Structure's Influence on Reactivity in Metalloenzymes

描述（由申请人提供）：我们的研究项目侧重于了解硫酸盐配体如何促进N-O和O-O （O2-和O2）键激活。一氧化氮（NO）经常被用来探测O2结合位点，并形成关键的亚稳Fe-O2中间体的稳定类似物。的吗?NO的拉伸频率提供了N-O的度量，从而提供了O-O键激活性能。越来越多的金属酶在不改变功能的情况下交替使用Mn和Fe，其中大多数促进O-O键的激活和裂解，并涉及M-双氧、-超氧、-过氧和-氧（M= Mn, Fe）作为关键中间体。这些酶的功能是清除与癌症、阿尔茨海默病、帕金森病有关的有毒氧自由基，并合成关键的生物分子，如DNA、神经递质、脂肪酸和类固醇。硫代酸连接的Fe-和Mn-过氧、超氧和氧类的光谱和反应性仍未得到充分研究，Mn和Fe的O2和O2-化学性质在光谱可见性和反应中间体的稳定性方面是互补的。在拟建项目期间，我们将设计和合成新的易于衍生的硫代酸盐配体及其相应的Mn和Fe配合物。通过系统地改变取代基，我们将微调分子的电子和空间性质，并调整氧化还原电位、金属离子刘易斯酸度以及远端和近端过氧氧的相对pKa。使用系统的方法，我们将尝试确定哪些属性是促进反应性和功能的关键。通过探测氧化还原电位和？我们将研究M- SR键的可调性，并确定半胱氨酸是否能在保持功能的同时促进Mn和Fe的互换性。我们将充分表征通过O2还原形成的新的吡啶/硫代酸连接铁过氧中间体，并继续探索其他吡啶取代衍生物的O2反应性。最终，我们将寻找Hammett参数与反应性之间的相关性，并确定哪些性质是促进Fe-O与O-O键裂解的关键。我们将继续通过监测O2演化来寻找M3+ (M= Mn, Fe)促进O2-氧化活性。最终，我们将寻找一种催化SOD模拟物。我们将使用XAS， MCD，共振拉曼，平行模式EPR和DFT来全面表征我们的新Mn-dioxygen和Mn-OOR （R= tBu, Cm）中间体，并研究Mn-dioxygen物种形成的动力学和机制。我们将尝试稳定这些中间体，以及我们的新Mn=O，通过在配体中加入空间体。我们将继续探索新的Mn-dioxygen， Mn-oxo和Mn- OOR中间体与可氧化底物的反应性。

DESCRIPTION (provided by applicant): Our research program focuses on understanding how thiolate ligands promote N-O and O-O (O2- and O2) bond activation. Nitric oxide (NO) is frequently used to probe O2 binding sites, and form stable analogues of key metastable Fe-O2 intermediates. The ?NO stretching frequency provides a measure of N-O, and thus O-O bond activating properties. A growing number of metalloenzymes use Mn and Fe interchangeably without altering function, and a majority of these promote O-O bond activation and cleavage, and involve M-dioxygen, -superoxo, -peroxo, and -oxo (M= Mn, Fe) species as key intermediates. These enzymes function to remove toxic O2- radicals implicated in cancer, Alzheimer's, Parkinson's disease, and synthesize key biomolecules such as DNA, neurotransmitters, fatty acids, and steroids. The spectroscopic and reactivity properties of thiolate-ligated Fe- and Mn-peroxo, superoxo, and oxo species remain largely unexplored, and the O2 and O2- chemistry of Mn and Fe is complementary with respect to the spectroscopic visibility and stability of reactive intermediates. For the proposed project period we will design and synthesize new, readily derivatized thiolate ligands, and their corresponding Mn and Fe complexes. By systematically altering substituents we will fine-tune the electronic and steric properties of the molecule, and adjust the redox potential, metal ion Lewis acidity, and relative pKa of the distal versus proximal peroxo oxygens. Using a systematic approach we will attempt to determine which properties are key to promoting reactivity and function. By probing redox potentials and ?NO of structurally analogous Mn/Fe pairs we will examine the tunable nature of the M- SR bond, and establish whether cysteinates can facilitate the interchangeability of Mn and Fe while maintaining function. We will fully characterize our new pyridine/thiolate-ligated Fe-peroxo intermediates formed via O2- reduction, and continue to explore the O2- reactivity of additional pyridine- substituted derivatives. Ultimately we will be looking for correlations between Hammett parameters and reactivity, and determining which properties are key to promoting Fe-O versus O-O bond cleavage. We will continue to look for M3+ (M= Mn, Fe) promoted O2- oxidation activity by monitoring for O2 evolution. Ultimately we will be looking for a catalytic SOD mimic. We will fully characterize our new Mn-dioxygen and Mn-OOR (R= tBu, Cm) intermediates using XAS, MCD, resonance Raman, parallel- mode EPR, and DFT, and examine the kinetics and mechanism of the Mn-dioxygen species formation. We wil attempt to stabilize these intermediates, as well as our new Mn=O, by incorporating steric bulk into the ligand. We will continue to explore the reactivity of our new Mn-dioxygen, Mn-oxo, and Mn- OOR intermediates with oxidizable substrates. PUBLIC HEALTH RELEVANCE: Our research program focuses on understanding how thiolate ligands promote O-O bond activation in Mn- and Fe-containing enzymes that function to remove toxic O2- radicals (implicated in cancer, Alzheimer's, Parkinson's disease), and synthesize key biomolecules (e.g., DNA, and neurotransmitters). The proposed project will determine the metal ion properties that are key to promoting function, and establish whether the tunable nature of M-SR bonds can facilitate the interchangeable use of Mn and Fe without altering function. The spectroscopic and reactivity properties of thiolate-ligated Fe- and Mn-peroxo, superoxo, and oxo species remain largely unexplored, and the O2 and O2- chemistry of Mn and Fe is complementary with respect to the spectroscopic visibility and stability of reactive intermediates.