Double helical covalent polymers—which are spiraling collections of nature’s building blocks are fundamental to life itself, and yet, despite decades of research, scientists have never been able to synthesize them in their entirety like their non-helical brethren until now.
Scientists, led by a team at the University of Colorado Boulder, have cracked the code, creating synthetic versions of these large DNA-like molecules for the first time. Using dynamic covalent chemistry, which is a chemistry tool pioneered by these researchers that focuses on reversible bonding interactions with self-correction capabilities, they were able to not only construct a helical covalent polymer hat rivals the sophistication of those found in nature but confirm its existence with absolute certainty using single crystal X-ray diffraction (a powerful, non-destructive way to characterize single crystals using light).
Previously, scientists have only been able to solve individual parts of the puzzle. This new discovery out last week in Nature Chemistry, though, completes it, potentially opening this critical and understudied field to new research that could have implications on everything from artificial enzyme creation, which has already found success in various medical applications, to the creation of biomimetic materials (materials that mimic processes found in nature).
Synthetic polymers come in many forms depending on their construction—whether they are linear or helical, the number of strands, and the length of the strands. Of those, helical polymers have been the most challenging for scientists to synthetically replicate, with the double stranded being the most difficult of all, thus far limited to only short helical oligomers (a polymer with very few repeating units).
Fig: Optical images of the large single crystals of 1. 1 grew in elongated square bipyramid shapes. Inset: dark-field optical microscope image with high contrast at the edges.
Zhang and colleagues were able to use a chemical tool they’ve pioneered, dynamic covalent chemistry, to construct a DNA-like covalent helical polymer. When they did that, the large molecule wasn’t the only thing they discovered.
They also found single crystals. Using single-crystal synchrotron X-ray diffraction, the researchers were able to confirm, without a doubt, that they had created what had previously been impossible.
This discovery, though, is only the beginning both for them and this critical field of study. After they dive a little deeper into the structure itself, the researchers plan to play with and explore the structure itself, seeing if they can make the crystals themselves bigger (right now they are fairly small), and if they can control the chirality, or spiral nature, of the polymer, which could have broad implications for catalysis (chemical reaction process utilizing catalysts), signal transduction (how signals are sent throughout the cell) and sensing applications.
Yiming Hu et al. Single crystals of mechanically entwined helical covalent polymers,Nature Chemistry (2021). DOI: 10.1038/s41557-021-00686-2