Equilibrium and kinetic phenomena in a stiff homopolymer and possible applications to DNA

We study the bead-and-spring model of a stiff chain using a self-consistent mean-field approach. For high stiffness parameter the system may undergo a transition to the phase in which the globule acquires a toruslike shape. The phase diagram of the model contains one second- and two first-order transitions meeting at a bicritical point. The stability of the toroidal conformation and scalings of the torus geometry are analyzed. We investigate different kinetic regimes after an instantaneous quench between the extended coil, torus and the spherical globule phases. The kinetic laws that govern these conformational changes are obtained. (C) 1996 American Institute of Physics.