Kenso Soai Explains Nobel Chemistry Breakthrough and Plans New Research on Molecular Imbalances

From a tiny imbalance to a Nobel Prize

Japanese chemist Kenso Soai, whose experiments turned a nearly equal mixture of molecular mirror images into a product dominated by one form, told an audience in Tokyo on October 20, 2026, that he wants to investigate what starts those imbalances. About 2,000 people, including online participants, attended the lecture hosted by the Chemical Society of Japan.

The appearance followed the Royal Swedish Academy of Sciences' October 7 announcement that Soai and French chemist Henri B. Kagan would share the 2026 Nobel Prize in Chemistry. Their discoveries explain how chemical reactions can magnify a small preference for one molecular form, helping chemists understand a defining feature of living things and design reactions used in pharmaceutical research.

The Academy's chemistry prize announcement credits the pair with the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis. In everyday language, they found ways to make reactions produce more of one molecular mirror image than the other, sometimes with the product helping to make more of itself.

Soai, 76, is professor emeritus at Tokyo University of Science. Kagan is professor emeritus at Université Paris-Sud in France. They will divide the 12 million Swedish kronor prize equally, receiving 6 million kronor each.

At the Tokyo lecture, Soai described his next research interests during a question and answer session:

I hope to study a wide range of possible causes for the left-right imbalances.

His remarks extend the story beyond the October 7 prize announcement: the experiments explain how a tiny difference can grow, while the possible causes of that first difference remain a subject he wants to explore.

Why molecules can have a left and a right

Some molecules contain the same atoms connected in the same order yet have two arrangements that are mirror images. Like left and right hands, they cannot be placed on top of each other so that every part matches. Chemists call this property chirality and the two molecular forms enantiomers.

Living things distinguish between those forms because their own molecular machinery has a particular shape. A molecule that fits one biological structure may interact differently when its arrangement is reversed. The difference can affect a medicine's activity or even a substance's smell: the two forms of carvone smell of spearmint and caraway.

Proteins in living cells use almost exclusively one handedness of amino acids, while the sugars in DNA and RNA also have a consistent handedness. Glycine, the simplest amino acid, is an exception because it has no pair of distinct mirror image forms. The widespread use of one form is called homochirality, meaning the same handedness.

Laboratory reactions often produce equal amounts of both forms unless something steers them. The scientific puzzle was how an initially balanced chemical system could develop a strong preference. Kagan showed how a catalyst could magnify a preference; Soai developed reactions in which that preference could grow as the reaction generated more catalyst.

Kagan found that a mixed catalyst could do better than expected

Kagan's decisive advance came in 1986. A catalyst helps a chemical reaction proceed without being consumed in the reaction. In asymmetric catalysis, its molecular shape helps direct production toward one mirror image.

Chemists had expected a simple relationship between the balance of forms in a catalyst and the balance in its product. Kagan showed that the relationship could bend away from that expectation, producing a stronger preference than the catalyst's composition suggested. That departure is called a non-linear effect.

One explanation involves catalysts whose active structures contain pairs of molecular helpers. A mixture can form matching pairs of either handedness and mismatched pairs containing one of each. In some reactions, the mismatched pairs are much less active, leaving the matching pairs to do most of the work.

Consider a mixture with 75 helpers of one form and 25 of the other. If they pair randomly, matching pairs occur in a ratio of 75 squared to 25 squared, or nine to one. When mismatched pairs contribute little, the active matching pairs therefore behave like a 90 to 10 mixture. A modest starting preference becomes a stronger chemical influence.

Kagan's discovery gave researchers both a practical tool and a way to investigate catalysts. The shape of the relationship between catalyst composition and product composition can reveal clues about how molecules assemble and work inside a reaction vessel.

Soai made a reaction help produce itself

Soai's next step was asymmetric autocatalysis. Autocatalysis means that a reaction's product helps catalyse the production of more of that same product. If the process also favours the product's own handedness, a small initial advantage can feed back into further production.

The Academy's scientific background document traces an early result to 1990. Soai used diisopropylzinc and pyridine-3-carbaldehyde, with a catalyst prepared from the alcohol that the reaction itself produced.

The experiment demonstrated both autocatalysis and a preference for one mirror image. Its weakness was that the preference became smaller: the catalyst had an enantiomeric excess of 86%, while the product had an excess of 35%.

Enantiomeric excess, usually shortened to ee, measures the difference between the percentages of the two forms. A mixture containing 75% of one and 25% of the other has 50% ee. An equal mixture has zero ee, and a product containing only one form has 100% ee.

Soai's 1990 result therefore showed that the reaction could reproduce its own catalyst, but it diluted the starting preference. Five years later, his team found a reaction using pyrimidine-5-carbaldehyde in which the product had a greater excess than the catalyst. The feedback now strengthened the preference rather than weakening it.

What the striking purity figures actually mean

Soai's 1995 experiments began with a catalyst prepared using material at 5% ee. The first product reached 55% ee. Using the resulting material in another reaction raised the figure to 87%, and the sequence reached 90% ee over five consecutive runs.

A rise from 5% to 90% ee means a change from a mixture of 52.5% versus 47.5% to one of 95% versus 5%. The starting mixture was close to balanced; the final mixture contained 19 molecules of the favoured form for every one of its mirror image.

A later example started with a ligand, a molecule used to prepare the catalyst, at just 0.00005% ee. After three consecutive runs, the product exceeded 99.5% ee. That corresponds to more than 99.75% of the favoured form and less than 0.25% of the other.

The Academy describes the result as an amplification of the stereoisomeric ratio by a factor of 630,000. That figure concerns the relative balance of molecular forms, rather than the quantity of material produced.

The Nobel announcement identifies 2003 as the milestone when Soai presented a reaction forming only one of the two possible mirror images. Together, the experiments showed how repeated chemical feedback could carry an almost imperceptible imbalance toward homochirality.

Chance could favour either molecular form

Soai also investigated reactions starting without an added source of handedness. In such experiments, a tiny statistical fluctuation can give one form an advantage that the reaction then magnifies.

Across 37 experiments described in the Academy's scientific background, 18 favoured the form labelled R and 19 favoured S. The products ranged from 15% to 91% ee. The near even split between outcomes shows that either form could gain the advantage.

The letters R and S identify molecular configurations. They allow chemists to name the two arrangements precisely without relying on a drawing of a left or right hand. In these experiments, individual reactions developed a preference even though the series as a whole favoured neither configuration.

The Academy also credits Daniel Singleton with independently demonstrating symmetry breaking using the Soai reaction. Symmetry breaking is the emergence of an unequal outcome from an initially balanced system.

Heiner Linke, chair of the Nobel Committee for Chemistry, described the achievement when the prize was announced:

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.

The Academy places the reaction's relevance to life's origins within a specific boundary: it demonstrates a chemical route to homochirality in the laboratory, while the origin of biological handedness in water remains an open problem. Its scientific background says the Soai reaction is not relevant to the emergence of biological homochirality in aqueous systems.

Why medicine makers care about the difference

Drug development gives molecular handedness immediate practical importance. Two forms of a compound can interact differently with the body, so manufacturers may need a process that reliably produces the desired form.

Kovuru Gopalaiah, a Delhi University professor who worked in Kagan's laboratory, explains that amplification can reduce the need for extremely pure catalysts. Using material around 70% purity rather than 99% may reduce purification costs in suitable processes. A cited Merck example produced the compound L-699,392 at 95% purity from starting material at 70% purity.

India has a substantial interest in such manufacturing improvements. An Indian embassy brochure cited in discussion of the prize puts the country's share of global generic medicine supply at about 20% by volume. Any saving would depend on the particular reaction and manufacturing process; the Nobel discoveries provide principles that chemists can test when designing those processes.

Thalidomide illustrates why drug safety requires more than choosing a molecular form. The medicine caused severe birth defects and was withdrawn from markets in 1961. G Sekar, head of chemistry at IIT Madras, explains that its forms can convert into each other inside the body. A medicine's behaviour therefore depends on what happens after administration as well as on the material manufactured.

Decisions about whether to use a single molecular form depend on safety, effectiveness and regulatory requirements. Kagan's and Soai's discoveries help chemists control what they make, giving drug researchers more precise starting points for those assessments.

The milestones behind the award

The Nobel recognition brings together discoveries developed over decades. Kagan established that a catalyst's molecular imbalance could be magnified; Soai built reactions in which the product could strengthen that imbalance through repeated production.

• 1986: Kagan demonstrated non-linear effects in asymmetric catalysis.
• 1990: Soai published an asymmetric autocatalytic reaction, although the product's ee was lower than the catalyst's.
• 1995: Soai and colleagues demonstrated autocatalysis that increased ee, reaching 90% through five consecutive runs.
• 2003: The Nobel announcement dates Soai's presentation of a reaction forming only one mirror image to this year.
• October 7, 2026: The Royal Swedish Academy of Sciences announced the shared chemistry prize.
• October 20, 2026: Soai discussed the reaction and future research at the Tokyo lecture.
• December 10, 2026: The Nobel award ceremony is scheduled in Stockholm.

Soai plans to attend the Stockholm ceremony and deliver a lecture discussing his research alongside the contributions of Louis Pasteur, the French chemist and microbiologist whose work helped establish molecular asymmetry in the 19th century.

Soai keeps his focus on fundamental experiments

Soai learned that he had won while shopping near his home. He later credited the colleagues and students who helped sustain the experimental work behind the reaction that now bears his name.

At the news conference following his Tokyo lecture, Soai explained the curiosity that had driven the research:

I was interested in basic or rather fundamental matters.

His planned research returns to the beginning of the process: what can create the small left or right preference that autocatalysis magnifies. The prize recognises the reactions already developed, while his Tokyo remarks show that the initial imbalance still offers experiments he wants to pursue.

Key Points

• Kenso Soai and Henri B. Kagan share the 2026 Nobel Prize in Chemistry and 12 million Swedish kronor equally.
• Kagan showed how catalysts can produce a stronger molecular preference than their composition suggests.
• Soai developed reactions whose products help make more of themselves while increasing that preference.
• One experiment raised ee from 0.00005% to above 99.5% in three consecutive runs.
• At an October 20 lecture in Tokyo, Soai said he wants to study possible causes of molecular imbalances.
• The discoveries support pharmaceutical chemistry and laboratory research into homochirality.
• Soai plans to attend the December 10 Nobel ceremony in Stockholm.