Models of the Photosynthetic Oxygen-Evolving Complex

在这个由化学系化学催化计划资助的项目中，佛罗里达大学的乔治·克里斯托教授合成并研究了与放氧复合体(OEC)相关的化合物。OEC存在于植物和某些细菌中，25亿多年来，人们一直在利用阳光将水转化为氧气。因此，OEC负责生产和维护大气中的氧气，所有呼吸生命都依赖于它。OEC太脆弱，无法从自然来源中分离出来；因此，研究人员正寻求在实验室合成OEC，以研究其特性和它是如何制造氧气的。克里斯托实验室将为OEC合成模型化合物，并研究它们催化水转化为氧气的能力。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在合成和专业技术方面获得高级培训的机会，如磁化学和水氧化的电催化。本研究的目标是合成和研究作为OEC模型的Mn4Ca/oxo簇合物，使用最近发展起来的方法来制备混合的Mn/Ca立方烷化合物。将合成具有螯合诱导的结构扰动的衍生物，模拟多肽支架对OEC的影响，以及具有不同氧化状态的锰和以锶代替钙的衍生物，锶是唯一可以在保持显著活性的情况下取代钙的OEC中的金属。通过磁性测量以及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。这项拟议的工作将能够检验目前关于OEC结构扭曲的精确水平及其对OEC性质的影响的假设，关于锶取代的OEC是否与钙型同构，以及关于OEC在给定的氧化水平下与生成条件的电子性质截然不同的起源的假设。OEC模型和其他合成的锰化合物也将作为功能模型进行探索，即作为水氧化为氧的电催化剂，基于某些锰羧酸簇合物具有低过电位的这种活性的发现。

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.