The first room‐temperature X‐ray absorption spectra of higher oxidation states of the tetra‐manganese complex of photosystem II

Abstract
The manganese (Mn) complex of photosystem II catalyzes water oxidation. For the first time, its advancement through the reaction cycle was monitored by time-resolved X-ray absorption measurements at the Mn K-edge at room temperature. The complex was stepped through its four oxidation states by nano-second-laser flashes applied to samples exposed to the X-ray beam. Time courses of the X-ray fluorescence intensity were recorded during a flash sequence. Extended X-ray absorption fine-structure spectra were recorded with the S(1), S(2), and S(3) oxidation states highly populated. The room temperature data is compatible with the formation of a third di-mu-oxo bridge between two Mn atoms upon the S(2)-->S(3) transition.

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