O-O Bond Activation (and Formation) at Bimetallic Enzyme Active Sites

这个提议的总体目标是了解双氧是如何被非血红素双铁激活的 代谢关键转化中的酶。这些酶具有一系列显著的功能， 包括DNA的生物合成（核糖核苷酸还原酶（RNR））、有机底物的羟基化 （可溶性甲烷单加氧酶（sMMOH），甲苯单加氧酶），真核生物的羟基化， 调节真核细胞增殖的起始因子5a（人脱氧羟腐胺赖氨酸羟化酶（hDOHH））， 抗生素（CmlA、CmlI）的生物合成，以及生物柴油（蓝藻醛）的生产 脱甲酰化加氧酶（cADO））。重要的项目目标是了解初始二铁（II，III）的作用- 超氧物种和随后形成的二铁（III）-过氧中间体在底物氧化，如何 后者可以转化为相应的高价铁氧物种，通常作为关键的氧化剂， 底物转化，并描述高价的结构，电子和反应性能 中间体的这些目标将通过生物化学和仿生方法的组合来实现。 我们的生物化学工作集中在hDOHH和CmlI的二铁-过氧中间体（P）上，我们发现， 具有与sMMOH和RNR的羧基桥接中间体不同的核心结构。与尽可能多 作为四种不同的P物种进行动力学和光谱学比较，我们的目标是阐明这些 结构差异导致它们各自的酶催化的反应。 我们的仿生努力将集中在表征上面列出的各种二铁-O2中间体， 详细了解它们的电子结构和氧化反应性。例如， 二铁（II，III）-超氧物种羟基化甲苯像甲苯-4-单加氧酶？二铁（III）是否可能- 过氧物质氧化C-H键以模拟羟化酶，并且还模拟cADO在氧化酶中的作用。 醛的去甲酰基化？哪些因素会使一种反应优于另一种反应？最重要的是，二铁- 过氧中间体转化为高价二铁氧化剂， 氧化这些后一种配合物对于我们澄清高价二铁的性质也是至关重要的 核心的甲烷羟基化酶中间体sMMOH-Q使用新的光谱技术。 我们的仿生努力将扩展到Fe-O-Mn和Fe-O-Ce配合物的合成。的 Fe-O-Mn复合物模拟寄生虫核糖核苷酸还原酶的高价中间体 沙眼衣原体和致病菌中发现的相关R2 lox酶了解 高价FeFe和FeMn络合物的反应性性质的差异可能有助于 开发更好的方法来治疗来自这些人类病原体的感染。Fe-O-Ce配合物 将有助于我们理解CeIV铁催化水氧化的O-O键形成机制， 我们建议正好是双铁酶用于双氧活化的反应顺序的相反顺序。

The overall goal of this proposal is to understand how dioxygen is activated by nonheme diiron enzymes in metabolically critical transformations. These enzymes perform a remarkable range of functions, including the biosynthesis of DNA (ribonucleotide reductase (RNR)), the hydroxylation of organic substrates (soluble methane monooxygenase (sMMOH), toluene monooxygenase), the hydroxylation of the eukaryotic initiation factor 5a to regulate eukaryotic cell proliferation (human deoxyhypusine hydroxylase (hDOHH)), the biosynthesis of antibiotics (CmlA, CmlI), and the production of biodiesel (cyanobacterial aldehyde deformylating oxygenase (cADO)). Important project goals are to understand the roles of the initial diiron(II,III)- superoxo species and the subsequently formed diiron(III)-peroxo intermediates in substrate oxidation, how the latter can be converted to corresponding high-valent iron-oxo species that often serve as the key oxidants for substrate transformation, and to describe the structural, electronic, and reactivity properties of the high-valent intermediates. These goals will be accomplished by a combination of biochemical and biomimetic approaches. Our biochemical effort focuses on the diferric-peroxo intermediates (P) of hDOHH and CmlI we found to have different core structures from the carboxylate-bridged intermediates of sMMOH and RNR. With as many as four different P species to compare kinetically and spectroscopically, we aim to shed light on how these structural differences lead to the reactions their respective enzymes catalyze. Our biomimetic effort will focus on characterizing the various diiron-O2 intermediates listed above to gain detailed insight into their electronic structures and their oxidative reactivity. For example, can a diiron(II,III)-superoxo species hydroxylate toluene like toluene-4-monooxygenase? Is it possible for a diiron(III)- peroxo species oxidize C–H bonds to model a hydroxylase and also mimic the action of cADO in the oxidative deformylation of aldehydes? What factors favor one reaction over the other? Most importantly, how are diferric- peroxo intermediates converted into the high-valent diiron oxidants that carry out the most difficult substrate oxidations. These latter complexes are also critical to our efforts to clarify the nature of the high-valent diiron core in the methane-hydroxylating enzyme intermediate sMMOH-Q using new spectroscopic techniques. Our biomimetic efforts will be extended to the synthesis of Fe–O–Mn and Fe–O–Ce complexes. The Fe–O–Mn complexes mimic high-valent intermediates of the ribonucleotide reductase from the parasite Chlamydia trachomatis and the related R2lox enzymes found in pathogenic bacteria. Understanding the difference in the reactivity properties of high-valent FeFe and FeMn complexes may contribute to the development of better methods for treating infections from such human pathogens. The Fe–O–Ce complexes will help us understand the O–O bond formation mechanism of iron-catalyzed water oxidation by CeIV, which we propose to be just the reverse of the reaction sequence used by the diiron enzymes for dioxygen activation.