  We study the diffusion of a tracer particle, which moves in continuum space
between a lattice of excluded volume, immobile non-inert obstacles. In
particular, we analyse how the strength of the tracer-obstacle interactions and
the volume occupancy of the crowders alter the diffusive motion of the tracer.
From the details of the partitioning of the tracer diffusion modes between
trapping states when bound to obstacles and bulk diffusion, we examine the
degree of localisation of the tracer in the lattice of crowders. We study the
properties of the tracer diffusion in terms of the ensemble and time averaged
mean squared displacements, the trapping time distributions, the amplitude
variation of the time averaged mean squared displacements, and the
non-Gaussianity parameter of the diffusing tracer. We conclude that
tracer-obstacle adsorption and binding triggers a transient anomalous
diffusion. From a very narrow spread of recorded individual time averaged
trajectories we exclude continuous type random walk processes as the underlying
physical model of the tracer diffusion in our system. For moderate
tracer-crowder attraction the motion is found to be fully ergodic, while at
stronger attraction strength a transient disparity between ensemble and time
averaged mean squared displacements occurs. We also put our results into
perspective with findings from experimental single-particle tracking and
simulations of the diffusion of tagged tracers in dense crowded suspensions.
Our results have implications for the diffusion, transport, and spreading of
chemical components in highly crowded environments inside living cells and
other structured liquids.

Soft Condensed Matter;Biological Physics