Emergence of helical structures in weakly confined, semiflexible, charged polymers

Abstract

Helical motifs are ubiquitous in macromolecular systems at the nanometer to microns length scales. At the micron length scales, the formation of helical structures can be expected to be independent of the specific molecular chemical bonds and steric interactions, and instead be driven by relatively weak intermolecular forces. Emergence of helical order needs coordinated organization over long distances in polymeric macromolecules. We establish a generic mechanism to obtain spontaneous helicity by inducing screened Coulomb interactions between monomers in a semiflexible heteropolymer. In an experimental setup, change in solvent conditions locally can lead to different polymeric segments to attain charges of differing polarities and magnitudes. As we elucidate in this study using a coarse-grained bead spring model of a semiflexible polymer, this in turn can lead to spontaneous emergence of transient helical structures along the chain contour for a range of Debye-lengths. These transient helices can be made long-lived when they are subjected to weak geometric confinement to restrict the relaxation of the helical conformations. We have avoided using torsional potentials to obtain helical structures especially because emergence of torsional forces are unexpected at the micron length scales.