Perfect helical structure of semiflexible polyelectrolyte chain confined in a cylinder

Abstract

Conformations of a semiflexible polyelectrolyte (SPE) chain with neutralizing charged counterions confined in a cylinder have been investigated by off-lattice Monte Carlo simulations. Effects of electrostatic interactions of different Bjerrum length lB between PEs and counterions, PEs of different chain stiffness b, and cylindrical confinement of different radius R on the conformations of SPEs have been examined. At suitable combinations of the above parameters of lB, b, and R, perfect helical structures are observed, which can be well characterized by the tangent correlation function. The number of turns in perfect helix can be read accurately through counting the number of oscillation periods of correlation function. The expanded confined space with a larger cylindrical radius leads the helix phase region into a smaller range of b and lB. The physical mechanism for the formation of perfect helical structures is further explored by the distribution of chain monomers and counterions. Although helix formation has been associated with the electrostatic interactions and chain stiffness, the cylindrical confinement promotes the formation of perfect helical structures driven by entropy. This study can provide a deeper insight about mechanisms behind the conformation of biological macromolecules with oppositely charged counterions in confinement cavity.