Photo-induced oxidation of a dinuclear Mn2II,II complex to the Mn2III,IV state by inter- and intramolecular electron transfer to RuIIItris-bipyridine

Huang, Ping; Magnuson, Ann; Lomoth, Reiner; Abrahamsson, Malin; Tamm, Marcus; Sun, Licheng; Rotterdam, Bart J. van; Park, Jonathan; Hammarström, Leif; Åkermark, Björn; Styring, Stenbjörn

doi:10.1016/s0162-0134(02)00394-x

Cited by 91 publications

(112 citation statements)

References 34 publications

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“…In S 1 it is highly positive; approximately ϩ1 V (41). A potential increase upon the S 1 3 S 2 transition and a decrease in the S 0 * state is anticipated (41,42); the potential of the Mn II 4 state presumably is comparably low (Յ0 V) (43,44). That electrophilic centers are the primary target for reduction by electrons liberated because of x-ray exposure is also supported by investigations on protein crystals where disulfide bridges first became reduced at 100 K (18,19) and by EPR results (Ref.…”

Section: Discussionmentioning

confidence: 79%

Rapid Loss of Structural Motifs in the Manganese Complex of Oxygenic Photosynthesis by X-ray Irradiation at 10–300 K

Grabolle

Haumann

Müller

et al. 2006

Journal of Biological Chemistry

183

227

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Structural changes upon photoreduction caused by x-ray irradiation of the water-oxidizing tetramanganese complex of photosystem II were investigated by x-ray absorption spectroscopy at the manganese K-edge. Photoreduction was directly proportional to the x-ray dose. It was faster in the higher oxidized S 2 state than in S 1 ; seemingly the oxidizing potential of the metal site governs the rate. X-ray irradiation of the S 1 state at 15 K initially caused single-electron reduction to S 0 * accompanied by the conversion of one di--oxo bridge between manganese atoms, previously separated by ϳ2.7 Å , to a mono--oxo motif. Thereafter, manganese photoreduction was 100 times slower, and the biphasic increase in its rate between 10 and 300 K with a breakpoint at ϳ200 K suggests that protein dynamics is rate-limiting the radical chemistry. For photoreduction at similar x-ray doses as applied in protein crystallography, halfway to the final Mn II 4 state the complete loss of inter-manganese distances <3 Å was observed, even at 10 K, because of the destruction of -oxo bridges between manganese ions. These results put into question some structural attributions from recent protein crystallography data on photosystem II. It is proposed to employ controlled x-ray photoreduction in metalloprotein research for: (i) population of distinct reduced states, (ii) estimating the redox potential of buried metal centers, and (iii) research on protein dynamics.Numerous enzymes contain protein-bound metal centers forming their active site. A prominent example is the water-oxidizing manganese-calcium (Mn 4 Ca) complex of oxygenic photosynthesis bound to the D1 protein of photosystem II (PSII), 2 which is embedded in the thylakoid membrane of higher plants, green algae, and cyanobacteria (1). The manganese complex catalyzes the light-driven oxidation of two water molecules, yielding reducing equivalents, protons, and the dioxygen of the atmosphere. By the sequential absorption of four quanta of visible light by PSII that drive the stepwise abstraction of four electrons, the manganese complex cycles through four semi-stable states called S 1 , S 2 , S 3 , and S 0 , where the subscripts denote the number of accumulated oxidizing equivalents (2). The S 1 represents the dark-stable state; dioxygen is liberated only in the S 3 3 S 0 transition (for reviews see Refs. 1 and 3).Important structural information on the manganese complex has been obtained by x-ray absorption spectroscopy (XAS) (Refs. 4 -7 and the references therein) and recently also by protein crystallography (8 -11). The crystallographic results on PSII represent a long awaited breakthrough. With respect to the manganese complex, however, the question has emerged regarding to what extent the obtained structural information is invalidated by modifications caused by the numerous radicals that are inevitably created by x-ray irradiation (11-13). In all four structures (8 -11) manganese ions were found; however, there were inconsistencies in their probable number and position with respec...

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Section: Discussionmentioning

confidence: 79%

Rapid Loss of Structural Motifs in the Manganese Complex of Oxygenic Photosynthesis by X-ray Irradiation at 10–300 K

Grabolle

Haumann

Müller

et al. 2006

Journal of Biological Chemistry

183

227

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“…Several very recent reports of molecular catalysts sensitized by light absorbing complexes/materials have appeared. 80, 81 Non-molecular catalysts may also be sensitized by molecular light sensitizers. 4, 76 Successful light-driven charge transfer between a Mn complex and TiO 2 particles has been achieved using an acetylacetonate anchor with a catechol-linker group (Fig.…”

Section: Dye Sensitization Of Molecular Catalysts For Photoelectrochementioning

confidence: 99%

Molecular water-oxidation catalysts for photoelectrochemical cells

et al. 2009

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Photoelectrochemical cells that efficiently split water into oxygen and hydrogen, "the fuel of the future", need to combine robust water oxidation catalysts at the anode (2H(2)O -> O-2 + 4H(+) + 4e(-)) with hydrogen reduction catalysts at the cathode (2H(+) + 2e(-) -> H-2). Both sets of catalysts will, ideally, operate at low overpotentials and employ light-driven or light-assisted processes. In this Perspective article, we focus on significant efforts to develop solid state materials and molecular coordination complexes as catalyst for water oxidation. We briefly review the field with emphasis on the various molecular catalysts that have been developed and then examine the activity of molecular catalysts in water oxidation following their attachment to conducting electrodes. For such molecular species to be useful in a solar water-splitting device it is preferable that they are securely and durably affixed to an electrode surface. We also consider recent developments aimed at combining the action of molecular catalysts with light absorption so that light driven water oxidation may be achieved. Photoelectrochemical cells that efficiently split water into oxygen and hydrogen, "the fuel of the future", need to combine robust water oxidation catalysts at the anode (2H 2 O → O 2 + 4H + + 4e -) with hydrogen reduction catalysts at the cathode (2H + + 2e -→ H 2 ). Both sets of catalysts will, ideally, operate at low overpotentials and employ light-driven or light-assisted processes. In this Perspective article, we focus on significant efforts to develop solid state materials and molecular coordination complexes as catalyst for water oxidation. We briefly review the field with emphasis on the various molecular catalysts that have been developed and then examine the activity of molecular catalysts in water oxidation following their attachment to conducting electrodes. For such molecular species to be useful in a solar water-splitting device it is preferable that they are securely and durably affixed to an electrode surface. We also consider recent developments aimed at combining the action of molecular catalysts with light absorption so that light driven water oxidation may be achieved.

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“…25 However, only a few molecular photoactive systems with a designed charge accumulation site have been described so far. [26][27][28][29][30] Another requirement is crucial for efficient charge accumulation in such systems: when partially filled, the reservoir should not interfere with the photoactive moiety. Indeed, in classical donor-acceptor (D-A) systems, the electron acceptor, once reduced, potentially becomes an electron donor and often displays lightabsorbing properties.…”

mentioning

confidence: 99%

Charge photo-accumulation and photocatalytic hydrogen evolution under visible light at an iridium(iii)-photosensitized polyoxotungstate

Matt

Fize

Moussa

et al. 2013

Energy Environ. Sci.

147

115

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Steady-state irradiation under visible light of a covalent Ir(III)-photosensitized polyoxotungstate is reported. In the presence of a sacrificial electron donor, the photolysis leads to the very efficient photoreduction of the polyoxometalate. Successive formation of the one-electron and two-electron reduced species, which are unambiguously identified by comparison with spectroelectrochemical measurements, is observed with a significantly faster rate reaction for the formation of the oneelectron reduced species. The kinetics of the photoreduction, which are correlated to the reduction potentials of the polyoxometalate (POM), can be finely tuned by the presence of an acid. Indeed light-driven formation of the two-electron reduced POM is considerably facilitated in the presence of acetic acid. The system is also able to perform photocatalytic hydrogen production under visible light without significant loss of performance over more than 1 week of continuous photolysis and displays higher photocatalytic efficiency than the related multi-component system, outlining the decisive effect of the covalent bonding between the POM and the photosensitizer. This functional and modular system constitutes a promising step for the development of charge photoaccumulation devices and subsequent photoelectrocatalysts for artificial photosynthesis.Photoconversion of light into chemical fuels is emerging as a major scientific challenge. [1][2][3][4] In the past decades, molecular approaches have mostly focused on one hand on the design of photosensitive systems displaying long-lived photo-induced charge separation states to permit further electron transfers 5-10 and, on the other hand, on catalysts able to use these photogenerated charges for achieving either oxygen [11][12][13][14][15][16][17][18] or hydrogen evolution. [19][20][21][22][23][24] As these two reactions are multi-electronic processes while photosensitizers deliver electrons and holes sequentially, the charges need to be directed to a charge accumulation site. 25 However, only a few molecular photoactive systems with a designed charge accumulation site have been described so far. [26][27][28][29][30] Another requirement is crucial for efficient charge accumulation in such systems: when partially filled, the reservoir should not interfere with the photoactive moiety. Indeed, in classical donor-acceptor (D-A) systems, the electron acceptor, once reduced, potentially becomes an electron donor and often displays lightabsorbing properties. Thus it may act, in a subsequent light-driven process, as a deleterious 47,48 In the previously mentioned study, transient absorptions measurements only allowed for the characterization of the first photo-induced electron transfer. Charge photo-accumulation studies can be achieved in the presence of an additional electron donor in the solution that can irreversibly quench the charge separation state, regenerate the initial state of the photosensitizer and make a second photo-induced process possible. We herein provide unprecedente...

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Photo-induced oxidation of a dinuclear Mn2II,II complex to the Mn2III,IV state by inter- and intramolecular electron transfer to RuIIItris-bipyridine

Cited by 91 publications

References 34 publications

Rapid Loss of Structural Motifs in the Manganese Complex of Oxygenic Photosynthesis by X-ray Irradiation at 10–300 K

Rapid Loss of Structural Motifs in the Manganese Complex of Oxygenic Photosynthesis by X-ray Irradiation at 10–300 K

Molecular water-oxidation catalysts for photoelectrochemical cells

Charge photo-accumulation and photocatalytic hydrogen evolution under visible light at an iridium(iii)-photosensitized polyoxotungstate

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