不同pH环境下二价离子对聚电解质链的影响

Effect of divalent ions on the polyelectrolyte chains at different pH

基于郎之万动力学方法,研究了不同pH环境下二价反离子对半柔性聚电解质链构象变化的影响。聚电解质用粗粒度的珠簧模型表示,在pH-pK>0时,回转半径几乎不变,随着pH-pK值的降低,聚电解质链的回转半径减小并且逐渐发生了缩合。在实验中,通过改变Mg^2+介导下DNA溶液的pH环境,对DNA进行了原子力显微镜扫描成像,发现DNA在中性和弱酸性环境中保持自由松散状态,当pH降低到4以下,即酸性变强时DNA逐步缩合成球状并达到稳定,这一结果与模拟结果一致。

In this study, the effect of divalent counterions on the conformational change of the semi-flexible polyelectrolyte chains was investigated at different pH based on Langevin’s dynamics. Polyelectrolyte is represented by a coarse-grained bead spring model, with the radius of gyration(Rg) remaining almost constant at pH-pK>0. Rg reduces and the polyelectrolyte chain shrinks as the value of pH-pK decreases. Meanwhile, in the experiment, the atomic force microscopy images of the DNA mediated by Mg^2+ were obtained in different pH environments to denote that the DNA remained in a free and loose state in neutral and weakly acidic environments. At pH<4, i.e., strong acidity, DNA was gradually condensed into a spherical shape and stabilized. Further, the experimental result agrees with the simulation results.