An Offset Patterned Cross-β Structure in Assemblies of C3 -Symmetric Peptide Amphiphiles.

Developing peptide-based materials with controlled morphology is a critical theme of soft matter research. Herein, we report the formation of a novel, patterned cross-β structure formed by self-assembled C3 -symmetric peptide amphiphiles based on diphenylalanine and benzene-1,3,5-tricarboxamide (BTA). The cross-β motif is an abundant structural element in amyloid fibrils and aggregates of fibril-forming peptides, including diphenylalanine. The incorporation of topological constraints on one edge of the diphenylalanine fragment limits the number of β-strands in β-sheets and leads to the creation of an unconventional offset-patterned cross-β structure consisting of short 3×2 parallel β-sheets stabilized by phenylalanine zippers. In the reported assembly, two patterned cross-β structures bind parallel arrays of BTA stacks in a superstructure within a single-molecule-thick nanoribbon. In addition to a threefold network of hydrogen bonds in the BTA stack, each molecule becomes simultaneously bound by hydrogen bonds from three β-sheets and four phenylalanine zippers. The diffuse layer of alkyl chains with terminal polar groups prevents the nanoribbons from merging and stabilizes cross-β-structure in water. Our results provide a simple approach to the incorporation of novel patterned cross-β motifs into supramolecular superstructures and shed light on the general mechanism of β-sheet formation in C3 -symmetric peptide amphiphiles.