arXiv:cond-mat/9910223v1 [cond-mat.soft] 15 Oct 1999 EPJ manuscript No. (will be inserted by the editor) Interactions Between Charged Rods Near Salty Surfaces Rebecca Menes 1 Niels Grønbech-Jensen 2 and Phil A. Pincus 1 1 Materials Research Laboratory, University of California, Santa Barbara, California, 93106, USA 2 Department of Applied Science, University of California, Davis, California 95616, USA NERSC, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA Received: date / Revised version: date Abstract. Using both theoretical modeling and computer simulations we study a model system for DNA interactions in the vicinity of charged membranes. We focus on the polarization of the mobile charges in the membranes due to the nearby charged rods (DNA) and the resulting screening of their fields and inter-rod interactions. We find, both within a Debye-H¨ uckel model and in Brownian dynamics simulations, that the confinement of the mobile charges to the surface leads to a qualitative reduction in their ability to screen the charged rods to the degree that the fields and resulting interactions are not finite-ranged as in systems including a bulk salt concentration, but rather decay algebraically and the screening effect is more like an effective increase in the multipole moment of the charged rod. PACS. PACS-key describing text of that key – PACS-key describing text of that key 1 Introduction Recent experiments on various systems containing DNA strands and charged surfaces have raised an interest in understanding how these surfaces screen the electrostatic fields of the DNA and the resulting interactions between strands. The interest emanates from sources varying from understanding prokaryotic DNA replication[1], to non-viral gene therapy[2,3,4,5], and even DNA chip technology[6]. Send offprint requests to : In this paper we treat this problem using a two-dimensional salt solution model[7,8,9] to account for the charged sur- face (membrane), while the DNA strands are modeled by negatively charged rigid rods. We treat charge neutral sys- tems where the over all charging of the surface and the rod is zero, thus focusing either on overall neutrally charged mixed lipid fluid membranes[10], or highly charged sur- faces to which the counter-ions are strongly bound and therefore treated within a two-dimensional geometry. We