Solomon Edward I, Iyer Shyam R
Department of Chemistry, Stanford University.
Bull Jpn Soc Coord Chem. 2019;73:3-14. doi: 10.4019/bjscc.73.3. Epub 2019 May 31.
While two classes of non-heme iron enzymes use ferric centers to activate singlet organic substrates for the spin forbidden reaction with O, most classes use high spin ferrous sites to activate dioxygen. These Fe active sites do not exhibit intense absorption bands and have an integer spin ground state thus are mostly EPR inactive. We have developed new spectroscopic methodologies that provide geometric and electronic structural insight into the ferrous centers and their interactions with cosubstrates for dioxygen activation and into the nature of the intermediates generated in these reactions. First, we present our variable-temperature variable-field magnetic circular dichroism (VTVH MCD) methodology to experimentally define the geometric and electronic structure of the high spin ferrous active site. Then, we focus on using Nuclear Resonance Vibrational Spectroscopy (NRVS, performed at SPring-8) to define geometric structure and VTVH MCD to define the electronic structure of the Fe-OOH and Fe=O intermediates generated in O activation and the spin state dependence of their frontier molecular orbitals (FMOs) in controlling reactivity. Experimentally validated reaction coordinates are derived for the anticancer drug bleomycin in its cleavage of DNA and for an alpha- ketoglutarate dependent dioxygenase in its selective halogenation over the thermodynamically favored hydroxylation of substrate.
虽然两类非血红素铁酶利用三价铁中心来激活单线态有机底物，以进行与氧气的自旋禁阻反应，但大多数酶类利用高自旋二价铁位点来激活双氧。这些铁活性位点不表现出强烈的吸收带，且具有整数自旋基态，因此大多无EPR活性。我们开发了新的光谱方法，这些方法能深入了解二价铁中心的几何和电子结构、它们与双氧激活共底物的相互作用，以及这些反应中生成的中间体的性质。首先，我们介绍我们的变温变场磁圆二色性（VTVH MCD）方法，以通过实验确定高自旋二价铁活性位点的几何和电子结构。然后，我们着重利用核共振振动光谱（在SPring-8进行的NRVS）来确定几何结构，并用VTVH MCD来确定氧气激活过程中生成的Fe-OOH和Fe=O中间体的电子结构，以及它们的前沿分子轨道（FMO）的自旋态依赖性对反应活性的控制。通过实验验证了抗癌药物博来霉素切割DNA的反应坐标，以及一种依赖于α-酮戊二酸的双加氧酶在底物的选择性卤化反应中相对于热力学上更有利的羟基化反应的反应坐标。
