Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> http://www.scielo.br/rss.php?pid=0103-505320170009&lang=es vol. 28 num. 9 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Why to publish a special issue for young researchers?]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901585&lng=es&nrm=iso&tlng=es <![CDATA[The Chemical Conversion of Biomass-Derived Saccharides: an Overview]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901586&lng=es&nrm=iso&tlng=es Chemicals commodities and consumable, accounting for billions of ton of carbon per year, are produced in an industry based on non-renewable fossil feedstocks. Oil reserves are enough for feeding chemical industry for another century, and therefore, it is essential finding alternative sources of carbon for a progressive replacement of the industrial feedstock. In this context lignocellulosic, a renewable source of carbon composed mainly by polymers of sugars, appears as the most promising candidate. Herein, it will be discussed the status, challenges and prospective future of biomass as industrial feedstock in a raising biorefinery, aiming to clarify the real problems in the actual biomass processing. It will be shown that lignocellulosic biomass is able to replace oil in the production of several chemicals and also delivery new compounds with important applications. However, for a cost effective use of biomass, the development and improvement of solvent and catalytic systems play a leading role. The sustainability of biomass feedstock is also discussed from the economical, social and environmental points of view. <![CDATA[Nano-Sized Silver Colloids Produced and Stabilized by Amino-Functionalized Polymers: Polymer Structure-Nanoparticle Features and Polymer Structure-Growth Kinetics Relationships]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901608&lng=es&nrm=iso&tlng=es The synthesis of highly stable silver colloids has been successfully achieved by using reducing/stabilizer amino-functionalized polymers without the aid of any other external agent. The polymer coated inorganic nanoparticles have been detailed characterized via scattering, imaging and UV-Vis spectroscopy. The combination of transmission electron microscopy (TEM) and light scattering suggested nearly spherical structures stabilized by a lengthy polymeric shell with surface charge dependent on polymer nature and molecular weight. The hybrid nanomaterials are produced via an autocatalytic process where the onset of colloid formation is influenced by the available hydrophobic nitrogen units normalized by the weight of polymer. The induction period, however, does not influence the dimension of the metallic cores which are similar although with a high degree of dispersity. The coating confers a large hydrodynamic size to the silver nanoparticles and the length of the stabilizing shell is chiefly governed by the molecular weight of the amino-functionalized polymers. These features may significantly impact the cytotoxicity and bactericidal properties of the hybrid materials. These investigations are currently underway. <![CDATA[Nanostructured Antigen-Responsive Hydrogels Based on Peptides for Leishmaniasis Detection]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901619&lng=es&nrm=iso&tlng=es Hydrogels based on peptide nanostructures are biological entities that can be applied in a wide range of applications, such as scaffolds for tissue engineering, drug delivery, and biosensors. The aim of this research was to study peptide hydrogels based on N-(9-fluorenylmethoxycarbonyl)-L, L-diphenylalanine (Fmoc-FF) in two different media: water and phosphate buffer. These hydrogels were used for encapsulating Leishmania infantun chagasi soluble proteins. The structure of the matrices was investigated in detail through scanning and transmission electron microscopy, and small angle X-ray scattering (SAXS). The mechanical behavior of the hydrogels were assessed through rheology assays, demonstrating both the physical and chemical stability of the hydrogel scaffolds. The immunogenicity of immobilized antigens was studied using enzyme-linked immunosorbent assay (ELISA) detection after the reaction with positive and negative dog sera for Leishmania infantum chagasi. The hydrogel was efficient to encapsulate antigens, and can promote the development of novel devices that requires the storage of biomolecules under moist environmental conditions. <![CDATA[AgAu Nanotubes: Investigating the Effect of Surface Morphologies and Optical Properties over Applications in Catalysis and Photocatalysis]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901630&lng=es&nrm=iso&tlng=es We herein report the preparation of AgAu nanotubes displaying controlled surface morphologies and optical properties by varying the reaction temperature during the galvanic reaction between Ag nanowires and AuCl4-(aq). As the AgAu nanotubes presented similar sizes and compositions, they enabled us to isolate the influence of surface morphology and optical properties over their catalytic and plasmonic photocatalytic activities towards methylene blue oxidation. At 25 °C, AgAu nanotubes (AgAu 25) presented branched walls and surface plasmon resonance (SPR) band with low intensities in the visible were obtained. However, at 100 °C, the AgAu nanotubes (AgAu 100) presented smooth surfaces and SPR bands that closely matched the emission spectra of a commercial halogen-tungsten lamp. The AgAu 25 nanotubes displayed better catalytic performances in classical heterogeneous catalysis as a result of its branched walls that lead to increased surface areas relative to the smooth nanotubes. Conversely, AgAu 100 nanotubes showed better activities in plasmonic photocatalysis due to its broader and more intense SPR bands. Thus, our results demonstrate the potential of the control over morphological and optical features towards the optimization of distinct catalytic phenomena. <![CDATA[Silver Nanocoatings at Large Length Scales: Influence of the AgNPs Morphology and Capping Agents on the Coating Chemical Stability and Antimicrobial Effect]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901639&lng=es&nrm=iso&tlng=es We assessed at multiple length scales (nanometers to millimeters) the nanocoatings of silver nanoparticles (AgNPs) on model SiO2/Si substrates. The coatings from biogenic AgNPs (from yeasts Rhodotorula glutinis and Rhodotorula mucilaginosa) were compared to those formed from "synthetic" AgNPs capped with citrate and sodium dodecyl sulfate (SDS). With computational analysis of large-field (LF) X-ray images of the whole substrates (5 × 5 mm), we were able to assess the coatings homogeneity, relative amount of AgNPs, and their distribution as agglomerates. Surprisingly, by analyzing more than 100,000 elements (nanoparticles and agglomerates) in each sample, it was observed that the mentioned features have little dependence on the AgNPs morphology and capping agents. All silver nanocoatings resisted when immersed in phosphate-buffered saline medium by forming agglomerates of up to 10 µm2. However, coatings formed with synthetic AgNPs (capped with citrate and SDS) led to a higher antimicrobial efficiency against Staphylococcus aureus. <![CDATA[Batch-Injection Amperometric Determination of Pyrogallol in Biodiesel Using a Multi-Walled Carbon Nanotube Modified Electrode]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901650&lng=es&nrm=iso&tlng=es This work demonstrates the application of batch-injection analysis (BIA) with amperometric detection on a multi-walled carbon nanotube (MWCNT) modified electrode for the sensitive determination of the antioxidant pyrogallol in biodiesel. Samples were diluted in electrolyte (0.1 mol L-1 HClO4) before injection using an electronic micropipette on the BIA cell. The size effect of MWCNTs on electrochemical oxidation of pyrogallol was investigated and 3.5-fold increase in the amperometric sensitivity using the modified electrode with MWCNTs of shorter dimensions was obtained. This result was in agreement with cyclic voltammetry and electrochemical impedance spectroscopy measurements. After optimization of BIA parameters for the amperometric detection on the MWCNT-modified electrode, the proposed method presented a linear range from 0.3 to 1000 µmol L-1, detection limit of 0.013 µmol L-1, precision of 3%, and sample throughput of 240 h-1. Spiked biodiesel samples were analyzed and recovery values between 95-99% were obtained. <![CDATA[Determination of Inorganic Contaminants in Electrical and Electronic Equipment after Digestion Using Microwave-Assisted Single Reaction Chamber]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901657&lng=es&nrm=iso&tlng=es A method for digestion of plastics from waste of electrical and electronic equipment (WEEE) was developed using the microwave-assisted wet digestion in single reaction chamber (MAWD-SRC). The determination of As, Cd, Co, Cr, Cu, Ni, Pb, Sb and Zn by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP OES) was carried out after sample digestion. Mercury was determined by flow-injection cold vapor generation coupled to inductively coupled plasma mass spectrometry (FI-CVG-ICP-MS). Results obtained using MAWD-SRC for sample preparation were compared with those obtained using microwave-assisted wet digestion (MAWD) at high pressure. Acid mixtures (HNO3 or HNO3 + HCl) were evaluated and feasibility for further inorganic contaminants determination by ICP-MS and ICP OES was demonstrated. Sample preparation by MAWD-SRC using HNO3 + HCl mixture resulted in better digestion efficiency in comparison to MAWD. In addition, lower limits of quantification were obtained using MAWD-SRC due to the higher sample mass that can be digested (500 mg). The combination of HNO3 and HCl for digestion showed to be crucial for quantitative recovery of some elements, as Cr and Sb. Agreement with certified values was better than 96%. <![CDATA[Spectroscopic Characterization of Charge Transfer Complexes of TCNE with Aromatic Amines - The First Step of Tricyanovinylation Reaction]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901665&lng=es&nrm=iso&tlng=es The first step of electrophilic aromatic substitution reactions generally involves the formation of charge transfer complexes. Tetracyanoethylene (TCNE) in the presence of aromatic amines forms π-type complexes that subsequently lead to tricyanovinylation reaction. Although this kind of reaction was investigated in the past, the spectroscopic characterization of the charge transfer complexes is still lacking, since in many cases the first step of the reaction is too fast to allow their characterization by conventional techniques. In this paper, it is shown the UV-Vis and resonance Raman characterization of the charge transfer complexes formed between TCNE and substituted anilines. The magnitude of the charge transfer could be linearly correlated with the electronic absorpion energies, as well as to the Raman shifts observed for the characteristic ν(C≡N) mode of TCNE. In addition, the results were correlated to ionization potentials of amines, and theoretical calculations by density functional theory/time-dependent density functional theory (DFT/TDDFT) methods were performed to support the experimental data. <![CDATA[Microwave-Assisted Oxidation of Organic Matter Using Diluted HNO <sub>3</sub> under O <sub>2</sub> Pressure: Rationalization of the Temperature Gradient Effect for Acid Regeneration]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901673&lng=es&nrm=iso&tlng=es Oxidation using diluted HNO3 solution is dependent on reactions taking place in the gas phase, resulting in HNO3 regeneration, thus allowing sub stoichiometric reactions (16.7 mmol of C oxidized with 10.4 mmol of HNO3). Reactions for HNO3 regeneration are dependent on temperature gradient along reaction vessel. Thermographic images were obtained of external vessel wall after 2.5, 5 and 7.5 min of heating. Temperature inside reaction vessel was directly measured using a sapphire thermocouple in four different depth (3, 6, 12 and 16 cm). Reactions under inert atmosphere (7.5 bar Ar) were evaluated and normally presented higher temperature gradient than that performed with O2 pressure, since HNO3 regeneration reactions are exothermic. A better understanding of the regeneration of HNO3 and the dependence on the whole reaction vessel temperature in this system was possible combined to residual carbon content and residual acidity measurements to estimate the extent of organic matter oxidation. <![CDATA[Strategy for Treating a Landfill Leachate by Integration of Physico-Chemical and Photo-Fenton Processes]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901682&lng=es&nrm=iso&tlng=es This study reports a protocol for the treatment of a sanitary landfill leachate through integration between a stage of coagulation-flocculation, a step of filtration of the resulting suspension, and application of the photo-Fenton process using a ferrioxalate complex and solar irradiation. The best results for turbidity removal by coagulation-flocculation were reached using Al3+ as nitrate salt mainly using concentrations up close 4.4 mmol L-1, at the natural pH of the effluent (pH 7.9), when the removal of 66% of the turbidity was achieved. By using a ferrioxalate complex after adjusting the pH of the effluent to 5, it was possible to circumvent the classical limitations of the Fenton process (related to the pH of the medium limited to between 2.5 and 3.0), performing a removal of 68% of the remaining dissolved organic carbon. The global dissolved organic carbon removal in this process was of 86% after a membrane filtration step before the photo-Fenton process. <![CDATA[Feasibility of DLLME for the Extraction and Preconcentration of As and Cd in Sugar for Further Determination by ICP-MS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901691&lng=es&nrm=iso&tlng=es A method for determining low levels of As and Cd by dispersive liquid-liquid microextraction (DLLME) and inductively coupled plasma mass spectrometry (ICP-MS) was proposed. The following parameters that affect extraction efficiency were investigated: type and volume of extraction solvent (1000 µL acetone), type and volume of dispersive solvent (75 µL carbon tetrachloride), amount of ammonium pyrrolidinedithiocarbamate and sodium diethyldithiocarbamate as chelating agents, sample mass (0.5 g in 10 mL ultrapure water), pH of sample solution (2.0) and number of washing steps (one). Accuracy was evaluated by analytes determination in sugar samples by ICP-MS after digestion by microwave-induced combustion (MIC). No significant difference was observed between results of the proposed DLLME method and MIC in the case of both analytes. Instrument calibration was performed by the standard addition method and good linearity was achieved. Limits of quantification (LOQs) were 0.7 and 0.2 ng g-1 for As and Cd, respectively. The main advantages of this method are relatively high sample mass, low dilution, suitable preconcentration factors and significantly low LOQs (ng g-1 range). When the proposed method was used for determining As and Cd in four sugar samples, their concentrations ranged from 1.13 to 2.95 ng g-1 and from 0.31 to 0.43 ng g-1, respectively. <![CDATA[Bioelectrooxidation of Ethanol Using NAD-Dependent Alcohol Dehydrogenase on Oxidized Flexible Carbon Fiber Arrays]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901698&lng=es&nrm=iso&tlng=es Hierarchical 3-dimensional flexible carbon fiber (FCF) array is a candidate as flexible electrode for enzyme electrochemistry, with interesting properties for application in enzymatic biofuel cell and implantable biosensors. Here, we show the fabrication of oxidized FCF electrode (FCFO) based on chemical surface treatment, a wet oxidation method by using permanganate ions. Compared with pristine FCF, FCFO is rougher; the scratches become wider and deeper, with some defects in the basal planes and some cracked structures. X-ray photoelectron spectroscopy data suggests a correlation between the carbon structures and the appearance of chemical groups containing oxygen atoms. Finally, we show how the bioelectrocatalysis of ethanol by using FCFO arrays modified with NAD-dependent alcohol dehydrogenase (ADH) is positively influenced by the fibers treatment oxidation process. <![CDATA[Confocal Fluorescence Microscopy and Kinetics of the Cr <sup>3+</sup>-Chromate Ion Oxidation Equilibria at the Solid Liquid Interface]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901708&lng=es&nrm=iso&tlng=es Silica-borax pearl samples impregnated with 0.17 and 0.64% Cr3+ were characterized by specific surface area measurements, UV-Vis spectroscopy, energy-dispersive X-ray fluorescence and laser-scanning confocal microscopy. Pearl stability against oxidizing conditions was tested by adding samples to an aqueous hydrogen peroxide solution. The reaction was examined by UV-Vis spectroscopic measurements of the supernatant and laser-scanning confocal microscopy images of the substrate. Overall, hydrogen peroxide-induced Cr3+ to Cr6+ oxidation across the solid-liquid interface promoted solid matrix cleavage pearl degradation and concomitant formation of multiple scattering centers was observed. A dual-detection scheme was employed in the confocal microscopy measurements allowing us to separate scattering and absorptive contributions to the observed signals. The confocal microscopy images indicate that Cr3+ oxidation induced by hydrogen peroxide solutions occurs throughout the entire pearl sample and indicate that oxidation reactions induce leakage of chromate ion into aqueous solutions. <![CDATA[Tailored Silica Nanoparticles Surface to Increase Drug Load and Enhance Bactericidal Response]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901715&lng=es&nrm=iso&tlng=es Nanoparticles' surface properties can be used as triggers to regulate or even enhance biological response and generate tailored structures to substitute conventional antibiotics. Here, silica nanoparticles surface was duly tuned in order to increase the water-insoluble drug load (curcumin) and improve the antibacterial activity. Our main motivation was based on the electrostatic attraction between the positively charged amino groups and the negatively charged curcumin and/or bacteria membrane. In addition, the variation of amino grafting amount on silica nanoparticles indicated that the grafting increase was directly related to the extent of drug entrapped into the nanoparticles as well as to the bactericidal activity. The combination of amino-functionalized silica nanoparticles associated with the presence of curcumin allowed to produce a dual bactericidal system that shows promising perspective for its use in biomedical applications. <![CDATA[High Order Cyclic Voltammograms During Electrooxidation of Ethanol Catalyzed by Gold]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901725&lng=es&nrm=iso&tlng=es Under fixed limits, potential sweeps in some electrochemical systems depict current profile whose shape repeats in every n cycle (with n &gt; 1), receiving the name of high order voltammograms (HOV). HOV have been observed during electrooxidation of organic molecules catalyzed mainly by Pt. The present study shows HOV behavior during ethanol electrooxidation reaction onto gold in alkaline media. Firstly, a strong dependence of HOV with minimum potential is remarkable in this system and has not been considered in previous numeric models. Moreover, due to high sensibility of HOV to surface conditions, it was possible to follow effects caused by cation interactions with adsorbed oxygenated species. <![CDATA[Nickel-Copper Alloys Modified Electrodes: an Electrochemical Study on their Interfacial and Supercapacitive Properties]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901732&lng=es&nrm=iso&tlng=es In this manuscript, we report the electrodeposition of nickel-copper alloys in a two steps methodology. Firstly, the copper electrode is oxidized to generate Cu2+ ions followed by the reduction of both Ni2+ and Cu2+. The electrodes were further cycled in KOH to convert the metallic alloy into the respective electroactive hydroxide. This methodology created an electrode with high roughness and distinct electrochemical behavior. The modified electrodes were also characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Finally, the modified electrodes were studied in their supercapacitive properties by galvanostatic charge and discharge curves; the electrodes showed a good specific capacitance of 58 mF cm-2. The results indicated a new strategy using a simple methodology to modified Cu-electrodes to develop supercapacitors at low cost. <![CDATA[Influence of the Protonatable Site in the Photo-Induced Proton-Coupled Electron Transfer between Rhenium(I) Polypyridyl Complexes and Hydroquinone]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901741&lng=es&nrm=iso&tlng=es In the present work the influence of the distance of the protonatable site of different ancillary ligands to the metal center on the luminescence quenching of ReI polypyridyl complexes by hydroquinone are evaluated by means of experimental and theoretical studies. In these systems, it is expected the occurrence of proton-coupled electron transfer (PCET) reactions upon excitation, which is a key process in solar-to-fuels energy conversion. The series fac-[Re(CO)3(2,2-bpy)(L)]PF6, L = pyridine, 1,4-pyrazine, 4,4'-bipyridyl, 1,2-bis-(4-pyridyl)ethane were synthesized and the luminescence quenching rate constant (kq) by hydroquinone in CH3CN and 1:1 CH3CN/H2O were determined by steady-state and lifetime measurements. In bare acetonitrile, the 1,4-pyrazine exhibits the higher kq (3.49 ± 0.02) × 109 L mol-1 s-1 among the species investigated, followed by 4,4'-bipyridyl (kq = 2.50 ± 0.02) × 109 L mol-1 s-1. In 1:1 CH3CN/H2O, the kq values for all complexes are very similar evidencing the role of water molecules as proton acceptor following the reductive quenching of the complexes by hydroquinone. In CH3CN, the proton release for the solvent is not spontaneous and the higher basicity of the coordinated 1,4-pyrazine and 4,4'-bipyridyl in relation to 1,2-bis-(4-pyridyl)ethane after metal-to-ligand charge transfer (MLCT) excitation contributes to the proton transfer step. These results are corroborated by time-dependent density functional theory (TD-DFT) calculations. Moreover, the low H/D kinetic isotope effect (KIE) in 3:1 CH3CN/X2O (X = H or D) confirms that the major PCET pathway is the electron transfer followed by proton transfer, but for 1,4-pyrazine and 4,4'-bipyridyl the concerted proton-electron transfer seems to play a role at high hydroquinone concentrations. <![CDATA[Photoelectroanalytical Detection of Adrenaline Based on DNA and TiO <sub>2</sub> Nanoparticles Sensitized with Bis(ethylenedithio)tetrathiafulvalene Exploiting LED Light]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901752&lng=es&nrm=iso&tlng=es In this study, a photoelectroanalytical sensor for determination of adrenaline based on deoxyribonucleic acid (DNA) and anatase titanium dioxide (TiO2) nanoparticles sensitized with bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) was developed, which we henceforward call BEDT-TTF/DNA/TiO2/ITO. The photoelectroanalytical sensor showed high photocurrent to adrenaline under visible light emitting diode (LED) light irradiation in comparison to each component of the composite material. Under optimized conditions, the BEDT-TTF/DNA/TiO2/ITO sensor shows a linear response range from 10 nmol L-1 up to 100 µmol L-1 with a sensitivity of 8.1 nA L µmol-1 and limit of detection of 1 nmol L-1 for the detection of adrenaline. The photoelectrochemical sensor showed high photocurrent to adrenaline in comparison to photocurrent response to ascorbic acid and uric acid. The BEDT-TTF/DNA/TiO2/ITO photoelectrochemical sensor was successfully applied to urine samples, with recovery values between 96 and 106%. <![CDATA[Degrading Pesticides with Waste Product: Imidazole-Functionalized Rice Husk Catalyst for Organophosphate Detoxification]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901760&lng=es&nrm=iso&tlng=es Rice husk (RH) is one the largest agricultural waste products worldwide, and rice is one of the crops that use the most pesticides. Among these, organophosphates have been of increasing concern due to their high toxicity. Herein, we report the functionalization of RH with imidazole groups (RHIMZ) to obtain sustainable catalysts from waste for organophosphate degradation. The waste-derived catalyst showed prominent catalytic activity in dephosphorylation reactions with the model substrate diethyl 2,4-dinitrophenyl phosphate (DENDPP), over 105-fold, compared to the spontaneous reaction (lifetime = 1 month). Finally, RHIMZ was also effective in degrading the pesticide Paraoxon (spontaneous lifetime = 1 million years), degrading 60% in 20 days, giving a 107-fold enhancement. Overall, the proposed approach is environmentally friendly for reusing the waste for a noble cause, i.e., degrading toxic pesticides, which is promising for designing sensors and detoxification processes. <![CDATA[Improved NADH Electroanalysis on Nickel(II) Phthalocyanine Tetrasulfonic Acid/Calf Thymus Deoxyribonucleic Acid/Reduced Graphene Oxide Composite]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901768&lng=es&nrm=iso&tlng=es This work describes the electrochemical performance of a novel composite based on nickel tetrasulfonated phthalocyanine (NiTsPc), deoxyribonucleic acid from calf thymus (CT-DNA) and reduced graphene oxide (rGO) for the electroanalysis of reduced β-nicotinamide adenine dinucleotide (NADH), through electrocatalytic oxidation. The modified electrode was denoted as CT-DNA/NiTsPc/rGO. Fourier transform infrared and ultraviolet-visible spectroscopies were performed to characterize the composite material. The electrochemical performance of the composite for NADH oxidation was investigated by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). The CT-DNA/NiTsPc/rGO modified glassy carbon electrode (GCE) showed an excellent electrocatalytic activity for NADH oxidation with apparent electrocatalytic rate constant (kobs) of 7.35 × 105 L mol-1 s-1 and linear response range for NADH from 1 up to 1350 µmol L-1 for n = 12 (r = 0.999). The proposed sensor shows sensitivity, detection limit and quantification limit of 0.014 µA L mol-1, 0.3 and 1 µmol L-1, respectively. The prepared sensor was further tested for the determination of NADH in artificial human urine samples, showing promising biomedical applications. <![CDATA[Determination of Hg in Biological Samples and Ethanol Fuel by Photochemical Vapor Generation after Pre-Concentration in a Gold Trap]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901779&lng=es&nrm=iso&tlng=es In this work, the photochemical vapor generation (PVG) coupled with atomic absorption spectrometry and a pre-concentration step with an Au column was used for the determination of Hg in biological samples and ethanol fuel. PVG with pre-concentration showed an up to 250-fold higher sensitivity compared to the approach without pre-concentration. The accuracy of analysis of biological samples was evaluated using certified reference materials (fish tissues), while for ethanol fuel samples, recovery tests were employed (91%). Analytical curves were linear (R &gt; 0.99) in the studied range of 2.5 to 10 µg L-1 for conventional PVG and 0.2 to 0.5 µg L-1 for PVG with the pre-concentration step. For the last, the limits of detection reached for biological samples and ethanol fuel were 0.02 and 0.01 µg L-1, respectively. The systems presented are simple, sensitive and safe for the control of low Hg concentrations in different samples. However, only the system using pre-concentration with an Au column was capable of obtaining the reproduced signals of Hg in low concentrations of the order of 0.2 µg L-1. <![CDATA[Synthesis, Characterization, and Photocatalytic Activity of Pure and N-, B-, or Ag- Doped TiO<sub>2</sub>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901788&lng=es&nrm=iso&tlng=es This article reports the synthesis and characterization of pure and N-, B-, and Ag-doped TiO2 and the ability of these oxides to photodegrade methylene blue (MB) under sunlight or UV-ABC radiation. The compounds were synthesized using the sol-gel method and characterized by scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Photocatalytic efficiency was significantly increased by N-doping, resulting in 98% MB decomposition under UV-ABC irradiation for 180 min. Ag- and B-doped TiO2 lowered MB degradation rates to 52 and 73%, respectively, compared with pure TiO2. The same behavior was observed with exposure to UV-Vis, with 88, 65, 60, and 42% MB removal with N-doped, pure, B-doped, and Ag-doped TiO2, respectively. Under visible light alone, N-doped TiO2 exhibited higher photocatalytic efficiency than commercial P25-type TiO2. Photocatalysis with N-doped TiO2 proved to be a promising alternative for MB degradation, given the potential of employing solar energy, thus minimizing operating costs. <![CDATA[Investigation of Electrocatalysts for Selective Reduction of CO<sub>2</sub> to CO: Monitoring the Reaction Products by on line Mass Spectrometry and Gas Chromatography]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901803&lng=es&nrm=iso&tlng=es The carbon dioxide electrocatalytic reduction is central for the development of regenerative cycles of electrochemical energy conversion and storage. Herein, the gaseous products of the CO2 electroreduction were monitored by using an electrochemical cell on line coupled to a differential electrochemical mass spectrometer (DEMS), aiming at searching for electrocatalysts with high selectivity for CO formation. The results showed that, among the studied materials, the Cu4Sn/C alloy nanoparticles were stable during potentiostatic polarizations as revealed by in situ X-ray absorption spectroscopy (XAS), and the on line DEMS measurements showed the production of CO, suppression of methane and ethylene formations, and diminishing of the hydrogen evolution reaction, in relation to that on pure Cu2O-Cu/C. The faradaic efficiencies for CO formation were 13 and 23% for Cu4Sn/C and Au/C (a known electrocatalyst for CO), respectively, determined by experiments of in line gas chromatography (GC). The selectivity of Cu4Sn/C for CO formation was ascribed to the role of Sn atoms on stabilizing adsorbed HCOO intermediates, and hindering further hydrogenation, letting CO free for desorption. These results are expected to be used as a guide for further development of electrocatalysts with a fine-tuning of composition for increasing the faradaic efficiency of CO2 electroreduction to CO. <![CDATA[The Effect of Hydrothermal Treatment on the Morphologies and Optical Properties of Upconversion NaYF <sub>4</sub>:Ln <sup>3+</sup> Crystals]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901816&lng=es&nrm=iso&tlng=es This work deals with the synthesis and characterization of upconversion NaYF4:Ln3+ crystals. Co-precipitation and hydrothermal methods were used to synthesize NaYF4:Ln3+ crystals. The experimental procedures were modified to obtain crystals in the cubic (α) phase, hexagonal (β) phase or a mixture between cubic and hexagonal (α/β) phases. Reaction temperature was maintained at 200 °C and the time of hydrothermal treatments were maintained at 24 and 48 h. The average diameter of the crystals ranged from 25 nm to 6.4 µm, depending on the chosen synthetic route. These materials can be applied in areas such as photodynamic therapy and bioimaging. <![CDATA[Prediction of Total Acid Number in Distillation Cuts of Crude Oil by ESI(-) FT-ICR MS Coupled with Chemometric Tools]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901822&lng=es&nrm=iso&tlng=es Competitive adaptive reweighted sampling-partial least squares (CARS-PLS) and negative-ion mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI(-) FT-ICR MS) data were adopted to assess the total acid number (TAN) of crude oil distillation cuts. Two crude oil samples and 24 derivatives with TAN ranging from 0.20 to 0.39 mg of KOH g-1 were investigated. The multivariate calibration PLS model was built with 18 calibration samples and tested with 8 validation samples. CARS-PLS reduced the number of variables from 1610 to only 4, allowing the identification of molecular formulas that are truly related to the TAN. The root mean square error of prediction (RMSEP) obtained was 0.01 mg of KOH g-1, which is lower than the error when using all variables (0.03 mg of KOH g-1). Finally, it was observed that the N and O2 compound classes are the most important classes for providing a better correlation between ESI(-) FT-ICR mass spectra and TAN values. <![CDATA[Synthesis and Photophysical Characterization of Proton Transfer-Based Thiourea Derivatives: Potential Application as Colorimetric Naked-Eye Chemosensor for Fluoride Detection in Solution]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532017000901830&lng=es&nrm=iso&tlng=es Two new thiourea derivatives were synthesized through the reaction of photoactive aminohydroxybenzazoles and p-isothiocyanate benzoic acid via nucleophilic addition reaction. The compounds were characterized using high resolution mass spectrometry with eletrospray ionization (HRMS-ESI), Fourier transform infrared (FTIR), 13C and 1H nuclear magnetic resonance (NMR) spectroscopies. UV-Vis and steady-state fluorescence in solution were also applied to characterize their photophysical behavior. The compounds present absorption in the ultraviolet region (ca. 300 nm) and fluorescence emission with a large Stokes' shift in the UV-A and green region, with the longer wavelength related to phototautomerism in the excited state (ESIPT). Both compounds were investigated as optical sensors for the detection of anions in solution, presenting a potential application for fluoride ion detection by naked-eye and UV-Vis spectroscopy. The continuous variation method plot gave a 1:1 stoichiometric ratio between the chemosensors and F- for the new formed species. The UV-Vis and 1H NMR titration experiments reflect the establishment of a hydrogen bond interaction between the thiourea moiety of the chemosensors and fluoride. In addition, the presence of fluoride in solution tailored the fluorescence emission of one compound favoring the ESIPT emission.