Nobel Prize in Chemistry Awarded to Scientists for Tool That Builds Better Catalysts

 

"In 1835, the Swedish chemist Jacob Berzelius described a phenomenon in which certain substances could galvanize a chemical reaction. These substances were named catalysts, and the process was called catalysis. Since then, scientists have discovered many catalysts that can build up and break down molecules, enabling inventions such as plastics, perfumes and pharmaceuticals.

Before 2000, scientists assumed all catalysts were either a metal or an enzyme. Metal catalysts, which can temporarily accommodate electrons or offer them to other molecules during chemical processes, can be toxic and environmentally taxing. Precious metals used as catalysts, such as platinum, must be mined.

Enzymes, which are proteins found in nature, are the catalysts that form complicated and vital molecules, like cholesterol and chlorophyll. Because enzymes are so efficient, researchers in the 1990s tried to develop enzyme variants as catalysts to drive the chemical reactions needed by industry and in manufacturing. But “enzymes are cumbersome,” Dr. Cheng said, and the process led to vast amounts of waste.

In 2000, Dr. List and Dr. MacMillan — working independently of each other — developed a new type of catalysis that used organic molecules called asymmetric organocatalysis.

Organic molecules, such as carbohydrates, are called that because they build all living things. The researchers discovered “cheaper, smaller and safer” catalysts that used organic molecules had the same rich chemistry as metal compounds, according to Tehshik Yoon, a chemist at the University of Wisconsin-Madison. Their technique was also simpler and more environmentally friendly.

Dr. List was working on enzymes at the Scripps Research Institute in San Diego, in a research group run by Carlos F. Barbas III. He knew of research from the 1970s that used a simple amino acid called proline as a catalyst. The studies had garnered little attention at the time.

He tested whether proline could catalyze an aldol reaction, in which carbon atoms from two different molecules bond together. The reaction worked, proving that proline was an excellent catalyst and that an amino acid can drive what is known as asymmetric catalysis.

Many organic molecules exist in two, mirrored variants like human hands — what is known as chirality. For example, one version of the molecule limonene — the right-handed one — smells like lemon, and its mirror image, which is left-handed, smells like orange.

“Organic molecules that play a role in life have this important feature of being handed — a right-handed and left-handed version that can have very different chemistry and very different biological consequences,” said Dr. Francis Collins, the director of the National Institutes of Health, which has funded both Dr. List and Dr. MacMillan’s work, the latter continuously since 2000.

Chemists and pharmaceutical researchers often only want one version of a molecule, and typical catalysis produced both versions. Having both can lead to disastrous effects; in the 1950s and 1960s, one mirror image of the molecule thalidomide caused severe birth defects in thousands of babies.

But asymmetric catalysis can produce just one of these asymmetric molecules, the left or the right, a boon for safety and for reducing chemical waste.

Two years earlier, Dr. MacMillan had left a position at Harvard University where he was researching asymmetric catalysis in metals. He noticed these metal catalysts were rarely used in the real world, as they were expensive and difficult to maintain. Some metal catalysts need to be in an environment free of oxygen and moisture, which is hard to achieve at a larger scale.

So Dr. MacMillan, now working for the University of California, Berkeley, developed a more durable catalyst from organic molecules that, like metals, could temporarily accommodate or provide electrons. He tested the organic molecule’s ability to drive a Diels-Alder reaction, which can build rings of carbon atoms.

Like Dr. List’s experiment, Dr. MacMillan’s reaction worked perfectly. He said he remembers jumping up and down and telling himself, “I think I’m going to get tenure.”

His results showed that some of these organic molecules were excellent at asymmetric catalysis, producing more than 90 percent of the desired mirror image.

In 2000, Dr. List and Dr. MacMillan each published their papers. Dr. MacMillan’s coined the term for this new catalysis — organocatalysis — so that other researchers might seek out new organic catalysts.

“It was a watershed moment,” Dr. Yoon said. “This idea was so obvious and so elegant that it was very easy for other people to apply that central concept to other kinds of reactions.”

Since Dr. List’s and Dr. MacMillan’s concurrent discoveries, the two scientists and other researchers have designed a plethora of molecules used in drugs, agrochemicals and efficient, durable materials. Their research has also sped up the production of existing pharmaceuticals, such as the antidepressant paroxetine and the antiviral oseltamivir, which treats respiratory infections, the Committee wrote."

This method of catalysis could be applied in modeling the conditions during the formation of first living organisms:

"Macmillan used small organic molecules and replaced the metal atom in the catalyst with ions of organic origin with a bond between the nitrogen atom and the carbon atom. It is important in their numerous works to determine the reaction mechanism, which allows the design of the catalyst itself. Benjamin List and David Macmillan in their work focused on on organocatalysts - that is, catalysts that are small (compared to natural enzymes) organic molecules. Organocatalysts can be considered as some synthetic analogs of natural catalysts-enzymes that catalyze chemical processes in living nature.

List and Macmillan in their works, in fact, tried to model the biochemical processes occurring in nature at a lower chemical level. Still, enzymes are complex objects, and most organocatalysts have a low molecular weight, they are rather small (and inexpensive) objects specially synthesized for the catalysis of a single process needed by a researcher. The approach taken by them is called biomimetic (biomodelling).

Benjamin Liszt's work was largely based on natural compounds. Even the simplest natural building blocks - amino acids - can act as a catalyst and help make other organic molecules. For example, he took the natural alkaloid quinine, modified it to impart the required catalytic activity, and used it as a catalyst. This approach has resulted in very striking results in the field of synthetic organic chemistry. "