How Main Space Structure Feature of Molecules in Our Body, Homochirality, Was Synthesized at Beginning of Life

"Kagan discovered a very interesting effect in his work: when we use a catalyst containing only a slight excess of a particular chiral compound, the resulting reaction yields a mixture with a much higher excess of that chiral compound than was present in the catalyst. This is precisely what the nonlinear effect entails.“

 

The concept described here is known as asymmetric amplification via the positive nonlinear effect (+-NLE). This phenomenon provides a fundamental chemical framework for explaining how homochirality—the single-handedness of biological molecules like left-handed amino acids and right-handed sugars—emerged at the origin of life.

For their pioneering breakthroughs in explaining this century-old mystery, French chemist Henri B. Kagan and Japanese chemist Kensō Soai were jointly awarded the 2026 Nobel Prize in Chemistry.

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The Core Mystery: Breaking Prebiotic Symmetry

In a normal laboratory setting, chemical reactions that produce chiral molecules result in a racemic mixture—a strict 50/50 split of left- and right-handed mirror images. However, biology is highly asymmetrical. If early Earth started with a completely balanced 50/50 prebiotic soup, life as we know it could not have formed because mixing molecular "hands" prevents the neat replication of structured chains like RNA and DNA.

 

Scientists knew a physical agent (such as polarized light or magnetic mineral surfaces) could have broken the initial symmetry, creating a tiny, negligible imbalance. However, a mechanism was missing to explain how a minor fluctuation could dominate an entire planet.

Kagan’s Nonlinear Effect: Asymmetric Amplification

Before Henri Kagan’s work in 1986, chemists universally assumed that the "chiral purity" of a product would perfectly reflect the purity of the catalyst. If a catalyst had only a 10% excess of a left-handed form, the final reaction product was expected to yield a similarly small 10% excess.

Kagan proved this assumption wrong by identifying nonlinear effects:

•           The Mechanism: Kagan demonstrated that catalysts often form pairs, or "dimers" (combinations of two molecules) in a solution.

•           The Interaction: When a left-handed (\(L\)) and right-handed (\(D\)) catalyst bond together, they form a mixed (\(LD\)) heterochiral dimer. Conversely, matching pairs form homochiral dimers (\(LL\) or \(DD\)).

•           The Clean Out: If the mixed \(LD\) dimers are less active or completely dormant, they effectively lock up the minority "hand". This leaves the slight majority form free to perform the bulk of the catalysis.

•           The Result: Even if a catalyst pool possesses only a minute imbalance, the active pool filters out the opposition, generating a final product with a vastly multiplied chiral excess.

The Soai Reaction: Total Domination

Building directly upon Kagan’s discovery, Kensō Soai took the concept of amplification to its logical extreme by discovering asymmetric autocatalysis in 1995.

In the Soai reaction, the chiral product of a reaction acts as its own catalyst. A trace advantage of one form produces more of itself, which then accelerates the production of that exact same form. Soai demonstrated that an initial imbalance of just 0.0005% could self-amplify through consecutive reaction cycles until it yielded an almost 100% homochiral product—a 630,000-fold amplification without any external chiral assistance.

 Implication for the Origin of Life

Kagan and Soai's work fundamentally shifted origin-of-life science. It mathematically and chemically proved that nature did not require an extraordinarily flawless cosmic event to establish homochirality. Instead, any tiny, random fluctuation on the primordial Earth—magnified by Kagan's nonlinear interactions and driven forward by Soai's autocatalytic loops—was capable of universally casting the molecular mold for all living organisms.

„Since all living organisms are composed of substances belonging to only one isomeric type, other types—representing a different form of chirality—can be dangerous. For instance, modern medicines and antibiotics contain only one of the optically active isomers. The other optically active isomer might be ineffective, inert, or even harmful.

 

It is somewhat unexpected to see a renewed focus on this type of catalysis. Henri Kagan is a figure well known to all chemists working in asymmetric catalysis. At the time, it was highly surprising that he did not receive the 2001 Nobel Prize for advancing this field, given that he was one of its pioneers.

 

This methodology is primarily used to manufacture drugs where the presence of a specific mirror-image isomer is crucial. The most famous example is the drug thalidomide: while it has sedative and sleep-inducing effects, its mirror-image molecule can cause severe birth defects."