Most of the O₂ in the atmosphere that supports life on earth is generated by plants, algae, and cyanobacteria by the photo-induced oxidation of water to dioxygen:

2H₂O → O₂ + 4e^– + 4H⁺

This reaction is catalyzed by a manganese/calcium complex (Mn₄Ca), which sequentially stores four oxidizing equivalents that are used to oxidize two molecules of water to molecular oxygen.

In our lab, we use synchrotron radiation X-ray sources and electron paramagnetic resonance (EPR) spectroscopy to investigate the oxidation state, the structure and the associated cofactors calcium and chloride of the catalytic Mn cluster.