Catecholamines are biologically important neurotransmitters and hormones that may also contribute to endogenous antioxidant defense. In this work, the anti-peroxyl radical capacity of dopamine and norepinephrine, together with the model catechol compounds catechol and caffeic acid, was studied toward tert-butylperoxyl radicals \(\left(tert-{\text{butylOO}}^{\bullet }\right)\) . The proper anti-peroxyl radical capacity was directly determined using a kinetic-EPR method with pulsed reagent injection, which enables real-time monitoring of peroxyl radical consumption during reaction with antioxidants. The capacity values of all investigated compounds were found to be close to 2, indicating similar stoichiometry of their interaction with peroxyl radicals. These results show that the catechol moiety, containing two ortho phenolic hydroxyl groups, is the key structural fragment responsible for the antiradical capacity of catecholamines. Side-chain differences did not significantly affect the measured capacity, consistent with the literature BDE data showing lower O-H-bond dissociation energies in the catechol moiety.
