Hi, I am nano-poly[22]catenane, recently appeared in Nature, 2020, 583, 400-405. You must be wondering what "22" is. I know that you (readers) define your growth by your age. In my case, number of interlocked rings refers my growth. Therefore, I am a nanoscale molecular assembly containing twenty-two “interlocked” nanorings. My cousins (conventional catenanes), which are generally made of covalent molecular rings, are well known from past few decades¹. However, I am special because I am composed of large number of small molecules (~13200) held together by noncovalent bonds.

Although I am developed to ‘22’ recently, Prof. Yagai’s group (Chiba University, Japan) serendipitously discovered me much earlier as a baby i.e., nano-[2]catenane. I first appeared as nano-[2]catenane when the research group was investigating temperature-controlled self-assembly process of a barbituric acid based molecule². Driven by curiosity, the research group employed a more suitable preparation protocol (rapid solvent mixing) and condition (n-alkanes as solvent instead of cycloalkanes), which stimulated my growth to become nano-[5]catenane. Prof. Yagai was so excited that he called me “nanolympiadane” because of my structural similarity with the symbol of the Olympic Games. I am large enough to be visible by atomic force microscopy (AFM) that also distinguishes me from my cousin, “olympiadane” ([5]-catenane containing covalent molecular rings), prepared earlier by Stoddart and coworkers³. While playing with a model of my structure, Prof. Yagai pointed out that my five rings, fixed on the surface, do not adopt the helical orientation seen in the Olympic logo! But it doesn’t matter because my constituent rings can freely move in solution.

Coincidentally, the 2020 Summer Olympic was announced to be held in Tokyo, Japan. There was no end of happiness in the lab members after hearing the news. They thought it would be great to report my AFM image representing the Olympic symbol from the host country in the same year because it will arouse interest in not only scientific community but also general people. Prof. Yagai and his group members even planned to enjoy the Tokyo Olympic games wearing a special T-shirt printed with my AFM image. Since the event has been rescheduled to next year, they are waiting for the celebration.

But this is not the end of my story. The endeavors of the research group with the aid of collaborators in UK and Italy further continued towards a marked evolution of my topology. While searching for the mechanism of interlocking of nanorings responsible for my growth, the research group found that adding the nanorings to a hot solution containing monomeric molecules could promote the formation of new assemblies on the surface of the nanorings, which is a process known as “secondary nucleation”. Accordingly, they redesigned the preparation protocol to meet a condition optimal for secondary nucleation which remarkably increased my length. Currently, I am nano-poly[22]catenane and my length is about 500 nm! Unlike you, I do not become old as I grow. Prof. Yagai believes that I have potential to grow further. He also wants to unveil the glamour of my properties in near future. Check me out here. "Self-assembled poly-catenanes from supramolecular toroidal building blocks", Nature, 2020, 583, 400-405. https://www.nature.com/articles/s41586-020-2445-z

References

1. Dietrich-Buchecker, C. O., Sauvage, J. P. & Kintzinger, J. P. Une nouvelle famille de molecules: les metallo-catenanes. Tetrahedr. Lett. 24, 5095–5098 (1983).
2. Yagai, S., Kitamoto, Y., Datta, S. & Adhikari, B. Supramolecular polymers capable of controlling their topology. Acc. Chem. Res. 52, 1325–1335 (2019).
3. Amabilino, D. B., Ashton, P. R., Reder, A. S., Spencer, N. & Stoddart, J. F. Olympiadane. Angew. Chem. Int. Ed. Engl. 33, 1286–1290 (1994).

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