Molecular Crowding Increases Knots Abundance in Linear Polymers

Stochastic simulations are used to study the effects of molecular crowding on the self-entanglement of linear polymers. We consider flexible chains of beads of up to 1000 monomers and examine how their knotting properties vary in the presence spherical crowders that are 4 times smaller than the chains themselves and which occupy 35% of the solution volume. We find that crowding boosts the incidence of physical knots by more than an order of magnitude for all considered chain lengths. Furthermore, most crowding-induced knots are found to be significantly longer than in the free case. We show that the observed properties follow from the screening of excluded volume interactions mediated by the crowders at length scales larger than their size.