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.
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.
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, Australian Capital Territory 2601, Australia.
authors.forename: Wooi Yee
authors.initials: WY
authors.lastname: Chuah
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, Australian Capital Territory 2601, Australia.
authors.forename: Rob
authors.initials: R
authors.lastname: Stranger
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, Australian Capital Territory 2601, Australia.
authors.forename: Ron J
authors.initials: RJ
authors.lastname: Pace
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, Australian Capital Territory 2601, Australia.
authors.forename: Elmars
authors.initials: E
authors.lastname: Krausz
authors.affiliation: Research School of Chemistry, Australian National University , Canberra, Australian Capital Territory 2601, Australia.|School of Physical, Environmental and Mathematical Sciences, University of New South Wales , Canberra, Australian Capital Territory 2600, Australia.
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Frankcombe
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry; D008024:Ligands; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D011522:Protons; D014867:Water
chemical_list: D002264:Carboxylic Acids; D008024:Ligands; D045332:Photosystem II Protein Complex; D011522:Protons; D014867:Water