Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> vol. 26 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Metrological Traceability of Measurement Results in Pharmaceutical and Chemical Sciences: Selection and Use of Certified Reference Materials]]> Metrological traceability is a key technical requirement of the ISO/IEC 17025:2005 standard, applied to calibration and testing laboratories that intend to prove their technical competence. In this work, the concept of metrological traceability is discussed, with focus on chemical and pharmaceutical testing laboratories. Practical recommendations for the selection and use of certified reference materials (CRM) are given. <![CDATA[Three-Component Reactions of 7-Hydroxy Coumarin Derivatives, Acetylenic Esters and Aromatic Aldehydes in the Presence of NEt<sub>3</sub>]]> Three-component reactions of 7-hydroxy-4-methyl coumarin or 7-hydroxy-4-(trifluoromethyl) coumarin, dialkyl acetylenedicarboxylates and aromatic aldehydes in the presence of NEt3 lead to dialkyl (2E)-2-[aryl(hydroxy)methyl]-3-[(4-methyl-2-oxo-2H-chromen-7-yl)oxy]but-2-ene dioate or dialkyl (2E)-2-[aryl(hydroxy)methyl]-3-{(2-oxo-4-(trifluoromethyl)-2H-chromen-7-yl)oxy} but-2-ene dioate in good yields under mild reaction conditions. <![CDATA[Upgrade of Biofuels Obtained from Waste Fish Oil Pyrolysis by Reactive Distillation]]> Bio-oil is classified as second-generation biofuel and it is produced mainly through the pyrolysis of a waste lignocellulosic biomass base. The application of this product is still very limited, due to some of its chemical characteristics. This paper presents a proposal for the reduction of the acidity of bio-oil obtained from waste fish oil, previously produced and characterized as described in the literature, applying the reactive distillation process. This process is primarily based on the conversion of carboxylic acids into their corresponding esters by adding a widely available alcohol and a simple and cheap catalyst in the process for the fractional distillation of crude bio-oil to obtain light and heavy bio-oil, that is, fractions which are equivalent to the fossil fuels gasoline and diesel, respectively. The alcohols tested were methanol and ethanol and the catalysts were H2SO4, H3PO4, NaOH and Na2CO3, in proportions of 10 and 0.5 wt.%, respectively. The light bio-oil was obtained within a temperature range of 42 to 198 ºC with yields of 27.0 to 43.1% and the heavy bio-oil was recovered at 93 to 230 ºC with yields of 42.6 to 49.2%. The greatest acidity reduction was observed employing methanol+H2SO4 (95% and 43% for light and heavy bio-oils, respectively). The fractions produced were characterized by gas cromatography/mass spectrometry (GC-MS) and gas chromatography with flame ionization detector (GC-FID), applying the compound classification process PIONA (Paraffins, Iso-paraffins, Olefins, Naphtenes and Aromatics), revealing a homologous series of 1-alkenes and n-alkanes along with some aromatic compounds. The 1H and 13C NMR analysis showed that the process had no significant influence in relation to the carbons and hydrogens associated with the methyl, methylene, methyne and olefinic groups. <![CDATA[Chemical Composition and Cytotoxic Activity of the Root Essential Oil from <em>Jatropha ribifolia</em> (Pohl) Baill (Euphorbiaceae)]]> The essential oil of roots of Jatropha ribifolia, obtained by hydrodistillation, was characterized in terms of its chemical composition by chromatographic method with flame ionization detection (GC-FID) and gas chromatography coupled to electron ionization mass spectrometry (GC-MS). The analyses and identification pointed by mass fragmentation pattern and retention index revealed the presence of 49 compounds, representing 91.4% of the total oil, with 39.5% of monoterpenes, 43.0% of sesquiterpenes and 8.5% of phenylpropanoids. The major compounds of the oil were β-pinene (9.2%), isoeugenol methyl ether (8.5%), vatirenene (8.4%), α-gurjunene (7.0%), endo-8-hydroxy-cycloisolongifolene (6.6%), α-pinene (6.4%) and p-menth-1-en-8-ol (5.2%). The fractionation by preparative thin layer chromatography (TLC) allowed obtaining five fractions (F1-F5) with different compound contents from the original oil. Some essential oil components showed a significant increase in their levels after fractionation, as borneol (17.9%, F1), 3-thujopsanone (19.1%, F4), isoeugenol methylether (21.2%, F2), 8-oxo-9H-cycloisolongifolene (21.4%, F4), 8-cis-5(1H)-azulenone,2,4,6,7,8,8a-hexahydro-3,8-dimethyl-4-(1-methylethylidene) (23.1%, F4) e endo-8-hydroxy-cycloisolongifolene (38.6%, F2). These fractions and oil were tested in vitro against nine human cancer cell lines by sulforhodamine B assay. The Jatropha oil was more effective in inhibiting the growth of cells NCI-H460 (drug resistant ovarian; GI50 6.2 µg mL–1) and OVCAR-3 (ovarian; GI50 8.0 µg mL–1). The cancer cells line PC-3 (prostate) was more sensitive to the effects of the fractions showing significant values of GI50 such as for fraction F1, F2 and F4 (&lt; 0.25 µg mL–1). In general the antiproliferative activity of the fractions was more pronounced than that of crude oil. <![CDATA[Metalloproteomic Profile Determination of Muscle Samples from Nile Tilapia (<em>Oreochromis niloticus</em>) Using AAS and ESI-MS/MS after 2D-PAGE Separation]]> This study evaluated the metalloproteomic profile of muscle tissue samples from Nile tilapia (Oreochromis niloticus). Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) methods was used for protein fractionation and identification based on image analysis. Determination of Ca, Cu, Fe, Mn and Zn was performed in the protein spots by flame and/or graphite furnace atomic absorption spectrometry (FAAS, GFAAS), the protein spots were characterized by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). FAAS and GFAAS determinations have indicated the presence of calcium in seven protein spots, iron in only one spot, manganese in six spots, and zinc in two spots. Of the seventeen protein spots where the presence of metal ions was detected, ten were characterized by ESI-MS/MS. <![CDATA[Improving Yield of 1,3-Diglyceride by Whole-Cell Lipase from <em>A. Niger</em> GZUF36 Catalyzed Glycerolysis via Medium Optimization]]> 1,3-Diglyceride (1,3-DG) has attracted considerable attention as a healthful food oil component. In this study, we reported a novel method to synthesis of 1,3-DG via glycerolysis of triglyceride (TG) catalyzed by whole-cell lipase from a new isolated strain, Aspergillus niger GZUF36. The glycerolysis products include major diglyceride and minor monoglyceride. To improve yield of 1,3-DG, the optimized medium for the strain was obtained by combination of single-factor experiments, Plackett-Burman (PB), the steepest ascent and Box-Behnken design (BBD). Using the optimized medium, yield of 1,3-DG synthesized by the whole-cell lipase was 26.90 mol% and 1.42-fold yield was improved. The optimized medium lays the foundation for further studies of the reaction system for synthesis of 1,3-DG. The whole-cell catalyzed-glycerolysis process represents a significant advance toward achieving economical production of 1,3-DG at industrial scale. <![CDATA[The Correlation Between Electronic Structure and Antimalarial Activity of Tetrahydropyridines]]> In this study, correlations between electronic structure and the antimalarial activities reported for a group of 21 tetrahydropyridines were evaluated by multivariate methods. Simple and multiple linear regressions, principal component analyses, and linear discriminant analyses were employed to evaluate possible correlations between quantum-mechanical descriptors and pharmacological activity. The results obtained provide useful information on the position of active sites of tetrahydropyridines and identify some specific features associated with active derivatives. Based on these findings, simple substitution rules are proposed for designing more efficient tetrahydropyridine derivatives. <![CDATA[Synthesis of Poly(Dimethylsiloxane) Networks Functionalized with Imidazole or Benzimidazole for Copper(II) Removal from Water]]> Functionalized elastomeric networks were obtained via a polycondensation reaction between poly(dimethylsiloxane) (PDMS) containing Si(CH3)2OH as end groups and an imidazole- or benzimidazole-modified alkoxysilane. The structure of the polymeric materials was characterized via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and solid-state 13C and 29Si NMR spectroscopy, which indicated the presence of silsesquioxane units that acted as nodes on the PDMS chains and linked the functional groups. Thermogravimetric analysis (TGA) of the product indicated high thermal stability with an initial weight-loss temperature around 450 K. The capacity for the removal of copper(II) from aqueous solution was estimated from adsorption isotherms, yielding values of 35.74 and 66.09 mg g-1, respectively, for benzimidazole-and imidazole-functionalized materials. The major adsorption models were evaluated to fit the removal data of copper(II) and the model elaborated by Sips was determined to provide the best fit for both prepared materials. <![CDATA[Preparation, Characterization, Cytotoxicity and Antioxidant Activity of DOPA Melanin Modified by Amino Acids: Melanin-Like Oligomeric Aggregates]]> Two new synthetic melanin-like oligomers inspired by the synthesis of pheomelanin (cys-DOPA) were prepared using L-DOPA as a precursor and the amino acids serine (ser-DOPA) and threonine (thr-DOPA) for modifications. The products obtained exhibited appreciable antioxidant activity. The compounds were characterized by liquid chromatography-mass spectrometry (LC-MS), elemental analysis and infrared spectroscopy. The pKa values of the groups present in each melanin suspension were determined in aqueous solution by potentiometric and spectrophotometric titration. Cytotoxicity assays showed an IC50 &gt; 500 mg L-1 resulting in non-toxic compounds for living cells. Finally, cys-DOPA, ser-DOPA and thr-DOPA exhibited antioxidant activity determined by the DPPH scavenging assay, with EC50 = 7.69, 1.02 and 27.60 mg L-1, respectively. <![CDATA[Subcritical Extraction of <em>Salvia hispanica</em> L. Oil with <em>N</em>-Propane: Composition, Purity and Oxidation Stability as Compared to the Oils Obtained by Conventional Solvent Extraction Methods]]> This study evaluated the Chia (Salvia hispanica L.) oil composition in terms of fatty acids (FA), sterols, acylglycerols and oxidative stability obtained via subcritical n-propane fluid extraction (SubFE-propane), in different temperatures and pressure conditions, as compared to Bligh &amp; Dyer (BD), Soxhlet (SE) and Folch (FLS) extractions. Total lipid varied from 23.25 to 30.21% and the best yield was obtained by both SubFE-propane extraction at 45 ºC and 12 MPa (A). α-Linolenic acid (18:3n-3) was the most abundant FA and SubFE-propane extraction provided the best results for the sum of n-3 and PUFA. All oil samples were similar in regard to triacylglycerols (TAG) profiles as measured via direct electrospray ionization mass spectrometry (ESI-MS) analysis. The total amounts of stigmasterol, β-tocopherol and tocopherol total were highest in the Chia oil obtained by BD, campesterol and sitosterol by SE and γ-tocopherol by SubFE-propane extraction. The SubFE-propane oil also presented the best (2 to 5 times) oxidation stability. SubFE-propane was the most efficient extraction method for Chia oil, providing the highest extraction yields, purity, oxidation stability and diverse profile of sterols. <![CDATA[Synthesis of SAPO-34/ZSM-5 Composite and Its Catalytic Performance in the Conversion of Methanol to Hydrocarbons]]> SAPO-34/ZSM-5 composite was synthesized with nano-sized ZSM-5 zeolite as seeds and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen sorption, Fourier transform infrared (FTIR) and temperature-programmed desorption of ammonia (NH3-TPD); its catalytic performance in the conversion of methanol to hydrocarbons (MTH) was investigated. The results indicated that the as-synthesized SAPO-34/ZSM-5 composite takes the form of sphere-like particles with a diameter ranging from 2.3 to 4.8 µm, through the accumulation of tiny ZSM-5 and SAPO-34 crystals; a large quantity of mesopores was formed in the interspaces between the ZSM-5 and SAPO-34 crystals. Owing to its proper acidity and porosity, the SAPO-34/ZSM-5 composite exhibits higher stability in MTH and favors the formation of aromatics and alkanes, compared with the parent SAPO-34 and ZSM-5 zeolites and their mechanical mixture. <![CDATA[Interlaboratory Comparison of Quantifying Hydrocarbons and Trace Elements in Sediment Samples from a Tropical Estuary]]> The Marine and Environmental Studies Laboratory at PUC-Rio, in partnership with the PETROBRAS R&amp;D Center (Brazil), conducted an interlaboratory comparison of aliphatic and aromatic hydrocarbons and trace element determinations. The goal of this study was to produce a homogeneous and stable material and obtain consensus concentration values for its use as a reference material (RM) for sediments from tropical regions. The prepared material is adequate for use as a reference material because it has remained stable (Test F, ANOVA, p &lt; 0.05) since its preparation in 2007. In this study, several alkylated polycyclic aromatic hydrocarbon (PAH) compounds were included, and the resulting dispersion was the same order of magnitude as the parental PAH (16 PAH USEPA). <![CDATA[Electric Field-Assisted Solid Phase Extraction: Study of Electrochromatographic Parameters with an Anionic Model Compound]]> Electric field-assisted solid phase extraction using syringe type cartridges (E-SPE) is a recent approach with a high capacity to obtain differential selectivity and/or recovery in comparison with conventional solid phase extraction (SPE). In this work, E-SPE was employed for the extraction of the anionic dye sunset yellow. During the washing step the electric field was evaluated with the top electrode negatively (E-SPE(–/+)) or positively charged (E-SPE(+/–)) and the results were compared with conventional SPE to understand how the electrochromatographic parameters can influence the recovery of the dye. Using the E-SPE(–/+) the electric field can increase the elution of the dye from the cartridge by over 57-fold. This notable result can be attributed to the electrophoretic velocity of the dye in the direction of the flow rate of the eluent. These results demonstrated that E-SPE is an interesting approach to elute ionic compounds with reduced volumes of eluent or less amount of organic solvent. <![CDATA[High Throughput Enzymatic Enantiomeric Excess: Quick-<em>ee</em>]]> High throughput techniques to evaluate enantiomeric excess (ee) and enantiomeric ratio (E) of enzymatic reactions are fast and efficient tools that can be applied large quantities of enzymes, microorganisms and clones. The Quick-ee technique proposed in this study produces the ee and conversion values separately. <![CDATA[An Uncommon Naphthaquinoid and a New Lignan Derivative from the Roots of <em>Cordia leucocephala</em> Moric]]> Two uncommon compounds, a meroterpene naphthoquinoid (cordiaquinone P) and a new lignan derivative, were isolated from the hexane extract of roots of Cordia leucocephala Moric and their structures, including the relative stereochemistry, were determined by nuclear magnetic resonance (NMR) (1H and 13C NMR, HSQC, HMBC and NOESY) and high resolution electrospray ionization mass spectrometry (HRESIMS) techniques. <![CDATA[Electrochemical and Optical Investigation of Conductive Polymer and MWCNT Nanocomposite Film]]> Composites of multi-walled carbon nanotubes (MWCNT) and conductive polymer with good uniformity were prepared by electropolymerization. Molecular modeling calculations were carried out for electroactive monomer (OAP) polymerization with density functional theory (DFT) level using 6-311G(d,p) basis set for all atoms and Gaussian 03 program package. The reflectance and transmittance amplitudes of the composite were obtained, using the continuity of the tangential components of electrical and magnetic fields at interfaces and solving the algebraic matrix equation. The calculated absorbance spectra as a function of wavelength for MWCNTs dispersed in the conductive polymer are depicted. Band gap of the p-type semiconducting film was obtained from the plot of (αhv)2 vs. photon energy. <![CDATA[Anionic Aliphatic Polyesteramide Copolymers: Evaluation of Dielectric Properties]]> This study looks at the effects on the dielectric behavior as result of the incorporation of ester sequences along the nylon 6 chains. The aliphatic polyesteramide copolymers and nylon 6 homopolymer were synthesized via anionic ring-opening copolymerization using the rotational molding technique by varying the ratio of the ε-caprolactam (CLA) and ε-caprolactone (CLO) comonomers. The ester units are correlated with biodegradable potential of polymers and the polar amide groups are able both to confer the polymer semicrystalline character and to be sensitive to the electric stimulus. The dielectric properties of the anionic nylon 6 and polyesteramides have been carried out as a function of frequency (100 Hz-106 Hz), at ambient temperature. Regarding to dielectric permittivity, ε*(f), it was observed that the samples exhibit same behavior at increasing of the frequency. Experimental data revealed that the real part of electric modulus, M'(f) of the copolymers are many lower than those corresponding of the homopolymer. The presence of a single arc in the complex impedance plane plots confirms that, within the studied frequency range, the samples have a highly capacitive behavior. The results related to dielectric, crystalline and thermal properties of copolymers were compared with those obtained for homopolymer. <![CDATA[Seasonal Effects on HPLC-DAD-UV and UPLC-ESI-MS Fingerprints and Analgesic Activities of <em>Vernonia Condensata</em> Baker Extracts]]> Vernonia condensata Baker leaves have different uses in Brazilian folk medicine, including as analgesic and anti-inflammatory agents. The purpose of this study was to evaluate the seasonal effects on their high performance liquid chromatography with a diode array detector (HPLC-DAD-UV) and ultra-performance liquid chromatography coupled to a mass spectrometer with an electrospray interface (UPLC-ESI-MS) fingerprints, as well as their analgesic activities in mice. There were significant seasonal effects on the relative abundances of the metabolites of the V. condensate leaves as well as on their activities. Analgesic activities in the writhing test were observed with the polar fraction of the leaf extracts collected in autumn, winter and summer (400 mg kg-1); and with the intermediate fraction of leaves collected in autumn (25 and 400 mg kg-1) and in the summer (100 mg kg-1). In conclusion, the results confirm peripherally-mediated anti-inflammatory and analgesic activities for V. condensata leaves and suggest that these are influenced by the harvesting season. N-oxides alkaloids as well as vernonioside play important roles in determining this activity. <![CDATA[Determination of Metal Loading in Heterogeneous Catalyst by Slurry Sampling Flame Atomic Absorption Spectrometry]]> Quantification of metal loading in supported catalysts is imperative; however, the analytical methods are usually time-consuming, expensive, and require sophisticated equipment and sample extraction with hazardous and corrosive strong acids. Herein, we report a new method for quantification of metal in supported catalysts using slurry sampling flame atomic absorption spectrometry. The slurry sampling method was used for determination of gold and the results were similar to those obtained with the traditional extraction method using aqua regia; however, it overcomes the main drawbacks associated with sample digestion by avoiding the use of concentrated toxic reagents, minimizing sample manipulation, and consequently, reducing the risks of contamination and the sample preparation time. Ultrasound radiation optimization associated with the solvent, mass of sample, concentration, and matrix effect in the slurry analysis allowed direct analysis by using the calibration in aqueous medium. The slurry sampling procedure could be applied to other catalysts with different supports and in bimetallic systems. <![CDATA[Non-Targeted Electrospray Mass Spectrometry-Based Metabolic Fingerprinting and PLS-DA-Based Classification of Brazilian “Malvas”]]> Malva sylvestris, popularly known as "malva" in Brazil, is a medicinal plant used for its antiinflammatory effects. However, multiple plants are known as "malvas" in Brazil; these species include Sida cordifolia ("malva-branca") and Pelargonium graveolens ("malva-cheirosa"). In this work, electrospray mass spectrometry metabolic fingerprints from these species were obtained by direct infusion of extracts of commercial samples, purchased as crushed dried leaves. The spectral data were used to classify these species using a partial least squares discriminant analysis method. The identities of all samples were confirmed by morphological analyses, emphasizing the trichomes morphology. While over 80% of the samples were labeled as M. sylvestris or "malva", in the present study only 37% of these samples were classified as M. sylvestris species. Approximately 50% of these samples were classified as S. cordifolia, whose consumption may be dangerous for patients with cardiovascular diseases. Thus, these analytical and chemometric procedures worked as a fast and simple method for classifying species of "malvas". <![CDATA[Colloidal Dispersion Stability: Kinetic Modeling of Agglomeration and Aggregation]]> In this work we present a simple model for the kinetics of agglomeration and aggregation of colloidal particles. We consider that particles agglomerate rapidly and endothermically forming oligomers. These oligomers can, in turn, aggregate irreversibly, in a process that leads to the destabilization of the colloidal system. As these two processes have very different relative energy activations, they occur in different time-scales: the first step is faster and reaches a state of quasi‑equilibrium. Because of this, the enthalpy change during the agglomeration can be experimentally determined through the variable temperature multiple light scattering (VTMLS) method. Interestingly, this value is related to the relative kinetic stability of the system and can be used to evaluate the stability of new colloidal compositions. Our results are in qualitative agreement with experimental data of low concentration colloidal dispersions consisted of polymer particles and/or surfactant-coated particles. <![CDATA[Thiazolidin-4-ones from 3-(Aminomethyl)pyridine, Arenealdehydes and Mercaptoacetic Acid: Synthesis and Radical Scavenger Activity]]> The efficient synthesis of fifteen novel thiazolidin-4-ones from reaction of 3-(aminomethyl) pyridine (3-picolylamine), arenealdenhydes and mercaptoacetic acid was described. The desired compounds were obtained in moderated to good yields by two methodologies: conventional heating and ultrasound irradiation. The thiazolidin-4-ones were fully identified and characterized by nuclear magnetic resonance (NMR), gas chromatography coupled to mass spectrometry (GC‑MS) and high resolution mass spectrometry (HRMS) techniques. Four compounds showed radical scavenger activity in the 2,2’-azinobis-3-ethyl-benzothiazoline-6-sulfonic acid (ABTS) assay. <![CDATA[Potential Insecticidal Activity of Steroidal C-17 Pyrazolinyl Derivatives]]> Agrochemical research, over the last two decades, has resulted in the discovery of chemically novel insecticides, of which steroids-based compounds that mimic the action of hormones have been considered as safe insecticides. In this study, eight steroidal C-17 pyrazolinyl derivatives were resynthesized through molecular hybridization and their insecticidal activities against 4th instar larvae of Mythimna separate were evaluated. These results showed that some compounds exhibited significant insecticidal activities and the susceptibility assays were expressed as the median lethal dose (LD50), of which one of the compounds exerted the most potent insecticidal activity (LD50 = 296 µg g-1), comparable to that of the natural product insecticide, celangulatin V (LD50 = 260 µg g-1). This strategy led to a promising candidate for the development of new steroidal insecticidal agents. <![CDATA[Correlation Between the Composition and Flash Point of Diesel-Biodiesel Blends]]> Methyl ester biodiesels from vegetable oils, including soy, corn, canola and sunflower, and from swine lard, were prepared. They were mixed with mineral diesel to produce blends from 5% v/v to 50% v/v of biodiesel, i.e., B5, B10, B20 and B50. The flash points of these mixtures, the pure diesel (B0) and the pure biodiesel (B100) were determined. In all cases, it was observed that there was a second order polynomial correlation between the flash point and the percentage of biodiesel in the blend, it was concluded that is possible to estimate the flash point of a diesel-biodiesel mixture if its composition and the flash points of the pure components are known. Quasi-linear correlations between the increase of the flash point and the increase in biodiesel content were observed for B0 to B20 mixtures. If a mean linear correlation is applied, independently of the oil or fat used, in this case where the flash point of the petrol diesel is 40.1 ºC, the estimated flash points for the blends from B5 to B20 will be approximately 45 ± 3 ºC. <![CDATA[Synthesis, Molecular Structure of Diethyl Phenylenebis(Methylene)Dicarbamates and FTIR Spectroscopy Molecular Recognition Study with Benzenediols]]> The synthesis, density functional theory (DFT) molecular structure and Fourier transform infrared spectroscopy (FTIR) molecular recognition study of diethyl phenylenebis(methylene) dicarbamates with 1,2- and 1,3-benzenediols is described. The formation of the complexes was confirmed by the shift of the O-H stretching bands in the IR spectra of the complexes compared with the IR spectra of the noncomplexed benzenediols.