Self‐Assembled Multimetallic/Peptide Complexes: Structures and Unimolecular Reactions of [M n (GlyGly−H) 2 n −1 ] + and M n +1 (GlyGly−H 2 n ] 2+ Clusters in the Gas Phase

The unimolecular chemistry and structures of self‐assembled complexes containing multiple alkaline‐earth‐metal dications and deprotonated GlyGly ligands are investigated. Singly and doubly charged ions [M n (GlyGly−H) n ‐1 ] + ( n =2–4), [M n +1 (GlyGly−H) 2 n ] 2+ ( n =2,4,6), and [M(GlyGly−H)GlyGly] + were observed. The losses of 132 Da (GlyGly) and 57 Da (determined to be aminoketene) were the major dissociation pathways for singly charged ions. Doubly charged Mg 2+ clusters mainly lost GlyGly, whereas those containing Ca 2+ or Sr 2+ also underwent charge separation. Except for charge separation, no loss of metal cations was observed. Infrared multiple photon dissociation spectra were the most consistent with the computed IR spectra for the lowest energy structures, in which deprotonation occurs at the carboxyl acid groups and all amide and carboxylate oxygen atoms are complexed to the metal cations. The N−H stretch band, observed at 3350 cm −1 , is indicative of hydrogen bonding between the amine nitrogen atoms and the amide hydrogen atom. This study represents the first into large self‐assembled multimetallic complexes bound by peptide ligands.