1. Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
2. Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
3. Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
4. Department of Physics, Duke University, Durham, North Carolina 27708, United States
5. Department of Biochemistry, Duke University, Durham, North Carolina 27710, United States