The 2021 Nobel prize in chemistry has been awarded to Benjamin List and David MacMillan for developing an entirely new kind of catalyst for making chemical reactions take place, and allowing chemists to choose the “handedness” of their molecules.
“This new toolbox is used widely today, for instance in drug discovery. It’s already benefiting humankind greatly,” said Pernilla Wittung-Stafshede, a member of the Nobel committee, during the prize announcement.
Up until 2000, said Wittung-Stafshede, we only knew about two kinds of catalysts for making chemical reactions take place. One kind is enzymes, which are large molecules made of hundreds or thousands of amino acids strung together. The other kind is metal catalysts, such as the platinum in catalytic converters. Often the metal is embedded within a molecule.
List, now at the Max Planck Institute for Coal Research in Germany, wondered whether an entire enzyme was really needed to catalyse one reaction. He tried using a single amino acid called proline instead.
“When I did this experiment, I thought maybe it’s a stupid idea,” said List. “When I saw it worked, I did feel this could be something big.”
David MacMillan at Princeton University was working with a metal catalyst, in the form of a small molecule that contains a copper atom. The problem was that this molecule was unstable. So MacMillan tried using simple organic molecules – molecules that contain carbon – that don’t contain any metal atoms. He found one that worked.
The work of List and MacMillan showed for the first time that small organic molecules can act as catalysts. Crucially, these small organic catalysts can generate molecules with a specific “handedness“. Many molecules come in left or right-handed mirror images that can have different properties. For this reason, the field is known as asymmetric organocatalysis.
“You can use small organic molecules to do the same job as big enzymes and metal catalysts, in reactions that are precise, cheap, fast and environmentally friendly,” said Wittung-Stafshede. “Their discoveries initiated a totally new way of thinking about how to put together organic molecules.”
List says the potential of this new kind of catalyst is now starting to be realised. “Our early-days catalysts were maybe a million times less efficient,” he said. “The real revolution of our discoveries is only surfacing now with these extremely reactive organic catalysts that can do stuff you cannot do with enzymes or even with the most sophisticated metal complexes.”
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