A mystery that has intrigued the scientific community for more than 50 years has finally been solved. A team from Linköping University, Sweden, and Helmholtz Munich have discovered that a certain type of chemical reaction may explain why organic matter in rivers and lakes is so resistant to degradation. Their study was published in the journal Nature.
In the study, the researchers showed that oxidative dearomatization changes the three-dimensional structure of certain components of biomolecules, which can in turn activate a cascade of subsequent and differentiated reactions, resulting in millions of diverse molecules. Image credit: Pixabay (Free Pixabay license)
“It has been the Holy Grail in my field of research for over 50 years,” says Norbert Hertkorn, an analytical chemistry scientist previously at Helmholtz Munich and currently at Linköping University.
Let’s take things from the beginning. When, for example, a leaf breaks off a tree and falls to the ground, it immediately begins to decompose. Before the leaf decomposes, it is made up of a few thousand distinct biomolecules; molecules found in most living materials.
The decomposition of the leaf takes place in several phases. Insects and microorganisms begin to consume it, while sunlight and humidity affect the leaf, causing further degradation. Eventually, molecules from the decomposed leaf are washed into rivers, lakes and oceans.
Désaromatisation oxydative
However, at this point, the thousands of known biomolecules have been transformed into millions of molecules with very different appearances and complex and generally unknown structures. This spectacular chemical transformation process has remained a mystery that has baffled researchers for more than half a century, until today.
“We can now understand how a few thousand molecules present in living matter can give rise to millions of different molecules which quickly become very resistant to further degradation,” explains Norbert Hertkorn.
The team discovered that a specific type of reaction, known as oxidative dearomatization, lies behind the mystery. Although this reaction has long been studied and widely applied to pharmaceutical synthesis, its natural occurrence has remained unexplored.
In the study, the researchers showed that oxidative dearomatization changes the three-dimensional structure of certain components of biomolecules, which can in turn activate a cascade of subsequent and differentiated reactions, resulting in millions of diverse molecules.
Nuclear magnetic resonance
Scientists previously thought that the journey to dissolved organic matter involved a slow process with many sequential reactions. However, the present study suggests that the transformation occurs relatively quickly.
The team examined dissolved organic matter from four tributaries of the Amazon River and two Swedish lakes. They used a technique called nuclear magnetic resonance (NMR) to analyze the structure of millions of diverse molecules. Remarkably, regardless of climate, the fundamental structure of dissolved organic matter remained consistent.
“Key to the results was the unconventional use of NMR in a way that allowed studies of the deep interior of large dissolved organic molecules, thereby mapping and quantifying the chemical environment around carbon atoms. » explains Siyu Li, scientist at Helmholtz Munich and lead author of the study.
Rare in biomolecules
In biomolecules, carbon atoms can be linked to four other atoms, most often to hydrogen or oxygen. However, to the team’s surprise, a very large fraction of the organic carbon atoms were not bonded to hydrogen but mainly to other carbon atoms. Particularly intriguing was the large number of carbon atoms bonded specifically to three other carbons and one oxygen atom, a very rare structure in biomolecules.
According to David Bastviken, professor of environmental change at Linköping University, this makes organic matter stable, allowing it to persist for a long time and preventing it from quickly returning to the atmosphere as carbon dioxide or methane.
“This discovery helps explain our planet’s significant organic carbon sinks, which reduce the amount of carbon dioxide in the atmosphere,” explains David Bastviken.
The study received key funding from the Alexander von Humboldt Foundation, the Swedish Research Council, Formas and the European Research Council.
Article: Dearomatization drives the generation of complexity in freshwater organic matterSiyu Li, Mourad Harir, David Bastviken, Philippe Schmitt-Kopplin, Michael Gonsior, Alex Enrich-Prast, Juliana Valle, Norbert Hertkorn; Nature 2024 published online April 25, 2024. DOI: 10.1038/s41586-024-07210-9
Written by Anders Törneholm
Source: Linköping University
Originally published in The European Times.
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