Past Seminars and Events 2017

Abstract:
Understanding the chemical principles of natural photosynthetic water oxidation has advanced to a point where it has already been applied to designing artificial catalysts for water splitting and will be used in future devices for applications to energy storage and solar fuels. Among the design principles for catalysis learned from Nature: use 4 redox active metal  atoms (manganese) as catalyst to store 4 holes needed for the overall reaction, avoid high energy steps by separating H+/e- steps, avoid free H2O2 formation by achieving the concerted four electron pathway directly to the O2 product, use a slow catalyst (manganese) that has slow recombination kinetics thus allowing operation at low solar intensities, tune the Mn oxidation potentials by coordination to a Ca ion via oxo-bridges, coordinate them in two structural forms – cubane CaMn3O4 and gateway MnOCa, direct substrate water binding to occur at a gateway Mn ion, use carboxylate ligands to control the coordination geometry and deprotonate substrate waters, raise the oxidation potential of the gateway Mn(III) to suppress its oxidation until the final oxidation reaction that triggers water oxidation and O-O bond formation. Recent results from model complexes and from first principles calculations on the mechanism of the enzyme (collaboration with David Case and He Chen) will be presented.