Switchable Coacervate Formation via Amino Acid Functionalization of Poly(dehydroalanine)

Our group recently developed a family of side-chain amino acid-functionalized poly(S-alkyl-l-homocysteines), Xaa-C (Xaa = generic amino acid), which possess the ability to form environmentally responsive coacervates in water. In an effort to further study how the molecular structure affects polypeptide coacervate formation, we prepared side-chain amino acid-functionalized poly(S-alkyl-rac-cysteines), Xaa--C, via post-polymerization modification of poly(dehydroalanine), A. The use of the A platform allowed straightforward synthesis of a diverse range of side-chain amino acid-functionalized polypeptides via direct reaction of unprotected l-amino acid 2-mercaptoethylamides with A. Despite their differences in the main-chain structure, we found that Xaa--C can form coacervates with properties similar to those seen with Xaa-C. These results suggest that the incorporation of side-chain amino acids onto polypeptides may be a way to generally favor coacervation. The incorporation of l-methionine in Met--C allowed the preparation of coacervates with improved stability against high ionic strength media. Further, the presence of additional thioether groups in Met--C resulted in an increased solubility change upon oxidation allowing facile reversible redox switching of coacervate formation in aqueous media.