Scielo RSS <![CDATA[Química Nova]]> vol. 41 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[FATTY ACID ETHYL ESTERS FROM MICROALGAE OF <em>Scenedesmus ecornis</em> BY ENZYMATIC AND ACID CATALYSIS]]> Microalgae are an indispensable food source for the various growth stages of mollusks, crustaceans, and several fish species. Using a microalgae biomass present in the Amazonian ecosystem (Macapá-AP), we study extraction methods for fatty acid such as solvent extraction (magnetic stirring and/or Soxhlet) and/or hydrolysis (acid and/or enzymatic catalysis) followed by esterification and/or direct transesterification. Extraction of crude triacylglycerides by mechanical stirring at room temperature was more efficient than continuous reflux (Soxhlet). Subsequently, the lipid extract was subject to transesterification with ethanol and CAL-B as a biocatalyst, leading to production of fatty acid ethyl esters (FAEE). Additionally, FAEEs were prepared by hydrolysis of crude triacylglycerides followed by acid-mediated esterification or enzymatic catalysis (lipase). In this case, the type of catalyst did not significantly influence FAEE yields. In the lipid extract, we identified palmitic, linoleic, oleic, and stearic acids with palmitic acid being the most abundant. Our results suggest that enzymatic catalysis is a viable method for the extraction of lipids in the microalga, Scenedesmus ecornis. <![CDATA[OXIDATION OF CYCLOHEXANOL ON PHOSPHOTUNGSTIC ACID ANION INTERCALATED LAYERED DOUBLE HYDROXIDES WITH AQUEOUS H<sub>2</sub>O<sub>2</sub> AS OXIDANT]]> The layered double hydroxides (LDH) of Mg2AlNi and Mg3Al pillared by Keggin-type phosphotungstic acid anion (POM), i.e. Mg2AlNi-POM LDH and Mg3Al-POM LDH were synthesized by an ion-exchange method. The synthesized POM intercalated LDH compounds were characterized using various techniques such as FTIR, XRD, TGA and BET. The observed results show that the obtained catalysts retain the layer structure of LDH. Compared with the binary Mg3Al-POM LDH, the ternary Mg2AlNi-POM LDH catalyst indicated a higher thermal and chemical stability. The catalytic activity of the resulting LDH-POM was also assessed in the green oxidation of cyclohexanol with aqueous H2O2 as an oxidant. The Mg2AlNi-POM LDH showed a much higher conversion and selectivity for cyclohexanone than the corresponding Mg3Al-POM LDH catalyst. <![CDATA[HOMOGENEOUS ESTERIFICATION AND TRANSESTERIFICATION OF VEGETABLE OILS WITH HIGH FREE FATTY ACIDS CONTENT]]> The high free fatty acids content in some vegetable oils can have a negative impact in the sustainable production of biodiesel. The previous treatment of these feedstock oils can contribute to the reduction of the process total costs as well as the environment, turning the biodiesel a more competitive in relation to the fossil diesel. The aim of this work was to adequate low cost vegetable oils to the production of biodiesel by homogeneous catalysis. The feedstock was evaluated by its acidity, by its free fatty acids content, by its saponification index and its specific mass. The Biodiesel produced was characterized by high performance liquid chromatography. The results showed significant free fatty acids and humidity content, which are the main factors in the raising of the production costs. The results also showed that the esterification of the vegetable oils reduced its acidity in about 99%. The transesterification of the Brazilian nut oil previously esterified yields about 98% of biodiesel. Even though the biodiesel processing presents an alternative to the energetic self-sufficiency of Brazil, there are many challenges in the adequacy of these high acidity oils and fats for its production. <![CDATA[ELECTROCHEMICAL TREATMENT OF WASTEWATER FROM BIODIESEL PRODUCTION USING A DSA KIND ELECTRODE: Ti/IrO<sub>2</sub>-Nb<sub>2</sub>O<sub>5</sub>]]> This work presents the electrochemical treatment of wastewater of biodiesel production, using DSA based on IrO2 and Nb2O5. The anode was prepared by modified Pechini method and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), in order to evaluate structural and morphological properties and by electrochemical impedance spectroscopy, cyclic voltammetry and accelerated stability test to investigate the electrochemical behavior. The SEM image shows the typical mud-cracked layer. By the XRD measurements, the oxides onto the support were crystallized as tetragonal IrO2 and hexagonal Nb2O5. The amount of glycerin and methanol in the wastewater were 1.60 and 0.31% (w/w), respectively. The electrochemical treatment of the wastewater was evaluated by electrolysis at different current densities and time. The total organic carbon (TOC) and UV-Vis spectra were performed during the electrolysis. The UV-Vis spectra obtained during the electrolysis at 100 and 150 mA cm-2, shows the disappearance of an absorption band at 264 nm and the appearance of one at 290 nm, which the absorption increases as current and the time of the electrolysis increases. The electrochemical treatment with the proposed DSA leads to 80% of removal of TOC by electrolysis at 150 mA cm-2 during the first 6 hours of the electrochemical treatment. <![CDATA[ALCOHOLIC FERMENTATION OF HEMICELLULOSIC HYDROLYZATE FROM SUNFLOWER CAKE BY <em>Galactomyces geotrichum</em> UFVJM-R10 AND <em>Candida akabanensis</em> UFVJM-R131]]> The use of the hemicellulosic fraction of plants for the production of second generation bioethanol depends on microorganisms capable to ferment pentoses. Two yeast strains habile to xylose fermenting in synthetic medium, Candida akabanensis UFVJM-R131 and Galactomyces geotrichum UFVJM-R10, not yet registered in the literature for the production of bioethanol, were evaluated here in the alcoholic fermentation of the hemicellulosic hydrolyzate from sunflower cake. The biomass hydrolysis was performed by 38 minutes at 120 °C / 1 atm with 6% H2SO4 solution and solid / liquid ratio of 1:3.2. Chromatographic characterization of the hemicellulosic hydrolyzate showed the presence of glucose (7.57 g L-1), xylose (19.53 g L-1) and arabinose (8.85 g L-1), besides 5-hydroxymethylfurfural (0.71 g L-1), furfural (0.05 g L-1) and acetic acid (5.27 g L-1). Both yeasts were able to produce ethanol from the acid hydrolyzate from sunflower cake. The fermentation carried out with G. geotrichum UFVJM-R10 and C. akabanensis UFVJM-R131 presented YP/S values of 0.29 and 0.27 g ethanol g-1sugars, respectively. The amounts of the inhibitors identified in the hydrolyzate did not affect the efficiency of the alcoholic fermentation. The supplementation of the hydrolyzate with nitrogen and mineral sources increased the rate of consumption of xylose and arabinose. <![CDATA[CALCULATION OF CATALYTIC REACTIVITY FOR PREPARING DICHLORODIMETHYLSILANE UTILIZING PRE- AND POST-MODIFIED 24T AlCl<sub>3</sub>/ZSM-5]]> Dichlorodimethylsilane is the most important raw material for the preparation of organic silicon materials. Currently, the preparation of dichlorodimethylsilane is mainly based on disproportionation method. This method can turn wastes (by-products) into treasures but the mechanism is still indeterminate. In this study, MP2/6-311++G (3df, 2pd) basis set was used to study the mechanism of the disproportionation for producing dichlorodimethylsilane. Dichlorodimethylsilane is catalyzed by 24T cluster AlCl3/ZSM-5 catalyst and modified by (AlCl2)+, and (BCl2)+. The calculation results show that the rate-determining step is the reaction of the catalyst with trimethylchlorosilane . The activation energy of the rate-determining step of main reaction is: 393.83, 427.73, and 527.61 kJ mol-1, respectively. The structure analysis, activation energy analysis and LOL analysis for different catalysts all show that the catalytic effect of unmodified AlCl3/ZSM-5 is better. <![CDATA[DEVELOPMENT AND OPTIMIZATION OF A MICROWAVE-ASSISTED EXTRACTION OF PLUMIERIDE FROM <em>Allamanda cathartica</em> L. FLOWERS]]> A simple and efficient microwave-assisted extraction process has been developed in order to extract plumieride from Allamanda cathartica flowers. The extracts have been obtained through microwave-assisted extraction (MAE) process with ethanol and ethyl acetate at different time, power and temperatures. Static maceration at room temperature with ethanol and ethyl acetate was obtained in order to compare the efficiency of extraction. HPLC method was validated to quantify plumieride in the extracts. The analyzed parameters: linearity (R2 = 0.999), precision (CV 3.3%), recovery (98%), specificity (97%), limit of detection (1 µg mL-1), and limit of quantification (2 µg mL-1) were satisfactory. The yield of plumieride reached 43% in the extracts under the optimal MAE conditions (10 min, 300W). Plumieride recoveries by conventional extraction method were 12% with ethanol and 22% with ethyl acetate. Time and power parameters on plumieride extraction yield was determined by applying a factorial design and surface plots. Ethanol was the best extractor solvent and it was possible to obtain high contents (52 mg g-1 of dry flowers) at optimized conditions. It can be concluded that MAE process has actual advantages over the conventional extraction method in terms of shorter time and higher efficiency to recover plumieride from A. cathartica flowers. <![CDATA[SEQUENTIAL INJECTION ANALYSIS WITH SQUARE WAVE VOLTAMMETRY DETECTION AT GOLD ELECTRODE FOR DETERMINATION OF As(III) IN WATER SAMPLES]]> A sequential injection method with square wave anodic stripping voltammetry (SI-SWASV) using screen printed and crystalline gold electrode was developed for determination of As(III). The carrier solution used for electrode conditioning and stripping medium was composed of 0.050 mol L-1 HCl, whereas the supporting electrode for samples (deposition medium) was 0.50 mol L-1 HCl. The limits of detection and quantification were 20 and 70 nmol L-1 (1.5 and 5.2 µg L-1), respectively. This limit of quantification is almost two times lower than the maximum concentration of As(III) allowed in waters by World Health Organization (10 µg L-1). The sampling throughput was 20 analyses per hour using a sample volume of 1500 µL, pumped through the flow cell at the flow rate of 15 µL s-1. Screen printed gold electrodes were not suitable for work with 0.50 mol L-1 HCl because the results were strongly dependent on the lot of sensors. Crystalline gold electrodes provided reproducible results and the method was applied for determination of As(III) in river water samples. The accuracy was evaluated by recovery studies and analyses by Graphite Furnace Atomic Absorption Spectrometry, providing recoveries between 95 and 108%. <![CDATA[DFT STUDY ON THE MECHANISTIC, ENERGETIC AND STRUCTURAL ASPECTS OF ADSORPTION OF TIRAPAZAMINE ONTO PRISTINE AND FUNCTIONALIZED CARBON NANOTUBES]]> Using density functional theory, noncovalent interactions and two mechanisms of covalent functionalization of drug tirapazamine with pristine, COOH and COCl functionalized carbon nanotube (NT, NTCOOH and NTCOCl) have been investigated. Quantum molecular descriptors of noncovalent configurations were studied. It was specified that binding of drug tirapazamine with NTCOOH has more binding energy than NTCOCl and NT, so NTCOOH can act as a favorable system for tirapazamine drug delivery within biological and chemical systems (noncovalent). NTCOOH and NTCOCl can bond to the amino group of tirapazamine through OH (COOH mechanism) and Cl (COCl mechanism) groups, respectively. The activation parameters of two pathways were calculated and compared with each other. The activation parameters related to COOH mechanism are higher than those related to COCl mechanism and therefore COCl mechanism is suitable for covalent functionalization. These results could be generalized to other similar drugs. <![CDATA[ALTERNATIVE SOURCE APPORTIONMENT IN THE SURROUNDING REGION OF A LARGE STEEL INDUSTRY APPLYING <em>Tillandsia usneoides</em> AS BIOMONITOR]]> From the beginning of its operation, this large steel industrial complex in the Santa Cruz Industrial District, Rio de Janeiro, Brazil, with an annual capacity of 5 million tons, has been at the center of controversy related to its atmospheric emissions. Since the air filter used for its routine air particulate monitoring network is not appropriate for a source apportionment study, biomonitoring was tested as an alternative way to carry out this evaluation. Thus, the bromeliad species Tillandsia usneoides was used as a bioindicator in the Santa Cruz Industrial District, Rio de Janeiro, Brazil. Six samplings were performed over a period of approximately one year. The results showed that the sampling point located inside the industrial complex presented higher elemental concentration values for all samples. Among the quantifiable elements found in the biomonitor samples, iron seems to be the element that best represents the emissions from the steelwork complex, which was corroborated based on the analysis of dust jar samples collected inside the complex area. <![CDATA[PEROVSKITES SOLAR CELLS: A NEW EMERGING TECHNOLOGY]]> Solar energy has been considered as an important source of clean and safe energy to overcome the problems associate to the burn of fossil fuels (e.g. climate changes, pollution, health problems, etc.). In the area of photovoltaics, devices that convert solar energy into electricity, perovskites solar cells (PSC) have attracted great attention due to their rapid development, high energy conversion efficiency, diversification of the processing methods and different materials. The fantastic properties of the hybrid perovskite materials, such as high absorption coefficient, direct and tunable bandgap, ambipolar charge carrier, simple preparation, etc., have quoted this technology as one the most important in this century. The rapid development of PSC has provided a significant increase in energy conversion efficiency, which was first reported, in 2009, as 3.8% and now reaches up to 22.10%, according to the National Laboratory of Renewable Energy (NREL). Many studies have been carried out to further increase the efficiency of devices and solve problems as the instability of the material, and the presence of lead, so that the PSC can be applied commercially. This paper presents a review on PSC and the major advances reported in device’s architecture, preparation methods, novel materials and interface engineering. <![CDATA[METABOLOMICS: DEFINITIONS, STATE-OF-THE-ART AND REPRESENTATIVE APPLICATIONS]]> Metabolomics is an emerging and promising omics approach used to understand biological mechanisms. By untargeted and targeted metabolomics analyses, metabolites are determined in biological samples (fluids, cells, tissues, etc.) by comparison of control groups with altered groups, undergoing different therapies, submitted to differing stress levels, dietary modulation, or promoted by a disease, or specific condition, etc., using sophisticated analytical techniques, and advanced data treatment and statistical analyses. In this review, the concepts involved in metabolomics studies were presented, describing in details all steps involved in the metabolomics workflow, for untargeted and targeted strategies. Finally, the potential of metabolomics is illustrated by applications in representative areas: clinical, environmental, food and nutrition, forensic toxicology, microbiology, parasitology, plants, and sports. Relevant reviews were compiled to characterize each of these areas, and a corresponding application of untargeted and targeted metabolomics were described. <![CDATA[PREPARATION OF α-ACETYLOXY-<em>N</em>-CYCLOHEXYLAMIDES VIA PASSERINI REACTION USING DIMETHYLCARBONATE AS ECO-FRIENDLY SOLVENT]]> A series of α-acetyloxy-N-cyclohexylamides was efficiently obtained via Passerini reaction of cyclohexyl isocyanide, acetic acid, and different aromatic and aliphatic aldehydes using refluxing dichloromethane or dimethylcarbonate (DMC). Reactions performed with DMC led to desired products in moderate to good yields, corroborating this solvent as a eco-friendly alternative to the chlorinated solvents commonly used in this transformation. The α-acetyloxy-N-cyclohexylamides thus obtained were tested against Escherichia coli, Bacillus cereus, Pseudomonas aeruginosa, and Staphylococcus aureus, as well as promastigote forms of L.(L.) amazonensis. The α-(Acetyloxy)-N-cyclohexyl-pentanamide showed low antibacterial activity against Gram-positive (S. aureus and B. cereus) and Gram negative (E. coli and P. aeruginosa) bacteria (MIC = 8,3-16,5 mmol L-1), while α-(acetyloxy)-N-cyclohexyl-4-bromo-benzeneacetamide showed leishmanicidal activitity (IC50 = 0,099 mmol L-1). <![CDATA[ZEOLITE 4A FOR CLEANSING OF LANDFILL GAS]]> The anaerobic decomposition in landfills produces a gas mixture known as landfill biogas. This biogas consists mainly of CH4 and CO2. The CO2 removal can be carried out by means of adsorption. In order to promote CO2 removal, zeolite type 4A was used as solid adsorbent. The synthesized zeolite was characterized by scanning electron microscopy and X-ray diffraction. CH4/CO2 mixture isotherms were obtained in a magnetic suspension balance equipped with a gas dosing unit and Extended Langmuir and Extended Sips models were used to predict mixture isotherms from monocomponent data. Three biogas emissions drains in a sanitary landfill in Caucaia (Ceará State, Brazil) - ASMOC - were chosen to test the performance of zeolite as CO2 adsorbent under real conditions. Zeolite 4A has proven to be very selective for CO2 even in the presence of H2S. <![CDATA[ASSEMBLY OF LOW-COST LAB-MADE PHOTOREACTOR FOR PREPARATION OF NANOMATERIALS]]> In this paper, a low-cost and versatile lab-made photoreactor was constructed for the preparation of nanomaterials such as gold nanoparticles and reduced graphene oxide. The power of the lab-made photoreactor can be easily adjusted according to the number of lamps turned on. Moreover, the lab-made photoreactor allows the utilization of different sources of irradiation with distinct wavelengths. Performance tests for production of gold nanoparticles showed reproducibility and equal efficiency as compared to the literature. Also, the photoreactor powered with UV-A and UV-C as sources of irradiation can be used for modulation of the reduction degree of graphene oxide. <![CDATA[DIDACTIC APPROACH FOR THE DEVELOPMENT OF BIOATIVE MOLECULES: LIPINSKI’S FIVE-RULE AND PREPARATION OF 1,3,4-OXADIAZOL HETEROCYLIC IN DOMESTIC MICROWAVE OVEN]]> In Brazil, the development of new chemical entities (NEQ) is still limited to small advances in the academic and public research sectors, the authors understand that this is a sector of the pharmaceutical industry that needs encouragement. Accepting that education transforms society, educate students in the development of bioactive molecules, it’s a way to stimulate the national pharmaceutical industry to invest in the sector. Thus, this work brings a didactic sequence, applicable in undergraduate courses, which exemplifies some stages of development of the NEQ through its rational planning. The synthesis of a 1,3,4-oxadiazole heterocycle was planned and its potentiality assessed through the Lipinski’s Rule of Five (RO5), using the ChemSpider® database. Once in accordance with RO5, the heterocycle was prepared using a simple and accessible methodology, using microwaves for domestic use as heating source. The 2-phenyl-5-(pyridin-4-yl)-1,3,4-oxadiazole was synthesized by oxidative cyclization of acylhydrazone and an overall yield of 90%. So was possible to demonstrate in a practical way some steps for the development of a substance with potential biological activity and thus to attract greater interest of undergraduate students by this follow-up of the Medicinal Chemistry. <![CDATA[MECHANOCHEMICAL CHLORINATION OF ACETANILIDE]]> We described herein a solvent-free synthesis of 4-chloroacetanilide both under hand grinding and mechanical grinding of stoichiometric amounts of acetanilide with trichloroisocyanuric acid. The synthetic approach was developed in the context of undergraduate organic chemistry and is the greener preparation of this compound already described.