Propeller Induced Complete Transformation of the Secondary Structure of a Dipeptide on Water Surface Controlled by Chiral Supramolecular Assembly

Water surface provides a unique platform for the directed formation of self-assembly and transformation of secondary structures of peptides and proteins. Here we report a well-defined supramolecular assembly controlled complete one-step transformation of the secondary structure from β-sheet to α-helix of an amyloid-derived dipeptide system on the water surface. Spherical aggregates and molecular wires containing β-sheet structure are converted into two-dimensional (2D) molecular sheets comprising large planar area yet with a molecular level thickness with α-helix structure. The conformational features of the β-sheet to α-helix structure transformation are dominated by the abundant intermolecular hydrogen bonding, π–π stacking and C–H ··· π interactions. Strikingly, the dynamic change in the dihedral angle between the aromatic rings of dipeptide at the water surface alters the molecular packing and shortens intermolecular hydrogen bonds with larger binding energies required for the secondary structure transformation. The novel one-step strategy reported herein offers an exciting example of the supramolecular assembly controlled secondary structural transformation of the dipeptide on water surface.