Theoretical and experimental study of a new antioxidant xanthone: Solvent and intramolecular hydrogen bond effects

Free radicals are harmful reactive species that cause various problems in the human body. Antioxidant compounds, such as xanthones found in natural products, can help prevent these effects. This study focuses on the antioxidant behavior of ravenelin (RVL) and ravenelin B (RVLB), a newly discovered xanthone in the Exserohilum rostratum fungus. Both experimental and in silico tests were conducted, comparing them to ascorbic acid, a standard antioxidant. The results showed that RVL has a lower bond dissociation energy (312 kJ/mol) than ascorbic acid (313 kJ/mol), indicating comparable antioxidant performance. This difference is mild but agrees with the experiment that indicates RVL efficiency is equivalent to ascorbic acid at low concentrations. RVLB, however, demands higher dissociation energy (323 kJ/mol) and consequently it has a lower antioxidative efficiency. Thus, antioxidant capacity is found as RVL > ascorbic acid > RVLB. From experimental assays, the RVL performance was confirmed through experimental tests at different solute concentrations. The study also examines the effects of solvents and intramolecular hydrogen bonds. Ravenelin molecules present three hydroxyl groups involved in intramolecular OH & ctdot;O interactions. However, analysis based on the infrared spectra, as well as Bader's theory and non -covalent interactions done in water solvent showed that the two strongest H -bonds (approximate to -37 kJ/mol) better stabilize the molecular structure, but are not favorable to antioxidant reactions, indicating that hydrogen scavenging occurs at the less hydrogen -bonded hydroxyl group. The solvent also plays an active role first in facilitating hydrogen abstraction besides changing the hydrogen scavenging mechanism according to the environmental polarizability. Additionally, the antioxidant mechanism of ravenelin molecules changes from nonpolar to polar solvents, allowing for hydrogen abstraction.