Diffusion and reaction in crowded environments

The effects of molecular crowding on small molecule diffusion and chemical reaction rate coefficients are investigated. The systems considered comprise a random distribution of stationary spherical obstacles occupying a volume fraction phi of the system and a large number of small molecules whose dynamics are followed. Chemical reactions are studied in such crowded systems where, in addition to the obstacles, a large reactive sphere C is present that catalyses the reaction A + C -> B + C. Using a mesoscopic description of the dynamics employing multiparticle collisions among the small molecules, the f dependence of the diffusion and reaction rate coefficients is computed. Both the diffusion and reaction rate coefficients decrease with increase of the obstacle volume fraction as expected but variations of these quantities with f are not predicted by simple models of the dynamics.