Hydrogen Atom Transfer from HOO ^. to <i>ortho</i> ?Quinones Explains the Antioxidant Activity of Polydopamine

Melanins are stable and non-toxic biomaterials with a great potential as chemopreventive agents for diseases connected oxidative stress, but the mechanism of their antioxidant action is unclear. Herein, we show that polydopamine (PDA), well-known synthetic melanin, becomes an excellent trap alkylperoxyl radicals (ROO., typically formed during autoxidation lipid substrates) in presence hydroperoxyl (HOO.). The key reaction explaining this peculiar activity reduction ortho-quinone moieties present PDA by HOO.. This occurs via H-atom transfer mechanism, demonstrated large kinetic solvent effect model quinone (3,5-di-tert-butyl-1,2-benzoquinone) HOO. (k=1.5×107 1.1×105 M?1 s?1 PhCl MeCN). chemistry disclosed herein important step to rationalize redox-mediated bioactivity melanins quinones.