One hand takes over

Hold up your hands. They are mirror images: alike in every way, yet one will not fit exactly on top of the other. Many molecules exist in the same two forms: a left-handed version and a right-handed version.

Life is strangely one-sided about this. It builds its proteins from one form of amino acid and its sugars from one form only. Chemistry without life makes both forms in equal amounts. How the living world came to use just one hand was a long-standing mystery.

It matters for medicine, too. In many drugs, one form does the beneficial work while its mirror image does nothing, or causes harm. Chemists need reliable ways to produce only the form they want.

Henri Kagan (1986)

Chemists make one-handed molecules with the help of one-handed catalysts. The working assumption was simple: a half-pure catalyst should yield a half-pure product. Kagan proved that this is not always true. In some reactions, the product came out purer than the catalyst that made it.

The explanation lies in how catalyst molecules pair up, because pairs of the same hand and mixed pairs behave differently. His "non-linear" plots became a standard way for chemists to find out what their catalyst is really doing.

Kenso Soai (1995)

Soai discovered a reaction in which the product acts as its own catalyst. Each new molecule helps make more molecules like itself, with the same handedness. Start with a tiny excess of one hand, and it snowballs. In a 2003 experiment, an excess of about 0.00005 per cent grew to more than 99.5 per cent in three rounds. Over those rounds, the leading form multiplied about 630,000 times; its mirror image, fewer than 1,000 times.

In 1953, the physicist F. C. Frank had suggested that a self-copying molecule could tip an even mixture towards one hand. For more than forty years, nobody had a laboratory reaction that did it. Soai's was the first.

What it means

Does this explain why life is one-handed? Not on its own. The Soai reaction is not one that could plausibly have run on the early Earth, and the search for a simpler, prebiotic version continues. What it proves, however, is that chemistry alone can turn a tiny imbalance into near-total dominance.

The work changed everyday practice as well. Non-linear analysis is now a standard tool in asymmetric catalysis, and the Soai reaction remains the benchmark experiment for chirality amplification.

The Nobel Prize in Chemistry 2026 was awarded to Henri B. Kagan of Université Paris-Sud, now part of Université Paris-Saclay, and Kenso Soai of Tokyo University of Science, "for the discovery of non-linear effects and autocatalysis in asymmetric organic synthesis".