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.