Thermodynamics and Kinetics on the Folding Transition of Single Molecular Chain

我们对单分子水平的折叠相变的理论和实验研究都取得了很大的进展。在理论方法中，我们采用了分子动力学模拟，结合布朗运动和单个分子折叠过程的动力学分析。结果表明，纳米尺度的有序结构是通过成核生长过程产生的。研究还表明，核的形成是一个泊松过程，核的生长是一个时间线性过程。无序球形凝聚结构是由高度非平衡的旋量分解产生的。在实验方法上，利用红外激光对单链聚合物的输运和结构调控进行了研究。在波长为1000 nm的YAG激光中，将聚焦设置在约1 μm范围内，进行了介电诱捕。在这样的实验条件下，避免了DNA分子的化学降解。我们发现，通过折叠跃迁形成的结构紧凑的长DNA分子可以很容易地在溶液中运输，而不需要任何化学修饰。我们进一步发现，通过将样品运送到具有不同化学成分的溶液中，无需任何机械处理即可调节长DNA分子的结构。我们的研究为μm级微观化学和分子生物学实验室的建立提供了基础技术。

A great progress has been attained with our studies on the folding phase transition at the level of a single molecule both in theoretical and experimental approaches. In the theoretical approach, we have employed simulations of molecular dynamics incorporating Brownian motion and kinetic analyses on folding processes of a single molecule. As a result, it has become clear that ordered structures in nanometer scale are generated through the process of nucleation ＆ growth. It has also been indicated that the probability of the nuclear formation is a Poisson-like process and the growth is a time-linear process. It has also become clear that disordered spherical condensed structure is generated by spinodal decomposition in high degree of non-equilibrium. In the experimental approach, studies on transportation and structure regulation of a single polymer chain by use of infrared laser have been developed. Dielectric traps by YAG laser light beam at 1000 nm in wave length were performed with setting the focus within about 1 μm. Under such experimental conditions, chemicai degradation on DNA molecules is avoided. We showed that a long DNA molecule in compact structure formed through folding transition can be easily transported in solution without any chemical modification. We further found that the structure of a long DNA molecule is regulated without any mechanical treatment, by transporting the specimen to the solution with different chemical compositions. Our study provides the principle technology that leads to a LABORATORY for the μm-scaled microscopic chemistry and molecular biology.