1. Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, Departments of Physics and Applied Physics, University of Michigan, Ann Arbor, Michigan 48109, Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan 48109-0650, Department of Biological Chemistry, School of Medicine, University of Michigan, Ann Arbor, Michigan 48109-1065, Interdepartmental Program in Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065