Controlling Amphiphilic Polymer Folding Beyond the Primary Structure with Protein-Mimetic Diphenylalanine

Abstract

While methods for polymer synthesis have proliferated, their functionality pales in comparison to natural biopolymers – strategies are limited for building the intricate network of noncovalent interactions necessary to elicit complex, protein-like functions. Using a bioinspired diphenylalanine acrylamide (FF) monomer, we explored the impact of various non-covalent interactions in generating ordered assembled structures. Amphiphilic copolymers were synthesized that exhibit β-sheet-like secondary structure upon collapsing into single-chain assemblies in aqueous environments. Systematic analysis of a series of amphiphilic copolymers illustrated that the collapse is primarily driven by hydrophobic forces. Hydrogen-bonding and aromatic interactions stabilize local structure, as β-sheet-like interactions were identified via circular dichroism and thioflavin T fluorescence. Similar analysis of phenylalanine (F) and alanine-phenylalanine acrylamide (AF) copolymers found that distancing the aromatic residue from the polymer backbone is sufficient to induce β-sheet-like secondary structure akin to the FF copolymers; however, the interactions between AF subunits are less stable than those formed by FF. Further, hydrogen-bond donating hydrophilic monomers disrupt internal structure formed by FF within collapsed assemblies. Collectively, these results illuminate design principles for the facile incorporation of multiple facets of protein-mimetic, higher-order structure within folded synthetic polymers.