Browsing by Author "Mechler, Adam"

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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.
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.