Conformation-dependent dynamics of macromolecular ions in the gas phase under an electrostatic field: A molecular dynamics simulation

摘要

Highly charged macromolecular ions exhibit various conformations in gas. Intramolecular charge-to-charge interaction induces a transformation from a globular structure into a stretched one. The change in the molecular conformation brings a complex dynamic behavior of ions under an electrostatic field. In the present study, we visualized the movement of a monovalent and multiply charged straight chain macromolecules, polyethylene glycol (PEG), by a molecular dynamics (MD) simulation. The simulation showed that a singly charged PEG ion (899 < M-W < 4,643) takes a globular conformation. The electrical mobilities of these ions determined from the migration distance under an electric field were compared with the experimental data and those determined by the classical Mason-Schamp theory under an assumption of spherical shape. As a result, we obtained a good agreement between the MD, theoretical, and experimental data for the monovalent ions. We also found that the MD simulation successfully predicts the electrical mobility of the multiply charged stretched PEG ions, but the classical theory fails. We were able to visualize the periodic bending and stretching motion by the MD simulation. This unique motion results from the localization of charges on the PEG molecule and may have a significant effect on the dynamic behavior of macromolecule ions in gas.