scholarly journals Tuning the Catalytic Water Oxidation Activity through Structural Modifications of High-Nuclearity Mn-oxo Clusters [Mn18M] (M = Sr2+, Mn2+)

Water ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2042
Author(s):  
Joaquín Soriano-López ◽  
Rory Elliott ◽  
Amal C. Kathalikkattil ◽  
Ayuk M. Ako ◽  
Wolfgang Schmitt
Keyword(s):  
Catalytic Activity ◽  
Water Oxidation ◽  
Fossil Fuels ◽  
Structural Changes ◽  
Mixed Valence ◽  
O2 Evolution ◽  
Oxygen Evolving Complex ◽  
Oxidation Activity ◽  
Ps Ii ◽  
Redox Active

The water oxidation half-reaction is considered the bottleneck in the development of technological advances to replace fossil fuels with sustainable and economically affordable energy sources. In natural photosynthesis, water oxidation occurs in the oxygen evolving complex (OEC), a manganese-oxo cluster {Mn4CaO5} with a cubane-like topology that is embedded within a redox-active protein environment located in photosystem II (PS II). Therefore, the preparation of biomimetic manganese-based compounds is appealing for the development of efficient and inexpensive water oxidation catalysts. Here, we present the water oxidation catalytic activity of a high-nuclearity mixed-metal manganese-strontium cluster, [MnIII12MnII6Sr(μ4-O8)(μ3-Cl)8(HLMe)12(MeCN)6]Cl2∙15MeOH (Mn18Sr) (HLMe = 2,6-bis(hydroxymethyl)-p-cresol), in neutral media. This biomimetic mixed-valence cluster features different cubane-like motifs and it is stabilized by redox-active, quinone-like organic ligands. The complex displays a low onset overpotential of 192 mV and overpotentials of 284 and 550 mV at current densities of 1 mA cm−2 and 10 mA cm−2, respectively. Direct O2 evolution measurements under visible light-driven water oxidation conditions demonstrate the catalytic capabilities of this cluster, which exhibits a turnover frequency of 0.48 s−1 and a turnover number of 21.6. This result allows for a direct comparison to be made with the structurally analogous Mn-oxo cluster [MnIII12MnII7(µ4-O)8(µ3-OCH3)2(µ3-Br)6(HLMe)12(MeOH)5(MeCN)]Br2·9MeCN·MeOH (Mn19), the water oxidation catalytic activity of which was recently reported by us. This work highlights the potential of this series of compounds towards the water oxidation reaction and their amenability to induce structural changes that modify their reactivity.

scholarly journals Water Oxidation in Natural Photosynthesis

2014 ◽  
Vol 70 (a1) ◽  
pp. C723-C723
Author(s):  
Jan Kern ◽  
Rosalie Tran ◽  
Ruchira Chatterjee ◽  
Guangye Han ◽  
Roberto Alonso-Mori ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Structural Changes ◽  
Cluster Structure ◽  
Oxidation Mechanism ◽  
Catalytic Cycle ◽  
Oxygen Evolving Complex ◽  
Ps Ii ◽  
X Ray ◽  
Theoretical Approaches ◽  
State Changes

The photosynthetic water oxidation reaction is energetically demanding and mechanistically complex because of the difficulties in managing the four electron, four proton redox chemistry required for the evolution of molecular oxygen starting from two water molecules. The reaction takes place in Photosystem II (PS II), a multi-subunit membrane protein present in plants, algae, and cyanobacteria. This sunlight-driven reaction is catalyzed by an oxygen-evolving complex (OEC), that consists of an oxo-bridged four Mn and one Ca cluster. O2 is formed and released only after four oxidation equivalents are accumulated at the OEC. The structure of the Mn4CaO5 cluster has been studied by various spectroscopic and diffraction methods. The recent XRD study by Umena et al.[1] has shown the oxo-bridged Mn4Ca cluster structure at 1.9 Å resolution. Based on this high-resolution XRD structure, there have been efforts to obtain chemically optimized structures and structural changes of the Mn4CaO5 cluster during the catalytic cycle using spectroscopic parameters and theoretical approaches. EXAFS spectra of the PS II S states show that the structure of the Mn4CaO5 cluster changes during the catalytic cycle.[2] In particular, the short Mn-Mn distances change in the range of 2.7 to 2.9 Å. Such changes in oxygen-bridged Mn-Mn distances can reflect several chemical parameters; Mn oxidation state changes, protonation state changes of bridging oxygens, ligation modes (e.g. bidentate/monodentate), as well as fundamental changes in geometry. We have also used femtosecond X-ray spectroscopy and crystallography to study the catalytic process of the OEC.[3] The femtosecond X-ray pulses of the free-electron laser allows us to out-run X-ray damage at room temperature, and the time-evolution of the photo-induced reaction can be probed using a visible laser-pump followed by the X-ray-probe pulse. We will discuss a possible water oxidation mechanism based on these results.

scholarly journals Photosystem II: Thermodynamics and Kinetics of Electron Transport from QA- to QB(QB- ) and Deleterious Effects of Copper(II)

1993 ◽  
Vol 48 (3-4) ◽  
pp. 234-240 ◽  
Author(s):  
G. Renger ◽  
H. M. Gleiter ◽  
E. Haag ◽  
F. Reifarth
Keyword(s):  
Oxygen Evolution ◽  
Manganese Content ◽  
Fluorescence Emission ◽  
Laser Flash ◽  
Fluorescence Induction ◽  
Oxygen Evolving Complex ◽  
Ps Ii ◽  
Thermodynamics And Kinetics ◽  
Redox Active ◽  
Kinetics Of

Studies on thermodynamics and kinetics of electron transfer from QA- to QB(QB-) were performed by monitoring laser flash induced changes of the relative fluorescence emission as a function of temperature (220 K < T < 310 K) in isolated thylakoids and PS II membrane fragments.In addition, effects of bivalent metal ions on PS II were investigated by measuring conventional fluorescence induction curves, oxygen evolution, manganese content and atrazine binding mostly in PS II membrane fragments. It was found: a) the normalized level of the fluorescence remaining 10 s after the actinic flash (Ft/F0) steeply increases at temperatures below -10 to - 20 °C, b) the fast phase of the transient fluorescence change becomes markedly retarded with decreasing temperatures, c) among different cations (Cu2+, Zn2+, Cd2+, Ni2+, Co2+) only Cu2+ exhibits marked effects in the concentration range below 100 μᴍ and d) Cu2+ decreases the normalized variable fluorescence, inhibits oxygen evolution and diminishes the affinity to atrazine binding without affecting the number of binding sites. The content of about four manganeses per functionally competent oxygen evolving complex is not changed by [Cu2+] < 70 μᴍ.Based on these findings it is concluded: i) a temperature dependent equilibrium between an inactive (I) and active (A) state of QA- reoxidation by QB(QB- ) is characterized by standard enthalpies ΔH° of 95 kJ mol-1 and 60 kJ mol-1 and standard entropies ΔS° of 370 kJ K-1 mol-1 and 240 kJ K-1 mol-1 in isolated thylakoids and PS II membrane fragments, respectively, ii) the activation energies of QA- reoxidation by plastoquinone bound to the QB site are about 30 kJ mol-1 (thylakoids) and 40 kJ mol-1 (PS II membrane fragments) in 220 K < T < 300 K, and iii) Cu2+ causes at least a two-fold effect on PS II by modifying the atrazine binding affinity at lower concentrations ( ~ 5 μᴍ) and interference with the redox active tyrosine Yz at slightly higher concentration ( ~ 10 μᴍ) leading to blockage of oxygen evolution.

scholarly journals Simulation of the isotropic EXAFS spectra for the S2 and S3 structures of the oxygen evolving complex in photosystem II

2015 ◽  
Vol 112 (13) ◽  
pp. 3979-3984 ◽  
Author(s):  
Xichen Li ◽  
Per E. M. Siegbahn ◽  
Ulf Ryde
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Density Functional ◽  
Structural Changes ◽  
Complete Agreement ◽  
Oxygen Evolving Complex ◽  
Chemical Modeling ◽  
Oxygen Evolving ◽  
High Degree ◽  
Exafs Spectra

Most of the main features of water oxidation in photosystem II are now well understood, including the mechanism for O–O bond formation. For the intermediate S2 and S3 structures there is also nearly complete agreement between quantum chemical modeling and experiments. Given the present high degree of consensus for these structures, it is of high interest to go back to previous suggestions concerning what happens in the S2–S3 transition. Analyses of extended X-ray adsorption fine structure (EXAFS) experiments have indicated relatively large structural changes in this transition, with changes of distances sometimes larger than 0.3 Å and a change of topology. In contrast, our previous density functional theory (DFT)(B3LYP) calculations on a cluster model showed very small changes, less than 0.1 Å. It is here found that the DFT structures are also consistent with the EXAFS spectra for the S2 and S3 states within normal errors of DFT. The analysis suggests that there are severe problems in interpreting EXAFS spectra for these complicated systems.

scholarly journals Untangling the sequence of events during the S2→ S3transition in photosystem II and implications for the water oxidation mechanism

2020 ◽  
Vol 117 (23) ◽  
pp. 12624-12635 ◽  
Author(s):  
Mohamed Ibrahim ◽  
Thomas Fransson ◽  
Ruchira Chatterjee ◽  
Mun Hon Cheah ◽  
Rana Hussein ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Donor Site ◽  
Oxidation Mechanism ◽  
Oxygenic Photosynthesis ◽  
Acceptor Site ◽  
Oxygen Evolving Complex ◽  
Ps Ii ◽  
Sequence Of Events ◽  
Large Channel

In oxygenic photosynthesis, light-driven oxidation of water to molecular oxygen is carried out by the oxygen-evolving complex (OEC) in photosystem II (PS II). Recently, we reported the room-temperature structures of PS II in the four (semi)stable S-states, S1, S2, S3, and S0, showing that a water molecule is inserted during the S2→ S3transition, as a new bridging O(H)-ligand between Mn1 and Ca. To understand the sequence of events leading to the formation of this last stable intermediate state before O2formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S2→ S3transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, QAand QB, are observed. At the donor site, tyrosine YZand His190 H-bonded to it move by 50 µs after the second flash, and Glu189 moves away from Ca. This is followed by Mn1 and Mn4 moving apart, and the insertion of OX(H) at the open coordination site of Mn1. This water, possibly a ligand of Ca, could be supplied via a “water wheel”-like arrangement of five waters next to the OEC that is connected by a large channel to the bulk solvent. XES spectra show that Mn oxidation (τ of ∼350 µs) during the S2→ S3transition mirrors the appearance of OXelectron density. This indicates that the oxidation state change and the insertion of water as a bridging atom between Mn1 and Ca are highly correlated.

scholarly journals Synthesis, crystal structure and water oxidation activity of [Ru(terpy)(bipy)Cl]+ complexes: influence of ancillary ligands on O2 generation

RSC Advances ◽  
2017 ◽  
Vol 7 (62) ◽  
pp. 39325-39333 ◽  
Author(s):  
Rekha Dhiman ◽  
Namita Singh ◽  
Bharat Ugale ◽  
C. M. Nagaraja
Keyword(s):  
Crystal Structure ◽  
Catalytic Activity ◽  
Water Oxidation ◽  
Chemical Oxidation ◽  
Oxidation Activity ◽  
Ancillary Ligands

Synthesis of four new complexes [RuII(MeMPTP)(bpy)Cl]PF6 (1), [RuII(MeMPTP)(dmbpy)Cl]PF6 (2), [RuII(MeMPTP)(dmdcbpy)Cl]PF6 (3) and [RuII(MeMPTP)(Pic)2Cl]PF6 (4) and their catalytic activity for chemical oxidation of water into O2 generation has been demonstrated.

Slow magnetic relaxation and water oxidation activity of dinuclear CoIICoIII and unique triangular CoIICoIICoIII mixed-valence complexes

2020 ◽  
Vol 49 (19) ◽  
pp. 6328-6340
Author(s):  
Ritwik Modak ◽  
Biswajit Mondal ◽  
Yeasin Sikdar ◽  
Jayisha Banerjee ◽  
Enrique Colacio ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Coordination Compounds ◽  
Magnetic Relaxation ◽  
Mixed Valence ◽  
Oxidation Catalysts ◽  
Oxidation Activity ◽  
Slow Magnetic Relaxation

Mixed valence cobalt based coordination compounds acting as single ion magnets and water oxidation catalysts.

Isolation and Partial Characterization of a Manganese Requiring ʟ-Arginine Metabolizing Enzyme Being Present in Photosystem II Complexes of Spinach and Tobacco

1995 ◽  
Vol 50 (9-10) ◽  
pp. 638-651 ◽  
Author(s):  
Achim E. Gau ◽  
Hubert H. Thole ◽  
Elfriede K. Pistorius
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Cation Binding ◽  
Active Group ◽  
Anion Exchange Column ◽  
Ps Ii ◽  
Cation Binding Site ◽  
Redox Active ◽  
Metabolizing Enzyme ◽  
Ph Range

Abstract A low ʟ-arginine metabolizing enzyme (L-AME) activity leading to ornithine, urea and additional products not identified so far could be detected in photosystem II (PS II) membranes of spinach and of the chlorophyll deficient tobacco mutant Su/su. The detectable L-AME activity was very low in untreated PS II membranes, but increased significantly (about 10 fold) when the extrinsic peptides (psbO, P and Q gene products) were removed - suggesting that the L-AME is exposed at the lumen side of PS II. It was possible to isolate the detergent-solubilized protein from CaCl2-washed PS II membranes of spinach by a combination of anion and cation exchange columns. On the basis of SDS PAGE the protein was homogenous and had an apparent molecular mass of 7 kDa. N-terminal sequencing of the polypeptide gave a contiguous sequence of 20 amino acids showing no homologies to PS II polypeptides as yet sequenced. After chromatography of the L-AME on an anion exchange column at pH 9.5 (last purification step) a completely inactive enzyme was obtained. Maximal reactivation was achieved by dialyzing the protein against Hepes-NaOH buffer in the pH range of 6.5 to 7.5 containing 100 mᴍ chloride or sulfate (being the most effective anions). The L-AME activity was totally dependent on manganese added to the reaction mixture. Moreover, there were indications of a second cation binding site being more sequestered and requiring bound Ca2+ or Mn2+ for activity (Sr2+ was less effective and Mg2+ was ineffective). There are indications that the protein contains a redox active group - possibly an aminoacid- derived quinonoid (based on a redox cycling assay with glycine and nitroblue tetrazolium). The capability of this PS II associated protein to bind the cofactors of water oxidation and having a redox active group (preliminary results) suggests that this protein might be functional in photosynthetic water oxidation. This is further supported by the fact that the isolated L-AME has a low catalase activity

scholarly journals Structural dynamics in the water and proton channels of photosystem II during the S2 to S3 transition

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Rana Hussein ◽  
Mohamed Ibrahim ◽  
Asmit Bhowmick ◽  
Philipp S. Simon ◽  
Ruchira Chatterjee ◽  
...  
Keyword(s):  
Amino Acid ◽  
Photosystem Ii ◽  
Water Oxidation ◽  
Water Molecules ◽  
Back Reaction ◽  
Side Chains ◽  
Oxygen Evolving Complex ◽  
Proton Release ◽  
Ps Ii ◽  
Amino Acid Side Chains

AbstractLight-driven oxidation of water to molecular oxygen is catalyzed by the oxygen-evolving complex (OEC) in Photosystem II (PS II). This multi-electron, multi-proton catalysis requires the transport of two water molecules to and four protons from the OEC. A high-resolution 1.89 Å structure obtained by averaging all the S states and refining the data of various time points during the S2 to S3 transition has provided better visualization of the potential pathways for substrate water insertion and proton release. Our results indicate that the O1 channel is the likely water intake pathway, and the Cl1 channel is the likely proton release pathway based on the structural rearrangements of water molecules and amino acid side chains along these channels. In particular in the Cl1 channel, we suggest that residue D1-E65 serves as a gate for proton transport by minimizing the back reaction. The results show that the water oxidation reaction at the OEC is well coordinated with the amino acid side chains and the H-bonding network over the entire length of the channels, which is essential in shuttling substrate waters and protons.

Photosystem II: the engine of life

2003 ◽  
Vol 36 (1) ◽  
pp. 71-89 ◽  
Author(s):  
James Barber
Keyword(s):  
High Resolution ◽  
Photosystem Ii ◽  
Water Oxidation ◽  
Structural Models ◽  
Reaction Centre ◽  
Ps Ii ◽  
X Ray ◽  
X Ray Crystallography ◽  
Redox Active ◽  
Resolution Electron

1. Introduction 712. Electron transfer in PS II 723. (Mn)4cluster and mechanism of water oxidation 734. Organization and structure of the protein subunits 755. Organization of chlorophylls and redox active cofactors 816. Implications arising from the structural models 827. Perspectives 848. Acknowledgements 869. Addendum 8610. References 87Photosystem II (PS II) is a multisubunit membrane protein complex, which uses light energy to oxidize water and reduce plastoquinone. High-resolution electron cryomicroscopy and X-ray crystallography are revealing the structure of this important molecular machine. Both approaches have contributed to our understanding of the organization of the transmembrane helices of higher plant and cyanobacterial PS II and both indicate that PS II normally functions as a dimer. However the high-resolution electron density maps derived from X-ray crystallography currently at 3·7/3·8 Å, have allowed assignments to be made to the redox active cofactors involved in the light-driven water–plastoquinone oxidoreductase activity and to the chlorophyll molecules that absorb and transfer energy to the reaction centre. In particular the X-ray work has identified density that can accommodate the four manganese atoms which catalyse the water-oxidation process. The Mn cluster is located at the lumenal surface of the D1 protein and approximately 7 Å from the redox active tyrosine residue (YZ) which acts an electron/proton transfer link to the primary oxidant P680.+. The lower resolution electron microscopy studies, however, are providing structural models of larger PS II supercomplexes that are ideal frameworks in which to incorporate the X-ray derived structures.

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