Structures, Unimolecular Fragmentations, and Reactivities of the Self‐Assembled Multimetallic/Peptide Complexes [Mn_n(GlyGly‐H)_2n−1]⁺ and [Mn_n+1(GlyGly‐H)_2n]²⁺

Abstract

Complexes of Mn(2+) with deprotonated GlyGly are investigated by sustained off-resonance irradiation collision-induced dissociation (SORI-CID), infrared multiple-photon dissociation spectroscopy, ion-molecule reactions, and computational methods. Singly [Mnn (GlyGly-H)2n-1 ](+) and doubly [Mnn+1 (GlyGly-H)2n ](2+) charged clusters are formed from aqueous solutions of MnCl2 and GlyGly by electrospray ionization. The most intense ion produced was the singly charged [M2 (GlyGly-H)3 ](+) cluster. Singly charged clusters show extensive fragmentations of small neutral molecules such as water and carbon dioxide as well as dissociation pathways related to the loss of NH2 CHCO and GlyGly. For the doubly charged clusters, however, loss of GlyGly is observed as the main dissociation pathway. Structure elucidation of [Mn3 (GlyGly-H)4 ](2+) clusters has also been done by IRMPD spectroscopy as well as DFT calculations. It is shown that the lowest energy structure of the [Mn3 (GlyGly-H)4 ](2+) cluster is deprotonated at all carboxylic acid groups and metal ions are coordinated with carbonyl oxygen atoms, and that all amine nitrogen atoms are hydrogen bonded to the amide hydrogen. A comparison of the calculated high-spin (sextet) and low-spin (quartet) state structures of [Mn3 (GlyGly-H)4 ](2+) is provided. IRMPD spectroscopic results are in agreement with the lowest energy high-spin structure computed. Also, the gas-phase reactivity of these complexes towards neutral CO and water was investigated. The parent complexes did not add any water or CO, presumably due to saturation at the metal cation. However, once some of the ligand was removed via CO2 laser IRMPD, water was seen to add to the complex. These results are consistent with high-spin Mn(2+) complexes.

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

“…This is evidenced by the absence of OH bands and the presence of NH bands in vibrational spectra of the complexes. 4,[7][8][9][10] We previously showed 5 that collision-induced dissociation (CID) products of [CuÁPheGlyGly-H] þ are of different types from those observed for [MnÁPheGly Gly-H] þ , [FeÁPheGlyGly-H] þ , and [ZnÁPheGlyGly-H] þ due to unusually strong metal ion-deprotonated peptide ligand interactions. Formation of unique dissociation products from the copper ion-bound peptide was also observed 6 for [CuÁangiotensin II] 2þ , suggesting that the identity of the binding metal ion plays a role in dissociation mechanisms of these complexes.…”

“…Metal ion–peptide complexes undergo facile fragmentation in the gas phase to yield metal-bound peptide sequence ion products under low-collision energy dissociation condition. 1–6 More diverse product ion types are observed for metal-bound short peptides than for protonated peptides, providing additional information for sequence coverages and elucidating dissociating mechanisms. Infrared spectroscopy-based structure assignments 4,7–10 show that multiple conformers can exist for these complexes due to their large degrees of freedom.…”

“…1–6 More diverse product ion types are observed for metal-bound short peptides than for protonated peptides, providing additional information for sequence coverages and elucidating dissociating mechanisms. Infrared spectroscopy-based structure assignments 4,7–10 show that multiple conformers can exist for these complexes due to their large degrees of freedom. However, one general feature in these complexes is that, regardless of the metal ion type, carbonyl oxygen atoms along the peptide backbone are the preferred ion-binding sites, forming O-bound structures with the deprotonation site being the terminal carbonyl OH, which is the most acidic group in the peptide ligand.…”

“…This is evidenced by the absence of OH bands and the presence of NH bands in vibrational spectra of the complexes. 4,7–10…”

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

“…Structures and dissociation behavior of metal cationpeptide complexes have been studied extensively for many years through spectroscopy [1][2][3][4][5][6][7][8][9] and tandem mass spectrometry. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] The metal ion in these complexes interacts with peptide ligands at the partially negatively charged carbonyl oxygen atoms on the peptide backbone, adopting multi-dentate structures where the ion is encapsulated by the ligands.…”