Theoretical Study for Exploring the Diglycoside Substituent Effect on the Antioxidative Capability of Isorhamnetin Extracted from Anoectochilus roxburghii

Nguyen Minh Thong; Quan V Vo; Trinh Le Huyen; Mai Van Bay; Dinh Tuan; Pham Cam Nam

doi:10.1021/acsomega.9b01780

Theoretical Study for Exploring the Diglycoside Substituent Effect on the Antioxidative Capability of Isorhamnetin Extracted from Anoectochilus roxburghii

ACS Omega. 2019 Sep 5;4(12):14996-15003. doi: 10.1021/acsomega.9b01780. eCollection 2019 Sep 17.

Authors

Nguyen Minh Thong¹, Quan V Vo², Trinh Le Huyen³, Mai Van Bay⁴, Dinh Tuan⁵, Pham Cam Nam⁶

Affiliations

¹ The University of Danang, Campus in Kon Tum, 704 Phan Dinh Phung, Kon Tum 580000, Vietnam.
² Quang Tri Teachers Training College, Quang Tri 520000, Vietnam.
³ Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan.
⁴ Department of Chemistry, The University of Danang, University of Science and Education, 459 Ton Duc Thang, Da Nang 550000, Vietnam.
⁵ Department of Chemistry, Hue University's College of Sciences, 77 Nguyen Hue, Hue 530000, Vietnam.
⁶ Department of Chemistry, The University of Danang, University of Science and Technology, 54 Nguyen Luong Bang, Da Nang 550000, Vietnam.

Abstract

Radical-scavenging activity of isorhamnetin (1) and its diglycosides, named isorhamnetin-3,5'-O-β-D-diglucoside (2) and isorhamnetin-3,7-O-β-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^• 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 × 10⁵ 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.