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

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 O-2 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.Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3040

Andreev Reflection Spectroscopy Study of Spin Polarization in Co₂Cr(Fe)Al Heusler Alloys

The present paper is dealing with the experimental study of the influence of Fe substitution on the Curie temperature and spin polarization in Co₂CrAl Heusler alloys. A recently successfully introduced new rapid quenching method has been used for the preparation of Co₂CrAl and $Co₂Cr_{0.6}Fe_{0.4}Al$ ribbon samples. The Curie temperatures have been determined from magnetization measurements being 378 K for Co₂CrAl and much above 400 K for $Co₂Cr_{0.6}Fe_{0.4}Al$. The spin polarization parameter P₀ of the studied samples has been estimated from point-contact Andreev reflexion spectroscopy measurements. In pure Co₂CrAlP₀ = 0.5 - 0.9, and in the case of $Co₂Cr_{0.6}Fe_{0.4}AlP₀$ = 0.4 - 0.9. Hence, it is shown that Fe substitution of Cr in $Co₂Cr_{1-x}FeₓAl$ Heusler alloys at a concentration of x=0.4 significantly increase the Curie temperature without marked influence on the spin polarization