Iwaki T, Yoshikawa K
Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Sep;68(3 Pt 1):031902. doi: 10.1103/PhysRevE.68.031902. Epub 2003 Sep 8.
Single-molecule observations of giant DNA have clarified that individual molecules undergo a marked discrete transition between an elongated coil state and a compact globule state. There is a relatively wide region of coexistence between the coil and the globule states, i.e., interchain phase segregation, with a change in intensive variables such as the concentration of the condensing agent, salt concentration, temperature. Very recently, the coexistence of coil and globule conformations within a single long DNA chain, i.e., intrachain phase segregation, has been reported under certain experimental conditions. In this study, we investigated general conditions for intrachain phase segregation in a single polyelectrolyte molecule, based on a simple statistical model. We consider the contribution of condensed counterions and the interaction energy of a charged coiled region. Intrachain phase segregation is stable with regard to free energy within a suitable parameter region. Our results suggest that intrachain phase segregation occurs when the electrostatic screening effect by the salt solution is negligible or when the screening effect is large and there is attractive interaction between polyelectrolyte segments.
对巨型DNA的单分子观测已经表明，单个分子在拉长的线圈状态和紧密的球状体状态之间经历了明显的离散转变。在线圈状态和球状体状态之间存在一个相对较宽的共存区域，即链间相分离，随着诸如凝聚剂浓度、盐浓度、温度等强度变量的变化而变化。最近，在某些实验条件下，已经报道了在单个长DNA链内线圈和球状体构象的共存，即链内相分离。在本研究中，我们基于一个简单的统计模型，研究了单个聚电解质分子中链内相分离的一般条件。我们考虑了凝聚抗衡离子的贡献以及带电卷曲区域的相互作用能。在合适的参数区域内，链内相分离在自由能方面是稳定的。我们的结果表明，当盐溶液的静电屏蔽效应可忽略不计时，或者当屏蔽效应很大且聚电解质链段之间存在吸引相互作用时，会发生链内相分离。
