Speaking of catalysts, I believe it is no stranger to it, it is a substance that can accelerate chemical reactions. At present, metal catalyst and enzyme are two commonly used catalysts. In recent years, chemists have developed a third kind of catalyst - organic catalyst after hard exploration. German scientist Benjamin Lister (left) and American scientist David Macmillan (right) are among the pioneers of this third type of catalyst, winning the 2021 Nobel Prize in Chemistry for advancing the field of asymmetric organic catalysis.
Deficiency of metal catalyst and enzyme
Many chemical reactions are not only difficult but slow. For example, it's hard to mix nitrogen and hydrogen and get them to automatically make ammonia. Industrial synthesis of ammonia requires a high temperature of 500℃ and a high pressure of 20 ~ 50 mpa. Of course, only high temperature, high pressure conditions are not enough, also need iron to do the catalyst. This is the first catalyst - metal catalyst, is the traditional chemical industry used more of a catalyst.
There are chemical reactions going on in living things all the time. These chemical reactions involve biopolymers and are more demanding, so they use a second kind of catalyst, enzymes. Enzymes are also biological macromolecules in nature, which may be proteins or RNA. For example, amylase is a protein in our digestive system that breaks down starches in foods such as rice and noodles and converts them into energy for the body.
Because of enzymes, chemical reactions in living things can take place efficiently under extremely mild conditions. With the deepening of the understanding of enzymes and related reactions, more and more enzymes are used as catalysts in organic chemical, pharmaceutical and other industries. However, in this process, people also encountered some difficulties. For example, there are problems with chiral molecules in the synthesis of some drugs.
Chiral molecules that act differently
Chiral molecules are generally asymmetric in structure, which often includes two molecules with the same composition but different structures. Like our hands, these two molecules can be distinguished by left and right. They can be identified by polarized light, some can rotate it to the left, and that's a left-handed chiral molecule; Some can rotate polarized light to the right, and those are dextral molecules.
Left-handed and right-handed molecules look like "twins", often appearing together and indistinguishable from each other. However, their roles are quite different. For example, while the left-handed molecules in thalidomide are lifesaving, its right-handed molecules are responsible for birth defects. The drug is now banned in countries around the world.
If there is a catalyst that can control the synthesis of chiral molecules in the process, only let the useful molecule appear, eliminate the useless or even harmful molecule, that "merit is boundless". Chemists have indeed found such a catalyst, and it is an asymmetric organic catalyst.
Green environmental protection, a lot of benefits
Chemists discovered organic catalysts as early as 1970. They are small organic molecules that, in addition to carbon and hydrogen, typically contain common elements like oxygen, nitrogen, sulfur and phosphorus and are relatively simple to make. Organic catalysts are cheap and easy to extract compared with expensive, fragile and polluting metal catalysts.
The application of organic catalysts has been questioned because of their much lower efficiency and narrower range of adaptation than metal catalysts and enzymes. It wasn't until 2000 that Lister and Macmillan discovered that organic catalysts had the ability to catalyze asymmetrically. In other words, it can make only the useful one of the "twin" chiral molecules present, resulting in "asymmetric synthesis". Since then, organic catalysts on the "elegant hall", and won the "third catalyst" reputation. At present, the most widely used organic catalysts are asymmetric synthesis, so these catalysts are also known as "asymmetric organic catalysts".
Lister began his research on organic catalysts by thinking about enzymes. We all know that some enzymes are proteins, and proteins are made from multiple amino acids. Lister thought that since enzymes catalyzed chemical reactions, amino acids, simpler than proteins, might do the same. Eventually, he found that proline, extracted from collagen, was a highly efficient catalyst that could drive asymmetric synthesis. At present, proline has become a famous asymmetric organic catalyst, widely used in drug production. In Lister's view, the field of asymmetric catalysis is still full of opportunities, and continuing to design and screen these catalysts is one of his future goals.
Macmillan worked on using metal catalysts to perform asymmetric catalytic reactions, but then found that the metal catalysts he had developed in the lab were difficult to use in industry. After various attempts, Macmillan found that simple amine organic molecules could act as catalysts for asymmetric synthesis. He chose the right solvent to convert amine molecules into imine ions with strong catalytic activity, and realized a variety of types of asymmetric catalysis. When Macmillan was ready to publish his results, he realized that the catalysis he had discovered did not yet have a name, and he coined the term "organic catalysis" for the first time in chemistry.
Although Lister and Macmillan are not the first discoverers of organic catalysts, they are the promoters of organic catalysts in asymmetric synthesis and important promoters in the field of asymmetric organic catalysis. Their research has had a huge impact on drug research and made the chemical industry greener and more environmentally friendly.
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