Pulse-radiolytic investigations of catechols and catecholamines. I. Adrenaline and adrenochrome.
Adrenaline (epinephrine), adrenochrome and C4-substituted catechol model compounds were pulse-irradiated in aqueous neutral and alkaline solutions. Transient spectra are reported after oxidizing adrenaline and reducing adrenochrome. All species appearing during 20 msec interval after the pulse have been identified: the OH adduct with an absorption maximum at 300-310 nm, the semiquinone (at 245 nm), and adrenaline quinone (at 340 nm). The reaction of superoxide anions (O2-) with adrenaline was less efficient, compared with OH radicals. A novel oxidation product, derived from the semiquinone and O2-, has been identified as the 4-hydroxy-3,6-dioxo derivate. The pulse-radiolytic reduction of adrenochrome by hydrated electrons (eaq-) yielded the semiquinone of adrenochrome (absorbing at 470 nm), which subsequently decays by a second-order process. The dismutation products leuco-adrenochrome (absorbing at 300 nm, pH 9-8) and the adrenochrome tautomer (absorbing at 375 nm) are unstable, forming 5,6-dihydro-N-methyl indole and regenerating adrenochrome.