1. Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
2. Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital / Harvard Medical School, Charlestown, MA 02129
3. Division of Pharmacology and Toxicology, College of Pharmacy, Institute for Cellular and Molecular Biology, and Institute for Neuroscience, The University of Texas at Austin, Austin, TX 78712