https://repositorio.ufu.br/handle/123456789/5095 2026-09-21T20:31:19Z https://repositorio.ufu.br/handle/123456789/50327 Title: Isolamento e identificação de alcaloides piperidínicos minoritários presentes nas flores de Senna spectabilis (Fabaceae) Abstract: Senna spectabilis belongs to the Fabaceae family and is popularly known as cassia. This species is widely used in urban landscaping and is considered an important source of specialized metabolites, particularly the major piperidine alkaloids (–)-cassine and (–)-spectaline. These compounds have attracted scientific interest due to their acetylcholinesterase inhibitory activity, an enzyme associated with Alzheimer’s disease. Previous studies have reported the occurrence of epimers of (–)-cassine and (–)-spectaline at C-6 of the piperidine ring, known as 6-iso-cassine and 6-iso-spectaline. The investigation of these diastereomers is relevant because changes in stereochemistry may result in different physicochemical properties and potentially affect their biological activities. Therefore, this study aimed to expand the knowledge of the piperidine alkaloids present in S. spectabilis, focusing on the isolation and identification of minor metabolites. Chromatographic techniques, including thin-layer chromatography (TLC), column chromatography (CC), high-performance liquid chromatography (HPLC), and gas chromatography with flame ionization detection (GC-FID), were employed for the separation of the compounds. The isolated metabolites were identified by mass spectrometry (MS) and 1H nuclear magnetic resonance spectroscopy (1H NMR). The results demonstrated that S. spectabilis is an important source of specialized metabolites, whose separation required the application of advanced analytical techniques, particularly HPLC-MS and GC-FID. The isolated diastereomers and homologues provide a basis for future studies aimed at determining the absolute stereochemistry of their stereogenic centers, as well as evaluating their biological activities and elucidating their mechanisms of action. 2026-08-03T00:00:00Z https://repositorio.ufu.br/handle/123456789/50269 Title: Estudo químico e biológico de Microlicia parviflora (Melastomataceae): sazonalidade dos óleos essenciais, metabolômica comparativa e isolamento de metabólitos Abstract: Microlicia parviflora (Melastomataceae) is a poorly studied species, but plants of the genus have been reported to exhibit promising biological activities. Therefore, in the present study, the chemical composition and biological potential were evaluated through three distinct approaches. Initially, the essential oils from leaves collected throughout one year were investigated for their antimicrobial potential, and their chemical compositions were determined by mass spectrometry. The oils exhibited promising antibacterial activity against different oral pathogens, with the most notable inhibitory results obtained against Porphyromonas gingivalis and Actinomyces naeslundii, with minimum inhibitory concentration (MIC) values of 0.39 µg mL–1. Through multivariate statistical analyses, it was possible to group the oils obtained at different times of the year, relating their chemical composition to the rainy and dry seasons; the chemical profile and biological potential of the essential oils from the flowers were also evaluated, which showed a slightly different composition from that of the leaves and were active against the same bacteria. In a second approach, extracts were obtained by maceration of the leaves, flowers, and branches using hexane and ethanol. These extracts were tested against the same bacteria, Candida species, and the protozoa Trypanosoma cruzi and Leishmania infantum. The hexane extracts were active against six of the bacteria tested, with MIC values ranging from 12.5 to 100 µg mL–1, and against L. infantum, with an effective concentration (EC50) ranging from 0.9 to 3.8 µg mL–1. The ethanolic extracts from the three organs and the more polar partitions of the leaves and branches were active against Candida species, including the multidrug-resistant species C. auris, with MIC values of 2.93 µg mL–1. Finally, a comparative study of the chemical composition of leaves, flowers, branches, and roots was performed using metabolomic techniques. With the aid of mass spectrometry and statistical analyses, it was possible to differentiate the organs, showing that the chemical composition of the branches and roots is similar, whereas that of the leaves and flowers is more distinct. These results were also observed by nuclear magnetic resonance spectroscopy. The methanolic extracts of the four organs were tested against phytopathogens associated with different cultivars and against human colorectal and prostate cancer cells. The extracts were active in both assays, showing 100% inhibition of the pathogen Phytophthora infestans and against both types of cancer cells tested. In addition, the study led to the isolation of two compounds obtained from different organs: quercitrin obtained from the ethyl acetate partition of the leaves and tricoumaroyl-spermidine obtained from the ethyl acetate partition of the flowers. Both were reported for the first time in the species, and the spermidine derivative was reported for the first time in the genus. This was the first study conducted on other organs of the species, as well as the first study to investigate the biological activities tested. 2026-07-09T00:00:00Z https://repositorio.ufu.br/handle/123456789/50149 Title: Equidade digital na educação pós-pandemia: mediação pedagógica com plataformas digitais para o ensino de eletroquímica em contextos educacionais diversos Abstract: Electrochemistry presents notorious and well-documented teaching and learning difficulties, which were substantially aggravated by the implementation of emergency remote teaching. This context demanded greater student autonomy and required educators to develop effective didactic alternatives for conceptual mediation at a distance, thereby deepening long-standing obstacles. This qualitative investigation aimed to evaluate the impacts of implementing digital educational resources—an offline application and a website titled Electrochemistry in Everyday Life—on the teaching and learning process. The goal was to overcome historical obstacles exacerbated by the remote context and promote equity in access to meaningful learning across distinct educational settings (public, private, and rural) in Itumbiara, Goiás, Brazil. The study unfolded sequentially in five methodological stages: first, a systematic literature review was conducted to map obstacles in electrochemistry education and analyze the effectiveness of active methodologies; subsequently, the challenges of emergency remote teaching in Science/Chemistry were investigated through the perceptions of teachers and students from three educational contexts, which were contrasted with institutional documents; third, after development and classroom implementation, the digital resources underwent rigorous validation by teachers and students (focusing on usability, user experience, and learning principles), resulting in an improved version and demonstrating feasibility even in contexts with limited technological infrastructure; finally, the impacts of these resources on student participation and cognitive performance were evaluated using pre- and post-intervention questionnaires across the three contexts. Initial diagnostic results confirmed the severity of the situation, with 63% of students rating their remote Chemistry classes negatively and citing a lack of concentration at home as the primary hindrance. These challenges were most pronounced in the Rural School, which exhibited a significant lack of teacher training and technical support. Following the intervention with the digital tools, quantitative data showed significant progress, noting a considerable improvement in conceptual understanding—exemplified by the Public School achieving approximately 50% correct answers in a Moodle Quiz—indicating the overcoming of cognitive obstacles. Qualitatively, students reported increased motivation and a clearer grasp of abstract concepts, attributing this progress to the resources' effective contextualization of content with everyday phenomena. Nevertheless, difficulties associated with prior curricular gaps persisted in the Rural School, despite these students showing notable engagement in practical activities. In conclusion, the complexity of challenges inherent to remote teaching, which manifest heterogeneously, tends to intensify pre-existing educational disparities. However, the developed digital resources, designed with a contextualized approach and subjected to a rigorous validation process, represent promising pedagogical strategies for mitigating learning gaps in electrochemistry. These tools demonstrated potential to catalyze student engagement, foster autonomy, and outline feasible pathways for promoting educational equity in diverse contexts, particularly in scenarios with infrastructural limitations. The research's legacy points toward transforming an emergency experience into lasting progress through continuous investment in evidence-based digital resources and teacher training for critical implementation. 2026-08-12T00:00:00Z https://repositorio.ufu.br/handle/123456789/50087 Title: Redução eletrocatalítica de CO2 utilizando um novo complexo de Re(I) contendo o ligante (z)-n-metil-2-(6-oxo-1,10-fenantrolin-5 (6H)-ilideno) hidrazinacarbotiamida Abstract: Tricarbonyl rhenium(I) complexes, commonly represented as fac-[Re(CO)₃(NN)Cl], where NN denotes bipyridine-derived ligands, have been extensively investigated as homogeneous catalysts for CO₂ reduction. This study aimed to synthesize a new complex, fac-[Re(CO)₃(Phmt)Cl], where Phmt = (Z)-N-methyl-2-(6-oxo-1,10-phenanthrolin-5(6H)-ylidene)hydrazinecarbothioamide, and to investigate its electrochemical behavior as a potential electrocatalyst for CO₂ reduction. The synthesis of fac-[Re(CO)₃(Phmt)Cl] was carried out by first preparing the Phmt ligand under reflux in toluene, followed by reaction with the metal precursor [Re(CO)₅Cl] under reflux to afford the desired complex. The product was characterized by Fourier-transform infrared (FTIR) spectroscopy and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy to confirm its molecular structure. The ¹H NMR spectrum displayed signals predominantly between 7 and 15 ppm, with the two most downfield resonances assigned to the amine hydrogen atoms, while the remaining signals corresponded to the aromatic protons. The FTIR spectrum provided further structural confirmation, exhibiting characteristic bands assigned to ν(N–H) (≈3268 cm⁻¹), ν(C≡O) (≈2027, 1900, and 1890 cm⁻¹), and ν(Re–N) (≈260 cm⁻¹), indicating the presence of amine groups, the facial geometry of the tricarbonyl complex, and metal–ligand coordination, respectively. The electrochemical properties were investigated by cyclic voltammetry (CV) in anhydrous dimethylformamide (DMF) under argon and CO₂ atmospheres. Under argon, the complex exhibited an irreversible oxidation peak corresponding to the Re(I)/Re(II) redox process. In the cathodic region, three irreversible reduction peaks were observed at −1.0, −1.6, and −2.1 V vs. Fc⁺/Fc, consistent with values reported for structurally related compounds. Under a CO₂ atmosphere, a significant catalytic current enhancement was observed (Ic/Ip = 2.41), with the first reduction peak shifting to −1.93 V vs. Fc⁺/Fc. These electrochemical results indicate that the synthesized complex is a promising candidate for the electrocatalytic reduction of CO₂ to CO. 2026-07-29T00:00:00Z