Understanding Coupled Transfers of Electrons and Protons

描述(申请人提供)：许多生化过程涉及电子和质子的耦合转移。例如，对于一系列酶(例如，细胞色素C氧化酶、光系统I和II、细胞色素P450)和在捕捉活性氧物种(例如，通过维生素E和超氧化物歧化酶)方面，这是一个关键步骤。拟议研究的目标是对这些过程有一个基本的和预测性的理解。这种理解在一系列生化系统中将是有价值的，就像目前关于纯电子转移的知识非常有价值一样。拟议的工作包括各种化合物、反应和技术，以揭示化学的基本特征。 氢原子转移反应是该提议的主要焦点，基于最近的发现，一系列H原子转移反应遵循马库斯交叉关系。马库斯方法能够预测反应速率，并根据驱动力和内在障碍为这些反应提供新的基本直觉。内在的障碍可以通过研究自身交换率来测量，这将被确定为许多化合物。我们将研究电子、质子和氢原子转移的本征势垒之间的关系。讨论了氢化物转移反应的扩展，包括马库斯方法的可能应用。 将发展分子内质子转移与分子间电子转移相耦合的新化学体系。这种质子耦合电子转移(PCET)过程是非常常见的，例如在光系统II中酪氨酸Z-组氨酸单元的氧化过程中。在这类系统中，质子转移是否先于、之后或与电子转移相协调将被确定。我们将利用反应的内在势垒和热力学来探讨采用这样或那样的机制的原因。还将研究涉及金属过氧化物络合物的化学反应，包括分离的过氧化物反应和可能形成O-O键的反应。 这项拟议的工作具有广泛的视角--研究铁、钴、锰、Ru和Os体系以及各种类型的反应--以便为生物学中发生的各种质子耦合电子转移提供新的和有价值的见解。

DESCRIPTION (provided by applicant): Many biochemical processes involve the coupled transfer of electrons and protons. This is a key step, for instance, for a range of enzymes (e.g., cytochrome c oxidase, photosystems I and II, cytochromes P450) and in the trapping of reactive oxygen species (e.g., by vitamin E and superoxide dismutases). The goal of the proposed research is to develop a fundamental and predictive understanding of these processes. This understanding will be valuable in a range of biochemical systems, much as the current knowledge of pure electron transfer has been very valuable. The proposed work encompasses a variety of compounds, reactions, and techniques to uncover the essential features of the chemistry. Hydrogen atom transfer reactions are a primary focus of the proposal, building on the recent discovery that a range of H-atom transfer reactions follow the Marcus cross relation. The Marcus approach enables prediction of reaction rates and provides a new fundamental intuition for these reactions, based on driving force and intrinsic barriers. The intrinsic barriers can be measured through studies of self-exchange rates, which will be determined for a number of compounds. The relationship between the intrinsic barriers for electron, proton, and hydrogen atom transfer will be examined. Extensions to hydride transfer reactions are discussed, including possible application of the Marcus approach. New chemical systems will be developed in which an intramolecular proton transfer is coupled to intermolecular electron transfer. Such proton-coupled electron transfer (PCET) processes are very common, as in the oxidation of the tyrosine Z-histidine unit in photosystem II. It will be determined whether proton transfer precedes, succeeds, or is concerted with electron transfer in such systems. The reasons for adopting one mechanism or another will be probed, using the intrinsic barriers and thermodynamics of the reactions. Chemical reactions that involve metal peroxide complexes will also be examined, both reactions of isolated peroxides and reactions that could form O-O bonds. The proposed work takes a broad view - studying iron, cobalt, manganese, ruthenium and osmium systems and a variety of types of reactions - in order to provide new and valuable insights into the various kinds of proton-coupled electron transfer that occur in biology.