Synthetic Models of the Oxygen Evolving Complex of Photosystem II

California Institute Of Technology, Pasadena CA

Investigators

Abstract

With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Agapie to study the way in which the structure of clusters of manganese and calcium ions affect their ability to convert water into molecular oxygen. This research can provide information about the chemical reactions that underscores photosynthesis in plants, the process by which the plants capture solar energy and use it to transform carbon dioxide and water molecules in other, more complex molecules like sugars needed for their survival. The conversion of water to oxygen is catalyzed in plants by a manganese and calcium cluster and Dr. Agapie synthesizes analogues in his lab. Dr. Agapie and his team study the reactions of these artificial analogues in comparison with the natural systems. The results of his research provide information on how to build catalysts from different metal ions that may be used in artificial photosynthesis. These studies allow graduate students to acquire expertise in a range of synthetic and analytical characterization techniques for complex coordination compounds and to prepare for 21st century STEM careers. Dr. Agapie's research lab performs structure-reactivity studies of a series of manganese cluster models of the Oxygen Evolving Complex (OEC). OEC is responsible for converting water into oxygen in Photosystem II (PSII), a protein complex that captures photons from sunlight and uses them to create electrons needed in chemical reactions in plants. The conversion of water to dioxygen is important for energy storage and conversion in artificial photosynthesis. The transformation of water into oxygen generates reducing equivalents used to transform low-energy precursors, such as carbon dioxide into energy-rich ones, such as sugars (in biological systems) or liquid hydrocarbons (an attractive target in artificial systems). Despite significant advances in the study of PSII, the atomic level mechanism of water oxidation continues to be debated. Supported by preliminary results that demonstrate that structural motifs relevant to the OEC and desired O-O bond formation chemistry can be accessed, mechanistic and reactivity studies are performed. Cluster models of the OEC displaying the dangler metal motif are prepared. In these clusters, the metal centers are site differentiated, which allows for systematic evaluation of the effect of remote metals on their properties. The effect of the cluster geometry, composition, redox state and spin state, on reactivity and spectroscopy are addressed. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.