Addition of carbon-centered radicals to aromatic antioxidants: mechanistic aspects.

Several recent studies have shown that the rates of formation of adduct radicals between carbon-centred radicals and aromatic molecules are virtually diffusion-controlled and reversible. This contrasts with "radical addition", the well-known multistep reaction in preparative organic chemistry where the rate-determining initial formation of radical adducts is perceived to be several orders of magnitude slower and virtually irreversible. Using pulse radiolysis and spectroscopic analysis, we have now re-examined parts of this complex mechanism. The results have significant implications for biological systems: electron-rich, aromatic structures may act like buffers for radicals, moderating their reactivity resulting in a much slower reaction determining the overall rate of oxidation. In vivo, an organism would gain time for an appropriate antioxidant reaction.