Determining Manganese Oxidation States in the Oxygen Evolving Complex via S₂ CW-EPR Signal Simulation and Spin Density Analysis

Determining Manganese Oxidation States in the Oxygen Evolving Complex via S₂ CW-EPR Signal Simulation and Spin Density Analysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Determining Manganese Oxidation States in the Oxygen Evolving Complex via S₂ CW-EPR Signal Simulation and Spin Density Analysis Ofentse Ramonnye, Bernard Baituti, Taye B. Demissie This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7354979/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Water oxidation is a biological process that contributes a lot to the ecosystem. Interestingly, it produces abundant hydrogen gas, which can be used as an alternative energy source according to the recent demands of green technology. The mechanism of water oxidation in the photosystem II (PSII), catalysed the oxygen evolving complex (OEC)/ Mn 4 O 5 Ca cluster is of great interest. This is because understanding the electronic properties of the Mn 4 O 5 Ca cluster can enhance innovation of technologies for the biological catalysis of water oxidation. The oxidation states of each Mn ions in the Mn 4 O 5 Ca cluster are still not concluded. Electron paramagnetic resonance (EPR) spectroscopy has been widely used in the study of the OEC in the PSII. Among the 𝑆 𝑛 states of the Kok cycle, the 𝑆 2 state is the most studied due to the multiline (ML) EPR signal it generates at \(\:g=\:2\) and \(\:g=\:4.1\) . These ML signals are the hyperfine (HF) structured 55 Mn EPR signals with a total spin of ½ in the ground state and can be obtained by trapping PSII prepared samples (either membranes or cores) in the 𝑆 2 or 𝑆 0 state at cryogenic temperatures, and we used approximately 7 K in this study. This study therefore details an insight to understanding the electronic properties of the Mn 4 O 5 Ca cluster using EasySpin simulations and Density Functional Theory (DFT) calculations. Even though research has been done before, the HF contribution of each Mn ion to the fine structure of OEC remains inconclusive. The EPR generated signal has been instrumental in determining the HF contributions of each Mn ion to the fine structure and the oxidation states of each Mn ion through simulation of these ML signals. Simulation of the X-band continuous wave (cw) EPR generated spectra, for low field, wide field and upper field at g = 2 in this study, revealed that three of four Mn ions with large anisotropy which are more certainly Mn III centres that support the ‘low oxidation state’ and supported by the spin density of the Mn ions obtained from DFT calculations. Manganese hyperfine simulation EPR DFT Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7354979","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":533458993,"identity":"caf910dc-e8c9-470c-81dc-2e9191ee109c","order_by":0,"name":"Ofentse Ramonnye","email":"","orcid":"","institution":"University of Botswana","correspondingAuthor":false,"prefix":"","firstName":"Ofentse","middleName":"","lastName":"Ramonnye","suffix":""},{"id":533458994,"identity":"7720aa5e-f333-4dd4-bb48-dfd9e3f4057a","order_by":1,"name":"Bernard Baituti","email":"","orcid":"","institution":"Botswana International University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Bernard","middleName":"","lastName":"Baituti","suffix":""},{"id":533458995,"identity":"2630ffba-0a19-43db-a156-d3b594546cb3","order_by":2,"name":"Taye B. 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Analysis","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Manganese, hyperfine, simulation, EPR, DFT","lastPublishedDoi":"10.21203/rs.3.rs-7354979/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7354979/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWater oxidation is a biological process that contributes a lot to the ecosystem. Interestingly, it produces abundant hydrogen gas, which can be used as an alternative energy source according to the recent demands of green technology. The mechanism of water oxidation in the photosystem II (PSII), catalysed the oxygen evolving complex (OEC)/ Mn\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003eCa cluster is of great interest. This is because understanding the electronic properties of the Mn\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003eCa cluster can enhance innovation of technologies for the biological catalysis of water oxidation. The oxidation states of each Mn ions in the Mn\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003eCa cluster are still not concluded. Electron paramagnetic resonance (EPR) spectroscopy has been widely used in the study of the OEC in the PSII. Among the \u0026#119878;\u003csub\u003e\u0026#119899;\u003c/sub\u003e states of the Kok cycle, the \u0026#119878;\u003csub\u003e2\u003c/sub\u003e state is the most studied due to the multiline (ML) EPR signal it generates at \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:g=\\:2\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:g=\\:4.1\\)\u003c/span\u003e\u003c/span\u003e. These ML signals are the hyperfine (HF) structured \u003csup\u003e55\u003c/sup\u003eMn EPR signals with a total spin of \u0026frac12; in the ground state and can be obtained by trapping PSII prepared samples (either membranes or cores) in the \u003cem\u003e\u0026#119878;\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e or \u003cem\u003e\u0026#119878;\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e state at cryogenic temperatures, and we used approximately 7 K in this study. This study therefore details an insight to understanding the electronic properties of the Mn\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003eCa cluster using EasySpin simulations and Density Functional Theory (DFT) calculations. Even though research has been done before, the HF contribution of each Mn ion to the fine structure of OEC remains inconclusive. The EPR generated signal has been instrumental in determining the HF contributions of each Mn ion to the fine structure and the oxidation states of each Mn ion through simulation of these ML signals. Simulation of the X-band continuous wave (cw) EPR generated spectra, for low field, wide field and upper field at g\u0026thinsp;=\u0026thinsp;2 in this study, revealed that three of four Mn ions with large anisotropy which are more certainly Mn\u003csup\u003eIII\u003c/sup\u003e centres that support the \u0026lsquo;low oxidation state\u0026rsquo; and supported by the spin density of the Mn ions obtained from DFT calculations.\u003c/p\u003e","manuscriptTitle":"Determining Manganese Oxidation States in the Oxygen Evolving Complex via S₂ CW-EPR Signal Simulation and Spin Density Analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-27 10:49:13","doi":"10.21203/rs.3.rs-7354979/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"11905202-cd09-4c46-9605-5afe400a33dc","owner":[],"postedDate":"October 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-02-24T09:27:31+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-27 10:49:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7354979","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7354979","identity":"rs-7354979","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}