https://tedebc.ufma.br/jspui/handle/tede/5116 Tue, 21 Jul 2026 08:22:16 GMT 2026-07-21T08:22:16Z https://tedebc.ufma.br/jspui/handle/tede/7076 Título: Desenvolvimento e caracterização de microemulsão a base do óleo de alfavaca (Ocimum gratissimum) para avaliação da atividade antioxidante, citotóxica e antimicrobiana Autor: FERREIRA, Jonny Erick dos Santos Primeiro orientador: MONTEIRO, Odair dos Santos Abstract: Ocimum gratissimum, popularly known in Brazil as “alfavaca,” “manjericão,” “alfavacão,” or “alfavaca-cravo,” belongs to the Lamiaceae family, is native to Africa and Asia, and is widely distributed throughout Brazil. Studies on its therapeutic applications have revealed significant pharmacological diversity, with antibacterial, antifungal, hypoglycemic, and antioxidant properties documented in different experimental models. Several biologically active monoterpenes and sesquiterpenes have been described for this genus, especially regarding its antimicrobial potential. In this context, the aim of this study was to develop a microemulsion containing Ocimum gratissimum essential oil (OGEO), obtained by hydrodistillation of the leaves. The essential oils were analyzed by gas chromatography coupled with mass spectrometry (GC-MS) and subsequently evaluated regarding seasonal and circadian influences on chemical composition, as well as antioxidant, cytotoxic, antibacterial, and antifungal activities. Significant variations were observed in both yield and concentration of the essential oil constituents throughout the evaluated periods. On average, 23 compounds were identified, with carvacrol (38.4%–63.5%), p-cymene (9.3%– 19.3%), and γ-terpinene (8.7%–27.9%) being the major constituents in all samples. For microemulsion development, a phase diagram was constructed, allowing the identification of the most stable system proportion, composed of 18.2% oil, 72.7% surfactant/cosurfactant, and 9.1% water. The selected formulation (ME6) was characterized in terms of particle size (43.82 ± 0.319 nm), polydispersity index (0.416 ± 0.021), zeta potential (−26.2 mV), thermal stability, conductivity (76.8 μS/cm), and pH (6.42–5.37). Headspace GC-MS analysis confirmed the incorporation of the essential oil into the microemulsion matrix, highlighting carvacrol (40.39%), γ-terpinene (22.51%), and p-cymene (12.57%) as the major constituents present in ME6. The microemulsion exhibited superior biological performance compared to the Negative Control (ME-Negative Control) and the isolated essential oil (EO) against all tested microorganisms, both in terms of bacteriostatic activity (MIC) and bactericidal activity (MBC). Notably, it demonstrated strong inhibitory effects against Staphylococcus aureus and Klebsiella pneumoniae, maintaining high microbial growth inhibition even at a concentration of 2000 mg/mL. Microbiological analyses demonstrated that the microemulsion (ME6) presented MIC values ranging from 15.62 to 250 mg/mL against the tested bacteria, whereas the isolated essential oil exhibited MIC values ranging from 250 to 2000 mg/mL, indicating up to a 16- fold increase in antimicrobial potency after microemulsification. Antifungal activity was also enhanced, with a reduction in the minimum fungicidal concentration (MFC) from 500 mg/mL (EO) to 15.62 mg/mL (ME6) against Candida albicans and Candida parapsilosis strains. In the antioxidant assay, the microemulsion exhibited an IC50 value of 39.38 mg/mL, whereas the isolated essential oil showed an IC50 value of 70.51 mg/mL, confirming a 44.14% increase in antioxidant capacity after microemulsification. In hemolysis assays, OGEO showed values below 10% only at concentrations lower than 500 μg/mL, ranging from 9.8% (500 μg/mL) to 9.6% (15.62 μg/mL). In contrast, the microemulsion maintained hemolysis values below 10% even at higher concentrations (2000 μg/mL), reaching 0.3% at the lowest tested concentration (15.62 μg/mL), demonstrating a considerably milder cytotoxic profile compared to the free essential oil. Taken together, these results demonstrate that the microemulsion containing Ocimum gratissimum essential oil exhibited clear superiority over the non-formulated essential oil, presenting enhanced antimicrobial and antioxidant activities associated with a significant reduction in cytotoxicity. This combination of high physicochemical stability, improved biological efficiency, and enhanced safety profile reinforces the potential of this formulation as a promising candidate for the development of topical pharmaceutical products with antibacterial and antifungal properties. The findings of this study contribute to the advancement of pharmaceutical technologies applied to natural products and highlight relevant perspectives for future clinical and biotechnological applications. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese Wed, 21 Jan 2026 00:00:00 GMT https://tedebc.ufma.br/jspui/handle/tede/7076 2026-01-21T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/7008 Título: DESENVOLVIMENTO DE SENSORES ELETROQUÍMICOS BASEADOS EM MATERIAIS NANOESTRUTURADOS E HÍBRIDOS PARA DETECÇÃO DE FLOROGLUCINOL E L-CISTEÍNA Autor: RIBEIRO, Danilo Braga Primeiro orientador: LUZ, Rita de Cássia Silva Abstract: Phloroglucinol (FG) is a phenolic compound of relevance in pharmaceutical, environmental, and industrial applications, whereas L-cysteine (L-CIS) is a biologically important amino acid associated with metabolic processes and widely used as a biomarker in clinical analyses. In this context, the development of sensitive and selective analytical methods for the determination of these species is of great interest. In this work, electrochemical sensors based on glassy carbon electrodes modified with nanostructured and hybrid materials were developed for the sensitive and selective detection of FG and L-CIS. For FG determination, a sensor composed of multi-walled carbon nanotubes (MWCNTs), carboxyl-functionalized cadmium telluride quantum dots (CdTe-COOH), and chitosan (CTS) was proposed. The combination of these materials promoted a synergistic effect, resulting in a significant enhancement of the electrochemical response in phosphate buffer solution (PBS, pH 7.5). The sensor exhibited, by linear sweep voltammetry (LSV), a linear range from 1 to 2000 µmol L⁻¹ and a limit of detection of 0.8 µmol L⁻¹. By differential pulse voltammetry (DPV), two linear ranges were observed, from 0.05 to 250 and from 250 to 1000 µmol L⁻¹, with a limit of detection of 0.03 µmol L⁻¹. Selectivity, repeatability, and reproducibility studies confirmed the robustness of the device, with relative standard deviation (RSD) values of 1.72% for repeatability and 2.56% for reproducibility. The applicability was demonstrated in water and artificial urine samples, with recoveries ranging from 104.6% to 107.7% and from 97.7% to 101.6%, respectively. For L-CIS determination, a second sensor was developed using a glassy carbon electrode modified with MWCNTs, trimetallic oxides (Fe₂O₃–MgO–CuO), and Nafion. Morphological analyses indicated the formation of aggregated structures with nanostructured characteristics. Under optimized conditions (PBS, pH 7.5) and using linear sweep voltammetry (LSV), the sensor exhibited a significant improvement in charge transfer kinetics and electrocatalytic performance. The analytical response showed a linear dependence on the logarithm of L-CIS concentration, with two linear ranges (0.5–100 and 100–1000 µmol L⁻¹) and high correlation coefficients (R² ≥ 0.990). The detection limit was 0.004 µmol L⁻¹. Repeatability and reproducibility tests yielded RSD values of 1.58% and 1.82%, respectively, while selectivity studies demonstrated good tolerance toward potential interferents. The applicability of the sensor was confirmed for the determination of L-CIS in artificial plasma and human urine samples, with recoveries ranging from 106.00% to 108.82% and from 96.43% to 103.08%, respectively, demonstrating high accuracy even in complex matrices. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese; Trabalho sob Sigilo. Motivo do sigilo: Parte do trabalho ainda será publicado. Prazo previsto para disponibilização total: após 2 anos. Fri, 24 Apr 2026 00:00:00 GMT https://tedebc.ufma.br/jspui/handle/tede/7008 2026-04-24T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6947 Título: Hidróxidos duplos lamelares e derivados como materiais multifuncionais para processos de adsorção, fotocatálise e energia limpa Autor: CAMPOS, Vanessa Niely Soares Primeiro orientador: ALCÂNTARA, Ana Clécia Santos de Abstract: This thesis investigates the development and application of layered double hydroxides (LDHs) and their derivatives, mixed metal oxides (MMOs), as multifunctional materials aimed at environmental remediation and clean energy production. The research was structured in interconnected chapters, ranging from a systematic literature review to the experimental evaluation of the synthesized materials. The systematic review revealed a growing interest in LDHs and MMOs for adsorption, photocatalysis, and photocatalytic hydrogen production processes, highlighting limitations related to efficiency, stability, and action mechanisms. Based on these challenges, bimetallic (CoAl and NiAl) and trimetallic (NiCoAl) systems were synthesized, along with their calcined derivatives, which were extensively characterized in terms of their structural, morphological, textural, and electronic properties. The results demonstrated that CoAl-LDH exhibited a high adsorption capacity for naproxen, with rapid kinetics influenced by parameters such as pH, initial concentration, and temperature. The process was well described by kinetic and isothermal models, indicating a predominance of chemical and electrostatic interactions. In the energy context, NiAl-LDH and CoAl-LDH showed photocatalytic activity for hydrogen production via water splitting, highlighting the influence of metallic composition on charge separation and process efficiency. Furthermore, mixed metal oxides, particularly the trimetallic NiCoAl-MMO system, exhibited high performance in the photodegradation of ciprofloxacin, with effective removal under different operating conditions and evidence of mechanisms mediated by reactive species. Overall, the results reveal a direct relationship between composition, structure, and functional performance, demonstrating that modulation between lamellar phases and derived oxides is a promising strategy for the development of multifunctional materials. Thus, this thesis contributes significantly to scientific advancement in the area of materials applied to environmental remediation and clean energy generation, offering perspectives for sustainable applications in the real world. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese Fri, 13 Mar 2026 00:00:00 GMT https://tedebc.ufma.br/jspui/handle/tede/6947 2026-03-13T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6939 Título: Nanoplataformas híbridas a base de pontos quânticos de carbono e suportes inorgânicos naturais e sintéticos Autor: CUTRIM, Elaine Sá Menezes Primeiro orientador: ALCÂNTARA, Ana Clécia Santos de Abstract: Clays are widely combined with other nanomaterials to improve their properties and to obtain multifunctional hybrid systems. These materials offer advantages such as enhanced mechanical and rheological performance, reduced toxicity, and compatibility with green chemistry principles, making them suitable platforms for incorporating functional nanostructured materials. In this work, hybrid nanomaterials based on carbon quantum dots (CQDs) and inorganic supports with different morphologies were developed, including fibrous sepiolite (SEP), layered montmorillonite (MMT), and ZIF-8. CQDs were synthesized by a solvothermal route using citric acid and urea in dimethylformamide and subsequently associated with the supports either using preformed CQDs or through in situ synthesis. Spectroscopic analyses indicate that CQDs interact with SEP mainly through surface silanol groups and hydroxyl groups associated with zeolitic water, as evidenced by FT-IR spectroscopy. Photoluminescence (PL) spectroscopy demonstrates that the association between CQDs and clay minerals does not compromise the PL properties of the CQDs. The hybrid nanomaterials exhibit shifts in the maximum emission wavelength, indicating modification of the emissive states induced by the clay environment. In addition, most hybrid systems display dual-emission behavior. Raman analysis shows an increase in the sp² carbon network for sepiolite–CQD hybrids synthesized in situ, accompanied by a decrease in the ID/IG ratio, indicating higher structural ordering as a function of synthesis time. For the MMT-based hybrid nanomaterials, X-ray diffraction (XRD) analysis reveals both the presence of diffraction features associated with CQDs and an increase in the basal spacing of MMT. Drug intercalation studies demonstrate that 5-fluorouracil is incorporated into MMT as a monolayer with planar orientation, producing an increase in basal spacing from approximately 1.21 nm to values close to 1.27 nm, depending on drug loading. The resulting clay–CQD–drug systems exhibit stable structural organization without collapse of the layered framework. The ZIF-8/CQD hybrid nanomaterial preserves the crystalline structure and porosity of ZIF-8, as confirmed by XRD and nitrogen adsorption–desorption analyses, although a reduction in specific surface area is observed due to the incorporation of CQDs. Hemolysis assays performed over a concentration range from 5000 to 36 µg mL⁻¹ show hemolysis percentages below 5%, indicating good hemocompatibility. Overall, the results demonstrate that the association of CQDs with clays and metal–organic frameworks leads to structurally stable hybrid nanoplatforms with tunable optical properties, preserved porosity, and low toxicity. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese Fri, 06 Mar 2026 00:00:00 GMT https://tedebc.ufma.br/jspui/handle/tede/6939 2026-03-06T00:00:00Z