Experimental Description of Biomimetic NiII-Superoxo δ-Bond: Franck-Condon Analyses on Its Vibronically-Resolved Spectrum
Experimental Description of Biomimetic NiII-Superoxo δ-Bond: Franck-Condon Analyses on Its Vibronically-Resolved Spectrum
复制标题
仿生 NiII-Superoxo δ-键的实验描述：Franck-Condon 对其振动分辨光谱进行分析
DOI：
10.1021/acs.jpcc.0c02841
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发表时间：
2020
期刊：
影响因子：
3.7
通讯作者：
Y. Kuroda
中科院分区：
文献类型：
--
作者：
A. Oda;T. Nanjo;T. Ohkubo;Y. Kuroda
一价金属-双氧物种（M-O2）是由血红素和非血红素金属酶介导的多种氧化转化过程中的关键中间体。在轨道水平上理解它们的O2活化机制仍然具有科学意义。在本工作中，我们光谱分析仿生镍超氧δ键：其异常亲电反应性的起源。我们通过在MFI沸石中的NiI与O2的室温反应制备了仿生NiII-超氧物种。在真空条件下，这种孤立的物种在气相中的行为类似于金属氧化物分子，它给出了通常在气相中看到的振动分辨光谱。这种类型的光谱探针从来没有观察到过去的M-O2复合物。通过同位素实验和量子化学计算相结合的方法，我们成功地将所观察到的振动精细结构归属为伸缩O-O振动结构中的电子振动过程，该过程与双占据δ轨道到单占据δ* 轨道（SOMO）的激发有关.该光谱探针提供了δ通道相互作用如何促进O2分子中O-O键活化的信息。采用正方形平面NiII-superoxo位的DFT集团计算很好地再现了深奥的电子振动级数特征，成功地得到了能很好地描述NiII-superoxo δ键的DFT集团模型.该模型揭示了Ni Ⅱ-超氧代δ-键是离子键而不是共价键。δ键的高离子性导致亲电氧化反应的重要前线分子轨道（FMO）中的高氧特征，即，未占据的β-自旋O2-π* 轨道。这就是为什么Ni离子使具有异常亲电反应性的超氧配体稳定。本研究的结果提供了镍超氧δ键的一般描述，可能有助于我们揭示金属蛋白的结构-反应性关系。
Mononuclear metal–dioxygen species (M–O2) are key intermediates in a variety of the oxidative transformation processes mediated by heme and nonheme metalloenzymes. Understanding their O2-activation mechanism at an orbital level is still of scientific significance. In the present work, we spectroscopically analyzed the biomimetic NiII–superoxo δ-bond: the origin of its abnormal electrophilic reactivity. We prepared the biomimetic NiII–superoxo species through the room temperature reaction of the NiIsite with O2in MFI zeolite. Under vacuum condition, this isolated species acts likea metal oxide molecule in the gas phase, and it gives the vibronically resolved spectrum that is generally seen in the vapor phase. This type of spectroscopic probe has never been observed for past M–O2complexes. Through a combination of an isotopic experiment and quantum chemical calculations, we successfully assigned the observed vibrational fine structure as the vibronic progression in a stretching O–O vibrational structure associated with the excitation from doubly occupied δ orbital to singly occupied δ* orbital (SOMO). This spectroscopic probe provides information on how the δ channel interaction contributes to the activation of O–O bond in an O2molecule. The recondite vibronic progression feature was well reproduced by DFT cluster calculation assuming the square planar NiII–superoxo site, by which we successfully obtained the spectroscopically calibrated DFT cluster model that well describes NiII–superoxo δ-bond. This model revealed that NiII–superoxo δ-bond is ionic rather than covalent. The high ionicity of the δ bond results in the high oxygen character in the important frontier molecular orbital (FMO) for the electrophilic oxidative reaction, i.e., the unoccupied β-spin O2-π* orbital. This is why that Ni ion stabilizes superoxo ligand having abnormal electrophilic reactivity. The findings in the present study provide general description of the Ni–superoxo δ-bond and maybe can help us to uncover the structure–reactivity relationships of the metalloprotein.