Importance of oxidation products in coumarin-mediated Fe(hydr)oxide mineral dissolution
Importance of oxidation products in coumarin-mediated Fe(hydr)oxide mineral dissolution
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DOI：
10.1007/s10534-020-00248-y
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发表时间：
2020-10-05
期刊：
影响因子：
3.5
通讯作者：
Weber, Guenther
中科院分区：
文献类型：
--
作者：
Baune, Matthias;Kang, Kyounglim;Weber, Guenther
由于铁在碱性土壤中的低溶解度，植物进化出了不同的铁获取策略，这些策略要么基于铁还原(策略I)，要么基于植物铁素络合(策略II)。最近，香豆素在铁获取中的重要作用已被发现，但其各自机制的细节仍不清楚。由于香豆素可以作为铁结合配体，也可以作为还原剂，不同的反应顺序是可能的，导致不同的铁物种和氧化香豆素。在这方面，人们经常忽视氧化香豆素不仅是铁(III)还原的副产物，而且可能积极参与进一步的铁动员步骤。为了验证氧化香豆素在铁(氢)氧化物溶解中的这一活性作用，我们用单一香豆素(七叶皂素、东苍子内酯、秦皮内酯)及其氧化产物的数据补充了铁的溶解数据，这些数据随时间、pH和矿物(针铁矿、利洛石)的变化而变化。我们的结果表明，香豆素的氧化有四种不同的途径，导致苯二酮、二聚体、羟基化香豆素、去甲基化香豆素以及它们的组合。依赖时间的物种模式因矿物、pH和香豆素分子而不同。氧化的香豆素通常比原始的香豆素更具活性，这解释了东苍子内酯出人意料的铁动员作用，东苍子内酯被脱甲基化为七叶树内酯。此外，氧化羟化和二聚化增加了酚基的数量，并产生了新的螯合性能。在这三种香豆素中发现了几种铁物种。由于氧化反应是直接在矿物表面启动的，它们通常非常有效-但这并不总是导致更多的铁动员。
Due to the low iron solubility in alkaline soils, plants have evolved different iron acquisition strategies, which are either based on ferric iron reduction (strategy I) or complexation by phytosiderophores (strategy II). Recently, a prominent role of coumarins for iron acquisition has been discovered, but details of the respective mechanism remain unclear. Since coumarins may act as iron-binding ligands but also as reductants, various reaction sequences are possible, resulting in different iron species and oxidized coumarins. In this context, it is often overlooked that oxidized coumarins are not just byproducts of iron(III) reduction, but may be actively involved in further steps of iron mobilization. In order to verify this active role of oxidized coumarins in Fe(hydr)oxide dissolution, we complemented iron dissolution data with data of single coumarins (esculetin, scopoletin, fraxetin) and their oxidation products, as a function of time, pH, and mineral (goethite, lepidocrocite). Our results demonstrate that there are four different routes for coumarin oxidation, leading to quinones, dimers, hydroxylated coumarins, demethylated coumarins, and combinations of these. The time-dependent species pattern differs with respect to mineral, pH, and coumarin molecule. Oxidized coumarins are often more reactive than the original coumarins, explaining unexpected iron mobilization by scopoletin, which is demethylated to esculetin. Also oxidative hydroxylation and dimerization increase the number of phenolic groups and yield new chelating properties. Several iron-species are identified for the three coumarins. Since oxidation reactions are initiated directly at mineral surfaces, they are often very effective-but this does not always result in more iron mobilization.