Helical Toroids Self-Assembled from a Binary System of Polypeptide Homopolymer and its Block Copolymer

Abstract

Toroids and helices are fundamental geometrical structures in nature. Polymers can self-assemble into various nanostructures, including both toroids and helices; however, nanostructures combining toroidal and helical morphologies (that is, helical toroids) are rarely observed. A binary system is reported containing polypeptide homopolymer and its block copolymer, which can hierarchically self-assemble into uniform helical nanotoroids in solution. The formation of the helical toroids is a successive two-step process. First, the homopolymers aggregate into fibrils and convolve into toroids, thereby resembling the toroidal condensation of deoxyribonucleic acid (DNA) chains. Second, the block copolymers self-assemble on the homopolymer toroids and result in helical surface patterns. Additionally, the chirality of the surface helical patterns can be varied by the chirality of the polypeptide block copolymers.

Keywords: helices; hierarchical assembly; polypeptides; theoretical simulation; toroids.