Coordinate and redox interactions of epinephrine with ferric and ferrous iron at physiological pH

Abstract

Coordinate and redox interactions of epinephrine (Epi) with iron at physiological pH are essential for understanding two very different phenomena – the detrimental effects of chronic stress on the cardiovascular system and the cross-linking of catecholamine-rich biopolymers and frameworks. Here we show that Epi and Fe³⁺ form stable high-spin complexes in the 1:1 or 3:1 stoichiometry, depending on the Epi/Fe³⁺ concentration ratio (low or high). Oxygen atoms on the catechol ring represent the sites of coordinate bond formation within physiologically relevant bidentate 1:1 complex. Redox properties of Epi are slightly impacted by Fe³⁺. On the other hand, Epi and Fe²⁺ form a complex that acts as a strong reducing agent, which leads to the production of hydrogen peroxide via O₂ reduction, and to a facilitated formation of the Epi–Fe³⁺ complexes. Epi is not oxidized in this process, i.e. Fe²⁺ is not an electron shuttle, but the electron donor. Epi-catalyzed oxidation of Fe²⁺ represents a plausible chemical basis of stress-related damage to heart cells. In addition, our results support the previous findings on the interactions of catecholamine moieties in polymers with iron and provide a novel strategy for improving the efficiency of cross-linking.