Swelling of biological and semiflexible polyelectrolytes

Abstract

We have developed a theoretical model of swelling of semiflexible (biological)polyelectrolytes in salt solutions. Our approach is based on separation of length scaleswhich allowed us to split a chain’s electrostatic energy into two parts that describe localand remote electrostatic interactions along the polymer backbone. The local part takes intoaccount interactions between charged monomers that are separated by distances along thepolymer backbone shorter than the chain’s persistence length. These electrostaticinteractions renormalize chain persistence length. The second part includes electrostaticinteractions between remote charged pairs along the polymer backbone located at distanceslarger than the chain persistence length. These interactions are responsible forchain swelling. In the framework of this approach we calculated effective chainpersistence length and chain size as a function of the Debye screening length, chaindegree of ionization, bare persistence length and chain degree of polymerization.Our crossover expression for the effective chain’s persistence length is in goodquantitative agreement with the experimental data on DNA. We have been able to fitexperimental datasets by using two adjustable parameters: DNA ionization degree (α = 0.15–0.17) and a barepersistence length (lp = 40–44 nm).