化学の謎が解けた-大きな炭素吸収源を説明する反応(A chemical mystery solved – the reaction explaining large carbon sinks)

2024-04-25 リンショーピング大学

＜関連情報＞

• https://liu.se/en/news-item/en-kemisk-gata-lost-reaktionen-som-forklarar-stora-kolsankor
• https://www.nature.com/articles/s41586-024-07210-9

淡水有機物における複雑性生成の原動力となる脱芳香族化 Dearomatization drives complexity generation in freshwater organic matter

Siyu Li,Mourad Harir,David Bastviken,Philippe Schmitt-Kopplin,Michael Gonsior,Alex Enrich-Prast,Juliana Valle & Norbert Hertkorn
Nature  Published:24 April 2024
DOI:https://doi.org/10.1038/s41586-024-07210-9

Abstract

Dissolved organic matter (DOM) is one of the most complex, dynamic and abundant sources of organic carbon, but its chemical reactivity remains uncertain^1,2,3. Greater insights into DOM structural features could facilitate understanding its synthesis, turnover and processing in the global carbon cycle^4,5. Here we use complementary multiplicity-edited ¹³C nuclear magnetic resonance (NMR) spectra to quantify key substructures assembling the carbon skeletons of DOM from four main Amazon rivers and two mid-size Swedish boreal lakes. We find that one type of reaction mechanism, oxidative dearomatization (ODA), widely used in organic synthetic chemistry to create natural product scaffolds^6,7,8,9,10, is probably a key driver for generating structural diversity during processing of DOM that are rich in suitable polyphenolic precursor molecules. Our data suggest a high abundance of tetrahedral quaternary carbons bound to one oxygen and three carbon atoms (OC_qC₃ units). These units are rare in common biomolecules but could be readily produced by ODA of lignin-derived and tannin-derived polyphenols. Tautomerization of (poly)phenols by ODA creates non-planar cyclohexadienones, which are subject to immediate and parallel cycloadditions. This combination leads to a proliferation of structural diversity of DOM compounds from early stages of DOM processing, with an increase in oxygenated aliphatic structures. Overall, we propose that ODA is a key reaction mechanism for complexity acceleration in the processing of DOM molecules, creation of new oxygenated aliphatic molecules and that it could be prevalent in nature.