Kinetic studies on the manganese(II) complex catalyzed oxidation of epinephrine

The manganese complex [Mn2(HL)2](BPh4)2 was found to be a selective catalyst for the oxidation of epinephrine (a catecholamine derivative) to adrenochrome at room temperature in sodium carbonate–bicarbonate buffer. The epinephrine auto-oxidation rate significantly increases upon the addition of manganese complex. The kinetics of reaction was studied by spectrophotometric method, monitoring the increase in concentration of adrenochrome product. According to the proposed mechanism, O2 binding to the manganese complex is followed by the formation of a ternary catalyst–dioxygen–substrate complex as active intermediate, which decomposes in a rate-determining step, generating the adrenochrome.

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► Dioximato-manganese(II) complex is a functional catechol oxidase model.
► Epinephrine auto-oxidation rate significantly increases upon the addition of Mn(II).
► Detailed kinetic studies of the oxidation were followed by UV–vis, EPR spectroscopy.
► The reaction mechanism was found consistent with the observed kinetic behaviour.
► It can be conclude that the manganese complex has no SOD-like activity.