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Photosynthesis, one of Nature’s most essential processes, is known to be reliant on the oxidation of water to dioxygen. However, this process has yet to be synthetically replicated, or its mechanism fully elucidated. Fundamental understanding of nature’s water oxidation reaction could offer clues to the design of superior catalysts for solar water splitting as a source of alternative energy. In order to work towards this, various structural mimics of nature’s CaMn4 water oxidation catalyst (the Oxygen Evolving Complex) have been synthesized and characterized. These clusters were prepared from Manganese and Cobalt, precursors and complexed to 2-pyridinemethanol. The resulting biomimetic models consisted of Mn-O and Co-O bridges, which are similar to the nature of the OEC itself. Electrocatalytic reactivity of these systems will be presented.
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Geometrically flexible synthetic manganese-oxygen and calcium-manganese-oxygen cubane clusters as reactive biomimics of the oxygen evolving complex of photosystem II.
The oxygen evolving complex (OEC) of photosystem II is responsible for the four-electron oxidation of water to dioxygen in oxygenic photosynthetic organisms. These organisms use light to drive this thermodynamically uphill process to harvest high-energy electrons from water for cellular energy, generating O2 as a byproduct. While numerous details of the operation of the OEC are well understood, the molecular mechanism of O=O formation remains under debate. Model complex chemistry from our group will be presented wherein we have prepared cluster systems with little or no terminal multidentate ligation in order to generate geometrically flexible and reactive clusters. Two systems will be presented: a series of Ca-Mn-O hemicubane clusters with variable calcium content, and their electrocatalytic activity in activation of water in oxidation reactions, and a Mn cubane cluster with a pendant Mn=O moiety that evolves dioxygen from an oxidation state analagous to the turnover state of the natural system
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- Award ID(s):
- 1800105
- PAR ID:
- 10187690
- Date Published:
- Journal Name:
- ACS Spring 2020 National Meeting and Expo
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Water oxidation and concomitant dioxygen formation by the manganese-calcium cluster of oxygenic photosynthesis has shaped the biosphere, atmosphere, and geosphere. It has been hypothesized that at an early stage of evolution, before photosynthetic water oxidation became prominent, light-driven formation of manganese oxides from dissolved Mn(2+) ions may have played a key role in bioenergetics and possibly facilitated early geological manganese deposits. Here we report the biochemical evidence for the ability of photosystems to form extended manganese oxide particles. The photochemical redox processes in spinach photosystem-II particles devoid of the manganese-calcium cluster are tracked by visible-light and X-ray spectroscopy. Oxidation of dissolved manganese ions results in high-valent Mn(III,IV)-oxide nanoparticles of the birnessite type bound to photosystem II, with 50-100 manganese ions per photosystem. Having shown that even today’s photosystem II can form birnessite-type oxide particles efficiently, we propose an evolutionary scenario, which involves manganese-oxide production by ancestral photosystems, later followed by down-sizing of protein-bound manganese-oxide nanoparticles to finally yield today’s catalyst of photosynthetic water oxidation.more » « less
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A series of Ca–Mn clusters with the ligand 2-pyridinemethoxide (Py-CH 2 O) have been prepared with varying degrees of topological similarity to the biological oxygen-evolving complex. These clusters activate water as a substrate in the oxidative degradation of propylene carbonate, with activity correlated with topological similarity to the OEC, lowering the onset potential of the oxidation by as much as 700 mV.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1021/scimeetings.0c03947
