EPR Spectroscopy and the Electronic Structure of the Oxygen-Evolving Complex of Photosystem II

Lohmiller, Thomas; Ames, William; Lubitz, Wolfgang; Cox, Nicholas; Misra, Sushil K.

doi:10.1007/s00723-012-0437-3

Cited by 23 publications

(59 citation statements)

References 169 publications

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“…The set of scaling factors r i , termed spin projection coefficients, are primarily determined by the set of pairwise exchange couplings as detailed in ref. 18,30,31,33,34,36, 37 and 63. However, additional terms must be included to correctly estimate such spin projections for the OEC, specifically the relevant on-site fine structure parameters d i for the individual Mn i ions, 18,30,33,34,63 yielding what are more accurately described as spin projection tensors.…”

Section: Calculated Magnetic Properties For the Native And Modified Smentioning

confidence: 99%

“…18,30,31,33,34,36, 37 and 63. However, additional terms must be included to correctly estimate such spin projections for the OEC, specifically the relevant on-site fine structure parameters d i for the individual Mn i ions, 18,30,33,34,63 yielding what are more accurately described as spin projection tensors. As the coordination geometries of the three Mn IV ions of the S 2 state are all octahedral, their local electronic structure should be of approximate spherical symmetry, their orbitals of t 2g origin (d xy , d xz and d yz ) being half-filled (local high-spin d 3 configuration).…”

Section: Calculated Magnetic Properties For the Native And Modified Smentioning

confidence: 99%

“…Electron paramagnetic resonance (EPR) spectroscopy represents a powerful methodology in this endeavour. [16][17][18][19] The S 2 state, being readily generated from the dark-stable S 1 state, is the most extensively characterized S state by EPR. It is intrinsically heterogeneous, [20][21][22] existing in two ground state configurations.…”

Section: Introductionmentioning

confidence: 99%

“…[30][31][32][33][34] OEC models developed from broken-symmetry (BS) density functional theory (DFT) have been crucial for the interpretation of EPR and related magnetic resonance results. 12,14,18,33,[35][36][37][38][39][40][41][42][43][44] These calculations now allow different S-state models to be assessed based on the spin multiplicities and relative energies of their lowest magnetic levels, and, by means of the spin projection formalism (see ref. 18 and 36), the metal and ligand hyperfine couplings.…”

Section: Introductionmentioning

confidence: 99%

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Structure, ligands and substrate coordination of the oxygen-evolving complex of photosystem II in the S2 state: a combined EPR and DFT study

Lohmiller

Krewald

Navarro

et al. 2014

Phys. Chem. Chem. Phys.

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152

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The S2 state of the oxygen-evolving complex of photosystem II, which consists of a Mn4O5Ca cofactor, is EPR-active, typically displaying a multiline signal, which arises from a ground spin state of total spin ST = 1/2. The precise appearance of the signal varies amongst different photosynthetic species, preparation and solvent conditions/compositions. Over the past five years, using the model species Thermosynechococcus elongatus, we have examined modifications that induce changes in the multiline signal, i.e. Ca(2+)/Sr(2+)-substitution and the binding of ammonia, to ascertain how structural perturbations of the cluster are reflected in its magnetic/electronic properties. This refined analysis, which now includes high-field (W-band) data, demonstrates that the electronic structure of the S2 state is essentially invariant to these modifications. This assessment is based on spectroscopies that examine the metal centres themselves (EPR, (55)Mn-ENDOR) and their first coordination sphere ligands ((14)N/(15)N- and (17)O-ESEEM, -HYSCORE and -EDNMR). In addition, extended quantum mechanical models from broken-symmetry DFT now reproduce all EPR, (55)Mn and (14)N experimental magnetic observables, with the inclusion of second coordination sphere ligands being crucial for accurately describing the interaction of NH3 with the Mn tetramer. These results support a mechanism of multiline heterogeneity reported for species differences and the effect of methanol [Biochim. Biophys. Acta, Bioenerg., 2011, 1807, 829], involving small changes in the magnetic connectivity of the solvent accessible outer MnA4 to the cuboidal unit Mn3O3Ca, resulting in predictable changes of the measured effective (55)Mn hyperfine tensors. Sr(2+) and NH3 replacement both affect the observed (17)O-EDNMR signal envelope supporting the assignment of O5 as the exchangeable μ-oxo bridge and it acting as the first site of substrate inclusion.

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Section: Calculated Magnetic Properties For the Native And Modified Smentioning

confidence: 99%

Section: Calculated Magnetic Properties For the Native And Modified Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Structure, ligands and substrate coordination of the oxygen-evolving complex of photosystem II in the S2 state: a combined EPR and DFT study

Lohmiller

Krewald

Navarro

et al. 2014

Phys. Chem. Chem. Phys.

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152

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“…Com base nesses dados, diversos grupos têm proposto mecanismos para a foto-oxidação da água e a formação da ligação O=O. 46,[48][49][50][51][52][53][54][55][56][57][58][59] Quimicamente, o OEC é um cluster contendo quatro íons manganês e um íon cálcio ligados por pontes oxo. Na estrutura proposta por Ferreira et al, 46 60,61 e é termodinamicamente estável no escuro.…”

Section: Introductionunclassified

Coordination Chemistry and Solar Fuel Production

Sousa¹,

Patrocínio²

2014

Química Nova

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COORDINATION CHEMISTRY AND SOLAR FUEL PRODUCTION. Life on earth depends on the absorption and conversion of solar energy into chemical bonds, i.e. photosynthesis. In this process, sun light is employed to oxidize water into oxygen and reducing equivalents used to produce fuels. In artificial photosynthesis, the goal is to develop relatively simple systems able to mimic photosynthetic organisms and promote solar-to-chemical conversion. The aim of the present review was to describe recent advances in the application of coordination compounds as catalysts in some key reactions for artificial photosynthesis, such as water splitting and CO 2 reduction.Keywords: solar fuels; artificial photosynthesis; coordination chemistry; photochemistry. INTRODUÇÃOAtualmente, o tópico energia tem despertado o interesse de diversos setores da sociedade devido ao dilema de suprir a crescente demanda sem aumentar os danos ambientais já causados pela exploração dos combustíveis fósseis.1-5 O incentivo a novas tecnologias para energia renovável ganhou ainda mais força com estudos recentes que mostram o aumento da concentração de CO 2 na atmosfera devido à queima de combustíveis fósseis, o que causa o chamado efeito estufa. 6,7 Nesse contexto, o aproveitamento da energia solar torna-se extremamente atraente devido ao seu baixo impacto ambiental e à grande oferta de energia. Anualmente, o fluxo de radiação sobre a terra chega a 3,4×10 24 J, o que supera em milhares de vezes o consumo de energia atual do mundo.7 De fato, o sol é nossa fonte primária de energia, responsável pela formação da biomassa, dos ventos, da maré, enfim, da vida no planeta.O aproveitamento da energia solar envolve sua conversão em outras formas de energia. Atualmente, já se encontram amplamente difundidos nas residências sistemas para aquecimento de água a partir da luz solar. Outra possibilidade envolve a conversão da energia luminosa em eletricidade por meio de sistemas fotovoltaicos. Tais sistemas são baseados em células solares tradicionais de silício ou, mais recentemente, em novas gerações de dispositivos como as DSCs (dye-sensitized solar cells) e as OPVs (organic photovoltaics), cuja eficiência e estabilidade têm avançado constantemente. [8][9][10][11][12][13][14][15] A energia solar pode ainda ser convertida e armazenada na forma de ligações químicas, como ocorre nos organismos fotossintéticos, em que espécies químicas de alto conteúdo energético (carboidratos) são formadas a partir de CO 2 e H 2 O, equação 1.(1) Biologicamente, a fotossíntese promove a quebra de água em oxigênio e prótons, enquanto a respiração combina essas espécies de forma controlada e eficiente para produzir metabólitos. Assim, a síntese desses metabólitos representa a fixação de hidrogênio e consequente armazenamento da energia solar na forma de ligações químicas. Estima-se que os organismos fotossintéticos produzem mais de 100 bilhões de toneladas de biomassa seca anualmente, o que equivale a 100 vezes o peso de toda a população humana na Terra e representa um estoque de energia de ap...

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Water oxidation in oxygenic photosynthesis studied by magnetic resonance techniques

2022

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The understanding of light‐induced biological water oxidation in oxygenic photosynthesis is of great importance both for biology and (bio)technological applications. The chemically difficult multistep reaction takes place at a unique protein‐bound tetra‐manganese/calcium cluster in photosystem II whose structure has been elucidated by X‐ray crystallography (Umena et al. Nature 2011, 473, 55). The cluster moves through several intermediate states in the catalytic cycle. A detailed understanding of these intermediates requires information about the spatial and electronic structure of the Mn4Ca complex; the latter is only available from spectroscopic techniques. Here, the important role of Electron Paramagnetic Resonance (EPR) and related double resonance techniques (ENDOR, EDNMR), complemented by quantum chemical calculations, is described. This has led to the elucidation of the cluster's redox and protonation states, the valence and spin states of the manganese ions and the interactions between them, and contributed substantially to the understanding of the role of the protein surrounding, as well as the binding and processing of the substrate water molecules, the O‐O bond formation and dioxygen release. Based on these data, models for the water oxidation cycle are developed.

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EPR Spectroscopy and the Electronic Structure of the Oxygen-Evolving Complex of Photosystem II

Cited by 23 publications

References 169 publications

Structure, ligands and substrate coordination of the oxygen-evolving complex of photosystem II in the S2 state: a combined EPR and DFT study

Structure, ligands and substrate coordination of the oxygen-evolving complex of photosystem II in the S2 state: a combined EPR and DFT study

Coordination Chemistry and Solar Fuel Production

Water oxidation in oxygenic photosynthesis studied by magnetic resonance techniques

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