Simulation Studyon The Configuration Change Ofsemi-rigid Polymer Chain Under Polyvalent Countrrion

Polyelectrolytes interact with cations is key to biophysics.Many experiments have been conducted to investigate the interaction of cations with Polyelectrolytes,such as metal ions introduce DNA conformation change.Few studies have focus on the interaction of cations with DNA in terms of simulations.It is necessary to explore the interaction between cations with different valence and DNA through Brownian dynamics simulations.In this paper,we study the conformation change of isolated flexible polyelectrolyte chain interact with counterions by using coarse-grained model and Brownian dynamics simulation.The polyelectrolyte has different conformations after the interaction with counterions at different valence.With the increase of the effective charge ratio,Rg(radius of gyration)rises under the weak Coulomb strength,however,it rises and then keep constant under the strong coulomb strength.The conformation of polyelectrolyte is neither a folded structure nor a double layer ring structure after mixing monovalent ions and polyvalent ions and.As the ratio of univalent to polyvalent ions increases,the radius of gyration is almost constant.We guess that the transform in configuration is the statistical average result of coulombic repulsion interactions between monovalent and polyvalent counterions.