The complex formation of europium(III) with the zwitterionic form of amino acids (alanine, phenylalanine, and threonine) has been studied in aqueous solution. Measurements were performed at <i>I</i> = 0.1 M (NaCl/NaClO<sub>4</sub>), room temperature, and trace metal concentrations in the range of pH 2 to 8 using ultraviolet–visible (UV-Vis) and time-resolved laser-induced fluorescence spectroscopy (TRLFS). While complexation leads to a significant luminescence enhancement in the emission spectrum of the metal ion, absorption in the UV-Vis spectrum of the amino acid (AA) decreases. As zwitterionic species (AAH), all three ligands form weak complexes with 1:1 stoichiometry and a general formula of EuAAH<sup>3+</sup> with the metal. The complex stability constants were determined to be log <i>K</i> ∼ 1 for all complexes, indicating the negligible contribution of the amino acid side chain to the complex formation reaction.
Vol. 5, Iss. 12 Virtual Journal for Biomedical Optics
Anne Heller, Olivia Rönitz, Astrid Barkleit, Gert Bernhard, and Jörg-Uwe Ackermann, "Complexation of Europium(III) with the Zwitterionic Form of Amino Acids Studied with Ultraviolet–Visible and Time-Resolved Laser-Induced Fluorescence Spectroscopy," Appl. Spectrosc. 64, 930-935 (2010)