SELF-DIFFUSION AND COOPERATIVE DIFFUSION OF A RODLIKE DNA FRAGMENT

The self-diffusion and cooperative diffusion of a 150 base pair DNA fragment have been studied as a function of DNA concentration at three different salt concentrations (in the range of 1 mM to 1 M NaCl) in semidilute solution. In the 1 mM NaCl concentration, slow and fast relaxation modes were observed by quasi-elastic light scattering while only one relaxation mode was observed by forced Rayleigh scattering. The slow mode is shown to be not a self-diffusion process. In the high-salt conditions, the dynamics of rodlike DNA were discussed in the context of Doi and Edwards theory. The experimental results in low-salt conditions are compared with the scaling theory and the coupled-mode ion diffusion theory of Lin, Lee, and Schurr.