1. Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
2. Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
3. School of Cellular and Molecular Medicine, University of Bristol, Bristol BS8 1TD, U.K.
4. Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K.
5. Stanford Synchrotron Radiation Lightsource, Stanford University, Menlo Park, California 94025, United States
6. Department of Chemistry, Stanford University, Stanford, California 94305, United States