Structures and fragmentations of zinc(II) complexes of amino acids in the gas phase IV. Solvent effect on the structure of electrosprayed ions

A combination of mass spectrometric and quantum chemical techniques is used to study solvent effects on the structure of desolvated [AA-H+Zn]⁺ complexes (AA: amino acid), formed in the gas phase by electrospray ionization. By studying the collision-induced fragmentations of such complexes, we show that the solvent used may have a direct impact on the structure of the gaseous ions formed. In the case of [Gly-H+Zn]⁺, four isomers may be potentially formed, and ions extracted from methanol/water and acetonitrile/water solutions show different fragmentations patterns. The formation of different isomers when using these two solvents is further evidenced by the fragmentation spectra of [Asn-H+Zn]⁺, and [Asp-H+Zn]⁺. These cases illustrate the fine tuning which can sometimes be exerted on the structures of electrosprayed ions. Ab initio calculations are used to show the decisive role of the solvent binding energies on the last steps of the electrospray process. It is concluded that both the solvent and the cone voltage in the electrospray source may have a strong influence on the structure of fully desolvated, gaseous ions.