Dynamic Model for Locally Stiff Ring and Straight Chain Polymers

The Rouse–Bueche bead–spring model for high polymers is extended to account for stiffness arising from local torsional and bending interactions. A mechanical model including second- and third-nearest-neighbor bead–spring interactions is developed. The effect of local stiffness is introduced into the normal-mode eigenvalue spectrum via second- and third-nearest-neighbor Hooke's law spring constants. A calculation is made of the effect of stiffness on both the free-draining and hydrodynamic interaction properties of linear and circular high polymers. Experiments for supercoiled circular DNA where local stiffness is expected to be large and circular DNA are compared with theory. The effect of local stiffness is sufficient to account for the differences in intrinsic viscosity between the two species.