Effect of the Electrostatic Interactions on Stretching of Semiflexible and Biological Polyelectrolytes

Using combination of the molecular dynamics simulations and theoretical Calculations, we have demonstrated that the bending rigidity of biological polyelectrolytes (semiflexible charged polymers) is force dependent. The effective chain bending rigidity decreases with increasing the value of the applied force. At small and intermediate values of the applied forces a semiflexible polyelectrolyte chain behaves similar to a neutral chain with the effective bending rigidity equal to the sum of the bare chain bending rigidity and electrostatic bending rigidity which has a well-known Odijk-Skolnick-Fixman (OSF) form with a quadratic dependence on the Debye radius. However, at large values of the applied force when the magnitude of the external force exceeds ail electrostatic force responsible for the local chain stretching the effective chain bending rigidity is controlled by the bare chain elastic properties. This dependence of the bending rigidity on the applied force is a result of the scale dependent effect of the electrostatic interactions on the chain bending properties that can be approximated by two characteristic length scales. One describes the chain's elasticity at the distances along the polymer backbone shorter than the Debye screening length while another controls the long-scale chain's orientational correlations. By applying an external force to a semiflexible polyelectrolyte chain one probes different chain's deformation modes. Simulation results and theoretical model demonstrate a good quantitative agreement.