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Avaliação de biocarvões na miniaturização da MSPD para determinação de resíduos de pesticidas em alimentos para bebês

Thu, 30 Jul 2026 00:00:00 GMT

Título: Avaliação de biocarvões na miniaturização da MSPD para determinação de resíduos de pesticidas em alimentos para bebês Autor(es): Nascimento, Roseane dos Santos Abstract: Commercially available foods based on fruits, vegetables, meat and cereals are offered to babies from the age of six months chemical such as pesticides are used in crop cultivation to boost production meeting market demand and controlling pests that hinder plant and fruit growth. Residues of these compounds can remain in the final product and potentially affect a baby’s health; consequently, analytical methods are developed to detect contaminants in various samples. The use of miniaturized methods emerged as a way to reduce solvent volume and the amounts of adsorbents, as well as to eliminate steps compared to conventional method. Thus, this study aimed to develop a miniaturized MSPD method using pipette tips to extract the pesticides abamectin, acephate, acetamiprid, azoxystrobin, bifenthrin, clothianidin, difenoconazole, dimethoate, epoxiconazole, flutriafol, imidacloprid, lufenuron, malathion, methomyl, permethrin, pyraclostrobin, teflubenzuron, thiacloprid, thiamethoxam and thiophanate – methyl from pasty baby foods, in conjunction with liquid chromatography and DAD/UV-Vis detection. Commercial adsorbents C18, sílica gel, PSA, florisil, neutral alumina and the synthetic adsorbent TEOS were tested, as were solventes including methanol, acetonitrile, and mixtures with dichloromethane and ethyl acetate, evaluated at various volumes and ratios. The optimal extraction conditions involved using 40 mg of sample (fortified at 1 µg mL 1 ), 60 mg of sílica gel and 1000 µL of MeOH:ethyl acetate (50:50 v,v), yielding recoveries between 70 – 108 %. Subsequently, the parameters of the sample preparation method using corn cob biochar the adsorbent material that proved most efficient for analyte extraction under the same conditions previously established for sílica, but employing MeOH for analyte elution recovery rates ranged from 62 % to 112 %. Finally, the two methods developed in this study were validated by evaluating the parameters of linearity, sensitivity, selectivity, limit of detection, limit of quantification, accuracy, and precision. Subsequently, the methods were applied to samples of different brands and compositions marketed in Sergipe, but the pesticides under study were not found.

Investigação teórica de complexos luminescentes de eu3+: elucidação dos mecanismos de transferência de energia e desenvolvimento de um protocolo computacional para predição do rendimento quântico

Mon, 27 Jul 2026 00:00:00 GMT

Título: Investigação teórica de complexos luminescentes de eu3+: elucidação dos mecanismos de transferência de energia e desenvolvimento de um protocolo computacional para predição do rendimento quântico Autor(es): Rodrigues, Jocelia Silva Machado Abstract: This work aimed to theoretically investigate the luminescent propertiesof Eu3+complexes containing β-diketonate ligands, focusing on understandingtheenergytransfer and backtransfer mechanisms responsible for the luminescent efficiencyofthese systems. Using semi-empirical methodologies, four complexes withpotential technological applications were studied: [Eu(tta)3(5,5’-dmbpy)] and [Eu(btfa)3(5,5’-dmbpy)], applied in the construction of OLED devices, and [Eu(tta)3(δ-val)(H2O)] and[Eu(btfa)3(δ-val)(H2O)], investigated as luminescent markers for gunshot residue.The theoretical investigation of these systems was necessary to understand, at themicroscopic scale, the photophysical processes that govern the luminescentperformance of the complexes, allowing them to be correlated withtheoptical properties observed experimentally. The theoretical results obtained agreedwell withthe experimental data provided by collaborators, demonstrating that thecalculatedproperties consistently describe the luminescent behavior of the studiedcompoundsand explain their efficiency in different technological applications. Inadditiontophotophysical studies, this thesis also involved the development of anewcomputational protocol for predicting the quantum yield in Eu 3+ complexes. Themodel was parameterized and validated using experimental quantumyield dataavailableinthe literature for a library composed of 17 Eu 3+ complexes. The results demonstratedhigh accuracy in reproducing the experimental quantum yields, presentingameanabsolute error of around 10%, a value significantly lower than those observedfortheanalytical models traditionally employed in the literature, whose mean errorsrangedbetween approximately 20% and 55%. Thus, this work contributes to theelucidationof the photophysical mechanisms of Eu 3+ complexes and presentsanewcomputational methodology for the precise prediction of quantumyield.

Crescimento e caracterização de monocristais das famílias RCuGa3 (R = Ce, Pr, Nd, Gd) e RNiIn4 (R = La, Ce, Pr, Nd) por meio do método de fluxo metálico: estudos estruturais, magnéticos e do campo elétrico cristalino

Wed, 27 Aug 2025 00:00:00 GMT

Título: Crescimento e caracterização de monocristais das famílias RCuGa3 (R = Ce, Pr, Nd, Gd) e RNiIn4 (R = La, Ce, Pr, Nd) por meio do método de fluxo metálico: estudos estruturais, magnéticos e do campo elétrico cristalino Autor(es): Possidonio, Daykson Neves Abstract: This work presents a systematic experimental study on the synthesis, structural characterization, and investigation of the magnetic properties of single crystals belonging to two families of rare-earth-based intermetallic compounds, RCuGa3 (R = Ce, Pr, Nd, Gd) and RNiIn4 (R = La, Ce, Pr, Nd). The single crystals were grown using the high-flux method, employing gallium (Ga) and indium (In) as solvents for the RCuGa3 and RNiIn4 series, respectively, enabling the growth of samples with high crystalline quality. Structural characterization was performed by X-ray diffraction (XRD), with crystallographic parameters refined using the Rietveld method implemented in the DBWS software, revealing that the RCuGa3 compounds crystallize in a tetragonal structure with space group I4/mmm, whereas the RNiIn4 compounds adopt an orthorhombic YNiAl4-type structure belonging to the Cmcm space group. Complementary scanning electron microscopy (SEM) analyses, particularly for PrNiIn4, confirmed the chemical homogeneity and high structural quality of the crystals, in good agreement with the XRD results. The magnetic properties were investigated through temperature-dependent magnetic susceptibility measurements for both families, and through specific heat (Cp) measurements for the RNiIn4 series, revealing antiferromagnetic behavior at low temperatures, with magnetic transitions characterized by N´eel temperatures (TN ) ranging from 2.2 K to 9.3 K, namely TN ≈ 3 K (Ce), 4.4 K (Pr), 2.2 K (Nd), and 9.3 K (Gd) for the RCuGa3 series, and 2.8 K < TN < 4.2 K for the RNiIn4 series. The analysis of the inverse magnetic susceptibility in the paramagnetic regime, based on the Curie-Weiss model, allowed the determination of the Curie-Weiss temperature (θCW), the experimental effective magnetic moment (µexp), and the magnetic frustration factor (f), revealing a pronounced magnetic anisotropy in the RNiIn4 series, expressed by ratios χeasy/χhard > 1, which is attributed to the significant influence of crystalline electric field (CEF) effects. Similar CEF-related effects were also identified in the RCuGa3 series, particularly for the Ce- and Pr-based compounds, influencing both the values of TN and the deviations observed from the scaling behavior predicted by the De Gennes rule. The specific heat measurements corroborated the magnetically determined transition temperatures and further reinforced the central role of CEF effects in defining the magnetic ground state of these systems, providing, overall, a comprehensive comparative analysis of the correlations between crystal structure, electronic interactions, and magnetic properties in rare-earth intermetallic compounds.

Comportamento dos fônons e magnetismo gerado por vacâncias em nanocristais de CeO2− dopado com Mn

Mon, 02 Feb 2026 00:00:00 GMT

Título: Comportamento dos fônons e magnetismo gerado por vacâncias em nanocristais de CeO2− dopado com Mn Autor(es): Assis, Maria Suêd Macêdo Abstract: We investigated the influence of doping CeO2 nanocrystals with Mn through structural, spectroscopic, and magnetic analyses. The materials were synthesized by the sol-gel method and characterized by X-ray diffraction, X-ray absorption spectroscopy (XANES), Raman spectroscopy, and magnetic measurements. The results of Rietveld refinement together with the Raman spectrum confirm the formation of a single phase of CeO2 with a fluorite-type cubic structure. These results show that Mn insertion modifies the lattice parameters, crystallite size, and microdeformation in a non-monotonic manner, revealing a balance between local disorder and lattice relaxation induced by phonons and vacancy formation. The XANES results reveal mixed valence of Mn ions as Mn3+ /Mn2+ , resulting in charge compensation through partial reduction of Ce4+ to Ce3+ . The ZFC/FC curves suggest an anisotropic distribution originating from Mn–vacancy and show blocked superparamagnetic behavior at low temperatures. The study identified an antiferromagnetic regime derived from Dzyaloshinskii-Moriya (DM) influenced by oxygen vacancies. These results present a framework that quantifies the defect chemistry and magnetic behavior in (Ce1−xMnxO2−, 0 ≤ x ≤ 0.09) nanocrystals, highlighting the role of oxygen vacancies and doping-induced structural disorder.