A KINETIC-STUDY OF THE ANAEROBIC REACTIONS BETWEEN ADRENALINE AND IRON(III)

Iron(III) reacts reversibly in aqueous acid with adrenaline [epinephrine, L-1-(3,4-dihydroxyphenyl)-2-(methylamino)ethanol, H2LH+] to give FeLH2+ and FeHLH3+. Both species decompose to yield iron(II) and the semiquinone, which in turn is oxidised further to the quinone. The latter cyclises to form leucoadrenochrome, which is finally oxidised by iron(III) to adrenochrome presumably via a semiquinone. The rate of appearance and disappearance of the complexes, quinone, and adrenochrome could be followed by stopped-flow photometric methods. Mechanisms are proposed for the various steps, rate constants evaluated, and the reversibility of the various redox steps discussed. These mechanisms are compared and contrasted with those of the analogous reactions between iron(III) and L-3-(3,4-dihydroxyphenyl)alanine.