title: Spectroscopic Characterization of the 3+ and 2+ Oxidation States of Europium in a Macrocyclic Tetraglycinate Complex.
abstract: The 3+ and 2+ oxidation states of europium have drastically different magnetic and spectroscopic properties. Electrochemical measurements are often used to probe EuIII/IIoxidation state changes, but a full suite of spectroscopic characterization is necessary to demonstrate conversion between these two oxidation states in solution. Here, we report the facile conversion of an europium(III) tetraglycinate complex into its EuIIanalogue. We present electrochemical, luminescence, electron paramagnetic resonance, UV-visible, and NMR spectroscopic data demonstrating complete reversibility from the reduction and oxidation of the 3+ and 2+ oxidation states, respectively. The EuII-containing analogue has kinetic stability within the range of clinically approved GdIII-containing complexes using an acid-catalyzed dissociation experiment. Additionally, we demonstrate that the 3+ and 2+ oxidation states provide redox-responsive behavior through chemical-exchange saturation transfer or proton relaxation, respectively. These results will be applicable to a wide range of redox-responsive contrast agents and Eu-containing complexes.
authors.affiliation: Department of Chemistry, Wayne State University , 5101 Cass Avenue, Detroit, Michigan 48202, United States.
authors.forename: Levi A
authors.initials: LA
authors.lastname: Ekanger
authors.affiliation: Department of Chemistry, Wayne State University , 5101 Cass Avenue, Detroit, Michigan 48202, United States.
authors.forename: Devin R
authors.initials: DR
authors.lastname: Mills
authors.affiliation: Department of Neurology, Henry Ford Hospital , 1 Ford Place, Detroit, Michigan 48202, United States.
authors.forename: Meser M
authors.initials: MM
authors.lastname: Ali
authors.affiliation: Department of Oncology, Wayne State University School of Medicine , 110 East Warren Avenue, Detroit, Michigan 48201, United States.|Barbara Ann Karmanos Cancer Institute , 4100 John R Street, Detroit, Michigan 48201, United States.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Polin
authors.affiliation: Department of Radiology, Wayne State University School of Medicine , 3990 John R Street, Detroit, Michigan 48201, United States.
authors.forename: Yimin
authors.initials: Y
authors.lastname: Shen
authors.affiliation: Barbara Ann Karmanos Cancer Institute , 4100 John R Street, Detroit, Michigan 48201, United States.|Department of Radiology, Wayne State University School of Medicine , 3990 John R Street, Detroit, Michigan 48201, United States.
authors.forename: E Mark
authors.initials: EM
authors.lastname: Haacke
authors.affiliation: Department of Chemistry, Wayne State University , 5101 Cass Avenue, Detroit, Michigan 48202, United States.|Barbara Ann Karmanos Cancer Institute , 4100 John R Street, Detroit, Michigan 48201, United States.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Allen