Stereochemistry represents an attractive design parameter to enable the preparation of nanostructures with similar compositions, and yet highly tunable sizes, shapes, fluidity, degradation profiles, among other properties. Complexation of complementary stereoregular polymers, or stereocomplexation, has led to marked enhancements in thermal and mechanical properties relative to the individual components. While stereocomplexation has been studied extensively with hydrophobic polymers, such as poly(lactic acid) (PLA) and poly(methyl methacrylate) (PMMA), functional amphiphilic polymer systems in which the stereochemistry can be controlled in both the hydrophobic and hydrophilic blocks remain relatively unexplored. Anticipating that such interactions may impart interesting and advantageous properties to amphiphilic block copolymer assemblies, this work explores the impact of stereocomplexation on nanostructures formed from amphiphilic block polypeptides. Sequential ring-opening polymerization of benzyl- and propargyl-substituted glutamate N-carboxyanhydrides produced well-defined functional block polypeptides, wherein the monomer stereochemistry determined the secondary structure (e.g., d- and l-type α-helices) of the individual blocks. Modification of the alkyne groups with hydrophilic thiols using photo-initiated thiol-yne click chemistry yielded an array of amphiphilic polypeptides. Solid- and solution-state atomic force microscopy revealed distinct differences in the dispersion and morphology of polypeptide nanostructures formed from d- vs. l-type helical hydrophilic blocks connected to l-type helical hydrophobic blocks, attesting to the substantial impact of stereochemistry on assembly. Intertwining stereocomplexation interactions and amphiphilic block copolymer assembly is envisioned to have implications well beyond these fundamental studies to influence a wide range of nanostructure properties, including cargo release, secondary structure, and morphology, opening new opportunities for block copolymer nanostructures to enable a broad range of advanced applications.

Stereochemistry-directed assembly of amphiphilic block polypeptides

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.