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)

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2024-04-25 リンショーピング大学

解析化学者であるノルベルト・ヘルトコルン氏によると、樹木から落ちた葉が分解する過程は、何千もの生物分子が数百万の異なる分子へと変化する現象で、この複雑な化学変換が研究者を50年以上も悩ませていました。最近の研究では、この変化が「酸化的脱芳香化」という反応によるものであることが判明しました。この反応は医薬品合成で広く研究されていましたが、自然界での発生は未解明でした。研究チームはNMRを使用して、アマゾン川の支流やスウェーデンの湖から得た有機物の構造を分析し、有機物が安定し、大気中の二酸化炭素量を減少させることが明らかになりました。

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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

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)

Abstract

Dissolved organic matter (DOM) is one of the most complex, dynamic and abundant sources of organic carbon, but its chemical reactivity remains uncertain1,2,3. Greater insights into DOM structural features could facilitate understanding its synthesis, turnover and processing in the global carbon cycle4,5. 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 scaffolds6,7,8,9,10, 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 (OCqC3 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.

0500化学一般
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