Resumo em Inglês:

This article reports the synthesis of two bimetallic zinc(II) complexes containing phenoxy-imine ligands and their application as initiators of ring opening polymerization (ROP) of L-lactide (LA). The phenoxy-imine ligands were obtained from salicylaldehyde derivatives and 2,3,5,6-tetramethylphenylenediamine, yielding two bidentate regions per ligand. The reactions of both phenoxy-imine ligands with ZnEt2 in the presence of n-BuOH afforded [Zn2(L1)(OBu)2] and [Zn2(L2)(OBu)2], which were characterized by elemental analysis, Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) spectroscopy. In addition, the geometries of both complexes were investigated by DFT (B3LYP/LACVP**) calculations. [Zn2(L1)(OBu)2] and [Zn2(L2)(OBu)2] were tested as initiators of ROP of LA at 180 °C using different LA/Zn molar ratios, namely 500, 1000 and 2500. Both complexes showed good activity, resulting in conversions up to 96% in 2 h. The poly-LLA exhibited average molecular weight (Mw) ranging from 45,000-92,000, relatively low polydispersity (Mw/Mn = 1.6-2.0) and high stereoregularity with melting temperature Tm = 164 °C.

Resumo em Inglês:

A nanostructured porous gold film (NPGF) was fabricated onto a gold electrode surface by an electrochemical approach involving anodization followed by electrochemical reduction in absence of binary alloys, templates and chemical reducing agents. The electrocatalytic activity of the as-fabricated electrocatalyst was examined towards hydrogen evolution reaction (HER) and very low onset potential (−0.048 V) and overpotential values of −0.070 and −0.083 V at current densities of 10 and 20 mA cm -2, respectively, were obtained in 0.5 mol L -1 sulfuric acid solution, along with exchange current density (jo) of 0.126 mA cm -2. A small Tafel slope of ca. 36 mV decade -1 was achieved, indicating the HER takes place according to a Volmer-Heyrovsky mechanism and that the electrochemical desorption of hydrogen is the rate determining step. The performance of the NPGF electrode was compared with that of bulk gold and platinum electrodes, and a platinum-like behavior was noticed for HER. Finally, the durability of the proposed electrocatalyst was examined using voltammetric and amperometric techniques and an excellent stability was achieved.

Resumo em Inglês:

As a kind of important water pollutant, heavy metal ions have a detrimental effect on the health of human. In this study, Au@Ag core-shell nanoparticles were synthesized by simple reduction of Ag + around Au nanoparticles and functionalized by DNAzyme. Based on thymine-Hg2+-thymine binding mode, a sensitive aptamer biosensor was constructed by utilizing functionalized Au@Ag core-shell nanoparticles as labels, and the sensitivity was enhanced by DNAzyme due to the catalysis toward H2O2. Under optimal conditions, square wave voltammetry was carried out to measure the current derived from Au@Ag nanoparticles labels. The current response of biosensor increased with the increasing of Hg2+ concentration, which presented linear relation in the range of 0.002-20 μg L -1 with limit of detection of 0.006 μg L -1. Meanwhile, the electrochemical biosensor showed superior reversibility, stability, repeatability, and selectivity.

Resumo em Inglês:

Macauba is a palm tree which provides large amount of oil. Particularly its oil from the kernel presents excellent stability to oxidation as it is mainly constituted by saturated organic chains. This stability is inherited by the biodiesel prepared with this oil. Paradoxically, contrarily to the expectation as it is mainly constituted by saturated esters, the biodiesel prepared from the macauba kernel oil presents low cold filter plugging point (CFPP). This can be understood on the basis of the high level of content of saturated esters with relatively short carbon chain. Considering these two properties of the biodiesel prepared from the macauba kernel oil, i.e., excellent oxidation stability and low CFPP, it was studied if such characteristics could be transferred to blends constituted by it and another vegetable oil. Blends with biodiesels from soy, corn, macauba pulp and fry oil were studied and it was observed that, indeed, partial transference occurs, meaning that the inconvenient characteristics of such biodiesels were favorably ameliorated, allowing the use, as fuels, of the biodiesels prepared from other oils which original properties do not attaint the quality specified by the regulatory agencies.

Resumo em Inglês:

Saffron is a widespread consumed spice with potential health promoting compounds. In dairy technologies it is often used to enhance color and flavor of cheeses, so it would be recommended to know the content of saffron functional compounds in cheese made with this spice, as they could still have potential bioactivity. For this purpose, an UHPLC (ultra high performance liquid chromatography) method was developed, with the aim of reducing analysis time and solvent consumption. A methanol:water solution (80:20 v/v) was used to extract saffron compounds from cheese with stirring for 1 h in the dark at room temperature, then the samples were centrifuged at 3500 rpm, for 5 min at 4 °C and the residues were extracted twice. A linear gradient elution of acetonitrile in water allowed to simultaneously determine picrocrocin and crocins in saffron in a short time (16 min), and allowed a quantitative determination of crocins in commercial cheeses.

Resumo em Inglês:

Heterocyclic chalcones have been prominent in the scientific community due to various biological activities reported for these compounds. The structural knowledge of heterocyclic chalcones can help in the understanding of their mechanism of action. The Hirshfeld surfaces were used to study the supramolecular arrangement of two conformers present into asymmetric unit of the heterocyclic chalcone (2E)-3-(4-methylphenyl)-1-(pyridin-3-yl)-prop-2-en-1-one on crystalline state. In addition, the linear polarizability (α), the first hyperpolarizability (β||z), and the second hyperpolarizability (γ) of the conformers were calculated to get a better insight on the linear and nonlinear optical behaviors of these structures in presence of solvent medium, as well as their band-gap energies. The Hirshfeld surfaces confirmed the presence of C−H···N, C−H···O and C−H···C interactions in packaging stabilization. Finally, the 2D fingeprint plot was used to the quantification of contacts and indicated that there are both π···π and C−H···π interactions present in the compound.

Resumo em Inglês:

Chagas disease is included in the neglected tropical diseases list and is endemic to 21 Latin American countries. The two drugs currently available for treating Chagas disease are nifurtimox and benznidazole and both result in many significant side effects. The study describes the synthesis and biological evaluation of 3,5-disubstituted isoxazoles. Isoxazoles were obtained by reaction of flavones and hydroxylamine and either alkylated at the free hydroxyl group and/or nitrated at the isoxazole ring. These compounds were evaluated for their in vitro anti-Trypanosoma cruzi activity against trypomastigote and amastigote forms of the parasite in T. cruzi-infected cell lineages. Benznidazole was used as a reference compound for the in vitro assay and mammalian L929 cells were employed to evaluate cytotoxicity. A majority of the compounds tested were very active and the most active isoxazole against amastigote and trypomastigotes of T. cruzi was slightly more potent than the current medicine benznidazole.

Resumo em Inglês:

In this work, it is proposed a new strategy to improve the dispersion of inorganic fillers in polymeric matrices by producing surface carbon nanostructures. Clay/carbon nanofibers particles were prepared and used as fillers to improve the mechanical and thermal properties of ultra-high molecular weight polyethylene (UHMWPE). Thermogravimetry (TG), differential scanning calorimetry (DSC), elemental analyses, Raman, X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that chemical vapor deposition (CVD) with ethanol at different temperatures, i.e. 700, 800 and 900 °C with and without Fe catalyst, can be used to produce carbon (0.5-3.6 wt.%), mainly as nanofibers, on the clay surface. The use of these clay/carbon particles as fillers in UHMWPE at 1 and 3 wt.% produced an increase in the yield stress from 16 to ca. 20 MPa and Young modulus from 314 MPa for pure UHMWPE to values near 395-408 MPa. Moreover, the presence of the carbon/clay composites led to a strong improvement of the thermal properties of the UHMWPE increasing the decomposition Tonset (degradation start temperature) from 445 up to 472 °C. It was also observed by the crystallization enthalpies that the UHMWPE increased the crystallinity from 55 to 80-85% in the presence of the carbon composites. These results are discussed in terms of the strong interactions of the hydrophobic carbon nanostructures on the clay surface with the polymer hydrophobic chains.

Resumo em Inglês:

The objective of this study was to evaluate the concentration of Cu, Zn, Cr and Pb in different species of fish collected in the estuarine and limnic regions of the São Gonçalo channel, located in the Patos-Mirim lagoon complex in the coastal plain of Rio Grande do Sul State (Southern Brazil) during 2013 (autumn, winter and spring) and 2014 (summer). Fish samples were decomposed in a digester block with a reflux system under conditions optimized using a central composite design as it follows: 250 mg of fish sample, 5 mL HNO3, 2 mL H2O2 during 2 h at 150 °C. The concentrations obtained ranged from 6.7 to 12.0 mg kg -1 for Cu; 1.8 to 23.6 mg kg -1 for Zn; 37 to 487 µg kg -1 for Pb; and 40 to 1268 µg kg -1 for Cr. The highest concentrations of Cu, Zn and Pb, were observed in fishes collected at locations in the estuarine region and Cr showed high levels, especially in the limnic region. The samples of the species Loricariichthys anus (viola) showed the highest concentrations of all analytes investigated.

Resumo em Inglês:

Biofilms are widely present in many human chronic infections, often more resistant to treatment with antibiotics. Bacterial diguanylate cyclases (DGCs) synthesize cyclic dimeric guanosine monophosphate (c-di-GMP) from two guanosine-5'-triphosphate (GTP) molecules. c-di-GMP is a central second messenger controlling biofilm formation, turning this class of enzymes an attractive target to prevent and disrupt biofilms of pathogenic bacteria. Here, we apply an in silico ligand- and target-based hybrid method to screen potential DGC inhibitors from an FDA-approved drug databank. Mass spectrometry assays confirmed that seven screened compounds selectively bound to the GTP active site of P. aeruginosa WspR GGDEF domain. Four out of those, including the anti-inflammatory sulfasalazine and the anti-hypertensive eprosartan, inhibited distinct DGCs (P. aeruginosa WspR and E. coli YdeH) in the micromolar range. Sulfasalazine and eprosartan reduced aggregation in solution of E. coli overexpressing WspR or YdeH. Similar anti-aggregation effects were also observed for sulfasalazine-related anti-inflammatory drugs sulfadiazine and sulfathiazole, the latter a previously described anti-biofilm agent. The optimized pharmacokinetic properties and toxicological profiles of the DGC inhibitors could be promising candidates for new anti-microbial agents based on the drug reposition strategy.

Resumo em Inglês:

An imprinted amino-functionalized silica gel material was prepared by surface molecular imprinting technique combined with a sol-gel process on the supporter of activated silica gel and used as a solid-phase extraction for the extraction and determination of methyldopa (MTD). Non-imprinted silica adsorbent was synthesized without the addition of MTD using the same process. MTD-imprinted and non-imprinted silica adsorbents were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and the static adsorption experiments. The prepared MTD-imprinted silica sorbent demonstrated high adsorption capacity and significant selectivity for MTD in the presence of competitive substances. The maximum adsorption capacity of surface imprinted and non-imprinted silica adsorbent for MTD were 14565.81 and 2990.56 µg g -1, respectively. The imprinted 3-aminopropyl triethoxysilane (APS) modified silica gel adsorbent provided fast kinetics for the adsorption of MTD. In the operational mode of solid phase extraction (SPE), calibration curve of MTD solution was linear in the range of about 15 to 100 µg mL -1. The limit of detection (LOD) and precision (RSD) during five replicates were 2.31 µg mL -1 and 5.69%, respectively. At last, the MTD-imprinted material was used as SPE adsorbent to determine the MTD in non-spiked and spiked pharmaceutical samples with satisfactory recovery higher than 94%.

Resumo em Inglês:

The synthesis and use of functionalized materials is growing every year. Thus, this work presents a methodology for the functionalization of bentonite and vermiculite after the acid leaching of the raw materials. Leaching was performed with sulfuric acid (H2SO4), and the functionalization was performed with (3-mercaptopropyl)trimethoxysilane (MPTS), which was oxidized after being anchored to the support. Compared to the results in the literature for directly functionalized raw bentonite, the materials had a greater number of anchored propyl sulfonic acid groups, and the greatest number of these groups led to an increase in the acidity of the raw materials. The raw and functionalized bentonite and vermiculite were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), thermogravimetric analysis (TGA), N2 adsorption and the surface acidity was determined by acid-base titration.

Resumo em Inglês:

Two mesoporous SBA-15 materials with different morphologies (spherical and fiber-shaped) were synthesized and evaluated as supports for nickel-based catalysts for polymerization reactions. The supports were pretreated with trimethylaluminum (TMA), and the catalyst dibromo-bis(4-amino-2,3,5,6-tetramethylimino)acenaphthene nickel(II) was attached to the supports and activated with TMA or MAO (methylaluminoxane). Characterization showed that the insertion of cetyltrimethylammonium bromide (CTABr) as a cosurfactant led to spherical SBA-15 with a decrease in particle and pore sizes to 4.8 nm compared to 6.5 nm in traditional fiber-shaped SBA-15. The spherical SBA-15 showed thicker walls than the fiber-shaped SBA-15, attributed to the increase in functional groups of the cosurfactant. The different spherical and fiber-shaped morphologies did not show any significant difference in the productivity of polyethylene. The catalyst supported on spherical SBA-15 materials showed 58% productivity compared to its homogeneous analogue using TMA as a cocatalyst.

Resumo em Inglês:

In this study, tetraethylenepentamine modified magnetic graphene oxide nanomaterial (TMGO) was prepared and characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and vibration sample magnetometer (VSM). All the characterizations proved that the modification and preparation of TMGO were successful. The TMGO nanomaterial was used in the adsorption of Acid Red 18 (AR) in aqueous solution. The parameters like pH of solution, adsorption kinetics and isotherms were all investigated. The results indicated that the TMGO nanomaterial had satisfied adsorption ability and the maximum adsorption capacity was 524.2 mg g -1 at 45 °C and pH 6. The adsorption capacity remained at 91.8% of the initial value after five cycles. The adsorption process with AR was found through fitting the pseudo-second-order kinetics equations and the Freundlich adsorption model. The experimental results demonstrated that the TMGO nanomaterial could be rapidly extracted from the medium and had a good adsorption ability to remove dyes in wastewater.

Resumo em Inglês:

Thiosemicarbazones are a class of compounds of interest for Medicinal Chemistry, as they are structurally diverse and have numerous biological activities reported in the literature. This study describes the synthesis of seventeen thiosemicarbazones, which were investigated as potential therapeutic agents for the treatment of Alzheimer's disease through antioxidant tests and an inhibitory assay of the acetylcholinesterase enzyme. All compounds showed excellent inhibition of acetylcholinesterase and exhibited excellent antioxidant action when compared to the standards. In addition, a quantum study was carried out, in which the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy values of each compound were obtained. From these theoretical data, chemical properties were calculated and correlated with the experimental data.

Resumo em Inglês:

This paper proposes a method for chicken tissues preparation using tetramethylammonium hydroxide (TMAH) for Pb determination by graphite furnace atomic absorption spectrometry employing multivariate approaches. Combining Raman spectroscopy with scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy to monitor the solubilization process it was possible to show that TMAH acts in the solubilization of proteins, amino acids and lipids. Besides, this investigation showed that the small residual masses of samples have organic and inorganic compounds. Accuracy tests indicated that such residues have not interfered in the analytical results (recovery between 90-95%). The obtained limits of detection (0.099 µg g -1) and quantification (0.33 µg g -1) are compatible with the detectability required for regulatory purposes. Linearity (R2 = 0.9925) and characteristic mass (13 pg) were also reported. Considering the set of 15 samples comercialized in Brazil, any Pb contamination was successfully observed and this was confirmed by the analysis of digested samples.

Resumo em Inglês:

Old age is a risk factor for cancer development in humans and animals, and studies have shown that tumors in animals are acceptable models for studying human cancers, considering the similarities between their factors. This work was conducted in a 53-year-old captive female common hippo (Hippopotamus amphibious) with a left leg tumor and metastatic mass. Histopathological and immunohistochemical analyses were carried out with a final diagnosis of a high grade pleomorphic sarcoma. A proteomic study using mass spectrometry was added in order to identify further aspects of the primary tumor and metastasis which could improve our understanding, and each tissue showed a proteomic profile indicative of its pathologic state with significant differences between healthy tissue, primary and metastatic tumors. Low levels of β-actin in primary tumors were identified, and this may be associated with a possible consequence of cytoskeleton dynamic modification. In metastatic tissue, these dynamics may be affected by the presence of HSP chaperone 60.

Resumo em Inglês:

The effect of selenate and selenite enrichment on mineral composition of a red type of lettuce cv. “Veneza roxa” was evaluated using inductively coupled plasma-optical emission spectroscopy (ICP OES), molecular modeling and principal component analysis (PCA). Both Se species did not show toxicity, while selenate promoted the greatest Se accumulation by the plant. There was an increase of 886 µg of Se per 100 g of fresh sample at different concentrations of selenate, but for selenite the maximum variation was only of 114 µg per 100 g. Selenate promoted the absorption of Mo and S and the reduction of K, Mn and P, meanwhile selenite increased Mn and decreased Mo accumulation. Copper and Fe absorption was negatively affected, Ca and Mg showed a slight increase, and Na and Zn were not affected by Se species. Despite the changes in the nutritional balance, Se-enriched lettuce can still be considered a potential dietary source of this essential element.

Resumo em Inglês:

This work evaluated the photocatalytic activity of suspended TiO2, and TiO2-coated glass Raschig rings with respect to degradation of estrogens estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2) in aqueous solutions and wastewater effluent samples. Gas chromatography/tandem mass spectrometry (GC-MS/MS) studies were carried out to identify degradation products for EE2. TiO2 suspensions allowed degradation rates higher than 90% for all studied estrogens in 30 min for an artificial (ultraviolet A) UVA-assisted process and aqueous solution. Immobilized TiO2 showed less favorable degradation kinetics, requiring ca. 60 min to achieve almost complete estrogen degradation. Some derivatized degradation products were identified for the first time by GC-MS/MS applying ultraviolet C (UVC) photolysis and TiO2/UVA photocatalysis. A degradation route was suggested for EE2 in UVC photolysis and TiO2/UVA processes. In the degradation of pretreated sewage samples, the immobilized TiO2 was more efficient than free TiO2, allowing ca. 85% removal of E2 and EE2 in 60 min.

Resumo em Inglês:

The characterization of the lipid profiles of oils extracted from the kernel of seeds and nuts of peanut (Arachis hypogaea), babassu (Attalea speciosa), coconut (Cocos nucifera), castor (Ricinus communis) and grape (Vitis vinifera) was performed by using Raman spectroscopy and gas chromatography with flame ionization detector (GC-FID). Chromatographic analyses showed that coconut and babassu oils are composed essentially by saturated fatty acids (SFA), whereas the others are composed mainly by unsaturated fatty acids (UFA). The comparison of commercial and homemade castor oils showed the former have a lower level of ricinoleic acid at ca. 58%. Spectroscopic analyses of three distinct castor oils showed their profiles could be differentiated by marker features ascribed to carbonyl modes which were correlated with storage time. The comparison between the Raman spectra of standard samples of fatty acids with the samples of oils allowed the assignment of the spectroscopic features and the characterization of marker bands for the degree of unsaturation.

Resumo em Inglês:

Piperidine alkaloids are predominant in ant venom glands of S. invicta and S. saevissima. These ants are broadly sympatric in Southeastern Brazil, and potentially diagnostic compounds could assist in ant identification. We determined the absolute configuration of 2,6-dialkyl-piperidines of S. invicta and S. saevissima workers and used these data to group Southeastern Brazil species. The monitoring of venom samples by chiral gas chromatography coupled to a flame ionization detector (GC-FID) revealed that S. saevissima produces the four stereoisomers of 2-methyl-6-undecyl-piperidines, 2-methyl-6-tridecyl-piperidines and 2-methyl-6-tridecenyl-piperidines, while S. invicta venom consisted primarily of a single enantiomer cis and trans from each piperidine alkaloid. Our findings showed that the absolute configuration of piperidine alkaloids of fire ant venom may be a potential chemical tool to distinguish S. invicta and S. saevissima sympatric species in Southeastern Brazil.

Resumo em Inglês:

In this work, thermal properties and kinetics of Al-nanoparticles/α-MnO2 nanorods thermite were reported. The α-MnO2 nanorods were synthesized using a hydrothermal method and were characterized by X-ray powder diffraction (XRD) and X-ray photoelectron spectra (XPS), then combined with Al nanoparticles based on the ultrasonic mixing method to prepare the nanostructure thermite. Besides, both pure components and mixture were characterized by field emission scanning electron microscopy (FE-SEM) to observe their morphologies and structures. Subsequently, the thermal properties of Al/α-MnO2 nanostructure thermite were studied on the basis of thermogravimetric-differential scanning calorimetry (TG-DSC). According to the TG-DSC tests, the calculation results of activation energy for kinetics of Al/α-MnO2 thermite were obtained using different isoconversional methods. It was found that Al/α-MnO2 nanostructure thermite has high heat release and low onset temperature, and the heat release of the nanostructure thermite was approximately 1146.6 J g -1.

Resumo em Inglês:

The oxidative polymerization of linseed oil was investigated comparing the classical catalysts cobalt(II) 2-ethylhexanoate and manganese(II) 2-ethylhexanoate and their derivatives modified by the presence of chelating nitrogen ligands, i.e., 2,2'-bipyridyl, 2-(acetyl-2,6-diisopropylphenylimine)-pyridine and [N-(2,6-diisopropylphenyl)imine]acenaphthoquinone. The suitable stoichiometries between the two precursor complexes with the three ligands were determined by UV-visible spectroscopy. All complexes were characterized by infrared spectroscopy, and one complex was characterized also by X-ray diffraction. The apparent kinetic constants of oxidative polymerization of linseed oil was determined, for each catalytic system, via the periodic measurements of the oil viscosity during the oxidation reaction. The results indicated that the modifications of the classical two complexes with the chelating nitrogen ligands improved the catalytic efficiency at least to the manganese complex.

Resumo em Inglês:

Some Eucalyptus species produce oils with biological activities and the effect of their interspecific hybridization on the enantiomeric composition of terpenes has not been reported. The enantiomeric excesses of monoterpenes in the essential oil of Eucalyptus grandis × E. tereticornis and its parental taxa were determined by gas chromatography-mass spectrometry (GC-MS), and to resolve coelutions problems by preparative high performance liquid chromatography (HPLC) and GC-MS with two columns in series. The essential oil composition of the hybrid presented qualitative and quantitative differences with the composition of its parental taxa. Great differences were found for the enantiomeric ratio in monoterpene alcohols among the three essential oils. Our results suggest that the enantiomeric analysis can be a reliable method for the study of how the interspecific hybridization can module the enantiomeric chemical profile in Eucalyptus essential oils. These results suggest the use of interspecific hybridization to improve or expand the source of bioactive compounds.

Resumo em Inglês:

Acid catalyzed decomposition of C5 and C6 sugars has been considered an important source of biomass derived chemicals. An essential step in this process is the extraction of furfural, hydroxymethylfurfural and levulinic acid from aqueous phase. In this work, a computational screening of 178 organic solvents for simultaneous extraction of these chemicals from aqueous phase has been done with the continuum SMD (solvation model based on density) model. Our analysis has taken in account the partition coefficient, water miscibility, boiling point and toxicity of the organic solvents. The present theoretical results indicate that C6 and C7 ketones are the most adequate solvents, and 4-heptanone is predicted to be particularly useful.