Antioxidant Activity and Mechanism of Avenanthramides: Double H⁺/e^– Processes and Role of the Catechol, Guaiacyl, and Carboxyl Groups

Abstract

Avenanthramides (AVAs), unique phenolic compounds in oats, have attracted increasing interest due to their health benefits. Eight representative AVAs were studied using the density functional theory (DFT) method to elucidate their antioxidant activity and mechanism. Preference of different mechanisms was evaluated based on thermodynamic descriptors involved in double (2H + /2e − ) free radical scavenging reactions. It was found that the hydrogen atom transfer (HAT) mechanism is more favorable in the gas and benzene phases, while sequential proton loss electron transfer (SPLET) is preferred in polar media. The results suggest the feasibility of the double HAT and double SPLET mechanisms for 2s and c-series AVAs. The sequential triple proton loss double electron transfer (StPLdET) mechanism represents the dominant pathway in aqueous solution at physiological pH. In addition, the sequential proton loss hydrogen atom transfer (SPLHAT) mechanism provides an alternative pathway to trap free radicals. Results also revealed the important role of the catechol, guaiacyl, and carboxyl moieties.

Sprouting and Hydrolysis as Biotechnological Tools for Development of Nutraceutical Ingredients from Oat Grain and Hull

“…Avenanthramides, which have a soluble character, may be responsible for the increment observed in the SO-soluble fraction (FP) after sprouting. The mechanism of action of these compounds has been studied, with three main pathways identified: hydrogen atom transfer (HAT), single electron transfer followed by proton transfer and sequential proton loss electron transfer (SPLET) in both polar and non-polar media [ 97 ]. The process of enzymatic hydrolysis increased 10 times the ABTS •+ ), radical capacity of the OH FP fraction when using UltrafloxL, and 9.5 times with Viscoferm, probably due to the release of ferulic, p -coumaric, caffeic and 4-hydroxybenzaldehyde ( Table 2 and Table 3 ).…”

Avenanthramides, Distinctive Hydroxycinnamoyl Conjugates of Oat, Avena sativa L.: An Update on the Biosynthesis, Chemistry, and Bioactivities

“…In support of the antimicrobial activity, Avns also exhibit potent anti-oxidant and radical scavenging activities that, in addition to the cinnamic acid structure, also involves the hydroxyanthranilic acid moiety [ 29 , 53 ]. Structure–activity relationship results revealed that the substitution pattern on both aromatic rings of the AA and PA moieties plays a role, and that both catechol and guaiacyl substitution, as well as carboxyl groups, are involved [ 54 ].…”

The Progress of Nomenclature, Structure, Metabolism, and Bioactivities of Oat Novel Phytochemical: Avenanthramides

“…A recent publication also demonstrated that the antioxidative mechanism of Avns was involved in double (2H­(+)/2e(−)) free radical scavenging reactions and catechol, guaiacyl, and carboxyl moieties played essential roles during this reaction . In addition, the total Avn content and Avn ratio with different structures vary widely in diverse oat cultivars with Avn-C possessing the highest antioxidant activity .…”