Heme/Copper and Heme/Nonheme Iron O(2) and NO Reactivity

项目摘要 长期的研究目标是设计，合成和研究模型化合物系统， 有助于阐明结构的基本方面，金属连接，光谱学和反应性相关的 在血红素-铜氧化酶中发生的双氧（O2）和氮氧化物（NOx）化学（例如，CcOs），硝酸 氧化还原酶（NORs）和相关蛋白质。HCO和NOR是进化上相关的酶， 在需氧和厌氧生物体内的细胞过程中起关键作用。它们有一个血红素/M（M = Cu或 非血红素Fe）活性位点，其分别还原切割O2或偶联NO。该研究计划将 有助于更好地了解酶的结构和机制，通过提供一个全面的， 与O2和NO的生物处理相关的基本基础，甚至超出了血红素和Cu 金属蛋白球具体目标包括：（A）研究低自旋血红素-（μ-1- 2）-过氧-Cu络合物，通过添加适当的H+/e-源，包括酚或衍生物。大 卟啉和铜配体的合成可变性程度，以及不同PKa和/或pH的底物的合成可变性程度，沿着 E0，将被用来仔细研究导致成功的O2-活化和还原的因素。 裂解（与其他途径）的背景下的结构-功能关系的CcO和模型系统。（B） 产生新的血红素-过氧-Cu络合物（具有结合的仿生或H-键合部分）， 它们的结构和电子性质的详细表征。(C)两种化学品加工 设计用于测试CcO（生物）化学如何导致铜配体His-Tyr的实际形成的系统 交联详细的研究将涉及新的新的配体支架轴承开放咪唑N-H网站准备 共价偶联到外源酚底物。将包括氧化元素，例如 过氧基团或高价铁-氧物种的存在。(D)有输入化学系统的研究 血红素轴'基地'配体的变化，其中血红素/NO/O2配位化学将进行研究 关于过氧亚硝酸盐的形成及其随后的衰变或底物反应性，这 化学发生在NO双加氧酶中，这些酶关键地参与细胞NO稳态（和细胞内NO稳态）。 信号传导）。(E)与NORs、血红素/铜或 血红素/非血红素Fe组装体，其能够实现NO还原偶联。一个明确的重点将是研究 推定的次硝酸盐中间体的形成，它们的结构和它们导致N2 O作为产物的反应性。 这些信息是理解N-N偶联和N-O裂解化学的关键， 质子化事件这些过程相对于其他生物金属酶具有广泛的兴趣 氮氧化物处理在手血红素/铜组装也使这种化学和进一步的机械 探测是必要的;这些过程对NO信号传导至关重要，并与细胞对变化的反应有关 在[O2]浓度。

Project Summary The long-term research objective is to design, synthesize and investigate model compound systems which can help elucidate fundamental aspects of structure, metal-ligation, spectroscopy and reactivity relevant to the dioxygen (O2) and nitrogen oxide (NOx) chemistry which occurs in heme-copper oxidases (e.g., CcOs), nitric oxide reductases (NORs) and related proteins. HCOs and NORs are evolutionarily related enzymes which play critical roles in cellular processes within aerobic and anaerobic organisms. They have a heme/M (M = Cu or non-heme Fe) active site that reductively cleaves O2 or couples NO, respectively. The research proposed will contribute to a better understanding of enzyme structure and mechanism by providing a comprehensive and fundamental basis relevant to biological processing of O2 and NO that extends even beyond the heme and Cu metalloprotein sphere. Specific aims include: (A) the study of O–O cleavage chemistry in low-spin heme-(μ-1- 2)-peroxo-Cu complexes by addition of appropriate H+/e– sources, including phenols or derivatives. The large degree of synthetic variability in porphyrins and copper ligands, along with substrates of varying pKa's and/or E0, will be utilized in order to meticulously study the factors which lead to successful O2-activation and reductive cleavage (vs. other pathways) in the context of structure-function relationships of CcO & model systems. (B) the generation of new heme-peroxo-Cu complexes (with incorporated biomimetic or H-bonding moieties) and detailed characterization of their structural and electronic properties. (C) the elaboration of two chemical systems designed to test how CcO (bio)chemistry leads to the actual formation of the copper-ligand His-Tyr crosslink. Detailed studies will involve new new ligand scaffolds bearing open imidazole N-H sites poised for covalent coupling to an exogenous phenolic substrate. An oxidative element will be included, such as the presence of a peroxo group or high-valent iron-oxo species. (D) investigation of chemical systems with input variations of the heme axial `base' ligand, where heme/NO/O2 coordination chemistry will be studied mechanistically with regard to peroxynitrite formation and its subsequent decay or substrate reactivity. This chemistry occurs in NO dioxygenases, enzymes critically involved in cellular NO homeostasis (and cellular signaling) via amino-acid nitration chemistry. (E) the study of chemistry relevant to NORs, heme/Cu or heme/non-heme Fe assemblies that enable NO reductive coupling. A clear focus will be on the study of the formation of putative hyponitrite intermediates, their structures and their reactivity leading to N2O as product. Such information is key to the understanding of N-N coupling and N-O cleavage chemistries which also involve protonation events. These processes are of broad interest with respect to other biological metalloenzyme nitrogen oxide processing. In-hand heme/Cu assemblies also enable this chemistry and further mechanistic probing is necessary; these processes are critical to NO signaling and linked to cellular responses to changes in [O2] concentrations.