Scaling regimes for wormlike chains confined to cylindrical surfaces under tension.

ABSTRACT

We compute the free energy of confinement [Formula see text] for a wormlike chain (WLC), with persistence length [Formula see text], that is confined to the surface of a cylinder of radius R under an external tension f using a mean field variational approach. For long chains, we analytically determine the behavior of the chain in a variety of regimes, which are demarcated by the interplay of [Formula see text], the Odijk deflection length ([Formula see text]), and the Pincus length ([Formula see text], with [Formula see text] being the thermal energy). The theory accurately reproduces the Odijk scaling for strongly confined chains at [Formula see text], with [Formula see text]. For moderate values of f, the Odijk scaling is discernible only when [Formula see text] for strongly confined chains. Confinement does not significantly alter the scaling of the mean extension for sufficiently high tension. The theory is used to estimate unwrapping forces for DNA from nucleosomes.