Eur. Phys. J. E (2003) 12: 255-264
https://doi.org/10.1140/epje/i2003-10057-y

Stability of dense hydrophobic-polar copolymer globules: Regular, random and designed sequences

¹ Physics Department, Moscow State University, 119992, Moscow, Russia
² Polymer Science, University of Ulm, 89069, Ulm , Germany
³ Institut Charles Sadron, 6 rue Boussingault, 67083 , Strasbourg Cedex, France

^* e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Stability of dense globular structures formed by amphiphilic copolymers consisting of hydrophobic (insoluble) units and a small fraction of single polar (soluble) monomer units is considered in the mean-field approximation for different types of unit distributions along the chain. Polar (P) units are located in a relatively thin surface layer due to their strong repulsion from hydrophobic (H) monomer units. We compared globules formed by different copolymer sequences with the same gross numbers of P- and H-units: regular HP-sequences (P-units separated by equal H-blocks), random copolymers (uncorrelated positions of P-units, i.e. Flory distribution of H-block lengths), proteinlike (PL) sequences (designed sequences involving both long H-blocks dominating by total mass, and short blocks dominating by number). We showed that PL-globules are more stable (lower free energy) and are characterized by a higher temperature of the coil-to-globule transition when compared with the other sequences mentioned above. We also considered HP-H-copolymers consisting of one long and many short hydrophobic blocks; we showed that it is these sequences that yield the dense globules corresponding to the lowest free energy.