  Packing and crowding are used in biology as mechanisms to (self-)regulate
internal molecular or cellular processes based on collective signalling. Here,
we study how the transition kinetics of an internal switch of responsive
macromolecules is modified collectively by their spatial packing. We employ
Brownian dynamics simulations of a model of responsive colloids (RCs), in which
an explicit internal degree of freedom, here, the particle size, moving in a
bimodal energy landscape responds self-consistently to the density fluctuations
of the crowded environment. We demonstrate that populations and transition
times for the two-state switching kinetics can be tuned over one order of
magnitude by self-crowding. An exponential scaling law derived from a
combination of Kramers' and liquid state perturbation theory is in very good
agreement with the simulations.
