Electrochemical Study of the EuIII/EuII Redox Properties of Complexes with Potential MRI Ligands

Properties of the EuIII/EuII redox couple, in the presence of one of a group of different ligands of ligands, were investigated using several electrochemical methods. Ligands used in this study included cyclodextrins, polyazamacrocycles and poly(aminocarboxylates). The poly(aminocarboxylate) containing ligands currently used as MRI contrast agents (DTPA, DOTA) as well as newly developed ligands [1,4‐DOTA(GAC12)2, 1,7‐DOTA(GAC12)2] with potential use as MRI contrast agents were studied. Cyclic voltammetry, phase sensitive AC voltammetry, DC polarography and highly effective electrochemical impedance spectroscopy were utilised to elucidate the mechanism of the reduction/oxidation of the Eu ion in the presence of these compounds. Stability constants of the EuIII and/or EuII complexes and heterogeneous rate constants of the charge transfer were determined. Theoretical calculations of molecular volumes and diffusion coefficients were performed as well.