Scielo RSS <![CDATA[Química Nova]]> vol. 38 num. 10 lang. en <![CDATA[SciELO Logo]]> <![CDATA[EVALUATION OF PHYSICAL AND CHEMICAL PROPERTIES OF ELECTRODEPOSITED Ni–W–P OBTAINED IN HULL CELL]]> Ni–W–P electrodeposits were synthesized in a Hull cell in order to simulate the obtainment under industrial conditions. Complete coverage of panels was accomplished by applying total currents of 1.0 and 2.0 A. Panels obtained with a current of 1.0 A appeared brighter. The best compositional uniformities, as determined by Energy Dispersive Spectrometer (EDS) occurred in the current density ranges of 0.6 to 3.0 A dm−2 and 1.6 to 6.0 A dm−2 obtained with 1.0 and 2.0 A, respectively. However, the best morphological characteristics, as determined by Scanning Electro Microscope (SEM), were observed in those obtained with a total current of 1.0 A. Analysis of corrosion resistance by Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Linear Polarization (PLP) in NaCl have shown significant variations in the amount of corrosion potential, polarization resistance, and even total impedance. The alloys exhibited amorphous character (XRD) and crystallized above 400 °C to Ni and Ni3P phases, and possibly Ni–W, with a subsequent increase in hardness. The results suggest that under industrial conditions, current density variations due to the large and complex geometric shapes of substrates lead to formation of distinct alloys. Furthermore, these materials are potential substitutes for chromium deposits in many applications. <![CDATA[SYNTHESIS AND DETERMINATION OF THE RELATIVE STEREOCHEMISTRY OF A NEW EPOXIDE ALDEHYDE CYCLOPENTANE MONOTERPENOID]]> In this study, we report the preparation of a new tetra-substituted epoxide aldehyde cyclopentane, which acts as a starting material for the synthesis of plinol, from (R)-(+)-epoxy-limonene. The synthesis was performed in three steps and resulted in a good yield. The structural determination was performed by 1H and 13C NMR, and the relative stereochemistry was defined by nuclear Overhauser effect (NOE) experiments with computer calculations of molecular modeling, particularly with respect to indirect coupling constant calculations. <![CDATA[EFFECT OF CARBON DIOXIDE ON THE STABILITY OF THE Ca<sub>2</sub>Fe<sub>2</sub>O<sub>5</sub> PHASE APPLIED IN THE PHOTOCATALYTIC DEGRADATION PROCESS OF METHYLENE BLUE]]> Solid samples containing a Ca2Fe2O5 phase were synthesized using the Pechini method. The samples were characterized using X-ray diffraction, thermogravimetric analysis, differential thermal analysis, X-ray fluorescence, nitrogen adsorption/desorption isotherms, and scanning electron microscopy. The stability of the Ca2Fe2O5 phase was evaluated in the photocatalytic degradation of methylene blue (MB) in aqueous solution in the presence of bubbling gas (air, N2, or CO2). The presence of CO2 is known to suppress MB degradation. After the photocatalytic test, changes were observed in the crystalline phase of all systems. These results suggest the low stability of the Ca2Fe2O5 phase in aqueous systems and the significant effect of CO2 on the photocatalytic activity of the Ca2Fe2O5 phase. <![CDATA[COMPARISON OF METHODS BY LIQUID CHROMATOGRAPHY FOR THE DETERMINATION OF PESTICIDE MULTIRESIDUES IN STRAWBERRIES]]> Liquid chromatography is often used for the determination of pesticide multiresidues in foods. In Brazil, the strawberry crop is an example of a food with high levels of irregularities because of the application of pesticides. This is a major concern from the perspective of food safety, environmental protection, and certification for food export. The purpose of this study is to evaluate and compare chromatographic separation and detection methods in relation to a newly developed and validated method using ultra high performance liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) for the analytical determination of pesticides in strawberries. The comparisons were based on evaluations of the analysis time, consumption of the solvent in the mobile phase, injection volume, detectability, matrix effect, and recovery. The results showed that the LC–MS/MS and UHPLC–MS/MS techniques were both extremely efficient at analyzing pesticide residues with different physico-chemical parameters that were present at low concentrations in a complex matrix. The UHPLC separation method provided better chromatographic performance and productivity, which contributed favorably to routine analytical determinations. Detection by MS/MS had better detectability and selectivity compared with the diode array detector. <![CDATA[SYNTHESIS AND ANTIFUNGAL ACTIVITY OF PALMITIC ACID-BASED NEOGLYCOLIPIDS RELATED TO PAPULACANDIN D]]> A series of six new palmitic acid-based neoglycolipids related to Papulacandin D were synthesized in five steps, resulting in good yields, and they were evaluated against Candida spp. All twelve synthetic intermediates were also evaluated. The synthesis involved the initial glycosylation of two phenols (4-hydroxy-3-methoxybenzaldehyde and 3-hydroxybenzaldehyde) via their reaction with peracetylated glucosyl bromide. This was followed by deacetylation with potassium methoxide/metanol solution and the protection of two hydroxyls (C4 and C6 positions) of the saccharide unit as benzilidene acetals (10-11). The next step involved the acylation of the acetal derivatives with palmitic acid, thereby affording a mixture of two isomers mono-acylated at the C2 and C3 positions and a di-acylated product (12-17). After being isolated, each compound was subjected to the removal of the acetal protecting group to yield the papulacandin D analogues 18-23. Three compounds showed low antifungal activity against two species: C. albicans (compounds 7 and 23) and C. tropicalis (compound 17) at 200 µg mL−1. <![CDATA[CONSTITUENTS OF ESSENTIAL OIL AND HYDROLATE OF LEAVES OF <em>Campomanesia viatoris</em> LANDRUM]]> The chemical composition of the essential oil and hydrolates of Campomanesia viatoris Landrum were investigated by gas chromatography/mass spectrometry (GC/MS) and a GC flame ionization detector (GC-FID). The major constituents were tasmanone (70.50, essential oil; 74.73%, hydrolate), flavesone (12.77, essential oil; 12.24%, hydrolate) and agglomerone (6.79, essential oil; 10.84%, hydrolate). Tasmonone was isolated and its structure was characterized by spectrometric analysis, specifically 1D and 2D nuclear magnetic resonance (NMR) and mass spectrometry (MS). These findings supports the quimiotaxonomic relationship with Campomanesia and Eucalyptus genera. <![CDATA[ANION-BINDING AND SENSING PROPERTIES OF NOVEL RECEPTORS BASED ON N-(INDOL-3-YLGLYOXYLYL)BENZYLAMINE]]> Indole-based receptors such as biindole, carbazole, and indolocarbazole are regarded as some of the most favorable anion receptors in molecular recognition. This is because indole groups possess N–H groups as hydrogen-bonding donors. The introduction of amide groups in the indole framework can induce strong binding properties and good water solubility. In this study, we designed and synthesized a series of N-(indol-3-ylglyoxylyl)benzylamine derivatives as novel and simple anion receptors. The receptors derived by aryl and aliphatic amines can selectively recognize F– based on a color change from colorless-to-yellow in DMSO. The receptors derived by hydrazine hydrate can recognize F–, AcO–, and H2PO4– by similar color changes in DMSO and can even enable the selective recognition of F– in a DMSO–H2O binary solution by the naked eye. Spectrographic data indicate that complexes are formed between receptors and anions through multiple hydrogen-bonding interactions in dual solutions. <![CDATA[Fe<sup>3+</sup>-SELECTIVE ENHANCED FLUORESCENCE PROBE BASED ON A RHODAMINE DERIVATIVE]]> A novel Fe3+-selective and turn-on fluorescent probe 1 incorporating a rhodamine fluorophore and quinoline subunit was synthesized. Probe 1 displayed high selectivity for Fe3+ in CH3CN–H2O (95:5 v/v) in the presence of other relevant metal cations. Interaction with Fe3+ in 1:1 stoichiometry could trigger a significant fluorescence enhancement due to the formation of the ring-open form. The fluorescent response images were investigated by a novel Euclidean distance method based on red, green, and blue values. A linear relationship was observed between fluorescence intensity changes and Fe3+ concentrations from 7.3 × 10−7 to 3.6 × 10−5 mol L−1. <![CDATA[MATHEMATICAL PROCESSING COMPARISON OF VOLTAMMETRIC DATA: APPLICATION WITH THE SIMULTANEOUS DETERMINATION OF FLUOROQUINOLONES]]> This paper describes a comparative study between the procedures of deconvolution and the second-order derivative of square wave voltammograms to achieve separation of the voltammetric peaks of levofloxacin (LEVO) and norfloxacin (NOR), for their simultaneous quantification in urine samples. The obtained results indicate that the use of second-derivative voltammograms coupled with carbon screen-printed electrodes is the most efficient approach for completely separating the voltammetric peaks of LEVO and NOR. In addition, this approach has produced detection limits lower than 1.0 µmol L-1 and a wide linear range for both drugs. The proposed method was successfully used to simultaneously determine LEVO and NOR in spiked human and bovine urine samples with recovery percentages close to 100% for all analyzed samples. <![CDATA[BIODIESEL PRODUCTION FROM FATTY ACIDS OF REFINED VEGETABLE OILS BY HETEROGENEOUS ACID CATALYSIS AND MICROWAVE IRRADIATION]]> This work presents the biofuel production results of the esterification of fatty acids (C12-C18) and high-acid-content waste vegetable oils from different soap stocks (soybean, palm, and coconut) with methanol, ethanol, and butanol by acid catalysis. We used Amberlyst-35 (A35) sulfonic resin as a heterogeneous acid catalyst and p-toluenesulfonic acid as a homogeneous catalyst for comparison. Both the heterogeneous (A35) and homogeneous (p-toluenesulfonic acid) reactions were performed with 5% w/w of catalyst. The final products were analyzed by proton nuclear magnetic resonance (1H NMR). The homogeneous catalyzed esterification of fatty acids with methanol, ethanol, and butanol produced esters with yields higher than 90%. In the reaction with fatty acids and methanol catalyzed by A35, the best results were achieved with lauric acid and methanol, with a yield of 97%. An increase in the hydrocarbon chain decreased the rate of conversion and yield for stearic acid with methanol, which was 90%. Maximum biodiesel production was achieved from coconut and soybean soap stocks and methanol (96%-98%), which showed conversions very close to those obtained from their respective fatty acids. Microwave irradiation reduced the reaction time from 6 to 1 h in the esterification reaction of fatty acids with butanol. <![CDATA[STATE OF THE ART IN HYDROGEN BOND]]> Along the historical background of science, the hydrogen bond became widely known as the universal interaction, thus playing a key role in many molecular processes. Through the available theoretical approaches, many of these processes can be unveiled on the basis of the molecular parameters of the subject intermolecular system, such as the variation of bond length and mainly the frequency shift observed in the proton donor. Supported by the natural bond analysis (NBO) with the quantification of the hybridization contributions, the structural deformations and vibrational effects cited above are also attributed to the outcome of the intermolecular interaction strength, which consequently can be estimated by means of the quantum theory of atoms in molecules (QTAIM) as well as evaluated by the symmetry-adapted perturbation theory (SAPT). Moreover, to identify the preferential interaction sites for proton donors and acceptors, the molecular electrostatic potential (MEP) is useful in this regard. <![CDATA[SELECTIVE FLUORINATION METHODS OF ORGANIC MOLECULES]]> Presently, the world depends on a wide variety of new materials based on organofluorine compounds. These compounds can be used as surfactants, high resistance polymers, liquid crystals, agrochemicals, radiopharmaceuticals for positron emission tomography, and drugs. However, the selective formation of C–F bonds remains a challenge. This study reviews our knowledge of organofluorine compounds and describes conventional and modern selective fluorination methods for obtaining these compounds. Here, we highlight the most common fluorination reagents and describe the fluorination reactions. This review is organized by the type of fluorine transfer: nucleophilic, electrophilic, and enzymatic <![CDATA[DEVELOPMENT OF AN ULTRASONIC TECHNIQUE TO ASSESS OIL AND GREASE CONTENTS IN BIOFUEL WASTEWATER]]> Ultrasound as a metrology tool has many applications in health care, industrial, and chemical analyses. Ultrasonic techniques are rapid, low-cost, non-invasive, and highly repeatable. Although ultrasound can be used to measure emulsions, no effort had been made thus far to optimize its sensitivity for metrological analysis. In this work, a technique for analyzing oil in water was validated. The wave velocity and attenuation were chosen as the ultrasonic parameters. The technique was implemented in the boundary region established by law for effluents from industrial plants involved with biofuel manufacturing. A technical effort of this study was to establish stable emulsions in concentrations close to the desired limit of study. The phase behaviours of pseudo-ternary oil, sodium chloride, and sodium lauryl sulphate were studied. The composition in the widest region of the diagram allowed for the formation of a stable emulsion, from which the ultrasound measurement was carried out. An analytical curve was obtained using ultrasonic attenuation to determine the content of oils and greases in wastewater ranging 15–240 ppm. The speed of sound did not appear to be an applicable parameter for this application. The technique was demonstrated to be an important alternative solution for the continuous monitoring of wastewater with regard to oil concentrations. <![CDATA[STEREOCHEMICAL ASSIGNMENT OF α-SANTONIN USING RESIDUAL DIPOLAR COUPLING]]> The measurement of nuclear magnetic resonance parameters in an anisotropic media, such as residual dipolar coupling (RDC), has proven to be an excellent methodology for the refinement of chemical structures, being used as a complementary tool in the determination of the relative configuration, conformation, and constitution of organic compounds. In this study, we applied this methodology to determine the relative configuration of α-santonin, a natural product with four stereocenters, while assigning its prochiral methylene protons using only the RDCs obtained in a polyacrylonitrile polymer gel swollen in DMSO-d6. <![CDATA[INTERACTIONS: DESIGN, IMPLEMENTATION AND EVALUATION OF A COMPUTATIONAL TOOL FOR TEACHING INTERMOLECULAR FORCES IN HIGHER EDUCATION]]> Intermolecular forces are a useful concept that can explain the attraction between particulate matter as well as numerous phenomena in our lives such as viscosity, solubility, drug interactions, and dyeing of fibers. However, studies show that students have difficulty understanding this important concept, which has led us to develop a free educational software in English and Portuguese. The software can be used interactively by teachers and students, thus facilitating better understanding. Professors and students, both graduate and undergraduate, were questioned about the software quality and its intuitiveness of use, facility of navigation, and pedagogical application using a Likert scale. The results led to the conclusion that the developed computer application can be characterized as an auxiliary tool to assist teachers in their lectures and students in their learning process of intermolecular forces. <![CDATA[SOLAR CELLS SENSITIZED WITH NATURAL DYES: AN INTRODUCTORY EXPERIMENT ABOUT SOLAR ENERGY FOR UNDERGRADUATE STUDENTS]]> An interesting practical experiment about the preparation of dye–sensitized solar cells (DSSC) using natural dyes were carried out by the undergraduate students in the chemistry course at UNICAMP . Natural dyes were extracted from blueberries (Vaccinium myrtillus L.), jabuticabas (Myrciaria cauliflora), raw and cooked beets (Beta vulgaris L.), and annattos (Bixa orellana L.), which were used to sensitize TiO2 films that composed the photoanode in the DSSC. A polymer electrolyte containing an iodide/triiodide redox couple was used in lieu of the use of liquid solutions to prevent any leakage in the devices. A maximum solar-to-electric energy conversion of 0.26 ± 0.02% was obtained for the solar cell prepared with annatto extracts. This experiment was an effective way to illustrate to the undergraduate students how to apply some of the chemical concepts that they learned during their chemistry course to produce electric energy from a clean and renewable energy source. Teachers could also exploit the basics of the electronic transitions in inorganic and organic compounds (e.g., metal-to-ligand charge transfer and ϖ-ϖ* transitions), thermodynamics (e.g., Gibbs free energy), acid–base reactions in the oxide solid surface and electrolyte, and band theory (i.e., the importance of the Fermi level energy). <![CDATA[PREPARATION OF CARBON DOTS AND THEIR OPTICAL CHARACTERIZATION: AN EXPERIMENT OF NANOSCIENCE FOR UNDERGRADUATE COURSE]]> Carbon dots (CDs) constitute a new class of carbon-based nanomaterials that measure less than 10 nm and display attractive physical and chemical features such as fluorescence. CDs have been considered the new “power” carbon nanomaterials since their accidental discovery in 2004. This study reports a simple, easy, and accessible experiment for undergraduate courses. The experiment involves the preparation of CDs by pyrolysis using commercial gelatin as a low cost precursor as well as CD purification and optical characterization. The optical properties of CDs such as absorption and emission properties make them a promising material for teaching the basic concepts and techniques used for characterization of nanomaterials. Also, the reactants and final product are suitable for undergraduate courses since they are non-toxic materials. The prepared CDs can be used in such applications as bioimaging, solar cells, and photocatalysis. <![CDATA[WOMAN IN CHEMISTRY. JANE MARCET, A RELEVANT FIGURE IN CHEMISTRY EDUCATION]]> A historiographical study of Jane Marcet’s role in spreading chemistry knowledge to a wider audience in the 19th century is presented here. Her efforts to spread scientific knowledge were crucial to sharing the most important theories of chemistry among different audiences, particularly women and young people. Through her book, “Conversations on Chemistry,” which was published in several editions from 1806 to 1853, she contributed significantly to chemistry education. Despite controversy over the large number of editions, this text is a strong witness to the active participation of women in science. Her scientific rigor and contribution to narrative strategies in chemistry pedagogy have given Jane Marcet consideration not only as an important woman in the scientific community of England during the first half of the 19th century but also as a central figure in the early development of chemistry diffusion and education.