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

本提案的总体目标是了解非血红素二铁是如何激活氧气的。 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(核糖核苷酸还原酶)的生物合成，有机底物的羟化 (可溶性甲烷单加氧酶(SMMOH)、甲苯单加氧酶)，真核生物的羟化 调控真核细胞增殖的起始因子5a(HDOHH)， 抗生素(CmlA、CmlI)的生物合成和生物柴油(蓝藻醛)的生产 去甲酰化加氧酶(CADO))。重要的项目目标是了解初始双铁(II、III)的作用- 在底物氧化中，超氧物种和随后形成的二铁(III)-过氧基中间体是如何 后者可以转化为相应的高价铁氧物种，这些物种通常是 底物转化，并描述高价化合物的结构、电子和反应性能 中间体。这些目标将通过生化和仿生相结合的方法来实现。 我们的生化工作集中在hDOHH和CmlI的二铁-过氧基中间体(P)上，我们发现 具有不同于sMMOH和RNR的羧酸桥联中间体的核心结构。用同样多的 作为四种不同的磷物种进行动力学和光谱比较，我们的目标是阐明这些 结构上的差异导致了它们各自的酶催化的反应。 我们的仿生工作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活性。例如，是否可以使用 二铁(II，III)-超氧物种羟化甲苯类-4-单加氧酶？双铁(III)是否有可能- 过氧基物种氧化C-H键来模拟羟基酶，并模仿CADO在氧化过程中的作用 醛的脱甲酰化？哪些因素有利于一种反应而不是另一种？最重要的是，差铁是怎么- 过氧基中间体转化为高价二铁氧化剂，进行最困难的底物 氧化作用。这些后一种络合物对于我们澄清高价二铁的性质也是至关重要的 使用新的光谱技术在甲烷羟基化酶中间体sMMOH-Q中的核心。 我们的仿生努力将扩展到Fe-O-Mn和Fe-O-Ce配合物的合成。这个 铁-氧-锰复合体模拟寄生虫核糖核苷酸还原酶的高价中间体 病原菌中发现的沙眼衣原体和相关的R2lox酶。了解 高价FeFe和FeMn络合物反应性的差异可能有助于 开发更好的方法来治疗这种人类病原体的感染。Fe-O-Ce络合物 这将有助于我们理解CeIV铁催化水氧化O-O键的形成机理。 我们建议与双铁酶用于氧气活化的反应顺序正好相反。

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.