1. Department of Chemistry, Vassar College, Poughkeepsie, New York 12604, USA
2. RCSB Protein Data Bank, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA
3. Argonne National Laboratory Advanced Photon Source, Lemont, Illinois 60439, USA
4. Department of Chemistry, East Tennessee State University, Johnson City, Tennessee 37614, USA