Direct end-group modification of poly(Aib)-polymers: heterogeneous peptide coupling and chiral folding

Abstract

Helical poly(α-aminoisobutyric acid) is a foldamer capable of transmitting chiral information along achiral polymer-backbones. Yet its post-polymerization modifications after ring opening polymerization (ROP) remain challenging due to its poor solubility and limited reactivity. We here report a robust strategy for end-group functionalization of poly(Aib), obtained after ROP under heterogeneous conditions, enabling efficient coupling of a wide variety of end groups using stereochemically distinct initiators, such as point chiral amines, axially chiral binaphthols, and overcrowded alkene-based Feringa's photoswitches. The resulting polymers were post-functionalized via peptide-type coupling under varying conditions, employing different carboxylic acids and coupling agents in various solvents to introduce chemically distinct termini. MALDI-TOF mass spectrometry was used to assess purity and to monitor characteristic mass shifts associated with the respective end-group incorporation, thereby proving successful post-polymerization modification. Circular dichroism spectroscopy further confirmed transfer of chiral information from the initiators and the preservation of the helical secondary structure after functionalization. Among the tested polymers, the lipoic-acid-endgroups exhibited the highest coupling efficiency able to adsorb onto gold surfaces via disulfide–gold affinity, forming thin polymer films as evidenced by AFM and XPS analyses. The work establishes a versatile, heterogeneous post-functionalization strategy for tailoring helical poly(Aib) architectures with defined chiralities and surface-binding functionality, enabling the design of both static and dynamic chiral interfaces for next-generation molecular devices.