Resumo em Inglês:

This work describes the electrochemical oxidation study of three short chain carboxylic acids (acetic, oxalic and formic 0.18 mol L-1) using different electrolysis conditions (electrolyte composition and current density) in an electrochemical reactor fitted with niobiumsupported/BDD electrode (Nb/BBD) as anode and titanium plate as cathode. The experiments were focused to elucidate if the oxidation of these carboxylic acids involved a direct or a mediated oxidation pathway, as well as their electrochemical incineration efficiency using this electrochemical reactor. The amount of oxidizing species (hydroxyl radicals, hydrogen peroxide, and persulfate) produced at Nb/BDD electrode was spectroscopically determined. The electrochemical kinetics study in H2SO4 and HClO4 solutions, as well as the chemical oxygen demand and total organic carbon analysis for each one of the carboxylic acids studied in both media, gave us information to propose a degradation mechanism for the electrochemical degradation of the carboxylic acids in each electrolytic media. The degradation in H2SO4 is promoted by the persulfate production, whereas in HClO4 by •OH.

Resumo em Inglês:

Two ruthenium complexes of the type [RuCl(dmso)(L)2]Cl {L = 4,4’-dimethyl-2,2’-bipyridine (dmbpy); 4,4’-dinonyl-2,2’-bipyridine (dnbpy)} have been synthesized and characterized by elemental analysis, 1H NMR, FTIR, electronic spectra, and molar conductivity. The IR spectral studies revealed that the DMSO molecule is S-bound ( νSO= 1100 cm-1; 1079 cm-1). For complexes, MLCT bands were observed around 390 nm and 440 nm. The measurements of conductivity revealed the presence of 1:1 electrolyte. Interactions of ruthenium complexes with human serum albumin were examined by fluorescence spectroscopy. The results revealed a combined quenching mechanism of HSA fluorescence by [RuCl(dmso)(dmbpy)2]Cl, with binding constant of 5.82 ± 0.08 x 105 mol-1 L (297 K), 5.29 ± 0.06 x 105 mol-1 L (303 K), and 4.68 ± 0.06 x 105 mol-1 L (313 K), whereas the [RuCl(dmso)(dnbpy)2]Cl caused static quenching predominantly, with binding constant of 9.87 ± 0.05 x 105 mol-1 L (297 K), 3.41 ± 0.04 x 105 mol-1 L (303 K), and 0.89 ± 0.05 x 105 mol-1 L (313 K). The binding process occurred spontaneously and was mainly driven by enthalpy, as evidenced by thermodynamic parameters. Site marker competitive experiment showed that ruthenium complexes bind to the warfarin binding site in subdomain IIA of HSA.

Resumo em Inglês:

Silver nanoparticles (AgNPs) stabilized with glutathione (GSH) were used as nanosensors for the determination of fluoroquinolones such as ciprofloxacin (CIP), norfloxacin (NOR) and enrofloxacin (ENRO) in aqueous systems. The AgNPs were stabilized with GSH (Ag-GSH NPs), whereas the decrease of the surface plasmon resonance (SPR) band at 400 nm and the bathochromic shift of the absorption band were monitored. The method was validated and the analytical performance was verified. The results were satisfactory, with recoveries between 83.7 and 110% in almost all the experimental conditions and the repeatability and intermediate accuracy of less than 20%. The limits of detection were 0.397, 0.437 and 0.398 µmol L-1, and the limits of quantification were 1.203, 1.323 and 1.205 µmol L-1 for ciprofloxacin, norfloxacin and enrofloxacin, respectively. The method was selective in a group of drugs and applied in the determination of fluoroquinolones in potable water samples.

Resumo em Inglês:

The feasibility of obtaining cellulose acetate from lignocellulosic precursors is of great interest from the environmental, economic and technological points of view. Herein, sugarcane bagasse and vegetable sponge (Luffa cylindrica ) were used as precursors to produce cellulose using the organosolv extraction procedure. From the extracted celluloses, the production of cellulose acetate was carried out by the homogeneous acetylation method. The obtained materials were characterized by FTIR, solid-state 13C NMR, XRD, TG and DSC techniques. The results revealed the success of both the extraction and the acetylation processes, which provided cellulose with high crystallinity and cellulose acetates with high degrees of substitution (cellulose triacetates).

Resumo em Inglês:

This work presents a simple electrochemical method for 2-naphthylamine (2NAP) determination in perfume by differential-pulse voltammetry (DPV) employing a boron-doped diamond (BDD) electrode cathodically treated. Simple dilution of sample in supporting electrolyte was performed before electrochemical analysis. A borate buffer solution of pH 10.0 containing 20% (v/ (LOD) of 0.0046 µmol L-1 with a linear range between 0.5 and 90 µmol L-1, and RSD < 2.9%, respectively. Recovery values for spiked samples with 2NAP were between 102 and 104%. The proposed method is feasible to be applied for 2NAP detection and quantification on perfume samples with simple sample preparation.

Resumo em Inglês:

In this manuscript we have evaluated the computational methods performance in the calculation of thermochemical properties using graphical analysis. The analysis was carried out in a set of 74 organic molecules considering the following thermochemical properties: standard enthalpy of formation, ionization energy and electron and proton affinities. The evaluated methodologies were: G3, G3MP2, G3B3, G3MP2B3, G4 and G4MP2, and the exchange-correlation func- tionals: SOGGA11, RevTPSS, B3LYP, PBE0, B98, M06-2X, BMK and HSE06. Larger basis function sets (G3LargeXP) were employed with these functionals. It was observed that Gaussian-4 theory using reduced order perturbation theory (G4MP2) offered the best relationships between accuracy and computational cost.

Resumo em Inglês:

Buffered solutions, additives, and column temperature are widely used in high-performance liquid chromatography to promote adequate retention of compounds and to improve the chromatographic separation. However, these factors can dramatically reduce the column lifetime. In this work, the effect of column temperature, pH and the salt type and concentration in buffered mobile phases were evaluated on the stability of a typical commercial C18 stationary phase. A method for rapid evaluation of stationary phase degradation caused by these variables was employed to avoid the generation of large volumes of organic waste. By monitoring the performance of stationary phase in the separation of a standard test mixture, it was possible to verify that the pH of the mobile phase is the most drastic condition to reduce the column lifetime. Buffer solutions of inorganic salts as well as the use of temperatures above 40 °C also significantly reduce the column lifetime. However, a column can have its use extended working with low concentrations of organic additives in the mobile phase, under moderated temperature, and adjusting the pH to the safety range of silica-based materials.

Resumo em Inglês:

Excessive use of pesticides can lead to the accumulation of residues in different parts of plants, endangering various species and contaminating foods. Honey can be used as an indicator of agricultural contamination and pre-mature bee mortality by pesticides. However, to quantify pesticide residues in honey, high sensitivity analytical methodologies are required. In this work, a new method was proposed for the determination of seven pesticides, widely used in Triângulo Mineiro, in honey samples based on QuEChERS method and quantification by UHPLC-MS/MS. The method was optimized and validated according to the protocol recommended by the European Community. The method presented LOQ in the range of 0.6-4.0 µg kg-1, lower than the MRLs established for the pesticides studied. Also, the methodology showed high accuracy, with recoveries ranging from 89-107%, and good accuracy, RSD <14%. Honey samples obtained in the Triângulo Mineiro region and subjected to the determination of pesticide residues were analyzed by the analytical methodology, indicating the presence of methomyl and imidacloprid residues in all samples. These results indicate that beehives close to the grain and sugarcane crops are being affected by the application of pesticides in the Triângulo Mineiro Region, Brazil.

Resumo em Inglês:

Endophytic microorganisms have been shown to be an important source of bioactive compounds, and much has been studied about their metabolites. For example, compounds with different biological activities have been isolated from Phomopsis sp. The metabolic study of this genus may lead to a better understanding of the routes of production of metabolites of interest. The aim of this study was to map the metabolic profile of Phomopsis sp., isolated as an endophyte of Syzygium jambolanum DC, using culture filtrate. The fungus was cultivated for six weeks in potato dextrose medium under hypoxia and at room temperature. The filtrate was collected weekly, and the analyses were performed using proton nuclear magnetic resonance (1H NMR) spectroscopy by applying NOESY1D with suppression of the water signal. The occurrence of reductive routes was verified: alcoholic fermentation throughout cultivation and reductive tricarboxylic acid cycle in the cytosol until the third week of cultivation were observed.

Resumo em Inglês:

The objective of this work was to determine the chemical composition, total phenolic compounds content, antioxidant capacity through the ABTS (2,20-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) method, as well as to evaluate the use of paper spray ionization mass spectrometry (PS-MS) to obtain fingerprints in different brands of mixed industrialized beverage based on fruits and vegetables with “detox” denomination. The carbohydrate contents ranged from 4.17% (sample D) to 12.72% (sample G). The differences may be related to the composition and proportion of the ingredients present in each formulation. The contents of total phenolic compounds varied between 26.75 mg GAE (gallic acid equivalents) g-1 (sample F) to 48.61 mg GAE g-1 (sample D). The samples A, B and C contain cabbage, spinach and parsley and presented significantly higher phenolic compounds content than the other samples. The antioxidant activity values varied between 1.76 µmol L-1 Trolox g-1 (sample B) to 18.95 µmol L-1 Trolox g-1 (sample E). The brands E, F, and G, that presented higher antioxidant potential, have ingredients pineapple, apple, cabbage, and ginger as common. The analysis of PS-MS allowed for the identification of a number of substances, including organic acids, sugars, and phenolic acids. PS-MS is a relatively simple method, fast and efficient to obtain fingerprints of mixed beverages.

Resumo em Inglês:

A series of nitramino-derivatives of pyrrole were designed through introducing the nitramino group into pyrrole ring to look for high-energy-density compounds. The molecular stabilities are explored thoroughly based on the calculated heats of formation, bond dissociation energy, and bond order at the B3PW91/6-311+G(d,p) level. The results indicated that the molecules designed in this paper have enough stability not only thermally but also kinetically. To evaluate the potential application as high-energy-density compounds, the detonation velocity and detonation pressure are calculated by using the Kamlet-Jacobs equation. Based on the calculation both of stability and detonation characters, four nitramino-derivatives of pyrrole (D1: 2,3-trinitramino-1H-pyrrole, D2: 2,3,4-trinitramino-1H-pyrrole, D3: 2,3,5-trinitramino-1H- pyrrole and E: 2,3,4,5- tetranitramino- 1H-pyrrole) are screened out as potential high-energy-density molecules for further study.

Resumo em Inglês:

Metabolomics has played a central role in various areas of plant sciences, offering new perspectives for the advancement of agriculture, drug discovery, chemical ecology and taxonomy. Plant metabolomics (identification and quantification) aims to understand the relationship between biological systems and genetic, pathological and or environmental stimuli in terms of differential expression of the metabolism. Owing to the unique challenges, such studies require multidisciplinary skills involving biology, chemistry, statistics, and computer science for the extraction and complete understanding of information. In this sense, this review summarizes the main procedures that involve the steps of plant metabolomic study (design of experiments, sample preparation, analytical methods and data analysis), providing a comprehensive overview, showing the main challenges and limitations and possible solutions for the different approaches used.

Resumo em Inglês:

The present work describes a mini oven built to be applied in the preparation of monolithic stationary phase through the thermal polymerization approach. The developed device was successfully tested for functionalization of monolithic stationary phase in the internal surface of the silica capillary column fused with gold nanoparticles.

Resumo em Inglês:

This paper presents the application of a Short ARG built to be applied in a single class, instead of a longer interval, as it is common in strategies such as ARG. ARGs are games based on role-playing experiences that involve role playing using a particular place, in this case, two classrooms and an education lab. Whereas ARG’s characters are the participants/players themselves, in this study, they were the Chemistry undergraduate students. The students/players were aimed of various clues and moments involving chemical concepts to find a lost student. We could notice ARG can be a teaching strategy, we mean, an alternative for conceptual discussion in the classroom as well as a diagnostic and formative assessment tool, characteristic of the use of games and recreational activities in teaching scientific concepts.

Resumo em Inglês:

A teaching experiment on supervised pattern recognition in chemometrics was proposed in this tutorial to introduce partial least squares discriminant analysis (PLS-DA). A new approach of the experiment published in the first tutorial of this series was revisited and employed to the classification of edible vegetable oils. The spectra of olive, canola, soybean and corn oils were obtained using an attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrometer in the range of 600 to 4000 cm-1. The combination of ATR-FTIR and PLS-DA classification method was able to correctly classify 100% of the validation samples. The Matlab commands, routines and functions were presented, and a didactic explanation of the concepts and interpretation of the data was provided.

Resumo em Inglês:

This work aims to analyze the contribution of a training action to the awareness and improvement of the knowledge of students of Chemistry and Chemical Engineering of Universidade Federal do Rio Grande do Sul (UFRGS) courses, regarding the processes of management and treatment of chemical wastes and wastewater generated in the experimental course. The research was performed with 66 students enrolled in the Experimental General Chemistry subject in the second semester of 2017. For that purpose, a two-hour lesson action training course was offered. As data collecting tools, an Initial Questionnaire was applied before the training stage and a Final Questionnaire was applied after the training stage. In order to do the analyses of the questionnaire answers, were elaborated also images about the frequency of the words by using NVivo 12(®) software. The data set indicates a scientific inculturation/alphabetization of concepts by students in terms of the main treatment types used to mitigate residues that are generated in teaching labs, as Coprocessing, Incineration and Sanitary Landfill. It can also be inferred that the activity offered to the students contributed to the formation of values necessary for the formation of professionals more aware of their performance in society.