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Item Antioxidant activity of (+)-bergenin : a phytoconstituent isolated from the bark of Sacoglottis uchi Huber (Humireaceae).(2008) Abreu, Heitor Avelino de; Santos, Izandina Aparecida Lopes dos; Souza, Gilmar Pereira de; Veloso, Dorila Piló; Duarte, Hélio Anderson; Alcântara, Antônio Flávio de Carvalho(+)-Bergenin (1) was isolated from Sacoglottis uchi, a species of vegetable found in the Amazon region and popularly used for the treatment of several hepatic problems. The structure of 1 was fully characterized using IR, GC–MS and NMR (1D and 2D) analyses. This phytoconstituent has been used as an oriental folk medicine for the treatment of many diseases and shows antihepatotoxic properties. Tests with b-carotene, DPPH and a heterogeneous Fenton system were carried out, confirming the antioxidant activity of 1. Theoretical calculations were performed to investigate the formation of the radical derivatives of 1 using •H, •OH, •CH3, and •CCl3 as initiator radicals. DFT thermodynamic calculations showed that the methoxyl group (O-6–CH3) is the most favorable site for radical attack. Frontier molecular orbital analysis showed that nucleophilic radical attack is favored on the aromatic ring of 1 where the LUMO is localized, with antibonding character with respect to the O-6–CH3 bond. The possibilities of attack at other sites on 1 were investigated in detail in order to understand the regiospecificity of this reaction.Item Structural characterization of a new dioxamic acid derivative by experimental (FT-IR, NMR, and X-ray) analyses and theoretical (HF and DFT) investigations.(2012) Souza, Gilmar Pereira de; Konzen, Cibele; Simões, Tatiana Renata Gomes; Rodrigues, Bernardo Lages; Alcântara, Antônio Flávio de Carvalho; Stumpf, Humberto OsórioVery few investigations concerning the crystal structure and chemical properties of dioxamic acids have been related in the literature. This work describes the chemical properties of ortho-phenylenebis(oxamic acid) (2) and its new derivative, hydrogeno ortho-phenylenebis(oxamato) benzimidazolium (3) using experimental (FT-IR, NMR, and X-ray single crystal diffraction) and theoretical (HF/3-21G_ and B3LYP/ 6-31G_ calculations) methodologies. Compound 2 displays intramolecular hydrogen bonding between the hydrogen of an amide group and the oxygen atom of another amide group present in the structure. Compound 3 was prepared by a newly developed synthetic route involving decomposition of the dioxamic acid in solution without the presence of metallic ions. Thermodynamic calculations indicate a process via two successive hydrolyzes of the amide groups of 2, followed by condensation with formic acid and finally dehydration. The structure of 3 was solved by X-ray single-crystal diffraction and it consists of meso-helical chains stabilized by intra and intermolecular hydrogen bonds and p–p stacking interactions.