Pattanayak Santanu, Cantú Reinhard Fabián G, Rana Atanu, Gupta Sayam Sen, de Visser Sam P
Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER), Kolkata, Mohanpur, 741246, India.
Manchester Institute of Biotechnology and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK.
Chemistry. 2019 Jun 18;25(34):8092-8104. doi: 10.1002/chem.201900708. Epub 2019 May 20.
High-valent metal oxo oxidants are common catalytic-cycle intermediates in enzymes and known to be highly reactive. To understand which features of these oxidants affect their reactivity, a series of biomimetic iron(V) oxo oxidants with peripherally substituted biuret-modified tetraamido macrocyclic ligands were synthesized and characterized. Major shifts in the UV/Vis absorption as a result of replacing a group in the equatorial plane of the iron(V) oxo species were found. Further characterization by EPR spectroscopy, ESI-MS, and resonance Raman spectroscopy revealed differences in structure and the electronic configuration of these complexes. A systematic reactivity study with a range of substrates was performed and showed that the reactions are affected by electron-withdrawing substituents in the equatorial ligand, which enhance the reaction rate by almost 10 orders of magnitude. Thus, the long-range electrostatic perturbations have a major influence on the rate constant. Finally, computational studies identified the various electronic contributions to the rate-determining reaction step and explained how the equatorial ligand periphery affects the properties of the oxidant.
高价金属氧代氧化剂是酶中常见的催化循环中间体，并且已知具有高反应活性。为了了解这些氧化剂的哪些特征会影响其反应活性，合成并表征了一系列具有周边取代的缩二脲修饰四酰胺大环配体的仿生铁（V）氧代氧化剂。发现由于在铁（V）氧代物种的赤道平面中取代一个基团，紫外/可见吸收发生了重大变化。通过电子顺磁共振光谱、电喷雾电离质谱和共振拉曼光谱进行的进一步表征揭示了这些配合物在结构和电子构型上的差异。对一系列底物进行了系统的反应活性研究，结果表明反应受到赤道配体中吸电子取代基的影响，这些取代基使反应速率提高了近10个数量级。因此，远程静电扰动对速率常数有重大影响。最后，计算研究确定了对速率决定反应步骤的各种电子贡献，并解释了赤道配体周边如何影响氧化剂的性质。
