Coupled Transfers of Electrons and Protons

项目概要/摘要 该研究将为质子耦合电子的研究提供一个概念性和定量的框架 质子转移（PCET）过程，其中质子和电子在单个化学步骤中转移。此类反应 是一系列重要的生物化学过程的关键，包括呼吸作用，光合作用和其他 生物能量学方面，氧化还原酶和其他金属酶的催化作用，以及反应性 氧物种和抗氧化剂。这些化学反应不同于氢原子转移（HAT），其中 这两个粒子“一起”移动，质子和电子移动到（或来自）不同的过程。 位置（多位点协同质子-电子转移，MS-CPET）。根据我们先前的研究和 上一个时期的具体进展。本项目将研究这些反应的速率和选择性 是由热化学以外的因素控制的。 许多生物化学过程使碳中心自由基和C-H键相互转化，但它们中的一些 反应在标准有机化学中几乎没有先例。例如，等能和上坡H-转移 碳原子之间的反应在溶液中非常缓慢，但这种反应被酶家族广泛使用。 与自由基-SAM和维生素B-12辅因子，通常是可逆的。MS-CPET的解决方案示例很少 C-H键的反应，但这些被预测用于生物学中的各种酶。实验中使用 有机和过渡金属模型系统将探测这些反应的基本性质。这些 将包括（i）缩短H-转移距离;（ii）极性效应;和/或（iii）具有异步转移 由于反应自由能面的不对称性，HAT和MS-CPET工艺 可能以不同的方式涉及这些因素。 生物系统中O-H键的氧化通常通过MS-CPET发生，质子转移到 氢键结合的基础上耦合到长距离电子转移。实例范围从酪氨酸-组氨酸 在光系统II中与核糖核苷酸还原酶中的多个酪氨酸配对。我们最近对蒽的研究- 苯酚-吡啶三元组提供了新的方法来解开影响这些反应的关键参数， 固有的障碍，振动耦合，和性质的氢键。这些系统经历了非常快速的 光诱导PCET，包括Marcus反转区域中的PCET的第一示例，并且可以用 各种替代品。这是一个很好的平台，以研究在氢气中的MS-CPET的关键参数- 键合系统，这是常见的生化反应。 本计画将建构一个更全面及量化的了解其内在性质 与一系列重要的生物化学过程相关的PCET。这些基本的见解 C-H和O-H键的氧化还原反应将有助于揭示生物学如何进化以控制困难的转化。

PROJECT SUMMARY/ABSTRACT The proposed research will develop a conceptual and quantitative framework for proton-coupled electron transfer (PCET) processes, in which the proton and electron transfer in a single chemical step. Such reactions are key to a wide range of essential biochemical processes, including respiration, photosynthesis and other aspects of bioenergetics, catalysis in oxidoreductases and other metalloenzymes, and the behavior of reactive oxygen species and antioxidants. These chemical reactions vary from hydrogen atom transfer (HAT), in which the two particles move ‘together,’ to processes where the proton and electron move to (or come from) different locations (multiple-site concerted proton-electron transfers, MS-CPET). Building on our prior studies and the specific advances in the last period. this project will examine how the rates and selectivities of such reactions are controlled by factors beyond the thermochemistry. Many biochemical processes interconvert carbon-centered radicals and C–H bonds, yet some of their reactions have little if any precedent in standard organic chemistry. For example, isoergic and uphill H-transfer between carbon atoms are extremely slow in solution, yet such reactions are widely used by the enzyme families with radical-SAM and vitamin B-12 cofactors, often reversibly. There are few solution examples of MS-CPET reactions of C–H bonds, yet these are predicted to be used in various enzymes in biology. Experiments using both organic and transition metal model systems will probe the essential properties of these reactions. These will include (i) shortening the H-transfer distance; (ii) polar effects; and/or (iii) having asynchronous transfer of the electron and proton due to asymmetry of the reaction free energy surface. HAT and MS-CPET processes may involve these factors in different ways. The oxidations of O–H bonds in biological systems often occur by MS-CPET, with proton transfer to a hydrogen-bonded base coupled to long-distance electron transfer. Examples range from the tyrosine-histidine pair in photosystem II to the multiple tyrosines in ribonucleotide reductases. Our recent studies of anthracene- phenol-pyridine triads provide new approaches to disentangle the key parameters affecting these reactions, their intrinsic barriers, vibronic couplings, and the nature of the hydrogen bonds. These systems undergo very rapid photo-induced PCET, including the first example of PCET in the Marcus Inverted Region, and can be tuned with various substitutions. This is an excellent platform to investigate the key parameters of MS-CPET in hydrogen- bonded systems, which are common biochemical reactions. This project will construct a more comprehensive and quantitative understanding of the intrinsic properties of PCET that are relevant to a range of important biochemical processes. These fundamental insights about redox reactions of C–H and O–H bonds will help unravel how biology evolved to control difficult transformations.