Translocation Dynamics of an Asymmetrically Charged Polymer through a Pore under the Influence of Different pH Conditions.

We study the translocation of a polymer with oppositely charged segments at both ends of the chain passing through a pore under the effect of an external electric field in the presence of a pH gradient using Langevin dynamics simulations. As observed in experiments, the electrostatic interactions between the pore and the polymer are tuned by altering the pH gradient. Our simulation studies show that with the change in charge distribution on the polymer and the pore that can mimic different pH conditions, the external driving force and the polymer-pore electrostatic interactions play a significant role in the translocation process. The external electric forces are dominant during the entry stage, and the entry time decreases with increase in the charge asymmetry of the pore-trapped polymer. During the exit stage, the electrostatic interactions as well as the external electric field act in concert in determining the exit time through the pore. Our simulation results can capture many features observed in experiments. Our results are explained qualitatively by calculating the free-energy change of the polymer chain during the translocation process.