Phase Transitions in the Higher Order Structure of Giant DNA

总体而言，名古屋和莫斯科之间的国际合作取得了成功，包括聚合物物理基本概念的发展，以及介观体系物理化学的发展。通过合作，名古屋的研究小组利用荧光显微镜的单链观察，证明了单个单链双链DNA链经历了拉长的卷曲和紧密的球状之间的大的离散相变(卷曲-球状转变)，而DNA整体具有扩散或连续转变的特征。从单链观察，我们发现这种一级相变是由合成聚合物、阳离子表面活性剂、低分子多价阳离子和酒精等各种缩合剂诱导的。基于这些实验结果，名古屋和莫斯科在单链高分子链相变的理论分析方面进行了积极的合作，包括蒙特卡罗模拟和平均场理论。通过这些理论分析和计算，再现了长DNA链坍塌跃迁的本质。值得注意的是，这些理论可以很好地解释坍塌产物中形态变化的存在。

As a whole, the international collaboration between Nagoya and Moscow has been performed successfully, including the development on basic concept in polymer physics and also in physical chemistry in mesoscopic system. Through the collaboration, the research group of Nagoya has demonstrated that individual single duplex DNA chains undergoes large discrete phase transition between elongated coil and compacted globule (coil-globule transition), based on the single chain observation by use of fluorescence microscopy, whereas ensemble of DNA has the characteristics of diffuse or continuous transition.From single chain observation, we found this first order phase transition is induced by various kinds of condensation agents such as synthetic polymer, cationic surfactant, low molecular multivalent cation, and alcohol. Based on these experimental findings, active collaboration between Nagoya and Moscow has been performed on the theoretical analysis of the phase transition in a single polymer chain, including Monte Carlo simulation and mean field theory. The essential aspects in the collapsed transition of long DNA chain has been reproduced with these theoretical analysis and calculations. It is to be noted that the existence of the morphological variation in the collapsed products can be interpreted well in these theories.