Tese (Química)

Formação e estabilidade de espumas líquido-gás a partir de soluções aquosas de surfactantes derivados de cardanol.

2023-08-10T00:00:00Z

Formação e estabilidade de espumas líquido-gás a partir de soluções aquosas de surfactantes derivados de cardanol. Lopes, Carolina Ravazzano Azevedo Ferreira, Guilherme Augusto Aqueous foams are liquid-gas dispersions that fall within the colloidal scale and sport multiple applications both in the field of industry and in household products. However, being dispersions, these constitute non-equilibrium systems, making the use of agents capable of promoting their formation and ensuring their kinetic stability a necessity. Surfactants constitute the most common class of such agents. These substances display affinity for both phases (liquid and gas) and contribute to reduce the energy investment needed as of their mixing. Most conventional surfactants are synthesized from petroleum derivatives and count with other undesirable properties from an environmental perspective – such as a toxic effect on marine organisms – and these have prompted the study and development of environmentally friendlier alternatives. In this sense, the present work investigated the formation and stability of foams prepared from aqueous solutions of three non-ionic surfactants derived from cardanol, a compound extracted from the liquid of cashew nutshells that has garnered attention as a sustainable precursor for molecules of interest in a wide variety of industrial fields. The surfactants, which were studied individually and as part of binary mixtures prepared with sodium dodecyl sulfate (SDS), differ between one another only in the number of ethoxy groups (EO) that make up the hydrophilic moieties of their molecules (nEO, n = 7, 9 or 12). Foamability tests were conducted with foams prepared by mechanical agitation of a fixed volume of solution. Foam stability, in its turn, was comparatively assessed for dispersions produced using the Tessari technique. The obtained results were corroborated by studies on the thermoresponsive behavior of the cardanol-derived surfactants, by static and dynamic tensiometry measurements and by dynamic light scattering, turbidity and bulk rheology analyses. No significant synergistic effect was observed for the nEO-SDS mixtures at all tested concentrations; in particular, the stability of foams prepared from these binary solutions proved equal to that attained with SDS solutions of same concentration. For the individual systems, the solutions prepared with the cardanol-derived surfactant with 9 ethoxy units in its hydrophilic moiety (9EO) at 1.0% and 2.0% v/v produced the most kinetically stable foams. The greater stabilization capability of these systems was attributed to the morphology adopted by 9EO aggregates at the temperature at which the experiments were conducted: the aforementioned aggregates constituted elongated, rod-like micelles that entangle with each other, increasing bulk phase viscosity and hindering liquid drainage. The gathered results prove themselves relevant due to the fact that they (1) demonstrate the potential of new, sustainable compounds as ingredients for high-quality foaming formulations as well as (2) evidence the existence of a delicate – and, more often than not, neglected in the specialized literature – balance between the surface properties of a system and the characteristics of its continuous phases. Universidade Federal da Bahia Dissertação

Planejamento, síntese e estudo de novos cristais líquidos luminescentes derivados da triazina

2023-03-06T00:00:00Z

Planejamento, síntese e estudo de novos cristais líquidos luminescentes derivados da triazina Silva, Fabrícia Nunes da Vieira, André Alexandre In this work, two series of discotic molecules were designed, synthesized and characterized, one symmetrical and the other non-symmetrical, both derived from the s-triazine heterocycle. The methodology used initially used the trimerization of benzonitriles in an acid medium and later the triphenyltriazine was functionalized with one, two or three arms of the phenanthryl or [4]helicenyl type from Perkin-Mallory reactions. The final molecules were designed with short-chain alkyl ester-type groups to induce glass transitions and also columnar mesomorphism. All compounds were characterized using spectroscopic and spectrometric techniques. The thermal properties of the final molecules were investigated by DSC, TGA, POM and XRD techniques. The phenanthryl- and helicenyl-substituted symmetrical triazine esters showed glass transitions conveniently above room temperature and within the hexagonal columnar liquid crystal phase, resulting in a solid columnar order at room temperature. Clearing points > 375°C were recorded for phenanthryl derivatives. For the ideal alignment of a liquid crystal, it is important that the melting and clearing temperatures are attainable, which was achieved only for the moderately non-planar symmetrical (> 205°C) helicenyl derivatives. To overcome this challenge, a second series of non-symmetrical molecules was prepared from the functionalization of triphenyltriazine with one or two phenanthryl or helicenyl arms but keeping the methyl benzoate group in the structure. Non-symmetrical triazines also showed hexagonal columnar liquid-crystalline behavior, but with lower melting points (< 290°C). Glass transitions were also observed at approximately 70, 50, 40 and 0°C for the non-symmetrical compounds, depending on the substitution pattern. The photophysical properties were evaluated for the symmetrical triazines in solution and solid phase. The materials showed absorbance between 272-342 nm and emission between 409-458 nm. The average quantum yield was 22% for phenanthryl derivatives and 12% for helicenyl. From the photophysical data it was possible to infer the energies of the first excited singlet state S1 of 3.31 eV for phenanthrenes and 2.95 eV for helicenes. DFT calculations showed good correlation between experimental and calculated energy values for S1 and allowed a good estimate for T1. The calculated values for the T1 orbital of the symmetric triazines are close to 2.5 eV, therefore, these materials can be considered as matrices for TADF emitters that emit light in the yellow-green range of the visible spectrum. Universidade Federal da Bahia Tese

Unindo fisiologia, bioquímica e metabolômica para desvendar respostas aos estresses abióticos da Glycine max e Ricinus communis.

2023-08-01T00:00:00Z

Unindo fisiologia, bioquímica e metabolômica para desvendar respostas aos estresses abióticos da Glycine max e Ricinus communis. Almeida, Catherine Pinheiro de Jesus, Paulo Roberto Ribeiro de Every year, plants suffer various damages caused by climatic conditions, such as drought and high temperatures, which considerably reduce crop yields worldwide. In arid and semi-arid regions, some cultivars are exposed to these two adverse conditions, causing a series of damages, mainly in seed germination, of extreme importance in the life cycle of plants. Glycine max L. Merrill (soybean) is one of the most important crops in the world due to its application in the fuel, chemical, food and agroindustry industries. Soybean plants are highly sensitive to thermal stress, especially in the reproductive phase. Ricinus communis is a plant native to Africa and Asia, belonging to the Euphorbiaceae family. It is a very productive and resistant culture, being easily cultivated in drier and hotter regions. Unlike cultures like soybeans that are sensitive to high temperatures, Ricinus communis manages to present good production results even under thermal stress. The main objective of this study is to characterize the GDSL esterase/lipase gene from Ricinus communis (RcGELP) and to evaluate the effect of its overexpression and silencing in Arabidopsis thaliana against abiotic stresses, and to evaluate the metabolome of soybean seeds against stress thermal. To achieve this objective, the germination of A. thaliana seeds that overexpress and silence the RcGELP gene against water and heat stress will be evaluated, as well as to identify and quantify primary metabolites in the seeds. Seed germination and establishment of soybean seedlings will also be evaluated at high temperature, followed by metabolomics analysis. As one of the main results, it is expected to relate the metabolomic analyzes with the behavior of seeds during germination under abiotic stress and the function that the GDSL esterase/lipase gene confers on A. thaliana seeds. Studies like this one can contribute to the understanding of the molecular and biochemical aspects of the mechanisms related to germination and establishment of seedlings in the face of abiotic stresses. Universidade Federal da Bahia Dissertação

Microextração líquido-líquido em fase reversa para a determinação de metais em óleo diesel e óleos vegetais por espectrometria de fluorescência de raios-X por dispersão de energia.

2023-03-01T00:00:00Z

Microextração líquido-líquido em fase reversa para a determinação de metais em óleo diesel e óleos vegetais por espectrometria de fluorescência de raios-X por dispersão de energia. Ferreira, Vanessa de Jesus Teixeira, Leonardo Sena Gomes X-ray fluorescence spectrometry (XRF) has been widely used for multielement determination in various samples. However, when quantifying inorganic species to trace amounts is required, separation and preconcentration procedures are often used to reduce interference and increase sensitivity. Liquid phase microextraction (LPME) is one of the most well-known and applied pretreatment techniques in various methods for analyzing traces due to its simplicity, speed, and ease of automation. The three main categories of LPME are single-drop microextraction (SDME), dispersive liquid-liquid microextraction (DLLME), and liquid phase microextraction of hollow fiber (HF-LPME). Two methods were developed using reversed-phase liquid-liquid microextraction (RP-LLME) combined with energy dispersion X-ray fluorescence spectrometry (EDXRF). The first method is based on vortex-assisted reverse-phase liquid-liquid microextraction (RP-VALLME) to determine Cu, Mn, Ni, and Pb in diesel oil samples by EDXRF. Nitric acid solution was the extraction phase. After centrifugation, the aqueous phase was placed into a filter paper disc for EDXRF determinations. The following variables were optimized: type of extraction phase solution (HNO3), extraction phase concentration (0.075 mol L-1), stirring time (45s), and sample volume (5.0mL). The limits of detection and enrichment factors were, respectively: 14 μg L-1 and 34 (Cu), 8 μg L-1 and 62 (Mn), 10 μg L-1 and 59 (Ni), and 7 μg L-1 and 64 (Pb). The method's relative standard deviation (RSD, %) for each element (200 μg L-1 and 400 μg L-1) ranged from 2.1 to 6.4%. The proposed procedure was efficiently applied to determine the four analyses in diesel oil samples. The second method used dynamic RP-LLME to prepare edible oil samples for subsequent determination of Cd, Cr, Mn, and Ni by EDXRF. The microextraction procedure is based on a system in which the donor phase flows through the extractor solvent contained in an extraction chamber. Then, the enriched phase is deposited in filter paper and subjected to detection. Type and concentration of extractor solution (HNO3 0.1 mol L-1), sample flow (10.0 mL min -1), and extraction time (15 min) were optimized parameters. The following limits of detection and enrichment factors were obtained, respectively: 6 μg kg-1 and 100 (Cd), 7 μg kg-1 and 65 (Cr), 8 μg kg-1 and 82 (Mn), and 11 μg kg-1 and 74 (Ni). The proposed method was applied to determine the elements in soybean, sunflower, corn, and canola oils samples. The results were compared with those obtained by inductively coupled plasma optical emission spectrometry (ICP OES). The methods developed are an excellent alternative for determining elements in oil samples due to the advantages obtained, such as simplicity, speed, little waste generation, sensitivity, and the possibility of automation and miniaturization. Universidade Federal da Bahia Tese