Scielo RSS <![CDATA[Química Nova]]> vol. 38 num. 5 lang. es <![CDATA[SciELO Logo]]> <![CDATA[EFFECTS OF SOLVENT, BASE, AND TEMPERATURE IN THE OPTIMISATION OF A NEW CATALYTIC SYSTEM FOR SONOGASHIRA CROSS-COUPLING USING NCP PINCER PALLADACYCLE]]> The optimisation of a new catalyst system using NCP pincer palladacycle 1 was investigated using the experimental design technique. NCP pincer palladacycle 1 was previously investigated in Suzuki-Miyaura and Heck-Mizoroki cross-couplings and found to be a highly efficient catalyst precursor. In this study, the effects of the type of base (K3PO4 or DABCO), solvent (DMF or dioxane) and reaction temperature (130 or 150 ºC) in the second step on the reactional yield in Sonogashira cross-coupling were assessed using the two-factor design. The results showed that temperature is statistically significant in relation to the reaction yield. <![CDATA[A THEORETICAL EVALUATION OF ELECTROCONDUCTIVE PROPERTIES FOR [1,2,4]-TRIAZOLE 4N-SUBSTITUTED POLYMERS]]> In order to evaluate a set of electrical and optical properties by using time-dependent density functional theory (TD-DFT), at level of theory B3LYP/6-31G(d), the 4N-substituted [1,2,4]-Triazole (TAZ) oligomers and substituted derivatives were studied using cyano, amino, methyl and fluoro functional groups. Additionally, specific properties were theoretically evaluated, namely electronic and geometrical properties, excitation energies, λmax, and the HOMO-LUMO orbital of the different oligomers TAZ with repeated units of 4 to 20 rings. These properties were extrapolated to polymer by using a second order polynomial fit. The oligomers studied exhibited a high molecular planarity, favoring electronic delocalization. Thus, an increase of the monomeric units in the different TAZ oligomers and their corresponding substituents led to an improvement in these properties, showing the best results for the cyano group. The findings contribute to the design of charge carrier polymeric materials and photoluminescent devices (OLEDs). <![CDATA[STUDY OF MATRIX EFFECT IN DETERMINATION OF METALS IN RE-REFINED BASIC OILS BY ENERGY DISPERSIVE X-RAY FLUORESCENCE - EDX]]> In this article, the results of the study of the matrix effect in the determination of metals calcium, chromium, iron, nickel, copper, zinc, molybdenum, cadmium, barium and lead in base oil using Energy Dispersive X-Ray Fluorescence (EDX) are presented. Sensitivities obtained for each calibration curve were evaluated where calcium, chromium, copper, cadmium, barium and lead had the lowest sensitivities. In the case of cadmium, this parameter was lagging and the studies were not carried forward. The curves of the other metals in different base oils were evaluated for linearity. The elements chromium, copper, molybdenum and lead showed linearity problems in some cases. Therefore, curves in different base oils showed distinct mathematical behavior where the matrix effect was confirmed. The other curves were evaluated and existence of the matrix effect attributed to interference of C / H ratio was confirmed in the quantification of all elements. Metals iron, nickel and zinc exhibited the highest sensitivity and determination coefficients, showing that the method has application potential. <![CDATA[CONTAMINATION OF AQUATIC ENVIRONMENTS BY "URBAN PESTICIDES”: THE CASE OF COCÓ AND CEARÁ RIVERS, FORTALEZA - CEARÁ, BRAZIL]]> Pesticides are used mostly in rural areas for agriculture, but urban pest control, public health campaigns, and household and veterinary products can also be important sources of these contaminants. This aim of this study was to estimate household pesticide contamination in sediments of two urban estuaries due to pest control: Cocó and Ceará rivers located in the metropolitan area of Fortaleza, Ceará, Brazil. Cypermethrin and malathion were found in both rivers. Cypermethrin levels had the same magnitudes as other studied urban areas and were highest in the estuary, while malathion was similar in both fluvial and estuarine zones. <![CDATA[SPECTROSCOPIC STUDY OF ALUMINUM PHTHALOCYANINE CHLORIDE (AlPcCl) IN HOMOGENEOUS AND MICRO-HETEROGENEOUS MEDIA CONSISTING OF P-123 AND F-127 POLYMERIC MICELLES]]> Aluminum phthalocyanine chloride (AlPcCl) is a photoactive compound which has been used as a photosensitizer (PS) in photodynamic therapy (PDT). Its spectroscopic properties have been studied in solvents of different polarities (ethanol, acetone, dimethylsulfoxide and chloroform). Its solubility has been found to decrease with increasing solvent polarity, together with full self-aggregation in aqueous solution. The binding of AlPcCl to the copolymer PluronicTM micellar class P-123 and F-127 used as solubilizer/carriers was studied. Greater interaction between the more hydrophobic copolymer P-123 and AlPcCl was observed, besides a complex interaction profile involving different AlPcCl forms (self-aggregate/monomeric form) in the copolymers. Time- and temperature-dependent structural organization of AlPcCl in the copolymers was also observed. Thus, AlPcCl has a strong tendency to self-aggregate with increasing solvent polarity, an effect also observed in micellar media. <![CDATA[CHEMICAL CONSTITUENTS AND PHYTOTOXIC ACTIVITY OF LEAVES OF <em>Annona nutans</em>]]> The phytochemical investigation and evaluation of the phytotoxic effect of the extract and fractions obtained from the leaves of Annona nutans (R. E. Fr.) R. E. Fr. were performed. Phytotoxic activity was assessed on radicle and hypocotyl of Allium cepa and Lactuca sativa, where chloroform and ethyl acetate fractions proved active. Phytochemical investigation of the chloroform fraction was allowed identification of polyketides derivatives: triacontanal, 16-hentriacontane, octacosanol and triacontanol, using the 1H NMR technique associated with data from GC/MS. Using ethyl acetate fraction, with low activity, flavonoids 3-O-β-D-galactopyranosyl-isorhamnetin, 3-O-β-D-galactopyranosyl-quercetin and 3-O-β-D-apiofuranosyl-(1→2)-galactopyranosyl-quercetin were identified, determined by spectrometric techniques one and two-dimensional NMR, combined with mass spectral data. All substances are being reported for the first time in Annona nutans. The phytotoxic activity of chloroform fraction may be related to the presence of triacontanol and similar substances. Triacontanol stimulates growth at very low concentrations, but can have an inhibitory effect at higher concentrations, such as those reported for auxin analogs. The toxicity assay using Artemia salina (BST) was also performed, with the chloroform fraction showing a negligible lethal dose, LD50 = 500 mg mL-1, while the other fractions and extracts showed no activity. Thus, the presence of acetogenins was ruled out. <![CDATA[SPECTROSCOPIC DATA OF LABDANE DITERPENES: A THEORETICAL ANALYSIS VIA NMR AND DFT]]> Labdane diterpenes exhibit important bioactivities such as cardiovascular effects in rats as well as effects in the treatment of autoimmune diseases and Alzheimer syndrome. Recently, the labdane diterpenes ent-13-epi-manoil oxide, ribenone and ribenol were isolated from Croton palanostigma. The computational method DFT/B3LYP/cc-pVDZ was used to optimize the structures of these diterpenes and to calculate infrared data. Chemical shifts (δH and δC) of the minimum energy structures (local minimum) were calculated and compared with the experimental data. Comparison of the NMR data by simple linear regression (SLR) showed satisfactory statistical results with a correlation coefficient (R2) and predictive ability (Q2) of over 98%. The predicted NMR data were used to confirm the δH values that have not been published. <![CDATA[EVALUACIÓN TÉRMICA DEL CURADO DE ADHESIVOS BASE SBR USANDO PERÓXIDO DE DICUMILO]]> Curing is an important process in adhesive formulation, but scant reports on the study of the kinetics of curing in adhesive are currently available, particularly for formulations including styrene-butadiene copolymers. The focus of the present work was to thermodynamically quantify the curing reaction in pressure-sensitive adhesives (PSA) obtained from styrene-butadiene copolymers, the effect of dicumyl peroxide (DCP) ratio, which acts as a crosslinking agent, and also evaluate the effect of two reactive adhesive resins, sylvalite and piccolyte. Kinetic parameters were determined by differential scanning calorimetry (DSC) in an isothermic and dynamic mode, gel content was determined as was swelling degree, given these characteristics can be associated with the curing reaction. The kinetic study showed the curing reaction was first order, according to the Ozawa and Kissinger equation. Resins have affinity to BR segment, while in the case of sylvalite and piccolyte to the PS segment, varying behavior with dicumyl peroxide in the adhesive mixture. Lower swelling values were associated with an increase in crosslinking, indicative a curing reaction took place, and the gel content test was used to corroborate the results. <![CDATA[COPPER ELECTROWINNING USING A SPOUTED-BED ELECTROCHEMICAL REACTOR]]> In this work, copper electrowinning using a three-dimensional spouted-bed electrode (SBE) was studied in order to investigate the effects of current density (i), concentration of supporting electrolyte (Cs), pH, electrolyte temperature, and bed thickness on the process current efficiency (EC), energy consumption (CE) and space-time yield (Y). The results indicated that the SBE may be successfully used for the electrowinning of copper when the copper ion concentration is high and the pH is between 1 and 2. In this case, 100% CE, 2.7 kWh kg-1 EC and 118 kg L-1 h-1 Y can be achieved. It was verified that an increase in the electrolyte temperature caused a decrease in the electrodeposition rate (from 3.97 g L-1h-1 to 1.17 g L-1 h-1), indicating that, despite the solution conductivity enhancement, temperature promoted the increase in the anodic dissolution kinetics. The results also showed that EC depends on the applied current density, whereby greater EC values can be obtained using high current densities. Finally, the copper particles were analyzed by scanning electron microscopy and it was confirmed that a smooth, uniform and compact electrodeposit can be obtained without using any chemical additives. <![CDATA[FAST AND SIMULTANEOUS DETERMINATION OF SULFAMETHOXAZOLE AND TRIMETHOPRIM USING BATCH INJECTION ANALYSIS WITH AMPEROMETRIC DETECTION AND BORON-DOPED DIAMOND ELECTRODE]]> A fast, simple procedure for simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) was performed using batch injection analysis with multiple pulse amperometric detection (BIA-MPA). The sample aliquot (150 µL) was directly injected onto the boron-doped diamond (BDD) electrode (wall-jet configuration) immersed in a BIA system. The analytical characteristics of the proposed method include high analytical frequency (up to 75 injections per hour), good stability (RSD &lt; 2.9%; n = 10), low detection limits (0.227 and 0.173 mg L-1 for SMX and TMP, respectively) and minimal waste generation. The proposed method yielded similar results to those obtained by liquid chromatography at a 95% confidence level. <![CDATA[THE ROLE OF ANIONS IN SINGLE CRYSTAL PLATINUM CYCLIC VOLTAMMOGRAMS]]> This review examined the state of the art of electrochemical and thermodynamic studies involving characteristic features related to the adsorption of anions present in the electrolyte solutions in contact with platinum single crystals electrodes. <![CDATA[LIQUID PHASE SYNTHESIS METHODOLOGIES FOR THE OBTAINMENT OF RARE EARTH-BASED INORGANIC NANOMATERIALS]]> Liquid phase synthesis techniques are commonly preferred for the preparation of nanosized inorganic solids due to several advantages over other methodologies, such as low energy consumption, safety, possibility of reactant recovery and, mainly, the homogeneity of the precursors and control of particle sizes and morphologies through bottom-up approaches. In this regard, Colloidal Chemistry plays a key role in the controlled production of different classes of nanoparticles, thus being a subject of growing interest in several fields of Materials, Inorganic, and Physical-Chemistry. Therefore, this article sought to present an introductory outline of Colloidal Chemistry, with a focus on the preparation of inorganic nanoparticles. Given the broadness of this subject, special attention was devoted to nanoparticles based on Rare Earth compounds, due to their current importance in several fields. Therefore, the work presents the principles involved in the most commonly applied methodologies for the liquid phase synthesis of nanoparticles, such as coprecipitations and hydro/solvothermal techniques, as well as precipitations into nanoreactors based on reverse microemulsions, with a brief survey of the main advances in these fields in recent years. <![CDATA[CONSIDERATIONS AND PRACTICAL IMPLICATIONS OF THE GUIDE FOR VALIDATION AND ANALYTICAL QUALITY CONTROL OF DRUGS IN FEED AND VETERINARY DRUGS]]> Recently, the Brazilian Ministry of Agriculture, Livestock and Supply (MAPA) published a validation and analytical quality control guide called the “Guia de Validação e Controle de Qualidade Analítica – Fármacos em Produtos para Alimentação Animal e Medicamentos Veterinários”, in order to guide officers and accredited laboratories in the validation of analytical methods for the quality control of veterinary medicines, drug contaminants in feed and depletion studies (residues of drugs in biological matrices). The aim of this study was to present a critical evaluation of the concepts and procedures defined in this document. The Guide was applied for the validation of chromatographic methods intended to be used for the quantification of antimicrobial and antiparasitic drugs in veterinary medicines. Methods for the determination of ivermectin, abamectin, sulfadiazine, sulfadimethoxine, sulfaquinoxaline, streptomycin, dihydrostreptomycin and florfenicol were validated using the Guide. Each validation parameter was evaluated and discussed. A total of 55 samples of veterinary drugs were analyzed. <![CDATA[DEVELOPMENT AND VALIDATION OF A HPLC-PDA METHOD AND PRELIMINARY STABILITY STUDY OF SYNEPHRINE IN <em>Citrus aurantium L.</em> DRY EXTRACT]]> A reversed-phase liquid chromatographic method was developed for the assay of synephrine in Citrus aurantium dry extract. The chromatographic separation used a C18 (250 × 4.6 mm, 5 µm) column and a mobile phase consisting of acetonitrile: 0.01% orthophosphoric acid (pH 3.0) at a 15:85 ratio, flow rate of 1 mL min-1 and detection at 220 nm. The detector response was linear in the range 15 - 45 mg mL-1. Specificity and stability, indicating suitability of the method, were confirmed using stress conditions (acid and basic hydrolysis, oxidation and photolysis). Intraday precision yielded RSD values of less than 1.77% and interday precision of 2.5%. The average recovery accuracy of the test was 102.03%. The method was validated according to international guidelines and can be used in routine quality control and stability studies of Citrus aurantium preparations. The preliminary stability study showed that synephrine is susceptible to hydrolysis, oxidation and photolysis. <![CDATA[SIMPLE AND SELECTIVE SPECTROPHOTOMETRIC ASSAY OF DIETHYLCARBAMAZINE CITRATE USING 2,3-DICHLORO-5,6-DICYANO-<em>p</em>-BENZOQUINONE AND 2,4-DINITRO PHENOL]]> Two simple, rapid and inexpensive spectrophotometric methods are described for the determination of diethylcarbamazine citrate (DEC) in bulk drug and formulations. The methods are based on the charge–transfer (CT) complexation reaction involving DEC as the n- donor and 2,3-dichloro-5,6-dicyano-p-benzoquinone [DDQ] (method A) and 2,4-dinitro phenol [DNP] (method B) as π-acceptors in chloroform. The absorbance of CT complexes was measured at 480 nm for method A, and 420 nm for method B. Under optimum conditions, Beer’s law was obeyed over the concentration ranges 4-90 and 4-100 μg mL-1 for methods A and B, respectively. <![CDATA[CONSTRUCTION OF A LOW-COST SYSTEM FOR HIGH FREQUENCY DATA ACQUISITION DURING ELECTROCHEMICAL EXPERIMENTS]]> This work reports the building of a low-cost experimental setup for high temporal resolution data acquisition. The setup is useful for different applications, especially for voltage data acquisition during electrochemical experiments. The proposed setup performed two hundred thousand measurements per second (5 µs time resolution) and revealed unknown curve characteristics during chronopotentiometry of the anodization of valve metals. This information can serve as a starting point for further investigations on the nature of voltage oscillations in the breakdown region during valve metal anodization. <![CDATA[THERMAL CRACKING OF CRUDE GLYCERIN: AN UNDERGRADUATE ORGANIC CHEMISTRY EXPERIMENT]]> In this work, an undergraduate organic chemistry experiment based on thermal cracking of glycerin is proposed. The reagent is obtained as a by-product from the practice of biodiesel synthesis, and allows reduction of waste produced in the lab. The main product obtained from thermal cracking was characterized by GC analysis as acrolein. This substance was also identified by chemical derivatization as 2,4-dinitrophenylhydrazone, allowing a combined experiment of identification by synthesis of the derivative. <![CDATA[FUNDAMENTALS OF CAPILLARY ELECTROPHORESIS: AN ANIMATION APPROACH]]> Among the analytical separation techniques, capillary electrophoresis (CE) has attracted attention in both academic and industrial fields, mainly owing to its efficiency, short analysis times, low reagent consumption and residue generation. This is also the case in Chemistry courses, books and papers, demonstrating CE´s well-established status. However, despite the range of available bibliographic material, there is a lack of animations showing the CE dynamic process. Therefore, the aim of this work was to show the development of a group of animations available for public access, where electrolyte and analytes movements under different CE modes; electropherogram formation; and online ultraviolet-visible spectra can be viewed. The normal or reverse electroosmotic flow generation in the vicinity of the silica capillary wall and the partition motion of neutral compounds between micellar and aqueous phases are also shown. Capillary zone electrophoresis, micellar electrokinetic chromatography, capillary electrochromatography, capillary isoelectric focusing, capillary isotachophoresis and capillary gel electrophoresis, are included in this package. This animation approach can be highly didactic and can complement the theoretical study of CE techniques, which may aid researchers, teachers and students interested in understanding the dynamism and potential of different CE modes. <![CDATA[TIPS ON ACTIVE SPACE CONSTRUCTION IN MULTICONFIGURATIONAL CALCULATIONS: A CASE STUDY]]> The choice of the active space is a crucial step for a successful multiconfigurational quantum chemical calculation. In this work, hints are provided on how to choose the right active space, illustrating each step with real calculations. The examples can be reproduced by following the input files included in the Supporting Information and employing the free software available on the internet. <![CDATA[SOLID-LIQUID SEPARATION: CENTRIFUGES AND FILTER PAPERS]]> This work describes the fundamentals and evolution of two current solid-liquid separation methods found in the chemical laboratory: the filter paper and the centrifuge. Both methods were developed in the 19th century and are recognized as valuable techniques for industrial and laboratory purposes. However, significant improvements were introduced only from the end of the 19th century. The classical manual centrifuge was replaced by electric models: safety, maximum speed and number of samples that can be centrifuged at a time were greatly increased. The manufacture of filter paper was initially done by hand, but later benefited from papermaking industrial technologies. Many pretreatments of the wooden fibers were developed, particularly after 1880, thus resulting in many filter paper types for qualitative and quantitative applications. These two separation techniques are also found in various procedures in our everyday life.