At 95, Henri Kagan shares chemistry Nobel for unlocking molecular handedness

A Nobel recognition at 95

Kagan was 95 on the announcement date. NobelPrize.org records his birth as December 15, 1930, in Boulogne-Billancourt, France. The Academy identifies him as a professor emeritus at the former Université Paris-Sud; Soai is a professor emeritus at Tokyo University of Science. ²

The award recognises work developed over decades. The Academy traces Kagan’s key discovery to 1986 and highlights Soai’s landmark results in 1995 and 2003. Together, their experiments helped establish how a small imbalance between molecular forms could become a pronounced preference.

Why a molecule can have a left and a right

Hold your hands side by side: they are mirror images, but turning one around will not make every part line up with the other. Some molecules have the same kind of distinction. Chemists call the property chirality, and the two mirror-image forms are known as enantiomers. The difference lies in their three-dimensional arrangement. ³

Soai’s group demonstrated a particularly striking route to amplifying that difference. In asymmetric autocatalysis, a reaction’s product helps catalyse the production of more of itself. Their experiments showed that an extremely small initial excess of one mirror-image form could grow into a product consisting overwhelmingly of that form. ⁴

This provided an experimental way to investigate a question about life’s chemistry: how a strong preference for one molecular handedness can arise. It offers a mechanism to study, rather than proof of the precise sequence of events that occurred when life began.

Why the distinction matters in medicine

Biological systems can distinguish between molecular mirror images even when many of their other properties are alike. The U.S. Food and Drug Administration’s scientific guidance explains that enantiomers may differ in their effects, toxicity and the way the body absorbs, processes or removes them. ⁵

That makes control over molecular shape important when developing and manufacturing medicines. It does not mean one form is always beneficial and the other always harmful. The effects have to be investigated for the particular substance. The chemistry honoured this year helps explain how reactions can produce the form researchers want to study and use.