Structures, Unimolecular Fragmentations, and Reactivities of the Self-Assembled Multimetallic/Peptide Complexes [Mnn(GlyGly-H)2n−1]+and [Mnn+1(GlyGly-H)2n]2+

Experimental and computational studies of monovalent metal cation-peptide interactions in [M·GlyGlyHis]+ (M = Li, Na, K, Rb, Cs, and Ag) complexes

[M·GlyGlyHis]⁺ (M = Li, Na, K, Rb, Cs, and Ag) complexes were generated using the electrospray ionization method and were subjected to collision-induced dissociation. Metal ion loss is the primary dissociation channel for [Cs·GlyGlyHis]⁺ whereas other complexes yield metal-bound peptide sequence ions and dehydrated ions as the main products. [Li·GlyGlyHis]⁺ and [Ag·GlyGlyHis]⁺ also generate product ions that are not observed for other complexes. Density functional theory calculations suggest that metal ion-peptide ligand interaction occurs through covalent interactions in [Li·GlyGlyHis]⁺ and [Ag·GlyGlyHis]⁺, and through electrostatic attraction in [Na·GlyGlyHis]⁺, [K·GlyGlyHis]⁺, [Rb·GlyGlyHis]⁺, and [Cs·GlyGlyHis]⁺. The calculations also suggest that fragmentation behavior of these complexes is affected by charge transfer to the ligand and ion-ligand interaction energy, and to a lesser extent by the ion size.

Investigation of collision-induced dissociation products and structures of gas-phase [ M·GlyGlyHis-H]+ ( M = Fe, Ni, Cu, and Zn) complexes

Collision-induced dissociation is carried out for electrosprayed [Fe·GlyGlyHis-H]⁺, [Ni·GlyGlyHis-H]⁺, [Cu·GlyGlyHis-H]⁺, and [Zn·GlyGlyHis-H]⁺ complexes. [Fe·GlyGlyHis-H]⁺, [Ni·GlyGlyHis-H]⁺, and [Zn·GlyGlyHis-H]⁺ yield metal-bound peptide sequence ions and dehydrated ions as primary products, whereas [Cu·GlyGlyHis-H]⁺ generates a more extensive series of metal-bound sequence ions and a product arising from the unusual loss of a formaldehyde moiety; dehydration is significantly suppressed for this complex. Density functional theory calculations show that the copper ion-deprotonated peptide binding energy is substantially higher than those in other complexes, suggesting that there is a correlation between ion-ligand binding energy and their fragmentation behavior.