A Quantum-Coherent Vortex Engine Drives Water Splitting in Photosystem II. (GQR23)

Biological water oxidation in photosystem II (PSII) is the sole natural source of atmospheric O2, yet thephysical principle governing its multi-electron, multi-proton chemistry remains unresolved. Classical PCET andredox-cycle models fail to account for the ultrafast coherence signals, abrupt geometric bifurcations, and nearlyisoelectronic S-state intermediates observed experimentally. Here we show that the CaMn4O5 cluster hosts arotating quantum-coherent tunnelling mode whose geometric evolution drives water splitting. Time-dependentquantum dynamics computed over experimentally determined S-state structures (8F4C–K) reveal a coherencevortex: a rotating corridor of maximal Ca–Mn3 tunnelling whose orientation shifts from ∼0◦in S2 to a near-vertical configuration in early S3, collapses entirely during O2 release (8F4G–J), and re-emerges in a re-alignedform in late S3 (8F4K). The rotation, suppression and reactivation of this vortex correlate precisely with protonrelease, Mn–O–Mn curvature changes and product extrusion, establishing the OEC as a curvature–coherenceengine rather than a static redox machine. This framework resolves long-standing mechanistic contradictions inPSII and provides a blueprint for designing quantum-enhanced, bio-inspired water-oxidation catalysts.