The oxygen evolving complex (OEC) of photosystem II catalyzes the oxidation of water to form molecular oxygen. The S₃-state is currently the last observable intermediate prior to O–O bond formation. Its electronic structure has been assigned to a homovalent Mn(IV)₄ core with an S = 3 ground state. In a recent publication (Lee, Marchiori, et al. JACS), the Agapie (Caltech) and Britt labs synthesized and characterized via XAS and multifrequency EPR spectroscopy a Mn(IV)₄O₄ cuboidal complex. Results show that this Mn(IV)₄O₄ complex has an S = 3 ground state and magnetic parameters that mimic the OEC in the S₃-state. This spectroscopic model provides a benchmark of the S₃-state and furthers our understanding of the OEC just prior to O–O bond formation.
More information at https://doi.org/10.1021/jacs.9b10371