Distinct mechanisms of bridging-oxo exchange in di-μ-O dimanganese complexes with and without water-binding sites

Implications for water binding in the O2-evolving complex of photosystem II

Ranitendranath Tagore, Robert H. Crabtree, Gary W Brudvig

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Abstract

Isotopic exchange between oxygens of water and μ-O bridges in the di-μ-O dimanganese complexes, [(mesterpy)2Mn2 III/IV(μ-O)2(H2O)2](NO 3)3 (1, mes-terpy = 4′-mesityl-2,2′:6′, 2″-terpyridine) and [(phen)4Mn2 III/IV(μ-O)2](ClO4)3 (2, phen = 1,10-phenanthroline), has been investigated by a study of the kinetics of exchange. The data provide evidence for distinct mechanisms of exchange in 1 and 2 and suggest that these differences arise due to the presence and absence of terminal water-binding sites in 1 and 2, respectively. Exchange of oxygen atoms between water and μ-O bridges must involve the elementary steps of bridge protonation, deprotonation, opening, and closing. On the basis of the existing literature on these reactions in oxo-bridged metal complexes and our present data, we propose pathways of exchange in 1 and 2. The mechanism proposed for 1 involves an initial fast protonation of an oxo-bridge by water coordinated to MnIV, followed by a slow opening of the protonated bridge as proposed earlier for an analogous complex on the basis of DFT calculations. The mechanism proposed for 2 involves initial dissociation of phen, followed by coordination of water at the vacated sites, as observed for rearrangement of 2 to a trinuclear complex. The subsequent steps are proposed to be analogous to those for 1. Our results are discussed in the context of data on 18O-labeled water isotope exchange in photosystem II and provide support for the existence of fully protonated terminal waters bound to Mn in the O2-evolving complex of photosystem II.

Original languageEnglish
Pages (from-to)2193-2203
Number of pages11
JournalInorganic Chemistry
Volume46
Issue number6
DOIs
Publication statusPublished - Mar 19 2007

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Photosystem II Protein Complex
Binding Sites
Water
water
Protonation
Oxygen
Deprotonation
Plant shutdowns
Coordination Complexes
closing
Discrete Fourier transforms
Isotopes
oxygen atoms
Ion exchange
isotopes
dissociation
Atoms
Kinetics
kinetics
oxygen

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

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title = "Distinct mechanisms of bridging-oxo exchange in di-μ-O dimanganese complexes with and without water-binding sites: Implications for water binding in the O2-evolving complex of photosystem II",
abstract = "Isotopic exchange between oxygens of water and μ-O bridges in the di-μ-O dimanganese complexes, [(mesterpy)2Mn2 III/IV(μ-O)2(H2O)2](NO 3)3 (1, mes-terpy = 4′-mesityl-2,2′:6′, 2″-terpyridine) and [(phen)4Mn2 III/IV(μ-O)2](ClO4)3 (2, phen = 1,10-phenanthroline), has been investigated by a study of the kinetics of exchange. The data provide evidence for distinct mechanisms of exchange in 1 and 2 and suggest that these differences arise due to the presence and absence of terminal water-binding sites in 1 and 2, respectively. Exchange of oxygen atoms between water and μ-O bridges must involve the elementary steps of bridge protonation, deprotonation, opening, and closing. On the basis of the existing literature on these reactions in oxo-bridged metal complexes and our present data, we propose pathways of exchange in 1 and 2. The mechanism proposed for 1 involves an initial fast protonation of an oxo-bridge by water coordinated to MnIV, followed by a slow opening of the protonated bridge as proposed earlier for an analogous complex on the basis of DFT calculations. The mechanism proposed for 2 involves initial dissociation of phen, followed by coordination of water at the vacated sites, as observed for rearrangement of 2 to a trinuclear complex. The subsequent steps are proposed to be analogous to those for 1. Our results are discussed in the context of data on 18O-labeled water isotope exchange in photosystem II and provide support for the existence of fully protonated terminal waters bound to Mn in the O2-evolving complex of photosystem II.",
author = "Ranitendranath Tagore and Crabtree, {Robert H.} and Brudvig, {Gary W}",
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TY - JOUR

T1 - Distinct mechanisms of bridging-oxo exchange in di-μ-O dimanganese complexes with and without water-binding sites

T2 - Implications for water binding in the O2-evolving complex of photosystem II

AU - Tagore, Ranitendranath

AU - Crabtree, Robert H.

AU - Brudvig, Gary W

PY - 2007/3/19

Y1 - 2007/3/19

N2 - Isotopic exchange between oxygens of water and μ-O bridges in the di-μ-O dimanganese complexes, [(mesterpy)2Mn2 III/IV(μ-O)2(H2O)2](NO 3)3 (1, mes-terpy = 4′-mesityl-2,2′:6′, 2″-terpyridine) and [(phen)4Mn2 III/IV(μ-O)2](ClO4)3 (2, phen = 1,10-phenanthroline), has been investigated by a study of the kinetics of exchange. The data provide evidence for distinct mechanisms of exchange in 1 and 2 and suggest that these differences arise due to the presence and absence of terminal water-binding sites in 1 and 2, respectively. Exchange of oxygen atoms between water and μ-O bridges must involve the elementary steps of bridge protonation, deprotonation, opening, and closing. On the basis of the existing literature on these reactions in oxo-bridged metal complexes and our present data, we propose pathways of exchange in 1 and 2. The mechanism proposed for 1 involves an initial fast protonation of an oxo-bridge by water coordinated to MnIV, followed by a slow opening of the protonated bridge as proposed earlier for an analogous complex on the basis of DFT calculations. The mechanism proposed for 2 involves initial dissociation of phen, followed by coordination of water at the vacated sites, as observed for rearrangement of 2 to a trinuclear complex. The subsequent steps are proposed to be analogous to those for 1. Our results are discussed in the context of data on 18O-labeled water isotope exchange in photosystem II and provide support for the existence of fully protonated terminal waters bound to Mn in the O2-evolving complex of photosystem II.

AB - Isotopic exchange between oxygens of water and μ-O bridges in the di-μ-O dimanganese complexes, [(mesterpy)2Mn2 III/IV(μ-O)2(H2O)2](NO 3)3 (1, mes-terpy = 4′-mesityl-2,2′:6′, 2″-terpyridine) and [(phen)4Mn2 III/IV(μ-O)2](ClO4)3 (2, phen = 1,10-phenanthroline), has been investigated by a study of the kinetics of exchange. The data provide evidence for distinct mechanisms of exchange in 1 and 2 and suggest that these differences arise due to the presence and absence of terminal water-binding sites in 1 and 2, respectively. Exchange of oxygen atoms between water and μ-O bridges must involve the elementary steps of bridge protonation, deprotonation, opening, and closing. On the basis of the existing literature on these reactions in oxo-bridged metal complexes and our present data, we propose pathways of exchange in 1 and 2. The mechanism proposed for 1 involves an initial fast protonation of an oxo-bridge by water coordinated to MnIV, followed by a slow opening of the protonated bridge as proposed earlier for an analogous complex on the basis of DFT calculations. The mechanism proposed for 2 involves initial dissociation of phen, followed by coordination of water at the vacated sites, as observed for rearrangement of 2 to a trinuclear complex. The subsequent steps are proposed to be analogous to those for 1. Our results are discussed in the context of data on 18O-labeled water isotope exchange in photosystem II and provide support for the existence of fully protonated terminal waters bound to Mn in the O2-evolving complex of photosystem II.

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