Conformationally-flexible, reactive manganese clusters to probe possible mechanisms of oxygen-oxygen bond formation in photosystem II

Temple University, Philadelphia PA

Investigators

Abstract

In the early stages of the development of life on earth, perhaps the most significant evolutionary breakthrough was the sunlight-driven oxidation of water to oxygen (O2) by the ancient ancestors of cyanobacteria and modern plants. These organisms discovered a way to make their own food using the virtually limitless supply of water and sunlight available near the surface of the oceans. As far as science knows, organisms have found only one way to perform this water oxidation process, and it is possible that modern plants and photosynthetic organisms are still using that same evolutionary innovation from billions of years ago, although presumably significantly evolved. The enzyme that performs this reaction is called Photosystem II, and despite the central importance of this reaction to the fields of biology and energy, many questions remain about how this enzyme works. Professor Zdilla is working to build molecular models of the enzyme active site, which is a cube-shaped cluster of metal atoms containing manganese and calcium. The working models developed by Professor Zdilla may lead to insights on how photosynthetic organisms are able to perform this important reaction. Professor Zdilla continues his community engagement of youth and adult communities through talks during the Philadelphia Science Festival and at Philadelphia elementary schools. Professor Zdilla also develops the Database of Educational Crystallographic Online Resources (DECOR), a free, downloadable source of educational materials for the study of crystallography. The primary source of cellular energy on earth is the sun, whose visible light energy is harvested by photosynthetic organisms to drive the oxidation of water to O2 and drive the concomitant reduction of carbon dioxide(CO2) to organic molecules, which are then used as fuel and as raw materials for the construction of living things. Photocatalytic water oxidation coupled to proton reduction is also an important goal for the generation of sustainable solar fuels. The enzyme responsible for the biological water oxidation reaction is photosystem II (PSII), a multi-subunit enzyme containing a tetramanganese-calcium-oxo cluster as the catalytic active site. Since enzymes are often a challenge to study directly due to their complexity, bioinorganic chemists frequently turn to biomimetic model complexes. Despite hundreds of examples of synthetic manganese oxo-cluster, very few show compelling reactivity that models PSII. Professor Zdilla and his group develop new approaches to designing biomimetic manganese clusters by prioritizing low-coordination number(to provide water binding sites) and cluster flexibility (to promote molecular rearrangement). These approaches have resulted in clusters that perform a diverse set of difficult reactions including N-N, C-H, C-N, and O=O bond making/breaking reactions, and catalytic water oxidation. This project seeks to further mechanistically investigate their molecular mechanisms, which may inform understanding of the function of the enzyme, and provide clues on how to design superior water oxidation catalysts for energy purposes. Professor Zdilla continues his community engagement of youth and adult communities through talks during the Philadelphia Science Festival and at Philadelphia elementary schools. Professor Zdilla also develops the Database of Educational Crystallographic Online Resources (DECOR), a free source of educational materials for the study of crystallography. 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.