Reactivity of free radicals generated from neurotransmitters studied by electron spin resonance spectroscopy

Free phenoxy radicals derived from catecholamine-type neurotransmitters ( dopamine, noradrenaline, adrenaline) sigma-coordinated to Co(III) chelates were generated by the reaction of pi-coordinated tert-butylperoxy radicals with the neurotransmitters in non-polar solvent at ambient temperature. The ESR signals of the formed complexes are split into the basic octet line resulting from the interaction of the unpaired electron of the phenoxy radical with the Co-59 nucleus ( I = 7/2). Increasing the polarity of the solution starts the decomplexation and the liberated phenoxy radicals of the neurotransmitters disappear by recombination or by H-abstraction from the added antioxidant. When vitamin E is added to the system, only the ESR signal of the stable alpha-tocopheroxy radicals is detectable. Similarly, in the presence of the antiarrhytmic drug Stobadine, only the signal of the corresponding nitrogen-centred radical is seen. In the presence of both antioxidants, rapid H-transfer occurs from vitamin E to the Stobadine radicals.