Tandem mass spectrometric analysis of alkali metal cation-tripeptide clusters

•Alkali metal cation-tripeptide clusters are generated through electrospray ionization.•Fragmentation pathways of the clusters are dependent upon the identity of the metal ions.•Calculations suggest correlations between the ion-peptide binding energy, ion size, and the intermolecular distance.

Clusters of tripeptides bound to alkali metal cations are generated through electrospray ionization, and collision-induced dissociation tandem mass spectrometry is carried out. Fragmentation products of peptides bound to small ions are b- and y-type fragments with the ion attached, whereas fragmentation of peptides bound to larger ions leads to complete dissociation of the ion. Density functional theory calculations suggest that the ion-peptide binding energy decreases with both the increasing ion radius and the average distance between the ion and the carbonyl O atoms. There is no apparent relation between the binding energy and the partial ion charge.

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