Faculty of Physics, Lomonosov Moscow State University, Leninskie gory, 1-2, 119991, Moscow, Russia.
Soft Matter. 2018 May 2;14(17):3232-3235. doi: 10.1039/c8sm00346g.
The effect of an interplay between electrostatic and excluded volume interactions on the conformational behavior of a dipolar chain has been studied theoretically and by means of molecular dynamics simulations. Every monomer unit of the dipolar chain comprises a dipole formed by a charged group of the chain and an oppositely charged counterion. The counterion is assumed to freely move around the chain but keeping the distance between oppositely charged ions (the dipole length) fixed. The novelty of the developed mean-field theory is that variations of the dipole parameters (the dipole length and the counterion size) have been accounted for in both electrostatic and excluded volume contributions to the total free energy of the dipolar chain. It has been shown that conformational transitions between swollen and collapsed states of the chain can be induced by fine-tuning the balance between electrostatic and excluded volume interactions. In particular, in low-polar media not only globule but also extended coil conformations can be realized even under strong electrostatic attraction. The results of MD simulations of a dipolar chain with variable dipolar length support theoretical conclusions.
静电相互作用和排除体积相互作用之间的相互作用对偶极链构象行为的影响已通过理论和分子动力学模拟进行了研究。偶极链的每个单体单元都由链上的带电基团和带相反电荷的反离子形成的偶极组成。假设反离子可以自由地在链周围移动，但保持带相反电荷的离子之间的距离（偶极长度）固定。所开发的平均场理论的新颖之处在于，在偶极链的总自由能的静电和排除体积贡献中，都考虑了偶极参数（偶极长度和反离子大小）的变化。结果表明，通过微调静电相互作用和排除体积相互作用之间的平衡，可以诱导链的溶胀和塌陷状态之间的构象转变。特别是，在低极性介质中，即使在强静电吸引下，也可以实现不仅是球粒，还有扩展的线圈构象。具有可变偶极长度的偶极链的 MD 模拟结果支持了理论结论。
