Self‐Assembly of Hexagonal Peptide Microtubes and Their Optical Waveguiding

Abstract

Self-assembly of biological building blocks including proteins and peptides is attracting increasing attention due to the versatility for bottom-up fabrication, biocompatibility and biodegradability, and a wide range of applications in biology and in nanotechnology. [ 1 ] In the self-assembly process the precise control of supramolecular architectures is achieved through synergistic effects of some weak non-covalent interactions such as hydrogen bonds, electrostatic interaction, π – π stacking, hydrophobic forces, nonspecifi c van der Waals forces, and chiral dipole–dipole interactions. [ 2 ] These weak forces, in particular hydrogen bonds and hydrophobic interactions, are ubiquitous in biological systems. As a whole they govern the molecular selfassembly into superior and ordered structures. By learning from nature, one can purposefully devise and synthesize artifi cial building blocks amenable to self-assembly into superstructures, which are driven by the cooperative interactions of such weak forces. With respect to other biological building blocks, peptides have been of great interest as a strategy in material fabrication owing to their structural simplicity and tunability, functional versatility, cost effectiveness, and widespread applications. As one of the simplest peptide building blocks, diphenylalanine (L-PheL-Phe, FF), a core recognition motif of Alzheimer’s β -amyloid polypeptide, [ 3 ] has been proven to be an exciting candidate towards bottom-up fabrication. FF-based building blocks are able to self-assemble into a variety of nano structures including nanotubes, spheric vesicles, nanofi brils, nanowires, and ordered molecular chains. [ 1c ] These well-defi ned nanostructures can be regarded as an assembly of molecules into supramolecular systems, however, organization of these into crystalline materials with spatial dimensions remains a formidable challenge. We report here that the FF building block is capable of selfassembling into robust hexagonal crystalline microtubes as a result of confi ned organization of nanoscale tubular structures at long range during slow crystallization or aggregation. In biological systems, the oriented organization or alignment of substructures is a common protocol to achieve functions. For