Pulse-radiolytic Investigations of Catechols and Catecholamines

Summary

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 the 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 (e_aq⁻) yielded the semiquinone of adrenochrome (absorbing at 470 nm), which subsequently decays by a second-order process. The dismutation products leucoadrenochrome (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.