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Propriedades optoeletrônicas e estruturais de perovskitas híbridas de baixa dimensionalidade

Wed, 01 Jan 2025 00:00:00 GMT

Título: Propriedades optoeletrônicas e estruturais de perovskitas híbridas de baixa dimensionalidade Autor(es): Braga, Filipe Augusto Gomes Abstract: Thin films of semiconductors based on three-dimensional hybrid halide perovskites (3D-HHPs) have been attracting attention and are being applied in the efficient conversion of sunlight into electrical energy. Despite the record efficiencies achieved by solar cells based on methylammonium lead iodide (MAPbI3) 3D-HHPs, the inherent chemical instability of the ionic structure remains a challenge to overcome. In this context, the present work aims to investigate and correlate the structural factors governing the chemical stability of two-dimensional perovskites (2D-HHPs) under temperature variations and light exposure in thin films containing 2D-HHPs. To this end, semiconductors were synthesized in the form of 2D-HHP single crystals: tyramine (Tyr2PbI4) and methoxybenzylamine (Mtx2PbI4) tetraiodoplumbate(II). X-ray diffraction results of Mtx2PbI4 and Tyr2PbI4 single crystals confirmed crystallization in orthorhombic (Pbca) and triclinic [(P1 ̅(2)] symmetries, respectively, with average hydrogen bond (H···I) distances between the organic cations and the octahedral (inorganic) network of 2.8488 Å and 2.9117 Å, respectively. The study of electronic properties through diffuse reflectance revealed excitonic bands in the Mtx2PbI4 (Tyr2PbI4) single crystal centered at 2.27 eV and 2.41 eV (2.25 eV and 2.41 eV), with an optical bandgap of 3.11 eV (3.15 eV). Photoluminescence results at cryogenic temperatures for the Tyr2PbI4 crystal showed strong exciton-phonon coupling with an energy of 219.86 meV. A comparison of X-ray diffraction for Tyr2PbI4 at 298 K and 100 K confirmed the prevalence of the triclinic symmetry. The surface treatment of MAPbI3 (3D) thin films with a tyramine (2D - Tyr2PbI4) solution significantly improved stability under degradation conditions for 24 hours (air, humidity, and TiO2), because of hydrogen bonds that passivate and protect the outer layers of MAPbI3 thin films. Tipo: Dissertação

Avaliação do teor inorgânico e bioacessível de arsênio em amostras de macroalgas do litoral do Ceará-Brasil

Wed, 01 Jan 2025 00:00:00 GMT

Título: Avaliação do teor inorgânico e bioacessível de arsênio em amostras de macroalgas do litoral do Ceará-Brasil Autor(es): Nobre, Iago Gabriel Medeiros Abstract: Brazil has an extensive coastline where a wide variety of macroalgae species can be found, especially in the northeast region. The global production of macroalgae has increased significantly in recent years due to its growing use in the cosmetics, pharmaceutical, and food industries. Macroalgae are capable of bioaccumulating inorganic elements, including potentially toxic ones such as arsenic (As). For this element, toxicity depends on its chemical form, with its inorganic species, As (III) and As (V), considered carcinogenic, while arsenobetaine is non-toxic. Consequently, speciation analysis of As in macroalgae, the study of the bioaccessibility of this element and physicochemical analyses are crucial to ensure the safety of consumers. In this study, the levels of As in four species of macroalgae from the Ceará coast (Sargassum vulgare, Ulva lactuca, Gracilaria birdiae, and Solieria filiformis) were determined by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) after sample digestion in an acidic medium with microwave-assisted heating. The macroalgae samples showed As contents ranging from 2.5 to 34.6 mg kg-1. The water-soluble species of As, including iAs, were extracted in water and analyzed by ICP-OES, representing 34-52% of the total As content. The iAs levels were measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) after magnetic solid-phase extraction and ranged from 0.15 to 2.59 mg kg-1. The species Sargassum vulgare stood out for having higher levels of As and iAs. Arsenic in a certified reference material sample ERM-CD200 (Bladderwrack - Fucus vesiculosus) was determined with statistically similar values at a 95% confidence level. The macroalgae samples showed high moisture content (67.9% to 86.7%), ash (13.43% to 34.44%), carbohydrates (62.09% to 79.98%), and proteins (3.47% to 6.59%), and low lipid content (<1%). The bioaccessibility analysis of As in the samples yielded results ranging from 0.98 to 11.54 mg kg, with percentages of bioaccessible arsenic relative to the total ranging from 33.31% to 58.13%. For a more conclusive assessment regarding the absorption of As by the body, in vivo bioavailability studies are necessary due to the involvement of more complex metabolic activities. Tipo: Dissertação

Novos complexos bisbipiridínicos de rutênio(II) com potencial atividade farmacológica

Wed, 01 Jan 2025 00:00:00 GMT

Título: Novos complexos bisbipiridínicos de rutênio(II) com potencial atividade farmacológica Autor(es): Pereira, Walysson Gomes Abstract: Coordination compounds, such as cisplatin and sodium nitroprusside, have demonstrated relevant pharmacological applications but are often associated with significant side effects. Ruthenium-based complexes have emerged as promising alternatives due to their lower systemic toxicity. In this work, six novel ruthenium (II) complexes were synthesized and characterized: FOR006, FOR0D6, FOR076, FOR086, cis-[Ru(bpy)₂(NO₂)CO]⁺, and WP1. Characterization techniques included NMR spectroscopy, UV-Vis absorption, FTIR, cyclic voltammetry, conductivity measurements, and elemental analysis. Single crystals suitable for X-ray diffraction were obtained for three of the complexes. Most compounds underwent photolysis upon UV or blue light irradiation, with controlled release of ligands such as NO, NO₂⁻, HNO, or CO. FOR086 and cis-[Ru(bpy)₂(NO₂)CO]⁺ also released NO/HNO under chemical or electrochemical reduction. In addition, FOR086 showed antioxidant activity through superoxide radical scavenging. All complexes tested exhibited low cytotoxicity in cardiomyocyte (H9c2) and murine macrophage (J774) cell lines (IC₅₀ > 100 µmol·L⁻¹), indicating good biocompatibility. Complexes containing the 6-ain ligand showed significant vasodilatory effects via distinct mechanisms: FOR006 and FOR0D6 likely act through direct activation of guanylate cyclase (GCs), while FOR076 and FOR086 function via NO release, activating the NO-GCs-cGMP signaling pathway. cis-[Ru(bpy)₂(NO₂)CO]⁺ also exhibited vasodilatory activity, although to a lesser extent. G-quadruplex DNA binding studies revealed that cis-[Ru(bpy)₂(NO₂)CO]⁺ effectively stabilizes these structures, particularly the one associated with the c-MYC oncogene, indicating potential anticancer properties. WP1 showed electrostatic interaction with DNA and promoted photospecific DNA cleavage through ligand release and the generation of reactive species, such as superoxide radicals. These findings highlight WP1 as a promising photosensitizer candidate for photochemotherapeutic applications. Tipo: Tese

Desenvolvimento e validação de métodos para análise de clorato em água de processo e suco de acerola por cromatografia de íons

Thu, 01 Jan 2026 00:00:00 GMT

Título: Desenvolvimento e validação de métodos para análise de clorato em água de processo e suco de acerola por cromatografia de íons Autor(es): Menezes, Josália Liberato Rebouças Abstract: Brazil, as a major producer and exporter of fruits, including acerola, must meet international standards to remain competitive in the global market. These food products are often contaminated by chlorinated substances (DBPs) present in treated water, associated with the use of chlorine-based sanitisers. In fruits and vegetables, among the chlorinated inorganic contaminants, chlorate (ClO3⁻) stands out, which has aroused increasing concern among health and food safety authorities such as WHO, EFSA, and EPA. Considering that exposure to this substance occurs predominantly through the ingestion of contaminated water and food, international regulatory bodies have established maximum chlorate limits for the marketing of these products. Thus, the identification and quantification of this anion are essential to ensure food safety and public health. Since export specifications for fruit and its products allow for very low chlorate concentrations (MRL of 0.05 mg/kg for citrus), sensitive and selective analytical methods become indispensable for monitoring in the agro-industry. Ion chromatography (IC) stands out as a regulated technique for the determination of ClO3⁻, offering high selectivity, rapid result acquisition, the ability to detect multiple ionic species, and low cost compared to LC-MS. In 2024, fifty years after the first survey on DBPs, chlorate was reaffirmed as a target analyte in several methods published by the USEPA. Aiming to contribute to advances in chlorate determination, this work reports the development of two methods for chlorate quantification, one in process water and the other in acerola juice. For water analysis, a more sensitive method than direct injection was developed, using solid-phase extraction coupled with ion chromatography in conductimetric detection (SPE-IC-DC), through factorial design to optimize the extraction conditions. The method showed selectivity, absence of matrix effect, and detection and quantification limits of 0.2 and 0.6 µg/L, respectively. A method based on liquid-liquid extraction combined with solid-phase extraction and ion chromatography (LLE-SPE-IC) was also developed for the analysis of concentrated acerola juice, obtaining a quantification limit three times lower (18 µg/Kg) than the European limit. Thus, the SPE-IC-DC and LLE-SPE-IC methods proved to be viable and efficient for quality control in juice processing industries. Tipo: Tese