Bending stiff charged polymers: The electrostatic persistence length

Many charged polymers, including nucleic acids, are locally stiff. Their bending rigidity -quantified by the persistence length-depends crucially on Coulombic features, such as the ionic strength of the solution which offers a convenient experimental route for tuning the rigidity. While the classic Odijk-Skolnick-Fixman treatment fails for realistic parameter values, we derive a simple analytical formula for the electrostatic persistence length. It is shown to be in remarkable agreement with numerically obtained Poisson-Boltzmann theory results, thereby fully accounting for non-linearities, among which counter-ion condensation effects. Specified to double-stranded DNA, our work reveals that the widely used bare persistence length of 500 angstrom is overestimated by some 20%. Copyright (C) EPLA, 2016