| NSF Org: |
CHE Division Of Chemistry |
| Recipient: |
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| Initial Amendment Date: | April 16, 2018 |
| Latest Amendment Date: | June 21, 2021 |
| Award Number: | 1800105 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Tong Ren
CHE Division Of Chemistry MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | September 1, 2018 |
| End Date: | August 31, 2022 (Estimated) |
| Total Intended Award Amount: | $420,000.00 |
| Total Awarded Amount to Date: | $488,766.00 |
| Funds Obligated to Date: |
FY 2019 = $280,000.00 FY 2021 = $68,766.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
1805 N BROAD ST PHILADELPHIA PA US 19122-6104 (215)707-7547 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1901 N. 13th St Philadelphia PA US 19122-6018 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Chemical Catalysis |
| Primary Program Source: |
01001920DB NSF RESEARCH & RELATED ACTIVIT 01002122DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.049 |
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.
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The generation of oxygen by higher plants from sunlight and water is the most important fundamental process for fueling the complex life that exists on earth. The high-energy electrons extracted from water ultimately are used by the plants to make food for themselves, and for heterotrophs that consume plants, which form the base of the food web that extends across the planet. The generation of oxygen gas and hydrogen fuel from water and sunlight is also an important goal for humanity to achieve a renewable energy economy, and catalysts to achieve this may be inspired by nature's oxygen evolving catalyst. Our work has made important strides in the last three years towards understanding how nature achieves This goal by generating reactive molecules similar in structure and reactivity to nature's catalyst, the Oxygen Evolving Complex (OEC, Figure 1, center). The OEC is a cube-shaped cluster with manganese metal ions at three corners, and a calcium at the fourth corner. A fourth "dangler" manganese atom forms the back of a chair-like structure. While many groups have prepared structural models or catalysts that perform this reaction, we have striven to generate synthetic models of this cluster in the lab that are similar structurally AND reactively.
During this award period, we performed new experiments on a manganese cubane cluster with a "dangler" manganese ion (Compound 1, Figure 1, left). We showed previously that despite it's similarity to the OEC and it's unique dangler manganese-oxygen group, this cluster does not oxidize water or generate oxygen. However, we showed that by removing one of the three oxygen atoms on the dangler, we generate a more reduced version of the cluster that does spontaneously evolve oxygen. This is the first example of a synthetic cubane cluster with a dangler manganese that evolves O2, and it does so from a state of oxidation similar to nature's cluster (one manganese(V) ion and the rest are manganese(IV) ions; this means one manganese has a formal 5+ charge and the others have a formal 4+ charge).
In another objective, we can generated a different cluster. This one is a manganese-calcium cluster very similar in structure to the OEC, Cluster 2 (Figure 1 right). This cluster is an improvement over cluster 1 in that it has both calcium and manganese, and in that it has bridging oxygen atoms between the metal ions. However, it is much more reduced (has more electrons) than nature's cluster. Nevertheless, this cluster, when oxidized by an electrode, activates water molecules when they are in a dilute solution of organic solvent, showing that this structural and compositional analog of the OEC can activate water for oxidation reactions. However, rather than generating oxygen, this molecule oxidized the organic solvent in which the system was dissolved.
In the third objective, we sought to make versions of compound 2 that are soluble in pure water, so that we can avoid the undesirable reaction with the solvent. In the final year of the project, we achieved this, and isolated two water soluble molecules: compounds 13 and 14, shown in Figure 2. These may be dissolved in polar solvent like water, and we will propose to study their biomimetic reactivity in our future work.
With support from NSF, we have demonstrated the generation of synthetic clusters that possess BOTH structural and reactive similarity to the OEC, which is rare. These are important steps toward understanding how nature achieves the generation of oxygen from water, and possibly to inform design of catalysts that can achieve humanity's goal of solar water splitting.
Last Modified: 12/30/2022
Modified by: Michael J Zdilla
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