Navegando por Autor "Silva, Valter Henrique Carvalho"
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- ItemArylsulfonamide chalcones as alternatives for fuel additives: antioxidant activity and machine learning protocol studies(2023) Duarte, Vitor Santos; Borges, Igor Dalarmelino; D´Oliveira, Giulio Demetrius Creazzo; Faria, Eduardo Coelho da Mata; Almeida, Leonardo Rodrigues de; Silva, Valter Henrique Carvalho; Noda Pérez, Caridad; Napolitano, Hamilton BarbosaBiodiesel is a promising fuel with the potential to reduce some negative aspects of fossil fuels, such as the emission of pollutants and greenhouse gases (GHGs), the scarcity of natural resources and market instability. To amplify its low durability and stability the use of technologies based on molecular compounds that reduce the oxidation rate of biodiesel and preserve its physical–chemical properties is very common and necessary throughout the world. To reduce oxidative stability problems of diesel–biodiesel blends, arylsulfonamide chalcones were evaluated as potential additives for B20 blends. In this study, comprehensive structural, computational, and experimental analyses were undertaken to understand the antioxidant potential of these compounds as possible additives. The supramolecular arrangements were stabilized by weak molecular interactions (C–H⋯O and C–H⋯π), which are related to antioxidant and antibacterial action, and groups can act as electron-donating substituents. The energy range of 593.1–570.2 kJ mol−1 in the frontier molecular orbitals indicates high structural stability, due particularly to sulfonamide groups which enable electrophilic attack. Furthermore, the Fukui function aligned with kinetics parameters, obtained using machine learning protocols, provided information to clarify and expand the comprehension of chalcone antioxidant features mediated by free-radical capture. The heat of combustion indicated good energy availability (6530.5–7306.5 kcal kg−1), close to those of conventional fuels. In addition, the oxidative stability of the diesel–biodiesel blend (B20) remained at around 27 hours, after 140 days of storage, which is better than for some commercial additives. We hope that this comprehensive study will support the understanding of chalcone-based compounds as alternatives to fuel additives.
- ItemEstudo químico quântico da adsorção dos gases O2 e H2 sobre a ftalocianina de alumínio(2008-06) Silva, Valter Henrique Carvalho; Camargo, Ademir João; Napolitano, Hamilton Barbosa; Oliveira, Anselmo Elanca deAiming a development of new materials suitable to building a selective chemistry sensors for oxygen and storing devices of the hydrogen, the theoretical calculations DFT/ B3LYP/6–31G(d) were carried out to complexes [AlPc]+, [AlPc]0, [(O2)AlPc]+, [(O2)AlPc]0, [(H2)AlPc]+ and [(H2)AlPc]0 through Gaussian03. The results show a strong adsorption of O2 by AlPc in both oxidated state (–44,62 Kcal/mol) and reduced state (–108,71Kcal/ mol). The chemistry adsorption takes a structural and electronic changes of AlPc which makes possible its utilization to building the selective chemistry sensors for detection of O2. Also the physical adsorption of H2 shows AlPc suitable for development of the storing devices of H2.
- ItemInsights into chalcone analogues with potential as antioxidant additives in diesel–biodiesel blends(2022) Borges, Igor Dalarmelino; Faria, Eduardo Coelho da Mata; Custodio, Jean Marcos Ferreira; Duarte, Vitor Santos; Fernandes, Fernanda de Sousa; Alonso, Christian Gonçalves; Silva, Valter Henrique Carvalho; Oliveira, Guilherme Roberto de; Napolitano, Hamilton BarbosaBiodiesel production is one of the promising strategies to reduce diesel consumption and an important contribution to climate change. However, biodiesel stability remains a challenging problem in biofuel use in the global energy matrix. In this context, organic additives have been investigated to minimize these problems and reduce harmful emissions to comply with fuel requirement standards. In this study, we discuss a comprehensive structural description, a behavior of B15 [85% volume of diesel and 15% volume of biodiesel (B100)] stability in the presence of antioxidants (chalcone analogues), and a theoretical calculation to pave the way for clarifying and expanding the potential of title compounds as an antioxidant additive for diesel–biodiesel blends. Finally, a systematic description of the oxidation stability was undertaken using a specialized machine learning computational pySIRC platform.
- ItemZinc complexes with 1,2-disubstituted benzimidazole ligands: experimental and theoretical studies in the catalytic cycloaddition of CO2 with epoxides(2019) Milani, Jorge Luiz Sônego; Bezerra, Werberson de Almeida; Valdo, Ana Karoline Silva Mendanha; Martins, Felipe Terra; Camargo, Lilian Tatiane Ferreira de Melo; Silva, Valter Henrique Carvalho; Santos, Sailer Santos dos; Gomes, Danielle Cangussu de Castro; Chagas, Rafael Pavão dasThe synthesis and characterization of four zinc(II) complexes with monodentate 1,2-disubstituted benzimidazole ligands and their catalytic activity in the cycloaddition of CO2 and epoxides are reported. The complexes were characterized by 1H and 13C NMR, thermal analysis, infrared absorption and FT-Raman spectroscopy and ESI-HRMS. Complex Zn3 had its structure determined by single-crystal X-ray diffraction and a description of intra- and intermolecular interactions has been done. All complexes were able to catalyze the production of cyclic carbonates selectively, and complex Zn1 was used in the transformation of various epoxides to carbonates, using tetrabutylammonium bromide as cocatalyst. Quantum chemistry approaches were used to comprehend the initial step of catalytic cycle: the epoxide coordination to the metallic center. The calculations show that one benzimidazole ligand should be dislocated from the metal center before the catalyst interacts with the epoxide to activate it.