Exploring antioxidative properties of xanthohumol and isoxanthohumol: An integrated experimental and computational approach with isoxanthohumol pKa determination
Jelena Tošović, Zala Kolenc, Gregor Hostnik, Urban Bren
Abstract
This study explores the antioxidative activities of xanthohumol (XN) and isoxanthohumol (IXN), prenylated flavonoids from Humulus lupulus (family Cannabaceae), utilizing the oxygen radical absorption capacity (ORAC) and ferric reducing antioxidant power (FRAP) assays along with computational Density Functional Theory methods. Experimentally, XN demonstrated significantly higher antioxidative capacities than IXN. Moreover, we determined IXN pKa values using the UV/Vis spectrophotometric method for the first time, facilitating its accurate computational modeling under physiological conditions. Through a thermodynamic approach, XN was found to efficiently scavenge HOO• and CH 3 O• radicals via Hydrogen Atom Transfer (HAT) and Radical Adduct Formation (RAF) mechanisms, while CH 3 OO• scavenging was feasible only through the HAT pathway. IXN exhibited its best antioxidative activity against CH 3 O• via both HAT and RAF mechanisms and could also scavenge HOO• through RAF. Both Single Electron Transfer (SET) and Sequential Proton Loss-Electron Transfer (SPLET) mechanisms were thermodynamically unfavorable for all radicals and both compounds. • Xanthohumol outperformed isoxanthohumol in both ORAC and FRAP assays. • The pKa values of isoxanthohumol were determined for the first time. • Xanthohumol was found to efficiently scavenge HOO•, CH 3 O• and CH 3 OO• radicals. • Isoxanthohumol showed its best antioxidative activity against CH 3 O•. • HAT and RAF were identified as likely pathways for scavenging of studied radicals.