The control over artificial double-helical structures, crucial for creating advanced molecular systems, remains a complex challenge. A recent study has introduced innovative double-helical monometallofoldamers that can switch helicity and transfer chiral information when stimulated by external factors. These monometallofoldamers hold the potential to create new artificial supramolecular systems for tasks such as molecular information transmission, amplification, replication, and various technological applications.
Deoxyribonucleic acid (DNA), a molecular system that contains the genetic blueprint of living organisms, is capable of transcribing and amplifying information with its paired helical strands. Scientists are keenly interested in designing artificial molecular systems that can mimic or even surpass the functionality of DNA. Double-helical foldamers are one example of such advanced molecular systems.
Helical foldamers are a type of synthetic molecule that naturally form defined helical shapes, similar to the helices found in proteins and nucleic acids. They have gained significant interest for being responsive to stimuli, adjustable chiral materials, and for their capacity to form cooperative supramolecular systems, thanks to their unique ability to switch chirality and conformations. Double-helical foldamers demonstrate enhanced chiral traits and possess extraordinary abilities, such as transferring chiral information from one chiral strand to a non-chiral strand, which opens up possibilities for higher-order structural control relevant to replication, akin to nucleic acids. Nevertheless, efficiently managing the chiral switching in these synthetic structures remains a challenge, as achieving the necessary balance between dynamic switching and stability proves difficult. Despite various helical molecules being developed, instances of changing the twisting direction in double-helix molecules and supramolecules are rare.
In a significant advancement, a group of researchers from Tokyo University of Science, Japan, under the leadership of Professor Hidetoshi Kawai from the Department of Chemistry in the Faculty of Science, alongside Mr. Kotaro Matsumura, have created a new mechanical motif called double-helical monometallofoldamers that allow for controllable chiral switching. Professor Kawai states, “Our research successfully synthesized a double helical mononuclear complex using a single metal cation at the center of the helices to balance stability and dynamic properties. These structures can switch helicity by altering the left and right winding of both helical strands in response to varying solvents.” Their findings were published in the Journal of the American Chemical Society on July 19, 2024.
The researchers created the double-helical monometallofoldamers using two bipyridine-type strands shaped like an L that formed double-helical structures upon interacting with a zinc cation. X-ray crystallography confirmed the existence of double-helical formations with a metal cation at their core. The team examined how these monometallofoldamers could switch in response to external stimuli and found that the terminals of the helical structures could unfold in solvent solutions, transforming into an open form favored in warmer temperatures, and refolding into a double-helical structure favored in cooler temperatures.
Notably, the helicity of the double-helical monometallofoldamer equipped with chiral chains can be manipulated by using achiral solvents. For instance, in non-polar solvents like toluene, hexane, and diethyl ether, it adopts a left-handed or M-form, whereas in Lewis basic solvents like acetone and DMSO, it converts to a right-handed or P-form. The arrangement of chiral chains within the helix strands was crucial for this M/P switching phenomenon. Moreover, the researchers found that pairing a chiral strand with one that lacks chiral chains allowed the winding direction of the chiral strand to be conveyed and amplified by the non-chiral strand, preserving the ability to invert helicity.
Highlighting the importance of this new molecular structure, Mr. Matsumura notes, “The double-helical monometallofoldamers we developed have the potential for use in innovative switching chiral materials that can display a wide range of chiral properties with minimal input, which can lead to the creation of chiral sensors. Furthermore, we believe this groundbreaking molecular design will facilitate the creation of organized supramolecular systems, similar to those found in nature, through the transmission and amplification of their superior chiral attributes.”
In conclusion, this study represents a major advancement in the pursuit of creating artificial controllable double-helical structures, setting the stage for new high-order molecular systems and enhancing molecular information processing.
