Translational and Reorientational Dynamics of Entangled DNA

The end-group mean square displacement, molecular reorientation time, and radius of gyration of entangled lambda-phage DNA molecules were measured with fluorescence microscopy. A frequency-dependent, complex diffusivity is derived by Fourier transformation of the mean square displacement. From a comparison of the diffusion moduli with the predictions of DoiEdwards theory, the tube renewal time, step length, mean square end-to-end distance, Rouse relaxation time, and entanglement time are obtained. The reorientation time is derived from the orientation correlation of the radius of gyration tensor. The concentration dependencies of the tube renewal, reorientation, Rouse time, and entanglement time as well as the number of entanglements per DNA molecule agree with the relevant scaling laws for salted polyelectrolytes with screened electrostatics. Furthermore, the similarity in time scale for tube renewal and molecular reorientation brings into view the coupled translational and reorientational motion of DNA molecules in the entangled regime.