Reversible Self-Organization of Poly(ethylene glycol)-Based Hybrid Block Copolymers Mediated by a De Novo Four-Stranded α-Helical Coiled Coil Motif

Abstract

This paper describes the synthesis and supramolecular organization of two novel hybrid diblock copolymers based on poly(ethylene glycol) (PEG) and peptide sequences inspired by the coiled coil protein folding motif. The self-organization of the diblock copolymers is driven by the tendency of the peptide segments to form well-defined tertiary structures. In contrast to conventional amphiphilic block copolymers, whose self-organization is driven by unspecific hydrophobic interactions and leads to polydisperse aggregates, it was anticipated that this approach could allow precise control over the aggregation number in aqueous solution. Circular dichroism and analytical ultracentrifugation experiments indicated that the self-organization properties of the peptide segments are retained upon conjugation of PEG, and discrete, well-defined supramolecular aggregates are formed. No evidence was found for unspecific self-organization of the diblock copolymers to large polydisperse structures, as it is the case for conventional amphiphilic block copolymers. In contrast, the self-organization of the PEG- b -peptide diblock copolymers is described as an equilibrium between unimeric block copolymer molecules and dimeric and tetrameric coiled coil aggregates. The relative amounts of these species depend on concentration, temperature, solvent, and the molecular weight of the PEG block.