PULSED EPR STUDIES OF NICKEL MODEL COMPLEXES

在本申请中提出的研究的长期目标是 表征镍在两个重要类别中的配位结构 并进一步发展脉冲电子顺磁共振技术 电子自旋回波包络调制(ESEEM)与电子自旋回波 顺磁性表征的检测Endor谱 生物系统中的中心。具体的实验旨在实现 第一个目标是研究镍(III)和镍(I)模型络合物。 使用CW-EPR、CW-Endor、ESEEM和ESE-的生物相关结构- 恩多光谱仪。将研究镍(III)多肽模型络合物 用ESEEM、CW和ESE-Endor方法获得磁耦合 14N，2H和1H的参数和耦合张量取向 以确定这些磁性参数如何与 结构。这些数据将提供必要的背景知识 解读已公布和正在进行的ESE和Endor的结果 镍铁氢酶中镍中心的研究。倪(I) 辅因子F430的衍生物，被认为在甲烷中发挥关键作用 产甲烷细菌的生产，也将使用脉冲和 CW-EPR技术。在这里，配体超精细耦合常数和张量 方向将提供有关轴向连接的详细信息 余因子的性质和余因子约化的结果 与Corphin大周期扭曲和“褶皱”的变化有关。这些 性质被认为是定义这种独特化学物质的关键因素 F430及其在甲基还原酶中的催化作用。在课程期间 在这项研究中，ESE-Endor方法学将得到发展，其 性能直接与CW-Endor的性能进行比较。此外, 目前的数据分析方法将得到改进。因为金属酶 是许多基本氧化还原反应的催化剂 在顺磁离子处于某个阶段的生物系统中 在这些过程中，本研究的结果将提供有针对性的 信息和增强的光谱工具，用于调查许多 与健康相关的问题。

The long-range objectives of the research proposed in this application are to characterize the ligation structures of nickel in two important classes of nickel enzymes and to further develop the pulsed-EPR techniques of electron spin-echo envelope modulation (ESEEM) and electron spin-echo detected ENDOR spectroscopy for the characterization of paramagnetic centers in biological systems. The specific experiments aimed at achieving the first goal involve the study of Ni(III) and Ni(I) model complexes of biologically relevant structure using cw-EPR, cw-ENDOR, ESEEM, and ESE- ENDOR spectroscopies. Ni(III) peptide model complexes will be studied using ESEEM, cw- and ESE-ENDOR methods to obtain magnetic coupling parameters and coupling tensor orientations for 14N, 2H, and 1H containing ligands to determine how these magnetic parameters are related to structure. These data will provide the necessary background for interpreting the results of published and ongoing ESE and ENDOR investigations of the nickel center in Ni-Fe hydrogenases. Ni(I) derivatives of cofactor F430, thought to play a key role in methane production by methanogenic bacteria, will also be studied using pulsed- and cw-EPR techniques. Here, ligand hyperfine coupling constants and tensor orientations will yield detailed information concerning the axial bonding properties of the cofactor and the consequences of cofactor reduction as related to changes in corphin macrocycle distortion and "puckering". These properties are thought to be key elements in defining the unique chemistry of F430 and its catalytic function in methyl reductases. During the course of this research, ESE-ENDOR methodology will be developed and its capabilities compared directly with those of cw-ENDOR. In addition, current methods of data analysis will be improved. Because metalloenzymes serve as catalysts for a number of essential oxidation-reduction reactions in biological systems with paramagnetic ions being involved at some stage in these processes, the results of this research will provide pertinent information and enhanced spectroscopic tools for the investigation of many health-related problems.