Pulse-radiolytic Investigations of Catechols and Catecholamines

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Abstract
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 ms interval after the pulse were 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-, was 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 2nd-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.