Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> vol. 27 num. 9 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Application of a Novel Micro-Cloud Point Extraction for Preconcentration and Spectrophotometric Determination of Azo Dyes]]> A novel room temperature micro-cloud point extraction procedure using triton X-114 surfactant as extracting phase was developed for preconcentration and extraction of three azo dyes (orange G, methyl orange, and acid red 18) from aqueous samples using molecular absorption spectrophotometry in the visible region. The effects of different parameters such as concentration of surfactant and added salting out reagent (Na2SO4), pH and type of diluting solvent on microextraction were studied and optimized. Under optimum conditions, calibration curves were linear in the range of 2.0-10.0, 0.2-1.0 and 2-12 mg L-1 with the detection limit of 1.6, 0.6 and 111.0 µg L-1 for orange G, methyl orange and acid red 18, respectively. The relative standard deviation was better than 13.12%. The method was applied to the determination of the azo dyes in water samples. <![CDATA[Soil Organic Carbon Determination Using NIRS: Evaluation of Dichromate Oxidation and Dry Combustion Analysis as Reference Methods in Multivariate Calibration]]> Dichromate oxidation and dry combustion analysis were evaluated as reference methods to determine organic carbon in Brazilian soils using near infrared spectroscopy (NIRS) as an alternative. The main objective of this study was to evaluate which of the reference methods could provide a calibration model with higher predictive ability. A total of 161 soil samples obtained from horizons in full profiles (Parque Estadual da Mata Seca, Minas Gerais State, Brazil) were used. Models were mean centered and built from partial least squares. The dichromate oxidation method presented a lower accuracy when compared to dry combustion analysis as reference for NIRS. Figures of merit such as sensitivity, analytical sensitivity, detection and quantification limits, adjust and linearity presented results very similar. A paired t-test was applied to the figures of merit results and with 95% confidence did not show significant differences between the two methods used as reference for NIRS. The non-parametric Mann Whitney test showed that the samples provided with the partial least squares (PLS) model when the reference method was the dichromate oxidation or dry combustion analysis come from the same population, indicating that the reference methods employed for multivariate calibration from NIRS provide the same results practically. <![CDATA[Evaluation of QuEChERS Sample Preparation and Gas Chromatography Coupled to Mass Spectrometry for the Determination of Pesticide Residues in Grapes]]> An effective analytical method for pesticides multiresidue determination in grape samples was developed and validated. A modified quick, easy, cheap, effective, robust and safe (QuEChERS) method was used to extract the target compounds. Several sorbent materials were tested for the clean-up step using dispersive solid phase extraction (d-SPE) and Florisil® was selected. Samples extracts were evaporated before injection in the gas chromatography with mass spectrometry (GC-MS) system in order to improve detectability. Recoveries from blank samples spiked at 0.04, 0.3 and 1.0 mg kg−1 ranged from 95 to 102% with relative standard deviation (RSD) from 1.3 to 19.7%. Method limits of detection (LODm) and quantification (LOQm) ranged from 0.006 to 0.012 and 0.02 to 0.04 mg kg−1, respectively. The positive matrix effect caused an increase in the peak areas of all compounds and matrix matched calibration curve linearity (coefficient of determination, r2) was higher than 0.98 for all target analytes. The validated method was successfully applied for the determination of 19 pesticides in grape samples. <![CDATA[Combining the Pharmacophore Features of Coumarins and 1,4-Substituted 1,2,3-Triazoles to Design New Acetylcholinesterase Inhibitors: Fast and Easy Generation of 4-Methylcoumarins/1,2,3-triazoles Conjugates via Click Chemistry]]> Coumarins are a large class of compounds that display a range of interesting biological properties, being considered privileged structures because of the ability of their 2H-chromen-2-one nuclei to bind to multiple pharmacological targets. We hypothesized that the linkage of a second pharmacophore nucleus to the 2H-chromen-2-one core, the 1,2,3-triazole moiety, would entail more selective and pharmacologically active coumarins. Therefore, we describe the synthesis of fourteen 4-methylcoumarins/1,4-substituted 1,2,3-triazole conjugates, which were predicted by in silico methods to inhibit acetylcholinesterase (AChE) and proved to be moderate in vitro inhibitors of this enzyme. Molecular docking simulations suggest that the most active of these compounds has a putative binding mode similar to donepezil, both occupying the peripheral anionic site of AChE, which is associated with the secondary noncholinergic functions of the enzyme. This highlights the potential of this series for further optimization in the search of new coumarins for the treatment of Alzheimer's disease. <![CDATA[Gas-Phase Polycyclic Aromatic Hydrocarbons in the Parking Lot Impacted by Light-Duty Vehicles Burning Gasoline and Ethanol Blends]]> In order to study the emission of vapor-phase polycyclic aromatic hydrocarbons (PAHs) by light-duty vehicles burning gasoline and ethanol blends, air samplings were performed at a parking lot in Londrina, PR, Brazil. The samples were obtained during the summer and winter 2012. The semi-volatile PAHs were collected using a cartridge packed with XAD-2 resin, extracted under sonication and subsequently analyzed by liquid chromatograph equipped with fluorescence and photodiode array detectors. Acenapthene (ACE) appears as the most abundant PAH, followed by acenapthylene (ACY) (summer) and fluorene (FLU) (winter). From the total PAHs analyzed (83.5 ng m−3 in winter and 574 ng m−3 in summer), low molecular weight PAHs (LM-PAHs) corresponded to 93%. The PAH source fingerprint identified in this study was obtained from local and identified sources, and the fluoranthene (FLT) / (FLT + pyrene (PYR)) and anthracene (ANT) / (ANT + phenanthrene (PHE)) ratios corresponding to 0.94 and 0.46, respectively, were characteristic of gasoline and ethanol blend emission. <![CDATA[Interaction of β-Carbolines with DNA: Spectroscopic Studies, Correlation with Biological Activity and Molecular Docking]]> Quantitative interaction of twelve β-carboline derivatives with calf thymus deoxyribonucleic acid (ctDNA) using spectroscopic techniques was evaluated. The values of the binding constants (Kb) obtained for the complexes formed with the ctDNA ranged from 3.30 × 102 to 1.82 × 106 mol L−1, being the β-carbolines with the N,N-dimethylaminophenyl group at position 1 the ones which presented the highest Kb values. The binding mode between the β-carbolines evaluated and ctDNA was proposed from the KI assay, competition with ethidium bromide, and DNA thermal denaturation profile (Tm), where it was possible to infer that the evaluated alkaloids interact with ctDNA preferably via intercalation. Additionally, the correlation of Kb values obtained with the IC50 of seven human cancer cell lines was carried out. From this study, it was possible to observe a linear relation among most of the evaluated derivatives, obtaining r2 values from 0.5360 to 0.9600. In addition, in silico molecular docking was performed to corroborate the experimental results. <![CDATA[Microwave-Induced Combustion of Coal for Further Sulfur Determination by Inductively Coupled Plasma Optical Emission Spectrometry or Ion Chromatography]]> In this work, a method using microwave-induced combustion (MIC) was optimized in order to obtain a fast, simple, efficient and greener sample preparation method for coal digestion and further determination of sulfur by inductively coupled plasma optical emission spectrometry (ICP OES). Accuracy was evaluated by comparison of the results with those obtained using elemental analysis by UV-fluorescence, microwave-assisted acid digestion with determination by ICP OES and by analysis of certified reference materials of coal. Some parameters that influence MIC method, such as the type and concentration of absorbing solution, the necessity of using a reflux step as well as the cooling time were carefully optimized. No statistical difference was observed for combustion without reflux followed by 5 min of cooling, in comparison to the reference values obtained by elemental analysis. Complete digestion was obtained with this fast and simple method (total digestion program required only 6 min) and using a diluted acid solution for quantitative recovery. The feasibility of digests for sulfur determination as sulfate by ion chromatography (IC) with conductivity detection was also demonstrated. The possibility of determining other elements, commonly monitored in coals, is another advantage of this high-efficiency digestion method (MIC) combined with the multielemental capacity of ICP OES or IC instruments. <![CDATA[Novel Non Enzymatic TBHQ Modified Electrochemical Sensor for Hydrogen Peroxide Determination in Different Beverage Samples]]> A nanosensor was developed for hydrogen peroxide determination based on nafion/graphene oxide/silver nanoparticles/tertiary butylhydroquinone (TBHQ) modified glassy carbon electrode (N-GO/AgNPs/TBHQ/GCE). Cyclic voltammetry was used to investigate the electrochemical behavior of this modified electrode and differential pulse voltammetry was used for the reduction of H2O2. The limit of detection was 0.46 µmol L-1 and three linear calibration ranges were obtained for H2O2 determination from 1.52-9.79 µmol L-1 for first linear segment, 9.79-231.0 µmol L-1 for second linear segment and 231.0-8330.0 µmol L-1 for third linear segment. Finally, the reliability of the nanosensor was confirmed in the real sample analysis in different beverages with satisfactory results. <![CDATA[Lipophilicity Study of Thiazolo[3,2-<em>a</em>]pyrimidine Derivatives as Potential Bioactive Agents]]> Systems containing fused thiazole and pyrimidine rings play a significant role in organisms due to their biological activity. Lipophilicity, as important parameter to expect biological activity of the compounds, was evaluated for 27 potentially active thiazolo[3,2-a]pyrimidine derivatives using chromatographic methods: reversed phase thin layer chromatography (RP-TLC) and reversed phase high performance liquid chromatography (RP-HPLC) methods. Methanol was used as the organic modifier of the mobile phases. The corresponding relationship between compound's structure and lipophilicity parameters (RM0 and log kw) values were observed and featured. RM0 and log kw parameters were compared with computed log P values. For all of analyzed compounds, determined lipophilicity's parameters values are &gt; 0 which means that there are hydrophobic substances, soluble in the lipid phase. Simultaneously, these values are &lt; 5, i.e., are in accordance with Lipinski's rule in the range of lipophilicity. In the case of the possibility of their use as drugs, they will be active after oral application. <![CDATA[UV-Assisted Digestion of Petrochemical Industry Effluents Prior to the Determination of Zn, Cd, Pb and Cu by Differential Pulse Anodic Stripping Voltammetry]]> A petrochemical effluent is usually a matrix of very high complexity and composition variability, requiring robust and suitable methods for routine analysis. In this paper, the feasibility of applying a voltammetric technique for the determination of metals species in the petrochemical industry effluent was demonstrated after UV-assisted digestion procedure. Voltammetric (electrolyte volume, deposit time, pulse time, pulse amplitude and scan rate) and digestion variables (hydrogen peroxide volume, nitric acid volume and digestion time) were studied using a 2-level factorial design. The developed voltammetric method using anodic stripping voltammetry (ASV) presented limits of quantification of 11, 5, 15 and 5 µg L−1 for Zn, Cd, Pb and Cu, respectively, and was effective to analyze petrochemical effluents after UV-digestion. <![CDATA[The Role of the Conformational Dynamics of Glutathione S-Transferase Epsilon Class on Insecticide Resistance in <em>Anopheles gambiae</em>]]> Glutathione S-transferases (GSTs) are enzymes capable of metabolizing cytotoxic compounds. The enzyme AgGSTE2, member of epsilon class GSTs (GSTE), is the most important GST conferring resistance to dichloro-diphenyl-trichloroethane (DDT) in Anopheles gambiae. We have investigated the conformational dynamics of three GSTE variants (GSTE2, GSTE2-I114T/F120L, GSTE5) from A. gambiae. Large-scale motions of helices H2 and H4 and conformational transition of the C-terminal governs the opening of the G-site and is expected to affect substrate binding and product release. This structural rearrangement places Glu116 (Glu120 in GSTE5) close of the thiol group of the tripeptide glutathione (GSH) cofactor, making this residue a candidate to act as a base in the activation of DDT. The structural rearrangement is noticeable for AgGSTE2-F120L, which has been shown to confer increased DDT-resistance. The other variants exhibit a more subtle rearrangement. These findings corroborate the hypothesis that the increase of the conformational dynamics of GST Epsilon class isoforms from A. gambiae promotes higher DDTase activity. <![CDATA[Cholinesterases Inhibition by Novel <em>cis-</em> and <em>trans-</em>3<em>-</em>Arylaminocyclohexyl <em>N,N</em>-Dimethylcarbamates: Biological Evaluation and Molecular Modeling]]> The present study describes the synthesis, assessment of the anticholinesterase activity and the inhibition type of novel cis- and trans-3-arylaminocyclohexyl N,N-dimethylcarbamates. In vitro inhibition assay by Ellman's method with human blood samples showed that carbamates were selective for butyrylcholinesterase (BuChE) with compound concentration that inhibits 50% of enzyme activity (IC50) between 0.11 and 0.18 mmol L-1. cis- and trans-3-(4-Methoxyphenylamino)cyclohexyl N,N-dimethylcarbamate hydrochloride were the most active for BuChE, showing that the presence of methoxyl group enhanced the anticholinesterase activity. The enzyme kinetics studies indicate a noncompetitive inhibition against acetylcholinesterase (AChE) and mixed type inhibition for BuChE. Molecular modeling studies confirm the ability of carbamates to bind both the active and peripheral sites of the BuChE. <![CDATA[Determination of Pesticides in Grape Juices by QuEChERS and Liquid Chromatography-Tandem Mass Spectrometry]]> In this study, we describe a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying 25 pesticides in grape juice. This method was optimized and validated according with INMETRO (Instituto Nacional de Metrologia Qualidade e Tecnologia) for the simultaneous determination of pesticide, which are widely used in grape culture in Brazil. The method was based on the QuEChERS (quick, easy, cheap, effective, rugged and safe) methodology. We used AOAC Official Method 2007.01 and Standard Method EN 15662 for sample preparation, both methods presented statistically equivalent recoveries and coefficients of variation. At 0.005 and 2 mg L-1, fortified blank grape juices had average recoveries of 101 and 112% and average coefficients of variation of 16 and 11%, respectively. The repeatability was tested in three concentrations 0.005, 0.1 and 2 mg L-1, affording coefficients of variation 16.4, 20.7 and 10.8%, respectively. <![CDATA[New PPARα/γ/δ Optimal Activator Rationally Designed by Computational Methods]]> The peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor that acts as a transcription factor, regulating glucose, lipid and inflammation signaling and it is exploited in type 2 diabetes treatment. However, the selective activation of this PPAR subtype has been linked to important adverse effects which can be mitigated through concomitant activation of PPARα and PPARδ. In this study, we proposed new PPARγ agonists using PharmaGist Server for pharmacophore prediction, the molecular docking was performed by GOLD (genetic optimization for ligand docking) v2.2, AutoDock 4.2 and AutoDock Vina 1.1 and QikProp v4.0 and Derek for absorption, distribution, metabolism, excretion and toxicity (ADMET) assessment. One molecule showed high predicted affinity to PPARγ and favorable pharmacokinetic and toxicity properties. It was then evaluated against PPARα and PPARδ and showed greater affinity to these receptors than the controls. Therefore this molecule is a promising drug lead for the development of derivatives and for the treatment of metabolic syndrome with the benefits of a PPAR pan activation. <![CDATA[Development, Optimization and Validation of an HPLC-PDA Method for Quantification of Taxifolin in the Bark Extract of <em>Pinus pinaster</em>]]> The aqueous extract of the bark of Pinus pinaster has a high concentration of polyphenols represented by a mixture of procyanidins, besides taxifolin, phenolic acids, cinnamic acids and their glycosides. Its quality control is specified in the United States Pharmacopeia, and the assay test is performed by determination of the total procyanidins content. However, determining the individual polyphenol content may represent an additional quality parameter for this extract. In this sense, the present study aimed to develop and optimize a method of high performance liquid chromatography with photodiode array detection (HPLC-PDA) for quantification of taxifolin in the bark extract of P. pinaster, using a 33 Box-Behnken factorial design. The proposed method was validated for specificity, linearity, limits of detection and quantification, precision, accuracy and robustness and it has shown that taxifolin may be used as a chemical marker for quality control of the bark extract of P. pinaster. <![CDATA[Rapid and Highly Sensitive Determination of Melamine in Different Food Samples by Corona Discharge Ion Mobility Spectrometry after Dispersive Liquid-Liquid Microextraction]]> In this work, for the first time, a highly sensitive method based on dispersive liquid-liquid microextraction coupled with positive corona discharge ion mobility spectrometry as a fast and inexpensive technique has been evaluated for the direct determination of melamine. The effective parameters influencing the microextraction efficiency, such as pH, the properties of extraction and dispersion solvent were investigated. Under the optimum conditions, analytical parameters such as linearity, precision and limit of detection were evaluated. The calibration graph of melamine determination using the proposed method has two regions of linearity from 0.5 to 70 ng mL-1 and 70 to 1500 ng mL-1, the limit of detection and limit of quantification are 0.25 and 0.5 ng mL-1, respectively, and the relative standard deviation was less than 3% for all experiments. The proposed method was successfully applied for the determination of melamine in the milk, dairy products and egg yolk. <![CDATA[A Kinetic, Equilibrium, and Thermodynamic Study on the Biosorption of Tl<sup>+</sup> and Cd<sup>2+</sup> by Eichhornia crassipes Roots Using Carbon Paste Electrode]]> In this work, Eichhornia crassipes roots were used as a modifier for carbon paste electrode in a biosorption study of thallium (Tl+) and cadmium (Cd2+) ions. The ions were accumulated on modified electrode surfaces at open circuit potential and analyzed by square wave anodic stripping voltammetry. Before the biosorption study, the effect of ratio of biomass and binder in uptake metal was evaluated. The biosorption study shows that adsorption of ions was dependent on pH. The kinetic study showed that, for both ions, experimental data were well described by the pseudo-second order model (R2 &gt; 0.99) and the equilibrium was better described by the Langmuir model. The value of dimensionless equilibrium parameter (RL) obtained in the equilibrium study showed that Eichhornia crassipes can be considered an effective biomaterial for Tl+ and Cd2+ removal from an aqueous solution. The thermodynamic parameters calculated, enthalpy (ΔHº), entropy (ΔSº) and Gibbs energy (ΔGº), indicated that the biosorption process was spontaneous and endothermic. <![CDATA[Characterization of Polylactide-Stabilized Gold Nanoparticles and Its Application in the Fabrication of Electrochemical DNA Biosensors]]> In this work, two different approaches to gold nanoparticles (AuNPs) have been explored for the modification of screen-printed electrode based on AuNPs and AuNPs stabilized with polylactic acid (PLA). The modified substrate has been characterized using UV-Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and cyclic voltammetry. Both synthesized AuNPs were studied in terms of stability, sensitivity and reproducibility to enhance the sensing capability of modified electrodes. The PLA-stabilized AuNPs form strong structured nanoparticles and stabilize in aqueous solution. A larger active surface area (0.41 cm2) and lower charge transfer resistance (Rct) value were reported in the modification of sensing material with PLA-stabilized AuNPs, which resulted in enhancement of sensitivity. Therefore, AuNPs in PLA can be used as a potential alternative modifier for sensing chemicals and biomolecules in electrochemical sensors. <![CDATA[Decomposition Dynamics of Typha angustifolia under Aerobic Conditions]]> The study of the Typha species has gained attention in tropical areas due to their rapid growth, nutrient release, and contribution to detritus in lakes. Analysis of the degradation of Typha angustifolia has shown that the first stage of decomposition is marked primarily by the release of soluble compounds, indicating that microorganisms have a minor influence at this stage. In subsequent stages, microorganisms act by degrading and consuming phenolic compounds and phosphorus. The remaining compounds form humic substances and are retained in the detritus. Thus, microorganisms significantly degrade organic matter, resulting in a two-fold increase in decomposition. Different forms of phosphorus could be detected in the remaining mass by 31P NMR (nuclear magnetic resonance). By comparing the 31P NMR data between the samples with and without the antibiotic, we can better understand the slow decomposition process of Typha angustifolia. <![CDATA[Phytochemical Profile of Seed Extracts of Plants Typical of the Brazilian Semiarid and their Potential Application in Brackish Water Desalination]]> The phytochemical profile of typical seeds from semiarid areas of Bahia was explored. The desalination capacity of the seeds discovered in previous studies considered the seeds potentially suitable for desalination of water. Coals composed of crushed seeds of umbu (Spondias tuberosa Arr. Cam.) and umburana (Amburana cearensis A. C. Sm.) were prepared by heating at 250 ºC. As the desalination process using these materials involves ion exchange besides adsorption, it became necessary to study their chemical composition to check the possibility of transferring undesirable chemical species to the water during the contact between material and water. None of the tested metabolites were found in umbu coal, which enabled its use in desalination. However, the presence of coumarin and alkaloids in the umburana seeds coal indicated that this material is not suitable for that use.