1. Contribution from the Laboratory of Synthetic Protein Chemistry, The Rockefeller University, New York, New York 10021, Graduate Program in Biochemistry and Structural Biology, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller University, New York, New York 10021, and Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400