The 2026 Nobel Prize in Chemistry was awarded to Henri Kagan and Kenso Soai in recognition of research showing that chemical reactions can strongly favor one of a molecule’s two mirror-image forms, rather than producing an equal mixture of both. This achievement matters because life depends on strict molecular selectivity, whereas most chemical reactions do not possess this selectivity automatically.
Why does molecular “handedness” matter?
This property is scientifically known as chirality, and the two symmetrical forms are usually designated by the letters D and L. The two forms have the same chemical components, but the arrangement of their bonds in space makes them non-superimposable mirror images, like the right and left hands.
This difference is not merely cosmetic. Enzymes, proteins that carry out biological reactions, have binding sites shaped to fit specific molecules. Therefore, an enzyme may react with one form but be unable to interact with its mirror image. The source states that life uses one form of sugars, and that many enzymes do not react with the corresponding form.
From the hypothesis to a measurable reaction
Researchers proposed several theoretical explanations for how this bias might arise. A catalyst that slightly favors one form may be enough for that form to accumulate over time, or the reaction product itself may act as a catalyst for producing more of its own form while inhibiting the formation of the opposite form.
Henri Kagan studied these possibilities using chiral catalysts. He found that the two mirror-image forms of the catalyst could be present in equal amounts, but that one of them was much more active, making it possible to direct a reaction producing chiral molecules toward a single form. By the mid-1960s, he had identified three reactions capable of producing an excess of one form. Later work showed that adding achiral substances could alter or inhibit the activity of the catalysts, enabling more precise control that benefited the pharmaceutical industry.
Soai’s self-amplification
About a decade later, Kenso Soai studied reactions in which one of the products acts as a catalyst for the reaction itself. He found a reaction that selected chirality: one of the forms catalyzed the formation of more molecules of the same form. When he started with a small excess, the proportion rose to 55% after one cycle and then reached 90% after the process was repeated several times.
In other conditions, the excess of one form began at a very small proportion of 0.00005%, then exceeded 99% after a few cycles, because the product catalyzed the formation of its own form and inhibited the formation of the mirror image.
What changes in practice?
These results provide a practical basis for producing pharmaceutical compounds with a specific chirality. The incorrect form of some medicines may be ineffective or harmful, so selective reactions offer a way to reduce the production of the unwanted form.
The discovery’s connection to the origin of life remains indirect. The reactions mentioned have not been demonstrated using biological molecules close to those on which living organisms depend, so they do not by themselves establish how life selected a single molecular form. However, they indicate that small differences in the abundance of one form may arise naturally and perhaps helped drive early chemistry toward the intense selectivity that characterizes life today.