Scielo RSS <![CDATA[Química Nova]]> vol. 39 num. 9 lang. en <![CDATA[SciELO Logo]]> <![CDATA[THE FORMATION OF PROTECTIVE IRON CARBONATE FILMS AND THE CONTROL OF CO<sub>2</sub> CORROSION IN TURBULENT FLOW]]> The formation of a protective layer of iron carbonate (FeCO3) can reduce the rates of corrosion and prolong the useful life of carbon steel. However, turbulent flow conditions in this layer can easily be damaged and thus compromise the protection of the steel. In this work, will be presented a methodology based on the chemical aspects of the mechanism of formation of iron carbonate layer in a Thin Channel Flow Cell (TCFC). Electrochemical techniques were used to measure the corrosion rate and corrosion potential on the surface of steel API X65 exposed to aqueous solution of 1 wt.% NaCl purged with CO2 at 2 atm, pH 6.6 and 80°C in turbulent flow conditions. The surfaces and cross sections of the samples were characterized by means of Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDS) analysis. The results confirm the nucleation and growth of iron carbonate layer: the extension of supersaturation of the solution and the corrosion rate have decreased, and the corrosion potential has increased. The surface analysis showed dense and uniform FeCO3 layer with c.a. 20 µm thick after 120 hours in turbulent flow conditions. <![CDATA[LIPID NANOSTRUCTURED CARRIERS SYSTEMS FOR IVERMECTIN AND METHOPRENE AIMING PARASITE CONTROL]]> The study of characteristics of nanoscale structures and applications now has great interest of researchers from different areas. In this regard, lipid carriers can improve the bioavailability of drugs and the reduction of possible toxicological effects. Thus, the development of nanostructured systems for the agricultural sector, aimed at combating parasites may reduce extensive damage caused to livestock producers and animal health. This study aimed to prepare and characterize lipid carrier systems, such as Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC), as well as evaluate the potential of cyto and genotoxicity of these systems in order to improve and produce alternatives to the use targeting these compounds in veterinary applications. Lipid nanoparticles had become spherical with an average size of 250 nm and remained stable over 120 days. The encapsulation efficiency was greater than 99% for both drugs and release tests showed a strong interaction between drugs and nanoparticles. Cyto- and genotoxicity tests show that nanoparticles made possible changes in cellular viability of the tested cells. Thus, the results showed that the nanoparticles had good colloidal characteristics without changes in its characteristics, enabling the development of carrier systems for these drugs , aiming veterinary applications. <![CDATA[MODIFICATION OF POLYAMIDE MEMBRANE BY SOL-GEL AND INCORPORATION OF LUMINESCENT EUROPIUM (III) COMPLEX]]> Over the last decades, the combination of different technologies to search for systems with new properties and features has brought various segments of biological and earth sciences together. Additive manufacturing, known as rapid prototyping, combined with the sol-gel methodology enables the production of novel systems with applications in many scientific fields. In this work, flexible polyamide membranes were obtained by additive manufacturing, functionalized by the sol-gel methodology, and incorporated with the coordination compound between Eu(III) and 1,10-phenanthroline. The presence of vibrations at 1100 cm-1 in the FTIR spectrum of the material, which is a band typical of the Si-O-Si group in the alkoxide employed during the process, confirmed the polyamide membrane functionalization. The thermogravimetric curve showed that a residue remained after heating at 700 ºC, which was attributed to SiO2. The membrane was highly luminescent, which confirmed incorporation of the Eu3+ compound into the material and pointed to the possible application of this system as a topical medication for the treatment of skin diseases. <![CDATA[ELECTROCHEMICAL OXIDATION OF REACTIVE BLACK 5 AND BLUE 19 DYES USING A NON COMMERCIAL BORONDOPED DIAMOND ELECTRODE]]> We have studied the treatment of Reactive Black 5 (RP5) and Blue 19 (RA19), which are respectively azo and anthraquinone textile dyes, by electrochemical oxidation using a non commercial boron doped diamond electrode supported on titanium metallic with a relation between B and C equal to 15,000 ppm. Pt was used as counter electrode and Ag/AgCl(sat) was the reference electrode. The variables investigated to optimize the degradation were support electrolyte concentration (0.05, 0.1 and 0.2 mol L-1 of K2SO4), temperature (25, 35 and 45 ºC) and pH (2.5 and 10) by applying a current density of 75 mA cm-2. Total decolorization was observed in all electrochemical conditions studied. The highest rates of mineralization and chromatographic area removal were attained at high support electrolyte concentration due to the increase of conductivity, which caused more generation of hydroxyl radicals. RP5 was degraded at lower electrolysis time than RA19 with smaller requirement of electric charge. The mineralization rate increased in acid medium and at higher temperature since the increase in temperature favors the generation reactions of persulfate. These conditions led to the highest levels of current efficiencies and lower energy consumed. <![CDATA[BIODEGRADABLE FILMS OF CASSAVA STARCH, PULLULAN AND BACTERIAL CELLULOSE]]> The largest consumption of plastics in the world is referred to the synthetic polymers, which are not biodegradable and have a non-renewable source, generating a large environmental impact, especially in urban centers. As a result, in the last two decades several polymers obtained from renewable sources (biopolymers) have been studied as potential raw materials for the production of new biodegradable materials with different applications. The objectives of this study were to produce biodegradable films based on cassava starch, pullulan and bacterial cellulose, and also to characterize these films according to their microstructure, barrier, thermal and mechanical properties. The addition of bacterial cellulose and pullulan to the starch films resulted in films with more homogeneous surfaces, and also decreased solubility and water vapor permeability, and increased elongation and thermal stability. <![CDATA[SIMULTANEOUS DETERMINATION OF METALS AND SULFUR IN CRUDE OIL DISTILLATION RESIDUES BY ICP-OES]]> A method for digestion of crude oil distillation residues (atmospheric residue, AR and vacuum residue, VR) using microwave-induced combustion (MIC) was developed for simultaneous determination of metals (Ba, Co, Fe, Mg, Mn, Ni and V) and sulfur by inductively coupled plasma optical emission spectrometry (ICP-OES). Samples were wrapped in polyethylene films and combusted using 20 bar of oxygen. Nitric acid solutions were evaluated using 5 min of reflux after combustion. Accuracy was evaluated using certified reference material and comparison with the results obtained by microwave-assisted wet digestion (MAWD). No statistical difference was observed between the certified values and those obtained using MIC as well as between the values obtained using MAWD or MIC. In spite of both methods have been apparently suitable for crude oil digestion, MIC was preferable in view of the possibility of using 3 mol L-1 HNO3 as absorbing solution. Furthermore, it is important to notice that using MIC, C content in digests was lower than 10 mg L-1, preventing interferences in ICP-OES. In addition, the simultaneous digestion of eight samples was possible in less than 30 min and without using concentrated acids and/or longer heating times, making the proposed method well-suited for routine analysis. <![CDATA[THE USE OF A NOVEL ALDEHYDE-FUNCTIONALIZED CHITOSAN HYDROGEL TO PREPARE POROUS TUBULAR SCAFFOLDS FOR VASCULAR TISSUE ENGINEERING APPLICATIONS]]> In this work, porous tubular scaffolds were prepared from a novel water soluble aldehyde-functionalized chitosan (ALDCHIT) hydrogel, which was obtained by dissolving this chitosan derivative in water and using oxidized dextrose (OXDEXT) as the crosslinking agent at different ALDCHIT:OXDEXT mole ratios (10:1, 10:2 and 10:4). By increasing the amount of OXDEXT in respect to ALDCHIT the hydrogels became more rigid and could absorb more than 200% of its weight in water. Since the ALDCHIT:OXDEXT 10:4 was the most stable hydrogel, its ability to form porous tubular scaffolds was investigated. The tubular scaffolds were prepared by the lyophilization method, where the orientation of the pores was controlled by exposing either the internal or the external surface of the frozen hydrogel during the sublimation step. When only the inner surface of the frozen hydrogel was exposed, tubular scaffolds with a highly porous lumen and a sealed outer surface were obtained, where the orientation of the pores, their sizes and interconnectivity seem to be optimum for vascular tissue engineering application. <![CDATA[BIOSSORPTION OF Pb(II) BY URUCUM SHELLS (<em>Bixa orellana</em>) IN AQUEOUS SOLUTIONS: KINETIC, EQUILIBRIUM AND THERMODYNAMIC STUDY]]> This study describes the application of new and low cost biosorbent, shells of urucum (Bixa Orellana), for removal of lead ions (Pb(II)) from water solution. The urucum shells were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Batch adsorption experiments were performed in order to evaluate the effect of pH, agitation speed, adsorbent dosage, contact time, temperature, presence of interfering ions and matrix effect on the adsorption of process. The kinetics of biosorption followed pseudo-second-order model. Langmuir and Freundlich isotherm models were applied to describe the biosorption of Pb(II) by urucum shells. The Langmuir model showed better fit and the estimated biosorption capacity was 43.6 mg g-1. The negative Gibbs free energy, ΔG°, confirms the spontaneous nature and positive value of enthalpy, ΔH°, the endothermic character of the process. Furthermore, we also performed an evaluation of matrix and others ions effect on the biosorption process. <![CDATA[THE PARADIGM OF PROTON DONOR STRUCTURE ON HYDROGEN BOND FORMATION: C<sub>2</sub>H<sub>2</sub>···6(HF) COMPLEX]]> The DFT, QTAIM, NBO and ChelpG methods were used in a theoretical study of structural parameters, vibration stretch modes and absorption intensities, electronic properties, molecular orbital analyses and molecular topography of the heptamer C2H2···6(HF) complex. One of the great aims concerns to the studying of the proton donor structure, which is considered as two 3(HF) cyclic moieties. The structures of the HF trimer interact with acetylene in an opened configuration because the energies of the F···HF hydrogen bonds are enhanced from 34.45 to 58.43 as well as 61.48 kJ.mol-1. Moreover, instead of the unusual π····H hydrogen bonds formed on the middle of the π bond of acetylene, the more uncommon C···H contact was certified. The red-shifts on the stretch frequencies of HF bonds were evaluated aiming to unveil the covalent character in the F···HF hydrogen bonds. <![CDATA[CHEMICAL CONSTITUENTS AND <em>IN VIVO</em> ANTIOXIDANT ACTIVITY OF FLAVONOIDS ISOLATED OF <em>Clusia lanceolata</em> (Clusiaceae)]]> The phytochemical investigation of Clusia lanceolata leaves yielded fourteen compounds including six flavones, vitexin, isovitexin, isovitexin-2"-O-α-L-rhamnopyranoside, vitexin-2"-O-α-L-rhamnopyranoside, orientin and isoorientin, two phaeophytins [132-hydroxy-(132-S-)-phaeophytin a and 132-hydroxy-(132-R)-phaeophytin a], two triterpenes, α- and β-amyrin, and four steroids, β-sitosterol, stigmasterol, sitosterone and stigmasterone. Their structures were assigned based on spectroscopic analysis, including two-dimensional NMR techniques and comparison with literature data. The antioxidant capacity in vivo of vitexin and mixing isovitexin-2"-O-α-L-rhamnopyranoside and vitexin-2"-O-α-L-rhamnopyranoside was evaluated using the yeast Saccharomyces cerevisiae as the biological system model and hydrogen peroxide as a stressor agent. The results showed that the tested flavonoids were able to protect the yeast cell against the oxidative damage caused by H2O2. <![CDATA[LOCALIZED SURFACE PLASMON RESSONANCE APPLIED TO BIOSENSORS AND SOLAR CELLS]]> Within the last decades, the research on nanoparticles presenting localized surface plasmon resonance has increased constantly. In these materials, the interaction between electrons and incident light results in charge separation, enhancement of the electromagnetic field on the nanoparticles surface and in unique optical properties. Although many metals such as gold, silver, copper and aluminum present localized surface plasmon resonance within the visible range, gold and silver are the most commonly studied metals, due to the chemical inertia of gold and intense plasmon resonance from silver. In this review, we provide a description of the origin of localized surface plasmon resonance through the works developed by Mie, Maxwell and Maxwell-Garnett and a description of many examples of application of plasmonic nanoparticles on biosensors and solar cells, detailing the contribution of these plasmonic nanoparticles on the performance of these devices. <![CDATA[COCRYSTALS: A PROMISING STRATEGY IN PHARMACEUTICAL SCIENCES]]> Pharmaceutical cocrystals have emerged as a useful strategy to improve the aqueous solubility of poorly water soluble drugs by aiming to enhance their oral absorption and bioavailability. Aqueous cocrystal solubility can be orders of magnitude higher than that of the constituent drug and this solubility advantage can be fine-tuned based on environmental conditions such as pH and the presence of drug solubilizing agents. This review presents a brief overview of pharmaceutical cocrystals regarding cocrystal design, obtainment methods, with particular focus on cocrystal solubility, and the solubility modulation by solution phase chemistry. <![CDATA[ANALYSIS OF THERMAL AND AQUEOUS SUSPENSION STABILITIES OF CHITOSAN BASED NANOENCAPSULATED VITAMINS]]> The food nutritional content is reduced as result of vitamins degradation. In order to minimize such losses, the encapsulation technique into polymeric nanoparticles (NPs) could offer an additional protection, extending the stability. The crosslinking formed by the ionic gelation process of chitosan and tripolyphosphate (Chi-TPP) has been widely used as an encapsulating matrix for several chemical compounds. In this way, Chi-TPP was used for encapsulation of C, B9 and B12 vitamins. The stability of the vitamins in NPs was evaluated in aqueous suspension by UV-Visible spectroscopy under different conditions: stored in dark, light exposure and effect of oxygen bubbling. The results indicated that encapsulation had a positive effect in preserving the vitamins, mainly vitamin C. The encapsulation preserved 47% of the initial concentration of vitamin C by the tenth day and around 28% after 17 days. Conversely, in non-encapsulated controls (neutral and acidic medium) the losses were higher, reaching 13% by the tenth day and almost 3% after 17 days of storage in both medium. When exposed to light and O2 the protection provided by the encapsulation was even greater. By thermogravimetric analysis, the pure and the encapsulated vitamins showed distinct thermal behavior confirming Chi-TPP as a potential encapsulation material. <![CDATA[SIMULTANEOUS ANALYSIS OF BIOLOGICAL INDICATORS OF EXPOSURE TO ETHYLBENZENE, STYRENE, TOLUENE AND XYLENE SOLVENTS IN URINE BY HPLC-UV]]> A method for simultaneous analysis of phenylglyoxylic (PGA), mandelic (MA), hippuric (HA), orto-, meta- and para-methylhippuric (o-, m- and p-MHA) acids in urine, by high performance liquid chromatography with UV detection was developed and validated. The substances are biotransformation products used as biological indicators to assess the exposure of workers, respectively, to ethylbenzene, styrene, toluene and xylene. The urinary metabolites were separated using a C18 column and a mixture of 5 mM phosphate buffer pH 2.6:acetonitrile (92:8, v/v) as mobile phase. Urine samples were extracted with dichloromethane:ethyl acetate (70:30, v/v). The method used phenacetin as internal standard and was linear in the interval of 100-500 µg mL-1 for PGA and MA and 150-700 µg mL-1 for HA and MHA. The detection limits in µg mL-1, were 19.8 for PGA, 1.7 for MA, 4.1 for HA, 3.9 for o-MHA, 3.3 for m-MHA and 7.3 for p-MHA. Intra- and inter-assay precisions (as relative standard deviation) were all less than 15% and accuracy (as relative standard error) did not exceed 12.3%. The recovery was higher than 65% for all metabolites. The developed method will be applied to biological evaluation of workers exposure to these solvents. <![CDATA[BREATHING AND INSTRUCTING WITH AIR]]> A set of quasi-quantitative experiments are described to relate volume and pressure variations associated to the phase changes of the main components of the air. The processes are promoted by variation of temperature using liquid nitrogen to refrigerate the air and get liquid oxygen, traces of dry ice and ice. The changes in volume and pressure associated to oxygen phase changes are used to discuss and rationalize phenomena as different as the effects of intermolecular forces on the properties of substances, industrial accidents resulting from a sudden pressure increase due to undesired reactions or even rationalize how popcorns are made. The ludic character of some of the experiments aims to promote the interest and curiosity of youngsters on scientific issues. <![CDATA[THE CHEMISTRY OF INDIGENOUS PEOPLE OF SOUTHAMERICA]]> The contribution of non-European cultures to science and technology, primarily to chemistry, has gained very little attentions until now. Especially the high technological intelligence and inventiveness of South American native populations shall be put into a different light by our contribution. The purpose of this essay is to show that mainly in the area of chemical practices the indigenous competence was considerable and has led to inventions profitable nowadays to millions of people in the western world and especially to the pharmacy corporations. We would like to illustrate this assumption by giving some examples of chemical practices of transformation of substances, mainly those unknown in the Old World. The indigenous capacity to gain and to transform substances shall be shown here by the manufacture of poisons, such as curare or the extraction of toxic substances of plants, like during the fabrication of manioc flower. We shall mention as well other processes of multi-stage transformations and the discovery and the use of highly effective natural substances by Amazonian native populations, such as, for example, rubber, ichthyotoxic substances or psychoactive drugs.