Natural polypeptides with a specific sequence of amino acid constituents adopt structural motifs such as α-helices, β-sheets, and random coils through non-covalent interactions providing them with particular biological functions. The occurrence of such features in synthetic polymers is rarely found.
N-carboxyanhydride ring-opening polymerization (NCA ROP) is a polymerization technique that permits the highly controlled generation of homopolypeptides consisting of repeating units of a single amino acid. Homopolypeptides can be created to a targeted molecular weight, with high levels of control and without unfavourable side reactions, by using contemporary polymerization method. Combining two or more of these homopolypeptide blocks allows a polymer chemist to produce block copolypeptides with specific chemical functionalities and properties, and the ability to self-assemble into a plethora of interesting architectures.
Noteworthy block copolypeptide macromolecular assemblies such as micelles, vesicles and hydrogels can all be formed, depending on the nature of each polypeptide block selected. Such structures have considerable individual features and all have found application in medicine due to their biocompatibility, biodegrability and the ease at which stimuli-sensing elements can be incorporated into their composition. Indeed, block copolypeptides produced by NCA ROP have been used in a vast array of applications including targeted therapeutic delivery, mimics of natural proteoglycans, and the polypeptidic modification of inorganic surfaces.
A recent review article by Paul. D. Thornton and co-workers gives an excellent overview of these exciting materials. It highlights advances in the synthetic methodologies employed to create homopolypeptides and block copolypeptides via NCA ROP, before discussing the numerous interesting structures and applications that block copolypeptides have found within current (bio)chemical research.
Other interesting contributions to the field of polymer conjugates can be found in an ongoing series guest edited by Harm-Anton Klok.