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

我们从实验和理论两方面对聚合物单链的折叠跃迁进行了系统的研究。(1)通过蒙特卡罗数值模拟和分子动力学，推导出了单个聚合物的相图。一般情况下，细长线圈向有序紧致结构转变的过渡是离散的，即失序-有序过渡。而从细长线圈状态连续转变为类液球状态；即，无序-无序过渡。(2)建立了观察单个DNA链结构转变的实验方法。研究发现，在多阳离子存在的情况下，DNA随着温度的升高，从细长态向致密态发生折叠转变。与此相反，DNA链在peg溶液中随着温度的升高呈现出展开转变。(3)构建了红外激光捕获DNA单链的实验系统。研究发现，单个DNA分子在水溶液中选择性地转移长达厘米。作为这一研究的延伸，我们成功地观察到了在合适的非平衡条件下单链DNA在长链和紧链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.