Self‐Assembled Multimetallic/Peptide Complexes: Structures and Unimolecular Reactions of [M_n(GlyGly−H)_2n−1]⁺ and M_n+1(GlyGly−H_2n]²⁺ Clusters in the Gas Phase

Abstract

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 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.

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

“…Other fragment ions observed at m/z 1093 and 1049 were related to the loss of CO 2 and GlyGly-CO 2 ,r espectively.A ny attemptf or MS/MS on the fragment ions was unsuccessful in this case due to very small ion intensities. Doubly charged clusters of Mn 2 + show similar fragmentation patterns to the Mg 2 + clusters observed in ar ecently published work; [23] Absolutely no charge separation processes were observed for Mn 2 + and Mg 2 + complexes, in contrast to what was observedf or Ca 2 + and Sr 2 + complexes.T his observation can be explained by the similarc ationics ize of these metals. Compared to Ca 2 + and Sr 2 + with ionic radii of 1.14 and 1.32 ( for coordination number of six), both high (0.97 ) and low spin (0.81 ) Mn 2 + cations show similarm etal ion size to the Mg 2 + (0.86 ).…”

“…The experimental spectra for the Mg 2 + , Ca 2 + and Sr 2 + complexes were consistent with the lowest energy structures in which metal ions were coordinated with all carbonyl oxygens and the amine nitrogens were hydrogen bonded to amide hydrogens. [23] The IRMPD spectrum obtained for [Mn 3 (GlyGly-H) 4 ] 2 + is quite similar to that for [Mg 3 (GlyGly-H) 4 ] 2 + and shows four main features centred at 3300, 3345, 3390 and 3470 cm À1 . The 3300 cm À1 band corresponds to the amide N-H stretch (amide A band) that has been significantly red-shifted due to hydrogen bonding with the terminal amine.…”

“…[22] In previous work, [23] it was shown that alkaline earth metal cations, Mg 2 + , Ca 2 + and Sr 2 + form singly and doubly charged clusters with deprotonated GlyGly. It was shown that the main dissociation pathway for the singly charged clusters is the loss of GlyGly competing with the loss of NH 2 CHCO.…”

“…[27] Thisi si na greement with the conclusions reachedi n Section2.1.3 based on the similar fragmentation patternso bserved for the presentM n 2 + complexes and those observed for similar Mg 2 + complexes in apreviousstudy. [23]…”

“…Fragmentation studies of [Zn(Proline) 2 -H] + complex showedt hat the main dissociation pathway leads to dehydrogenation of deprotonated prolinei nw hich hydrogen atoms originate from the amine group and C 5 . [22] In previousw ork, [23] it was shown that alkaline earth metal cations,M g 2 + ,C a 2 + and Sr 2 + form singlya nd doubly charged clusters with deprotonated GlyGly.I tw as shown that the main dissociation pathway for the singly charged clusters is the loss of GlyGly competing with the loss of NH 2 CHCO. In doubly chargedc lusters, the loss of GlyGly and charge separation were the main fragmentation channels.…”