Potential of mean force and transient states in polyelectrolyte pair complexation.
Potential of mean force and transient states in polyelectrolyte pair complexation.
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DOI：
10.1063/1.4958675
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发表时间：
2016-02
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影响因子：
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通讯作者：
Xiao Xu;M. Kanduč;Jianzhong Wu;J. Dzubiella
中科院分区：
文献类型：
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作者：
Xiao Xu;M. Kanduč;Jianzhong Wu;J. Dzubiella
通过粗粒、隐式溶剂、显式盐体系的计算机模拟，系统研究了两种大小相同但电荷相反的聚电解质（PE）之间的电子对缔合作用，并计算了它们的平均力势（PMF）沿着质心反应坐标.重点是设置在发病和中间过渡阶段的络合。在高于反离子缩合阈值的条件下，PE缔合过程表现出明显的滑动棒状行为，其中聚合物链通过首先在接近其轮廓长度的临界距离处伸展，然后“握手”并以平行方式沿沿着彼此滑动，然后最终折叠成中性复合物来彼此接近。高电荷PE的PMF的基本部分可以很好地描述了一个简单的理论基础上滑动带电的“德拜-休克尔”棒重整化的电荷，除了一个明确的熵贡献，由于释放凝聚的抗衡离子。有趣的是，在复合物形成的开始，PE链之间的平均力被发现是不连续的，反映了双峰结构的行为，所产生的相互连接的杆和孤立的线圈状态的共存。PE复合物的这两种微观状态通过微妙的反作用力释放效应而平衡，并且由于不利的拉伸熵而被自由能垒分开。
The pair association between two polyelectrolytes (PEs) of the same size but opposite charge is systematically studied in terms of the potential of mean force (PMF) along their center-of-mass reaction coordinate via coarse-grained, implicit-solvent, explicit-salt computer simulations. The focus is set on the onset and the intermediate transient stages of complexation. At conditions above the counterion-condensation threshold, the PE association process exhibits a distinct sliding-rod-like behavior where the polymer chains approach each other by first stretching out at a critical distance close to their contour length, then "shaking hand" and sliding along each other in a parallel fashion, before eventually folding into a neutral complex. The essential part of the PMF for highly charged PEs can be very well described by a simple theory based on sliding charged "Debye-Hückel" rods with renormalized charges in addition to an explicit entropy contribution owing to the release of condensed counterions. Interestingly, at the onset of complex formation, the mean force between the PE chains is found to be discontinuous, reflecting a bimodal structural behavior that arises from the coexistence of interconnected-rod and isolated-coil states. These two microstates of the PE complex are balanced by subtle counterion release effects and separated by a free-energy barrier due to unfavorable stretching entropy.