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EXPLAINED: How A Novel Way To Make Molecules Paved Way For Greener Chemistry And A Nobel Prize

Benjamin List (L) is the director of the Max Planck Institute for Coal Research in Germany while David MacMillan is a professor at Princeton University in US

Benjamin List (L) is the director of the Max Planck Institute for Coal Research in Germany while David MacMillan is a professor at Princeton University in US

Benjamin List and David MacMillan have been honoured with a Nobel for making chemistry greener through the development of a new method of creating molecules

‘Organocatalysis’, the term sounds complicated, but it encapsulates a simple idea — using organic material to drive the process through which chemists can devise new molecules. A technology that has wide uses, it has won German scientist Benjamin List and British-origin researcher David MacMillan this year’s Nobel prize for chemistry. Here’s all you need to know.

Why Is Their Discovery Important?

Chemists are all the time building new molecules, which are nothing but a group of atoms bonded together. Molecules represent the smallest unit of any chemical compound that can take part in a chemical reaction. So, when you think of polythene, or batteries, think of molecules that were artificially created in a laboratory. But, as the Nobel Foundation notes, chemists’ ability to create artificial molecules has been far more rudimentary than the ease and precision with which nature manages to build them. It was only very gradually that “chemistry has progressed from chiselling in stone to something more like fine craftsmanship".

But the work of this year’s chemistry Nobel winners, it has been said, “has taken molecular construction to an entirely new level", not only making chemistry greener, but also making it much easier to produce asymmetric molecules. It has been hailed as a great step forward for modern chemistry because asymmetric molecules help solve the problem, frequently encountered by chemists, of how the process to form a new molecule gives rise to two of them that are exact mirror replicas of each other. However, the similarity ends there because these mirror images can have properties that are not at all common to the both of them.

The Nobel Foundation says that List and MacMillan’s solution, termed asymmetric organocatalysis, “is as simple as it is brilliant", so much so that “many people have wondered why we didn’t think of it earlier".

What Have Catalysts Got To Do With It?

If you think back to your high school chemistry lessons, you will recall the process known as catalysis, which is defined as the acceleration of a chemical reaction by a catalyst. The catalyst, while driving the chemical process, does not undergo any change itself. After the phenomenon was identified in the early 19th century, a whole lot of catalysts have been discovered that can break down molecules or fuse them.

Catalysts are behind the multiplicity of different substances we use in our everyday lives, from medicines to plastics to food flavourings, to the extent that it is estimated “that 35 per cent of the world’s total GDP in some way involves chemical catalysis".

However, remarkably, till the year 2000, all the known catalysts only belonged to one of two groups: metals or enzymes.

Metal catalysts, though very efficient, come with the issue that they are very sensitive to oxygen and water and, hence, need an environment free of oxygen and moisture to work, which can prove tough to achieve in large-scale industries. Further, some metal catalysts can be harmful to the environment.

Enzymes in that respect are slicker. These are basically proteins produced by living organisms that act as a catalyst to drive specific biochemical reactions that are vital to life. As has been known, many of these enzymes are specialists in asymmetric catalysis, that is, they “always form one mirror image out of the two that are possible".

Given how efficient enzymes are in catalysing reactions, researchers had tried to artificially develop new enzymes that can be useful in various chemical reactions.

How Did They Arrive At Their Discovery?

Working separately in the 1990s in the US, List and MacMillan focused on asymmetric catalysis and how they could be driven by organic material. Pursuing his postdoctoral research, List got to ponder on amino acids, which are the building blocks of enzymes themselves. While a large chunk of enzymes contain metals, many of them catalyse chemical reactions without their help. So, List wondered whether amino acids always have to be part of an enzyme in order to catalyse a chemical reaction?

List was aware of research in the early 1970s based on the use of an amino acid called proline as a catalyst. However, what he couldn’t fathom was why nobody had continued to work on proline if it had proven to be an effective catalyst. On a hunch he used proline to catalyse a reaction in which carbon atoms from two different molecules are bonded together. To his surprise, it worked like a charm and List had thus shown that proline can be an excellent catalyst that can also drive asymmetric catalysis.

“Unlike the researchers who had previously tested proline as a catalyst, Benjamin List understood the enormous potential it could have. Compared to both metals and enzymes, proline is a dream tool for chemists," the Nobel Foundation said.

MacMillan was at the time moving from Harvard — where he had been doing research into the use of metals to drive asymmetric catalysis — to the University of California at Berkeley. He realised, however, that there were hardly any takers in industry for metal catalysts, perhaps because they were tough to use in large-scale operations. So, in California, he focused on simple organic molecules, which are the building blocks of life. He zeroed in on specific organic molecules to test their ability to drive chemical reactions, finding in the process that some of these molecules were also able to help in asymmetric catalysis.

As he got ready to publish his findings, he realised he had to come up with a name for this new method of catalysis. His chosen term: organocatalysis.

The Nobel Foundation says that the work of List and MacMillan sparked a “gold rush" of the discovery of new organocatalysts, an area in which the duo, both aged 53 years, remain the top names. The industry where organocatalysis has had a big inpact is pharmaceutical research, where there is a frequent need for asymmetric catalysis.

“Using organocatalysis, researchers can now make large volumes of different asymmetric molecules relatively simply. For example, they can artificially produce potentially curative substances that can otherwise only be isolated in small amounts from rare plants or deep-sea organisms," the Nobel Foundation said.

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first published:October 06, 2021, 19:13 IST