Abstract. We propose that semiflexible polymers in poor solvent collapse in two stages. The first stage is the well-known formation of a dense toroidal aggregate. However, if the solvent is sufficiently poor, the condensate will undergo a second structural transition to a twisted entangled state, in which individual filaments lower their bending energy by additionally orbiting around the mean path along which they wind. This "topological ripening" is consistent with known simulations and experimental results. It connects and rationalizes various experimental observations ranging from strong DNA entanglement in viral capsids to the unusually short pitch of the cholesteric phase of DNA in sperm heads. We propose that topological ripening of DNA toroids could improve the efficiency and stability of gene delivery.

PACS numbers: 64.70.Nd, 87.15.He, 61.30.Pq

Print publication: Issue 3 (August 2004)
Received 17 March 2004, in final form and accepted for publication 19 May 2004