Space and Physics
PUBLISHED
The 2026 Nobel Prize in Chemistry has been awarded to Henri Kagan and Kenso Soai for their work on chiral chemistry, a massively important field for pharmaceutical manufacturing that also touches on one of biology's biggest mysteries. The award is worth 12 million Swedish kronor (around $1.2 million at the time of publication). It will be shared equally between the two winners.
From our title, the Nobel announcement, and the mention of chiral chemistry, you might be confused about what we are on about. We talk about left- and right-handed molecules, but how can a molecule be “right-handed” or “left-handed”? They don't even have hands!
Worry not, we haven't been sniffing solvents left open in the lab; let us go on a journey into the world of chirality, something you will have certainly experienced already without realizing.
Take, for example, the molecule carvone (C10H14O). In nature, it comes in two versions made of exactly the same elements connected in almost the exact same way, but the arrangements look like mirror images of each other. How different can mirror images of the same molecule be, you might ask? Well you can actually go to your kitchen or a supermarket to find out.
One version, the right-handed or "laevo" form, is a crucial component of the spearmint smell and flavor; the other is the earthy-woody smell of caraway seeds. Or take limonene: one version is found in citrus fruit and in all lemon-scented products; its mirror image instead smells like pine and turpentine.
The word chiral” comes from the Greek word for “hand”, because our hands are mirror images. If you have two hands, you can try this now: put one on top of the other, and you will see there is no way you could possibly rotate or otherwise re-orient one hand so that it occupies the exact same space as the other – palms facing the same way, thumbs on the same side and everything.
One of the simplest ways for a molecule to be chiral is to be built around a carbon atom with each of its four bonds connected to something different, making it asymmetric. As it happens, all but one of the 20 fundamental amino acids used by our bodies to make proteins is chiral for this exact reason – each of them has one of these asymmetric carbons right in the middle.
Generally, in on-organic contexts, chemical reactions end up producing an equal proportion of right-handed and left-handed versions of any chiral molecule. This is because they are fundamentally very similar to one another, and most reaction mechanisms simply can't discriminate between the two.
Biology loves a lefty
Life, however, is different. For reasons that aren't entirely understood, living things have developed a chiral preference towards the left-handed versions of amino acids, a phenomenon called homochirality.
Since pretty much all the reactions that go on in our cells are catalyzed by enzymes, and enzymes are made of amino acids, this situation perpetuates itself and means that the inner workings of our cells are sensitive to the chiral form of many molecules we interact with – hence being able to tell the difference between spearmint and caraway, for example.
It's pretty straightforward, knowing this, to see how we might have a problem: if a chemical production method creates a drug with equal proportion of chiral molecules, but our body recognizes half of them as one thing and the other half as another, there is a risk we end up producing something that is half useful and half hazardous.
In other words, while you might think you have one molecule, you really get two different effects.
.png "chiral forms of the amino acid serine")
Consider novrad, which is a drug used in cough medicine, while its mirror image, darnov, is a painkiller. You might also notice that the name darnov is an anagram of novrad, 'cause chemists love to be punny. A more tragic example is thalidomide, whose left-handed enantiomer causes birth defects while the right-handed version works as a treatment for some cancers.
This year's Nobel Prize recognizes key developments in learning how to drive chemical reactions to produce just one of the two possible versions of a chiral molecule. By forcing reactions towards homochirality like this, we can be certain what version of a molecule is being produced.
Kagan, then at Paris-Sud University in France, took the first decisive step in 1986 when he discovered a new way of manipulating chemical reactions. This allowed him to create a greater excess of one of the mirror images than had previously been thought possible.
Almost a decade later in 1995, Soai, then at the Science University of Tokyo, designed the first reaction that had the potential to be truly homochiral. It would take him until 2003 before he achieved it in the laboratory. As the press release accompanying the announcement of the Nobel Prize puts it: "He presented a reaction in which only one of the two possible mirror images was formed. Other than life itself, no one had previously achieved this feat."
“Henri Kagan and Kenso Soai have provided a solution to a chemical mystery that is over a century old: how homochirality can emerge spontaneously. The chemical reactions they have developed are spectacular,” Heiner Linke, chair of the Nobel Committee for Chemistry, said in the release.
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