Some biological molecules with efficient non-covalent binding sites can use their binding properties to make well-defined assemblies of a single class of molecules, ie they assemble with each other. These molecules, often seen in nature, are called “self-complementary assemblies.” For example, the p24 protein hexamer, which is part of the capsid of the HIV (human immunodeficiency virus), consists of six protein subunits that self-assemble complementary using many hydrogen bonds.
This phenomenon allows well-designed molecules to form higher-order assemblies without the metal ions commonly used as “links” between monomer molecules. Indeed, many self-complementary assemblies based on intrinsic hydrogen bonds, π interactions and coordination bonds have been reported.
However, self-complementary assembly based on host-guest systems is rare and notoriously difficult to control. To advance our understanding of self-complementary assembly with higher-ordered structures, many new strategies have emerged in recent years.
Now, a team of researchers from the School of Science at the Tokyo Institute of Technology (Tokyo Tech) may have just cracked the code to develop these innovative systems. The team, led by assistant professor Masahiro Yamashina and professor Shinji Toyota, has constructed a novel self-complementary macrocyclic assembly using an anthracene-based tweezer-like molecule with a pyridine dicarboxamide (PDA) linker as the monomeric species. Their work is described in nature communication.
“The molecule we’re using has an interesting property: it can bond with itself in two ways and form complementary structures to itself. It doesn’t just show head-tail–π interactions between the electron-rich tweezer tail (the anthracene groups) and the electron-deficient head.” , but also shows hydrogen bonding via the amide (-NH) functional group. By including these two interactions, a preferred direction of self-assembly is achieved, and this leads the formation of the macrocycle,” explains Prof. Yamashina.
This type of double interaction leads to much more control over the formation of synthetic macrocycles and in this case gives rise to a stable self-complementary hexameric structure upon crystallization. These hexamers can be further assembled into even larger self-complementary structures under the right conditions.
“When we added trifluoroacetic acid (TFA), we found that the cyclic hexamers further assemble into two predominant, stable supramolecular structures: rhombohedral lattice assemblies and giant spherical cuboctahedrons, a so-called hierarchical assemblage,” says Prof. Toyota. “The latter structure is particularly impressive because it is formed from 108 monomeric tweezers.”
Current methods of forming supramolecular assemblies require metals that can be harmful to the environment and ecosystems. The metal-free alternative method described here could produce novel supramolecular structures using a simple anthracene-based tweezer molecule. It opens the door to a new range of supramolecular assemblies with optical and electronic functions. This work adds another important tool to chemistry’s toolbox, one that is sure to play a major role in the metal-free supramolecular structures of the future.
Decoding the dynamics of protein assembly with artificial protein needles
Yuta Sawanaka et al, A self-complementary macrocycle through a dual interaction system, nature communication (2022). DOI: 10.1038/s41467-022-33357-y
Quote: Developing self-complementary macrocycles with ingenious molecules (2022, October 13) retrieved October 13, 2022 from https://phys.org/news/2022-10-self-complementary-macrocycles-ingenious-molecules.html
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