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Title: Charging and Release Mechanisms of Flexible Macromolecules in Droplets

Abstract

We study systematically the charging and release mechanisms of a flexible macromolecule, modeled by poly(ethylene glycol) (PEG), in a droplet by using molecular dynamics simulations. We compare how PEG is solvated and charged by sodium Na{sup +} ions in a droplet of water (H{sub 2}O), acetonitrile (MeCN), and their mixtures. Initially, we examine the location and the conformation of the macromolecule in a droplet bearing no net charge. It is revealed that the presence of charge carriers do not affect the location of PEG in aqueous and MeCN droplets compared with that in the neutral droplets, but the location of the macromolecule and the droplet size do affect the PEG conformation. PEG is charged on the surface of a sodiated aqueous droplet that is found close to the Rayleigh limit. Its charging is coupled to the extrusion mechanism, where PEG segments leave the droplet once they coordinate a Na{sup +} ion or in a correlated motion with Na{sup +} ions. In contrast, as PEG resides in the interior of a MeCN droplet, it is sodiated inside the droplet. The compact macro-ion transitions through partially unwound states to an extended conformation, a process occurring during the final stage of desolvation andmore » in the presence of only a handful of MeCN molecules. For charged H{sub 2}O/MeCN droplets, the sodiation of PEG is determined by the H{sub 2}O component, reflecting its slower evaporation and preference over MeCN for solvating Na{sup +} ions. We use the simulation data to construct an analytical model that suggests that the droplet surface electric field may play a role in the macro-ion–droplet interactions that lead to the extrusion of the macro-ion. This study provides the first evidence of the effect of the surface electric field by using atomistic simulations. .« less

Authors:
;  [1]
  1. The University of Western Ontario, Department of Chemistry (Canada)
Publication Date:
OSTI Identifier:
22776847
Resource Type:
Journal Article
Journal Name:
Journal of the American Society for Mass Spectrometry
Additional Journal Information:
Journal Volume: 28; Journal Issue: 11; Other Information: Copyright (c) 2017 American Society for Mass Spectrometry; http://www.springer-ny.com; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1044-0305
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; CHARGE CARRIERS; CHARGE STATES; COMPARATIVE EVALUATIONS; DROPLETS; ELECTRIC FIELDS; EVAPORATION; INTERACTIONS; IONIZATION; MIXTURES; MOLECULAR DYNAMICS METHOD; MOLECULES; POLYETHYLENE GLYCOLS; SIMULATION; SODIUM IONS; SURFACES

Citation Formats

Oh, Myong In, and Consta, Styliani. Charging and Release Mechanisms of Flexible Macromolecules in Droplets. United States: N. p., 2017. Web. doi:10.1007/S13361-017-1754-4.
Oh, Myong In, & Consta, Styliani. Charging and Release Mechanisms of Flexible Macromolecules in Droplets. United States. doi:10.1007/S13361-017-1754-4.
Oh, Myong In, and Consta, Styliani. Wed . "Charging and Release Mechanisms of Flexible Macromolecules in Droplets". United States. doi:10.1007/S13361-017-1754-4.
@article{osti_22776847,
title = {Charging and Release Mechanisms of Flexible Macromolecules in Droplets},
author = {Oh, Myong In and Consta, Styliani},
abstractNote = {We study systematically the charging and release mechanisms of a flexible macromolecule, modeled by poly(ethylene glycol) (PEG), in a droplet by using molecular dynamics simulations. We compare how PEG is solvated and charged by sodium Na{sup +} ions in a droplet of water (H{sub 2}O), acetonitrile (MeCN), and their mixtures. Initially, we examine the location and the conformation of the macromolecule in a droplet bearing no net charge. It is revealed that the presence of charge carriers do not affect the location of PEG in aqueous and MeCN droplets compared with that in the neutral droplets, but the location of the macromolecule and the droplet size do affect the PEG conformation. PEG is charged on the surface of a sodiated aqueous droplet that is found close to the Rayleigh limit. Its charging is coupled to the extrusion mechanism, where PEG segments leave the droplet once they coordinate a Na{sup +} ion or in a correlated motion with Na{sup +} ions. In contrast, as PEG resides in the interior of a MeCN droplet, it is sodiated inside the droplet. The compact macro-ion transitions through partially unwound states to an extended conformation, a process occurring during the final stage of desolvation and in the presence of only a handful of MeCN molecules. For charged H{sub 2}O/MeCN droplets, the sodiation of PEG is determined by the H{sub 2}O component, reflecting its slower evaporation and preference over MeCN for solvating Na{sup +} ions. We use the simulation data to construct an analytical model that suggests that the droplet surface electric field may play a role in the macro-ion–droplet interactions that lead to the extrusion of the macro-ion. This study provides the first evidence of the effect of the surface electric field by using atomistic simulations. .},
doi = {10.1007/S13361-017-1754-4},
journal = {Journal of the American Society for Mass Spectrometry},
issn = {1044-0305},
number = 11,
volume = 28,
place = {United States},
year = {2017},
month = {11}
}