Henri Kagan and and Kenso Soai have won this year’s Nobel Prize in Chemistry for showing how a reaction can end up making mostly one of two mirror-image molecules, Nature News reports (open copy).
Some molecules exist in two forms that are mirror images of each other. That property is called chirality, from the idea of left and right hands. Life uses only one form of many of its building blocks, a pattern called homochirality. DNA is right-handed, while the amino acids in proteins are left-handed. In the laboratory, reactions that create such molecules usually give an even mix. How nature avoids that mix has been a puzzle for more than a century.
A catalyst speeds a reaction without being used up. If the catalyst is itself chiral, it can favor one mirror image. This year’s Prize is for reactions that create their own catalyst.
Kagan, in the 1980s, showed that a small imbalance in a catalyst’s handedness can become a much larger imbalance in the products. Soai then found a reaction in which the product is also the catalyst. That is called autocatalysis: the product helps make more of itself. In 1995 he used a chiral alcohol, 5-pyrimidyl alkanol. A starting excess of 2 percent of one form ended as an excess of 87 percent.
From a random excess to a single form
In 2003 Soai reported what is now called the Soai reaction. It starts with ingredients that are not chiral and forms two mirror-image catalysts. Whichever appears in a slight, random excess eventually accounts for as much as 99.99 percent of the product.
The reaction does not explain why life picked one handedness. It only supplies a mechanism by which the problem could be solved. The reaction cannot run in water and uses reagents unlikely on the early Earth.
The findings also matter for drugs, because the two mirror images often behave differently.