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Degradação fotocatalítica de antibióticos sulfonamidas empregando nitreto de carbono grafítico (g-C3N4) e g-C3N4/Fe3O4 magneticamente recuperável”

2026-04-01T12:44:05Z

Título: Degradação fotocatalítica de antibióticos sulfonamidas empregando nitreto de carbono grafítico (g-C3N4) e g-C3N4/Fe3O4 magneticamente recuperável” Autor: MACEDO, Jhonatan Nunes Primeiro orientador: LIMA, Rafaely Nascimento Abstract: The presence of sulfonamide antibiotics in aquatic environments represents a significant environmental concern due to their persistence and potential to promote the spread of bacterial resistance. In this work, two visible-light-active photocatalysts were synthesized: graphitic carbon nitride (g-C₃N₄), obtained by urea pyrolysis, and the magnetic composite 3% Fe₃O₄/gC₃N₄, prepared from melamine through a combined pyrolysis and solvothermal route. The materials were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), UV–Vis Diffuse Reflectance Spectroscopy (DRS), textural analysis (BETBJH), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS). FTIR spectra of g-C₃N₄ showed bands between 1200–1650 cm⁻¹ associated with C–N and C=N vibrations of the heptazine framework and a band at ~799 cm⁻¹, characteristic of triazine/heptazine ring breathing modes. In the g-C₃N₄ / Fe₃O₄ (3%) composite, an additional absorption at ~586 cm⁻¹ corresponding to the Fe–O stretching vibration confirmed the incorporation of magnetite. XRD patterns revealed characteristic peaks of g-C₃N₄ at 2θ ≈ 13° (100) and 27° (002), while Fe₃O₄ exhibited reflections of the cubic spinel structure at 18.3° (111), 30.1° (220), 35.6° (311), 43.3° (400), 53.5° (422), 57.3° (511) and 62.9° (440), consistent with PDF 01-075-0449. The composite showed the coexistence of both phases. DRS analysis indicated a band gap of ~2.8 eV for g-C₃N₄. Morphological analysis revealed a sponge-like structure for g-C₃N₄, while the composite exhibited structural stability and magnetic recoverability. Photocatalytic tests showed that g-C₃N₄ outperformed photolysis, achieving degradation efficiencies of 94% for sulfathiazole (k = 7.8 × 10⁻³ min⁻¹), 77% for sulfadiazine (k = 8.8 × 10⁻³ min⁻¹), and 72% for sulfapyridine (k = 6.9 × 10⁻³ min⁻¹), maintaining stability over six reuse cycles. The 3% Fe₃O₄/g-C₃N₄ composite achieved 80% sulfathiazole degradation (k = 1.4 × 10⁻² min⁻¹) within 100 min, showing stability over four cycles and the advantage of magnetic separation. Mechanistic studies indicated that photogenerated holes (h⁺) were the dominant reactive species, followed by superoxide radicals (O₂•⁻) and hydroxyl radicals (•OH). These results highlight the high photocatalytic efficiency of urea-derived g-C₃N₄, while the magnetic composite offers operational advantages related to catalyst recovery and reuse, demonstrating strong potential for advanced oxidation processes aimed at the removal of antibiotics from aqueous systems. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação

Anotação química e potencial antiproliferativo dos extratos metanólicos e frações das folhas e flores de Parkia platycephala (Fabaceae)

2026-04-01T11:44:09Z

Título: Anotação química e potencial antiproliferativo dos extratos metanólicos e frações das folhas e flores de Parkia platycephala (Fabaceae) Autor: MELONIO, Matheus Chagas Primeiro orientador: ROCHA, Cláudia Quintino da Abstract: Maranhão state hosts one of the richest and most diverse biodiversities in Brazil, a result of its unique geographical position where the Amazon, Cerrado, and Caatinga biomes converge. This ecological confluence favors the occurrence of plant species that remain under-explored regarding their chemical and biological potential. In this context, the present study investigated the chemical profile and antiproliferative potential of extracts and fractions from the leaves and flowers of Parkia platycephala, an endemic Cerrado species belonging to the Fabaceae family. The methanolic extracts of leaves (EBFL) and flowers (EBFR) underwent liquid-liquid partitioning, yielding hexanic (FHFL; FHFR) and ethyl acetate (FAFL; FAFR) fractions. Analysis by Liquid Chromatography coupled with Electrospray Ionization Ion Trap Mass Spectrometry (LC-ESI-IT/MS) allowed the annotation of phenolic compounds. Molecules from the classes of shikimic acid derivatives, flavonoids, proanthocyanidins, and lignans were putatively annotated, the latter potentially not yet reported in the Parkia genus. Cytotoxic activity was evaluated using the MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide) against five human tumor cell lines (A549, PC–3, HT–29, BxPC–3, and MCF–7) and one non-tumor cell line (HPrEpiC) to determine the Half-Maximal Inhibitory Concentration (IC50) and Selectivity Index (SI). The results revealed that the crude extracts were inactive at the tested concentrations, while the FHFL and FAFL fractions exhibited IC50 values between 8.4 and 50 μg/mL. Notable results included the antiproliferative activity (IC50 = 8.4 μg/mL) and high selectivity (SI = 11.90) of FHFL against the MCF–7 cell line. Flower fractions (FHFR and FAFR) demonstrated activity against BxPC–3, albeit with high toxicity toward non-tumor cells (SI < 1). The data indicate that fractionation concentrated the bioactive compounds and that P. platycephala leaves constitute a promising source of selective biomolecules, reinforcing the biopharmacological potential of the species for the development of new antitumoral agents. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação

Limites de segurança e aplicação anestésica do óleo essencial de Dizygostemon riparius em Tambaqui e sua relação com o perfil químico dos constituintes voláteis

2026-03-20T11:26:24Z

Título: Limites de segurança e aplicação anestésica do óleo essencial de Dizygostemon riparius em Tambaqui e sua relação com o perfil químico dos constituintes voláteis Autor: CALDAS, Marcus Vinicius Lima Primeiro orientador: MONTEIRO, Odair dos Santos Abstract: The use of anesthetics in aquaculture is important to reduce stress and minimize physical damage to fish during management procedures such as biometrics, transportation, marking, and biological sampling, contributing to animal welfare. In this context, natural compounds such as essential oils have been investigated as possible alternatives. Dizygostemon riparius, known as “melosa”, is an aromatic species belonging to the Plantaginaceae family and endemic to the state of Maranhão, Brazil, whose essential oil remains little explored regarding its applications in aquaculture. Thus, the objective of this study was to chemically characterize the essential oil of Dizygostemon riparius and evaluate its behavioral effects and acute toxicity in juveniles of Colossoma macropomum from different size classes. The essential oil was obtained by hydrodistillation of the leaves and characterized by gas chromatography coupled with mass spectrometry (GC–MS), allowing the identification of 32 constituents, with predominance of oxygenated monoterpenes. The major compounds were endo-fenchyl acetate (42.66%) and endo-fenchol (34.88%), which together represented more than 70% of the total oil composition.Toxicological evaluation revealed a response dependent on concentration and fish size. In smaller fish (≈3.3 g), acute toxicity was observed from approximately 46.9 mg·L−1, with total mortality at concentrations close to 70 mg·L−1. In larger fish (≈15 g), no mortality was observed under the evaluated conditions. In behavioral assays, the essential oil produced concentration-dependent sedative and anesthetic effects: concentrations between 75 and 100 mg·L−1 were associated with sedation, while approximately 120 mg·L−1 induced anesthesia, with shorter induction times as dose increased and longer recovery times at higher concentrations. These results indicate dose- and body size-dependent responses and suggest an association between the chemical profile of the oil and the observed effects. The conclusions of this study are limited to the evaluation of acute toxicity and behavioral parameters, and further studies including subchronic or chronic toxicity, pharmacokinetics, residue analysis, histopathological, reproductive, and environmental assessments are required for a broader evaluation of the applicability of D. riparius essential oil in aquaculture. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação

SÍNTESE E APLICAÇÃO DE MATERIAIS CATALÍTICOS PARA REAÇÕES DE CONVERSÃO ELETROQUÍMICA DE ENERGIA

2026-03-18T18:08:51Z

Título: SÍNTESE E APLICAÇÃO DE MATERIAIS CATALÍTICOS PARA REAÇÕES DE CONVERSÃO ELETROQUÍMICA DE ENERGIA Autor: CAMPOS, Ingrid Reis Primeiro orientador: LIMA, Roberto Batista de Abstract: This work investigated the development and application of catalytic materials as alternatives to platinum for electrochemical energy conversion systems. In the first chapter, silver phosphate (Ag₃PO₄) and its derived phase, silver(I) oxide (Ag₂O), were evaluated as catalysts for the oxygen reduction reaction (ORR) in alkaline média. X-ray diffraction analyses confirmed the partial transformation of Ag₃PO₄ into Ag₂O after contact with the electrolyte, indicating the in situ formation of the catalytically active phase. Electrochemical measurements revealed onset and half-wave potentials close to those of the commercial Pt/C (20%) catalyst, highlighting the promising electrocatalytic performance of Ag₂O. Mechanistic analysis, combining experimental results and theoretical calculations based on slab geometry relaxation, indicated that the ORR proceeds predominantly via a four-electron pathway, initially following a peroxide-mediated route, along with favorable kinetics in alkaline conditions. In the second chapter, a Co₃O₄|HCNS|Pt nanocomposite was investigated for the hydrogen evolution reaction (HER) and the methanol oxidation reaction (MOR). Optical analyses indicated a narrowing of the band gap compared to the FTO substrate, suggesting photoelectrochemical potential. Electrochemical responses showed a strong dependence on the operating regime, with a photoassisted effect evidenced by chronoamperometry under constant potential. The composite also exhibited electrocatalytic activity toward methanol oxidation, with improved performance at intermediate potentials. Overall, the results indicate that Ag₂O exhibits good electrocatalytic performance for the oxygen reduction reaction in alkaline media, while the Co₃O₄|HCNS|Pt composite shows promise for electrochemical and photoelectrochemical energy conversion applications. However, for the latter, structural and interfacial limitations still require optimization of the synthesis route and material architecture. Instituição: Universidade Federal do Maranhão Tipo do documento: Dissertação