Self-Assembled Multimetallic/Peptide Complexes: Structures and Unimolecular Reactions of [Mn(GlyGly−H)2n−1]+ and Mn+1(GlyGly−H2n]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 [Mn(GlyGly−H)n‐1]+ (n=2–4), [Mn+1(GlyGly−H)2n]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 Mg2+ clusters mainly lost GlyGly, whereas those containing Ca2+ or Sr2+ 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. A complex situation: The unimolecular dissociation reactions of singly and doubly charged clusters of Mg2+, Ca2+, and Sr2+ with deprotonated GlyGly are studied by using collision‐induced dissociation and infrared multiple photon dissociation spectroscopy together with simulated annealing and electronic‐structure calculations. This represents the first study of large self‐assembled multimetallic complexes bound by peptide.