In this work, we present the first computational study on a biomimetic cysteine dioxygenase model complex, [Fe ~II(LN _3S)] ~+, in which LN 3S is a tetradentate ligand with a bis(imino)pyridyl scaffold and a pendant arylthiolate group. The reaction mechanism of sulfur dioxygenation with O _2 was examined by density functional theory (DFT) methods and compared with results obtained for cysteine dioxygenase. The reaction proceeds via multistate reactivity patterns on competing singlet, triplet, and quintet spin state surfaces. The reaction mechanism is analogous to that found for cysteine dioxygenase enzymes (Kumar, D.; Thiel, W.; de Visser, S. P. J. Am. Chem. Soc.2011, 133, 3869-3882); hence, the computations indicate that this complex can closely mimic the enzymatic process. The catalytic mechanism starts from an iron(III)-superoxo complex and the attack of the terminal oxygen atom of the superoxo group on the sulfur atom of the ligand. Subsequently, the dioxygen bond breaks to form an iron(IV)-oxo complex with a bound sulfenato group. After reorganization, the second oxygen atom is transferred to the substrate to give a sulfinic acid product. An alternative mechanism involving the direct attack of dioxygen on the sulfur, without involving any iron-oxygen intermediates, was also examined. Importantly, a significant energetic preference for dioxygen coordinating to the iron center prior to attack at sulfur was discovered and serves to elucidate the function of the metal ion in the reaction process. The computational results are in good agreement with experimental observations, and the differences and similarities of the biomimetic complex and the enzymatic cysteine dioxygenase center are highlighted.
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机译：在这项工作中，我们提出了关于仿生半胱氨酸双加氧酶模型复合物[Fe〜II（LN _3S）]〜+的首次计算研究，其中LN 3S是具有双（亚氨基）吡啶基骨架和侧基芳基硫醇盐的四齿配体组。用密度泛函理论（DFT）方法研究了硫与O _2加氧的反应机理，并与半胱氨酸双加氧酶的结果进行了比较。反应通过竞争单重态，三重态和五重态自旋态表面上的多态反应性模式进行。该反应机制类似于半胱氨酸双加氧酶的发现（Kumar，D。; Thiel，W。; de Visser，S.P.J.Am.Chem.Soc.2011，133，3869-3882）。因此，计算表明该复合物可以紧密模拟酶促过程。催化机理从铁（III）-超氧配合物开始，并且超氧代基团的末端氧原子攻击配体的硫原子。随后，双氧键断裂以形成具有键合的磺酰氨基的铁（IV）-氧配合物。重组后，第二个氧原子转移到底物上，得到亚磺酸产物。还研究了另一种机制，该机制涉及双氧直接攻击硫，而不涉及任何铁氧中间体。重要的是，发现了在侵蚀硫之前显着的能量优先选择与铁中心配位的双氧，这有助于阐明金属离子在反应过程中的功能。计算结果与实验观察结果吻合良好，强调了仿生复合体与酶半胱氨酸双加氧酶中心的异同。
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