MECHANISM OF MN-OXO/HYDROGEN ATOM ABSTRACTION

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。分子高价金属氧物种涉及各种重要的生物，合成和工业应用。血红素和非血红素的高价金属-氧代络合物都被认为是许多金属酶（例如细胞色素P450、过氧化物酶、脂氧合酶、甲烷单加氧酶、光合反应中心）和相关合成系统（例如金属卟啉氧化、基于Salen的不对称环氧化）机制中可能的关键中间体。虽然被广泛调用，参与的高价M=O复合物的直接证据往往是缺乏的，这些物种已被推断为关键中间体的产品分析，动力学数据，或其他间接方法。我们已经开发了一种连续流动的X射线荧光光谱仪，可用于记录时间分辨的X射线吸收光谱与毫秒分辨率。作为第一个测试，我们已经使用它来研究在Mn催化的烯烃环氧化（在广泛的药物合成中的重要步骤）期间形成的中间体。我们的结果表明，鉴于不存在任何可检测到的Mn=O中间体，必须重新评估解释一大类锰催化氧代转移反应的标准机制。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Molecular high-valent metal-oxo species are implicated in a wide variety of important biological, synthetic, and industrial applications. Both heme and non-heme high-valent metal-oxo complexes have been cited as possible crucial intermediates in the mechanisms of many metalloenzymes (e.g. Cytochrome P450, peroxidases, lipoxygenase, methane monooxygenase, photosynthetic reaction center), and related synthetic systems (e.g. metalloporphyrin oxidations, salen-based asymmetric epoxidations). Although widely invoked, direct evidence for the participation of a high-valent M=O complex is often lacking, and these species have been inferred as key intermediates from product analyses, kinetic data, or other indirect methods. We have developed a continuous flow x-ray fluorescence spectrometer that can be used to record time-resolved x-ray absorption spectra with msec resolution. As a first test, we have used this to investigate the intermediate formed during Mn catalyzed olefin epoxidation (an important step in a wide range of pharmaceutical syntheses). Our results suggest that the standard mechanisms for explaining a large class of Mn-catalyzed oxo transfer reactions must be reevaluated in light of the absence of any detectable Mn=O intermediates.