Supramolecular Architecture

Foldectures : 3D Molecular Architectures by the Self-Assembly of Foldamers

The goal of this research is to develop a methodology for creating unprecedented 3D organic nano- and microstructures by the self-assembly of foldamers. Knowledge from this fundamental study will find a variety of applications for biological and material science. The ultimate goal is to improve our ability to develop new biofunctional molecular systems that can induce specific biological responses by rational design. We discovered for the first time that a β-peptide heptamer with a specific folding propensity self-assembles in aqueous solution to form 3D molecular architectures with unprecedented shapes. This study has encouraged us to devise a new term, “foldectures” (a compound of “foldamer” and “architectures”), to describe any 3D molecular architectures that are derived from the self-association of foldamers in solution. The ability to relate the secondary structures of foldamers to their 3D shapes will clarify the interactions that underlie molecular recognition and self-assembly, and help rationalize the macroscopic properties of organic materials in terms of their microscopic molecular structures. The concept of “folding into architectures or shapes” can be expanded to the study of the fundamental links between constituents and shapes on multiple scales by using systematic experimental and theoretical methods.

Biomolecular self-assembly is a powerful tool for constructing nano-/microscale complex functional systems. In particular, peptides or small protein fragments have been frequently used as building blocks for various applications. However, in contrast to the morphologies found in inorganic nanostructures, the morphologies of the peptide-based self-assembled nano- and microstructures are limited to round shapes such as spheres, tubes and rods. Recently we have reported the first example of highly homogeneous, well-defined, and finite molecular architectures by the self-assembly of a helical β-peptide in aqueous solution. Owing to its rigid and unique conformational features in solution, the short-length β-peptide made it possible to generate unprecedented 3D morphologies that have not been obtained from any other molecular building block. The results will provide a new route for the creation of diverse (chiral) functional molecular complexes as well as give an insight into the underlying mechanism of self-association of natural counterparts.

We have identified phenomena that have not been previously predicted. We showed that a helical β-peptide foldamer, an artificial protein fragment, with well-defined hydrophobic surfaces self-assembles to form an unprecedented 3D molecular architecture with a molar tooth shape in a controlled manner in aqueous solution. We found that four individual left-handed helical monomers constitute a right-handed superhelix in an asymmetric unit of the assembly, similar to that found in the supercoiled structure of collagen. This work demonstrates how one can use nondirectional noncovalent interactions by design. We anticipate that our strategy can be a starting point for the rational design of 3D organic molecular architectures with various functions. Furthermore, the self-assembly behavior of artificial protein fragments will be relevant for the development of synthetic foldamer proteins. 

Biomimetic Approach to Structure Control of 3D Organic/Inorganic Hybrids

The purpose of the proposed research is to realize the synthesis of 3D organic/inorganic silica hybrids, the structure of which is tightly controlled in the nanometer scale, by the molecular-scaled design and synthesis of the self-assembled structures of β-peptides that act as a catalytic template for biomimetic silicification. Biosilicification found in diatoms is to be chemically mimicked based on the self-assembly of β-peptides, leading to the formation of 3D organic/inorganic silica hybrid structures for the development of next-generation materials. The relationship between organic catalytic templates and the structure/property of resulting organic/inorganic silica hybrids will suggest a methodology for investigating the information transfer from organic to inorganic species in the formation of organic/inorganic hybrids in a systematic manner.(Collaboration with Prof. Insung S. Choi, KAIST)