Structures and fragmentations of zinc(II) complexes of amino acids in the gas phase. III. Rearrangement versus desolvation in the electrospray formation of the glycine-zinc complex

The zinc complex of deprotonated glycine (Gly), denoted [Gly-H+Zn]⁺, is readily formed in the gas phase by electrospray ionization. Low energy collisional activation of [Gly-H+Zn]⁺ leads to three primary fragments, resulting from the losses of CO₂, H₂O+CO, and CO. Previous work has shown that the first two reactions require isomerization of the glycinate to nonclassical structures before the last desolvation step, and that loss of CO can only occur from a N-deprotonated glycine complex. It is shown herein, using accurate ab initio calculations, that such a structure does not pre-exist in solution, and that it is also formed in the electrospray process, during one of the last desolvation steps. Solvent molecules participate in this mechanism as proton relays between the two functional groups of Gly. These results provide a complete picture of the fragmentation of gaseous [Gly-H+Zn]⁺: each of the primary fragmentations arises from a specific precursor, none of which is the parent structure formed in solution.