Models of the Photosynthetic Oxygen-Evolving Complex

在这个由化学部化学催化项目资助的项目中，佛罗里达大学的George Christou教授合成并研究了与氧进化复合物（OEC）相关的化合物。OEC存在于植物和某些细菌中，在超过25亿年的时间里，它一直在利用阳光作为能源将水转化为氧气。因此，OEC负责生产和维持所有呼吸生命所依赖的大气氧气。OEC太脆弱，无法脱离自然资源；因此，研究人员正在寻求在实验室中合成OEC，以研究其性质以及它如何制造氧气。Christou实验室将为OEC合成模型化合物，并研究它们催化水转化为氧的能力。这项研究对目前利用和储存太阳能的努力有更广泛的影响。它还为研究生提供了获得合成和专门技术（如磁化学和水氧化电催化）的高级培训的机会。本研究的目的是合成和研究作为OEC模型的Mn4Ca/oxo簇，使用最近开发的方法来制备混合Mn/Ca cubane化合物。将合成具有螯合剂诱导的结构扰动的衍生物，模拟肽支架对OEC的影响，以及具有不同氧化态的锰和以锶代替钙的衍生物，Sr是唯一可以在OEC中取代Ca并保留显著活性的金属。通过磁测量、EPR和x射线光谱对化合物进行表征将为OEC的研究提供有用的基准。拟议的工作将能够测试关于OEC结构扭曲的精确程度及其对OEC性质的影响的现有假设，关于sr取代的OEC是否与Ca形式是同结构的，以及关于OEC在给定氧化水平和取决于生成条件下明显不同的电子性质的起源。OEC模型和其他合成Mn化合物也将作为功能模型进行探索，即作为水氧化成氧的电催化剂，建立在某些Mn羧酸盐簇的低过电位活性的基础上。

In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professor George Christou of the University of Florida synthesizes and studies compounds related to the oxygen-evolving complex (OEC). The OEC is found in plants and certain bacteria, and for over 2½ billion years has been converting water to oxygen gas using sunlight as an energy source. Hence the OEC is responsible for the production and maintenance of the atmospheric oxygen on which all respiring life depends. The OEC is too fragile to be isolated from natural sources; therefore researchers are seeking to synthesize the OEC in the laboratory to study its properties and how it makes oxygen. The Christou lab will synthesize model compounds for OEC and study their ability to catalyze conversion of water to oxygen. This research has broader impacts on current efforts to harness and store solar energy. It also creates opportunities for graduate students to acquire advanced training in synthesis and specialized techniques such as magnetochemistry and electrocatalysis of water oxidation. The goal of the research is to synthesize and study Mn4Ca/oxo clusters as models of the OEC, using recently developed methodologies to make mixed Mn/Ca cubane compounds. Derivatives with chelate-induced, structural perturbations that mimic the effect of the peptide scaffold on the OEC will be synthesized, as will be derivatives with manganese in different oxidation states and with strontium instead of calcium, Sr being the only metal that can replace Ca in OEC with retention of significant activity. The characterization of the compounds by magnetic measurements, and by EPR and X-ray spectroscopy will provide benchmarks useful in the study of OEC. The proposed work will enable the testing of current hypotheses about the precise level of structural distortion of the OEC and its influence on the properties of OEC, about whether the Sr-substituted OEC is isostructural with the Ca form, and about the origin of the distinctly different, electronic properties of the OEC at a given oxidation level and depending on generation conditions. The OEC models and other synthetic Mn compounds will also be explored as functional models, namely as electrocatalysts for water oxidation to oxygen, building on the discovery of such activity with low overpotential by certain Mn carboxylate clusters.