Energetics of proton-coupled electron transfer in high-valent Mn{sup 2} ({mu}-O){sup 2} systems: Models for water oxidation by the oxygen-evolving complex of photosystem II
- Univ. of Michigan, Ann Arbor, MI (United States)
Structural studies of the intermediate S-states of the oxygen evolving complex (OEC) by X-ray absorption spectroscopy have suggested a structural motif for the tetranuclear manganese cluster consisting of a pair of bis oxo-bridged, high-valent Mn dimers [Mn{sup 2}({mu}-O){sup 2}]. In order to understand the possible roles for the Mn{sup 2}({mu}-O){sup 2} structural unit in the chemistry of the OEC, we have studied a series of model complexes that are also effective catalysts of H{sup 2}O{sup 2} disproportionation, reminiscent of the catalase activity in the S{sup 2}{yields}S{sup 0} cycle. Thus the [Mn(X-salpn)({mu}-O)]{sup 2} complexes are both structural and partial functional models for the OEC. Here, we explore the energetics of proton-coupled electron transfer from protonated Mn{sup 2}({mu}-O){sup 2} units by studying the individual energy contributions of the oxidation and deprotonation steps for [Mn(X-salpn)({mu}-O)]{sup 2} with X = H, 3,5-di(Cl), and 3,5-di(NO{sup 2}). Providing a range of 8 pK{sup a} units and 800 mV for each oxidation or protonation state, these complexes allow quantitation of the critical role protons may play in the highly efficient oxidation of the OEC. 21 refs., 1 fig., 1 tab.
- OSTI ID:
- 426232
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 45 Vol. 118; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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