Research has discovered a breakthrough method for accelerating molecular recognition in supramolecular chemistry.

Catalysts are materials that increase the rate of, but are not consumed in, chemical reactions. Often catalysts are complex molecules with finely tuned shapes to match an intermediate structure known as the transition state between the reactant and the product of the targeted reaction. However, this requires precise design and synthesis of the catalyst, a difficult and time-consuming process. Another approach is to use single particles, protons and electrons, as catalysts, relying on electrostatic interactions to allow reactants to overcome energy barriers faster than otherwise possible. The use of electrons as catalysts of chemical reactions for the formation of covalent bonds is well established, but the catalysis of molecular recognition and assembly – interactions involving non-covalent bonds – is rare. The few existing examples of catalysts for these assembly reactions have relied on sophisticated catalyst design.

In a study published March 10, 2022 in the journal Nature, a team of scientists from six institutions around the world, including the University of Maine, described a simple and versatile strategy to facilitate molecular recognition using electrons as catalysts . The researchers found that the formation of a host-guest complex is accelerated 640 times by introducing a chemical reducing agent as an electron source. Electrons lower the activation barrier of this process by decreasing the Coulomb repulsion between a cyclic compound and a dumbbell-shaped molecule, both of which are positively charged and therefore repel each other.

“These results show the possibility of a very flexible approach to accelerating the assembly of a wide variety of molecular components,” says R. Dean Astumian, professor of physics and astronomy and co-author of the study.

Astumian explains that the addition of electrons can also be accomplished electrochemically, where the ability to turn electricity on and off allows the reaction to be stopped where the ratio between assembled and unassembled molecules can be tuned with precision anywhere between all reactants and a balance amount of reactants and products.

The research is a major breakthrough in both supramolecular chemistry and catalytic science. This approach is not limited to a specific reducing agent, and can instead be performed with a variety of different reducing agents. Additionally, electrochemical reduction can completely eliminate the need for reducing agents.

This new type of catalysis will inspire chemists and biologists to explore strategies that can be used to fine-tune non-covalent events, control assembly at different length scales, and even create new forms of complex matter.

“The ability to fine-tune the steady-state levels of assembled and disassembled components allows a system to be tuned to its maximum sensitivity to external change – temperature, pressure, proton concentration and more – opening up the possibility of designing reactive sensors of optimally,” says Astumien.

Contact: Sam Schipani, [email protected]