Multiple substitution of protons by sodium ions in sodiated oligoglycines

Multiply-sodiated ions were observed by electrospraying oligoglycines and their N-acetylated and O-amidated derivatives in the presence of sodium hydroxide. These ions have all their hydrogens in the peptide linkages replaced by sodiums; one hydrogen in the C-terminal amide and the hydrogen in the C-terminal carboxylic group are also replaced. The N-terminal amine hydrogens are unreactive. These results are consistent with earlier postulations [Int. J. Mass Spectrom. 192 (1999) 303, J. Am. Sec. Mass Spectrom. 11 (2000) 967], and apparently confirm the gas-phase origin of these ions (formed in the electrospray source and/or the lens region). Collision-induced dissociation of multiply-sodiated oligoglycines showed that the major product ions are C-tenninal ions. (C) 2002 Elsevier Science B.V. All rights reserved.