Quenching of reactive species by Avenanthramides: theoretical insight to the thermodynamics of electron transfer

Avenanthramides (AVs) are the phytochemicals found in cereals exclusively in oats. These are widely known natural substances that have antioxidant properties. The free radical deactivation potential of the eight AVs against five reactive species has been studied in physiological pH. At physiological pH, the radical quenching processes were studied using the sequential proton loss followed by electron transfer (SPLET) from the phenolic hydroxyl groups. Using density functional theory (DFT) computations, theoretical studies have been carried out in the gas phase and aqueous solution at M06-2X/6-31 + G (d,p) level of theory. The free radical scavenging ability of the studied AVs was analyzed by using conceptual density functional theory-based parameters and electrostatic potential analysis. By examining the hydrogen atom and electron affinities of each reactive species, the relative destructive potential of each has been compared. The electron transfer capabilities between the studied compound and reactive species were identified by utilizing the ionization energy and electron affinity plots. Additionally, by calculating the redox potentials and equilibrium constants for the entire process in the aqueous solution, the viability of scavenging the free radical species by selected AVs (both in neutral and mono-deprotonated) has been investigated. From the analysis, the neutral as well as the mono-deprotonated form of AVs are found to scavenge • OH and • OOH, and • NO 2 radicals effectively, while they are inefficacious toward the O 2 •‾ and • NO radicals. Graphical Abstract