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

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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.