Stability of dense hydrophobic-polar copolymer globules: Regular, random and designed sequences
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
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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.
© EDP Sciences, Società Italiana di Fisica, and Springer-Verlag, 2003