Fig. 7. Schematic summarizing the structural changes in the O1, Cl1, and O4 channels leading to the first water insertion and proton release during the S₂ → S₃ transition.

Mn1 and Mn4 oxidations from (III) to (IV) are shown as a color change from pink to purple. The gray arrow represents the possible proton pathway, while the blue dashed arrow represents the potential stepwise water insertion pathway.