Lee Justin L, Biswas Saborni, Ziller Joseph W, Bominaar Emile L, Hendrich Michael P, Borovik A S
Department of Chemistry, University of California-Irvine Irvine CA 92697 USA
Department of Chemistry, Carnegie Mellon University Pittsburgh PA 15213 USA.
Chem Sci. 2023 Dec 27;15(8):2817-2826. doi: 10.1039/d3sc04900k. eCollection 2024 Feb 22.
Metalloproteins with dinuclear cores are known to bind and activate dioxygen, with a subclass of these proteins having active sites containing FeMn cofactors and activities ranging from long-range proton-coupled electron transfer (PCET) to post-translational peptide modification. While mechanistic studies propose that these metallocofactors access FeMn intermediates, there is a dearth of related synthetic analogs. Herein, the first well-characterized synthetic Fe-(μ-O)-Mn complex is reported; this complex shows similar spectroscopic features as the catalytically competent FeMn intermediate X found in Class Ic ribonucleotide reductase and demonstrates PCET function towards phenolic substrates. This complex is prepared from the oxidation of the isolable Fe-(μ-O)-Mn species, whose stepwise assembly is facilitated by a tripodal ligand containing phosphinic amido groups. Structural and spectroscopic studies found proton movement involving the FeMn core, whereby the initial bridging hydroxido ligand is converted to an oxido ligand with concomitant protonation of one phosphinic amido group. This series of FeMn complexes allowed us to address factors that may dictate the preference of an active site for a heterobimetallic cofactor over one that is homobimetallic: comparisons of the redox properties of our FeMn complexes with those of the di-Fe analogs suggested that the relative thermodynamic ease of accessing an FeMn core can play an important role in determining the metal ion composition when the key catalytic steps do not require an overly potent oxidant. Moreover, these complexes allowed us to demonstrate the effect of the hyperfine interaction from non-Fe nuclei on Fe Mössbauer spectra which is relevant to MnFe intermediates in proteins.
已知具有双核核心的金属蛋白能够结合并激活双氧，这些蛋白的一个亚类具有含有铁锰辅因子的活性位点，其活性范围从远程质子耦合电子转移（PCET）到翻译后肽修饰。虽然机理研究表明这些金属辅因子会生成铁锰中间体，但相关的合成类似物却很匮乏。在此，报道了首个得到充分表征的合成铁 -（μ - 氧）- 锰配合物；该配合物显示出与在Ic类核糖核苷酸还原酶中发现的具有催化活性的铁锰中间体X相似的光谱特征，并对酚类底物表现出PCET功能。这种配合物是由可分离的铁 -（μ - 氧）- 锰物种氧化制备而成，其逐步组装由含次膦酰胺基的三脚架配体促进。结构和光谱研究发现质子运动涉及铁锰核心，由此最初的桥连羟基配体转变为氧配体，同时一个次膦酰胺基发生质子化。这一系列铁锰配合物使我们能够探讨可能决定活性位点对异双核辅因子而非同双核辅因子偏好的因素：将我们的铁锰配合物与二铁类似物的氧化还原性质进行比较表明，当关键催化步骤不需要过强氧化剂时，获取铁锰核心相对热力学上的难易程度在决定金属离子组成方面可能起重要作用。此外，这些配合物使我们能够证明非铁原子核的超精细相互作用对铁穆斯堡尔谱的影响，这与蛋白质中的锰铁中间体相关。
