Synthesis and multimodal responsiveness of poly(α-amino acid)s bearing OEGylated azobenzene side-chains

Abstract

Stimuli-responsive poly(α-amino acids) (PαAAs) are protein mimics that can alter their conformational or other physicochemical properties in response to external triggers. We report here the synthesis and characterization of novel photo and thermal responsive PαAAs by the ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs). Specifically, a series of NCA monomers bearing azobenzene (Azo) and oligoethylene glycol (OEG) of different lengths (OEG_m-AzoNCA, m = 2, 4, 6) are synthesized in a modular route and polymerized in a controlled manner using hexamethyldisilazane (HMDS) as the initiator. The afforded P(OEG_m-Azo)_ns show interesting aggregation behaviors in both organic and aqueous solutions. Moreover, P(OEG_m-Azo)_ns exhibit a reversible photo-responsiveness accompanied by the conformational switch of the peptidic backbone, and an irreversible thermal-responsiveness. This new biodegradable and stimuli-responsive system holds considerable promise for applications such as on-demand delivery, liquid crystalline, and hierarchical self-assembly.