Core/Shell Structures of Proteinlike Copolymers: Are Finite Aggregates Thermodynamically Stable?

Abstract

We propose a theory of aggregation in solutions of amphiphilic copolymers consisting mostly of insoluble H (hydrophobic) units with a small fraction of soluble (P, polar) monomer units. When P units are arranged along the sequence in a periodic (regular) fashion, the resultant HP copolymers are essentially insoluble: they precipitate. The main result is that finite aggregates of HP copolymers can be made stable by an appropriate smart arrangement of the same number of soluble P units in the chemical sequence. An analytical approach yielding the thermodynamic quantities of H-core/P-shell copolymer structures in the weak stretch limit is developed. We show that different types of copolymer aggregates and microdomain structures can be thermodynamically stable depending on the copolymer chemical sequence. The relationship between the block-length distribution and copolymer aggregation is illustrated by a few phase diagrams. Copolymers that can form stable finite aggregates with H-core/P-shell structure (including single-chain globules) are often referred to as the proteinlike copolymers. Thus, the present theory sheds a new light as to the essential features of proteinlike copolymer sequences.