Entropically driven transition to a liquid-crystalline polymer globule

TL;DR

This study uses self-consistent-field theory to reveal a novel entropically driven transition from a coil-globule to a nematic liquid-crystalline globule in helix-coil copolymers, highlighting the role of surface energy anisotropy.

Contribution

It demonstrates for the first time that a nematic LC-globule can form without explicit rod-rod interactions, driven by hydrophobic attraction and surface anisotropy.

Findings

Identification of a new nematic LC-globule phase

Phase diagram distinguishing open chain, amorphous, and LC-globule states

Explanation for helix bundle formation in globular proteins

Abstract

A self-consistent-field theory (SCFT) in the grand canonical ensemble formulation is used to study transitions in a helix-coil multiblock copolymer globule. The helices are modeled as stiff rods. In addition to the established coil-globule transition we show for the first time that, even without explicit rod-rod alignment interaction, the system undergoes a transition to a nematic liquid-crystalline (LC) globular state. The LC-globule formation is driven by the hydrophobic helical segment attraction and the anisotropy of the globule surface energy. The full phase diagram of the copolymer was calculated. It discriminates between an open chain, amorphous globule and LC-globule. This model provides a relatively simple example of the interplay between secondary and tertiary structures in homopolypeptides. Moreover, it gives a simple explanation for the formation of helix bundles in certain globular proteins.