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Knots that can solve the problems of the future

Man with a beard.
Fredrik Schaufelberger. Photo: Åsa Karsberg, KTH
Published Apr 21, 2022

A new type of molecular knot that forms weaves recently led to a publication in the scientific journal Science.
”It was a satisfying aesthetic form. This type of knot exists everywhere in celtic mythology and it is very beautiful. But the reason that we wanted to build this form on a molecular level had nothing to do with aesthetics, we wanted to demonstrate the power of a new and powerful synthetic method that can lead to very advanced future materials” says KTH researcher Fredrik Schaufelberger at the department of organic chemistry.

Fredrik Schaufelberger became assistant professor in organic chemistry in September last year and has just welcomed several new coworkers to his newly started research group.

“I am new at work, and it has progressed rapidly, but we are still a very junior group. Recently, it has all been about starting up the lab and seeking funding. I have been incredibly lucky to have found extremely talented people that want to work with me, it makes the job super fun and exciting every day.”

The group does research in supramolecular chemistry, in particular a class of compounds called molecular machines. These are molecules whose movements can be controlled by applying external stimuli, and which can perform work if energy is added. Jean-Pierre Sauvage, Sir J. Frasier Stoddart and Bernard L. Feringa, who designed and synthesized the first molecules within this class, were awarded the Nobel prize in 2016 for their discoveries.

“Molecular machines is a rather new field with a lot of potential. It has not reached a commercial stage yet, and a lot of what is done is on basic research level.”

Behave like machines

A lot of molecular machines are based on so called mechanical bonds. They are separate molecules that have been connected mechanically, like links in a chain. By mechanically connecting molecules in different constellations, it is thereby possible to make them act as one single molecule, with the difference that you can easily control the movements around the mechanical bond.

For example, the resulting molecular machines can work as motors or transporters that move around other molecules.

“They behave as machines, move in predictable ways and can perform functions. So far, they are simple systems, molecules spinning in a specific direction or the like. But just like a waterwheel can drive a whole windmill, mechanical movement is extremely powerful on a molecular scale if it is connected to other processes.” says Fredrik Schaufelberger.

In March, he published an article in the scientific journal Science, which was about work he did within the framework of his postdoc. It was about developing a specific kind of mechanical bonds, so called molecular knots. In the article, the team from the University of Manchester showed the most complex molecular knot so far, the size of a minor protein and with a pattern that has been used a lot in celtic culture.

“For a long time, molecular knots were pretty hard to make, so a lot of my postdoc was about pushing further within the field. We used to joke about being molecular scouts, since we worked with knots everyday on a molecular level. The knots can be used in catalysts, as sensors, or for doping chiral materials. Other groups have also started looking at them as drugs. People have started to find quite a few applications for this kind of obscure molecules.” he says.

Formed with mirror shapes

According to Fredrik Schaufelberger, knots are particularly interesting since they possess an inherent chirality. That is, they are either turned to the right or to the left, depending on how the knot has been tied.

”Molecular knots are formed with different mirror shapes since they can be tied left over right or the other way around. This means that they are ”topologically chiral”, which is an unexplored and very exciting source of chirality. Since nature in itself has a rotation, everything that we let interact with biological systems – such as drugs – will act differently depending on its mirror shape. So new forms of chirality are always very interesting in broad contexts. For instance, in another article, we utilized that we could tie mirror shapes to create interesting materials, where the appearance of the material on centimeter scale can be changed drastically by just tying a knot on nanometer scale.” he says.

Now, the researchers have used a new and powerful method to create molecular knots. They let molecular chains fold over metals so that they tangle up in eachother and form advanced knot patterns. The next step is to use the technology to create complex molecular weaves.

What could molecular weaves be good for?

“We do not know, since they have not been possible to make in a large extent before. If there is something that you cannot do, you do not know what is good about it. But, for example, compare it to weaves on a macro-level. Until now, researchers have mostly been able to study individual molecular chains, which can be likened to separate threads. If you can weave, then suddenly you can study whole fabrics, or the things that you can sew from the fabrics.

However, the basic research that has led forward to the discovery is time consuming and costly. Therefore, Fredrik Schaufelberger says, his newly started group will now engage in research on mechanical bonds on a slightly simpler and more hands-on level. Right now, they are working on a class of dumbbell-shaped molecules with mechanical bonds called rotaxanes.

“We would like to see the research within molecular machines move towards application. We want to bring the molecules closer to biomedicine, and use them to control biological functions. We have integrated our background in organic chemistry with biochemistry and biomaterials. In practice, it is on a fairly simple level, where we take well-established molecular machines and look at how they can be integrated with biological systems.” says Fredrik Schaufelberger.

Text: Sabina Fabrizi