Exploiting Nuclear Spin Polarization to Investigate Enzyme-Mediated Free Radical Reactions via in situ NMR

自由基发生在酶介导的反应将通过核磁共振光谱研究使用CIDNP方法。将遵循一个三重战略：1。最初，假设的中间体的简单模型自由基将使用紫外准分子激光或通过在流动系统中混合适当的组分来产生光化学反应。在供体（三乙胺）和作为受体的含卤素前体之间的光引发电子转移在从含卤素的自由基阴离子中除去卤化物后产生所需的中性自由基。自由基阳离子排出一个质子，同样产生中性自由基。由此产生的自由基对引起CIDNP，这应该允许区分两种可选的反应途径，即片段化后重组与加入后消除。2. 类似地，酶产生自由基NO。何鸿燊。O2 -。它们的后续物种将通过流动系统产生。3. 产品的相关现象和极化模式将首先使用传统的核磁共振探针进行研究，但最终将通过圆柱形环面探针进行研究，以确保更高的灵敏度。同样的设置已经成功地用于研究不饱和底物的均匀加氢只用H2的一个自旋异构体，典型的对氢。这种现象被称为对氢诱导极化（PHIP），尽管在细节上有所不同，但具有与CIDNP相似的特征。

Radicals occuring in enzyme-mediated reactions will be studied via NMR spectroscopy using the CIDNP method. A threefold strategy will be followed: 1. Initially simple model radicals for the postulated intermediates will be generated either photochemically using an UV eximer laser or by mixing appropriate components in a flow system. Photoinitiated electron transfer between a donor (triethylamine) and as acceptor a halogen-containing precursor yields the desired neutral free radicals after eliminating a halide from the halogen-containing radical anion. The radical cation expels a proton, yielding a neutral free radical likewise. The resulting radical pairs cause CIDNP, which should allow to differentiate between the two alternative reaction pathways, i.e. fragmentation followed by recombination versus addition followed by elimination. 2. Analogously, the enzyme-produced radicals NO., HO., O2-. and their follow-up species will be generated via a flow system. 3. The associated phenomena and polarization patterns of the products will be studied initially using a conventional NMR probe, but eventually via a cylindrical torus probe, which insures higher sensitivity. This same setup has been used successfully to study homogeneous hydrogenation of unsaturated substrates using only one spin isomers of H2, typically of parahydrogen. This phenomenon, termed Parahydrogen Induced Polarization (PHIP), though different in detail, has features similar to CIDNP.