Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> vol. 28 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[MALDI Imaging Mass Spectrometry of Fresh Water Cyanobacteria: Spatial Distribution of Toxins and Other Metabolites]]> Cyanobacteria are among the most ancient forms of life, yet they are known to synthesize highly sophisticated defense molecules, such as the highly hepatotoxic cyclic peptides microcystins and nodularins produced by the genera Microcystis, Anabaena and Nodularia. These metabolites are released by cyanobacteria to water environments causing episodes of fatalities among animals and humans. To better understand the releasing of these metabolites, imaging mass spectrometry (IMS) using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) was herein applied to determine the spatial distribution of such toxins directly on agar-based cultures. Other key metabolites such as aeruginosin 602 and the siderophore anachelin were also mapped in mixed cyanobacterial cultures, showing the great potential of IMS to spatially monitor the biochemical details of cyanobacterial defense and interactions. <![CDATA[A Sensitive Voltammetric Determination of Anti-Parkinson Drug Pramipexole Using Titanium Dioxide Nanoparticles Modified Carbon Paste Electrode]]> In this study, a facile sensor based on TiO2 nanoparticles modified carbon paste electrode was developed for voltammetric determination of pramipexole in pharmaceutical formulations and biological samples. Surface of the fabricated electrode have been characterized using field emission scanning electron microscopy. Under the optimized experimental conditions, the modified electrode was exhibited excellent electrocatalytic activities and a sensitive oxidation peak at 0.9 V in the phosphate solution of pH 5.0 for electrooxidation of pramipexole. The plot of pH vs. Ep generated a slope of 62.5 mV per pH in the pH range of 3.0-13.0 indicating the contribution of an equal number of electrons and protons in the electrode process. A differential pulse voltammetry method was developed in the concentration range of 0.46-100 μmol L-1 with a limit of detection of 0.14 μmol L-1. The proposed method is simple, rapid, and inexpensive and also showed good selectivity and sensitivity toward pramipexole. <![CDATA[A Green Extraction of Trace Iodine in Table Salts, Vegetables, and Food Products Prior to Analysis by Inductively Coupled Plasma Optical Emission Spectrometry]]> In this study, we report a new method for iodine extraction from table salts, vegetables, and other food products using ultrasound-assisted extraction, prior to the iodine determination by inductively coupled plasma optical emission spectrometry. For the ultrasound-assisted extraction, deionized water as the extraction solvent and an extraction time of 5 min were found to be the most optimum condition. A linear calibration curve was plotted for 0.1 to 200.0 mg L-1 iodine convention. The limits of detection and quantification were 0.049 and 0.164 mg L-1, respectively. The precision for intra- and inter-day analyses was 2.75 and 4.54%, respectively. The accuracy of the method was confirmed with certified reference materials. Recoveries in 47 real samples were ranged between 80.48 and 118.1%. Therefore, the proposed method could be considered as a rapid, simple, and environmental-friendly method (the green extraction) to determine the trace amounts of iodine in different kinds of food products. <![CDATA[Synthesis of Submicrometer Calcium Carbonate Particles from Inorganic Salts Using Linear Polymers as Crystallization Modifiers]]> In this study, we report the synthesis of submicrometer calcium carbonate particles using the simplest approach of mixing solutions of calcium chloride and ammonium carbonate inorganic precursors in the presence of crystallization modifiers. Instead of the typical crystallization of CaCO3 into large calcite crystals with rhombohedral morphology, very small uniform spherical vaterite particles were formed with the addition of small amounts of the anionic homopolymer poly(sodium 4-styrenesulfonate) (PSS). In contrast, large spheres made of a collection of calcite polycrystallite aggregates formed in the presence of poly(acrylic acid) (PAA). Crystal growth in a pre-organized environment created by the selective distribution of CaII ions in the shell of polyestyrene-b-poly(acrylic acid) (PS-b-PAA) core-shell spherical micelles revealed a rather poor control of the size and morphology. Therefore, the PSS anionic homopolymer can be applied to the synthesis of submicrometer CaCO3 particles from solutions of inorganic salts, which is a much cheaper and sustainable method than controlled CO2 gas production and diffusion. <![CDATA[Anodic Oxidation of Sulfide to Sulfate: Effect of the Current Density on the Process Kinetics]]> The kinetics of the conversion of sulfide to sulfate by electro-oxidation, using a boron-doped diamond (BDD) electrode was studied. Different applied current densities were tested, from 10 to 60 mA cm-2. The results showed that the electrochemical conversion of sulfide to sulfate occurs in steps, via intermediate production of other sulfur species. The oxidation rate of the sulfide ion is dependent on its concentration and current density. The reaction order varies with the current intensity, being 2 for the lower applied current intensity and high S2- concentration, which is compatible with a mechanism involving two S2- ions to give S22-. For higher current densities, where current control is less important, reaction order varies from 0.15 to 0.44 for the current densities of 20 and 60 mA cm-2, respectively. For the formation of SO42- from S2- electro-oxidation, the reaction orders with respect to sulfide concentration and current intensity are 0 and 1, respectively. <![CDATA[Computational Study of Electronic Effects from β-Substituents on the Tautomerism of Naphthazarin Derivatives]]> In this work, semi-empirical AM1 and DFT B3LYP/6-31G** calculations were applied in the study of the interconversion among tautomers of several naphthazarin and 5-amino-8-hydroxy-1,4-naphthoquinone β-substituted derivatives bearing electron-donor or electron-withdrawing groups. Using a semi-empirical method, detailed potential energy landscapes for proton transfers were built, from which four tautomers and four transition states of interconversions were identified for each compound. These structures were recalculated without restraints and, using the Boltzmann distribution, the populations for each of the four tautomers and their respective molar fractions were calculated. The calculations showed that the tautomeric equilibrium is shifted to the tautomer where the ring with the substituent has a quinonic nature and is more pronounced when the β-substituent is an electron donor group. For derivatives of 5-amino-8-hydroxy-1,4-naphthoquinone, an equilibrium between an aromatic and a 1,5-naphthoquinonic non-aromatic enamine was observed, being the former the most stable. <![CDATA[Central Composite Design to Optimizate the Derivatization Procedure for Analysis of Biogenic Amines by HPLC-UV]]> A simple benzoylation procedure was optimized for the biogenic amines derivatization prior to high-performance liquid chromatography determination. The significant factors affecting biogenic amine benzoylation yield were optimized by central composite design (CCD). The obtained optimal conditions resulted in a chromatographic peaks area increase with fewer interferences. Moreover, the efficiency parameters for chromatographic separation of putrescine, histamine and tyramine were determined under optimum operating conditions, which included: capacity factors or retention (k') = 2.5-4.2, selectivity factors (α) &gt; 1 and resolution values (Rs) &gt; 1.5, indicating that the column provided good separation of the analytes. The optimized method was applied in spiked fish samples with standard solutions of putrescine, histamine and tyramine at concentrations of 50, 80 and 50 mg L-1, respectively, to achieve recovery rates in a range from 90.89 to 96.65% for putrescine; 93.36 to 95.87% for histamine; 86.57 to 93.33% for tyramine, with the relative standard deviation (RSD) less than 4%. <![CDATA[Non-Synergistic UV-A Photocatalytic Degradation of Estrogens by Nano-TiO<sub>2</sub> Supported on Activated Carbon]]> Many studies have reported significant improvements in the photocatalytic degradation capacity of TiO2 immobilized in carbonaceous materials, mainly due to a well-characterized synergistic effect. The photocatalytic degradation of the estrogens 17β-estradiol and 17α-ethynylestradiol was evaluated using 1 mg L-1 aqueous solutions, employing a nanocomposite containing TiO2 and activated carbon (TiO2-AC) prepared by sol-gel technique. The synthesized materials were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). These techniques allowed to estimate the carbon proportion (11.4 wt.%), the phase composition (anatase: 80.2%, brookite: 14.0%, and rutile: 5.8%) and the superficial morphology. Using UV-A radiation provided by a high pressure mercury vapor lamp (125 W) and the synthesized photocatalysts, it was observed the almost complete removal of both estrogens in times shorter than 10 minutes. Considering the similarity between the degradation percentage of nanocomposites (TiO2 and TiO2-AC), no synergistic effects between AC and TiO2 could be assumed. <![CDATA[Effect of Sulfamic Acid on 1,3-Dipolar Cycloaddition Reaction: Mechanistic Studies and Synthesis of 4-Aryl-<em>NH</em>-1,2,3-triazoles from Nitroolefins]]> A facile and new metal-free 1,3-dipolar cycloaddition reaction for the synthesis of 4-aryl-NH-1,2,3-triazoles from nitroolefins and NaN3 employing NH2SO3H has been developed. Sulfamic acid proved to be an efficient additive in this transformation by inhibiting the formation of triaryl benzene. Mechanistic aspects and key intermediates associated with this transformation have also been characterized by online monitoring of the reaction using electrospray ionization tandem mass spectrometry method (ESI-MS/MS). The protocol emphasizes broad substrate scope for many functionalities, simple reaction conditions such as stability to open air, less reaction time, easy work-up, eco-friendly and with good to excellent yields. <![CDATA[Warmingiins A and B, Two New Dimeric Naphthoquinone Derivatives from <em>Sinningia warmingii</em> (Gesneriaceae)]]> Chemical investigation of Sinningia warmingii (Gesneriaceae) tubers lead to the isolation of two new dimeric naphthoquinone derivatives, named warmingiins A and B, besides six known compounds, aggregatin E, aggregatin F, tectoquinone, halleridone, cleroindicin B, and cornoside. All compounds were identified by spectroscopic analysis, mainly nuclear magnetic resonance (NMR) and mass spectrometry (MS), and comparison with the literature. The structure of the warmingiin A, which is an artifact of warmingiin B, was confirmed by X-ray diffraction analysis. Antimicrobial activity of the ethanolic extract and fractions of S. warmingii was evaluated against Staphylococcus aureus, S. epidermidis, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, C. dubliniensis, C. glabrata and C. parapsilosis. All samples were inactive. <![CDATA[Distribution and Sources of Aliphatic and Polycyclic Aromatic Hydrocarbons in Surface Sediments of Itajaí-Açu Estuarine System in Brazil]]> The Itajaí-Açu estuarine system, located in southern Brazil, has great economic importance due to the presence of two ports (Itajaí and Navegantes). This system is affected by industrial and dredging activities, which can cause the remobilization of pollutants accumulated over time in the sediment. In this context, hydrocarbons were assessed in twelve surface sediment samples. n-Alkane and polycyclic aromatic hydrocarbons (PAH) concentrations were determined by gas chromatography and their sources assessed. Total concentrations ranged between 0.50 ± 0.04 and 69.70 ± 3.90 μg g-1 dry weight (d.w.) for n-alkanes and from 63.9 ± 12.1 to 1459.0 ± 43.5 ng g-1 d.w. for PAH. Most of the sediment samples presented carbon preference index (CPI) values close to unity, indicating that the area is submitted to petroleum-related sources, mainly close to Itajaí harbor, where an intense unresolved complex mixture (UCM) was observed. The presence at all stations of αβ-hopane biomarkers also indicated petrogenic input. Based on selected PAH ratios, the sedimentary PAH composition reflects a mixture of both petrogenic and pyrolytic sources. A comparison of the PAH concentrations found in this study with those listed in the sediment quality guidelines (SQGs) indicated that adverse biological effects on the biota are rarely expected. <![CDATA[Simultaneous Determination of Antimalarial Agents by LC-MS/MS and Its Application to Evaluation of Fixed-Dose Tablets]]> We developed and validated a liquid chromatography tandem mass spectrometry (LC-MS/MS) method to quantify the antimalarials artesunate (ARS) and mefloquine (MFQ) in fixed-dose tablets. The detection was performed by a triple-quadrupole mass spectrometer in multiple reaction monitoring (MRM) in positive ion mode via electrospray ionization. Chromatographic separation was achieved with an XBridge C18 column (50 × 2.1 mm, 5 μm), using isocratic elution (350 μL min-1) of water/acetonitrile/methanol (30:35:35, v/v/v) containing 0.1% formic acid. The method was validated according to the International Conference of Harmonization (ICH) guidelines. The calibration curves obtained for ARS (400 to 600 ng mL-1) and MFQ (800 to 1200 ng mL-1) showed good linearity (r2 &gt; 0.99), precision (relative standard deviation (RSD): ARS &lt; 2.0%; MFQ &lt; 1.9%), and accuracy (recoveries: ARS, 102.4-103.4%; MFQ, 97.4-101.6%), and were stable for 24 h at 8 ºC. The method was successfully applied to commercial tablets, and recoveries of 98.7 ± 4.7% (ARS) and 105.6 ± 3.13% (MFQ). The method developed is a reliable alternative for public quality inspection control with the advantage of tandem mass specificity and speed. <![CDATA[Production, Purification and Physicochemical Properties of an Exo-Polygalacturonase from Aspergillus niger SW06]]> In this study, exo-polygalacturonase (exo-PG) production from Aspergillus niger SW06 was optimized by central composition design and high amount of 21.51 units mL-1 could be achieved in optimizing growth conditions. Both gel filtration and ion exchange chromatography revealed a single exo-PG activity peak, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the purified protein showed a single band with a molecular mass of 66.2 kDa. The purified enzyme exhibited maximal activity in the presence of 1% citrus pectin at the temperature of 55 ºC and pH of 5.0. The enzyme was stable within the pH range of 3.0-5.0 and below 60 ºC. The Michaelis constant (Km) and maximum velocity (Vmax) of the enzyme was found to be 0.58 mg mL-1 and 20.66 μmol (mL min)-1, respectively. The thermostable and acidic nature for the activity of this exo-PG make it possible to have wide range of industrial applications. <![CDATA[Identification of Glycoside Compounds from Tobacco by High Performance Liquid Chromatography/Electrospray Ionization Linear Ion-Trap Tandem Mass Spectrometry Coupled with Electrospray Ionization Orbitrap Mass Spectrometry]]> In order to comprehensively screen and identify the glycoside compounds in tobacco, a simple, rapid and sensitive method of high performance liquid chromatography/electrospray ionization linear ion-trap tandem mass spectrometry (HPLC-ESI-LIT/MSn) coupled with electrospray ionization orbitrap mass spectrometry (ESI-Orbitrap-MS) was developed for the first time. As a result, twenty-two glycoside compounds, including eleven alcoholic glycosides, eight phenolic glycosides, two ester glycosides and an indole glycoside, were reliably identified from tobacco with high mass accuracy (within 5 mDa). Among them, four compounds were confirmed as novel molecules and other four compounds, as far as we know, were not reported previously in tobacco. This study provided a useful tool to identify the new structures of glycoside compounds in natural products, especially when there were no reference compounds available. <![CDATA[Influence of Textural Properties and Surface Fractal Dimensions on the Cobalt Adsorption Behavior of Rice Hull Ash Prepared via Solid Combustion]]> Rice hull ash was prepared via a fast chemical combustion method with ammonium nitrate, urea and milled rice hull. Urea was used as the chemical fuel. The mixture was heated to various temperatures (100 to 1000 °C), and the resulting products were compared with products obtained via calcination, in which samples were heated to the same temperatures for 2 hours. Changes in the structure, morphology, texture and surface fractal dimensions with respect to temperature were examined and found to be highly relevant for adsorption applications. The prepared powders were characterized physicochemically by X-ray diffraction and N2-physisorption measurements. The surface fractal dimensions of the prepared materials were calculated from N2-adsorption-desorption isotherms. The results indicate that the fast combustion samples have larger surface fractal dimensions than calcined samples. A correlation between fractal dimensions and Co2+ ion adsorption was found. The present study demonstrates the importance of textural properties and surface fractal dimensions in the adsorption performance of adsorbents. <![CDATA[Nanocomposites Based on Cassava Starch and Chitosan-Modified Clay: Physico‑Mechanical Properties and Biodegradability in Simulated Compost Soil]]> Organic-inorganic nanocomposites based on cassava starch, glycerol and chitosan-modified Veegum® HS clay mineral at two different low polymer-to-clay ratios (2.5 and 5.0 wt.%) were prepared by extrusion producing flexible, transparent and homogeneous plastics as potential candidates for agricultural purposes. X-ray diffraction and transmission electron microscopy images revealed the presence of both intercalated and exfoliated nanocomposites in all samples, in which exfoliation is the predominant type of microscopic structure. Statistically significant improvements of over 20% on the tensile strength and Young's modulus were observed for samples containing chitosan-modified clay in comparison to pristine thermoplastic starch. Chitosan deeply affects the conversion of polymer carbon to CO2 through biodegradation. Mineralization values for the sample loaded with 5.0 wt.% of chitosan-modified clay in simulated compost soil showed a reduction of almost 40% in comparison to thermoplastic starch, benefiting applications where delay degradation is required. <![CDATA[Concentration Profiles of Regulated and Unregulated Pollutants Emitted from the Combustion of Soybean Biodiesel and Diesel/Biodiesel Blend Originating of a Diesel Cycle Engine]]> This study evaluated the concentration profiles of regulated and unregulated pollutants emitted from a stationary diesel engine cycle, operating at the speed of 1800 rpm and 0% load, using biofuels and binary blends. The experimental test considered fuel burning time on three different periods and storage times. The operation of the engine when it is still cold, for example at 15 minutes, showed negative effect on particulate matter (PM), benzene and ethylbenzene emissions in pure soybean biodiesel (B100) compared to the blend of diesel with 5% biodiesel (B5). Regarding to the concentration of mono aromatics, aliphatic hydrocarbons and polycyclic aromatic hydrocarbons (PAH), this study showed similar results to those reported in the literature, where B5 fuel emits more pollutants than pure biodiesel. However, comparing some pollutants individually, benzene and ethylbenzene emissions were higher for B100 and pure soybean biodiesel with butil-hydroxyanisol additive (B100 Adt). The B5 showed the highest concentration profile for the PAH sum in the gaseous and particulate phases in longer engine operation periods. <![CDATA[Modification of Vietnam Natural Rubber via Graft Copolymerization with Styrene]]> Graft copolymerization of styrene onto deproteinized natural rubber (DPNR) using tert-butyl hydroperoxide (TBHPO) and tetraethylene pentamine (TEPA) as redox initiator have been investigated. The effects of initiator and monomer concentration on conversion and grafting efficiency were studied. The dynamic mechanical and thermal properties of the graft copolymer were investigated over the wide range of temperatures. It is shown that a high value of storage modulus for the graft copolymer, which was about 25 times as high as that of DPNR, was achieved. The graft copolymer (DPNR-graft -PS) showed the outstanding tensile strength and stable thermal properties. These enhancements were attributed to the interaction between NR and polystyrene as a result of the graft copolymerization. Morphology observation by transmission electron micrograph (TEM) revealed that the core-shell arrangement of the DPNR-graft -PS with about 30 nm in thickness of polystyrene nano-layer was achieved. <![CDATA[Influence of Water and Ultraviolet Irradiation on the Induction Period of the Oxidation of Biodiesel]]> Biodiesel degrades due to oxidative processes, causing a decrease in its quality. In the present work, it has been clearly shown that the incidence of ultraviolet radiation on biodiesels obtained from soy, canola, linseed and microalgae oils initiate oxidative processes which lead to the decrease in the induction period (IP) of the fuel. The influence of the residual water content of the same biodiesels on the oxidation process was also investigated with and without the incidence of ultraviolet radiation. Between 190 and 850 ppm of water in the biodiesel and without UV irradiation, no significant change in the IP values was observed under the experimental conditions. <![CDATA[Strategies for Molecular Diversification of 2-[Aminoalkyl-(1H-1,2,3-triazol-1- yl)]-1,4-naphthoquinones Using Click Chemistry]]> Click chemistry-based strategies for the synthesis of 2-amino-alkyl-1,2,3-triazole-1,4-naphthoquinone derivatives make it possible to obtain desired products from 1,4-naphthoquinone (1,4-NQ), and bio-based lawsone, nor-lapachol and lapachol. The first route (Strategy A) starting from 1,4-NQ and amino alcohols, then 2-amino-alkyl-1,4-NQ alcohols, were tosylated. The azide ion displaced the tosylate group to afford 2-azide-alkyl-1,4-NQ, which was submitted to a copper-catalyzed azide alkyne cycloaddition (CuAAC) condition. The triazole-naphthoquinones were obtained in an overall yield of roughly 47%. Another pathway (Strategy B) substituted bromo-alkyl-phthalimides using NaN3 as the nucleophile, sequential CuAAC and deprotection of phthalimide group with hydrazine producing amino-triazoles. The subsequent reaction with 1,4-NQ produced 2-amino-alkyl-1,2,3-triazole-1,4-NQ derivatives in an overall yield of 45-76% in four steps. After we developed these two strategies, linear synthesis (Strategy A) was chosen to prepare 2-[(2-(1H-1,2,3-triazol-1-yl)ethylamino)]-3-(3-methylpropenyl)-1,4-naphthoquinones from lawsone with an overall yield of approximately 27% in six steps. On the other hand, convergent synthesis (Strategy B) was employed for the synthesis of 2-[(4-phenyl-1H-1,2,3-triazol-1-yl)alkyl-amino)]-3-(3-methylbut-2-en-1-yl)-1,4-naphthoquinones from the reaction between 2-methoxy-lapachol with amino-triazoles with a global yield of about 21%. These synthetic strategies might lead us to new opportunities to build small-molecule libraries for future biological exploration. <![CDATA[Smartphone for Point-of-Care Quantification of Protein by Bradford Assay]]> We address in this paper a powerful point-of-care platform to conduct the Bradford assay. Our method was based on smartphone for colorimetric quantification of total protein in human blood plasma, presenting low cost, simplicity, portability, autonomy and ability for remote transmission of the data. Other advantage concerns the high number of smartphone's users worldwide. This feature contributes for the application of the method by non-specialist people. The interferences from external light were successfully solved by illuminating the samples with a straightforward negatoscope. Our method generated a satisfactory exactness, with accuracy percentages ranging from 87.2 to 99.1%.