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、合成和研究能够 帮助阐明与结构、金属连接、光谱和反应性相关的基本方面 氧(O2)和氮氧化物(NOx)化学，存在于血红素-铜氧化酶(例如，CCOs)、 氧化还原酶(NORs)及相关蛋白。HCOS和NORs是进化上相关的酶，它们发挥作用 在好氧和厌氧生物体内的细胞过程中的关键作用。他们有一个血红素/M(M=铜或 非血红素铁)活性部位，分别还原裂解O2或结合NO。提出的研究将 通过提供全面和全面的 与O2和NO生物处理相关的基本基础，甚至超出了血红素和铜的范围 金属蛋白球体。具体目标包括：(A)研究低自旋血红素-(μ-1-)的O-O裂解化学。 2)-通过添加适当的H/e源，包括酚类或衍生物，形成过氧铜络合物。大的 卟啉和铜配体以及不同的PKA和/或底物的合成可变性程度 E0，以便仔细研究导致O2-成功活化和还原的因素 在CcO和模型系统的结构-功能关系的背景下的切割(相对于其他途径)。(B) 生成新的血红素-过氧铜络合物(结合仿生或氢键部分)和 它们的结构和电子性质的详细表征。(C)两种化学品的精制 用于测试CcO(生物)化学如何导致铜配体His-Tyr实际形成的系统 交叉链接。详细的研究将涉及新的带有开放的咪唑N-H位的配体支架 与外源酚醛底物的共价偶联。将包括氧化元素，例如 存在过氧基团或高价铁氧物种。(D)调查有投入的化学系统 血红素轴向“碱”配体的变化，其中将研究血红素/NO/O2的配位化学 与过氧亚硝酸盐的形成及其随后的衰变或底物反应有关的机械方面。这 化学发生在NO双加氧酶中，这些酶关键地参与细胞内环境的不稳定(和细胞 信号)通过氨基酸硝化化学。(E)研究与NORs、亚铁血红素/铜或 无还原偶联的血红素/非血红素铁组件。一个明确的重点将是研究 推定的次亚硝酸盐中间体的形成、它们的结构和它们的反应性导致N2O作为产物。 这些信息是理解N-N偶联和N-O裂解化学的关键，N-N偶联和N-O裂解化学也涉及 质子化事件。这些过程与其他生物金属酶相比具有广泛的意义。 氮氧化物加工。手中的血红素/铜组件也使这种化学和进一步的机制成为可能 探测是必要的；这些过程是NO信号的关键，并与细胞对变化的反应有关 在[O2]浓度下。

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.