Helical structures are fundamental to biology, evident in the iconic double-stranded helix of DNA and the spiral arrangement of heart muscle cells.
Drawing inspiration from these remarkable designs, researchers at Hiroshima University‘s Graduate School of Advanced Science and Engineering have successfully created an artificial polymer that self-organizes into a precise helix. This innovation exemplifies how nature’s principles can be harnessed to advance materials science.
“Motivated by elegant biological helical structures, considerable effort has been devoted to developing artificial helical organizations with defined handedness for wide potential applications, including memory, sensing devices, chiral stationary phases, asymmetric catalysts, and spin filtering,” said corresponding author Takeharu Haino, professor in Hiroshima University’s Graduate School of Advanced Science and Engineering. “The helical supramolecular polymer presented here is a new type of helical polymer.”
Polymers represent a fascinating and expansive class of materials defined by their large molecular structures. Found abundantly in nature as proteins and DNA, they also play significant roles in various industries, particularly as integral components of synthetic plastics.
The molecules of a supramolecular polymer typically interact to form non-covalent bonds, which are highly directional and prompt specific behaviors depending on their arrangement.
The polymer that the Hiroshima University team developed is known as a pseudo-polycatenane, which contains mechanical bonds in addition to non-covalent bonds. Mechanical bonds can be broken via force without disrupting the chemical structure of the non-covalent bonds — an attractive property when developing materials that require precise control.
Generally, these helical structures are categorized as “one-handed,” meaning their twisting occurs in one specific direction. This unique property profoundly influences their interaction with other materials, as it is closely tied to the direction of their twist.
As such, the way they interact with other materials is dictated by the direction of their twist. If researchers can control whether that twist is left- or right-handed, so to speak, then researchers can control how the polymer behaves when applied in different scenarios.
Scientists at Hiroshima University developed brand-new helical supramolecular polymer chains from chirally twisted macrocyclic monomers. Credit: Takeharu Haino/Hiroshima University, CC BY-NC-ND 4.0
“Helical polymers are potentially useful for various purposes; however, the synthesis of helical polymers with preferred handedness has remained challenging,” Haino said. “Here, we present a novel synthetic method for helical polymers with preferred handedness via supramolecular polymerization controlled by complementary dimerization of the bisporphyrin cleft units.”
Bisporphyrin cleft units are molecular entities that can connect with other elements to create molecular complexes, such as polymers. By intentionally promoting the binding of these units — dimerization — researchers can proactively ascertain the chirality of the resulting polymer.
“The proposed novel strategy for controlling the handedness of supramolecular helical pseudo-polycatenane polymers paves the way for the study of supramolecular polymer materials with functions directed by controlled helicity and mechanical bonding,” Haino said. “Our goal is to apply these new helical supramolecular polymers to materials separation and catalysis — or the acceleration of chemical reactions — and to create a new functional chemistry of helical supramolecular polymers.”
Journal reference:
Naoka Fujii, Prof. Dr. Naoyuki Hisano, Prof. Dr. Takehiro Hirao, Prof. Dr. Shin-ichi Kihara, Kouta Tanabe, Masaya Yoshida, Prof. Dr. Shin-ichi Tate, Prof. Dr. Takeharu Haino. Controlled Helical Organization in Supramolecular Polymers of Pseudo-Macrocyclic Tetrakisporphyrins. Angewandte Chemie, 2024; DOI: 10.1002/anie.202416770