Theoretical Study on the Antioxidant Activity of Natural Depsidones

Mai Van Bay; Pham Cam Nam; Duong Tuan Quang; Adam Mechler; Nguyen Khoa Hien; Nguyen Thi Hoa; Quan V Vo

doi:10.1021/acsomega.9b04179

Theoretical Study on the Antioxidant Activity of Natural Depsidones

ACS Omega. 2020 Mar 31;5(14):7895-7902. doi: 10.1021/acsomega.9b04179. eCollection 2020 Apr 14.

Authors

Mai Van Bay¹, Pham Cam Nam², Duong Tuan Quang³, Adam Mechler⁴, Nguyen Khoa Hien⁵, Nguyen Thi Hoa⁶, Quan V Vo⁷

Affiliations

¹ Department of Chemistry, The University of Da Nang, University of Science and Education, Da Nang 550000, Vietnam.
² Department of Chemical Engineering, The University of Da Nang, University of Science and Technology, Da Nang 550000, Vietnam.
³ University of Education, Hue University, Hue City 530000, Vietnam.
⁴ Department of Chemistry and Physics, La Trobe University, Victoria 3086, Australia.
⁵ Mientrung Institute for Scientific Research, Academy of Science and Technology, Hue City 530000, Vietnam.
⁶ Academic Affairs, The University of Danang - University of Technology and Education, Da Nang 550000, Vietnam.
⁷ Institute of Research and Development, Duy Tan University, Danang 550000, Vietnam.

Abstract

Depsidones are secondary metabolites in lichens with a range of potential health benefits. Among others, these compounds are believed to exhibit high hydroxyl radical and superoxide scavenging abilities, warranting a detailed investigation of their antioxidant properties. In this study, the radical scavenging activity of natural depsidones from Ramalina lichenized fungi was investigated in silico. Calculations of the thermodynamic parameters suggested that the main radical scavenging pathway follows the formal hydrogen transfer (FHT) mechanism; however, unexpectedly low rate constants were found in the CH₃OO^• scavenging reaction. Establishing that the depsidones are mostly ionized in an aqueous environment suggested that the single-electron transfer (SET) mechanism should not be ruled out. Consistently, depsidones were revealed to be excellent HO^• and O₂ ^•- scavengers in aqueous solutions (k = 4.60 × 10⁵ - 8.60 × 10⁹ M^-1 s^-1 and k = 2.60 × 10⁸ - 8.30 × 10⁹ M^-1 s^-1, respectively) following the sequential proton loss electron transfer (SPLET) mechanism. These results suggest that natural fungal depsidones are potent hydroxyl and superoxide radical scavengers in aqueous solutions.