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Deprotonation of Water/Hydroxo Ligands in Clusters Mimicking the Water Oxidizing Complex of PSII and Its Effect on the Vibrational Frequencies of Ligated Carboxylate Groups.

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Title: Deprotonation of Water/Hydroxo Ligands in Clusters Mimicking the Water Oxidizing Complex of PSII and Its Effect on the Vibrational Frequencies of Ligated Carboxylate Groups.
Authors: Wooi Yee Chuah1 wychuah@yahoo.com, Stranger, Rob1 Rob.Stranger@anu.edu.au, Pace, Ron J.1 Ron.Pace@anu.edu.au, Krausz, Elmars1 krausz@rsc.anu.edu.au, Frankcombe, Terry J.1,2 t.frankcombe@adfa.edu.au
Source: Journal of Physical Chemistry B. Jan2016, Vol. 120 Issue 3, p377-385. 9p.
Subjects: Proton transfer reactions, Ligand analysis, Water analysis, Frequencies of oscillating systems, Carboxylates
Abstract: The IR absorptions of several first-shell carboxylate ligands of the water oxidizing complex (WOC) have been experimentally shown to be unaffected by oxidation state changes in the WOC during its catalytic cycle. Several model clusters that mimic the Mn4O5Ca core of the WOC in the S1 state, with electronic configurations that correspond to both the so-called "high" and "low" oxidation paradigms, were investigated. Deprotonation at W2, W1, or O3 sites was found to strongly reduce carboxylate ligand frequency shifts on oxidation of the metal cluster. The frequency shifts were smallest in neutrally charged clusters where the initial mean Mn oxidation state was +3, with W2 as an hydroxide and O5 a water. Deprotonation also reduced and balanced the oxidation energy of all clusters in successive oxidations. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:The IR absorptions of several first-shell carboxylate ligands of the water oxidizing complex (WOC) have been experimentally shown to be unaffected by oxidation state changes in the WOC during its catalytic cycle. Several model clusters that mimic the Mn4O5Ca core of the WOC in the S1 state, with electronic configurations that correspond to both the so-called "high" and "low" oxidation paradigms, were investigated. Deprotonation at W2, W1, or O3 sites was found to strongly reduce carboxylate ligand frequency shifts on oxidation of the metal cluster. The frequency shifts were smallest in neutrally charged clusters where the initial mean Mn oxidation state was +3, with W2 as an hydroxide and O5 a water. Deprotonation also reduced and balanced the oxidation energy of all clusters in successive oxidations. [ABSTRACT FROM AUTHOR]
ISSN:15206106
DOI:10.1021/acs.jpcb.5b09987