Journal of the Brazilian Chemical Society, Volume: 30, Issue: 10, Published: 2019
  • For Gender Equality in Science Editorial

    Vargas, Maria D.; Soares, Jaísa F.
  • DNA Damage by Endogenous and Exogenous Aldehydes Review

    Medeiros, Marisa H. G.

    Abstract in English:

    The present overview describes the formation of deoxyribonucleic acid (DNA) adducts from endogenous and exogenous aldehydes, such as acetaldehyde, acrolein, crotonaldehyde, malonaldehyde, 4-hydroxy-2-nonenal and 2,4-decadienal. Malonaldehyde reacts with 2’-deoxyguanosine, 2’-deoxyadenosine, and 2’-deoxycytidine, yielding cyclic pyrimidopurinone and acyclic adducts. The direct addition of ɑ,β-unsaturated aldehydes to DNA bases yields cyclic substituted propano adducts, such as 1,N2-propano-2’-deoxyguanosine. Alternatively, ɑ,β-unsaturated aldehydes can be oxidized to reactive epoxides, giving ethano or etheno derivatives upon reaction with DNA. In addition, information on highly sensitive techniques, employed for the in vivo detection and quantification of DNA-aldehyde adducts, is also provided. Some of these DNA-aldehyde lesions have been shown to be highly mutagenic. In fact, lipid peroxidation and exogenous aldehyde exposure could potentially account for the observed carcinogenicity of urban air pollution and cigarette smoke exposure.
  • Magneto-Responsive Hydrogels: Preparation, Characterization, Biotechnological and Environmental Applications Review

    Frachini, Emilli C. G.; Petri, Denise F. S.

    Abstract in English:

    Hydrogels are hydrophilic three-dimensional networks able to hold large amount of water and hydrophilic molecules. Magneto-responsive hydrogels comprise of magnetic nanoparticles dispersed in polymeric networks that can be manipulated under external magnetic field. This review aims at (i) giving a brief overview on the evolution of hydrogels until the design and development of magnetic hydrogels; (ii) describing the types of hydrogels and the basic concepts about superparamagnetic iron oxide nanoparticles, as well as the preparation and characterization of magneto-responsive hydrogels; (iii) displaying the relevant applications of magneto-responsive hydrogels for drug delivery, regenerative medicine of tissues, cancer therapy and environmental issues and (iv) highlighting the challenges and future trends of magneto-responsive hydrogels for 3D and 4D printing.
  • Aspergillus niger: A Hundred Years of Contribution to the Natural Products Chemistry Review

    Lima, Mary Anne S.; Oliveira, Maria da Conceição F. de; Pimenta, Antônia T. Á.; Uchôa, Paula K. S.

    Abstract in English:

    Aspergillus niger is a phytopathogenic fungus responsible for the plant disease called “black mold”, and it is considered the most versatile microorganism for producing acids, proteins, and enzymes of industrial value, besides a variety of compounds of pharmacological interest. This review presents a century of contribution of A. niger in the natural products chemistry under two different perspectives: (i) an overview of the structural diversity of secondary metabolites produced by A. niger from different habitats and their biological activities; (ii) a general discussion of the enzymatic potential of A. niger on the selective biotransformation of terpenes, highlighting the most uncommon microbial transformations.
  • A New Cytotoxic Naphthoquinone and Other Chemical Constituents of Sinningia reitzii Article

    Silva, Adson S.; Amorim, Magali S.; Fonseca, Mariana M.; Salvador, Marcos J.; Sá, Eduardo L. de; Stefanello, Maria Élida A.

    Abstract in English:

    Phytochemical study of Sinningia reitzii (Gesneriaceae) led to the isolation of three new naphtoquinones, 6,7-dimethoxydunnione, 7-hydroxy-6-methoxydunnione, and 5-hydroxy-6,7-dimethoxydunnione from the tubers, together with four known compounds, 7-hydroxydunnione, 8-hydroxydunnione, 5-hydroxy-6,7-dimethoxy-α-dunnione, and 8-hydroxydeydrodunnione. Aerial parts furnished five known compounds, 5-hydroxy-6,7-dimethoxydunniol, 6,8-dihydroxy-7-methoxy-2-O-methyldunniol, loureirin B, jacaranone, and methyl 4-hydroxyphenylacetate. Compounds 8-hydroxydunnione, 5-hydroxy-6,7-dimethoxy-α-dunnione, 8-hydroxydeydrodunnione, 5-hydroxy-6,7-dimethoxydunniol and 6,8-dihydroxy-7-methoxy-2-O-methyldunniol had been previously reported in the tubers of S. reitzii. Density functional theory was used to assign the absolute configuration of compounds 6,7-dimethoxydunnione, 7-hydroxy-6-methoxydunnione 5-hydroxy-6,7-dimethoxydunnione, 7-hydroxydunnione, 8-hydroxydunnione, 5-hydroxy-6,7-dimethoxy-α-dunnione. Compounds 6,7-dimethoxydunnione, 8-hydroxydunnione, 5-hydroxy-6,7-dimethoxy-α-dunnione and 8-hydroxydeydrodunnione were evaluated for cytotoxicity against PC3 (prostate), SKMEL 103 (melanoma), and HeLa (cervix) human cancer, and 3T3 fibroblast cell lines, using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Compound 6,7-dimethoxydunnione displays cytotoxic activity against all the tumor cell lines tested (half maximal inhibitory concentration, IC50, 4.47-26.2 µmol L-1), and was inactive against 3T3 fibroblasts (IC50 > 100 µmol L-1). Compounds 8-hydroxydunnione, 5-hydroxy-6,7-dimethoxy-α-dunnione and 8-hydroxydeydrodunnione were inactive against all tested cell lines.
  • Gold Nanoparticles and [PEDOT-Poly(D,L-Lactic Acid)] Composite: Synthesis, Characterization and Application to H2O2 Sensing Article

    Silva, Aruã C. da; Minadeo, Marco A. O. S.; Torresi, Susana I. C. de

    Abstract in English:

    Biocompatible electrochemical devices are challenging to develop due to the toxicity of many advanced electrode materials and the difficulty to degrade the discarded material. Few recent advances were made in the synthesis of conducting biodegradable composites of polymers for electrode materials. In this article we describe the synthesis of two new inorganic/organic nanocomposites of Au nanoparticles and conducting polymers based on the biodegradable polymer poly(D,L-lactic acid) (PDLLA): Au nanoparticles/oligomers of 3,4-ethylenedioxythiophene (EDOT)-PDLLA and Au nanoparticles with poly(3,4-ethylenedioxythiophene) (PEDOT)-PDLLA. The nanocomposites were carefully analyzed; the gold nanoparticles mean sizes were 8 ± 3 and 7 ± 2 nm, respectively. 1H and 13C nuclear magnetic resonance (NMR) demonstrated the polymerization of EDOT-PDLLA made through one-pot reaction with AuIII precursor. Raman spectra show that PEDOT-PDLLA is formed in the synthesis of Au/PEDOT-PDLLA. The immobilization of Au/PEDOT-PDLLA on glassy carbon electrodes is easy and more stable than the immobilization of simple PEDOT. Au/PEDOT-PDLLA catalyzes the reduction of H2O2(aq), which was detected by chronoamperometry. The sensor is stable and presents sensitivity of 8.36 × 10-3 A mol-1 L cm-2, linear range of 1-45 mmol L-1 and limit of detection of 0.17 mmol L-1.
  • Electrode Modified with the Ionic Liquid [P6,6,6,14+]2[MnCl42-] for the Determination of Bisphenol A in Plastic Samples Article

    Silva, Tânia Regina; Merib, Josias; Spudeit, Daniel A.; Carasek, Eduardo; Vieira, Iolanda C.

    Abstract in English:

    This paper describes a new and simple electrode for the determination of bisphenol A (BPA) in different plastic samples using carbon paste electrode (CPE) modified with a trihexyltetradecylphosphonium tetrachloromanganate(II) ([P6,6,6,14+]2[MnCl42-]) magnetic ionic liquid (MIL/CPE). Electrochemical characterization of MIL/CPE by cyclic voltammetry and electrochemical impedance spectroscopy indicated that MIL facilitated the electron transfer. Using squarewave voltammetry (SWV) under optimized conditions, the calibration curve showed a linear range for BPA from 2.0 to 53.0 µmol L-1, with limit of detection (LOD) of 0.87 µmol L-1. The proposed electrode demonstrated good precision with coefficients of variation of 4.5% (intra-day, n = 10), 2.0% (inter-day, n = 5) and 1.5% (electrode-to-electrode repeatability, n = 3). Recoveries of 93.0 to 101.1% demonstrated that the method is suitable for practical applications.
  • Integrated Chemometric Approach to Optimize Sample Preparation for Detecting Metabolic Changes Provoked by Abiotic Stress in Coffea arabica L. Leaf Fingerprints Article

    Marcheafave, Gustavo G.; Tormena, Cláudia D.; Afonso, Sabrina; Rakocevic, Miroslava; Bruns, Roy E.; Scarminio, Ieda S.

    Abstract in English:

    The effects of water-deficit stress on irrigated and unirrigated field plants of Coffea arabica L. genotype IAPAR 59 were investigated. Plant extracts were obtained following an ethanol-dichloromethane-hexane statistical mixture design. Proton nuclear magnetic resonance (1H NMR) fingerprints of the extracts were discriminated using factor analysis (FA) and hierarchical clustering techniques. Extracts from the 1:1:1 ternary mixture presented the largest discriminations compared with those from the pure solvents or their 1:1 binary mixtures. Metabolites resulting from fermentation processes and nutritional deficiencies as well as senescence and abscission precursors such as lactate, arginine and methionine were prevalent in unirrigated plants that can provoke expressive decreases in bean productivity as well as premature plant aging. Amino acids that control regulatory, physiological processes and soil salinization have higher concentrations in the irrigated plants. The NMR assignments of eighteen substances observed here were confirmed by electrospray ionization mass spectrometry.
  • Iridium-Based Catalysts for the Ethanol Electrooxidation in Acidic Media Article

    Silva, Fabiano R. P. da; Silva-Junior, Luiz C.; Camara, Giuseppe A.; Giz, Martha Janete

    Abstract in English:

    Herein we sinthesize and investigate Ir-based nanocatalysts (dispersed in carbon) in different atomic compositions combining two (IrRh) and three metals (IrRhSn). These materials were evaluated towards the ethanol electrooxidation in acidic electrolyte in presence of three ethanol concentrations using cyclic voltammetry, while the species produced during the reaction were monitored by in situ Fourier transform infrared spectroscopy (FTIR). Results show that IrRh binary electrocatalysts are selective to the production of CO2 from ethanol, but the catalytic activity is poor. This finding is interpreted in terms of a slow adsorption of ethanol that is assumed to be the rate determining step during the electrooxidation of the alcohol. Ternary catalysts, in turn, present higher electrooxidation currents and anticipate the production of CO2. However, the selectivity towards the CO2 pathway is lost and the higher catalityc activity is justified by a growing production of acetic acid, illustrating the influence of Sn on the eletrooxidation of ethanol.
  • Direct Assay to Evaluate Phosphoenolpyruvate Carboxykinase Activity Article

    Amaral, Bruno S. do; Correa, Katia Celina S.; Corrêa, Arlene G.; Souza, Dulce H. F. de; Cass, Quezia B.

    Abstract in English:

    Phosphoenolpyruvate carboxykinase (PEPCK) is a ubiquitous enzyme found in all known groups of organisms, acting in the reversible conversion of oxaloacetate (OAA) to phosphoenolpyruvate (PEP) in the presence of divalent metal ion, and dependent of adenosine 5’-triphosphate (ATP) or guanosine-5’-triphosphate (GTP). PEPCK is an important enzyme in the metabolism of some organisms, such as Trypanosoma cruzi, being suggested as a potential drug target to treat Chagas’ disease. Its catalytic activity is, classically, measured by coupled assays. Herein, a direct assay by liquid chromatography-tandem mass spectrometry (LC-MS/MS) capable of quantifying PEP, in co-elution with OAA by the differentiation obtained by the mass spectra, is reported. The developed assay was used throughout the purification protocol in order to measure the activity of PEPCK of T. cruzi, which was expressed in Escherichia coli. The purified enzyme was kinetically characterized by the developed method with Michaelis-Menten constant (KMapp) values of 96 ± 4 and 275 ± 18 µmol L-1 to OAA and ATP as substrates, respectively. The developed assay was also used for ligand screening and proved to be able to identify very low inhibitions for small molecules (50 µmol L-1).
  • Are Imidazoles Versatile or Promiscuous in Reactions with Organophosphates? Insights from the Case of Parathion Article

    Silva, Valmir B.; Orth, Elisa S.

    Abstract in English:

    Is the broad mechanistic versatility of imidazole towards organophosphates (OPs), that has inspired many catalysts and sensors, beneficial? Herein, a thorough analysis is given seeking to unravel this puzzle. For OPs from the P=O family, imidazole attacks the phosphorus atom exclusively (N-phosphorylates). With the P=S family which are less reactive, an unusual N-alkylation predominates. Surprisingly, imidazole reacts with methyl parathion exclusively at the aliphatic carbon, whilst for the ethylated analogue parathion, imidazole reacts by two pathways: at both the phosphorus and aliphatic carbon, with predominance for the latter. The preference for the electrophilic center can be modulated by the pH. Overall, a mechanistic structure-related trend is observed: imidazole tends to prefer other electrophilic centers than the phosphorus for less reactive OPs. Moreover, this gives important insights concerning the challenging chemistry of imidazole alkylation and the outcomes for monitoring systems that depend on the detection of degradation products. Finally, a thorough comparison with the literature is presented seeking to understand how imidazole reacts towards various OPs. We suggest that the promiscuity of imidazole boosts up its versatility.
  • Tianeptine Esters Derivatives: A Study of Protein-Drug Interaction Performed by Fluorescence Quenching and Molecular Docking Article

    Soares, Franciela A.; Ceschi, Marco A.; Franceschini, Daniel B.; Canto, Vanessa P. do; Netz, Paulo A.; Campo, Leandra F.

    Abstract in English:

    The nature of binding between bovine serum albumin (BSA) and the antidepressant tianeptine and a new series of esters derivatives were studied in this paper. The interactions with BSA were investigated by UV-Vis and fluorescence spectroscopy at three different temperatures. The fluorescence quenching experiments showed that BSA interactions with tianeptine could be dynamic while to its esters a static mechanism was observed. The results showed that tianeptine quenches the intrinsic fluorescence of BSA more efficiently than its esters due to the presence of the free acid portion. The number of binding sites determined by fluorescence spectroscopy is approximately equal to 1 indicating that there is one binding site between BSA tianeptine esters, but the presence of a second interaction site for tianeptine at higher temperatures could be not ruled out. Molecular docking calculations point out a strong affinity of tianeptine and its esters to the site IIA of protein, supporting the hypothesis of a static quenching mechanism.
  • Determination of Amino Acids in Plasma Samples of Preeclampsia Patients by Liquid Chromatography Coupled to High-Resolution Mass Spectrometry Article

    Nascimento, Eliane do; Menezes, Helvécio C.; Resende, Rodrigo R.; Goulart, Vânia A. M.; Cardeal, Zenilda L.

    Abstract in English:

    This work presents the application of a simple and sensitive method developed for the simultaneous analysis of the levels of twenty two underivatizated free L-amino acids in plasma samples of preeclampsia patients by high performance liquid chromatography coupled to high-resolution mass spectrometer (LC-HRMS) using hydrophilic interaction liquid chromatography (HILIC) silica column. The linearity was evaluated in the range of 0.009 to 8.018 µmol L-1 showing coefficients of determination (R2) in the range of 0.999 to 0.911 (p < 0.05). The intra- and inter-day precisions were above of 9.84 and 15.31, respectively. The limits of detection (LOD) and quantification (LOQ) were in the range of 0.003 to 0.683 µmol L-1 and 0.009 to 2.276 µmol L-1, respectively. The results of the investigation of free L-amino acids showed that the levels of GABA, Arg, Ser, Leu, Ile, Met, Val, Ala, Gly, Bet, His and Lys in plasma of patients with preeclampsia were significantly different from healthy patients.
  • Oxone®-Promoted One-Pot Synthesis of 1-Aryl-4-(organylselanyl)-1H-pyrazoles Article

    Jacob, Raquel G.; Oliveira, Daniela H. de; Peglow, Thiago J.; Nascimento, José E. R.; Bartz, Ricardo H.

    Abstract in English:

    We describe herein an efficient protocol for the one-pot synthesis of 4-organylselanylpyrazoles by direct cyclocondensation and C-H bond selenylation reactions starting from hydrazines, 1,3-diketones and diorganyl diselenides promoted by Oxone®. The products were obtained through a metal catalyst free methodology, under mild conditions, in short reaction times and moderate to excellent yields.
  • Linear Peptide Analogues from Jatropha’s Orbitides Promote Migration of Human Neonatal Foreskin Fibroblasts in vitro and Collagen Deposition Article

    Ramalho, Suelem D.; Pinto, Meri Emili F.; Andricopulo, Renata K.; Sanches, Paulo R. S.; Silveira, Edilberto R.; Cilli, Eduardo M.; Andricopulo, Adriano D.; Bolzani, Vanderlan S.

    Abstract in English:

    Orbitides are a class of small naturally occurring cyclic peptides with structural and functional diversities. Their chemical properties make this class feasible to be obtained by solid phase peptide synthesis (SPPS). Therefore, this synthetic accessibility enables useful application and facilitates the identification of analogues, bioactivity studies, and thus, enables them to be applied to obtain peptide libraries. The aim of this work was to investigate the effects of orbitides and their linear synthetic analogues on the migration of neonatal human foreskin fibroblasts. The screening of linear peptide analogues, originally designed from natural orbitides isolated from Jatropha species, demonstrated that some molecules (linear pohlianin B and linear ribifolin) have the potential to induce fibroblast migration and collagen deposition and may thus contribute to accelerating the processes of wound healing and tissue repair. These results also demonstrate the significance of using peptides as an important tool for the discovery of simple and novel drug scaffolds.
  • Gold Catalysis for Selective Hydrogenation of Aldehydes and Valorization of Bio-Based Chemical Building Blocks Article

    Silva, Rerison J. M.; Fiorio, Jhonatan L.; Vidinha, Pedro; Rossi, Liane M.

    Abstract in English:

    Gold catalysts are best known for their selectivity in oxidation reactions, however, there is a promising future for gold in selective hydrogenations. Herein, the hydrogenation of several aldehydes and important bio-based chemical building blocks, namely 5-hydroxymethylfurfural (5-HMF), furfural and vanillin, was performed throughout the combination of Au nanoparticles with Lewis bases. The Au-amine ligand (e.g., 2,4,6-trimethylpyridine) catalytic system could reduce the aldehyde carbonyl group selectively, without reducing alkene moieties or opening the furanic ring that occur on most traditional catalysts. Otherwise, the reduction of nitro group is preferential and the catalytic system was used for the synthesis of furfurylamines, important intermediates in the synthesis of different pharmaceuticals (e.g., furosemide), through the selective reductive amination of furfural starting from nitro-compounds. Moreover, a fully heterogeneous gold catalyst embedded in N-doped carbon (Au@N-doped carbon / TiO2) was able to perform these reactions in successive recycles without the addition of ligands, with impact in the development of a continuous flow process for biomass valorization.
  • Degradation of Acid Red 8 Dye Using Photo-Fenton Reaction Mediated by Titanium Modified Catalysts Article

    Bento, André C.; Emídio, Elissandro S.; Hammer, Peter; Nogueira, Raquel F. P.

    Abstract in English:

    Catalysts prepared by co-precipitation of iron and titanium were evaluated in heterogeneous photo-Fenton degradation of the azo dye Acid Red 8 under blacklight irradiation. Materials with different titanium contents (0 < Ti/Fe < 0.6) were characterized using X-ray diffractometry, scanning electron microscopy, X-ray fluorescence spectroscopy, specific surface area and X-ray photoelectron spectroscopy. Hematite was identified as main phase in materials with lowest Ti content, while titanomaghemite was predominant at high Ti content. Highest degradation was obtained using titanium free catalyst due to iron leaching, which promoted a homogeneous reaction. Addition of Ti led to a heterogeneous process with a maximum when Ti/Fe = 0.40 achieving 0.76 mol of dye mineralized per mol of soluble iron after 90 min, using 10 mmol L-1 H2O2 at pH 5.6, value at least three times higher than that observed for catalysts with lower Ti content. The results indicate that Ti stabilizes the catalyst and increases its heterogeneous activity in photo-Fenton process.
  • Catalytic Transformation Conditions of Ethanol on Dealuminated BEA Zeolites Article

    Clemente, Maria Clara H.; Valadares, Deborah S.; Lacava, André B.; Barbosa, Lais S.; Martins, Gesley A. V.; Dias, José A.; Dias, Sílvia C. L.

    Abstract in English:

    Catalysis is an important tool in obtaining a range of derivative products from renewable sources, such as ethanol. Solid-state dealumination using ammonium hexafluorosilicate on the BEA zeolite under the treatment at temperature of 190 °C, 70 mol% dealumination in the presence of humidity and washing with buffer solution at 25 °C generated larger pores. The absence of washing procedure for the same sample resulted in pore blockage. Ethanol dehydration reactions showed conversion of 72% (64% ethylene and 8% diethyl ether) for this sample at 300 °C and high weight hourly space velocity (WHSV, 3247 h-1), whereas, at the same temperature but at a low WHSV (57 h-1), the conversion was 88% (49% ethylene and 39% diethyl ether). Dealuminated BEA zeolite presented better diffusion conditions, higher hydrophobicity and generated larger pores. Impregnation with H3PW12O40, H4SiW12O40 and Nb2O5 explained the selectivity, showing that Lewis acid sites from Nb2O5 favored the diethyl ether production.
  • Chlorine and Fluorine Determination in Eye-Pencil: Development of an Eco-Friendly Sample Preparation Method for Ion Chromatography Analysis Article

    Mesko, Marcia F.; Costa, Vanize C.; Pereira, Rodrigo M.; Hartwig, Carla A.

    Abstract in English:

    In this paper, a feasible method was proposed for the chlorine and fluorine determination in eye-pencil samples using ion chromatography (IC). The microwave-induced combustion (MIC) was used to digest up to 200 mg of a sample, with 50 mg of microcrystalline cellulose as a combustion aid and only water for analytes absorption. Cl and F recoveries were 105 ± 1 and 93 ± 5%, respectively, when standard solutions were used in the recovery tests. Certified reference materials (CRM) were also digested mixed to the sample, and no significant difference between the obtained results and the certified values was observed. Precision was assessed in terms of repeatability and intermediate precision, with relative standard deviations (RSD) lower than 9%. Limits of detection (LOD) for Cl and F were 37 and 4 mg kg-1, respectively. Ultrasound-assisted extraction (UEA) was also evaluated; however, the results were not satisfactory. The proposed method was suitable for Cl and F determination in eye-pencil because it proved to be accurate, precise and safe, and also minimized waste generation and had high throughput.
  • Thermal Stability and Kinetic of Decomposition of Mono- and Dicationic Imidazolium-Based Ionic Liquids Article

    Bender, Caroline R.; Kuhn, Bruna L.; Farias, Carla A. A.; Ziembowicz, Francieli I.; Beck, Thaíssa S.; Frizzo, Clarissa P.

    Abstract in English:

    Phase transitions, thermal stability, thermokinetics and activation parameters of degradation reaction of the dicationic ionic liquids (ILs), 1,n-bis(3-methylimidazolium-1-yl)alkane ([BisAlk(MIM)2][2Br]) and monocationic ILs, 1-(3-methylimidazolium-1-yl)alkane ([Alk(MIM)][Br]), where Alk = Dec, DoDec, TetDec, (decane, dodecane, tetradecane) were evaluated. The influence of an additional cationic head and the alkyl chain length in thermal parameters were also evaluated. The dicationic ILs are more stable than monocationic and thermal degradation of ILs mono- and dicationic did not show linear dependence on the alkyl chain length. Thermokinetic parameters indicated degradation in multiple steps. The monocationic ILs showed a more persistent crystalline phase than dicationic IL, which became totally amorphous after heating. The estimate temperature decomposition, activation energy and thermal transitions enable the determination of which types of ILs are applicable for specific purposes, such as lubricants or solvents at high temperatures, while maintaining ILs physical and chemical properties.
  • Facile One-Step Electrodeposition Fabrication of Amorphous MoS2 Catalysts in Titanium for Hydrogen Evolution Reaction Article

    Medina, Marina; Corradini, Patricia G.; Mascaro, Lucia H.

    Abstract in English:

    Hydrogen is seen as a future energy carrier that will assist the global energy fuel demand. However, it is still necessary to study efficient and inexpensive catalysts that can be used on a large scale to make this technology practical. In this paper the electrodeposition of molybdenum disulfide (MoS2) film on titanium (Ti) substrate was performed by cyclic voltammetry and the film was evaluated for hydrogen evolution reaction (HER). The deposition optimized conditions was 25 cycles and 4 mmol L-1 (NH4)2[MoS4] in 0.1 mol L-1 NaClO4 solution. The film was characterized from X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and they showed an amorphous structure and high catalytic activity for HER. The Tafel slope was 85 mV dec-1 and overpotential at -10 mA cm-2 was -139 mV showing that Ti substrate compared with fluorine-tin doped oxide (FTO) substrate favored the HER and electroactivity of MoS2 films.
  • Compatibility of GROMOS-Derived Atomic Parameters for Lipopolysaccharide Membranes with the SPC/E Water Model and Alternative Long-Range Electrostatic Treatments Using Single Nonbonded Cutoff and Atom-Based Charge Schemes Article

    Lima, Manoela P. M.; Nader, Manuela; Santos, Denys E. S.; Soares, Thereza A.

    Abstract in English:

    Recent developments of GROMACS v.2016 ceased to support methodological approaches used in the development and validation of the GROMOS force field. We investigated the performance of a previously developed extension of the GROMOS force field for lipopolysaccharides to reproduce the structural dynamics of bacterial outer membrane (OM) using a single cutoff for nonbonded interactions and atom-based charge truncation. We further compared this setup for use with reaction field (RF) or particle mesh Ewald (PME) approximations in the presence of simple point charge (SPC) and extended simple point charge (SPC/E) water models. We find that the OM structural dynamics is well conserved in all simulated conditions, reproducing the available experimental data within the measurement uncertainty. The SPC/E model induces a small increase in OM fluidity, and when combined with the RF correction, shows a decrease in water orientation at the membrane surface. The present simulations support the compatibility of the GROMOS-derived lipopolysaccharide (LPS) parameters for use with single cutoff and atom-based charge schemes, either with RF or PME approximations, in GROMACS v.2016. Both SPC and SPC/E water models are suitable for use, but usage of SPC/E combined with the reaction field correction needs to be further investigated.
  • Physicochemical Study of the Interaction between Gold Nanoparticles and Lipase from Candida sp. (CALB): Insights into the Nano-Bio Interface Article

    Barros, Heloise R. de; Santos, Mary C.; Barbosa, Leandro R. S.; Piovan, Leandro; Riegel-Vidotti, Izabel C.

    Abstract in English:

    The surface interactions between gold nanoparticles (AuNPs) and lipase from Candida antarctica fraction B (CALB) were investigated at macromolecular and colloidal length-scales. In order to elucidate the reciprocal effect of the interactions on the individual component’s properties, CALB was either added during the synthesis of AuNPs or added to pre-synthesized AuNPs. In both cases, it was observed that the AuNPs are spherical and stable and, by fluorescence and circular dichroism spectroscopies, changes were observed in the secondary and tertiary structure of CALB, that were dependent on the AuNPs concentration. Nevertheless, the catalytic activity of CALB was maintained, although at a lower percentage (≥ 80%), thus new bio-functionalities were inserted into AuNPs upon interaction with CALB. Using simple and straightforward approaches and state-of-the-art techniques important knowledge about CALB/AuNPs bioconjugates was gained, thus contributing to the development of new nano-biomaterials and for the safe use of AuNPs in biomedical applications.
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