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 Fe(3+) form stable high-spin complexes in the 1:1 or 3:1 stoichiometry, depending on the Epi/Fe(3+) 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 Fe(3+). On the other hand, Epi and Fe(2+) form a complex that acts as a strong reducing agent, which leads to the production of hydrogen peroxide via O(2) reduction, and to a facilitated formation of the Epi-Fe(3+) complexes. Epi is not oxidized in this process, i.e. Fe(2+) is not an electron shuttle, but the electron donor. Epi-catalyzed oxidation of Fe(2+) 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.