1. Department of Chemistry, the Proteomics Center of Excellence, Northwestern University, Evanston, Illinois 60208, United States
2. Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, United States
3. Department Molecular and Biological Sciences, Northwestern University, Evanston, Illinois 60208, United States
4. Department of Chemistry, Harvard University, Cambridge, Massachusetts 02140, United States