Mestrado em Química
URI Permanente para esta coleção
Nível: Mestrado Acadêmico
Ano de início: 2006
Conceito atual na CAPES: 5
Ato normativo: Homologação da 85ª Reunião do CTC-ES, Parecer CNE/CES nº 163/2005.
Processo nº 23001.000081/2005-56 do Ministério da Educação.
Publicado no DOU 28/07/2005, seção 1, página 11)
Periodicidade de seleção: Anual
Área(s) de concentração: Química
Url do curso: https://quimica.vitoria.ufes.br/pt-br/pos-graduacao/PPGQ/detalhes-do-curso?id=954
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- ItemMétodos de aprendizagem de máquina aplicados à ciência do petróleo(Universidade Federal do Espírito Santo, 2025-03-17) Barboza, Maria Carolina da Vitória Alvarenga; Ferreira, Rafael de Queiroz; https://orcid.org/0000-0002-5190-8508; http://lattes.cnpq.br/5053247764430323 ; Filgueiras, Paulo Roberto; https://orcid.org/0000-0003-2617-1601; http://lattes.cnpq.br/1907915547207861; https://orcid.org/0009-0007-7744-4434; http://lattes.cnpq.br/6535362149640541 ; Oliveira, Emanuele Catarina da Silva; https://orcid.org/0000-0003-0699-6104; http://lattes.cnpq.br/1715851915787164 ; Souza, Murilo de Oliveira; https://orcid.org/0000-0002-5299-564X; http://lattes.cnpq.br/1832643912229312This study aims to present a new machine learning approach to classify crude oil samples based on their physicochemical properties, such as sulfur (S) concentration, total acid number (TAN), and API gravity (American Petroleum Institute). Crude oil is a complex mixture predominantly composed of carbon and hydrogen substances, along with heteroatomic elements such as nitrogen, oxygen, and sulfur. This complexity makes precise analysis essential, especially to avoid problems throughout the production chain. Proposed method seeks to overcome the limitations of traditional techniques, which are often time-consuming, require large sample volumes, and use excessive solvents. As a promising alternative, spectroscopic techniques have been employed for crude oil characterization, and machine learning methods have demonstrated high efficiency in analyzing complex mixtures. These methods offer faster and more accurate exploration of chemical variability compared to conventional approaches. This study, 196 crude oil samples, varying in sulfur content, TAN, and API gravity, were analyzed. The use of SVM (Support Vector Machine) ensembles was explored as a powerful approach to improve classification performance by reducing the variability of individual models, increasing robustness against overfitting, and enabling better generalization than a single model. To evaluate performance, criteria such as sensitivity, specificity, error rate, Matthews correlation coefficient, and accuracy were used, comparing SVM ensemble models with PLS-DA and standard SVM. The results demonstrated that the combination of NIR spectroscopy (Near Infrared Spectroscopy) with SVM ensemble models is an efficient and reliable method for the simultaneous qualification of sulfur content, TAN, and API gravity in crude oils. This is because SVM ensembles tend to perform better, reducing overfitting. Moreover, they create more robust models, reduce variance, and increase model stability.
- ItemUso de técnicas químicas avançadas para caracterização da identidade de méis de abelhas sem ferrão do Espírito Santo(Universidade Federal do Espírito Santo, 2025-03-13) Dias, Lucas Rodrigues de Oliveira; Ferreira, Rafael de Queiroz; http://lattes.cnpq.br/5053247764430323; Cunha Neto, Álvaro; https://orcid.org/0000-0002-1814-6214; http://lattes.cnpq.br/7448379486432052; http://lattes.cnpq.br/7422491599920966; Athayde, Geisamanda Pedrini Brandão; https://orcid.org/0000-0002-4315-0653; http://lattes.cnpq.br/8037324704189596; Morais, Verônica Santos de; https://orcid.org/0000-0002-7324-2057; http://lattes.cnpq.br/3680926664416715Stingless bee honey is considered a functional food due to the complex presence of chemical compounds with antioxidant properties. The chemical composition of honey is associated with several factors, such as the bee species, flowering, soil, and storage method. In this sense, this study investigated the chemical composition and antioxidant capacity of honey samples produced by Melipona species from different regions of the state of Espírito Santo - ES, Brazil. A comprehensive chemical characterization of each honey was conducted using advanced techniques, such as Fourier transform mid infrared spectroscopy (FT-MIR), gas chromatography-mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR), combined with chemometric tools. The flavonoid and total phenolic contents of the honey samples were determined using TPC (total phenolic compounds) and TFC (total flavonoid content) methods. Finally, the total antioxidant capacity (TAC) of each stingless bee honey sample was evaluated using FRAP (ferric reducing antioxidant power), DPPH (2,2-diphenyl-1-picrylhydrazyl), and CRAC (ceric reducing antioxidant capacity) assays. The PCA (principal component analysis) model based on FT-MIR signals showed the separation between the honey samples of Melipona capixaba and Melipona quadrifasciata. Volatile organic compounds (VOCs) were detected by GC-MS, and the most abundant classes were carboxylic acids, ketones, aldehydes and alcohols. The classification using the PCA model based on partial GC-MS chromatograms allowed the visualization of the clusters of honey samples from Melipona capixaba and Melipona quadrifasciata. Simple phenols such as p-cresol and allyl guaiacol were also identified in the honey. In addition, the TPC and TFC contents had selective correlations with TAC. A high Pearson correlation was observed between TPC and the CRAC antioxidant assay. Thus, chemometrics combined with chemical information obtained from the use of advanced FT-MIR, GC-MS, and NMR techniques; and from TFC and TPC, CRAC, FRAP, and DPPH methods are comprehensive tools that allow tracing an identity aligned with the quality of stingless bee honey from ES.
- ItemSimulação por dinâmica molecular de flavonoides como inibidores da proteína principal do SARS-CoV-2(Universidade Federal do Espírito Santo, 2024-09-26) Lima, Ana Paula Loureiro; Gonçalves, Arlan da Silva; https://orcid.org/0000-0002-5965-3191; http://lattes.cnpq.br/4139608457982550; https://orcid.org/0009-0004-7226-538X; http://lattes.cnpq.br/6445846880137792 ; Silva Filho, Elói Alves da; https://orcid.org/0000-0002-9306-7882; http://lattes.cnpq.br/8259708288584235; Fernandes, Tácio Vinício Amorim; https://orcid.org/0000-0001-5881-9519; http://lattes.cnpq.br/9875296235929103The pandemic triggered by SARS-CoV-2 has instigated many efforts to identify effective therapies against COVID-19. In parallel, technological advances have provided an expanded platform for the exploration of bioactive compounds, among which flavonoids emerge as promising therapeutic agents, given their wealth of bioactive properties. Within the scope of this research, a Molecular Modelling approach was adopted to investigate the complex interactions between flavonoids and the key proteins of SARS-CoV-2, notably the main protease 3CLpro (Mpro) and the Spike protein, which are crucial for viral replication and cellular infection. Molecular dynamics simulations were used to evaluate the potential of these compounds as drug agents against COVID-19. Among the flavonoids studied, Amentoflavone, identified in plant species such as Ginkgo biloba, Hypericum perforatum and Passiflora, stood out for its remarkable efficacy in inhibiting the active site of viral proteins. In addition, 7‘’-O-Methylsciadopitysin showed the same RMSD result as Amentoflavone, with an MMPBSA energy of approximately -220 kJ/mol. Despite showing deviations from Lipinski's rule, implying potential limitations, these flavonoids stood out, suggesting possible adaptations that could mitigate such restrictions, thus extending their therapeutic viability and outlining promising prospects for the development of new pharmaceutical agents.
- ItemDesenvolvimento de uma metodologia eletroanalítica para detectar e quantificar ocratoxina A em amostras de café(Universidade Federal do Espírito Santo, 2025-06-05) Medeiros, Jane Schneider de; Oliveira, Jairo Pinto de; https://orcid.org/0000-0001-7595-1183; http://lattes.cnpq.br/2228283301316218; Ferreira, Rafael de Queiroz; http://lattes.cnpq.br/5053247764430323 ; https://orcid.org/0009-0002-6386-6090; http://lattes.cnpq.br/2714176584280814; Janegitz, Bruno Campos; https://orcid.org/0000-0001-9707-9795; http://lattes.cnpq.br/7746094938977989; Freitas, Marcos Benedito José Geraldo de; https://orcid.org/0000-0003-1521-774X; http://lattes.cnpq.br/3485939623614913Ochratoxin A (OTA) is a mycotoxin produced by fungi of the genera Aspergillus and Penicillium, frequently found in food products such as coffee, cereals, and spices. Given its toxicity and potential carcinogenicity, this study developed a sensitive and selective electroanalytical methodology for the detection and quantification of OTA in roasted and ground coffee. The method employed screen-printed electrodes composed of carbon black and graphite (SPE CB-G), modified in situ with cetyltrimethylammonium bromide (CTAB). The technique used was adsorptive stripping differential pulse voltammetry (DPAdSV), optimized through a central composite design (CCD). Raman spectroscopy characterization of the SPE CB-G confirmed the presence of graphite and carbon black, with a conductive surface suitable for electrochemical detection. The electroanalytical response of OTA was investigated using cyclic voltammetry (CV) under different electrolytes and pH ranges, demonstrating an irreversible oxidation process, with the anodic peak potential (Epa) shifting toward less positive values as the pH increased. The optimal electrochemical condition was achieved using phosphate buffer (PB) 0.2 mol L−1 (pH 7.0) with CTAB (80 µmol L−1), which favored OTA adsorption onto the electrode surface through electrostatic interactions with its anionic forms. Epulse, tpulse, tdep, and CTAB concentration parameters in both differential pulse voltammetry (DPV) and DPAdSV techniques were optimized via CCD to maximize the peak current (Ip). The optimized conditions provided excellent sensitivity and selectivity. The calibration curve in PB with CTAB showed linearity in the range of 10.10 to 242.29 ng mL−1 (R2 = 0.994), with a limit of detection (LOD) of 1.39 ng mL−1 and a limit of quantification (LOQ) of 4.20 ng mL−1. In the coffee matrix, LOD and LOQ were 2.70 ng mL−1 and 8.20 ng mL−1, respectively, also with R2 = 0.994. Recovery assays yielded values ranging from 94% to 110% in buffer with CTAB, wheat, and coffee, validating the method even in complex matrices. The analysis of typical coffee interferents revealed variations in OTA Ip due to competition for active sites on the SPE CB-G surface, with CTAB playing a critical role in minimizing these effects. The proposed methodology demonstrated high analytical performance, low cost, and suitability for routine analysis, meeting regulatory limits established by Anvisa and the European Union.
- ItemDesenvolvimento de eletrocatalisadores metálicos de baixo custo (Ni, Cu e Zn) para redução de CO2(Universidade Federal do Espírito Santo, 2025-01-30) Barcelos, Marcela Miranda; Ribeiro, Josimar; https://orcid.org/0000-0002-9544-1647; http://lattes.cnpq.br/1265145498501171; https://orcid.org/0009-0000-4612-0524; Rosa, Thalles Ramon; https://orcid.org/0000-0001-9913-5885; http://lattes.cnpq.br/2629035369494897; Luz, Priscilla Paiva; https://orcid.org/0000-0002-9460-546X; http://lattes.cnpq.br/3663470249824660Due to a series of environmental problems resulting from the burning of fossil fuels, it has led to an increase in CO2 emissions into the atmosphere, and it is clear that alternatives need to be considered. For example, electrochemical reduction of CO2 (RECO2) appears as a promising alternative to mitigate the impacts of high CO₂ emissions into the atmosphere. Therefore, the objective of this work is to investigate the metallic electrocatalysts of Cu, Ni and Zn for electrochemical reduction of CO2. In order to characterize morphological modifications of the metallic electrodes, X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) techniques were used. The results of the XRD analyses revealed that the surface treatments did not alter the structure of the materials. The electrochemical polishing process of copper led to a mostly homogeneous morphology. On the other hand, the ultrasonic process in organic solvent allowed the increase of the roughness of the nickel and zinc electrodes, obtaining a heterogeneous morphology due to the surface reorganization of the materials. The electrochemical studies were performed using Linear Scanning Voltammetry (LSV), the potentiodynamic polarization technique and Electrochemical Impedance Spectroscopy (EIS). The EIS was performed at two different potentials: −0.4 V and −0.6 V vs. Ag/AgCl. The EIS results allowed the identification of substantial changes that occurred before and after the treatment of the electrodes. For the Cu and Ni electrodes, the EIS data indicate greater kinetics, i.e., lower charge transfer resistance. For the Zn electrode, the results indicate that there was competition in the hydrogen evolution reaction (HER). The LVS showed that the Cu and Ni electrodes showed a high current density for the electrochemical reduction reaction of CO2. It was observed that the uniform metallic copper surface acts as an inhibitor of the HER, resulting in a decrease in the overpotential and an increase in the current density for the CO2 reduction reactions. The nuclear magnetic resonance results obtained after the chronoamperometry experiments (constant potential of −2.0 V vs. Ag/AgCl in K2CO3 0.5 mol L–1 for 2 h) indicated the formation of some products from RECO2 such as: ethane, acetone and acetate. These results demonstrate the great potential of these electrocatalysts for the electrochemical reduction of CO2.