Ejection of Solvated Ions from Electrosprayed Methanol/Water Nanodroplets Studied by Molecular Dynamics Simulations Elias Ahadi Lars Konermann 10.1021/ja111492s.s003 https://acs.figshare.com/articles/media/Ejection_of_Solvated_Ions_from_Electrosprayed_Methanol_Water_Nanodroplets_Studied_by_Molecular_Dynamics_Simulations/2639104 The ejection of solvated small ions from nanometer-sized droplets plays a central role during electrospray ionization (ESI). Molecular dynamics (MD) simulations can provide insights into the nanodroplet behavior. Earlier MD studies have largely focused on aqueous systems, whereas most practical ESI applications involve the use of organic cosolvents. We conduct simulations on mixed water/methanol droplets that carry excess NH<sub>4</sub><sup>+</sup> ions. Methanol is found to compromise the H-bonding network, resulting in greatly increased rates of ion ejection and solvent evaporation. Considerable differences in the water and methanol escape rates cause time-dependent changes in droplet composition. Segregation occurs at low methanol concentration, such that layered droplets with a methanol-enriched periphery are formed. This phenomenon will enhance the partitioning of analyte molecules, with possible implications for their ESI efficiencies. Solvated ions are ejected from the tip of surface protrusions. Solvent bridging prior to ion secession is more extensive for methanol/water droplets than for purely aqueous systems. The ejection of solvated NH<sub>4</sub><sup>+</sup> is visualized as diffusion-mediated escape from a metastable basin. The process involves thermally activated crossing of a ∼30 kJ mol<sup>–1</sup> free energy barrier, in close agreement with the predictions of the classical ion evaporation model. 2011-06-22 00:00:00 surface protrusions Considerable differences methanol concentration ion secession nanodroplet behavior Solvated ions ion evaporation model conduct simulations energy barrier droplet composition ESI efficiencies Solvated Ions metastable basin NH ion ejection Molecular Dynamics SimulationsThe ejection droplets MD studies electrospray ionization ESI applications analyte molecules Molecular dynamics