Influence of “Beta-Blocking” Proline on the Internal Electronic Organization of Quaterthiophene π-Peptide Nanomaterials

Embedding π-conjugated units into peptide backbones enables control over π-π interactions and promotes energy transfer within fibrillar nanostructures resembling those formed from natural β-sheet-rich proteins. As a result, peptide sequences that naturally form or favor β-sheet architectures are commonly used in the construction of these systems. Most amino acid residues generally promote the formation of β-sheet structures; however, proline is usually viewed as a β-blocker that favors more helical structures. Consequently, our previous π-peptide studies excluded proline-containing sequences. In this study, we investigate how the incorporation of proline into π-peptides identified computationally for its ability to foster strong intermolecular electronic coupling affects the electronic and structural behavior of the resulting π -conjugated peptide nanostructures. Despite the expectation that proline would disrupt β-sheet organization, simulations and cryo-EM studies suggest that curved conformations of the π-peptide can still foster the formation of hydrogen-bonding and π-stacked assemblies. Using UV-vis, PL, and CD spectroscopies, we explore how proline's structure and stereochemistry (D/L form) influence the photophysical properties and supramolecular chirality of these assemblies.