DNA electrophoretic collisions with single obstacles

We analyze the electrophoretic collision between an obstacle, such as a gel fiber, and a large diffusing polyelectrolyte. This type of collision may be considered as the basic unit of elementary sieving behind all electrophoretic separation methods. The polymer first hooks around an obstacle and must escape using a simple ``pulley'' process which requires a molecular-size-dependent time. We demonstrate, using both analytical and simulation results, that simple isolated collisions cannot lead to separation due to large diffusion effects generated by the process (in spite of the stacking phenomenon).