Electrostatic effects on proton coupled electron transfer in oxomanganese complexes inspired by the oxygen-evolving complex of photosystem II

Muhamed Amin, Leslie Vogt, Serguei Vassiliev, Ivan Rivalta, Mohammad M. Sultan, Doug Bruce, Gary W Brudvig, Victor S. Batista, M. R. Gunner

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Abstract

The influence of electrostatic interactions on the free energy of proton coupled electron transfer in biomimetic oxomanganese complexes inspired by the oxygen-evolving complex (OEC) of photosystem II (PSII) are investigated. The reported study introduces an enhanced multiconformer continuum electrostatics (MCCE) model, parametrized at the density functional theory (DFT) level with a classical valence model for the oxomanganese core. The calculated pK a's and oxidation midpoint potentials (Em's) match experimental values for eight complexes, indicating that purely electrostatic contributions account for most of the observed couplings between deprotonation and oxidation state transitions. We focus on pKa's of terminal water ligands in [Mn(II/III)(H2O)6]2+/3+ (1), [Mn(III)(P)(H2O)2]3- (2, P = 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinato), [Mn 2(IV,IV)(μ-O)2(terpy)2(H2O) 2]4+ (3, terpy = 2,2′:6′,2″-terpyridine) , and [Mn3(IV,IV,IV)(μ-O)4(phen)4(H 2O)2]4+ (4, phen = 1,10-phenanthroline) and the pKa's of μ-oxo bridges and Mn Em's in [Mn 2(μ-O)2(bpy)4] (5, bpy = 2,2′-bipyridyl), [Mn2(μ-O)2(salpn)2] (6, salpn = N,N′-bis(salicylidene)-1,3-propanediamine), [Mn 2(μ-O)2(3,5-di(Cl)-salpn)2] (7), and [Mn2(μ-O)2(3,5-di(NO2)-salpn)2] (8). The analysis of complexes 6-8 highlights the strong coupling between electron and proton transfers, with any Mn oxidation lowering the pKa of an oxo bridge by 10.5 ± 0.9 pH units. The model also accounts for changes in the Em's by ligand substituents, such as found in complexes 6-8, due to the electron withdrawing Cl (7) and NO2 (8). The reported study provides the foundation for analysis of electrostatic effects in other oxomanganese complexes and metalloenzymes, where proton coupled electron transfer plays a fundamental role in redox-leveling mechanisms.

Original languageEnglish
Pages (from-to)6217-6226
Number of pages10
JournalJournal of Physical Chemistry B
Volume117
Issue number20
DOIs
Publication statusPublished - May 23 2013

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Photosystem II Protein Complex
Protons
Electrostatics
electron transfer
electrostatics
Oxygen
protons
Electrons
oxygen
Oxidation
oxidation
Ligands
2,2'-Dipyridyl
Deprotonation
ligands
Proton transfer
leveling
biomimetics
Biomimetics
Coulomb interactions

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Chemistry
  • Surfaces, Coatings and Films

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Electrostatic effects on proton coupled electron transfer in oxomanganese complexes inspired by the oxygen-evolving complex of photosystem II. / Amin, Muhamed; Vogt, Leslie; Vassiliev, Serguei; Rivalta, Ivan; Sultan, Mohammad M.; Bruce, Doug; Brudvig, Gary W; Batista, Victor S.; Gunner, M. R.

In: Journal of Physical Chemistry B, Vol. 117, No. 20, 23.05.2013, p. 6217-6226.

Research output: Contribution to journalArticle

Amin, Muhamed ; Vogt, Leslie ; Vassiliev, Serguei ; Rivalta, Ivan ; Sultan, Mohammad M. ; Bruce, Doug ; Brudvig, Gary W ; Batista, Victor S. ; Gunner, M. R. / Electrostatic effects on proton coupled electron transfer in oxomanganese complexes inspired by the oxygen-evolving complex of photosystem II. In: Journal of Physical Chemistry B. 2013 ; Vol. 117, No. 20. pp. 6217-6226.
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abstract = "The influence of electrostatic interactions on the free energy of proton coupled electron transfer in biomimetic oxomanganese complexes inspired by the oxygen-evolving complex (OEC) of photosystem II (PSII) are investigated. The reported study introduces an enhanced multiconformer continuum electrostatics (MCCE) model, parametrized at the density functional theory (DFT) level with a classical valence model for the oxomanganese core. The calculated pK a's and oxidation midpoint potentials (Em's) match experimental values for eight complexes, indicating that purely electrostatic contributions account for most of the observed couplings between deprotonation and oxidation state transitions. We focus on pKa's of terminal water ligands in [Mn(II/III)(H2O)6]2+/3+ (1), [Mn(III)(P)(H2O)2]3- (2, P = 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinato), [Mn 2(IV,IV)(μ-O)2(terpy)2(H2O) 2]4+ (3, terpy = 2,2′:6′,2″-terpyridine) , and [Mn3(IV,IV,IV)(μ-O)4(phen)4(H 2O)2]4+ (4, phen = 1,10-phenanthroline) and the pKa's of μ-oxo bridges and Mn Em's in [Mn 2(μ-O)2(bpy)4] (5, bpy = 2,2′-bipyridyl), [Mn2(μ-O)2(salpn)2] (6, salpn = N,N′-bis(salicylidene)-1,3-propanediamine), [Mn 2(μ-O)2(3,5-di(Cl)-salpn)2] (7), and [Mn2(μ-O)2(3,5-di(NO2)-salpn)2] (8). The analysis of complexes 6-8 highlights the strong coupling between electron and proton transfers, with any Mn oxidation lowering the pKa of an oxo bridge by 10.5 ± 0.9 pH units. The model also accounts for changes in the Em's by ligand substituents, such as found in complexes 6-8, due to the electron withdrawing Cl (7) and NO2 (8). The reported study provides the foundation for analysis of electrostatic effects in other oxomanganese complexes and metalloenzymes, where proton coupled electron transfer plays a fundamental role in redox-leveling mechanisms.",
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T1 - Electrostatic effects on proton coupled electron transfer in oxomanganese complexes inspired by the oxygen-evolving complex of photosystem II

AU - Amin, Muhamed

AU - Vogt, Leslie

AU - Vassiliev, Serguei

AU - Rivalta, Ivan

AU - Sultan, Mohammad M.

AU - Bruce, Doug

AU - Brudvig, Gary W

AU - Batista, Victor S.

AU - Gunner, M. R.

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N2 - The influence of electrostatic interactions on the free energy of proton coupled electron transfer in biomimetic oxomanganese complexes inspired by the oxygen-evolving complex (OEC) of photosystem II (PSII) are investigated. The reported study introduces an enhanced multiconformer continuum electrostatics (MCCE) model, parametrized at the density functional theory (DFT) level with a classical valence model for the oxomanganese core. The calculated pK a's and oxidation midpoint potentials (Em's) match experimental values for eight complexes, indicating that purely electrostatic contributions account for most of the observed couplings between deprotonation and oxidation state transitions. We focus on pKa's of terminal water ligands in [Mn(II/III)(H2O)6]2+/3+ (1), [Mn(III)(P)(H2O)2]3- (2, P = 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinato), [Mn 2(IV,IV)(μ-O)2(terpy)2(H2O) 2]4+ (3, terpy = 2,2′:6′,2″-terpyridine) , and [Mn3(IV,IV,IV)(μ-O)4(phen)4(H 2O)2]4+ (4, phen = 1,10-phenanthroline) and the pKa's of μ-oxo bridges and Mn Em's in [Mn 2(μ-O)2(bpy)4] (5, bpy = 2,2′-bipyridyl), [Mn2(μ-O)2(salpn)2] (6, salpn = N,N′-bis(salicylidene)-1,3-propanediamine), [Mn 2(μ-O)2(3,5-di(Cl)-salpn)2] (7), and [Mn2(μ-O)2(3,5-di(NO2)-salpn)2] (8). The analysis of complexes 6-8 highlights the strong coupling between electron and proton transfers, with any Mn oxidation lowering the pKa of an oxo bridge by 10.5 ± 0.9 pH units. The model also accounts for changes in the Em's by ligand substituents, such as found in complexes 6-8, due to the electron withdrawing Cl (7) and NO2 (8). The reported study provides the foundation for analysis of electrostatic effects in other oxomanganese complexes and metalloenzymes, where proton coupled electron transfer plays a fundamental role in redox-leveling mechanisms.

AB - The influence of electrostatic interactions on the free energy of proton coupled electron transfer in biomimetic oxomanganese complexes inspired by the oxygen-evolving complex (OEC) of photosystem II (PSII) are investigated. The reported study introduces an enhanced multiconformer continuum electrostatics (MCCE) model, parametrized at the density functional theory (DFT) level with a classical valence model for the oxomanganese core. The calculated pK a's and oxidation midpoint potentials (Em's) match experimental values for eight complexes, indicating that purely electrostatic contributions account for most of the observed couplings between deprotonation and oxidation state transitions. We focus on pKa's of terminal water ligands in [Mn(II/III)(H2O)6]2+/3+ (1), [Mn(III)(P)(H2O)2]3- (2, P = 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrinato), [Mn 2(IV,IV)(μ-O)2(terpy)2(H2O) 2]4+ (3, terpy = 2,2′:6′,2″-terpyridine) , and [Mn3(IV,IV,IV)(μ-O)4(phen)4(H 2O)2]4+ (4, phen = 1,10-phenanthroline) and the pKa's of μ-oxo bridges and Mn Em's in [Mn 2(μ-O)2(bpy)4] (5, bpy = 2,2′-bipyridyl), [Mn2(μ-O)2(salpn)2] (6, salpn = N,N′-bis(salicylidene)-1,3-propanediamine), [Mn 2(μ-O)2(3,5-di(Cl)-salpn)2] (7), and [Mn2(μ-O)2(3,5-di(NO2)-salpn)2] (8). The analysis of complexes 6-8 highlights the strong coupling between electron and proton transfers, with any Mn oxidation lowering the pKa of an oxo bridge by 10.5 ± 0.9 pH units. The model also accounts for changes in the Em's by ligand substituents, such as found in complexes 6-8, due to the electron withdrawing Cl (7) and NO2 (8). The reported study provides the foundation for analysis of electrostatic effects in other oxomanganese complexes and metalloenzymes, where proton coupled electron transfer plays a fundamental role in redox-leveling mechanisms.

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