title: DNA like-charge attraction and overcharging by divalent counterions in the presence of divalent co-ions.
abstract: Strongly correlated electrostatics of DNA systems has drawn the interest of many groups, especially the condensation and overcharging of DNA by multivalent counterions. By adding counterions of different valencies and shapes, one can enhance or reduce DNA overcharging. In this paper, we focus on the effect of multivalent co-ions, specifically divalent co-ions such as SO[Formula: see text]. A computational experiment of DNA condensation using Monte Carlo simulation in grand canonical ensemble is carried out where the DNA system is in equilibrium with a bulk solution containing a mixture of salt of different valency of co-ions. Compared to systems with purely monovalent co-ions, the influence of divalent co-ions shows up in multiple aspects. Divalent co-ions lead to an increase of monovalent salt in the DNA condensate. Because monovalent salts mostly participate in linear screening of electrostatic interactions in the system, more monovalent salt molecules enter the condensate leads to screening out of short-range DNA-DNA like charge attraction and weaker DNA condensation free energy. The overcharging of DNA by multivalent counterions is also reduced in the presence of divalent co-ions. Strong repulsions between DNA and divalent co-ions and among divalent co-ions themselves lead to a depletion of negative ions near the DNA surface as compared to the case without divalent co-ions. At large distances, the DNA-DNA repulsive interaction is stronger in the presence of divalent co-ions, suggesting that divalent co-ions' role is not only that of simple stronger linear screening.
authors.affiliation: Faculty of Physics, VNU University of Science, Vietnam National University, 334 Nguyen Trai Street, Thanh Xuan, Hanoi, Vietnam.
authors.forename: Viet Duc
authors.initials: VD
authors.lastname: Nguyen
authors.affiliation: Faculty of Physics, VNU University of Science, Vietnam National University, 334 Nguyen Trai Street, Thanh Xuan, Hanoi, Vietnam. toannt@hus.edu.vn.|VNU Key Laboratory "Multiscale Simulation of Complex Systems", VNU University of Science, Vietnam National University, 334 Nguyen Trai Street, Thanh Xuan, Hanoi, Vietnam. toannt@hus.edu.vn.|School of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, GA, 30332-0430, USA. toannt@hus.edu.vn.
authors.forename: Toan T
authors.initials: TT
authors.lastname: Nguyen
authors.affiliation: VNU Key Laboratory "Multiscale Simulation of Complex Systems", VNU University of Science, Vietnam National University, 334 Nguyen Trai Street, Thanh Xuan, Hanoi, Vietnam.|Computational Biomedicine, Institute for Advanced Simulation IAS-5, and Institute of Neuroscience and Medicine INM-9, Forschungszentrum Julich, 52425, Julich, Germany.
authors.forename: Paolo
authors.initials: P
authors.lastname: Carloni
mesh_terms: D004247:DNA / Q000737:chemistry*; D008958:Models, Molecular; D012492:Salts / Q000737:chemistry
chemical_list: D012492:Salts; D004247:DNA
keywords: DNA condensation; DNA overcharging; Multivalent coions; Multivalent counterions