1. Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, Illinois 60208, United States
2. International Institute of Nanotechnology, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
3. Magnetic Resonance Center (CERM), Consorzio Interuniversitario Risonanze Magnetiche di Metalloproteine (CIRMMP) and Department of Chemistry, University of Florence, 50019 Sesto Fiorentino, Italy