1. Biomedical Mass Spectrometry Facility, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-0001, United States
2. Department of Chemistry, Binghamton University, State University of New York, Binghamton, New York 13902, United States
3. Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, United States
4. Division of Basic and Translational Biophysics, Eunice Kennedy Shriver National Institute of Child Health and Human Development National Institutes of Health, Bethesda, Maryland 20892, United States