1. Departments of Chemistry, Molecular Biosciences, Neurobiology, 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 di Metalloproteine (CIRMMP), Via L. Sacconi 6, 50019 Sesto Fiorentino, Italy