One-Loop Fluctuation Entropy of Charge Inversion in DNA

Matthew D. Sievert, Marilyn F. Bishop, Tom McMullen

1902.05511

The DNA double helix in a solution of positively-charged dimers, which can attach to the surface in either of two configurations. Depending on the strength of the binding and the concentration of dimers in solution, the negatively-charged DNA molecule can have its total charge screened, or even inverted to become positively charged!

Experiments have revealed correlation-driven behavior of DNA in charged solutions, including charge inversion and condensation. This paper presents calculations of a lattice-gas model of charge inversion for the adsorption of charged dimers on DNA. Each adsorption site is assumed to have either a vacancy or a positively-charged dimer attached with the dimer oriented either parallel or perpendicular to the double helix DNA chain. The entropy and charge distributions of these three species are calculated including the lowest order fluctuation corrections to mean-field theory. We find that the inclusion of the fluctuation terms has a significant effect on the entropy, primarily in the regime where the dimers are repelled from the DNA molecule and compete with the chemical potential in solution.