Explainer: what are autocatalysis and non-linear effects and why have they won the 2026 Nobel prize in chemistry?

The 2026 Nobel prize in chemistry has been awarded to Henri Kagan from Paris-Saclay University in France and Kensō Soai from Tokyo University of Science in Japan for their work in the field of organic synthesis. Their discoveries provided key insights into an intriguing class of asymmetric catalytic reactions, and offer potential clues as to how homochirality first emerged in the essential molecules of life.

Kagan and Soai have been recognised specifically ‘for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis’. So what did Kagan and Soai actually do, and why has the Nobel committee deemed their research worthy of science’s most sought-after prize?

What are non-linear effects and asymmetric autocatalysis?

These terms are centred around the concept of molecular chirality, which describes two molecules that are mirror images of each other but that aren’t superimposable. Each molecule in a mirror-image pair, called enantiomers, can therefore be thought of as being either right- or left-handed, and are usually given the labels R and S (from rectus and sinistus). The enantiomers of a chiral pair can behave very differently – for example, enantiomers of drug molecules often have totally different biological effects. As such, understanding and controlling chirality is of critical importance to chemists.

In reactions that generate chiral products, we’d usually expect the two possible enantiomers to be produced in equal amounts. But often a chiral catalyst or auxiliary is used to steer the reaction towards one preferred enantiomer – these are asymmetric reactions because they produce more of one enantiomer than the other. The degree to which one enantiomer is produced in preference to the other is measured using a metric called enantiomeric excess.

Kagan’s discovery of non-linear effects here refers to his observation of asymmetric catalytic reactions that favour the formation of one particular chiral product over the other to an unexpected degree. Previously, scientists had assumed that the enantiomeric excess (the left–right balance of enantiomers) in the catalyst was directly proportional to the enantiomeric excess in the products. Kagan showed these reactions can actually make products with an enantiomeric excess that surpasses that of the catalyst.

Soai’s work looked at autocatalysis – reactions in which the product molecule then acts as a catalyst to make more of itself. Asymmetric autocatalysis, therefore, refers to reactions in which the final product molecule helps to bias the formation of one enantiomer over the other.

What did the laureates do?

In 1986, Kagan and his colleagues at Université Paris-Sud reported three experiments that demonstrated non-linear effects for the first time: two titanium-catalysed reactions – oxidation of methyl p-tolyl sulfide and a Sharpless epoxidation of geraniol – and a proline-catalysed Hajos–Parrish reaction.

Each of these reactions involved catalytic species that featured two chiral ligands. Kagan showed that when the ligand is available as a mixture of enantiomers, three different catalytic species could form: one that features two R ligands, one featuring two S ligands, or a ‘meso’ catalyst featuring a one R and one S ligand. In cases where the meso catalyst reacts more slowly than the others, the reactions generated products in a higher enantiomeric excess than that of the catalyst that had been added to the reaction.

Four years later, Soai and his team reported an autocatalytic reaction involving the addition to dialkylzinc reagents to pyridine-3-carbaldehyde. This produced a chiral pyridyl alkanol species that could catalyse its own formation. But the enantiomeric excess of the final products were lower than that of the initial catalyst.

In 1995, Soai’s team discovered a related reaction, but this time the products were generated with far higher enantiomeric excess than the initial catalyst. This meant that the catalyst was self-catalysing its own formation in an asymmetric manner, making it the first example of an asymmetric autocatalytic reaction carried out a chemical laboratory. The Nobel prize organisation describes the reaction as ‘one of the most spectacular chemical experiments ever conducted’.

What does this have to do with origins of life research?

In their 1995 report, Soai and his colleagues explained that their finding ‘provides a mechanism by which a small initial imbalance in chirality can become overwhelming’. The implications of this go far beyond being a simple lab curiosity.

One of the big questions in science is why important biomolecules like the amino acids in proteins and sugars in DNA, exist almost exclusively in one enantiomeric form (proteins are left-handed and DNA is right-handed). This phenomenon, known as homochirality, poses a big puzzle – how exactly did it emerge?

On the prebiotic planet Earth, it would seem to make sense that any chemical reactions generating chiral molecules, would produce equal quantities of the possible enantiomers. How, then, could one chiral molecule come to dominate over its mirror image?

In 1953 the physicist Charles Frank proposed a mathematical framework to explain this by theorising an asymmetric autocatalytic reaction and proving it could produce just one enantiomer from a mixture of enantiomers. Non-linear effects and asymmetric autocatalysis gave a means of realising such a system in the lab and therefore offer a plausible mechanism for how the first enantiomeric excesses could have begun to arise.

‘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,’ noted Heiner Linke, chair of the Nobel committee for chemistry.

Nobel committee member Peter Somfai writes in his notes on the award that the discovery of the Soai reaction ‘vitalised the search for the origin of biological homochirality’.

How has the field evolved since those first discoveries?

Since its discovery, other examples of the Soai reaction have provided even more striking demonstrations of its power for symmetry breaking. In 2003, Soai’s team reported a variant in which tiny imbalances of the catalyst enantiomers were amplified by a factor of 630,000 to provide a product in which 99.75% of the material existed as a single enantiomer. Other examples have shown Soai reactions in which asymmetric autocatalysis is induced using polarised light and even the chiral arrangement of crystals and surfaces.

Other researchers have also helped to expand chemists’ understanding of the mechanisms of non-linear effects and asymmetric autocatalysis. For example, Donna Blackmond from the Scripps Research Institute in California, US, has built on Kagan’s early work, revealing important mathematical relationships between reaction rates and non-linear effects. In 2006, her team also demonstrated an interesting reaction in which a non-linear effect is influenced by differences in solubility of the catalytic species.

In addition to Blackmond, researchers including Scott Denmark from the University of Illinois, us, and Oliver Trapp from the Ludwig-Maximilians University in Munich, Germany, have carried out detailed investigations to better understand exactly how the Soai reaction brings about its unusual effects.

According to the Nobel committee, Kagan and Soai’s work ‘reshaped our understanding’ of how chirality can be brought about and amplified in a closed system. Building on the concepts underpinning this year’s prize, the committee notes that the research community has been able to better understand asymmetric catalytic reactions, and even to search for new amplification mechanisms.