In supramolecular chemistry, researchers have discovered a game-changing method for accelerating molecular recognition.
Catalysts are materials that speed up but do not consume chemical reactions. Catalysts are frequently complex molecules with finely tuned shapes that correspond to an intermediate structure known as a transition state between the reactant and product of the targeted reaction. This, however, necessitates the precise design and synthesis of the catalyst, which is a difficult and time-consuming process. Another method is to use simple particles, such as protons and electrons, as catalysts, relying on electrostatic interactions to allow reactants to overcome energy barriers more quickly than would otherwise be possible. Although the use of electrons as chemical reaction catalysts for the formation of covalent bonds is well established, catalysis of molecular recognition and assembly – interactions involving noncovalent bonds – is uncommon. The few examples of catalysts for these assembly reactions that are currently available rely on sophisticated catalyst design.
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 in a study published March 10, 2022 in the journal Nature. The researchers discovered that using a chemical reducing agent as an electron source speeds up the formation of a host–guest complex by 640-fold. The electrons lower the activation barrier for this process by decreasing the Coulombic repulsion between a positively charged ring compound and a dumbbell-shaped molecule. They both being positive repel each other.
Professor of physics and astronomy R. Dean Astumian said the results suggest the possibility of a flexible approach to speed up the assembly of a wide range of molecular components.
According to Astumian, the addition of electrons can also be accomplished electrochemically, where the ability to turn the electricity on and off allows the reaction to be halted where the ratio between assembled and non-assembled molecules can be precisely set anywhere between all reactants and an equilibrium amount of reactants and products.
The findings represent a significant advance in both supramolecular chemistry and catalytic science. This method is not limited to a single reducing agent, but can be used with a variety of different reducing agents. Furthermore, electrochemical reduction can completely eliminate the need for reducing agents.
This novel type of catalysis will encourage chemists and biologists to investigate strategies for fine-tuning noncovalent events, controlling assembly at different length scales, and even creating new forms of complex matter.
"The ability to fine tune the steady state levels of assembled and disassembled components enables a system to be set at its maximum sensitivity to an external change – temperature, pressure, proton concentration, and more – opening up the possibility of designing optimally responsive sensors.
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By Shreeya Poojary
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