Coil-globule transition of a single semiflexible chain in slitlike confinement.

Liang Dai,Patrick S Doyle,Jie Yan,C Benjamin Renner

doi:10.1038/srep18438

Abstract

Single polymer chains undergo a phase transition from coiled conformations to globular conformations as the effective attraction between monomers becomes strong enough. In this work, we investigated the coil-globule transition of a semiflexible chain confined between two parallel plates, i.e. a slit, using the lattice model and Pruned-enriched Rosenbluth method (PERM) algorithm. We find that as the slit height decreases, the critical attraction for the coil-globule transition changes non-monotonically due to the competition of the confinement free energies of the coiled and globular states. In wide (narrow) slits, the coiled state experiences more (less) confinement free energy, and hence the transition becomes easier (more difficult). In addition, we find that the transition becomes less sharp with the decreasing slit height. Here, the sharpness refers to the sensitivity of thermodynamic quantities when varying the attraction around the critical value. The relevant experiments can be performed for DNA condensation in microfluidic devices.

Highlights

Single polymer chains undergo a phase transition from coiled conformations to globular conformations as the effective attraction between monomers becomes strong enough relative to the thermal energy, which is the so-called coil-globule transition[1,2]
Das and Chakraborty have performed Brownian dynamic simulations for a collapsing flexible chain in slitlike confinement[34]. These simulations focus on the collapse kinetics and provide limited information regarding the critical attraction for the coil-globule transition
The non-monotonic behavior is due to the competing of the confinement free energies of the coiled state and the globular states

Summary

Results and Discussions

We calculate the fluctuation in the number of contact number for any given attractive strength ε using the following equation: σ2 (ε) = ∑+N∞c=0 g eff (N c)exp(−βεN c)[N c − N c]2 Figure both bulk 3 shows the and in slits, fluctuation as a function the fluctuation exhibits a of the peak, attractive strength for κbend = 3 kBT and N m = corresponding to the critical attractive strength. The critical attraction as a function of the slit height has been calculated for the flexible chains in the previous study by Hsu and Grassberger[35], and is plotted in the thick green line of Fig. 4(a). Note that Mishra and Kumar[36] observed a non-monotonic behavior of ε⁎ versus H for flexible chains, and the critical slit height is only H⁎ = 2a.

The probability can be converted to the free energy using

Conclusions

Additional Information