https://repositorio.ufu.br/handle/123456789/5095 2026-07-12T22:37:01Z https://repositorio.ufu.br/handle/123456789/48800 Title: Prospecção química e avaliação do potencial antimicrobiano e antidiabético de espécies dos gêneros Cassia e Senna (Fabaceae) por CLUE-ESI-EM/EM Abstract: The Cerrado and the Atlantic Forest are Brazilian biomes rich in biodiversity, harboring a variety of medicinal plant species. Among them, species of Cassia and Senna have stood out for their medicinal properties and have aroused scientific interest due to the presence of special metabolites with biological potential. In this study, six species of these genera were collected (C. fistula, C. grandis, C. javanica, S. multijuga, S. rugosa, and S. velutina), and nine leaf and flower extracts were prepared and subjected to liquid-liquid extraction to obtain the organic fractions. The obtained extracts were analyzed by UPLC- IES-MS/MS, in negative and positive modes. In this process, flavonoids, an anthraquinone, and proanthocyanidins, along with other classes of compounds, were identified. In the antibacterial activity assay, using cariogenic bacteria, the EE demonstrated moderate activity, with minimum inhibitory concentration (MIC) values ranging from 100 to 400 μg mL–1, the exception being the EE from S. velutina leaves, which exhibited an MIC of 25 μg mL–1 for Streptococcus mitis and 50 μg mL–1 for Porphyromonas gingivalis. In the assay using anaerobic bacteria, the ethyl acetate fraction of S. velutina flowers exhibited a MIC of 50 μg mL–1 against S. mitis. In the assay using aerobic bacteria, the hexane fractions of S. rugosa (flowers) and C. javanica (leaves and flowers) showed antibacterial activity with MIC values ranging from 6.25 to 25 μg mL–1 against P. gingivalis and Actinomyces naeslundii. In the assay to evaluate antifungal activity using yeasts of the genus Candida, the most promising EE were those of S. rugosa and C. javanica flowers, as well as S. velutina leaves and flowers, exhibiting MIC values between 5.86 and 11.72 μg mL–1 against C. glabrata. The most polar fractions of S. rugosa leaves and flowers and C. javanica flowers showed MICs between 2.93 and 23.4 μg mL–1 against C. albicans and C. glabrata. A very promising result was obtained from the ethyl acetate fraction of S. velutina flowers, exhibiting an MIC of 1.46 μg mL–1 against C. glabrata. This fraction was selected for chemical study based on analysis by UPLC-ESI-MS/MS, which revealed the presence of proanthocyanidins, from which the compounds (ent)-cassiaflavan-gallocatechin (A), (ent)-cassiaflavan-(ent)-cassiaflavan- catechin (D), and a mixture of (ent)-cassiaflavan-(4→8)-(epi)-catechin B and C were isolated. The anti-Candida potential of these compounds was evaluated against strains of C. albicans, C. glabrata, and C. tropicalis, and they showed selectivity against C. glabrata with MICs between 1.95 and 15.69 μg mL–1. C. javanica, a species used in folk medicine for the treatment of diabetes, was selected for chemical and antidiabetic study. The dichloromethane fraction of C. javanica flowers was one of the most active in the enzymatic assay against α-amylase and α-glucosidase, and in anti-glycation assays. Chemical analysis of this fraction isolated kaempferol (E), rhein (F), elegentin (G), and afzelin (H), which were also subjected to α-glucosidase and anti-glycation assays. Compound E was one of the most active, particularly in inhibiting α-amylase with an IC50 of 0.04 ± 0.003 μg mL⁻¹ (positive control triticum, 0.2 ± 0.00 μg mL⁻¹). The results of the biological assays highlight the relevance of chemical and pharmacological investigation of Cassia and Senna species, which are still underexplored when it comes to investigating natural products with antimicrobial and antidiabetic potential. 2025-11-27T00:00:00Z https://repositorio.ufu.br/handle/123456789/48742 Title: Correlação estrutura-desempenho do ZnO na fotodegradação de poluentes e na redução eletroquímica de CO2 em CO Abstract: Anthropogenic activities generate excessive amounts of organic and inorganic pollutants, which are often released into water, air, and soil without adequate treatment. Heterogeneous photocatalysis has emerged as a promising approach for the photodegradation of organic contaminants, while electrocatalysis offers an efficient pathway for the electrochemical reduction of CO2. In this study, the effect of synthesis temperature and amine functionalization on the physicochemical properties and performance of zinc oxide (ZnO) was investigated in photo and electrocatalytic processes applied to:(i) the degradation of organic pollutants and (ii) the electrochemical reduction of CO2. The ZnO samples were tested for the photodegradation of pharmaceuticals (Amiloride and Ciprofloxacin) and dyes (Methylene Blue and Rhodamine B). The ZnO sample synthesized at 100 °C exhibited superior photocatalytic performance compared to those obtained at higher synthesis temperatures. This result can be attributed to the synergy between the Zn(OH)2/ZnO structural phases combined with the higher specific surface area of the material. (ii)The ZnO sample was modified with monoethanolamine, and its characterization revealed that the functionalization led to materials with distinct morphology and surface groups.The amino-functionalized sample, ZnO/Met-100, exhibited superior performance in the electrochemical reduction of CO2 to CO, achieving a Faradaic efficiency of approximately 90% for CO at current densities exceeding -100 mA cm-2.This result is attributed to the presence of amino groups on the ZnO surface, which enhance CO2 adsorption and increase selectivity toward CO formation. The in situ FTIR spectroscopy study enabled the monitoring of reaction intermediates and the proposal of a possible reaction mechanism. Electrochemical impedance spectroscopy (EIS) results confirmed that the presence of amino groups on the functionalized ZnO significantly reduced the charge-transfer resistance, thereby facilitating the kinetics of the electrocatalytic process. The stability of the amino-functionalized ZnO was investigated under electrochemical operating conditions, demonstrating excellent durability over 100 h of continuous operation in a membrane electrode assembly (MEA) cell. The system operated at a current density of 50 mA cm-2, maintaining a Faradaic efficiency above 70% and a total cell potential of approximately 2.7 V. These results reinforce the viability of the material for sustainable electrocatalytic applications. 2025-12-01T00:00:00Z https://repositorio.ufu.br/handle/123456789/48718 Title: Influência da co-dopagem com íons La3+ em sistemas binários de óxidos de SiO2-TiO2:Eu3+ obtidos pelo método sol-gel Abstract: This study investigates the synthesis and characterization of photoluminescent materials based on SiO2-TiO2 matrices co-doped with Eu3+ and La3+. Prepared via the sol-gel method and calcined at 750 °C, the matrices were analyzed by X-ray Diffraction (XRD), Raman spectroscopy, Fourier-Transform Infrared spectroscopy (FTIR), Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM), and Photoluminescence (PL). Structural results confirmed the stabilization of the anatase phase, where the incorporation of La3+ acted as a crystal growth inhibitor, except at concentrations of 0.3 and 1.0 mol%, which exhibited a singular bulk-like behavior regime. Diffuse reflectance analysis (DRS) revealed an adjustable direct band gap between 2.75 and 3.02 eV, correlated with the structural disorder monitored by the Urbach energy. Thermal treatment proved crucial, promoting the removal of hydroxyl suppressors and resulting in an average 6.5-fold (547%) jump in luminescence lifetimes (τ), which reached values exceeding 1000 µs. Spectroscopic analysis indicated that La3+ co-doping induces a symmetry breaking at the Eu3+ local site (site symmetries Cs, Cn ou Cnv), evidenced by the splitting of the 5D0→7F1 transition into three singlets and a 120% increase in the emission intensity of the 5D0→7F2 hypersensitive band. In situ PL monitoring as a function of temperature confirmed the reversibility and thermal robustness of the system, mitigating quenching effects. These findings demonstrate the high potential of SiO2-TiO2:Eu3+,La3+ composites for the development of advanced photonic devices, such as WLEDs and high-sensitivity sensors for optical thermometry. 2025-12-17T00:00:00Z https://repositorio.ufu.br/handle/123456789/48691 Title: Development of conductive and printable filaments for electrochemical sensors applied to environmental, pharmaceutical, food and biological analyses Abstract: Chemical sensors have been widely developed in response to the growing demand for the monitoring of analytes in environmental, biological, forensic and food samples. Among them, electrochemical sensors stand out for translating chemical information into measurable electrical signals and for offering advantages such as good selectivity, sensitivity, low limit of detection, ease of miniaturisation and versatility for both materials and designs. In this context, these devices have grown together with advances in new manufacturing technologies, especially additive manufacturing, which has emerged as a promising approach for the production of electrochemical sensors. In parallel, new conductive filaments have been developed to improve electrochemical responses, expand possibilities for new applications and incorporate sustainability perspective. However, as this is still a relatively recent field, challenges remain in regard to the achievement of improved electrochemical responses, better printability and the use of new polymers to broaden applications. Thus, this Thesis aimed to explore the fabrication and application of new alternative filaments produced in the laboratory for the monitoring of paracetamol, ascorbic acid, dopamine, uric acid, nitrite and carbendazim, demonstrating the versatility of these devices in environmental, biological and food samples. Divided into six chapters, the work presents: general introduction, filaments modified with carbon nanodiamonds and functionalised nanodiamonds, demonstrating the possibility of modifying and improving electrochemical responses; filaments with the addition of edible oils as plasticisers, with a focus on sustainability and demonstrating, for the first time, the influence of specific plasticisers on sensor responses; alternative thermoplastic polyurethane (TPU)-based filaments, used both as sensors obtained from the direct use of the filament itself and as printed electrodes which, compared with polylactic acid (PLA), show greater flexibility without loss of analytical performance, in addition to biocompatibility, thereby expanding the potential for application in wearable sensors; and, finally, more sustainable filaments produced from high-density polyethylene recycled (rHDPE) from cleaning-product packaging, with emphasis on greater chemical resistance and durability when compared with other polymers. All materials were extensively characterised, and the electroanalytical devices were evaluated against the proposed applications. The results expand the possibilities for the development and optimisation of electrochemical sensors, highlighting efficient, versatile, low-cost materials with low waste generation. 2026-05-08T00:00:00Z