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

*Bijbehorende auteur voor dit werk

OnderzoeksoutputAcademicpeer review

29 Citaten (Scopus)

Samenvatting

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 (PSI) 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 (E-m'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 pK(a)'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)(mu-0)(2)(terpy)(2)(H2O)(2))(4+) (3, terpy = 2,2':6',2 ''-terpyridine), and [Mn-3(IV,IV,IV)(mu-O)(4)(Phen)(4)(H2O)(2)](4+) (4, phen = 1,10-phenanthroline) and the pK(a)'s of mu-oxo bridges and Mn E-m's in [Mn-2(mu-O)(2)(bpy)(4)] (5, bpy = 2,2'-bipyridyl), [Mn-2(mu-O)(2)(salpn)(2)] (6, salpn = N,N'-bis(salicylidene)-1,3-propanediamine), [Mn-2(mu-O)(2)(3,5-di(Cl)-salpn)(2)] (7), and [Mn-2(mu-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 pK(a) of an oxo bridge by 10.5 +/- 0.9 pH units. The model also accounts for changes in the E-m'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.

Originele taal-2English
Pagina's (van-tot)6217-6226
Aantal pagina's10
TijdschriftJournal of Physical Chemistry B
Volume117
Nummer van het tijdschrift20
DOI's
StatusPublished - 23-mei-2013
Extern gepubliceerdJa

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