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Design and synthesis of benzimidazole phenol-porphyrin dyads for the study of bioinspired photoinduced proton-coupled electron transfer
摘要： Benzimidazole phenol-porphyrin dyads have been synthesized to study proton-coupled electron transfer (PCET) reactions induced by photoexcitation. High-potential porphyrins have been chosen to model P680, the photoactive chlorophyll cluster of photosynthetic photosystem II (PSII). They have either two or three pentafluorophenyl groups at the meso positions to impart the high redox potential. The benzimidazole phenol (BIP) moiety models the Tyrz-His190 pair of PSII, which is a redox mediator that shuttles electrons from the water oxidation catalyst to P680?+. The dyads consisting of a porphyrin and an unsubstituted BIP are designed to study one-electron one-proton transfer (E1PT) processes upon excitation of the porphyrin. When the BIP moiety is substituted with proton-accepting groups such as imines, one-electron two-proton transfer (E2PT) processes are expected to take place upon oxidation of the phenol by the excited state of the porphyrin. The bis-pentafluorophenyl porphyrins linked to BIPs provide platforms for introducing a variety of electron-accepting moieties and/or anchoring groups to attach semiconductor nanoparticles to the macrocycle. The triads thus formed will serve to study the PCET process involving the BIPs when the oxidation of the phenol is achieved by the photochemically produced radical cation of the porphyrin.
关键词： pentafluorophenyl porphyrin,benzimidazole derivatives,proton-coupled electron transfer (PCET),photosystem II
更新于2025-09-11 14:15:04
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Reconciling Structural and Spectroscopic Fingerprints of the Oxygen Evolving Complex of Photosystem II: A Computational Study of the S <sub/>2</sub> State
摘要： The catalytic cycle of photosynthetic water oxidation occurs at the Mn4CaO5 oxygen-evolving complex (OEC) of Photosystem II (PSII). Extensive spectroscopic data have been collected on the intermediates, especially the S2 (Kok) state, although the proton and electron inventories (Mn oxidation states) are still uncertain. The “high-oxidation” paradigm, assigns S2 Mn oxidation level (III, IV, IV, IV) or (IV, IV, IV, III), whereas a “low-oxidation” paradigm posits two additional electrons. Here we investigate the geometric (XRD, EXAFS) and spectroscopic (EPR, ENDOR) properties of the S2 state using quantum chemical DFT calculations, focusing on the neglected low paradigm. Two interconvertible electronic spin configurations are predicted as ground states, producing multiline (S = 1/2) and broad (S = 5/2) EPR signals in the low paradigm oxidation state (III, IV, III, III) and with W2 as OH– and O5 as OH–. They have “open” (S = 5/2) and “closed” (S = 1/2) Mn3CaO4-cubane geometries. Other energetically accessible isomers with ground spin states 1/2, 7/2, 9/2, or 11/2 can be obtained through perturbations of hydrogen-bonding networks (e.g. H+ from His337 to O3 or W2), consistent with experimental observations. Conformers with the low oxidation state configuration (III, IV, IV, II) also become energetically accessible when the protonation state is O5 (OH–), W2 (H2O) and neutral His337. The configuration with (III, IV, III, III) agrees well with earlier low temperature EPR and ENDOR interpretations, while the MnII-containing configuration agrees partially with recent ENDOR data. However, the low-oxidation paradigm does not yield isotropic ligand hyperfine interactions in good agreement with observed values. We conclude that the low Mn oxidation state proposal for the OEC can closely fit most of the available structural and electronic data for S2 at accessible energies.
关键词： EPR,low-oxidation paradigm,oxygen-evolving complex,ENDOR,Photosystem II,DFT calculations,S2 state
更新于2025-09-10 09:29:36
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Photoreduction of CO2 with a formate dehydrogenase driven by photosystem II using a semi-artificial Z-scheme architecture
摘要： Solar-driven coupling of water oxidation with CO2 reduction sustains life on our planet and is of high priority to contemporary research. Here, we report a photoelectrochemical tandem device, which performs photocatalytic CO2 reduction to formate. We employ a semi-artificial design, which wires a W-dependent formate dehydrogenase (FDH) cathode to a photoanode containing the photosynthetic water oxidation enzyme, photosystem II, via a synthetic dye with complementary light absorption. From a biological perspective, the system achieves a metabolically-inaccessible pathway of light-driven CO2 fixation to formate. From a synthetic point of view, it represents a proof-of-principle system utilizing precious-metal-free catalysts for selective CO2 to formate conversion using water as an electron donor. This hybrid platform demonstrates the translatability and versatility of coupling abiotic and biotic components to create challenging models for solar fuel and chemical synthesis.
关键词： Photoreduction,formate dehydrogenase,photosystem II,semi-artificial Z-scheme architecture,CO2
更新于2025-09-09 09:28:46
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Environmental pH and Glu364 to Gln mutation in the chlorophyll-binding CP47 protein affect redox-active TyrD and charge recombination in Photosystem II
摘要： In Photosystem II, loop E of the chlorophyll-binding CP47 protein is located near a redox-active tyrosine, YD, forming a symmetrical analog to loop E in CP43, which provides a ligand to the oxygen-evolving complex (OEC). A Glu364 to Gln substitution in CP47, near YD, does not affect growth in the cyanobacterium Synechocystis sp. PCC 6803; however, deletion of the extrinsic protein PsbV in this mutant leads to a strain displaying a pH-sensitive phenotype. Using thermoluminescence, chlorophyll fluorescence, and flash-induced oxygen evolution analyses, we demonstrate that Glu364 influences the stability of YD and the redox state of the OEC, and highlight the effects of external pH on photosynthetic electron transfer in intact cyanobacterial cells.
关键词： TyrD,oxygen-evolving complex,cyanobacteria,YD,CP47,Synechocystis sp. PCC 6803,Photosystem II
更新于2025-09-09 09:28:46