Juncus acutus is a plant found near ponds and brackish marshes, producing secondary metabolites like phenanthrenoid dimers with antibacterial, antioxidant, and anti‐inflammatory activities. Despite this, little is known about the detailed mechanisms behind their dimerization reactions. In this study, we used Density Functional Theory to explore the reaction mechanisms of phenanthrene and dihydrophenanthrene species in radical coupling, both in gas‐phase and solution. The dimerization reactions, initiated by the OH radical, result in the formation of two phenanthrenoid dimers (homodimer and heterodimer). The OH radical abstracts a hydrogen atom from the hydroxyl group, leading to the formation of radicals and water. Our analysis of electronic spin density highlighted the preferred reactive sites that drive regioselective dimer formation. Furthermore, the study identifies a triplet π‐π stacked intermediate preceding the diketone formation on the singlet potential energy surface, revealing a two‐state reactivity mechanism. The diketone dimers are then converted via a water‐mediated keto‐enol tautomerization into their dienolic forms, completing the reaction pathway. This work offers insights into the complex dimerization processes of phenanthrenoids in nature, using computational methods to shed light on poorly understood molecular mechanisms in plant organisms.

中文翻译：

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揭示 Juncus acutus 中的菲二聚化：DFT 指导的自由基偶联反应机制探索


Juncus acutus 是一种在池塘和咸水沼泽附近发现的植物，产生次生代谢物，如具有抗菌、抗氧化和抗炎活性的菲二聚体。尽管如此，人们对其二聚化反应背后的详细机制知之甚少。在这项研究中，我们使用密度泛函理论来探索菲和二氢菲物种在气相和溶液中自由基耦合的反应机制。由 OH 自由基引发的二聚化反应导致形成两个菲二聚体（同型二聚体和异二聚体）。OH 自由基从羟基中提取一个氢原子，导致自由基和水的形成。我们对电子自旋密度的分析突出了驱动区域选择性二聚体形成的首选反应位点。此外，该研究在单重态势能表面上确定了二酮形成之前的三重态 π-π 堆叠中间体，揭示了两种状态反应机制。然后，二酮二聚体通过水介导的酮-烯醇互变异构化转化为其二烯酸形式，完成反应途径。这项工作提供了对自然界中菲类化合物复杂二聚化过程的见解，使用计算方法来阐明植物生物中知之甚少的分子机制。