"Light Induced Water Oxidation:
Comparison of Mechanism in Photosystem II and Ru-based Molecular Catalyst"
CCB Special Seminar Series
|Speaker: Yulia Pushkar
Department of Physics and Astronomy
Abstract: The light driven water splitting achieved in the oxygen evolving complex (OEC) of Photosystem II is a critical process that sustains our biosphere. Photosynthetic water splitting is fascinating in its efficiency, however, it is not yet understood. Water oxidation catalysis is a critical component of future solar fuel production. At the heart of the water splitting process is the Mn4Ca cluster embedded in a fine tuned protein environment. While Mn is an earth abundant element, efficient Mn based molecular catalysts have not been yet demonstrated. Ru based molecular catalysts of water oxidation are available with variety of ligand environments and provide convenient systems for mechanistic analysis. In these catalysts chemical ligation affects the redox properties and catalytic reactivity but no structure-activity relationships are currently known. Researchers still have to develop catalysts by a trial-and-error approach. Upon oxidation (chemical, electrochemical or light induced) water splitting catalysts undergo proton coupled electron transfer (PCET), where protons are removed from the water ligand with formation of reactive Metal=O fragments. In this study we used in situ EPR, X-ray spectroscopy and resonance Raman measurements to characterize catalytic Ru complexes under water oxidation conditions and detect reactive intermediates. [1,2] In Photosystem II laser pump X-ray probe time resolved measurements allowed to follow evolution of electronic structure in the OEC and catalysis with microsecond time resolution. DFT analysis of PS II  and Ru complexes and comparison of mechanisms was conducted to predict changes in the Gibbs energies of catalytic steps and search for structure – activity relationships.
|Host: Professor Charles Dismukes|
|~ Coffee/tea will be served prior to lecture ~|