  Based on a coarse-grained model, we carry out molecular dynamics simulations
to analyze the diffusion of a small tracer particle inside a cylindrical
channel whose inner wall is covered with randomly grafted short polymeric
chains. We observe an interesting transient subdiffusive behavior along the
cylindrical axis at high attraction between the tracer and the chains, however,
the long time diffusion is always normal. This process is found to be enhanced
for the case that we immobilize the grafted chains, i.e. the sub-diffusive
behavior sets in at an earlier time and spans over a longer time period before
becoming diffusive. Even if the grafted chains are replaced with a frozen sea
of repulsive, non-connected particles in the background, the transient
subdiffusion is observed. The intermediate subdiffusive behavior only
disappears when the grafted chains are replaced with a mobile background sea of
mutually repulsive particles. Overall, the long time diffusion coefficient of
the tracer along the cylinder axis decreases with the increase in system volume
fraction, strength of attraction between the tracer and the background and also
on freezing the background. We believe that the simple model presented here
could be useful for a qualitative understanding of the process of
macromolecular diffusion inside the nuclear pore complex.
