> ## Content Index > Fetch the complete content index at: https://research-pop.com/llms.txt > Use this file to discover other available public pages before exploring further. # Osaka Metropolitan University-led team develops a chlorophyll-derived iron catalyst for light-driven water oxidation - URL: https://research-pop.com/osaka-metropolitan-university-led-team-develops-a-chlorophyll-derived-iron-catalyst-for-light-driven-water-oxidation/ - Published: 2026-10-21T09:44:09.000Z - Updated: 2026-10-21T09:44:09.000Z - Author: ResearchPOP ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/10/Screenshot-2026-10-21-at-11.40.52.png) Source: [https://pubs.acs.org/accacs/article/doi/10.1021/acscatal.6c02830/5454626/Extremely-High-Turnover-Number-and-Turnover](https://pubs.acs.org/accacs/article/doi/10.1021/acscatal.6c02830/5454626/Extremely-High-Turnover-Number-and-Turnover?ref=research-pop.com) ## At a glance A collaboration led by Osaka Metropolitan University uses a chlorophyll-a-derived ligand to support an iron catalyst for visible-light-driven water oxidation. In a system containing a ruthenium photosensitizer and persulfate as a sacrificial oxidant, the complex achieves a turnover frequency of 21.3 ± 0.3 s⁻¹ and a turnover number of 6,920 ± 110. The reported oxygen yield, calculated relative to persulfate, is 95.7 ± 1.3%. Isotope-labelling experiments support water as the source of the evolved oxygen, while kinetic and spectroscopic measurements point towards O–O bond formation through the interaction of two high-valent iron–oxo species. The study combines catalytic performance with an investigation of how the molecular catalyst changes during operation. Its results concern the water-oxidation half-reaction in a sacrificial-reagent system. ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/10/image-1.png) ## Background Water oxidation requires the removal of four electrons and four protons from two water molecules to produce one molecule of oxygen. Beyond transferring charge, a catalyst must bring two oxygen atoms together and form an O–O bond. Managing that sequence efficiently is a central challenge in artificial photosynthesis. Molecular catalysts provide a way to investigate these steps within a defined coordination environment. The ligands surrounding a metal influence which oxidation states it can access, how water binds and how reactive intermediates interact. They must also tolerate the strongly oxidizing conditions needed for oxygen evolution. Two broad mechanisms are often considered for O–O bond formation. In water nucleophilic attack, a water molecule reacts with an oxygen-containing intermediate at a single metal centre. In an interaction-of-two-metal–oxo mechanism, commonly abbreviated I2M, two metal-associated oxygen species couple. Distinguishing these pathways helps identify which structural and kinetic features a catalyst needs. Chlorins are macrocycles related to the light-absorbing pigments found in nature. Here, a chlorophyll-a-derived chlorin coordinates iron, creating a molecular platform for studying high-valent oxygen chemistry. The complex can also interconvert between oxygen-bridged dimers and mononuclear species, making its solution structure an important part of the catalytic question. Light absorption is assigned to a separate component, Ru(bpy)₃²⁺, while persulfate serves as the sacrificial oxidant. This arrangement allows the researchers to examine molecular water oxidation without integrating the complementary fuel-producing half-reaction. ## Research question Can a chlorophyll-derived iron chlorin combine rapid oxygen evolution with a high number of catalytic turnovers? Does the evolved oxygen originate from water, and does the iron remain part of a molecular catalyst during operation? The mechanistic investigation asks whether O–O bond formation involves water attack at one metal centre or coupling between two high-valent iron–oxygen species. The authors address this through solution characterization, isotope labelling, concentration-dependent kinetics, electrochemistry and spectroelectrochemistry. ## Inside the study ### Establishing the iron chlorin platform **Figure 1 introduces the chlorophyll-a-derived iron chlorin at the centre of the study.** Its macrocyclic ligand provides the coordination framework for the subsequent investigation of catalytic activity and mechanism. [pubs.acs.org](https://pubs.acs.org/accacs/article/doi/10.1021/acscatal.6c02830/5454626/Extremely-High-Turnover-Number-and-Turnover?utm%5Fsource=chatgpt.com) Structural and spectroscopic measurements show that the catalyst’s form depends on its environment. In the solid state, two iron chlorin units are joined through an oxygen bridge to form a μ-oxo dimer. The complex is also largely dimeric in the aqueous/acetonitrile reaction medium, although mononuclear species remain accessible. This distinction matters because the structure introduced into the reaction need not be the structure that performs every catalytic step. Understanding how the dimer responds to oxidation is therefore necessary for interpreting its activity. ### Following solvent-dependent molecular species **Figure 3 compares ESI-TOF mass spectra of the iron chlorin in acetonitrile and methanol.** The comparison contributes to the study’s examination of how the surrounding solvent influences the molecular species present in solution. [pubs.acs.org](https://pubs.acs.org/accacs/article/doi/10.1021/acscatal.6c02830/5454626/Extremely-High-Turnover-Number-and-Turnover?utm%5Fsource=chatgpt.com) Together with the other structural and spectroscopic observations, these measurements support a solvent-dependent relationship between dimeric and mononuclear forms. The authors subsequently examine how oxidation can move the catalyst between those forms under conditions relevant to water oxidation. The resulting picture treats molecular speciation as part of the catalytic cycle, rather than assuming that the starting μ-oxo dimer remains unchanged throughout operation. ### Measuring oxygen evolution The researchers optimize solvent composition and pH for visible-light-driven oxygen production using Ru(bpy)₃²⁺ and persulfate. Under the selected conditions, the iron chlorin reaches a turnover frequency of 21.3 ± 0.3 s⁻¹ and a turnover number of 6,920 ± 110\. These quantities describe different aspects of performance: turnover frequency measures catalytic rate, while turnover number records the cumulative amount of reaction relative to the catalyst quantity. The oxygen yield based on persulfate reaches 95.7 ± 1.3%. Isotope labelling supports water as the oxygen source, connecting the measured gas evolution to the intended water-oxidation chemistry. The rate and turnover values are evaluated within comparable homogeneous photocatalytic systems. Their interpretation depends on the photosensitizer, sacrificial oxidant and reaction conditions used. ### Testing whether the active catalyst remains molecular Strongly oxidizing conditions can transform a metal complex into other species, including metal-oxide particles. Oxygen evolution alone therefore cannot establish that the original molecular framework is responsible. The authors combine control experiments, dynamic light scattering and ESI-TOF mass spectrometry to examine that possibility. Their observations support a molecular iron chlorin catalyst as the dominant source of activity under the tested conditions. This evidence links the catalytic results to the proposed molecular chemistry, while avoiding an assignment based solely on the structure of the starting material. ### Identifying how the O–O bond forms The initial oxygen-evolution rate shows a quadratic dependence on iron chlorin concentration. Such second-order behaviour is consistent with a reaction step involving two catalyst-derived species. Two additional observations help constrain the interpretation: a kinetic isotope effect of 1.12 and no observed dependence on buffer concentration. The authors interpret this combination as supporting an I2M pathway involving two high-valent iron–oxo species. The kinetic evidence is particularly useful because the competing mechanisms involve different molecular encounters. A pathway requiring two catalyst-derived intermediates can produce a different concentration dependence from water attack at a single centre. The combined measurements favour the bimolecular coupling proposal. ### Connecting oxidation and structural change Electrochemical and spectroelectrochemical measurements follow oxidation of the μ-oxo dimer and its cleavage into mononuclear species. The proposed catalytic sequence then proceeds through three-electron oxidation to highly electron-deficient iron–oxo/oxyl intermediates. Two such species interact to form the O–O bond, ultimately leading to oxygen release. The precise electronic description of the reactive intermediate remains part of the mechanistic proposal. Its assignment draws on the combined kinetic, electrochemical and spectroscopic evidence rather than isolation of the high-valent species in bulk. ## Takeaways and outlook The study connects a chlorophyll-derived coordination framework with rapid and sustained molecular water oxidation. Its reported turnover frequency and turnover number demonstrate the performance of the iron chlorin within the specified Ru(bpy)₃²⁺/persulfate system. The mechanistic contribution extends beyond those values. Dimer–monomer interconversion, second-order catalyst dependence, a small isotope effect and oxidation-state measurements together support O–O bond formation through coupling of two high-valent iron–oxygen species. These findings provide a basis for designing chlorin-supported iron catalysts around both redox accessibility and molecular interactions. Further work can examine whether the same chemistry can be maintained with alternative photosensitizers, electrochemical driving forces or integrated systems that replace the sacrificial oxidant. ## About the researchers Takashi Nakazono of Osaka Metropolitan University is the first author and a corresponding author. Yusuke Yamada, also at Osaka Metropolitan University, is the other corresponding author. Ryo Mitsuda, Shinsuke Nakamura and Yuma Kawai are affiliated with Osaka Metropolitan University. Daichi Sugawara and Tohru Wada are affiliated with Rikkyo University, and Hitoshi Tamiaki with Ritsumeikan University. ## Original research Takashi Nakazono; Ryo Mitsuda; Shinsuke Nakamura; Yuma Kawai; Daichi Sugawara; Tohru Wada; Hitoshi Tamiaki; Yusuke Yamada. “Extremely High Turnover Number and Turnover Frequency of an Iron Chlorin Complex for Photocatalytic Water Oxidation.” *ACS Catalysis*, published 20 October 2026. Original paper: [https://doi.org/10.1021/acscatal.6c02830](https://doi.org/10.1021/acscatal.6c02830?ref=research-pop.com) --- ## Research POP Notes This article reflects the independent interpretation of the Research POP team and does not represent the views of the authors, their institutions or the journal. If you identify any inaccuracies or have concerns regarding the content, figures or attribution, please contact us at [team.researchpop@gmail.com](mailto:team.researchpop@gmail.com). 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