Theory for second virial coefficients of short DNA

Using the Poisson-Boltzmann equation, we model the interactions between charged cylindrical molecules of finite length. We model end effects by showing that the PB results for rods are well approximated by the Debye-Hückel linearization for "effective ellipsoids". Without adjustable parameters, the theory gives reasonable agreement with the second virial coefficient measurements of Nicolai and Mandel 1 on short DNA molecules.