Reactive MD Screening of Antioxidants for Substituent-Dependent Phenoxyl Radical Stability.

Oxidation limits the performance and lifetime of lubricants, and phenolic antioxidants are commonly used to slow this process by scavenging hydrocarbon peroxyl radicals. The performance of phenolic antioxidants is largely determined by the stability of the antioxidant radical that remains after hydrogen donation. To explore the relationship between antioxidant chemical structure and radical stability, we used REACTER-based reactive molecular dynamics simulations to model the reverse hydrogen transfer reaction from polyalphaolefin hydroperoxides to phenoxyl radicals. Simulations were run for 718 distinct single-ring phenoxyl radicals with varied substituent types and positions in a polyalphaolefin hydroperoxide environment. Reaction rates were obtained from the time evolution of hydrogen transfer events, where lower reaction rates correspond to higher radical stability and better antioxidant performance. Analysis of diffusivity, hydrogen bonding, and steric hindrance showed that strong hydrogen bonding and high steric hindrance around the phenoxyl oxygen atom decreased the reaction rate, while faster diffusion increased it. A multivariate linear model confirmed that hydrogen bonding was the dominant contributor to radical stability in the low reaction rate region. These results highlight the molecular features that influence antioxidant behavior and demonstrate that reactive simulations offer an efficient route for screening and designing antioxidant molecules.