Experimental and Computational Studies of Dissociation Behavior and Structures of [M·pSer]+ (M?=?Li, Na, Ag, Rb, and Cs) Complexes

Complexes of metal monocations and phosphoserine (pSer) were generated by electrospray ionization (ESI), and were subjected to collision-induced dissociation (CID). The primary fragmentation pathways of [Li·pSer]+, [Na·pSer]+, and [Ag·pSer]+ are dephosphorylation, dehydration, and Ser residue loss whereas metal ion loss is dominant for [Rb·pSer]+ and [Cs·pSer]+. Density functional theory (DFT) calculations suggest a correlation between structures, ion-ligand binding energies, and fragmentation behavior: [Li·pSer]+, [Na·pSer]+, and [Ag·pSer]+, which exhibit a preference for charge-solvated structures, have high binding energies and dissociate through intramolecular fragmentation of the ligand, whereas [Rb·pSer]+ and [Cs·pSer]+ likely have salt-bridge structures with low binding energies, making the metal ion loss the dominant dissociation channel. Calculations also suggest that the salt-bridge structure of [Na·pSer]+ may be present in the current work.