Left-handed or right-handed? For molecules, it matters

Your left and right hands look almost identical. 

But if you try putting a left-handed glove on your right hand, you'll quickly notice the difference.

Some molecules behave the same way. They come in two mirror-image forms and may look nearly identical — but the differences can have major consequences. One version of a molecule might help treat a disease, while the other could have a completely different effect on the body.

This phenomenon, known as chirality, is at the heart of the 2026 Nobel Prize in Chemistry, awarded Wednesday, Oct. 7, to Henri Kagan and Kenso Soai.

Their discoveries showed how tiny differences in molecular "handedness" can grow through chemical reactions, helping scientists better control the molecules used in a variety of medicines used to treat conditions ranging from acid reflux to HIV. 

To better understand the science and its significance, ASU News spoke with Di Liu, an assistant professor in Arizona State University's School of Molecular Sciences and a researcher in the Biodesign Center for Molecular Design and Biomimetics.

Question: What is chirality and why is it important?

Answer: Chirality is molecular "handedness." Our left and right hands are mirror images, but no matter how we rotate them, they cannot match exactly. Some molecules have the same relationship. They contain identical atoms, but those atoms are arranged differently in three-dimensional space. Our bodies can distinguish these mirror-image molecules, much like a glove fits one hand better than the other. That difference can have important biological consequences.

Q: What did Kagan and Soai discover, and why is it important?

A: Kagan discovered what chemists call positive nonlinear effects in asymmetric catalysis: that a small imbalance in the handedness of a catalyst — the substance that helps a chemical reaction happen — could produce a much larger imbalance in the molecules created. 

Soai discovered asymmetric autocatalysis, a remarkable process in which a chiral molecule could help create more copies of its own kind and handedness.

Together, their discoveries showed how tiny differences in molecular handedness can grow dramatically. This also provides important clues about how life might have developed its preference for particular molecular handednesses, including the sugars found in DNA and RNA and the amino acids that make up proteins.

Q: What does this research mean for medicine and drug development?

A: For a chiral drug, getting the molecular formula right isn't always enough. Its handedness matters, too. One mirror-image form may have the desired therapeutic effect, while the other may be less effective or have unwanted effects.

For example, a manufacturing process for a medication used to treat acid reflux called esomeprazole was developed using a chemical method pioneered by Kagan. Soai's research also helped inspire an improved method for producing a key building block used to make efavirenz, a medication used to treat HIV. These discoveries show how fundamental chemistry research can lead to better ways of making medicines.

Q: Does any of this connect to your own research on DNA and RNA at ASU?

A: Yes, the connection is that shape and handedness matter in biology! DNA and RNA aren't simply strings of genetic letters. Their three-dimensional shapes are essential to how they work. Even their sugars have handedness: natural DNA and RNA both use the D form, one of two mirror-image versions of these sugars. In my lab at ASU, we study how DNA and RNA twist, coil and interlock together, and how those shapes affect their biological functions.

Most people are familiar with the DNA double helix, which usually twists to the right. But DNA can also coil around itself and even form knots with their own handedness, adding another layer to the story. We're working to create right- and left-handed DNA knots, as well as DNA with positive or negative supercoiling, to understand how these different arrangements affect the way proteins interact with DNA.

It's another example of how a molecule's shape can influence what it does.

Q: What's the biggest takeaway from this year's Nobel Prize?

A: What excites me most is the connection between a practical challenge — making molecules with the desired handedness — and a fundamental question: Why does life favor particular molecular mirror images?

These experiments show how chemistry can amplify tiny differences. They don't tell us exactly what happened on early Earth, but they provide a foundation for exploring how life's handedness could have emerged.