Density Functional Theory-Based Mechanism of Antioxidant Activity of Phenols as Asphalt Antioxidants

The antioxidant qualities of phenolic chemicals found in asphalt have drawn a lot of attention. By comparing theoretical calculations with experimental results, we evaluate the applicability of various antioxidant indices for assessing the efficacy of phenolic antiaging compounds in asphalt and unveil the antiaging mechanism of phenolic antioxidants in asphalt. By analyzing the correlation between oxygen radical absorbance capacity values and asphalt experimental results as well as the correlation between bond dissociation energy (BDE) and asphalt experimental results, it can be observed that the antioxidant mechanism of phenolic compounds in asphalt aligns with the hydrogen atom transfer (HAT) mechanism. In contrast, ferric reducing antioxidant power values, vertical ionization potential, electronegativity (χ), chemical hardness (η), and electrophilicity index (ω) show no correlation with any asphalt experimental results, indicating that the antioxidant mechanism of phenolic compounds in asphalt is not based on the single electron transfer (SET) mechanism. This suggests that the antioxidant mechanism of phenolic antioxidants for asphalt is not the HAT mechanism but rather the SET mechanism, related to the phenolic hydroxyl content, the arrangement of hydroxyls in the ortho-dihydroxy conformation and BDE values of the phenolic O─ H bond. These results indicate that enhancing the antioxidant activity of phenolic antioxidants may be achieved by reducing the BDE of the phenolic O─ H bond, modifying the arrangement of hydroxyls, and increasing the phenolic hydroxyl group content.