On October 7, 2026, the Royal Swedish Academy of Sciences awarded the Nobel Prize in Chemistry to Henri B. Kagan and Kenso Soai for their discovery of nonlinear effects and autocatalytic phenomena in asymmetric organic synthesis. What exactly does their research mean, and what is its significance? Let's start with the left and right hands.
Left hand? Right hand? The stakes are high
Stretch out your two hands. They look almost identical, both have five fingers. But they are just mirror images of each other, and everyone can see that they are "opposite."
In the molecular world, there are also molecules that are related like "left hand" and "right hand". Some molecules are composed of exactly the same atoms, and the atoms are connected in exactly the same order. Just because of the different arrangements in the three-dimensional space, two structures are formed that are mirror images of each other but cannot completely overlap. Chemists call this phenomenon chirality, and the two molecules that are mirror images of each other are called enantiomers.
There are many molecules in biology that are chiral and highly "left-right". For example, the amino acids that make up proteins almost all use the same chiral series, and the sugars in nucleic acids also have a highly uniform chirality. Proteins almost uniformly choose L-amino acids, while the sugars in nucleic acids uniformly choose D-sugar. Enzymes, receptors and proteins in the human body also have fine three-dimensional structures. When faced with two molecules that look like mirror images of each other, they may react completely differently and have different effects on the body.
Just like a glove tailor-made for the left hand, even if the material and size are exactly the same, it will definitely feel awkward when worn on the right hand. For many functional chiral molecules used as drugs, whether the "left or right" is done correctly is often directly related to the efficacy and even safety of the drug. This is particularly important in pharmaceuticals.
For example, levodopa (L-DOPA), an important drug in the treatment of Parkinson's disease, is a typical example. The DOPA molecule also has two forms that are mirror images of each other, but the human body does not treat them equally. L-DOPA can be recognized by the body's relevant transport and enzyme systems and converted into dopamine in the brain, thereby exerting a therapeutic effect; its enantiomer D-DOPA cannot produce the same therapeutic effect. As for naproxen (a common anti-inflammatory analgesic), one of its pair of enantiomers has anti-inflammatory effects, while the other may bring health risks to patients.
When synthesizing these chiral molecules, it is often difficult to control which enantiomer is synthesized. The content of the two enantiomers in conventional synthesis is often equal. The trouble doesn't stop there. Since the physical properties of the enantiomers are almost identical, they are difficult to separate directly using conventional, low-cost methods. Therefore, instead of making the "left hand" and the "right hand" together and then laboriously taking them apart, chemists hope to make only the one they need from the beginning of the reaction.
And this is the problem that asymmetric synthesis aims to solve.
Go left, go right? Chemists want to have the final say
We learned about catalysts in middle school chemistry. The most important task of an ordinary catalyst is to make a reaction occur more easily. But in asymmetric synthesis, chemists place higher requirements on the catalyst: not only to allow the reaction to occur, but also to push the reaction to one of the chiral products as much as possible.
Think of it like a fork in the road. Raw materials can go either left or right, but a good chiral catalyst is like opening a green channel on one of the roads, allowing more molecules to go in the same direction.
To describe how strong this bias is, chemists compare the ratios of two enantiomers. If the left and right sides are equally divided, it means that there is no preference at all; if it reaches 99:1, it means that the reaction has almost only chosen one side.
According to intuition, the more "biased" the catalyst is, the more biased the product will be. But French chemist Kagan discovered that the real molecular world is not so obedient. In the 1980s, while studying asymmetric catalysis, Kagan and his colleagues discovered that the degree of chirality of the catalyst was not always simply proportional to the degree of chirality of the final product.
If you draw the two into a picture, the simplest case should be a straight line: if the catalyst is more biased, the product will be more biased. But in experiments, this line may be significantly curved. Sometimes the catalyst only has a certain degree of chiral bias, but the product shows stronger chiral selection; there are also some systems where the opposite is true. This phenomenon is called a nonlinear effect.
Why is this happening? Because catalyst molecules don't always work alone. They may combine with each other to form different molecular combinations that differ in quantity, stability, and catalytic ability. Therefore, a small change in composition may cause greater consequences than expected.
Kagan's work made chemists realize that in chiral catalysis, the relationship between input and output is not necessarily a simple straight line. Small differences may be further amplified by interactions between molecules.
So, is it possible for this amplification to go further? Can a left-right difference that is almost negligible at first become bigger and bigger on its own during a chemical reaction?
Find another way and make my own?
The truly surprising answer comes from Japanese chemist Kenzo Kip.
In 1995, a very special type of asymmetric autocatalytic reaction was reported by the team of Xian Hexian. The so-called autocatalysis is actually not difficult to understand. In an ordinary catalytic reaction, raw materials A and B produce product C, which requires the help of another catalyst D; in an autocatalytic reaction, the generated product C itself can act as a catalyst to help the raw materials continue to generate more C.
What's even more amazing is that the reaction of Xia Hexiansan's discovery is to "recognize left and right". Suppose that at the beginning of the reaction, there are almost the same amount of the two chiral products, but there happens to be a little more "left" than "right". The extra left-handed products will help produce more left-handed products; the newly generated left-handed products continue to participate in catalysis, so the advantages of the left hand become more and more obvious.
Initial experiments by Xia Hexiansan's team have demonstrated that small chirality deviations can be significantly amplified through a continuous autocatalytic process. Subsequent studies have shown that in a specific system, even if the initial chirality difference is so small that it is almost imperceptible, after multiple rounds of asymmetric autocatalysis, a product that is highly biased towards one chirality can finally be obtained.
The reason why this excites chemists is that it shows a very special possibility: a system does not need to have a huge advantage from the beginning, it only needs to be a little eccentric, and with the appropriate feedback mechanism, this eccentricity may become larger and larger.
life's first question
The work of Kagan and Kia Hexiansan first changed the way chemists understand and control asymmetric reactions, but it also brought people back to an older question: Why is life so "eccentric"?
Life on Earth today is remarkably "homochiral." For example, the amino acids used by life to synthesize proteins almost all belong to the same chiral series. But before the emergence of life, why did the initial geochemical environment gradually skew to one side?
Scientists still don't have a final answer. The Kip Constitutional Three Reaction cannot prove that life billions of years ago produced homochirality along this path. But it used real chemical experiments to demonstrate something that was previously unimaginable: an extremely weak initial chirality difference may indeed be continuously amplified through autocatalysis and nonlinear processes, eventually causing the entire system to shift significantly to one side.
In this sense, Kagan and Kia Hexiansan are not just studying how to better synthesize a molecule. They allow us to see how, in the microscopic world of chemistry, small differences can eventually turn into clear and stable trends through interactions and feedback between molecules.
