1. Departments of Chemistry, Molecular Biosciences, Neurobiology and Physiology, and Radiology, Northwestern University, Evanston, Illinois 60208, United States
2. Department of Chemistry and Magnetic Resonance Center (CERM), University of Florence, and Consorzio Interuniversitario Risonanze Magnetiche Metallo Proteine (CIRMMP), Via L. Sacconi 6, 50019 Sesto Fiorentino, Italy