Teses em Química (Doutorado) - PPGQ/ICEN

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/4047

O Doutorado Acadêmico pertence ao Programa de Pós-Graduação em Química (PPGQ) do Instituto de Ciências Exatas e Naturais (ICEN) da Universidade Federal do Pará (UFPA).

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Agora exibindo 1 - 5 de 5

Acesso aberto (Open Access)
Estudo computacional de arilpiperidina e arilpiperazina como inibidores de tirosinase: aplicações cosméticas e terapêuticas
(Universidade Federal do Pará, 2025-04-08) BENTES, Beatriz Alves; SILVA, José Rogério de Araújo; SILVA, Jerônimo Lameira; http://lattes.cnpq.br/7711489635465954
Tyrosinases (TYR) catalyze the oxidation of phenols and catechols, playing a crucial role in melanogenesis, which regulates melanin production and provides protection against UV radiation. However, pigmentation-related disorders drive the search for effective TYR inhibitors. Compounds such as hydroquinone, arbutin, and kojic acid have limitations, highlighting the need for new inhibitors. In this study, arylpiperidine- and arylpiperazine-based compounds demonstrated potent inhibitory activity against TYR. Computational analysis included molecular docking, molecular dynamics (MD) simulations, and binding free energy calculations using the Linear Interaction Energy (LIE) method, revealing a strong correlation with experimental affinity data. To enhance the understanding of structure-activity relationships (SAR), Free Energy Perturbation (FEP) transformations were performed for selected ligand pairs. Additionally, Density Functional Theory (DFT) calculations were applied to inhibitors L04 and L19, enabling the determination of electronic descriptors and frontier molecular orbitals. The inhibitors interact with TYR mainly through electrostatic interactions with the copper ion and van der Waals forces with critical residues such as Phe197, Pro201, Val218, Asn205, and Arg209. These findings are promising for both cosmetic and therapeutic applications, enabling the development of skin-lightening agents to treat melasma and sunspots, as well as potential treatments for hyperpigmentation-related diseases and melanomas. The development of more selective inhibitors with lower toxicity may expand the clinical and cosmetic use of these compounds, offering safer and more effective alternatives for melanin production modulation.
Acesso aberto (Open Access)
Intercalação do ibuprofeno em hidróxidos duplos lamelares: caracterizações físico-químicas e avaliações biológicas
(Universidade Federal do Pará, 2016-10-14) SOUSA, Paulo Robson Monteiro de; ALVES, Claudio Nahum; http://lattes.cnpq.br/8315600067791313; SILVA, Jerônimo Lameira; http://lattes.cnpq.br/7711489635465954
Ibuprofen-intercalated layered double hydroxides (LDH-IBU) have been successfully synthesized via a co-precipitation method with a nominal [Al3+]/[Mg2+] ratio of 0.5 and a variable molar IBU/([Al3+]+[Mg2+]) ratio of 0, 0.15, 0.18, 0.24, 0.36 and 0.72. After an accurate determination of the composition, the nature of the intercalated species and the effective intercalation yield from NO3 - to IBU, it is shown that the synthesis route used allows a good control of the quantity of intercalated IBU within the LDH framework. This results in different samples with full or partial IBU intercalation in the interlayer space in exchange of nitrate anions. The analysis of the X-ray diffraction basal reflections reveals that the intercalation of IBU in the framework only increases the basal distances with no alteration of the brucite-type layers. Also, a computational study used to model the positions and shapes of the basal reflections showed that the structure of the non-fully intercalated compounds follows a random interstratification scheme. Finally three samples ranging from slightly to fully IBU-intercalated galleries were selected for preliminary in vivo assays. These tests showed a strong tendency that after 24 hours the low yield of IBUintercalated compounds are almost as efficient as the fully intercalated sample.
Acesso aberto (Open Access)
Investigação de metabólitos secundários de folhas de Derris urucu (Killip et Smith) Macbr. com atividades biológicas
(Universidade Federal do Pará, 2009-06-30) LÔBO, Lívia Trindade; SILVA, Milton Nascimento da; http://lattes.cnpq.br/6742390457977989; ARRUDA, Mara Silvia Pinheiro; http://lattes.cnpq.br/8047078292358267
Derris urucu, belonging to the family Leguminosae / Fabaceae, is popularly known as “timbó”. The roots of this species are commonly used as pesticides and poison to fish. From Derris genus many phytochemical studies have been reported, the roots being of the most studied part from the plants of this genus. The name “timbó” is most general for the species Derris urucu and Derris nicou, which are the species that produce, in their roots, rotenoids such as rotenone and deguelin, from which derives the importance of these plants. The extracts, and the substances isolated from this genus are responsible for a wide range of biological activities, mainly the insecticidal activity. From the ethanolic extract of leaves of D. urucu, twelve compounds were isolated and purified by High Performance Liquid Chromatography: five stilbenes, six dihydroflavonols and one flavanone. The structural identification was based on the mass, 1H and 13C NMR spectrometric analysis and two dimensional NMR, beyond comparison with literature data . The ethanolic extract of leaves of D. urucu was submitted to bioassays to avaluate the allelophatic potential, presenting relevant percentage of inhibition of seed germination and development of weeds in pastures. Aiming to detect the substances responsible for allelophatic activity, three stilbenes and three dihydroflavonols were selected and submitted to bioassays of inhibition of germination and development of the radicle and hypocotyl of weeds. The allelophatic tests were performed with the substances isolated and with the combination of them, aiming to assess the synergism between them, but the magnitude of inhibition observed was very low. By other side, when the substances were tested in mixtures there was a significant increase in the percentage of inhibition, so these substances in mixtures, can be considered promising for future studies involving allelophatic activity. An other test was carried out with the isolated compounds. Three stilbenes and five dihydroflavonols were evaluated for DPPH radical scavenging activity (antioxidant activity). In this bioassay, was not observed a significant antioxidant activity, justified by the analysis in the structures of the substances tested.
Acesso aberto (Open Access)
Produção de biodiesel metílico e etílico de oleaginosas Amazônicas: caracterização físico-química e estudos térmico e cinético
(Universidade Federal do Pará, 2016-01-29) LIMA, Rogério Pereira; ROCHA FILHO, Geraldo Narciso da; http://lattes.cnpq.br/7580236895339455
This study aimed to synthesize methyl and ethyl biodiesel from six amazonian species of vegetable oils and fat through the transesterification reaction process using alkaline homogeneous catalysis, determine the heat capacity values of oils and methyl and ethyl biodiesel by differential scanning calorimetry (DSC) in the temperature range of 55 to 195°C, and correlate with information estimated by the group contribution method, to investigate the thermal stability of oils and biodiesel produced by thermogravimetric analysis (TG/DTG) and perform kinetic study of the decomposition thermal of biodiesels using the Ozawa method. Classic physicochemical analysis for the characterization the vegetable oils and the biodiesel synthesized samples were used. The results for the physicochemical properties of methyl biodiesel samples were consistent with the values specified by the Resolution No. 45 of 2014 of the National Agency of Petroleum, Natural Gas and Biofuels (RANP 45/14). The results of heat capacity determined by DSC showed that the methyl biodiesel pracaxi showed the highest values, while for ethyl, it was observed for the biodiesel buriti, andiroba and pracaxi. Most heat capacity data obtained for the methyl and ethyl biodiesel determined by DSC and by the group contribution method were satisfactory, as they showed smaller relative deviations or equal to 15% and showed good correlation coefficients ranged from 0, 8617 to 0.9947. The studies on the thermal stability by thermogravimetric analysis indicated that the oils and fat were stable in the temperature range of 110 to 220°C, in inert atmosphere and, in an oxidizing atmosphere, were thermally stable to 130 at 165°C. All the synthesized biodiesel samples is degraded at temperatures up to 150°C, which is highly volatile, a very important feature for the application in diesel engines. The kinetic study of the thermal decomposition of the methyl and ethyl biodiesel met activation energy values ranging from the 46.23 124.93 kJ.mol-1 and showed that the ethyl biodiesel were more stable than the methyl biodiesel.
Acesso aberto (Open Access)
Técnicas voltamétricas com eletrodo de filme de bismuto modificado com edta e ebt para determinação de Ca2+ e Mg2+ em biodiesel
(Universidade Federal do Pará, 2016-08-19) MULLER, Renata Medeiros Lobo; MARQUES, Aldalea Lopes Brandes; http://lattes.cnpq.br/0121030502015990; MÜLLER, Regina Celi Sarkis; http://lattes.cnpq.br/654941494386147
This study presents the development of alternative electrochemical methods for the determination of Mg2+ and Ca2+ through voltammetry technique of adsorptive stripping voltammetry (VAdR) with anodic scan. Bismuth film electrode modified with eriochrome black-T (EBT) was used for modification of the electrode in the determination of Mg2+ in the pulse differential mode (DPAdSV), while EDTA has been used for determination of Ca2+ in wave mode square (SWAdSV). The determination of Mg2+ was performed using acetate buffer (0.1 mol L-1) at pH = 4.5, EBT as supporting electrolyte and 1.0 x 10-3 mol L-1 as a binder. Successive additions of aliquots of the stock solution were made Mg2+ 1.0 x 10-3 mol L-1 so that the ion was pre-concentrated on the sensor surface under the following conditions optimized voltammetric: deposition potential (EDEP) = - 1.0 V; Pre time - concentration (Tpre) = 120 s; scan speed (v) = 0.050 V s-1; pulse amplitude (Amp) = 0.1 V. The complex formed Mg2+ EBT showed a peak current of about - 0.6 V. The determination of Ca2+ was made using ammonium buffer (0.01 mol L-1) at pH 9.4, as supporting electrolyte and EDTA 1.0 x 10-2 mol L-1 as a binder under the following optimum conditions: deposition potential (EDEP) = -1.0 V; preconcentration time (Tpre) = 90 sec; frequency (freq.) = 15 Hz; width = 0,075V and Step E) = 0.004 V. The complex formed Ca2+ EDTA showed a peak current of approximately - 0.2 V. The result was consistent statistically considering t -test for a 95% confidence level. The levels were lower CV of 11.0% (Mg2+ and Ca2+), recoveries were in the range 95.0 to 108.0% (Mg2+) and from 97.8 to 105.0% (Ca2+) and the values of detection limits were 1.05 x 10-6 mol L-1 (Mg2+) and 2.8 x 10-7 mol L-1 (Ca2+), and quantitation 3.51 x 10-6 mol L-1 (Mg2+) and 9.46 x 10-7 mol L-1 (Ca2+) for the samples analyzed, showing good accuracy and sensitivity of the proposed method. The values obtained for the samples ranged from 1.47 x 10-5 ± 1.28 x 10-6 mol L-1 (Mg2+) and 5.57 x 10-6 ± 3.77 x 10-7 mol L-1 (Ca2+) on samples of biodiesel. The determination of metals such as Ca2+ and Mg2+ by electrochemical techniques with chemically modified electrodes has as main advantages its detectability and the selectivity.

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