Browsing by Author "Vo, Quan V."

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A thermodynamic and kinetic study of the antioxidant activity of natural hydroanthraquinones
(2020-05-26)
Vo, Quan V.
;
Nguyen Minh Thong
;
Trinh Le Huyen
;
Pham Cam Nam
;
Nguyen Minh Tam
Novel hydroanthraquinones isolated from marine algal-derived endophytic fungus Talaromyces islandicus EN-501 exhibited promising antioxidant properties in preliminary studies, raising the prospect of adapting these compounds for therapeutic use in diseases caused by oxidative stress. For medicinal applications it is beneficial to develop a full understanding of the antioxidant activity of these compounds. In this study, the hydroperoxide radical scavenging activity of five natural hydroanthraquinones was evaluated by kinetic and thermodynamic calculations. The results showed that the radical scavenging of these hydroanthraquinones in the gas phase and in lipid solvents was defined by the formal hydrogen transfer mechanism, that for the polar environments was decided by the sequential proton loss electron transfer pathway. The hydroanthraquinones exhibited good hydroperoxide scavenging activity in both polar and non-polar media. The overall rate constant values for the radical scavenging reaction were in the range of 3.42 x 10(1) to 2.60 x 10(5) M-1 s(-1) and 3.80 x 10(6) to 5.87 x 10(7) M-1 s(-1) in pentyl ethanoate and water solvents, respectively. Thus the activity of 8-hydroxyconiothyrinone B (1) is about 2.6 and 444.6 times higher than that of Trolox in the studied solvents, identifying 8-hydroxyconiothyrinone B as a promising antioxidant.
Functionalization and antioxidant activity of polyaniline-fullerene hybrid nanomaterials: a theoretical investigation
(2020-04-15)
Nguyen Minh Thong
;
Vo, Quan V.
;
Trinh Le Huyen
;
Mai Van Bay
;
Nguyen Nho Dung
Functionalized fullerene is one of the most advantageous nanotechnologies to develop novel materials for potential biomedical applications. In this study, we applied the ONIOM-GD3 approach to explore the nucleophilic addition reaction mechanism between polyaniline (emeraldine and leucoemeraldine forms) and fullerene. Potential energy surfaces were also analyzed to predict the predominantly formed products of the functionalized reaction. The themoparameters, such as bond dissociation enthalpy (BDE), ionization energy (IE), and electron affinity (EA), characterized by two mechanisms HAT and SET, were used to evaluate the antioxidant activities of the selected compounds. Moreover, the calculated HOMO, LUMO, and DOS results indicate that the electronic structures of polyaniline-fullerene were significantly affected by the presence of fullerene. The computational results show that C60-L1 seems to be the best antioxidant following the SET mechanism.
The antioxidant activity of natural diterpenes: theoretical insights
(2020-04-15)
Vo, Quan V.
;
Nguyen Minh Tam
;
Le Trung Hieu
;
Mai Van Bay
;
Nguyen Minh Thong
Diterpenes that were isolated from Crossopetalum gaumeri (Loes.) Lundell (Celastraceae) plants are reported to exhibit a range of biological activities, in particular as radical scavengers. Thus further insight into the antioxidant activity of diterpenes in physiological environments is much needed but not studied yet. In this study, the antioxidant activity of nine natural diterpenes was evaluated using kinetic and thermodynamic calculations. It was found that the sequential proton loss electron transfer (SPLET) mechanism is favored in polar environments, whereas formal hydrogen transfer (FHT) is the main pathway for the radical scavenging of these diterpenes in the gas phase as well as in lipid media. The rate constants for the HOO & x2d9; radical scavenging of these compounds in the gas phase, polar and nonpolar solvents are in the range of 2.29 x 10(-2) to 4.58 x 10(7), 9.74 x 10(-3) to 1.67 x 10(8) and 3.54 x 10(-5) to 1.31 x 10(5) M-1 s(-1), respectively. 7-Deoxynimbidiol (6), exhibits the highest HOO & x2d9; radical scavenging with k(overall) = 1.69 x 10(8) M-1 s(-1) and 9.10 x 10(4) M-1 s(-1) in water and pentyl ethanoate solvents, respectively, that is about 1300 times higher than that of Trolox in polar environments. It is thus a promising natural antioxidant in physiological environments.
Theoretical Study for Exploring the Diglycoside Substituent Effect on the Antioxidative Capability of Isorhamnetin Extracted from Anoectochilus roxburghii
(2019-09-17)
Nguyen Minh Thong
;
Vo, Quan V.
;
Trinh Le Huyen
;
Mai Van Bay
;
Dinh Tuan
Radical-scavenging activity of isorhamnetin (1) and its diglycosides, named isorhamnetin-3,5'-O-beta-D-diglucoside (2) and isorhamnetin-3,7-O-beta-D-diglucoside (3) extracted from Anoectochilus roxburghii, has been studied through three main antioxidant pathways: hydrogen atom transfer (HAT), single electron transfer followed by proton transfer, and sequential proton loss electron transfer (SPLET). All thermodynamic parameters related to these radical-scavenging mechanisms were computed at the B3LYP/6-311G(d,p) level of theory both in the gas phase and in solution. The results suggest that HAT is the predominant mechanism in the gas phase, while SPLET is supported in an aqueous environment. In addition, the stability of radicals has also been explored by electron spin density and intramolecular hydrogen bonding. The potential energy profiles and kinetic calculations for the reactions between the selected compounds and the CH3OO center dot radical were calculated at 298.15 K. Among all investigated, compound 2 has the highest antioxidant activity with the lowest Gibbs free energy (-4.05 kcal/mol) and the highest hydrogen atom transfer rate constant (3.61 x 10(6) M(-1)s(-1)). Substitution of the OH and OMe groups by two glucoses at the 3 and 5' sites of isorhamnetin has a significant impact on its antioxidant activity.