Formation of Nano-Ordered Structure through Folding Transition of Single Polymer Chain

我们从实验和理论两个方面对单链聚合物的折叠转变进行了系统的研究。(1)通过蒙特卡罗和分子动力学的数值模拟，推导出了单链聚合物的相图。一般说来，这种转变是从细长线圈到有序致密结构的转变，即失谐-有序转变。然而，这种转变是从细长的盘绕到类液体的球状状态的连续转变，即无序-无序转变。(2)建立了观察单个DNA链结构转变的实验方法。研究发现，在聚阳离子存在的情况下，随着温度的升高，DNA发生从拉长到致密的折叠转变。反之，随着温度的升高，DNA链在聚乙二醇水溶液中呈现展开相变。(3)构建了红外激光捕获单个DNA链的实验系统。研究发现，单个DNA分子在水溶液中选择性迁移的长度可长达厘米。作为这种研究的延伸，我们已经成功地观察到在适当的非平衡条件下，单DNA链中克隆状态和紧凑状态之间的节律变化。

We have performed a systematic study on the folding transition of single polymer chains both from experiment and theory.(1) From numerical simulations of Monte Carlo and molecular dynamics, the phase-diagram of a single polymer has been deduced. In general, the transition is discerete for the change from elongated coil into order compact structure, i.e., discorder-order transition. Whereas, the transition is continuos from elongated coil into liquid-like globule state ; i.e., disorder-disorder transition.(2) Experimental method to observe the structural transition on individual DNA chains has been established. It was found that, in the presence of polycation, DNA undergoes folding transition from elongated the compact state with increase of temperature. Contrary this, DNA chains exhibit unfolding transition in PEG-solution with increase of temperature.(3) We have constructed an experimental system to trap individual DNA chains by IR laser. It was found that individual DNA molecules are transferred selectively as long as centimeter in aqueous solution. As an extension of such study, we have succeeded in observing rhythmic change between clongated and compact states in single DNA chains under suitable nonequilibrium condition.