Entropically driven transition to a liquid-crystalline polymer globule

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.

Simulating the collapse transition of a two-dimensional semiflexible lattice polymer

“…The globule-coil structural transition is a fundamental issue in polymer physics. The nature of this transition has been studied extensively in the past several decades by experimental, theoretical, and simulation approaches 1,2,5,9,10,11,12,13,14,15,16,17,18,19 . Certain degree of consensus has been achieved on various aspects of the poly-mer globule-coil transition, but there are still some unresolved important issues.…”

Globular structures of a helix-coil copolymer: Self-consistent treatment

“…(2.21) . For a given set of parameters, N (µ) can be computed 24 and a typical example of this curve is shown in Fig. (4).…”

“…In this subsection the ǫ-dependence of the transition from amorphous to liquid-crystalline globule is investigated 24 . In Section IIB, it was shown that the fraction of stiff segments increases with increasing energy gain ǫ per stiff segment.…”