Translocation Behaviors of Polyelectrolyte through a Small Pore in the Presence of Trivalent Salt: a Comparison with the Cases in Monovalent and Divalent Salt Solutions
Pai-Yi Hsiao1*
1Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:Pai-Yi Hsiao,
We investigate polyelectrolyte translocation in a trivalent salt solution by means of Langevin dynamics simulations. It is known that the presence of multivalent counterions can cause drastic collapse and charge-neutralization (or even overcharging) of polyelectrolyte chains in a solution due to the strong effect of ion condensation. Translocation in cooperation with trivalent salt is thus expected a hard process, which slows down the translocation speed and renders easier the detection of the monomers (referred to the genetic code if the concerned study is DNA translocation) when the chain is forced to pass the pore. We demonstrate here using trivalent salt, the translocation time can be largely increased. Analysis reveals that the system shows four characteristic scaling behaviors, depending on the strength of the driving field. In addition to the scaling exponents in each regime, we investigate the variational behaviors of the chain size, the ion condensation, the effective chain charge, the waiting time function, the drift velocity, the diffusion, and the probability density function during a process. The results are further compared with the counterpart cases performed in the monovalent and divalent salt solutions, to illuminate the impact of the salt valence on various properties of translocation. At the end, a direct comparison of the translocation time reported in experimental papers with our simulations is made. We find that the experiments were all performed in the weakly-driven force regime. We predict that using trivalent salt can largely enlarge the regime, which gives more working space to researchers to optimize or slow down the process. (This research is funded by the Ministry of Science and Technology, Taiwan, grant number MOST 106-2112-M-007-027-MY3.)

Keywords: polymer translocation, polyelectrolyte, scaling law, drift-diffusion property, molecular dynamics simulations