Hierarchical Self-Assembly of a Biomimetic Diblock Copolypeptoid into Homochiral Superhelices

The aqueous self-assembly of a sequence-specific bioinspired peptoid diblock copolymer into monodisperse superhelices is demonstrated to be the result of a hierarchical process, strongly dependent on the charging level of the molecule. The partially charged amphiphilic diblock copolypeptoid 30-mer, [N-(2-phenethyl)glycine](15)-[N-(2-carboxyethyl)glycine](15), forms superhelices in high yields, with diameters of 624 +/- 69 nm and lengths ranging from 2 to 20 mu m. Chemical analogs coupled with X-ray scattering and crystallography of a model compound have been used to develop a hierarchical model of self-assembly. Lamellar stacks roll up to form a supramolecular double helical structure with the internal ordering of the stacks being mediated by crystalline aromatic side chain-side chain interactions within the hydrophobic block. The role of electrostatic and hydrogen bonding interactions in the hydrophilic block is also investigated and found to be important in the self-assembly process.