Chemical repair, regeneration, and the role of superoxide in antioxidant activity

Antioxidant activity is commonly discussed in fields like chemistry, biology, nutrition, and medicine, but it is often viewed in functional terms rather than as a process controlled by basic radical kinetics. In many cases, antioxidant efficiency is described within a simple scavenging model, where antioxidants mainly intercept reactive radicals stoichiometrically and are then irreversibly consumed. While this model highlights an important aspect of antioxidant behavior, it does not fully capture the complexity of oxidative processes. In this review, antioxidant chemistry is examined as a competitive reaction network where chemical repair and regeneration pathways play a key mechanistic role. These pathways allow for the restoration of radical intermediates before damage terminates and enable the recycling of oxidized antioxidant species, thus extending antioxidant activity beyond just radical trapping. In this context, the identity of radicals, branching ratios, oxygen-dependent competition, and radical lifetimes are crucial factors that determine whether oxidative processes lead to propagation, termination, or repair. Special focus is given to phenolic antioxidants and to reaction networks involving the hydroperoxyl/superoxide couple (HO₂•/O₂•^-). Although superoxide is often described as a weak oxidant or a precursor to more reactive species, its reactivity depends heavily on conditions. Under the right kinetic conditions, superoxide can participate in reductive pathways that contribute to antioxidant regeneration and radical repair. By combining insights from radiation chemistry, electrochemistry, and computational kinetics, this review highlights chemical repair as an important mechanistic component of antioxidant activity and offers a unified framework for understanding antioxidant function in various chemical and biological settings.