Nature inspires self-assembling helical polymer

Helical structures are ubiquitous across biology, from the double-stranded helix of DNA to how heart muscle cells spiral in a band. Inspired by this twisty ladder, researchers from Hiroshima University’s Graduate School of Advanced Science and Engineering have developed an artificial polymer that organizes itself into a controlled helix.

They published their results on Oct. 24 in Angewandte Chemie.

“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 at Hiroshima University’s Graduate School of Advanced Science and Engineering.

“The helical supramolecular polymer presented here is a new type of helical polymer.”

Polymers are a broad class of materials characterized by the large molecules that comprise them. They can be found in nature as proteins and more, including DNA, and in a number of industrial roles, including as synthetic components of 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 the 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.

Typically, such helical structures are categorized as “one-handed,” meaning their twist turns in one direction only. 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.

“Helical polymers are potentially useful for various purposes; however, the synthesis of helical polymers with preferred handedness had 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 components that can join up with other components to form molecular complexes, including polymers. By strategically inducing joining of these units—dimerization—the researchers can pre-emptively determine the handedness 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 material separation and catalysis—or the acceleration of chemical reactions—and to create a new functional chemistry of helical supramolecular polymers.”