Europhys. Lett.
Volume 74, Number 1, April 2006
Page(s) 76 - 82
Section Condensed matter: structural, mechanical and thermal properties
Published online 08 March 2006
Europhys. Lett., 74 (1), pp. 76-82 (2006)
DOI: 10.1209/epl/i2005-10516-1

Entropically driven transition to a liquid-crystalline polymer globule

C. Nowak, V. G. Rostiashvili and T. A. Vilgis

Max Planck Institut for Polymer Research - Ackermannweg 10, 55128 Mainz, Germany

received 23 August 2005; accepted in final form 14 February 2006
published online 8 March 2006

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 may give a simple explanation for the formation of helix bundles in certain globular proteins.

61.30.Vx - Polymer liquid crystals.
87.14.Ee - Proteins.
87.15.-v - Biomolecules: structure and physical properties.

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