dsDNA persistence length with divalent ions

TL;DR

This study measures dsDNA persistence length across various salt concentrations and ions, validating a theoretical formula that accounts for ion effects and charge renormalization, revealing magnesium's specific binding behavior.

Contribution

It provides experimental validation for a theoretical formula of DNA persistence length across a wide salt concentration range, including divalent ions.

Findings

The formula fits the experimental data well.

Magnesium ions cause a smaller effective DNA radius.

Charge renormalization is significant in DNA-ion interactions.

Abstract

Finding a theoretical formula for the persistence length of polyelectrolytes for the whole experimental range of salt concentration is a long standing challenge. Using the Tethered Particle Motion technique, the double-stranded DNA persistence length is measured for four monovalent and divalent salts on a three-decade concentration range. The formula proposed by Trizac and Shen [EPL, 116 18007 (2016)] and extended to divalent ions fits the data. This formula mixes the high salt limit solution of the Poisson-Boltzmann equation together with the DNA charge renormalisation. Magnesium ions induce a fitted DNA radius smaller than the geometrical one, consistent with a site-specific binding.