Polyaniline is a conducting polymer that has recently been studied regarding its potential in the removal of contaminants by heterogeneous photocatalysis. Since it is a polymer with a high absorption capacity of photons in the visible region, it promotes the photosensitization of catalysts that are typically inactive in solar systems. The increasing number of publications applying photocatalysis and composite catalysts based on polyaniline highlights the importance of this subject. This review systematizes the most important and specific contributions of composite catalysts formed by polyaniline. The main mechanisms proposed for photosensitization, which show the synergism between the phases of the composite, are summarized. Moreover, the relevance of morphology and conductivity of the composite catalyst, operating parameters (eg. pH, and light source contaminant) are some of the aspects discussed, revealing how these differ from traditional catalysts. Future prospects for the continuation and improvement of this issue mainly involve a greater variety of contaminant removal tests and understanding of relations between the structure of the material and its photocatalytic property. <![CDATA[PHOTOELECTROCATALYSIS ON SEMICONDUCTORS: FROM THE FUNDAMENTALS TO ITS CONFORMATION AT THE NANOSCALE LEVEL]]> The science of semiconductors, essential in electronics, is pivotal also for the most active research fields of environmental science and engineering today - the development of solar energy conversions and advanced oxidation processes, exemplified by the harvesting of sun daylight to produce electric energy, environmentally friendly fuels and to clean up water from harmful pollutants. The advancement of such fields relies on the fundamentals of the photocatalysis at semiconductors, summarized in this review in language familiar to chemists. The theory and experimental onrush emerged mainly during the first half of the 20th century but the rising interest in the science of nanostructured materials in recent decades, besides many insights about the potential of this scale-down of sizes, also forced a revision of the theoretical models. Essentially, the interfacial model of the space-charge layer cannot explain the behavior of nanoparticulate films, even at doped conditions comparable to monocrystalline materials. The present work encompasses the conformation of classical photocatalytic models to the nanoscale size, critically reviewing their features and role for modern electrochemical applications. <![CDATA[USE OF COMMERCIAL STEEL WOOL PADS FOR THE TREATMENT OF WASTEWATER CONTAINING HEXAVALENT CHROMIUM FROM ELECTROCOLORATION PROCESSES OF STAINLESS STEELS]]> Residual solutions containing Cr(VI) ions can be harmful to the environment as well as to human health. Hence, practical and efficient methods for the treatment of such solutions are welcome. In this note, the treatment with commercial steel wool pads of a Cr(VI) residual solution from electrochemical coloration processes of stainless steel is described in detail. Successful treatment was achieved when an amount of steel wool equivalent to 20% in excess in relation to the theoretical stoichiometric amount was used, followed by chemical precipitation with sodium hydroxide up to pH 10-11 and separation by filtration under reduced pressure. The treatment yielded a final solution with concentrations of Cr(III) and Cr(VI) ions of only 0.29 ± 0.02 mg L-1 and &lt; 0.01 mg L-1, respectively. These concentration values are significantly lower than the maximum limits established by CONAMA for industrial wastewaters, attesting the efficiency of the treatment. <![CDATA[DIDACTIC EXPERIMENT OF CHEMOMETRICS FOR PHARMACEUTICAL PELLETS MAPPING USING NEAR-INFRARED SPECTROSCOPY AND MULTIVARIATE CURVE RESOLUTION WITH ALTERNATING LEAST SQUARES: A TUTORIAL, PART IV]]> The aim of this manuscript is to present a didactic experiment based on the combination of Near Infrared chemical imaging and Multivariate Curve Resolution for beginners, undergraduate and graduate students. In this tutorial, using MATLAB environment, the instrumental signals will be separated into two matrices, of spectral profiles and relative concentrations in the samples. Then, chemical images were generated to identify and verify the distribution of the components in the pellet samples. Chemical imaging was obtained from the mapping of predetermined area and the results for relative concentrations obtained in the ALS optimization for the analyzed area. This approach was successfully tested in chemistry undergraduate course at the Chemistry Institute of Campinas State University. <![CDATA[EXTRACTION OF R-(+)-LIMONENE FROM ORANGE PEELS: ASSESSEMENT AND OTIMIZATION OF THE GREENNESS OF TRADITIONAL EXTRACTION PROCESSES]]> This article reports a study, performed in educational context, to increase the greenness of the extraction of R-(+)-limonene from orange peels. Protocols from the literature were evaluated with the green star (GS)metric and new protocols, based in them, were designed to increase the overall greenness. These were tested in the laboratory and their greenness was assessed by traditional greenness metrics and metrics inspired in the industrial activity. Results showed that the steam distillation technique presents the largest overall greenness when evaluated by the GS, because organic solvents are not involved, but mass and energy metrics indicate that the extractions by solvent techniques are greener. This conflict denotes the complexity of the concept of chemical greenness and the need of using several types of metrics when greenness evaluation is at stake. The results show that the inclusion of experiments on the R-(+)-limonene extraction in the educational laboratory is efficient to show the difficulties of assessing the greenness of chemistry and of implementing Green Chemistry.