{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"55dfe13a71208cc9d3d1a931b5fe089fc640559bd44ad15c4bcd0e035b4e604f","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5dfd896fe59749c2c4830ce233fb2408fd8089f6d1b2f62bf9634dec153b913b","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"8efa69af61275c692bc0cec6cdd4842d7a45d7775a9c4bec54d3e2d22a567045","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"chem.catalytic-mechanisms.oec-oxygen-bond","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"Plants split water using a cluster of four manganese atoms and one calcium atom. The step where two oxygen atoms join to make $\\mathrm{O_2}$ has not been directly seen.","posed_since":"","precise":"For the $\\mathrm{Mn_4CaO_5}$ oxygen-evolving complex of photosystem II, identify the O-O bond-forming step in the S3 to S4 to S0 transition: which oxygen atoms couple (O5 with the inserted O6, or a water-derived ligand), the mechanism (oxyl-oxo radical coupling or nucleophilic attack), the Mn oxidation and spin states at the transition state, and its barrier consistent with the measured millisecond kinetics. An answer is a mechanism supported by time-resolved structural and spectroscopic data and by converged electronic-structure calculations.","problem_ref":"5dfd896fe59749c2c4830ce233fb2408fd8089f6d1b2f62bf9634dec153b913b","references":"","settled_by":"Time-resolved crystallography and X-ray emission spectroscopy capturing the S4 intermediate, matched by multireference calculations of the bond-forming step.","status_note":"In 2023 time-resolved crystallography (Bhowmick et al., Nature, https://doi.org/10.1038/s41586-023-06038-z) resolved intermediate structures in the $S3$ to $S0$ transition; the identity of the bond-forming step is still debated (not rechecked for 2025-2026).","title":"How the O-O bond forms in photosystem II","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"6a86375bad428457d50b40a9e773998758ab54defbe51bca71c391d401b6b598","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"23b6fab463bd773e3b3b8b2fb745d6de03ef57ad124f4272a23c4cea119951c3","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"9nBV0-OOq6tjzi_Wo_5gdkvPC5ydscVOm66FK6RGEWQkHKfDzzXKY_vZAwDXRk47oki8nbNlrBv97LJvghTLBg"},"schema":"pubphys.envelope/1"},"record_hash":"6a86375bad428457d50b40a9e773998758ab54defbe51bca71c391d401b6b598","leaf_index":2656}