ABSTRACT
The process of folding in single polymer chains has been attracting interest from biological and physicochemical points of view. In biological science, it is known that long DNA condense into a self-organized folded structure with various kinds of morphologies such as toroid, rod, and spherical. Such a collapse transition, or coil-globule transition, of DNA has been discussed in connection with the tight packing of long DNA chains in phage capsids, and with compact folding in living cells (Berg et al. 2002). However, due to the theoretical limitation of self-consistent eld theory for dilute or isolated polymer chain, the intrinsic property of the coil-globule transition still remains unclear. For example, some theoretical studies (Lifshitz et al. 1978) predict the discontinuous nature of the coil-globule transition in astiff polymer. However, almost all experimental studies have reported acontinuous character of the transition of polyelectrolytes including DNA chains. DNA represents semi£exible polyelectrolyte with rigidity that originates from secondary structure stabilized by hydrogen bond and electrostatic interaction that is affected by the Coulomb repulsion, which gives the sum of the persistent length of 50 nm in aqueous environment.
