1. Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
2. Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
3. Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
4. Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, United States
5. Department of Physics, Duke University, Durham, North Carolina 27708, United States
6. Department of Biochemistry, Duke University, Durham, North Carolina 27710, United States