Is Usnic Acid a Promising Radical Scavenger?

Nguyen Thi Hoa; Mai Van Bay; Adam Mechler; Quan V Vo

doi:10.1021/acsomega.0c02306

Is Usnic Acid a Promising Radical Scavenger?

ACS Omega. 2020 Jul 7;5(28):17715-17720. doi: 10.1021/acsomega.0c02306. eCollection 2020 Jul 21.

Authors

Nguyen Thi Hoa¹, Mai Van Bay², Adam Mechler³, Quan V Vo^{4

5}

Affiliations

¹ Academic Affairs, The University of Danang-University of Technology and Education, 48 Cao Thang, Danang 550000, Vietnam.
² Department of Chemistry, The University of Danang-University of Science and Education, 48 Cao Thang, Danang 550000, Vietnam.
³ Department of Chemistry and Physics, La Trobe University, Victoria 3086, Australia.
⁴ Institute of Research and Development, Duy Tan University, Danang 550000, Vietnam.
⁵ Faculty of Chemical Technology-Environment, The University of Danang-University of Technology and Education, 48 Cao Thang, Danang 550000, Vietnam.

Abstract

Usnic acid (UA) is a natural product found in the lichen genera. Because of the phenolic groups in its structure, UA is suspected to be an antioxidant. Therefore, in this study, the radical scavenging of UA was investigated in physiological environments in silico by using kinetic calculations. It was found that the overall rate constant for the hydroxyl radical scavenging activity was approximately 10⁹ M^-1 s^-1 in all environments, whereas the HOO^• and CH₃OO^• radical scavenging activities were only significant in the polar environments with k in the range of 10³-10⁴ M^-1 s^-1. The results also revealed that the HO^• scavenging activity followed the single electron transfer (SET) and radical adduct formation mechanisms; however, the SET pathway (for the dianion HU^2-) played a dominant role in the scavenging of other studied radicals, including CH₃O^•, CCl₃O^•, CCl₃OO^•, NO₂, SO₄ ^•-, and N₃ ^•. The activity of UA against these radicals was as high as that of typical phenolic acids such as ferulic acid, p-coumaric acid, caffeic acid, dihydrocaffeic acid, and sinapinic acid (k _f ∼ 10⁸ M^-1 s^-1) in polar solvents. Thus, UA is a promising natural antioxidant in aqueous environments.