ELECTRON-SPIN-RESONANCE STUDY OF SEMIQUINONES FORMED DURING THE AUTOXIDATION OF 6-HYDROXY-DOPAMINE (2,4,5-TRIHYDROXY-PHENYL-ETHYLAMINE)

6-Hydroxy-dopamine is easily oxidized in aqueous solutions within a pH range of 7-14. Depending on this parameter and the starting concentra tion of this catechol at least seven different paramagnetic species ca n be detected. Cyclization to two different indole derivatives of amin ochrome type could be demonstrated and the mechanism of formation is d iscussed. The indoloquinones can easily be reduced to the correspondin g semiquinone by an excess of 6-hydroxy-dopamine. All radicals observe d react with ascorbic acid in a redox reaction, forming the correspond ing catechol and the ascorbic acid semidione.